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Large Igneous Provinces and supercontinents: Toward completing the plate tectonic revolution
Abstract
Regional groupings of a majority, or all, of Earth's crustal blocks have occurred several times in Earth history, but only the most recent supercontinent Paleozoic Pangea/Gondwana, is well characterized. Prior Precambrian supercontinents are postulated: Rodinia (ca. 1 to 0.7 Ga), Nuna/Columbia (ca. 1.8 to 1.3 Ga) and Kenorland/supercratons (ca. > 2.7 to 2.0 Ga), but the configuration of each is poorly known. A new methodology using Large Igneous Provinces (LIPs) offers an opportunity for fast-tracking progress toward robust Precambrian reconstructions. Comparison of the LIP ‘barcode’ record between crustal blocks allows identification of which blocks were likely to have been nearest neighbors in past supercontinents. Restoration of the primary geometry (radiating or linear) of regional dyke swarms (the plumbing system of LIPs) offers another reconstruction criterion. A consortium of companies is providing funding for dating of essentially all major regional dyke swarms and sill provinces to complete the ‘barcoding of all major crustal blocks, and 13 of the papers in this special issue provides examples of this progress. Seven additional papers provide overviews of important LIPs. Together these 20 papers illustrate the potential for rapid progress using the LIP record for Precambrian supercontinent reconstructions toward completing the plate tectonic revolution which began nearly five decades ago.
... palaeomagnetism) or similarity in stratigraphy, tectonic setting, palaeontology, or igneous activity. While some of these methods, such as matching stratigraphy and sharing of fossils, were used over a century ago by Alfred Wegener in the development of the theory of continental drift (Wegener, 1929), palaeomagnetic and igneous barcoding analyses are more recent developments (Ernst and Bleeker, 2010;Ernst et al., 2013;Mitchell et al., 2021). A general issue with all comparative studies is that different data often support different relationships. ...
... This paper focuses on a cladistic analysis of large igneous province barcoding patterns compiled by Ernst et al. (2013) for all major Archaean and Proterozoic cratons. These data were supplemented from additional sources, which are detailed in the relevant sections. ...
... These data were supplemented from additional sources, which are detailed in the relevant sections. Bleeker and Ernst (2006), Söderlund et al. (2010) and Ernst et al. (2013) argued that mafic igneous intrusives associated with the emplacement of LIPs provided high quality comparative data for the reconstruction of Archaean and Proterozoic supercontinents. The characteristics that make these intrusives ideal include their wide geographic extent, rapid eruption, accurate dating, and long-lasting footprint. ...
... 555-550 Ma in Newfoundland (Cawood et al., 2001), ca. 550 Ma in the Central Iapetus Magmatic Province (CIMP; e.g., Ernst et al., 2013;Youbi et al., 2020) of the northern Appalachians and Morocco, and ca. 540-530 Ma in the Wichita igneous province of southern Oklahoma (Hanson et al., 2013;Wall et al., 2021). ...
... Of all supercontinent proxies, the most obvious are the association of worldwide collisional orogenesis, zircon age peaks and granitoid magmatism with continental assembly (e.g., Condie and Aster, 2013); and the association of mafic dike swarms, rift magmatism and large igneous provinces (LIPs) with continental breakup and dispersal (e.g., Yale and Carpenter, 1998;Ernst et al., 2008Ernst et al., , 2013Condie et al., 2021). Indeed, it was through interpretation of the geologic significance of these proxy records that the supercontinent cycle was first proposed (Fischer, 1984;Worsley et al., 1984Worsley et al., , 1985. ...
... This global-scale orogenic activity is coeval with a strong zircon age peak at 630-540 Ma (e.g., Puetz et al., 2018) (Fig. 3) and a major cluster of orogenic granitoid ages at 650-550 Ma (Condie and Aster, 2010;Condie and Aster, 2013). Conversely, evidence of continental rifting occurs in the form of mafic dike swarms, most notably in Laurentia and Baltica (e.g., Cawood et al., 2001;Weber et al., 2019), riftrelated igneous activity (see Cawood et al., 2001, Fig. 7) and LIPs such as the Wichita (e.g., Hanson et al., 2013;Wall et al., 2021), Baltoscandian (e.g., Kumpulainen et al., 2021) and Central Iapetus Magmatic Province (e.g., Ernst et al., 2013;Youbi et al., 2020), the ages of which collectively span the interval ca. 615-530 Ma. ...
Following a decade during which its presence was widely accepted, the existence of the putative Ediacaran supercontinent Pannotia has come into question since the turn of the millenium, largely due to the geochro-nology of Ediacaran-Cambrian orogens, which suggests that the supposed landmass had begun to break up well before it was fully assembled. Paleomagnetic data from this time interval have been used to both support and refute the existence of Pannotia, but are notoriously equivocal. Proxy signals for Ediacaran-Cambrian super-continent assembly and breakup, although collectively compelling, can be individually challenged, and efforts to detect the mantle legacy expected of supercontinent amalgamation, while promising, are inconclusive. Yet the existence of Pannotia is central to the nature, duration and evolution of the supercontinent cycle, and dictates the cycle's geodynamic pathway from the breakup of Rodinia to the assembly of Pangea. Hence, the question of Pannotia's existence, like that of Hamlet, is one of fundamental importance and demands far more attention than it has hitherto received.
... The source candidates previously described for the Lajeado Group On the African side, in the Angola portion of the Congo Craton (Table 2), Calymmian ages ~ 1,505 from dolerite sills and gabbronoritic dikes are proposed to be part of a Mesoproterozoic magmatic event identify in the supercontinent Nuna (Ernst et al. 2013). It is important to mention that the identification of three Mesoproterozoic magmatic events (ca. ...
... It is important to mention that the identification of three Mesoproterozoic magmatic events (ca. 1,505 -Calymmian; 1,380 -Ectasian; and 1,110 Ma -Stenian) represents a magmatic 'barcode' for this portion of SW-Congo Craton (Ernst et al. 2013). ...
... Considering a Curitiba microplate -Western Africa connection, the potential sources for this age-interval in Angola craton and are: i) intrusions of pyroxenite, gabbro and syenite emplaced into the Epupa Complex and the Kunene Intrusive Complex (Menge 1998, Drüppel et al. 2007) dated ~ 1,215 Ma (U-Pb zircon ages, Littmann et al. 2000); an ii) 1,110 Ma ages obtained for a gabbro-noritic dyke swarm in Southeastern Angola (Ernst et al. 2013), and, lastly, iii) Namaqua-like metamorphic grains, derived from leucogranites in Kaapvaal craton (South Africa). Bial et al. (2015) dated zircon grains between 1,220-1,180 Ma, followed by a second heat pulse at ~ 1100 Ma. ...
The reconstruction of ancient continental margins encompassed in continent–continent collision is a complex task. The continental blocks generally record a multiphase evolution with interaction of tectonic settings, plate polarities, basins and their depositional architecture.
The Ribeira belt (Southeast-Southern Brazil) resulted from the juxtaposition of several crustal blocks during the Brasiliano/Pan-African tectonic events (800–490 Ma) leading to the amalgamation of Western Gondwana. In this context, a series of pre-Brasiliano blocks underwent variable rates of tectonic reworking, including fragments derived from Rodinia.
Some of the metasedimentary strata of the Southern Ribeira belt are representative of Late Meso- to Neoproterozoic basins which bordered these pre-Brasiliano continental fragments, such as the Capiru Group.
The Capiru Group (Late Meso- to Neoproterozoic) is a low-grade metasedimentary unit that crops out on the Curitiba microplate and records passive to active continental margin stages.
In this work we show new provenance data (U-Pb geochronology of detrital zircon) of the Capiru Group and compare them to the other chrono-correlative continental margin units of the region (Lajeado and lower Itaiacoca groups).
Through the evolution of Capiru, Lajeado, and Itaiacoca groups we show that the post-Rodinia continental margins of the Southern Ribeira belt show similar Paleoproterozoic contributions (2,000 – 2,185 Ma) and slightly different Mesoproterozoic populations, suggesting distinct paleogeographic contexts: the Capiru Group was deposited on the Northern margin of the Curitiba-Angola block, with Mesoproterozoic “exotic” contribution (1,508 – 1,100 Ma). On the other hand, the Lajeado and Itaiacoca groups were deposited on the East-Southeastern margin of the Paranapanema continental block.
... The late Neoproterozoic Era was a dynamic period in the evolution of Earth, characterized by extensive lithospheric extension, flooding of mafic magmas, and the development of rift basins in response to the breakup of the Rodinia supercontinent (Li et al., 2003Ernst et al., 2013;Merdith et al., 2017). Deciphering the late Neoproterozoic tectonism and basin evolution on separated continental margins is of vital importance for understanding continental rifting history and palaeogeographic reconstruction (Dalziel, 1991;Yonkee et al., 2014). ...
... Ma Big Creek plutonic suite and ca.600 Ma gabbro sill in western Laurentia (Lund et al., 2010;Brennan et al., 2020), the mafic dykes and sills associated with Central Iapetus Magmatic Province (ca. 615-555 Ma) in eastern Laurentia and western Baltica (Ernst et al., 2013), the ca.670-650 Ma basaltic and rhyolitic interlayers in East Antarctica and southwestern Australia (Kim et al., 2023), the ca.600-580 ...
The spatiotemporal evolution of late Neoproterozoic sedimentary basins and their tectono-magmatic context
provide essential information regarding the continental rift process of the Tarim Craton during the fragmentation
of the Rodinia supercontinent. However, the incomplete exposure of strata and magmatism in the distal continental margin hinders the understanding of different rift phases that trigger continental breakup. The Sawapuqi
region is currently located at the northernmost margin of the Tarim Craton and presents an uninterrupted
sedimentary sequence and volcanic rocks from the latest Precambrian to the Cambrian period. Herein, we
perform an integrated analysis of the Sawapuqi sub-basin and provide critical insights into the Ediacaran
stratigraphic and tectono-magmatic evolution that shed light on the final rifting phase. The Sawapuqi sub-basin
preserves regressive and transgressive successions, ranging from thick-bedded siltstones and siliceous rocks at the
lower unit of the Sugetbrak Formation, through shore gravel-bearing laminated sandstone accumulation (upper
unit), and restricted platform stromatolitic carbonates (Qigebrak Formation), to Cambrian mature passive
margin sedimentation. An alkaline basaltic layer is interbedded within the coarsening-upward sedimentary
packages of the early Ediacaran, recording the final rift-related magmatic pulse in the northwestern Tarim
margin. The geochemical signatures of these basalts suggest a relatively shallow-depth derivation from the
enriched mantle reservoir in an intraplate setting. The detrital zircon provenance of the coarse-grained siliciclastic to pebbly feldspathic debris sandstone sequence of the upper Sugetbrak Formation indicates the hybrid
sediment infills from local metamorphic basements and Neoproterozoic igneous rocks, with progressively
increased contribution from the coeval granites in the northern periphery of the Tarim Craton. The stratigraphic
evolution from syn-rift clastic rocks to post-rift carbonates and the transition of detrital provenance observed in
the Sawapuqi sub-basin suggest the development of a breakup succession at the end of the early Ediacaran
period. The margin-localized continental extension and mantle-derived volcanism during the early Ediacaran
differed from the distributed extension and bimodal magmatism during the Cryogenian, indicating two-stage
extensional modes and subsidences prior to the lithospheric breakup. The rift system of the latter stage, which
migrated oceanwards, eventually led to the continental breakup in the northwestern margin of the Tarim Craton.
Comparable late Neoproterozoic stratigraphy and magmatic pulses between the Tarim Craton and Yili-Central
Tianshan Block (YCTB) support their reconstructions as two conjugate rifted margins. This study indicates
that the rift-drift tectonics triggered by this prolonged episodic rifting between the Tarim Craton and the YCTB
was closely associated with the final fragmentation of Rodinia.
... Global large igneous province (LIP) database ; Supplementary Material 4 for shapefile database and Excel tables). The global LIP record not only can be used for reconstructing past continental connections (Ernst et al., 2013a;Ernst et al., 2008;Evans et al., 2016b), it also provides a key argument for either the geodynamic model of coupled supercontinent-superplume cycles (Li et al., 2008a;Li and Zhong, 2009) or the opposing view (Torsvik et al., 2008b). In section 6.3 we use the data to discuss some of the alternative geodynamic models. ...
... Those which do not reach the threshold of 100,000 km 2 are included as probable LIPs based on satisfying proxy parameters such as having mafic dykes which are typically at least 10 m in width (Ernst, 2014). With an increasing number of LIP events being discovered during Earth history, LIP data, and especially their regional dyke swarms, provide an efficient tool for constraining palaeocontinental reconstructions (Bleeker and Ernst, 2006;Ernst and Bleeker, 2010;Ernst et al., 2013a). Comparison of LIP time "barcodes" from different crustal blocks can reveal which were nearest neighbours and over what time span (Bleeker and Ernst, 2006). ...
Establishing how tectonic plates have moved since deep time is essential for understanding how Earth’s geodynamic system has evolved and operates, thus answering longstanding questions such as what “drives” plate tectonics. Such knowledge is a key component of Earth System science, and has implications for wide ranging fields from core-mantle-crust interaction and evolution, geotectonic phenomena such as mountain building and magmatic and basin histories, the episodic formation and preservation of Earth resources, to global sea-level changes, climatic evolution, atmospheric oxygenation, and even the evolution of life. In this paper, we take advantage of the rapidly improving database and knowledge about the Precambrian world, and the conceptual breakthroughs, both regarding the presence of a supercontinent cycle and possible dynamic coupling between the supercontinent cycle and mantle dynamics, in order to establish a full-plate global reconstruction from 540 Ma back to 2000 Ma. We utilise a variety of global geotectonic databases to constrain our reconstruction, and use palaeomagnetically recorded true polar wander events and global plume records to help evaluate competing geodynamic models and also provide new constraints on the absolute longitude of continents and supercontinents. After revising the configuration and life span of both supercontinents Nuna (1600—1300 Ma) and Rodinia (900—720 Ma), we present a 2000—540 Ma animation, starting from the rapid assembly of large cratons and supercratons (or megacontinents) between 2000 Ma and 1800 Ma. This occurred after a billion years of dominance by small cratons, and kick-started the ensuing Nuna and Rodinia supercontinent cycles and the emergence of stable, hemisphere-scale (long-wavelength) degree-1/degree-2 mantle structures. We further use the geodynamicly-defined type-1 and type-2 inertia interchange true polar wander (IITPW) events, which likely occurred during Nuna (type-1) and Rodinia (type-2) times as shown by the palaeomagnetic record, to argue that Nuna assembled at about the same longitude as the latest supercontinent Pangaea (320—170 Ma), whereas Rodinia formed through introversion assembly over the legacy Nuna subduction girdle either ca. 90◦ to the west (our slightly preferred model) or to the east before the migrated subduction girdle surrounding it generated its own degree-2 mantle structure by ca. 780 Ma. Our interpretation is broadly consistent with the global LIP record. Using TPW and LIP observations and geodynamic model predictions, we further argue that the Phanerozoic supercontinent Pangaea assembled through extroversion on a legacy Rodinia subduction girdle with a geographic centre at around 0◦E longitude before the formation of its own degree-2 mantle structure by ca. 250 Ma, the legacy of which is still present in present-day mantle.
(the paper is of OPEN ACCESS at http://dx.doi.org/10.1016/j.earscirev.2023.104336)
... Mafic dyke/sill swarms associated with large igneous provinces (LIPs) commonly formed during continental extension related to mantle plume, and in some cases could extend more than 2000 km (Ernst et al., 1995(Ernst et al., , 2013aPark et al., 1995;Peng, 2015). Compared to their counterparts (e.g., flood basalts) that could be easily eroded away during later uplift, they tend to be remained due to their significant vertical extension in the crust (Ernst et al., 1995(Ernst et al., , 2013a. ...
... Mafic dyke/sill swarms associated with large igneous provinces (LIPs) commonly formed during continental extension related to mantle plume, and in some cases could extend more than 2000 km (Ernst et al., 1995(Ernst et al., , 2013aPark et al., 1995;Peng, 2015). Compared to their counterparts (e.g., flood basalts) that could be easily eroded away during later uplift, they tend to be remained due to their significant vertical extension in the crust (Ernst et al., 1995(Ernst et al., , 2013a. They thus could serve as geological "barcode" for reconstructing ancient supercontinents, if their emplacement ages are well-constrained (Ernst et al., 2013a, b;Li et al., 2008). ...
An integrated study involving both bulk rock and mineral compositions was conducted on a newly identified mafic sill in Helanshan area from northwest of China. Apatite U-Pb dating constrained its emplacement age at 772.6 ± 3.4 Ma (MSWD = 1.2). Its primary melts estimated based on clinopyroxene composition are enriched in LREEs and Sr, and depleted in HREEs, HSFEs, and Pb. Moreover, they have high Nb/U (33–99) and Zr/Hf (32–41) ratios. Combined with their depleted (⁸⁷Sr/⁸⁶Sr)i ratios (0.704146–0.705100), the primary melts of Helanshan sill were most probably generated by low degree melting of carbonated asthenosphere mantle in the transitional depths of garnet- to spinel stabilities, rather than from metasomatized lithospheric mantle as indicated by whole-rock compositions. Striking compositional discrepancy exists between the primary melts and bulk rocks, and were principally caused by significant crustal assimilation during their ascent to emplacement level. As a result, some pivotal information about primary melts including less radiogenic (⁸⁷Sr/⁸⁶Sr)i ratios, Zr, Hf and Ti depletions, superchondritic Nb/U ratio, was erased during this process. The Helanshan mafic sill represents a new pulse of Neoproterozoic mafic magmatism in northwestern North China Craton, and formed as result of regional continental extension, which was probably related to the breakup of Rodinia supercontinent.
... The two groups of metamafic rocks are similar to the Yanliao LIPs, and plot in the high-Fe tholeiitic affinity (Fig. 11h), indicating that the Oulongbuluke metamafic rocks were derived from a mantle source similar to those of (Aldanmaz et al., 2000), (f) Ti/1000 vs. V (Shervais, 1982), (g) Sm × 50-Ti/50-V (Vermeesch, 2006), and (h) Al 2 O 3 -(Fe 2 O 3 T + TiO2)-MgO (Jensen, 1976) Yanliao LIPs. It is generally believed that LIPs formed in response to mantle plume (Ernst et al., 2003(Ernst et al., , 2013a(Ernst et al., , 2013bHofmann et al., 1997Hofmann et al., , 2000. Moreover, the Yanliao LIPs have been proved to be induced by plume activity Wang et al., 2019b). ...
... From a global perspective, the plume-induced mid-Mesoproterozoic (1.3-1.2 Ga) magmatic event relevant to the final breakup of the Columbia supercontinent was widely recorded along both the margins and interior of Columbia supercontinent Santosh, 2002, 2003;Zhao et al., 2002Zhao et al., , 2004Evans and Mitchell, 2011;Ernst et al., 2008Ernst et al., , 2013aErnst et al., , 2013b. Here, we discuss the reconstruction and relationships among the Tarim Craton (including Oulongbuluke Block), North China Craton, and North Australia Craton. ...
In the Mesoproterozoic, there was an epic transition on Earth, the final breakup of the Columbia supercontinent. Understanding the dynamic mechanism responsible for the final breakup of Columbia supercontinent is crucial for establishing Earth’s evolution that includes geology, environment and life. However, there is little research on what drove the breakup of the Columbia supercontinent. Here we focus on this issue by integrating new zircon U-Pb ages, Lu-Hf isotopes, and whole-rock geochemical data for metamafic rocks from the Oulongbuluke Block in the southeast of Tarim Craton. These data show that the protoliths of these metamafic rocks were emplaced at ca. 1.37–1.35 Ga and were divided into high-Fe and low-Fe groups. The high-Fe and low-Fe groups show geochemical character similar to normal mid-ocean ridge basalt (N-MORB) and enriched mid-ocean ridge basalt (E-MORB), respectively. The high-Fe group was formed by high degree (7%-9%) partial melting of spinel-phase lherzolite mantle source, whereas the low-Fe group was derived from low degree (5%-6%) partial melting of spinel-phase lherzolite mantle source. We propose that the high-Fe and low-Fe groups may have been derived from magmas from different parts of a mantle plume. The formation of the 1.37–1.35 Ga metamafic rocks in the Oulongbuluke Block may be related to the separation of the Tarim Craton into North and South Tarim cratons, which resulted in the opening of the initial Middle Tarim Ocean Basin. By comparison with the plume-induced Yanliao Rift of North China Craton and McArthur Basin of North Australia Craton, we present that these three cratons may potentially dominated by a superplume, forming circular rift zone and radiating dykes. This superplume triggered the continuous extension to most parts of Columbia and led to the final breakup of the Columbia supercontinent.
... Because of the lack of reliable isotopic ages for the mid-Mesoproterozoic (1.3-1.2 Ga), magmatism and tectonism in the Oulongbuluke (Rogers and Santosh, 2002;Zhao et al., 2002Zhao et al., , 2004Ernst et al., 2008Ernst et al., , 2013aErnst et al., , 2013bZhang et al., 2012, and references therein). The globally widespread ca. ...
... 1.3-1.2 Ga magmatic event, which was possibly triggered by a superplume and the final breakup of the Columbia supercontinent, was an episode of extension related to the superplume activity (Evans and Mitchell, 2011;Hoffman, 1989;Rogers and Santosh, 2002;Zhao et al., 2002Zhao et al., , 2004Hou et al., 2008;Ernst et al., 2008Ernst et al., , 2013aErnst et al., , 2013b. Therefore, we suggest that the Oulongbuluke Block was involved in the final breakup of the Mesoproterozoic Columbia supercontinent, as evidenced by the ca. ...
The Oulongbuluke Block is an integral part of the Columbia and Rodinia supercontinents, but the lack of rock records from the transitional period between the Columbia and Rodinia supercontinents during the mid–late Mesoproterozoic has impeded our understanding of the tectonic relationship of the Oulongbuluke Block, which lies between the Columbia and Rodinia supercontinents. In this contribution, we present a systematic petrographic, geochemical, and zircon U-Pb-Hf investigation of newly discovered metamafic rocks in the Oulongbuluke Block. The results show that the metamafic rocks have a protolith age of ca. 1.35 Ga and an arcrelated metamorphic age of ca. 1.11–1.09 Ga. The metamafic rock samples are geochemically characterized by relatively high FeOT/MgO and FeOT and low SiO2, MgO, and K2O + Na2O, which shows tholeiitic affinity. These metamafic rocks exhibit slight light rare earth element (LREE) depletion and flat heavy rare earth element (HREE) content with no obvious Eu anomalies and slightly negative Nb, Sr, and Zr anomalies. These conditions are similar to those of enriched midoceanic-ridge basalt (E-MORB) and normal mid-oceanic-ridge basalt (N-MORB). The metamorphic rocks studied also have positive zircon εHf(t) values (2.96–7.04). Hence, the protoliths of the metamafic rocks may have been produced by variable degrees of melting of spinel-phase lherzolite mantle in a mid-oceanic ridge setting that was probably induced by a mantle plume. The presence of metamafic rocks indicates that the Oulongbuluke Block experienced the final breakup of the Columbia supercontinent at ca. 1.35 Ga, and the ca. 1.11–1.09 Ga arc-related metamorphism coincided with the convergence of the Rodinia supercontinent. The tectonic setting of the Oulongbuluke Block changed from a mid-oceanic ridge setting to an arc setting during the mid–late Mesoproterozoic, which was likely a response to the transition from the Columbia supercontinent to Rodinia supercontinent.
... It has been argued that passive plate margins that record magmatism and addition of juvenile crust during crustal rifting constitute the hallmark of continental dispersal. nile values between 2.8 Ga and 2.0 Ga may correspond to juvenile magmatism along passive margins during the protracted break-up of Archean supercratons, resulting in oceanic crust formation prior to the assembly of the Columbia supercontinent, and is supported by the high dT/dP gradient (apparent thermal gradient retrieved from global highgrade metamorphism) recorded in the rocks during the Siderian-Rhyacian (Bleeker, 2003;Ernst et al., 2013). The ca. 2.0 Ga juvenile excursions seem to be more prevalent and globally present (Fig. 11a-h). ...
... It has been argued that passive plate margins that record magmatism and addition of juvenile crust during crustal rifting constitute the hallmark of continental dispersal. nile values between 2.8 Ga and 2.0 Ga may correspond to juvenile magmatism along passive margins during the protracted break-up of Archean supercratons, resulting in oceanic crust formation prior to the assembly of the Columbia supercontinent, and is supported by the high dT/dP gradient (apparent thermal gradient retrieved from global highgrade metamorphism) recorded in the rocks during the Siderian-Rhyacian (Bleeker, 2003;Ernst et al., 2013). The ca. 2.0 Ga juvenile excursions seem to be more prevalent and globally present (Fig. 11a-h). ...
... Superimposed on this steady increase are smaller fluctuations, suggesting multiple factors were at play. The Neoproterozoic is notable for: 1) climatic upheavals, the most conspicuous being the two Cryogenian Period global glaciation events, 2) breakup of the supercontinent Rodinia and the assembly of Gondwana, and 3) emplacement of several continental flood basalts (CFBs) (Ernst et al., 2013;McCausland et al., 2011;Merdith et al., 2017;Rooney et al., 2014;Stern, 2018). The impact of these events may have been severe enough to impinge on the baselevel, long term 87 Sr/ 86 Sr changes caused by Rb decay (e.g. ...
The Ediacaran was a pivotal period, during which the first metazoans emerged and then experienced several biotic turnover events. At the same time, the oceans were undergoing large-scale geochemical changes, including oscillating redox conditions and nutrient fluxes. Understanding global patterns of biotic change during this interval, and any environmental drivers, is limited by our ability to correlate geochemical and palaeontological records between sections. The strontium isotope ratio of seawater (87Sr/86Sr) represents a powerful chemostratigraphic tool, because it is globally homogeneous, evolves on ∼ 1 myr timescales, and is well-preserved in a range of carbonate rocks. In addition, changes in 87Sr/86Sr track changes in continental weathering fluxes, which in turn can influence redox conditions and seawater chemistry. Recent age models for the Ediacaran have incorporated δ13C and 87Sr/86Sr data, but there is a dearth of high-resolution, age-constrained 87Sr/86Sr data from the critical Ediacaran-Cambrian Boundary interval. To address this, we collected a high-resolution stratigraphic transect through an expanded section of terminal Ediacaran carbonate rocks, from the Nama Group, South Africa and Namibia, deposited ∼550–538 Ma. The samples are interbedded with a series of closely-spaced, dated ash beds. To ensure that the 87Sr/86Sr ratios were reflective of primary seawater signals, we tested a sequential digestion procedure, already shown to be effective in Phanerozoic samples, on Ediacaran bulk rock carbonate powders. The successful implementation of the sequential digestion technique was verified through careful examination of samples for diagenetic alteration using petrography, trace element ratios and δ18O. This technique was then applied to 51 samples from a stratigraphic transect through the Kuibis Subgroup, collected at Zebra River, and the Schwarzrand Subgroup, collected at Orange River. The data through the Schwarzrand Subgroup are highly consistent, with an average of 0.708590 ± 0.000076. The isotopic signature is consistent with other terminal Ediacaran age rocks, with typically low, positive δ13C and relatively high 87Sr/86Sr ratios (∼0.7085). Based on correlation with other Ediacaran sections, our data reveal an 87Sr/86Sr peak of ∼0.7086 pre-550 Ma before a drop-off to ∼0.7084 immediately post-550 Ma. These data can help improve age models and provide important context for a critical period in metazoan evolution.
... Using some of those elements (Nb, Zr, Y, Th, Hf ), for the tectonic discrimination triangular diagrams (Hf/3-Th-Nb/16) after Wood [78] (Fig. 13), the studied samples fall within the E-MORB and within-plate tectonic domains. According to Rudnick and Gao [79], negative Ti, Ta and Nb anomalies are typical of continental crust and rocks whose chemical composition has been modified by subduction [80]. The enrichment in Nb, Ti and Ta of the mafic dykes exclude a contribution of the subducted slab to their formation [81,82]. ...
In the Central Cameroon Shear Zone, several studies were focused on granitoids and very few on mafic rocks. Here we report the petrography, geochemistry and mineralogy of the Mfengou-Manki mafic rocks in order to constrain their petrogenesis and tectonic settings and the role of lithospheric and asthenospheric mantle sources in their genesis. The studied mafic rocks are subdivided into columnar jointed basalts and mafic dykes. Clinopyroxene thermobarometry indicates that the mafic dykes crystallized at a temperature of 1071 to 1193 °C and a pressure of 4 to 12 kbar while the columnar jointed basalts emplaced at a temperature of 1064 to 1152 °C and 2 to 13 kbar pressure. The mafic dykes and columnar jointed basalts present high La/Sm, Sm/Yb, Nb/Yb and Th/Yb ratios, indicating garnet to spinel transition zone mantle source. The multi-element diagram of the mafic dykes display enrichment in Nb, Ta, Pb and Ti and depletion in Th, U, Ce and Zr compared to that of the columnar jointed basalts (slight depletion in Nb and Ta and pronounced depletion in U, Pb and Zr and enrichment in Cs, Ba and Rb) indicating the little involvement of the sub-continental lithospheric mantle to the formation of the columnar jointed basalts. The Nb/La ratio > 1 for the mafic dykes and < 1 for the columnar jointed basalts also suggest the derivation of the mafic dykes from the asthenospheric mantle and the columnar jointed basalts from the mixed lithospheric-asthenospheric mantle due to the sub-continental lithospheric mantle delamination under the Central Cameroon Shear Zone.
... 1000-900 Ma) interval is amongst the most intriguing periods for the Earth's evolution, including the formation of the Rodinia supercontinent (Moores, 1991;Dalziel, 1997). However, systematic periods of continental dispersion and subsequent assembly (Pisarevsky et al., 2003;Li et al., 2008;Ernst et al., 2013;Cawood et al., 2016Cawood et al., , 2020, drastically changed the early record during the assembly of Gondwana in the late Neoproterozoic (Cawood et al., 2022). ...
The Cariris Velhos event (ca. 1000-920 Ma) is a significant marker in the early Neoproterozoic lithospheric record of the Borborema Province in NE Brazil. Despite its importance, the nature of this event remains unresolved having been linked to either continental rifting or accretionary-collisional orogeny. In this study, we support a compressive setting for the Cariris Velhos event based on compiled geochemical and isotopic data (Sm–Nd and Lu–Hf) from metagranitic rocks in the Alto Pajeú Terrane (central Borborema) and in the Pernambuco-Alagoas Super Terrane, as well as in the Riacho do Pontal and Sergipano fold belts (Southern Borborema). Geochemistry of these rocks share similarities with calcic to alkali-calcic and ferroan magmas, along with some Cordilleran magnesian members. They also correspond to meta-to peraluminous I- and S-type granitic rocks. Trace element distribution on spider diagrams reveals negative anomalies of HFSE (high field strength elements) such as Nb and Ta, which are typically associated with subduction-related settings. Additionally, chondrite normalized REE (rare-earth element) diagrams indicate mixing of both crustal and mantle material. Tectonic discriminant diagrams using elements with low mobility supports the hypothesis of a continental margin subduction-related setting. Calculated εNd and εHf values vary from negative to slightly positive, suggesting contributions from juvenile inputs and reworking of Meso-Paleoproterozoic crust, as indicated by the associated TDM model ages. Although the nature of the Cariris Velhos event requires further investigation, we suggest that, at least partially, it corresponded to an orogenic episode that might have occurred concurrently with continental break-up, similar to modern continental arc-retro arc foreland settings.
... 200,000 km 3 (García-Arias et al. 2018). SLIPs are commonly attributed to the extensive melting of continental crust triggered by heat and fluids associated with underplating at the Moho by mafic magmas derived from a mantle plume (Díez Montes et al. 2010;Bryan and Ferrari 2013;Ernst et al. 2013). ...
We propose that the 495-470 Ma Ollo de Sapo magmatism in the Iberian Massif was the result of a mantle plume event in the Furongian-Early Ordovician. This plume was located beneath the northwestern margin of Gondwana and caused rapid and extensive melting of Ediacaran arc-related crustal rocks and their derived sediments. Mafic magmas due to plume partial melting underplated the crust and were emplaced at mid-lower crustal levels (~15km), and provided the heat for crustal melting. Manifestations of the plume include (i) pronounced magnetic anomalies in the region which match the distribution of Ollo de Sapo rocks, (ii) the Toledanian unconformity (and gap), which is attributed to thermal doming, and (iii) the significant thickness variations in Lower to Middle Ordovician sedimentary successions in adjacent areas. In a more regional context, we infer that the plume was one of a cluster of plumes impacting the Gondwana periphery and that it contributed to the birth and development of the Rheic Ocean throughout Gondwana margin breakup. ARTICLE HISTORY
... 2000 Ma ("Kenorland", e.g., Williams et al., 1991), or one or more transient and independent supercratons (e.g. Sclavia and Superia; Bleeker, 2003;Ernst et al., 2013, Liu et al., 2021, Nilsson et al., 2013, Nilsson et al., 2010. ...
... Intriguingly, accompanying those orogenic events, there were episodic mantle plume events at 1.27 Ga and 1.11-1.08 Ga (Ernst et al., 2008(Ernst et al., , 2013 and local 1.11-1.00 Ga intracratonic basin development (Greentree et al., 2006;Turner et al., 2016;Greenman et al., 2021). ...
We report three sets of newly identified late Mesoproterozoic mafic intrusions in the southwestern Yangtze Block, China. Secondary ion mass spectrometry (SIMS) baddeleyite and zircon U-Pb analyses yield crystallization ages of ca. 1.15 Ga for the Boka dolerites, ca. 1.07 Ga for the Lanniping gabbros, and ca. 1.06 Ga for the Tong’an mafic dikes. These are tholeiitic to alkaline rocks with enriched mid-ocean-ridge basalt (E-MORB)−like trace-element patterns and superchondritic εNd(t) values, indicating a partial melting origin from the asthenospheric mantle. These results, along with existing data, define two episodes of late Mesoproterozoic, rift-related mafic magmatism in the southwestern Yangtze Block: an early phase at 1.17−1.14 Ga and a late phase at 1.07−1.02 Ga. Initiation of the two episodes of extensional events in the southwestern Yangtze Block coincided with high-grade Grenville-aged metamorphism in Hainan Island and possible early collision of Cathaysia with the southwestern Yangtze Block, indicating an impactogen model. Therefore, we interpret the observed two episodes to have resulted from local collision between the southwestern Yangtze Block and the Cathaysia Block (including Hainan Island), which was possibly a part of western Laurentia during the assembly of Rodinia.
... The Franklin large igneous province (LIP) was the largest of a series of LIPs emplaced during the Tonian Period (1000-720 Ma) and has been linked to the break-up of the Rodinian supercontinent (Ernst et al., 2013). It produced basalts, mafic sills, and a large radiating dyke swarm, which together span a distance of 2500 km from Alaska, across northern Canada, to northwestern Greenland ( Fig. 1; Heaman et al., 1992;Denyszyn et al., 2009a;Cox et al., 2015;Macdonald and Wordsworth, 2017). ...
The Franklin igneous event (ca. 718 Ma) emplaced basalts and mafic intrusions across Arctic Laurentia just prior to the onset of the ca. 717-661 Ma Sturtian Snowball Earth event. Given the close association in time between these two events, it has been widely argued that the Franklin event contributed to the initiation of global glaciation. However, a lack of accurate high-precision geochronology has hampered establishing the timeframe of Franklin magmatism and discerning its precise temporal and possible causative relationship to glaciation. Here we present new high-precision U-Pb CA-ID TIMS zircon ages for two dykes and two sills from Baffin Island, Canada, and Avannaata, northwestern Greenland, related to the Franklin event. Combined with field relationships showing that the dykes crosscut the sills, these four dates indicate magmatic activity over 1.10 ± 0.74 Myr at ca. 718 Ma, immediately prior to Sturtian glaciation, which we estimate to have initiated at 717.19 +0.26/−0.33 Ma. Our results are consistent with recent high precision U-Pb CA-ID TIMS age estimates for the Franklin magmatic activity in the central and western parts of the province. Combining our new dates with the other high precision CA-ID-TIMS ages yields a duration for the Franklin event of 2.14 ± 0.75 Myr which is shorter than the previous estimates but somewhat longer than that for typical Phanerozoic large igneous events.
... Proterozoic Mafic dyke swarms preserved in Archean cratons represent the enduring erosional remnants of continental large igneous provinces (LIPs), and may be genetically linked with major episodes of continental rifting and supercontinent breakup, eruption of continental flood basalts (CFBs), and mantle plume activity Buchan 2001a, 2001b;Ernst and Srivastava 2008;Ernst et al., , 2013. These giant dyke swarms provide information on large scale extension occurring in the continental lithosphere, and thus they are important in interpreting continental evolution and plate or plume tectonics (e.g. ...
Continental flood basalts and major dyke swarms have their origin related in some way to the uprise of hot mantle plumes which may lead to rifting and eventual continental break-up. The association of mafic dykes with the initiation of basins and their geochemistry retaining ‘long term memories of subduction processes in the lithospheric mantle’. These mafic dyke giant dyke swarms provide information on large scale extension occurring in the continental lithosphere, and thus they are important in interpreting continental evolution and plate or plume tectonics and could be reveal information about petrogenesis of a magmatic event.
Many Large Igneous Provinces(LIP), particularly, continental flood basalts (CFB), have reported the presence of giant plagioclase. These giant plagioclase basalt(GPB) have low MgO content and are highly enriched in incompatible elements. In this study, detail mineral chemistry and petrographic study is carried out on the giant plagioclase-pyric mafic dykes from the Devarakonda area of eastern Dharwar craton.
... Being the most recent supercontinent in Earth history, Pangaea is the ideal candidate for studying the variables that influence the breakup of supercontinents due to its well-preserved and well-known geological history. Below, we first evaluate the ages and eruption centres of the consecutive LIP events related to the breakup of Pangaea (Fig. 2, Torsvik et al. 2006;Ernst et al. 2013;Ernst 2014). The association between orogens and the record of rift development is then discussed (Fig. 3) utilizing published geological information (e.g. ...
What drives the breakup of a supercontinent remains contentious. Previously proposed mechanisms include mantle plumes, subduction retreat, and basal traction from mantle convection. Here we review the geological record of plumes, orogens, and subduction zones during the Pangea breakup and investigate the potential roles played by these factors through 4D spherical geodynamic modelling. We found that mantle plumes provided the dominant force that drove Pangea's breakup, particularly in triggering the initial breakup. Young orogens as continental lithospheric weak zones generally guided the development of continental rifts, consistent with the geological record that rifting within Pangea commonly developed along pre-existing orogens. However, the marginal drag force produced by subduction retreat, and basal traction associated with subduction-related mantle flow, likely also played a role in Pangea's breakup. In addition, the weakening effect of plume-induced melts can sometimes help to break the continental lithosphere away from orogens, as exemplified by the breakup between Antarctica and Australia. Furthermore, geodynamic modeling suggests that subduction is responsible for generating mantle plumes. A particular such example is the formation of the Kerguelen plume, triggered by subduction along the northern margin of Australia, which facilitated the breakup between East Antarctica and Australia.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6670136
... Archean geodynamics are poorly constrained and highly debated due to the large volumes of crustal extraction, the drastic changes in the temperature and composition of the mantle, the formation of continental crust and episodic large-scale volcanic activity (Ernst and Buchan, 2001;Smithies et al., 2003;Ernst et al., 2013;Dhiume et al., 2015, and the references therein). The Archean crust was mafic in nature before 3,200-3,000 Ma (Tang et al., 2016). ...
Introduction: Metadolerite dykes in the Western Dharwar Craton represent the oldest generation of mafic dyke swarms in the craton. The emplacement of these dykes after a period of crust building activity and komatiite volcanism, helps to understand the evolution of Subcontinental Lithospheric Mantle (SCLM) and Archean dynamics.
Methods: We report whole rock major, trace element geochemistry and Sr-Nd isotope characteristics for this weakly metamorphosed suite of dykes. Remnant igneous textures and mineralogy are well preserved.
Results: The trace and rare earth element concentrations and an overall flat pattern suggests depleted mantle source for these dykes. Three groups are primarily identified: Group one with initial ⁸⁷Sr/⁸⁶Sr ratios varying between 0.70041 and 0.70102, Group two dykes and Group three dykes with initial ratios 0.70045–0.70154, and 0.70041–0.70153 respectively. Group one dykes show a good Rb-Sr isochron relationship and an errorchron age of ca. 3,003 ± 102 Ma is obtained. The initial ¹⁴³Nd/¹⁴⁴Nd ratios varies from 0.508,245 to 0.509,172. The epsilon Nd values are mostly negative, ranging between −12 and +5. Group one and two show an epsilon Nd value ranging between −1 and +5 and 0.1 to +5 respectively and group three varies between −0.5 and −12.
Discussion: The geochemical characteristics suggest that the group one dykes are derived from a homogenous depleted SCLM source, group two formed by a lower degree of partial melting of a source mantle with enriched components. Group three may have formed from a progressively enriched group one source. All these dykes can be considered as exposed remnants of feeders for the greenstone volcanism in the Western Dharwar Craton.
... At c. 615 Ma, the eastern segment of Iapetus (between Laurentia and Baltica) began to open in response to (super)plume activity of the Central Iapetus Magmatic Province (Ernst et al. 2013(Ernst et al. , 2021. Like Amazonia, the absence of coeval arc magmas and the presence of passive margin sequences along the margin of Baltica indicates that Baltica moved southward and collided with (1) a switch from sinistral to dextral transform relative motion between Baltica and Amazonia; and (2) an opportunity for subduction rollback to play a more important role in influencing the tectonic evolution of the West Gondwanan margin of the Mirovoi Ocean. ...
The late Neoproterozoic-Cambrian interval is characterized by global-scale orogenesis, rapid continental growth, and profound changes in Earth systems. Orogenic activity involved continental collisions spanning more than 100 million years, culminating in Gondwana amalgamation. Avalonia is an example of arc magmatism and accretionary tectonics as subduction zones re-located to Gondwana's periphery in the aftermath of those collisions, and its evolution provides significant constraints for global reconstructions. Comprising late Neoproterozoic (ca. 650-570 Ma) arc-related magmatic and metasedimentary rocks, Avalonia is defined as a composite terrane by its latest Ediacaran-Ordovician overstep sequence; a distinctive, siliciclastic-dominated cover bearing “Acado-Baltic” fauna. This definition implies Neoproterozoic Avalonia may consist of several terranes, and so precise paleomagnetic or provenance determination in one locality need not apply to all. On the basis of detrital zircon and Nd isotopic data, Avalonia and other lithotectonically-related terranes such as Cadomia, have long been thought to have resided along the Amazonian-West African margin of Gondwana between ∼650-500 Ma, Avalonia connected to Amazonia, and Cadomia to West Africa. These interpretations have constrained Paleozoic reconstructions; many imply the departure of several peri-Gondwanan terranes led to the Early Paleozoic development of the Rheic Ocean whose subsequent demise in the late Paleozoic led to Pangea amalgamation. Since these ideas were proposed, several new lines of evidence have challenged the Amazonian affinity of Avalonia. First, there is evidence that some Avalonian terranes may have been “peri-Baltican” during the Neoproterozoic. Baltica was originally excluded as a potential source for Avalonia because, unlike Amazonia, arc-related Neoproterozoic rocks were not documented. However, subsequent recognition of Ediacaran arc-related sequences in the Timanides of northeastern Baltica invalidates this assumption. Second, detailed paleontological and lithostratigraphic studies have been interpreted to reflect an insular Avalonia, well removed from either Gondwana or Baltica during the Ediacaran and early Cambrian. Third, recent paleomagnetic data have raised the possibility of an ocean (Clymene Ocean) between Amazonia and West Africa in the late Neoproterozoic, thereby challenging conventional reconstructions that show the “peri-Gondwanan” terranes as a contiguous belt straddling the suture zone between these cratons. In this contribution, we critically re-evaluate the provenance of the so-called “peri-Gondwanan” terranes, the contiguity of the so-called “Avalonian-Cadomian” belt, and the validity of the various plate tectonic models based on the traditional interpretation of these terranes. In addition, we draw attention to critical uncertainties and the challenges that lie ahead.
... LIPs or large-scale mafic magmatism in ancient cratons are usually related to continental rifting or extension and can provide important constraints on Precambrian paleogeographic reconstruction due to lack of other reliable evidence such as paleontology, glacial deposits and abundant paleomagnetic results (e.g., Ernst and Bleeker, 2010;Ernst et al., 2013Ernst et al., , 2016. The 1.24-1.21 ...
The Ectasion Period (1400–1200 Ma) represents a transition stage from Columbia (Nuna) to Rodinia supercontinents. LIPs and mafic magmatic events during this period can provide important constraints on deep processes and paleogeographic reconstructions during this transition. In this paper, we firstly reported some ca. 1.23–1.21 Ga flood basalts coeval with mafic sills from the Fanhe Basin in the northeastern North China Craton (NCC). New zircon/baddeleyite U-Pb/Pb-Pb dating on dolerite sills emplaced into the Fanhe Group yields emplacement ages from 1231 ± 9 Ma to 1206 ± 20 Ma. Whole-rock ⁴⁰Ar/³⁹Ar dating of two basalts from the Erdaogou Formation yields approximate total gas ages of ca. 1250 Ma and ca. 1210 Ma. These new geochronological results revealed that the Erdaogou basalts are coeval with some dolerite sills emplaced into the Kuangzhuangzi, Guanmenshan and Tongjiajie Formations and the dolerite sills emplaced into the Hutouling and Erdaogou Formations. These newly recognized ca. 1.23–1.21 Ga mafic rocks can be linked to the broader Licheng LIP of the previous studies. The ca. 1.23–1.21 Ga mafic rocks in the Fanhe basin can be divided into alkaline and sub-alkaline series and these two series exhibit distinct trace element and Nd isotopic compositions. The alkaline rocks show strongly fractionated chondrite-normalized REE patterns with high LaN/YbN values of 12.69–15.05. The sub-alkaline samples display less fractionated REE patterns with lower LaN/YbN values of 2.74–10.13. The alkaline rocks have OIB-like trace element patterns and slightly negative to positive εNd(t) values from −0.7 to 0.7. An OIB-like, asthenospheric mantle source is suggested as the source of the alkaline rocks. In contrast, the sub-alkaline rocks exhibit low negative εNd(t) values from −10.9 to −4.6 and are interpreted to be derived from a subduction-modified subcontinental lithospheric mantle. By comparisons with the coeval mafic magmatism in other parts of the NCC and other cratons, we suggest that the ca. 1.23–1.21 Ga mafic magmatism or LIP in the NCC was either related to the mantle plume that resulted in the Marnda Moorn LIP in Western Australia or related to a back-arc extension prior to the formation of a Grenvillian orogen located in another continent connected to the southeastern margin of the NCC during assembly of the Rodinia supercontinent.
... This approach applies a very selective filter to rocks and sampling sites, leaving many igneous events undated. Even so, recent works have been published on high-precision zircon U -Pb geochronology of LIPs in order to constrain global tectonic reconstructions (Bleeker and Ernst, 2006;Ernst et al., 2013) and to correlate mafic large igneous events to mass extinctions and environmental changes Heimdal et al., 2018;Schoene et al., 2019). It is the rarity and difficulty in concentrating zircon from mafic rocks that hinders our ability to extend these studies to other tectonomagmatic events. ...
Geochronology is a remarkable tool that allows for a direct assessment of geological problems or positioning of events on chronostratigraphic scales. Zircon U-Pb geochronology is the most successful method available, since zircon can survive a range of different alterations, the U-Pb method has in situ and isotope dilution techniques, and the dual decay of 238U–206Pb and 235U–207Pb provides an internal cross-check of closed system behavior of the mineral. Nevertheless, zircon dating is not always appropriate in mafic rock studies because of the magma emplacement temperatures and SiO2 saturation conditions that are often outside of the zircon crystallization window. Even so, it is the difficulty in concentrating zircon from mafic rocks that hinders our capability to apply this geochronometer to these tectonomagmatic events. Usually, large rock volumes are sampled in order to compensate this issue, meaning that if one can concentrate just a few crystals per kilogram, by sampling large quantities of rock enough crystals may be separated. However, do we really need large amounts of mafic rock samples to concentrate enough zircon crystals for a dating experiment? A continuous process of conceiving new techniques for concentration and separation of these minerals on a range of different rock compositions has been pursued. Here, we show that a separation technique that substitute physical process by a chemical dissolution makes it capable to concentrate viable amounts of zircon crystals from mafic rocks using, on average, only 1kg (or less) of rock sample. This is grounded on the idea that what hampers the capability of zircon concentration on mafic rocks is the relation between these crystals and magnetic phases that are particularly abundant on such rock types, and which are lost during magnetic treatments such as hand magnet and Frantz processing. Furthermore, crystal sizes are exceptionally important because, on sub-abyssal to extrusive environments, zircon may form crystals of less than 50 μm, which may be lost during density liquids treatment. Thus, by substituting the conventional physical separations for a bulk rock chemical digestion, the recovery rate in relation to the conventional zircon separation techniques is approximately one hundred times better. In the chemical dissolution technique, the sample is initially grounded to sand-size particles and the heavy minerals are concentrated via water table separation, this is the only physical treatment employed. Then, the heavy minerals portion is heated at 900 ºC for 60h on a muffle furnace and put through four steps of acid digestions: aqua-regia, hydrofluoric acid, aqua-regia and finally hydrochloric acid. This method allows the separation of a roughly pure zircon concentrate, since the method design was established so zircon is one of just a few mineral phases that can survive these acid attacks. In all, zircon concentrated from the chemical separation method allows for a cut of sample masses from tens of kilograms to only one kilogram or less, which is especially relevant to mafic rock studies but can also be expanded to other “difficult to concentrate zircon” rock types.
... Reconstruction of the Nuna supercontinent at 1640 Ma (modified from Mitchell et al. 2021). The location of 1680-1620 Ma mafic dykes and sills (age in Ma in parentheses) (Ernst et al. 2013;Baratoux et al. 2019;) and 1700-1200 Ma massif-type anorthosites (Ashwal 1993(Ashwal , 2010 are indicated. The shapes of the present day African and Pacific large low-shear-velocity provinces (LLSVPs) at the core-mantle boundary are indicated with light red filling (1 % slow-velocity contour in the lowermost layer of the mean shear-wave tomographic model SMEAN, Becker & Boschi 2002). ...
We have reappraised the age and composition of the mid-Proterozoic Häme dyke
swarm in southern Finland. The dominant trend of the dykes of this swarm is NW to
WNW. Petrographic observations and geochemical data indicate uniform, tholeiitic lowMg parental magmas for all of the dykes. Nevertheless, the variability in incompatible
trace element ratios, such as Zr/Y and La/Nb, provides evidence of changing mantle
melting conditions and variable crustal contamination. Our ID-TIMS 207Pb/206Pb ages
for four low-Zr/Y-type dykes indicate emplacement at 1639 ± 3 Ma, whereas the most
reliable previously published ages suggest emplacement of the high-Zr/Y-type dykes at
1642 ± 2 Ma. We propose that the Häme dyke swarm, and possibly also the other midProterozoic mafic dyke swarms in southern Finland, records a progressive decrease in
Zr/Y values due to magma generation under developing areas of thinned lithosphere.
We consider that the formation of mafic magmas was most probably associated with
the upwelling of hot convective mantle in an extensional setting possibly related to
the nearby Gothian orogeny. The generation of tholeiitic magmas below continental
lithosphere was probably promoted by the elevated mantle temperature underneath
the Nuna supercontinent. We speculate that the origin of most of the relatively small
mid-Proterozoic mafic dyke swarms, anorthosites, rapakivi granites, and associated
rocks found across Nuna was similarly triggered by extensional plate tectonics and the
convection of anomalous hot upper mantle below the supercontinent.
... It is well-established that the tectonic motion of a plate above a mantle plume can produce a hotspot track represented by a series of LIPs, such as the Hawaii-Emperor seamount chain (Koppers et al., 2021;Morgan, 1971). Giant mafic dike swarms are the well-preserved plumbing systems of LIPs, and their magma centers (Ernst, 2014;Ernst et al., 2013) can be used to reconstruct hotspot tracks even in Precambrian time (Betts et al., 2007;Wang et al., 2019). Assembly of North China craton at 1900 Ma (Kusky et al., 2016;Zhao et al., 2002) was followed by the emplacement of a group of LIPs distributed across much of the craton and centered on or adjacent to the Xiong'er rift (Fig. 2) (Peng, 2016). ...
Available online xxxx Editor: C.M. Petrone Keywords: plume subduction hotspot track large igneous province mantle dynamics Columbia supercontinent The concurrence of both global orogenesis and large igneous provinces (LIPs) from 2200-1600 Ma remains enigmatic. This apparent contradiction of top-down and bottom-up geodynamics occurred during assembly of Earth's oldest-known supercontinent. We present a multidisciplinary study combining the dismembered portions of major LIP worldwide and correlate them across supercontinent Columbia to the same plume center (Xiong'er of the North China craton). The succession of LIPs is then used to trace the oldest established hotspot track associated with a pulsating plume constraining ancient plate motion. Subduction-controlled plume generation can explain mantle upwelling occurring where subducted slabs forming the supercontinent had previously sunk to the base of the mantle and advected the Xiong'er mantle plume due to return flow. Tectonic motion detected by the hotspot track can account for both those regions of the supercontinent with and without LIPs. Such historical constraints on the interaction between plumes and subduction are critical in linking bottom-up and top-down tectonic processes at the dawn of the supercontinent cycle.
... How we might interpret mantle plumes and plate tectonics can well clarify the most of the tectonicmagmatic events on the planet Earth, and the connections between them has forever been the interesting issue in earth sciences. The Kerguelen mantle plume in the Indian Ocean is different from the typical short duration (1-5 Myr) of most mantle plumes as it had a long lifespan of time of 147 Myr (White 2010;Ernst et al. 2013;Shi et al. 2018;Jiang et al. 2021). Its long continuous activity (Kent 1991;Coffin 2002;Jiang et al. 2021) produced a huge amount of magmatic rocks from the Late Jurassic to the present, now widely dispersed from their original localities of emplacement due to the changing motions of Antarctic, Australian, Indian, and Tethyan Himalayan plates (Figure 1; Frey et al. 1996, Frey et al. 2015Ingle et al. 2002;Coffin 2002;Zhu et al. 2008, Zhu et al. 2009Storey et al. 2013;Olierook et al. 2015, Olierook et al. 2016, Olierook et al. 2017, Olierook et al. 2019Yang et al. 2015;Ma et al. 2016;Liu et al. 2015;Bian et al. 2019;Shi et al. 2018;Jiang et al. 2021). ...
The remnant Comei igneous province in SE Tibet has been recognized as a product of early Kerguelen mantle plume activity. In this paper, we investigate mafic dykes and sills intruded into Lakang Formation in the southeastern Tethyan Himalaya. Based on new whole-rock geochemical, Sr-Nd-Pb isotopic and SHRIMP zircon U-Pb geochronological data, these rocks can be divided into three groups. Group 1 is composed of OIB-like mafic dykes and sills with lower εNd(t) (+1.78-+2.55) and dated at 124.8 ± 1.7 and 133.3 ± 1.5 Ma. Group 2 consists of N-MORB-like mafic dykes and sills with lower TiO2 and P2O5 contents. Group 3 has geochemical compositions transitional between Group 1 and Group 2, with εNd(t) ranging from +1.98 to +2.24 and an age of 125.1 ± 2.1 Ma. We interpret Group 1 as being derived from an OIB-like source related to a mantle plume. Groups 2 and 3 are considered to have been generated from melts of the asthenosphere and the lower crust, with some involvement of melts from the upper crust. Considering the oldest (ca. 147 Ma) and the youngest (ca. 125 Ma) ages of the OIB-like mafic dykes and sills related to the Kerguelen mantle plume and their palaeogeographic location, we suggest that the Kerguelen mantle plume head had reached the lithosphere during the late Jurassic and was later directly underneath the Cona area. We propose a new model to describe the early activity of Kerguelen mantle plume, which put the mantle plume below the mid-ocean ridge and can well explain the long-lived magmatism related to Kerguelen mantle plume.
... This approach applies a very selective filter to rocks and sampling sites, leaving many igneous events undated. Even so, recent works have been published on high-precision zircon U -Pb geochronology of LIPs in order to constrain global tectonic reconstructions (Bleeker and Ernst, 2006;Ernst et al., 2013) and to correlate mafic large igneous events to mass extinctions and environmental changes Heimdal et al., 2018;Schoene et al., 2019). It is the rarity and difficulty in concentrating zircon from mafic rocks that hinders our ability to extend these studies to other tectonomagmatic events. ...
Zircon geochronology is applied to a variety of geological problems to precisely and accurately date rocks via UPb decay. Zircon is most abundant and easily recovered in intermediate to felsic rocks, including the silicic eruptives of bimodal large igneous provinces, or fractionated granophyres in mafic-ultramafic complexes. However, the concentration of zircon crystals by conventional density and magnetic separation methods is inefficient and/or ineffective for medium- to fine-grained mafic rocks, due to their rarity, small grain size, common association with ferromagnetic minerals, and/or occlusion by paramagnetic modal minerals. To address these shortcomings, we have developed and tested a zircon concentration method that is based on a combination of physical separation and chemical dissolution. The sample is initially ground to sand-size particles and heavy minerals concentrated via density on a water table. The heavy mineral-rich fraction is annealed by heating at 900 °C for 60 h, and then put through a series of acid digestions: aqua-regia, hydrofluoric acid, aqua-regia and finally hydrochloric acid. This new method allows the concentration of an almost pure zircon aliquot, since zircon is one of just a few minerals that can survive this bulk rock acid attack. The result is an efficient extraction of analytically viable amounts of zircon for UPb geochronology using tens of grams of rock sample, representing an increase up to a hundred times the recovery rates of conventional separation techniques for zircon concentration.
... cf. Ernst et al., 2013;Srivastava et al., 2019). However, rocks forming part of the dominantly mafic early Paleoproterozoic Karelian magmatism in Baltica have been included, since this magmatism is more varied and also contains felsic components. ...
A total of 4344 magmatic U-Pb ages in the range 2300 to 800 Ma have been compiled from the Great Proterozoic Accretionary Orogen along the margin of the Columbia / Nuna supercontinent and from the subsequent Grenvillian collisional orogens forming the core of Rodinia. The age data are derived from Laurentia (North America and Greenland, n = 1212), Baltica (NE Europe, n = 1922), Amazonia (central South America, n = 625), Kalahari
(southern Africa and Dronning Maud Land in East Antarctica, n = 386), and western Australia (n = 199). Laurentia, Baltica, and Amazonia (and possibly other cratons) most likely formed a ca. 10 000-km-long external active continental margin of Columbia from its assembly at ca. 1800 Ma until its dispersal at ca. 1260 Ma, after which all cratons studied were involved in the Rodinia-forming Grenvillian orogeny. However, the magmatic
record is not smooth and even but highly irregular, with marked peaks and troughs, both for individual cratons and the combined data set. Magmatic peaks typically range in duration from a few tens of million years up to around hundred million years, with intervening troughs of comparable length. Some magmatic peaks are observed on multiple cratons, either by coincidence or because of paleogeographic proximity and common tectonic setting, while others are not. The best overall correlation, 0.617, is observed between Baltica and Amazonia, consistent with (but not definitive proof of) their being close neighbours in a SAMBA-like configuration at least in Columbia, and perhaps
having shared the same peri-Columbian subduction system for a considerable time. Correlation factors between Laurentia and Baltica, or Laurentia and Amazonia, are below 0.14. Comparison between the Grenville Province in northeastern Laurentia and the Sveconorwegian Province in southwestern Fennoscandia (Baltica) shows some striking similarities, especially in the Mesoproterozoic, but also exhibits differences in the timing of events, especially during the final Grenville-Sveconorwegian collision, when the Sveconorwegian evolution seems to lag behind by some tens of million years. Between the other cratons, the evolution before and during the final Grenvillian collision is also largely diachronous. After 900 Ma, magmatic activity had ceased in all areas investigated, attesting to the position of most of them within the stable interior of Rodinia.
... In fact, the extension may have started at least as early as 1.85 Ga, as indicated by 1.85 Ga mafic dykes (Wan et al. 2013;Li et al. 2020a). Both sedimentary and magmatic events in the NCC provide evidence of a long-term extensional environment from 1.8 to 0.8 Ga without any evidence of block amalgamation, being similar to many other cratons (Ernst et al. 2013). This period is a key adjustment period of lithospheric structure and lower crust composition Zhai 2019), named Earth's 'middle age' (Cawood and Hawkesworth 2014). ...
The 2022 Winter Olympics will be held in the Beijing-Zhangjiakou area, which is located in the eastern North China Craton (NCC) and contains a comprehensive geological record from the Archaean to Cenozoic. In this paper, we first review the geology of the Beijing-Zhangjiakou area, then, combined with data from the rest of the NCC, we discuss the geological evolution of the area in the context of the NCC. The geological and tectonic evolution of the Beijing-Zhangjiakou area can be regarded as a proxy or analogue for the geological history of the whole of the NCC. Six stages have been divided as follows: 1) Neoarchean massive continental crust growth; 2) Paleoproterozoic cratonization; 3) Meso-Neoproterozoic multi-stage rifting; 4) Palaeozoic marginal orogeny; 5) Mesozoic craton destruction; and 6) Cenozoic intra-plate extension. We hope this paper will be helpful to both geologists and non-geologists who will attend the 2022 Beijing-Zhangjiakou Winter Olympics and may be interested in rocks and geology around the Winter Olympic sites.
We present new petrographic, whole-rock geochemistry, and SHRIMP U – Pb zircon geochronological data of metabasic rocks interlayered as sills in the metasedimentary units of the Perau and Betara formations, Votuverava Group, Southern Ribeira Belt, Brazil. These formations overlie ~ 1.8 Ga Paleoproterozoic metagranitoids that represent basement inliers from the Paranapanema Craton. Petrography and whole-rock geochemistry allow the recognition of four groups, ranging from primitive to evolved compositions: i) cumulatic metadolerites (G1), ii) isotropic metadolerites (G2), iii) ortho-amphibolites (G3); and iv) ferroan ortho-amphibolites (G4). They exhibit tholeiitic subalkali basaltic composition, near-flat REE patterns, and signatures between N- and E-MORB. Fractional crystallization under low fO2 conditions is the main petrogenetic process controlling the magmatic evolution, as observed by Ti/V and Cr/Y ratio and tholeiitic trends. Crustal contamination signatures are observed through negative Nb anomaly, Th/Nb-Ti/V proxies trends, LILE enrichment, and, also, assimilated xenocryst zircons aged ~ 2.2 Ga. REE and trace element systematics indicate that the basic magmas were generated by ~ 20–10% partial melting of a model asthenospheric mantle source within spinel facies. TiO2/Yb-Nb/Yb and Nb/Yb-Zr/Yb ratio proxies and P-MORB metabasic rocks, previously described in the literature within the Votuverava Group, suggest a plume-influenced melt. A new SHRIMP U – Pb zircon age of 1448 ± 11 Ma was determined for an ortho-amphibolite sample (G3 group). We propose an intracontinental tectonic setting for the genesis of the metadolerites whitin the Perau and Betara formations, suggesting that this extensional event is associated with the Paranapanema Craton rifting. Furthermore, the genesis of the studied metabasic rocks could be associated with a regional extensional event during Calymmian times (~1.5–1.45 Ga), which generated basic magmatism in several other cratons, such as the Congo, São Francisco, Siberian, Laurentian, and China cratons, linked to the break-up of the Columbia Supercontinent.
The Coorg Block in southern Peninsular India is one of the oldest crustal blocks on Earth that preserves
the evidence for continental crust formation during the Paleo-Mesoarchean through subduction related
arc magmatism, followed by granulite facies metamorphism in the Mesoarchean. In this study,
we report for the first time, the ‘bar codes’ of a major Paleoproterozoic Large Igneous Province in the
Coorg Block through the finding of mafic dyke swarms. The gabbroic dykes from the Coorg Block, dominantly
composed of plagioclase-pyroxene assemblage, show a restricted range in SiO2 values of 50.04–
51.27 wt.%, and exhibit a sub-alkaline tholeiitic nature. These rocks show relatively flat LREE and constant
HREE patterns and lack obvious Eu anomalies. Trace element modeling suggests that the dyke swarm was
fed from a melt that originated at a shallow mantle level in the spinel stability field. Zircon grains are rare
in the gabbro samples and those separated from two samples yielded 207Pb/206Pb weighted mean dates of
2214 ± 12 Ma and 2221 ± 7 Ma. The grains show magmatic features with depleted LREE and enriched
HREE and positive Ce and negative Eu anomalies. Baddeleyite grains were dated from five gabbro samples
which yielded 207Pb/206Pb weighted mean ages ranging between 2217 ± 7 Ma and 2228 ± 10 Ma. The
combined data show a clear age peak at ca. 2.2 Ga. The mafic dykes in the Coorg Block show geochemical
similarities with ca. 2.2 Ga mafic dyke swarms in different regions of the Dharwar and other cratons in
Peninsular India and elsewhere on the globe. The data also support the inference that the global mafic
magmatism at ca. 2.2 Ga was linked with intracontinental rifting of the Archean cratons through mantle
upwelling or plume activity. We correlate the mafic dyke swarms in the Coorg Block with attempted rifting
of the Neoarchean supercontinent Kenorland.
The Mongolian micro‐continental fragments play an important geodynamic role in the Palaeozoic evolution of the Central Asian Orogenic Belt. However, the original provenance of individual blocks within the Nuna/Columbia and Rodinia supercontinents is not well constrained. In this work, we present zircon U–Pb and Lu–Hf isotopic data from the Mesoproterozoic to Neoproterozoic metamorphosed cover of the Baidrag Block in central Mongolia. These data reveal important maxima in the Neoarchean, Palaeoproterozoic and locally Neoproterozoic. Although the majority of the new data can be attributed to local sources within the basement of the Mongolian micro‐continental fragments, an important contribution of juvenile 2.0 Ga zircons is linked to the western margin of the Siberian Craton, and 1.5 Ga zircons are either directly derived from North Australia or indirectly recycled from sediments in NW Laurentia.
The Mesoproterozoic Gawler Range Volcanics and Benagerie Volcanic Suite of the Gawler Craton and Curnamona Province, South Australia, together with associated intrusive magmatism, define an intracontinental, subaerial large igneous province (LIP) preserving an estimated 110 000 km³ of volcanic rock, which hosts one of the world's largest orebodies, the Fe oxide-Cu-Au-U deposit at Olympic Dam, and numerous other related Cu-Au deposits. New high-precision Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-TIMS) U-Pb dates on volcanic zircons allow for regional correlations between stratigraphic units of the GRV and BVS, and an understanding of how magmatic styles, temperatures, composition and mantle source input evolve over the duration of the LIP. The new dates indicate that the entire volcanic province erupted over a geologically short time interval of less than 10 million years, from c. 1595 to 1586 Ma, culminating in a widespread, voluminous flood rhyolite province that erupted in less than 1.5 million years, and most likely in 260,000 years or less. This follows a pattern of volcanism that is similar in duration and volume to mafic and bimodal continental LIPs, of which the mafic-dominated Phanerozoic continental flood basalt provinces are the more common end member.
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Refinements of the geological timescale driven by the increasing precision and accuracy of radiometric dating have revealed an apparent correlation between large igneous provinces (LIPs) and intervals of Phanerozoic faunal turnover that has been much discussed at a qualitative level. However, the extent to which such correlations are likely to occur by chance has yet to be quantitatively tested, and other kill mechanisms have been suggested for many mass extinctions. Here, we show that the degree of temporal correlation between continental LIPs and faunal turnover in the Phanerozoic is unlikely to occur by chance, suggesting a causal relationship linking extinctions and continental flood basalts. The relationship is stronger for LIPs with higher estimated eruptive rates and for stage boundaries with higher extinction magnitudes. This suggests LIP magma degassing as a primary kill mechanism for mass extinctions and other intervals of faunal turnover, which may be related to CO 2 , SO 2 , Cl, and F release. Our results suggest continental LIPs as a major, direct driver of extinctions throughout the Phanerozoic.
A Teoria dos Supercontinentes teve como seu instaurador principal Alfred Wegener, nos seus clássicos trabalhos nas primeiras décadas do século XX. Deve ser destacada a frente de contestação que lhe foi imposta de geocientistas dos dois mundos (então, todos “geossinclinalistas”). A retomada (e o crédito) só veio com Harry Hess, em 1962, quando este mostrou que os grandes empecilhos (fatores desconhecidos da deriva continental, não explicados devidamente), inibidores da teoria, passaram a ser cientificamente demonstráveis. Isso com suas pesquisas, com o conceito de convecção mantélica e mais ainda com proveito do ímpeto do surgimento da Tectônica de Placas (e o combate ao fixismo sensu lato). Seguindo Hess, alguns trabalhos foram acrescentados, com novas proposições, adendos, revisões, principalmente entre 1992 e 2005. Desde então, instalou-se fase notável de contribuições, publicações, livros e capítulos, todos com novos dados científicos. Temos que admitir que esse ramo das geociências ainda está em estágio de fluxo. A aplicação desses conceitos e conhecimentos, merecedora de um projeto internacional específico, foi estendida do Arqueano (no caso mais problemático de todos erátemas) até o fim do Mesoproterozoico (e.g. projetos “Gondwana”, “Rodínia” etc.). Concomitantemente a esses trabalhos e dados, já surgiram várias questões pendentes, para todos os casos de supercontinentes. Catalogamos uma série de problemas que queremos expor e as soluções que são demandadas. O conclusivo hoje é que o supercontinente Pangea, pelos seus dados geológicos gerais, geocronológicos e paleomagnéticos, é o único que pode ser colocado no status de fato científico. Todas as demais configurações propostas anteriores à Pangea são boas hipóteses de trabalho, a serem investigadas/exploradas de forma multidisciplinar.
Diabase sills (1.33–1.30 Ga) in the northern North China Craton (NCC) represent a large igneous province (Yanliao LIP) extending > 600 km from west to east. The Yanliao LIP in the NCC and the Derim Derim–Galiwinku LIP in Northern Australian Craton (NAC) are interpreted as fragmented parts of the same LIP, supporting a close connection between the northeastern margin of the NCC and the northern margin of the NAC during the Mesoproterozoic at ca. 1.32 Ga. However, the eastern edge and original size of the Yanliao LIP are less-constrained. Here, we present geochronological and geochemical data of a newly identified ca. 1.33 Ga dolerite dyke intruding the Paleoproterozoic Liaohe Group in the Liaodong Peninsula, northeastern NCC, and conclude a substantially broader extent of the Yanliao LIP than previously proposed. The dyke shows ophitic textures and contains mainly plagioclase, clinopyroxene and hornblende. LA–ICP–MS U–Pb dating of zircons from four dolerite samples yields a mean age of ∼1.33 Ga. The samples have 48.24–49.77 wt% SiO2, 12.41–13.75 wt% Fe2O3T, 4.61–7.18 wt% MgO and 2.54–3.51 wt% total alkalis (K2O + Na2O), exhibiting tholeiitic basalt compositions. In addition, the dolerites feature enrichments in light rare earth elements ((La/Yb)N = 3.00–3.61) and large ion lithophile elements (e.g., Rb and Pb) but depletions in some high field strength elements (e.g., Nb and Ta), with affinities to within-plate basalts. The dolerite samples have εNd(t) values of –0.6 to +1.0, Th/Nb (0.40–0.45) and Pb/Nb (0.49–1.59) ratios distinctly higher than those of E-MORB and OIB, consistent with derivation from a metasomatized subcontinental lithospheric mantle with insignificant crustal contamination. Our work and available investigations reveal spatial changes in the emplacement style of mafic sills in the central and mafic dykes in the eastern and western parts of the updated Yanliao LIP. The recognition of the ca. 1.33 Ga dolerite dyke in the Liaodong Peninsula reveals ∼500 km eastward extension for the Yanliao LIP to the northeastern margin of the NCC, which further supports the close link between the NCC and the NAC.
Although Neoproterozoic magmatic rocks extensively occur both in the southern and northern margins of the Tarim Craton (TC), their distinct characteristics indicate not only different petrogenesis but also different tectonic settings. What caused these differences remains unknown. Here, we present new geochronological and geochemical data for mafic dykes collected from the Aktash Tagh area in the southeastern TC, in order to constrain the petrogenesis and reconstruct the Neoproterozoic tectonic evolution of the TC. Zircon U–Pb dating of the mafic dykes yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 885 ± 4 Ma, which represents the crystallization age. The εHf(t) values of the zircons from the dykes vary from + 4.8 to + 14.2 with depleted mantle model ages (TDM1) of 1.25–0.87 Ga, among which the highest εHf(t) value nearly approaches to that of the coeval depleted mantle. The mafic dykes are characterized by relative uniform geochemical compositions with low SiO2 (46.89–48.49 wt%), K2O (0.36–0.70 wt%), and high Na2O (1.90–2.31 wt%), Fe2O3T (9.35–11.98 wt%) and TiO2 (0.96–1.50 wt%) components, which show tholeiitic affinities. Their slightly fractionated chondrite-normalized rare earth element patterns are similar to those of E-MORB, together with the positive εNd(t) (+4.9 to +6.3) of the dykes, indicating a slightly modified asthenospheric mantle source. In addition, the mafic dykes exhibit moderate enrichment in large ion lithophile elements, but show unconspicuous anomalies of the high field strength elements. On the basis of these geochemical and isotopic compositions, we suggest that these dykes were formed in an extensional setting likely related to intra-continent rifting and generated by ∼ 20% partial melting of a garnet- and spinel-bearing asthenospheric mantle source that had been modified by ancient slab-derived fluids. In combination with the previous studies on the Neoproterozoic magmatic rocks both of the southern and northern TC, we propose that the southern TC was located in the periphery of Rodinia and it most likely faced to the interior of this supercontinent during the time at 885–740 Ma.
The Tarim Craton (or Tarim Block) is geographically located in the Northwest of China and tectonically between the Central Asian Orogenic Belt (CAOB) to the north and the Tethys to the south, which underwent a secular Precambrian evolution history from Ecoarchaean to Ediacaran. Owing to its marginal positions both in the Columbia (or Nuna) and Rodinia supercontinent configurations, it could play a key role in understanding the geodynamics of the assembly and break-up of the Precambrian supercontinents. This paper aims to present a critical review on the comprehensive synthesis of the Tarim Craton, detailing the Precambrian evolution processes and discussing its coupling with the Precambrian supercontinents. The Tarim Craton shows a typical plateform-like and double-layered structure, comprising the pre-middle Cryogenian basement with the middle Cryogenian-Ediacaran cover sequence. During its protracted basement evolution, diverse types and multiple stages of pre-Ediacaran intrusions were emplaced in the basement. Since Pleoproterozoic to early Cryogenian, crust reworking, rather than juvenile crust addition, played a key role in the final cratonization of its basement. Despite the final cratonization of the Tarim completed in the middle Cryogenian, both the bulk-rock Sm-Nd and zircon Lu-Hf isotope compositions demonstrated that its crust mainly formed in Archaean. Its characteristics of sedimentary features, metamorphic temporal-spatial architecture, the multiple phases and diverse types of intrusions reveal that the Tarim Craton is possibly composed of two main terranes with distinct features, i.e. the Northern Tarim Terrane (NTT) and the Southern Tarim Terrane (STT). It has been suggested that the STT could be a continental fragment that has drifted from West Africa, while the NTT shows a significant affinity with the India–North China Craton before Calymmian. Both were involved in the assembly and break-up of the Columbia supercontinent, and amalgamated during the assembly of the Rodinia. At the same time, it docked at the northern margin of Australia in the middle Cryogenian. Nevertheless, the subduction along the northern margin of the NTT continued at least until ca. 760 Ma. The voluminous 820–760 Ma diverse-type intrusions in the NTT have been ascribed to a genetic relation in the interaction between the circum-Rodinia subduction and the Rodinian superplume. The upwelling of the Rodinian superplume terminated the long-lasting subduction along the northern margin of the Tarim Craton. Since 740 Ma, being consistent with the break-up of the Rodinia, the Tarim Craton started drifting from the Rodinia supercontinent. The transition from signature to the passive continental margin of the middle Cryogenian-Ediacaran (for its cover sequences) rules out the possibility of the circum subduction along its northern margin lasting to early Palaeozoic. Additionally, with the Rodinia breaking up into the assembly of the Gondwana, the Tarim Craton, together with other continents in Eastern Asia, had docked at the margin of the Eastern Gondwana in early Palaeozoic.
Proxies such as mercury and Hg/TOC anomalies document signatures for temporal correlations between major pulses of the Late Ordovician mass extinction (LOME) event and a postulated Large Igneous Province (LIP) as the main cause of extinction. Herein, for the first time, we report a series of voluminous intraplate volcanic events of the Middle Ordovician-Silurian from northern Iran, representing the erosional and deformed remnants of a LIP as well as a robust candidate as the cause of the LOME. These volcanic rocks, distributed over a length of ca. 1700 km and more than 1000 m thickness in some cases, were erupted during initial rifting of the Paleotethys Ocean in northern Gondwana. Based on fieldwork, relative ages, and high precision U-Pb ID-TIMS dating results we have identified one plutonic (granitic) and six volcanic (mainly basaltic) phases of mostly short duration for this chain of magmatism. The onset of volcanic events at 468.70±0.30 Ma (2σ) coincided with the earliest Darriwilian, followed by a huge bimodal volcanic event between the Sandbian-Katian boundary and 450.61±0.27 million years ago, and the climax of volcanism occurred during the late Katian-Hirnantian. An approximate coincidence between the onset of basaltic eruption and weathering in northern Iran and the beginning of significant global decline in seawater ⁸⁷Sr/⁸⁶Sr during the Darriwilian Stage may be a sign of the initial volcanic activities of our newly identified LIP. We suggest that the Middle Ordovician-Silurian volcanic rocks from northern Iran, and other related places, are remnants of this newly proposed LIP (herein labeled the Alborz LIP), with high potential to be the main cause of environmental and climatic changes that led to the LOME.
Identification of large-volume, short-duration mafic magmatic events of intraplate affinity in both continental and oceanic settings on the Earth and other planets provides invaluable clues for understanding several vital geological issues of current concern. Of particular importance is understanding the assembly and dispersal of supercontinents through Earth's history, dramatic climate change events including mass extinctions, and processes that have produced a wide range of large igneous province (LIP)-related resources, such as Ni–Cu–PGE, Au, U, base metals and petroleum. This volume comprises 21 contributions on the latest developments and new information on LIPs and their plumbing systems and presents methodical studies on different components of LIP plumbing systems. These articles are especially helpful in understanding continental break-up events, regional domal uplift and a variety of metallogenic systems, as well as the temporal and spatial distribution of LIPs, their origin and their likely links to mantle plumes/superplumes.
Banded iron formations of the ca. 2770-2405 Ma Hamersley province of Western Aus-tralia were locally upgraded to high-grade hematite ores during the Early Paleoprotero-zoic by a combination of hypogene and supergene processes after the initial rise of atmospheric oxygen. Ore genesis was associated with the stratigraphic break between the Lower and Upper Wyloo Groups of the Ashburton province, and has been variously linked to the Ophthalmian orogeny, late-orogenic extensional collapse, and anorogenic continental extension. Small-spot in situ Pb/Pb dating of baddeleyite by sensitive high-resolution ion microprobe (SHRIMP) has resolved the ages of two key suites of mafic intrusions, constraining for the first time the tectonic evolution of the Ashburton province and the age and setting of iron-ore formation. Mafic sills dated as ca. 2208 Ma were folded during the Ophthalmian orogeny and then cut by the unconformity at the base of the Lower Wyloo Group. A mafic dike swarm that intrudes the Lower Wyloo Group and has a close genetic relationship to iron ore is ca. 2008 Ma, slightly younger than a new syneruptive 2031 6 Ma zircon age for the Lower Wyloo Group. These new ages constrain the Ophthalmian orogeny to the period between ca. 2208 and 2031 Ma, before Lower Wyloo Group extension, sedimentation, and flood-basalt volcanism. The ca. 2008 Ma dikes present a new maximum age for iron-ore genesis and deposition of the Upper Wyloo Group, thereby linking ore genesis to a ca. 2050-2000 Ma period of continental extension similarly recorded by Paleoproterozoic terrains worldwide well after the initial oxidation of the atmosphere by ca. 2320 Ma.
Mafic dykes from North America and India are used to highlight certain structural features that may provide further insight into the origin and geodynamic significance of dyke swarms, particularly those of Precambrian age. Structural aspects of interest within any one swarm include regional variations in dyke attitude, preference in direction of dyke branching, radiating dyke patterns, and orthogonality of dyke trends with the structural grain of enclosing host rocks. Geological observations suggest that sub-horizontal magma flow is a common feature of dyke intrusion and thus changes in petrology, geochemistry and the orientation of flow-induced fabric along the length of a swarm might be expected which would have important bearing on problems concerning location of magma sources and the process of dyke injection.-Author
Large igneous provinces (LIPs) constitute voluminous accumulations of predominantly iron- and magnesium-rich rock that are emplaced in a relatively short geological interval of a few million years or less. Formed by processes unexplained to date by the plate tectonics paradigm, LIPs include oceanic plateaus, volcanic divergent margins, and continental flood basalts. Temporal correlation of LIPs with major global environmental changes, including mass extinctions and oceanic anoxic events, suggest causal relationships.
The sense of a magnetic polarity change in the Melville Bugt dyke swarm of western Greenland has been obtained from precise U-Pb dating on baddeleyite. A SW-directed down magnetization is older (1,635 ± 3 to 1,632 ± 1 Ma) than an upward, NE-directed remanence (1,629 ± 1 to 1,622 ± 3 Ma). Assuming only one polarity change during this interval, the same field reversal may be recorded by the 1,633 Ma Sipoo dykes of Finland, where approximately antipodal remanences of similar direction have the same relative age from magnetic overprinting studies. This observation, together with a comparison of paleomagnetic pole positions between Laurentia and Fennoscandia, allow the possibility that the 1.6 Ga Melville Bugt dyke swarm once trended towards the 1.5–1.6 Ga Fennoscandian rapakivi province, or its possible extension in Amazonia, raising the conjecture that the dyke swarm was fed laterally from this magmatic province. Satellite imagery from southeast Greenland shows several NNW-trending dykes that may represent a southerly continuation of the Melville Bugt swarm, necessary if the dykes are to have the rapakivi province as a source. The use of high precision U-Pb geochronology to establish the sense of paleomagnetic reversals promises to be a useful tool in continental reconstructions.
Abstract Mantle plumes are recognized by domal uplift, triple junction rifting, and especially the presence of a large igneous province (LIP), dominated in the Phanerozoic by flood basalts, and in the Proterozoic by the exposed plumbing system of dykes, sills, and layered intrusions. In the Archean, greenstone belts that contain komatiites have been linked to plumes. In addition, some carbonatites and kimberlites may originate from plumes that have stalled beneath thick lithosphere. Geochemistry and isotopes can be used to test and characterize the plume origin of LIPs. Seismic tomography and geochemistry of crustal and subcrustal xenoliths in kimberlites can identify fossil plumes. More speculatively, plumes (or clusters of plumes) have been linked with variation in the isotopic composition of marine carbonates, sea-level rise, iron formations, anoxia events, extinctions, continental breakup, juvenile crust production, magnetic superchrons, and meteorite impacts. The central region of a plume is located using the focus of a radiating dyke swarm, the distribution of komatiites and picrites, etc. The outer boundary of a plume head circumscribes the main flood basalt distribution and approximately coincides with the edge of domal uplift that causes shoaling and offlap in regional sedimentation.
Large Igneous Provinces (LIPs) represent large volume, short duration (or pulsed) igneous events of intraplate character (e.g., Coffin and Eldholm, 1994, 2005; Bryan and Ernst, 2008). They consist of continental flood basalts, volcanic rifted margins, oceanic flood basalts (oceanic plateaus and ocean basin flood basalts) and a plumbing system of giant dolerite dyke swarms, sill provinces and layered mafic–ultramafic intrusions. Some silicic and bimodal volcanic/plutonic provinces also belong to this magmatic class.
Anewly recognized remnant of a Paleoproterozoic Large Igneous Province has been identified in the southern Bastar craton and nearby Cuddapah
basin from the adjacent Dharwar craton, India. High precision U–Pb dates of 1891.1±0.9 Ma (baddeleyite) and 1883.0±1.4 Ma (baddeleyite and
zircon) for two SE-trending mafic dykes from the BD2 dyke swarm, southern Bastar craton, and 1885.4±3.1 Ma (baddeleyite) for a mafic sill
from the Cuddapah basin, indicate the existence of 1891–1883 Ma mafic magmatism that spans an area of at least ∼90,000 km2 in the south Indian
shield.
This record of ∼1.9 Ga mafic/ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved
along much of the south-eastern margin of the south Indian shield is a widespread geologic phenomenon on Earth. Similar periods of intraplate
mafic/ultramafic magmatism occur along the margin of the Superior craton in North America (1.88 Ga Molson large igneous province) and in
southern Africa along the northern margin of the Kaapvaal craton (1.88–1.87 Ga dolerite sills intruding the Waterberg Group). Existing paleomagnetic
data for the Molson and Waterberg 1.88 Ga large igneous provinces indicate that the Superior and Kalahari cratons were at similar
paleolatitudes at 1.88 Ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin
such as a Limpopo-like 2.0 Ga deformation zone in the Superior Province. The widespread occurrence of 1.88 Ga intraplate and plate margin mafic
magmatism and basin development in numerous Archean cratons worldwide likely reflects a period of global-scale mantle upwelling or enhanced
mantle plume activity at this time.
Various geological and geophysical evidence show that at least two supercontinents, Columbia and Rodinia, existed during the Paleoproterozoic and Mesoproterozoic eras. In this study, updated paleomagnetic and isotope age data has been used to define the amalgamation and break-up times of these supercontinents. Before putting the ancient continents to a supercontinent assembly, we have tested the validity of the geocentric axial dipole model (GAD) of the Paleo-Mesoproterozoic geomagnetic field using four methods. The tests yield support to the GAD-model, but do not rule out a ca. 10% non-dipole (octupole) field. In the whole of Proterozoic, Columbia and Rodinia were predominantly in moderate to low paleolatitudes, but during the Paleoproterozoic some parts of Columbia, notably India (Dharwar craton) and Australia (Yilgarn craton), occupied polar latitudes. In the Paleoproterozoic, there were unexpected low-latitude glaciations. The pre-Columbia orogenies were due to a complex set of collisions, rotations and transform or strike slip faultings that caused the orogenic belts to appear obliquely. No prominent difference was observed between paleomagnetically derived and recent geologic models of Columbia. The final amalgamation of Columbia didn't happen until ca. 1.53 Ga. Columbia broke up at ca. 1.18 Ga during several rifting episodes, followed by a short period of independent drift of most continents. The amalgamation of Rodinia didn't take place until 1.10 - 1.04 Ga.
Identical high precision U-Pb baddeleyite ages, together with
paleomagnetic and geochemical data, on mafic dykes occurring over an
area of 140,000 km2, define a Paleoproterozoic giant dyke
swarm at ca. 2.367 Ga in the Dharwar craton, south India, referred to
here as the Dharwar giant dyke swarm. All six U-Pb ages on these dykes
are identical within error and suggest emplacement of this swarm within
a geologically short time span of ˜5 Myr. A systematic southward
progression in the trend of dykes from N48°E to N90°E, defines a
fan angle of about 40° with convergence to a focal point about 300
km west of the present-day Dharwar craton boundary, resulting in a
spectacular radiating dyke swarm extending across the entire eastern
Dharwar craton. The large areal extent, radiating dyke pattern and short
duration imply a mantle plume origin for the Dharwar giant dyke swarm.
Despite their large areal distribution, all dykes in this swarm are
geochemically coherent and have similar primitive mantle-normalized
trace element patterns and rare earth element characteristics. Although
the NE part of the swarm is magnetically overprinted, a remanence
survives that has the same direction as primary magnetizations from
dykes in the southern part of the swarm.
Idealized conceptual models of supercontinent cyclicity must be tested against the geologic record using pre-Pangean reconstructions. We integrate tectonostratigraphic records and paleomagnetic data from Siberia, Laurentia, and Baltica to produce a quantitative reconstruction of the core of the Nuna supercontinent at 1.9-1.3 Ga. In our model, the present southern and eastern margins of Siberia juxtapose directly adjacent to, respectively, the arctic margin of Laurentia and the Uralian margin of Baltica. Consistent tectonostratigraphic records of the three cratons collectively indicate the history of Nuna's assembly and breakup. According to this reconstruction, the late Mesoproterozoic transition from Nuna to Rodinia appears to have been much less dramatic than the subsequent late Neoproterozoic transition from Rodinia to Gondwana.
During the main phase of Steens and Columbia River (United States) flood basalt eruptions between 16.7 and 15.0 Ma, ∼3900 km3 of silicic magma erupted from centers dispersed across ∼25,000 km2. The largest and oldest silicic centers, High Rock, McDermitt, and Lake Owyhee caldera complexes, lie along a narrow NNE trend at the transition between the craton and accreted oceanic crust, suggesting that silicic magma generation was greatest where mafic magma intruded more-felsic crust. Less voluminous and younger silicic centers track the spread of mafic dikes to the north. The High Rock caldera complex forms the western end of the Snake River Plain–Yellowstone trend of eastward-younging silicic centers. We attribute a regional lull in volcanism between ca. 23 and 7 Ma to lifting of the Juan de Fuca slab by a mantle plume beginning at ca. 25 Ma, and the distribution of main-stage flood basalts and coeval rhyolites to breakthrough of plume material at ca. 17 Ma to form a smaller plume head centered beneath Steens Mountain.
Large igneous provinces are exceptional intraplate igneous events throughout Earth’s history. Their significance and potential global impact are related to the total volume of magma intruded and released during these geologically brief events (peak eruptions are often within 1–5 m.y. in duration) where mil- lions to tens of millions of cubic kilometers of magma are produced. In some cases, at least 1% of Earth’s surface has been directly covered in volcanic rock, being equivalent to the size of small continents with comparable crustal thicknesses. Large igneous provinces thus represent important, albeit episodic, periods of new crust addition. However, most magmatism is basaltic, so that contributions to crustal growth will not always be picked up in zircon geochronology studies, which bet- ter trace major episodes of extension-related silicic magmatism and the silicic large igne- ous provinces. Much headway has been made in our understanding of these anomalous igneous events over the past 25 yr, driving many new ideas and models. (1) The global spatial and temporal distribution of large igneous provinces has a long-term average of one event approximately every 20 m.y., but there is a clear clustering of events at times of supercontinent breakup, and they are thus an integral part of the Wilson cycle and are becoming an increasingly important tool in reconnecting dispersed continental fragments. (2) Their compositional diversity in part reflects their crustal setting, such as ocean basins and continental interiors and margins, where, in the latter setting, large ig- neous province magmatism can be dominated by silicic products. (3) Mineral and energy re- sources, with major platinum group elements (PGEs) and precious metal resources, are hosted in these provinces, as well as magma- tism impacting on the hydrocarbon potential of volcanic basins and rifted margins through enhancing source-rock maturation, providing fluid migration pathways, and initiating trap formation. (4) Biospheric, hydrospheric, and atmospheric impacts of large igneous prov- inces are now widely regarded as key trigger mechanisms for mass extinctions, although the exact kill mechanism(s) are still being re- solved. (5) Their role in mantle geodynamics and thermal evolution of Earth as large igne- ous provinces potentially record the trans- port of material from the lower mantle or core-mantle boundary to the Earth’s surface and are a fundamental component in whole mantle convection models. (6) Recognition of large igneous provinces on the inner planets, with their planetary antiquity and lack of plate tectonics and erosional processes, means that the very earliest record of large igneous province events during planetary evolution may be better preserved there than on Earth.
The Avanavero Large Igneous Province (LIP) constitutes the most important Paleoproterozoic mafic magmatism event in the Guiana Shield, northern Amazonian Craton. It comprises voluminous dykes and sills, the latter intruded into regional sedimentary cover successions such as the Roraima Supergroup and Urupi Formation. Roughly contemporary mafic magmatism such as the Crepori Dolerite occurs in the southern part of the Amazonian Craton (Central Brazil Shield). This study reports new geochemical data for samples from the Avanavero Dolerite and the coeval Quarenta Ilhas Dolerite, as well as reassessing published information on roughly contemporaneous mafic dykes in the shield to address issues related with the tectonic significance of such an intraplate igneous event and paleogeographic reconstructions. The Avanavero magmatism is tholeiitic and is geochemically similar to E-MORB and subcontinental lithospheric mantle basalts. New U–Pb baddeleyite ages of 1795 ± 2 Ma and 1793 ± 1 Ma, respectively, from occurrences in both the Pakaraima and Urupi Blocks at the north and south portions of the Guiana Shield confirm that they belong to the Avanavero LIP. These two ages are within error of a U–Pb age of 1794 ± 4 Ma for an Avanavero dyke in Guyana. Slightly younger published U–Pb ages range from about 1780–1787 Ma, including the Crepori Dolerite in Central Brazil Shield (southern Amazonian Craton). This may indicate that two pulses of magmatism could be associated with the Avanavero event. The paleomagnetic data favour a Laurentia/Baltica/Amazonia link at 1.79 Ga, and this large landmass may have constituted the core of the Columbia supercontinent during Late Proterozoic times.
We identify 304 mafic magmatic events ranging in age from ca. 3500 Ma to the present and assess their potential for linkage to the arrival of mantle-plume heads. For each, we catalogue components (flood basalts or their erosional remnants, giant mafic dike swarms, mafic sill provinces, and mafic-ultramafic layered intrusions), age constraints, and references to published literature. On the basis of criteria involving large amounts of magma emplaced in a short time, and/or giant radiating dike swarms, 34 events have been confidently linked to the arrival of a mantle-plume head. By using other criteria including geochemistry, an additional 194 events are considered probably related to plume arrival. The remaining 76 events, the majority of which are rift related, require further study to assess the plume-head link. Our analysis of the events that are confidently or probably linked to plume arrival yields several preliminary conclusions. Plume-head events occur throughout the geologic record since at least 3500 Ma and probably since 3800 Ma, with no plume-free intervals greater than ∼200 m.y. Plume arrival does not follow any obvious periodicity. Plumehead locations are known for only a handful of events. However, in such cases, associated sills and flow packages can be emplaced (presumably via lateral flow in dikes) as far as 2500 km away from the plume center. There are numerous precise age correlations between mafic units on different continents. However, further work is required to determine which coeval events can be reconstructed into a single plume event and which represent separate events occurring at the same time.
The widespread Mesoproterozoic (ca. 1.1 Ga) Southwestern U.S. Diabase Province consisting of dikes, sills, and sheets, is located in southwestern Laurentia. Southwestern U.S. diabase has low to moderate whole rock Mg# (24–64) and concentrations of CaO and Al2O3 that suggest fractionation of olivine and plagioclase occurred before emplacement. Total alkali concentrations (Na2O + K2O) ranging from 2–5 wt.% indicate that diabase is transitional from tholeiitic to alkaline. Enrichments of large ion lithophile elements relative to mid-ocean ridge basalts and negative Nb anomalies relative to ocean island basalts suggest that diabase was derived from a weakly enriched mantle source. This is supported by whole rock εNd values of 3.2 to -0.5 that correlate with 87Sr/86Sri ratios for whole rock and single crystal plagioclases ranging from 0.694 – 0.710. Some plagioclase crystals have higher 87Sr/86Sri ratios than the corresponding whole rock samples, indicating assimilation of Proterozoic country rock occurred. Xenocrystic zircon in some samples provides further evidence for assimilation. We obtained a U-Pb ID-TIMS age on baddeleyite (ZrO2) from a diabase dike in the Pinaleño Mountains, Arizona, of 1087 ± 6 Ma (2σ), using the weighted mean 207Pb/206Pb age of 6 fractions. U-Pb SHRIMP dating of zircon from a diabase sill in the Salt River Canyon, Arizona yielded a weighted mean 207Pb/206Pb age of 1088 ± 11 Ma (2σ; 7 spots). Northwest-striking dikes in Arizona indicate extension occurred perpendicular to Grenville shortening. However, structural and geochemical relationships suggest a mantle plume created mantle-derived magmas that intruded into a faulted upper crust. The age of the Southwestern U.S. Diabase Province is similar to that of the Warakurna Large Igneous Province in Australia (~1075 Ma), supporting a close fit between Laurentia and Australia at this time. The projected intersection of the NW-SE trending dike swarm of the Diabase Province with the western margin of Laurentia may represent a piercing point that constrains the position of Australia along western Laurentia in the Rodinia supercontinent.
Proterozoic reconstructions of the Kaapvaal and Zimbabwe cratons have been limited by the scarcity of precisely dated paleomagnetic poles for the Zimbabwe craton. We present new U-Pb baddeleyite and apatite dates from two diabase sheets that have previously yielded paleomagnetic data from the Mashonaland igneous province in the Zimbabwe craton. Discordant baddeleyite analyses yield upper intercept dates of 1871.9 +/- 2.2 and 1882.7 +1.6/-1.5 Ma. Apatite data from the same samples give less precise but statistically indistinguishable dates, providing direct constraints on the post-magmatic thermal history of the diabases. The new U-Pb dates and other recently published baddeleyite dates from the Mashonaland province are coeval with mafic magmatism in the adjacent Kaapvaal craton (1879-1872 Ma), but paleomagnetic poles from the two intraplate suites differ by 39 degrees, suggesting that the two cratons underwent substantial relative motion after ca. 1.88 Ga. Paleomagnetic reconstructions are consistent with > 2000 km of lateral displacement being accommodated in the Limpopo orogenic belt that separates the two cratons.
Mafic sills occur within and in the vicinity of the Thabazimbi iron ore deposit, near the northern edge of the western limb of the Bushveld Complex. The sills are hosted in the 2.46 Ga Penge Iron Formation of the Transvaal Supergroup. The gabbroic sills have a primary mineral assemblage of clinopyroxene, plagioclase, accessory Fe–Ti oxides and titanite, with augites in places having been replaced by amphibole and/or biotite. K-feldspar veins crisscross through some of the more altered sill samples. Both primary and secondary titanite occurs in the sills, with the primary titanite rich in Fe (Fe/Al ∼0.65–0.88) and secondary titanite rich in Al (Fe/Al ∼0.17–0.47). SHRIMP U–Pb characterization of titanites separated from one of the sills (titanite Fe/Al in this sill ∼1) indicate an emplacement age of 2046.6 ± 3.4 Ma.
The geochemistry of a suite of lava flows, sills, and dikes from Axel Heiberg and Ellesmere islands in Arctic Canada has been examined to determine the Ni-Cu-platinum group element (PGE) sulfide prospectivity of the Canadian portion of the 130 to 80 Ma High Arctic large igneous province (HALIP). This event can be split into mildly alkaline or transitional and tholeiitic suites, each with distinct provenances, S saturation histories, and Ni-Cu-PGE prospectivity. The mildly alkaline magmas of the HALIP were sourced from a deep, variably enriched part of the mantle, and most probably represent lower-degree partial melts than the tholeiitic parts of the HALIP that were formed from magmas generated by shallower, higher-degree partial melting of a region of unenriched mantle. The two types of magma also differ in their Ni-Cu-PGE magmatic sulfide prospectivity, in that the geochemistry of the majority of the mildly alkaline samples is indicative of unfertile or poorly fertile S-saturated magmas which did not sequester significant amounts of chalcophile elements from the mantle during partial melting, and therefore may be unprospective. In comparison, the presence of chalcophile element-undepleted tholeiitic samples suggests that the magmas forming these rocks were S undersaturated and fertile, and sequestered significant amounts of Cu and PGEs from the mantle during partial melting. Furthermore, the presence of chalcophile-depleted and crustally contaminated samples within the tholeiitic suite indicates that the magmas that formed these samples assimilated crustal material and became sulfur saturated prior to emplacement, segregating magmatic sulfides that may have been deposited and left behind within ultramafic or mafic intrusive rocks associated with the tholeiitic segments of the Canadian HALIP. Interestingly, some tholeiitic flows are crustally contaminated but are only weakly Pd depleted; this suggests that these flows may have locally assimilated crustal material, which led to only minor S saturation and in situ formation of voluminously insignificant magmatic sulfides.
These observations suggest that the tholeiitic portion of the Canadian HALIP is prospective for Ni-Cu-PGE sulfide mineralization, and that mafic-ultramafic sequences associated with this suite should be targeted for mineral exploration. Identification of parts of the Canadian HALIP where magmas assimilated S-bearing sedimentary material could also be a useful tool for exploration. The data and interpretations presented here provide a number of scientific hypotheses that could be tested for other parts of the circum-Arctic HALIP event.
New geochemical data integrated in a petrogenetic model indicate
that the �30Ma Northern Ethiopian continental flood basalts
(CFBs) preserve a record of magmas generated from the centre to
the flanks of a plume head, currently corresponding to the ‘Afar hotspot’.
Basaltic lavas appear zonally arranged with Low-Ti tholeiites
(LT) in the west, High-Ti tholeiites (HT1) to the east and very
High-Ti transitional basalts and picrites (HT2,TiO2 4^6 wt%)
closer to the Afar triple junction. Modelling provides estimates of
the P^T^X conditions of magma generation showing that the
Ethiopian CFBs could be generated in the pressure range 1�3^3�0
GPa at an approximate depth of 40^100 km from mantle sources
that were increasingly metasomatized and hotter (1200^15008C)
from west to east; that is, from the outer zones (LT) to the core of
the plume head (HT2 ultra-titaniferous basalts and picrites).
Metasomatizing agents can be envisaged as alkali^silicate melts
that integrate various geochemical components (e.g.Ti and related
high field strength elements, low field strength elements, light rare
earth elements, H2O, noble gases, etc.) scavenged and pooled along
the plume axis, and derived from heterogeneous mantle materials
mixed during the plume rise. This has significant implications for
the current debate about mantle plumes, as the modelled compositionally
and thermally zoned plume head (Texcess�3008C with respect
to ambient mantle) is in accordance with seismic tomography and
buoyancy flux, as well as geochemical characteristics, thus supporting
a deep provenance of the Afar plume, which possibly originated
in the transition zone or lower mantle.
We review available data constraining the extent, volume, age and
duration of all major Phanerozoic continental flood basalts (CFB or
traps) and oceanic plateaus (OP), together forming the group of large
igneous provinces (LIP), going from the smallest Columbia flood basalts
at ˜16 Ma to the as yet ill-known remnants of a possible trap at
˜360 Ma in eastern Siberia. The 16 traps (CFB and OP) reviewed
form a rather unimodal distribution with an initial modal volume of the
order of 2.5 Mkm 3. Most provinces agree with a rather simple
first order model in which volcanism may have lasted of the order of 10
Ma, often resulting in continental break-up, but where most of the
volume was erupted in about 1 Ma or sometimes less. This makes CFBs/OPs
(LIPs) major geodynamic events, with fluxes exceeding the total output
of present day hot spots and even possibly exceeding over short times
the entire crustal production of mid-ocean ridges. The proposed
correlation between trap ages and the ages of several geological events,
including mass extinctions and oceanic anoxia, is found to have improved
steadily as more data have become available, to the point that the list
of trap ages may coincide with many major divisions in the geological
time scale. The four largest mass extinctions in the last 260 Ma
coincide to the best resolution available with four traps, making a
causal connection between the two through some form of catastrophic
climatic perturbations the most likely hypothesis. The time sequence of
LIPs appears to have been random and there is no robust evidence for
long time trends in the corresponding crustal production rate over the
last 260 Ma.
Original connections among the world's extant Archean cratons are becoming tractable by the use of integrated paleomagnetic and geochronologic studies on Paleoproterozoic mafic dyke swarms. Here we report new high-quality paleomagnetic data from the ∼2.41 Ga Widgiemooltha dyke swarm of the Yilgarn craton in western Australia, confirming earlier results from that unit, in which the primary origin of characteristic remanent magnetization is now confirmed by baked-contact tests. The corresponding paleomagnetic pole (10.2°S, 159.2°E, A95 = 7.5°), in combination with newly available ages on dykes from Zimbabwe, allow for a direct connection between the Zimbabwe and Yilgarn cratons at 2.41 Ga, with implied connections as early as their cratonization intervals at 2.7–2.6 Ga. The proposed “Zimgarn” supercraton was likely distinct from Vaalbara (Kaapvaal plus Pilbara) at 2.4 Ga, but both of those entities independently fragmented at ca. 2.1–2.0 Ga, reassembling into the Kalahari and West Australian cratons by 1.95–1.8 Ga.
Existing radio-isotopic age constraints indicate that the global Palaeoproterozoic Lomagundi-Jatuli large, positive carbonate carbon isotopic excursion, with δ13C values >+5‰, occurred between 2.2 and 2.06 Ga. In the North Transfennoscandian Greenstone Belt of the Kola Peninsula, NW Russia, northern Norway and Finland, the Lomagundi-Jatuli Event is recorded in the carbonate rocks of the Umba and Kuetsjärvi Sedimentary Formations in the Imandra-Varzuga and Pechenga greenstone belts. In both areas, thick mafic volcanic units (Umba and Kuetsjärvi Volcanic Formations) overlie the carbon isotopic excursion-bearing sedimentary units. Overlying and younger sedimentary units contain carbonate rocks with δ13C values typically ranging between c. −1 and +3‰, signalling the termination of the Lomagundi-Jatuli excursion.
The NNW- to NNE-trending Kaminak diabase dykes, exposed in the Hearne craton of the western Churchill Province, Canada, are components of a Neoarchean–Paleoproterozoic LIP that forms an important pin in plate tectonic reconstructions impacting models for the assembly of the Nuna supercontinent. This study provides the first detailed information on the age, geochemistry and isotopic composition of these dykes.A precise U–Pb baddeleyite date of 2497.6 ± 1.1 Ma, obtained for one dyke sample, provides the best estimate for the timing of Kaminak mafic magmatism. The dykes are tholeiitic basalts to basaltic andesites with consistent compositions over an areal extent of ∼10,000 km2. Major and compatible trace element variations indicate that the dykes were not in equilibrium with anhydrous peridotitic mantle and evolved through fractionation of Pl + Cpx ± Ol from parental melts in the deep crust. All dykes record remarkably similar, incompatible element enriched, closely parallel multi-element profiles with variable HFSE troughs, comparable to Phanerozoic low-TiO2 continental tholeiites. Time-corrected Nd isotopic compositions overlap, or are slightly below bulk Earth (εNd2500 Ma=+0.4εNd2500 Ma=+0.4 to −0.8), and yield TDM values (2.75–2.87 Ga) comparable to those of igneous crust in the Hearne craton. Implied short residence times, along with the geological, geochemical and isotopic data, are interpreted to imply that parental magmas of the dykes were low-TiO2 tholeiites generated via contamination of primary, depleted N-MORB-like magmas by low-degree, calc-alkaline lamprophyre melts in the continental lithospheric mantle. The melts homogenized in chambers near the Moho and underwent extensive fractional crystallization (Pl + Cpx ± Ol), and possibly minor assimilation of lower crust, prior to injection into the upper crust. Paucity of evidence for contemporaneous lithospheric rifting, homogeneous lithogeochemical and Nd isotopic compositions, and petrochemical variations distinct from the Matachewan and Mistassini swarms of the Superior Province suggest the Kaminak dykes are the magmatic products of a Late Archean–Early Paleoproterozoic mantle thermal anomaly that extended, but did not break apart the Hearne craton. The results of this study do not support direct correlation of the Kaminak and Matachewan or Mistassini dyke swarms. Further evaluation of the proposed linkage of the Hearne and Superior cratons prior to Nuna supercontinent assembly requires additional geochronological, lithogeochemical and radiogenic isotopic constraints.
Australia's Large Igneous Provinces (LIPs) span almost the entire Earth's geological history, ranging from Early Archean to Recent. LIPs in continental Australia are represented by continental flood basalts, fragments of oceanic plateaux, volcanic rifted margins, layered mafic–ultramafic intrusions, sill complexes, dyke swarms and silicic-dominated volcanic provinces. In the last decade or so, several geologists have started to focus on LIPs in Australia, mainly from the perspective of their mineral potential, particularly after the discovery of the Nebo–Babel Ni–Cu–PGE deposit in the West Musgrave Province, central Australia. Wingate et al. (2004a) further advanced the inventory of LIPs with the announcement of a new LIP (ca. 1070 Ma Warakurna, extending for nearly 1500 km along an E–W trend), based on U–Pb dating of baddeleyite from mafic sills and dykes. The list of LIPs increased by including other well-known igneous provinces, such as the Fortescue, Hart-Carson, Kalkarindji (formerly known as Antrim Plateau Volcanics) and various dyke swarms (e.g., Widgiemooltha, Marnda Moorn, Gairdner). The Bunbury Basalt, although only covering a small area in the Cape Naturaliste–Cape Leeuwin Peninsula, joined the list of LIPs, due to its age links with the huge Kerguelen Plateau in the Indian Ocean. As indicated by the world-class Nebo–Babel deposit (> 1 Mt contained metal) and further discoveries in the West Musgrave and in the Kimberley region, the LIPs in these regions have good mineral potential. In the case of orthomagmatic mineral systems, the selection of areas or specific intrusions requires focusing on trace- and major-element geochemical trends to filter out mafic–ultramafic intrusions that may not have undergone sulphur saturation from those that have experienced sulphur saturation from processes, such as crustal contamination. In addition, consideration must be given to hydrothermal mineral systems that may have been generated as a result of thermal energy inputs, related to the emplacement into the crust of mafic–ultramafic magmas, as exemplified by recent discoveries in the West Musgrave Province. In eastern Australia, the Early Cretaceous Whitsunday volcanic province, is the largest known silicic LIP and comparable to the Chon Aike silicic LIP in South America. The mineral potential associated with the Whitsunday province is as yet not fully assessed. Similarly, the mineral potential for the Bunbury, Tasman Dolerite and Kalkarindji volcano-plutonic provinces is poorly known and yet to be fully explored. We conclude our contribution by providing a short review of crustal and mantle dynamics associated with LIP emplacement.
The Blue Draw Metagabbro (BDM) in western South Dakota, is an 800 m thick, layered intrusion, which is interpreted to have been intruded as a rift-related subvolcanic sill during the Palaeoproterozoic. The age and tectonic setting of the BDM are similar to those recorded by the East Bull Lake Suite of layered intrusions in Southern Ontario. These similarities have led previous authors to suggest that the two sets of intrusions are cogenetic. The East Bull Lake Suite intrusions are relatively well studied and are known to host significant contact-type Ni–Cu–PGE sulphide mineralisation, however, prior to this work, relatively little was known of BDM both in terms of its geochemistry and mineralisation potential. Chemostratigraphic profiles through the BDM show that the intrusion is the product of at least two magma pulses which fractionated to produce a sequence of rocks which grade from peridotitic at the base of the intrusion to gabbronoritic at the upper margin. Closed-system fractionation following the intrusion of the second magma pulse caused the magma to become saturated in sulphur and precipitate Ni–Cu–PGE bearing sulphides—now preserved in a low-grade 50 m thick zone near the top of the intrusion. Petrological modelling shows that the parental melt of the BDM was a low-Ti tholeiite, with a trace element chemistry defined by enrichments in large-ion lithophile and light rare-earth elements and prominent negative Nb, Ta, and Ti anomalies. This ‘arc-like’ geochemistry recorded by the BDM parent magma is shared with parent magmas of the East Bull Lake Suite and may suggest that the BDM and its potential Canadian relatives share a common magmatic source. However, the relative ubiquity of such geochemical signatures in Archaean–Palaeoproterozoic intracontinental magmatic rocks coeval with the BDM suggests that the geochemical similarities recorded by the BDM and East Bull Lake Suite are non-unique and hence, are not definitive evidence of a genetic link between the two sets of intrusions. Instead, this geochemical signature that is common to many ancient igneous provinces may indicate the presence of a transient and (currently) poorly understood Archaean–Palaeoproterozoic mantle reservoir which was a globally significant magma source.
The Skellefte district, northern Sweden, is known for the occurrence of 1.89 Ga Palaeoproterozoic volcanogenic massive sulphide (VMS) deposits. The deposits are hosted by the older part of a volcanosedimentary succession, which was intruded at 1.88–1.86 Ga by multiple phases of the syn-volcanic, early orogenic Jörn intrusive complex (JIC). The oldest phase of the JIC hosts different styles of mineralisation, among them porphyry Cu–Mo–Au, intrusion-related Au, and mafic-hosted Fe and Cu–Ni deposits. To discriminate between the different intrusive and ore related events, U–Pb ages of zircons have been obtained for nine intrusive phases and from Na–Ca alteration spatially related to mineralisation, while U–Pb ages of baddeleyite (ZrO2) have been used to constrain intrusive ages of three mineralised and barren mafic–ultramafic intrusive rocks.
Ages and chemical and isotopic compositions of the Permian mafic dyke swarms from Kelamayi, eastern Tianshan and western Tianshan in western part of the Central Asian Orogenic Belt (CAOB), NW China, are reported here in order to gain more insights into the Permian Tarim Large Igneous Province (Tarim LIP). These CAOB mafic (-andesitic) dyke swarms from Kelamayi, eastern Tianshan and western Tianshan were emplaced at 267 ± 3 Ma, 278 ± 2 Ma and 260–290 Ma, respectively, and are coeval with the radiating mafic dyke swarm in the Tarim Block. The dykes in CAOB exhibit subalkalic character in major element compositions, and are enriched in LILE and LREE and depleted in HFSE and HREE, with the exception of a few LREE-depleted samples from western Tianshan. Isotopically, dykes from Kelamayi and western Tianshan are characterized by significant positive εNd(t) values (3.1 to 7.9 for Kelamayi; 7.2 to 7.3 for western Tianshan), while dykes form eastern Tianshan exhibit variable negative εNd(t) values (− 0.7 to − 3.3). Their geochemical features suggest that the mafic (-andesitic) dykes in CAOB were derived from a recently metasomatized lithospheric mantle source (sub-continental lithosphere mantle) with subsequent variable extents of assimilation of the crustal materials in a non-orogenic setting. In contrast, the mafic dykes in Tarim exhibit systematic chemical signatures similar to those of OIB, indicating that they were derived from a depleted sub-lithospheric mantle source. We thus propose that the Permian Tarim LIP has two different mantle domains for the coeval mafic rocks, i.e., the Tarim domain and the CAOB domain.
Regional mafic dyke swarms are commonly emplaced in extensional tectonic settings and are typically considered to be linked with continental break-up. A large number of mafic dykes (areal extent of ~ 40,000 km2) have recently been documented in the middle of the Qiangtang terrane, northern Tibet. Zircon U–Pb isotope analyses using a sensitive high-resolution ion microprobe (SHRIMP) indicate that the dykes were emplaced in the Early Permian (279 ± 2 Ma, 283 ± 1 Ma, 285 ± 1 Ma and 285 ± 3 Ma). Whole-rock geochemical data show that the Qiangtang mafic dykes are tholeiitic in composition and exhibit relative enrichment in light rare earth element (LREE) and depletion in Nb, Ta and Ti, resembling continental intra-plate basalts. Whole-rock Sr–Nd and zircon Hf isotopic data suggest that mafic dyke magma was derived from a depleted mantle source (εNd(T) = + 5.1 to + 7.6 and εHf(T) = + 4.9 to + 14.8). The chemical and isotopic characteristics make the mafic dykes similar to the Panjal Traps and Permian basalts in the Tethyan Himalayas. The contemporaneous and widespread emplacement of ca. 283 Ma continental intra-plate basaltic rocks in the Qiangtang terrane and in the Himalayas is suggestive of a Large Igneous Province (LIP). This LIP is linked to the initial rifting and opening of the Meso-Tethys Ocean during the Permian.
Southern Oklahoma and adjacent parts of Texas contain an extensive igneous province emplaced during Early Cambrian rifting within the Southern Oklahoma rift zone. The rift zone was initiated in association with the opening of the southern Iapetus Ocean during Rodinia supercontinent breakup and later became the site of a series of linked uplifts and basins as a result of late Paleozoic inversion. Igneous rocks within the rift are referred to as the Wichita province and are present mostly in the subsurface, although critical exposures occur in the Wichita and Arbuckle Mountains in southwestern and southern Oklahoma. Wells drilled into basement in the region provide a wealth of information on the distribution and relations of the major igneous units in the upper crust, and geophysical data provide important constraints on deeper levels of the rift zone.
Palaeoproterozoic magmatism throughout the North Atlantic Craton (NAC) has produced dyke swarms of diverse orientations and emplacement ages. In southern West Greenland, previously identified swarms include the ca. 2500 Ma Kilarsaarfik dykes, ca. 2215 Ma boninitic norite (BN) dykes, and the abundant ca. 2040 Ma Kangâmiut and coeval 2050–2030 Ma MD3 dykes. Additional insight into the distribution of swarms is provided by new baddeleyite U–Pb ID-TIMS dates interpreted as emplacement ages for six dykes. The geochemistry for a total of 42 samples on 40 dykes (including the dated dykes) provides some constraints on their petrogenesis. Two E–W trending dykes yield ages of 2365 ± 2 Ma and 2374 ± 4 Ma, representing a hitherto unknown magmatic event. We propose the name Grædefjord dykes for dykes of this age in southern West Greenland. One NE–SW trending dyke is dated at 2209 ± 5 Ma, close to a previously published 2214 ± 10 Ma age for a N–S trending dyke (member of BN dykes). Three dykes yield MD3 ages of 2053 ± 2 Ma (E–W trending), 2049 ± 6 Ma (N–S trending) and 2042 ± 2 Ma (WNW–ESE trending). Ca. 2.21 Ga old and predominantly NE–SE and NNE–SSE trending dolerites (some of which are high-Al basalts) were derived from a relatively depleted mantle and injected during a boninite–dolerite magmatic event, together with nearby BN dykes derived from a harzburgitic, yet highly LREE and LILE enriched, subcontinental lithospheric mantle (SCLM). Ca. 2.05 Ga Kangâmiut–MD3 dolerites were derived from a similar ambient asthenospheric mantle and subsequently experienced crustal assimilation during fractional crystallisation.
In this paper, we present geochronological, geochemical and palaeomagnetic results from the Hlagothi Complex and a NW-trending dolerite dyke swarm on the southeastern region of the Kaapvaal Craton in northern KwaZulu-Natal, South Africa. The Hlagothi Complex consists of layered sills of meta-peridotite, pyroxenite and gabbro intruding into the Pongola Supergroup. U–Pb baddeleyite ages on the Hlagothi Complex and a NW-trending dyke of 2866 ± 2 Ma and 2874 ± 2 Ma, respectively, reveal a ca. 2.87 Ga magmatic event on the southeastern Kaapvaal Craton. The geochemical signature of the Hlagothi Complex recognises two discrete groupings, with a magmatic source that is chemically distinct from those of the older rift-related Nsuze and Dominion groups. Additional units on the Kaapvaal Craton can be linked with this new ‘Hlagothi’ event based on spatial and temporal association, and geochemistry: 1) the Thole Complex, 2) parts of the Usushwana Complex, and 3) flood basalts within the Mozaan Group and Central Rand Group. The association between all these units suggests a previously unrecognised large igneous province in the southeastern Kaapvaal Craton. Our palaeomagnetic data identifies a possible primary magnetisation within the least-altered lithologies of the Hlagothi Complex (with a virtual geographic pole at 23.4°N, 53.4°E, dp = 8.2° and dm = 11.8°). The bulk of samples however, displayed two episodes of remagnetisation. These are likely to be associated with 2.85 to 2.75 Ga aged granitoids across the southeastern Kaapvaal Craton, and tectonic activity in the nearby Meso- to Neoproterozoic Namaqua–Natal mobile belt. A short-lived (≤ 8 Ma) mantle plume is proposed to have caused the ca. 2.87 Ga magmatism, and also may well have controlled sedimentation within the Pongola–Witwatersrand basin. Volcanism during uplift would have been fed through a series of feeder dykes and sills, of which the Hlagothi Complex and NW-trending dykes are part of.
The existence of a pre-Rodinia Precambrian supercontinent, variously called Nuna or Columbia, has been widely speculated in the past decade, but the precise timing of its existence and its configuration have been uncertain due to the lack of unequivocal paleomagnetic and geological constraints. Here we report high-quality paleomagnetic results from the well dated ∼1780 Ma Xiong'er Group in southern North China Block (NCB). A total of 110 paleomagnetic samples from 14 sites were collected and subjected to stepwise thermal demagnetization. After removing a low temperature component (CL) of viscous magnetic remanence acquired in recent geomagnetic field, a high temperature component (CH), carried by hematite and magnetite in redbeds and volcanic samples, has been isolated. It gives a mean direction of (D=18.4°, I=−3.7°, α95=7.6°, N=14) after bedding correction, and a corresponding paleomagnetic pole at 50.2°N, 263.0°E (A95=4.5°). The CH passed a reversal test and was interpreted as a primary remanence. This new pole plus three other high-quality poles from the NCB that have been more precisely dated at 1769±3 Ma, 1560–1440 Ma and 1437±21 Ma define a 1780–1440 Ma apparent polar wander path (APWP) for the NCB. This, together with an update of global high quality paleomagnetic dataset, allows us to demonstrate that the pre-Rodinia supercontinent Nuna likely existed at least between ∼1780 Ma and ∼1400 Ma. Our paleomagnetism-based global reconstruction, for the first time, quantitatively assembles all major cratons together; it encompasses previously proposed regional links including the SAMBA connection between Baltica, Amazonia and Western Africa (Johansson, 2009), connections between Laurentia, Baltica and Siberia at the core of Nuna (Evans and Mitchell, 2011), the proto-SWEAT connection between Laurentia, East Antarctica and Australian blocks (Payne et al., 2009), and the NCB–India connection (Zhao et al., 2011).
Understanding the dynamics of continental Large Igneous Provinces (LIPs) relies on precise dating of basaltic rocks. LIP research has traditionally focused on dating lavas, often neglecting the volumetrically important sill intrusions in underlying sedimentary basins. Here we present U–Pb zircon (and baddeleyite) ages for fourteen new samples of Karoo LIP sills and dykes spaced by as much as 1100 km across the half million square kilometer Karoo Basin. The samples yield remarkably coherent ages ranging from 183.0 ± 0.5 to 182.3 ± 0.6 myr. Probability modeling indicates that basin scale emplacement took place within an interval of about 0.47 myrs (less than 0.90 myrs with 95% confidence), and could even have represented a single magma emplacement event. Combining the new ages with the estimated volume of sills in the Karoo Basin gives an emplacement rate of 0.78 km3/yr, which is higher than previous estimates. Upper crustal magma storage may account for these high rates. The results challenge the view that melt emplacement in a sedimentary basin is a prolonged process, support a scenario of pulsating catastrophic events within a narrow time frame, and strengthens the hypothesis linking LIPs and sill emplacement to global environmental crises.
Published geochemical data pertaining to global continental flood basalts (CFBs) indicate that there are two contrasting distributions of high field strength elements (HFSEs) plotted on silicate Earth-normalized spider diagrams. Most CFBs plot close to a standard oceanic island basalt (OIB) line and are the product of magma from a mantle plume head mixed to varying degrees with magma from other sources. The compositional diversity of the OIB-like basalts is consistent with the interaction of plume heads with diverse mantle layers during gradual emergence followed by plume-tail magmatism along hotspot tracks. On the other hand, at least three CFBs, including those in the Central Atlantic magmatic province, the Siberian Traps, and the Lesotho basalt province of South Africa, plot close to a standard arc-basalt line. These arclike basalts contain virtually the same average HFSE contents. The much lower HFSE contents of the arclike CFBs are consistent with a sudden reactivation of dormant arc or backarc sources trapped under continental-plate sutures.
After thirty years of plate-tectonic theory, the reasons why supercontinents disintegrate and disperse to form smaller continental plates remain enigmatic. Possible causes range from abnormally hot mantle upwellings, or plumes, to changes in plate-boundary driving forces. The breakup of the Gondwanaland super-continent, which started about 180 million years ago, provides an excellent case history against which to test models.
The ˜2800-km-long Snowbird tectonic zone is one of the most controversial tectonic features of the Canadian shield. Metamorphic and in situ geochronologic data reported here reveal that a 1.9 Ga medium- to high-pressure belt extends along most of this tectonic zone. In contrast to recent interpretations, a collisional origin is indicated by the length of this metamorphic belt, tectonic thickening documented in parts of it, geological contrasts across it, and subduction-type microdiamonds within it. This collisional event marks a pre-1.865 Ga phase of the Hudsonian orogeny involving microcontinent accretion that was fundamental to the growth of Laurentia.
The eastern part of the Siberian craton is locus to a mid-Paleozoic large igneous province (LIP) distributed over an area of >0.7×106km. This Yakutsk LIP originated from a mantle plume that caused early domal uplift, formation of ‘triple junction’ rifts (with uplift of their shoulders), associated mafic magmatism including volcanics, sills and a giant radiating dyke swarm, and associated diamondiferous kimberlites (Mirnyi, Nakyn and Dladyn-Alakit fields).The mafic magmas are dominantly tholeiites with patterns that are overall similar to ocean island basalts (OIB), and isotope geochemistry suggests a mixture of enriched and depleted sources. Geochemistry is consistent with plume-lithospheric interactions.The main axis of failed rifting along the E–W trending Vilyui rift represents reactivation of the Akitkan belt along which at 1.9Ga was the proposed locus of collision between northern (Anabar) and southern (Aldan) superterranes, and subsequent aulacogen rifting in the Mesoproterozoic.
Large volumes of diabase sills occur within the late Paleoproterozoic to Mesoproterozoic sedimentary rocks in the northern part of the North China Craton (NCC) and previous geochronological studies suggest some of these were emplaced in the Mid-Mesoproterozoic (Ectasian). Here we present new zircon and baddeleyite SHRIMP, LA-ICP-MS and SIMS U–Pb analyses on representative samples of the diabase sills emplaced into the Wumishan, Tieling and Xiamaling Formations. The results show emplacement ages ranging from 1325±5Ma to 1316±37Ma, suggesting voluminous magmatism leading to the formation of the diabase sill swarms (the Yanliao mafic sill swarms) in the Mid-Mesoproterozoic. Zircon LA-ICP-MS U–Pb dating of the Shangdu-Huade granitic pluton in the northern NCC yielded similar emplacement ages ranging from 1331±11Ma to 1313±17Ma. These ages are comparable with the 1.4–1.2Ga rift-related anorogenic magmatism recorded elsewhere on the globe such as North America, Greenland, Baltica, and Siberia, associated with the breakup of the Columbia (Nuna) supercontinent. The Mid-Mesoproterozoic magmatic rocks in the northern NCC constitute a typical bimodal magmatic suite. The geochemical and Nd–Hf isotopic data suggest that the diabasic rocks were likely generated by partial melting of the depleted asthenosphere mantle coupled with slight crustal assimilation in a continental rift setting; however, the granitic rocks were generated mainly through partial melting of the ancient continental crust, probably induced by the upwelling of hot asthenosphere mantle during continent rifting processes. The recognition of these bimodal magmatic rocks indicates that the northern NCC experienced Mid-Mesoproterozoic rifting events that are considered to have led to the final breakup of the Columbia supercontinent. The breakup of the NCC from the Columbia supercontinent occurred during Mid-Mesoproterozoic time, probably at around 1.33Ga. The carbonatite rocks and rare earth element-niobium mineralization in the giant Bayan Obo ore deposit in the northern NCC were also probably related to the continental rifting event in the Mid-Mesoproterozoic.
Dike swarms hold one of the keys to the interpretation of plate tectonics, as they provide information on the extensional processes occurring both in the continental crust and in the oceanic lithosphere. Dikes are the primary channels for transporting basaltic magma into the crust from a source area in the mantle and thus they can also be used to assess the nature of parental magma for related lavas and intrusions. Mafic dike swarms are also useful time markers that often precisely register major episodes of crustal rifting. Knowledge of the timing of dike emplacement is essential for understanding the tectonic evolution of rift-related environments and for regional correlation of igneous activity. Dike swarms are extremely important in continental environments, because they are often the only surviving evidence of significant geological events (for example, rifting, mantle plumes, plate subductions, or crustal break-up) and can be used to monitor geological history of the continents over long periods of time.