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Guyana: the Lost Hadean crust of South America?
Abstract
A Hadean zircon xenocryst with a U-Pb zircon age of 4,219 ±19 Ma, along with several zircon xenocrysts of Archean age (ca. 2,510 to 3,811 Ma) were found in a rock of the Paleoproterozoic Iwokrama Formation, which includes felsic volcanics and co-magmatic granitic intrusions. It demonstrates the existence of an underlying "Lost Hadean Crust", representing the oldest crustal component of the Guiana Shield. Detrital zircons of late Archean age, up to 2,700 Ma, are also present in the high-grade rocks of the Kanuku Complex, located to the south, and may be derived from the same Hadean-Archean crustal block.
... Fragments of Archean terrains reworked during the Transamazonian orogeny (2.26 -1.95 Ga; Rosa-Costa et al., 2009) are known in the Guyana Shield in Venezuela (3.3-2.6 Ga; Imataca terrane; Cordani et al., 2009;Kroonenberg and Roever, 2010;Tassinari and Macambira, 2004) and in the Amapá State, Brazil (3.3-2.6 Ga; Amapá Block; Borghetti et al., 2018;Milhomem Neto and Lafon, 2019;Rosa-Costa et al., 2006;Rosa-Costa et al., 2009). Hadean zircon xenocrysts with U-Pb zircon ages up to 4,219 ± 19 Ma occur in Paleoproterozoic felsic volcanics and associated granites of the Iwokrama Formation in the Guyana Shield (Nadeau et al., 2013). These ages indicate that the occurrence of Archean crust in the Guyana Shield is not restricted to the Imataca terrane and Amapá Block (Fig. 1a). ...
... The oldest rocks of the Amazonian Craton are found in the Amapá Block in the eastern portion of the Amapá State (Barbosa Rosa-Costa et al., (2009) and Barbosa and Chaves (2015). (C) Comparative diagram showing the radiometric data (zircon U-Pb-Hf and whole-rock Sm-Nd) available for the Archean domains from the Amazonian craton (1) , (2) (Tavares et al., 2018;Trunfull et al., 2020) (3) Milhomem Neto and Lafon, 2019) (4) (Nadeau et al., 2013). and Chaves, 2015; Klein et al., 2003;Milhomem Neto and Lafon, 2019;Rosa-Costa et al., 2014;Rosa-Costa et al., 2006) (Fig. 1b-c). ...
... Ga, attesting the existence of a Paleoarchean/Eoarchean crust in the southern part of the Guyana Shield. The 3628 ± 37 Ma concordant age obtained on an inherited core in Grain 11 (Fig. 9b) is one of the oldest ages so far recorded in zircons in the SE part of the Guyana Shield (Borghetti, 2018;Milhomem Neto and Lafon, 2019;Nadeau et al., 2013;Rosa-Costa et al., 2006;. ...
The age and tectonic history of the chromite-mineralised Bacuri Complex, a layered mafic–ultramafic intrusion
emplaced into Archean terranes of the Guyana Shield in the Amazonian Craton, are here investigated. The
stratigraphy of the Bacuri Complex consists of an Ultramafic Zone composed of interlayered metaperidotites and
chromitites and two mafic zones composed of metamafic rocks (amphibolites). In this study we present wholerock
lithogeochemical data integrated with zircon U-Pb isotopic and trace-element data from amphibolites from
the Mafic Zone. The investigated amphibolites consist of hornblende + plagioclase ± diopside ± biotite with
whole-rock compositions like noritic rocks of Archean layered intrusions. These samples are representative of
amphibolites with variable proportions of hornblende and plagioclase, interpreted as resulting from amphibolite
facies metamorphism of interlayered norite and leuconorite. We suggest that progressive fractionation of a primitive
parental magma led to the formation of plagioclase and orthopyroxene cumulates in the mafic zones. We
found that zircons from three metanorite samples comprise euhedral crystals with oscillatory zoning (interpreted
to preserve a magmatic crystallisation age), as well as variably recrystallised metamorphic zircons. Their U-Pb
207Pb/206Pb ages span over 682 million years, from 3628 Ma to 2942 Ma. Trace element data suggest that magmatic
zircons precipitated from late-stage magmatic fluids at ∼ 3.34 Ga (3343 ± 3.5 Ma weighted average age,
n = 48, MSWD = 1.3), which defines the Bacuri Complex as one the oldest and best-preserved layered intrusions
known. We show that fluid-mediated coupled dissolution-precipitation recrystallisation during metamorphism
altered the composition and ages of magmatic zircons. We could not accurately define the number and age
of metamorphic events in the 2942–3379 Ma age interval of metamorphic or ‘disturbed’ zircon domains. Our results
indicate that continental crust was already established in the Amazonian craton in the Paleoarchean and
possibly in the Eoarchean and that it has been reworked since at least the Mesoarchean.
... As rochas vulcânicas do episódio Orocaima distribuem-se no Domínio Surumu, incluindo o Grupo Surumu (1984±9 Ma, U-Pb SHRIMP, Santos et al., 2003;1990±3 Ma, Pb-Pb, Fraga et al., 2010, no norte de Roraima (Reis et al., 2000;Dreher et al., 2005;Bezerra, 2010;Fraga et al., 2010; Bezerra e Nascimento, 2011), a Formação Iwokrama, oeste da Guiana (Berrangé 1977;Nadeau et al., 2013;Reis et al., 2017) Pierosan et al., 2011;Klein et al., 2012;Kroonenberg et al., 2016;Simões et al., 2017). ...
... The state of Roraima, the far north of the Amazonian Craton, has a large volume of 49 volcanic deposits (Fig. 1A), mainly of a volcanoclastic nature (Fraga et al., 2010), which 50 extend to Venezuela (Brooks et al., 1995), Suriname and Guyana 51 (Nadeau et al., 2013 Amazonian Craton, as no units with type-A affinity and similar age were identified (Fraga 58 et al., 2007(Fraga 58 et al., , 2010. The lack of data also made it impossible to clearly understand the Surumu Group and the granitoids of the Pedra Pintada Suite (Fraga et al., 2007(Fraga et al., , 2010, in 104 addition to rhyolites, with subordinate riodacites (Bezerra, 2010 rocks (Fraga et al., 2010). ...
... This magmatism presents important geochemical variations, which allow individualizing two sets: the high-K calc-alkaline rocks, metaluminous to weakly peraluminous and with 144 I-type signature (Reis and Fraga, 1996;Dreher et al., 2005); and subalkaline rocks, 145 transitional between metaluminous and weakly peraluminous, with A-type chemical 146 affinity (Fraga et al., 2010). The chemical characteristics of calc-alkaline rocks indicate a 147 post-collisional scenario (Reis et al., 2000;Fraga et al., 2010) or an arc linked to the late 148 phase of the Transamazonian Orogeny, as supported by several authors (for example, 149 Santos, 2003;Delor et al., 2003;Nadeau et al., 2013;Kroonenberg et al., 2016;Mahabier 150 and De Roever, 2019). Fraga et al. (2010) also use this post-collisional context to 151 characterize the contemporaneity between magmatism A and I types. ...
The studies carried out on the volcanic sequences of the Surumu Group and the Cachoeira da Ilha Formation are products of regional geological surveys. In view of the scarcity of lithofaciological and isotopic data from these units, this study aimed to understand the manner and timing of the emplacement of the volcanic rocks exposed in the northwest of Roraima, northern Brazil, their relationship and contextualization regarding large igneous provinces throughout the Proterozoic. These questions were tentatively answered from the faciological and petrographic characterization, supported by geochemical and geochronological data. The definition of pyroclastic facies allowed to understand that the large volume of ignimbrites resulted from the combination of caldera complexes, as already proposed for this volcanism in other portions, and by explosive eruptions of low eruptive columns probably associated with fissural volcanism. Correlation between the different facies also showed the proximity to the source of the pyroclastic material on the surface. Supported by geochemical data, this work proposes a tectonic setting related to an early post-collisional setting is inferred for the outcropping rocks in the north of Roraima, with local extension movements. The contemporaneity of among I and –A-type rocks (2,0-1,98 Ga), as well as their relationship with the Cauarane-Coeroeni belt and possible positioning in the late phase of the Transamazonian Orogeny, support this idea. Although not conclusive, the widespread occurrence of mafic fragments in various segments of the Cuchivero-Surumu-Iwokrama-Dalbana belt (CSID), as well as records of mafic dikes of the same age (1.99 Ga) in other portions of the Guiana Shield, suggests the coexistence of mafic magmas which are the probable heat source responsible for generating the great amount of silicic volcanism that occurs in Roraima, as already mentioned for other regions of the Guiana Shield. The isotopic data (TDM 2,0-2,47 Ga; εNd -2,3 and +0,5 to +3,47) indicate that, at least in Roraima, the parental magma of the volcanic rocks derived from the mantle or from melting of juvenile Rhyacian-Siderian crust, without involvement of Archean sources. Similarities with Proterozoic Silicic Large Igneous Province (SLIP), as well as the area distribution of ignimbrite deposits, age range and geochemical signatures suggest that the Orocaima event may be a SLIP that occurred in the Paleoproterozoic and, therefore, one of the oldest ever described. Such characteristics also allow to consider that the Orocaima event corresponds to a possible ignimbrite flare-up event during this era.
... Ga have been obtained for the Fig. 12; see below). In the Kanuku Belt one single 2.04 Ga U-Pb zircon age has been found for a garnet-sillimanite gneiss, with all other ages between 1.99 and 1.96 Ga (Nadeau et al., 2013). Also the two-phase anticlockwise metamorphic history of the three belts is similar (see below), although only in the Bakhuis Granulite Belt up to UHT conditions. ...
... This enormous magmatic province continues westwards into Guyana (Iwokrama metavolcanics and granites; Berrangé, 1977;Nadeau et al., 2013;Nadeau, 2014), Brazil (Surumu volcanics, Pedra Pintada granites; Reis et al., 2003Reis et al., , 2004Fraga & Dreher, 2010) and Venezuela (Caicará metavolcanics, Cuchivero granites; Cox et al., 1993;Wynn, 1993;Hackley et al., 2005), all with ages around 1.99-1.98 Ga (see Fig. 2). ...
... The charnockites are coeval with the widespread felsic magmatism surrounding the Bakhuis Granulite Belt. However, the charnockites have a juvenile composition whereas the felsic metavolcanics may contain inherited Archean zircons (Nadeau et al., 2013) and show rather high Nd T DM model ages of 2.43-2.44 Ga (De Roever et al., 2015), which may indicate that they were derived from a different source (Klaver et al., 2015). ...
The Proterozoic basement of Suriname consists of a greenstone–tonalite–trondhjemite–granodiorite belt in the northeast of the country, two high-grade belts in the northwest and southwest, respectively, and a large granitoid–felsic volcanic terrain in the central part of the country, punctuated by numerous gabbroic intrusions. The basement is overlain by the subhorizontal Proterozoic Roraima sandstone formation and transected by two Proterozoic and one Jurassic dolerite dyke swarms. Late Proterozoic mylonitisation affected large parts of the basement. Almost 50 new U–Pb and Pb–Pb zircon ages and geochemical data have been obtained in Suriname, and much new data are also available from the neighbouring countries. This has led to a considerable revision of the geological evolution of the basement. The main orogenic event is the Trans-Amazonian Orogeny, resulting from southwards subduction and later collision between the Guiana Shield and the West African Craton. The first phase, between 2.18 and 2.09 Ga, shows ocean floor magmatism, volcanic arc development, sedimentation, metamorphism, anatexis and plutonism in the Marowijne Greenstone Belt and the adjacent older granites and gneisses. The second phase encompasses the evolution of the Bakhuis Granulite Belt and Coeroeni Gneiss Belt through rift-type basin formation, volcanism, sedimentation and, between 2.07 and 2.05 Ga, high-grade metamorphism. The third phase, between 1.99 and 1.95 Ga, is characterised by renewed high-grade metamorphism in the Bakhuis and Coeroeni belts along an anticlockwise cooling path, and ignimbritic volcanism and extensive and varied intrusive magmatism in the western half of the country. An alternative scenario is also discussed, implying an origin of the Coeroeni Gneiss Belt as an active continental margin, recording northwards subduction and finally collision between a magmatic arc in the south and an older northern continent. The Grenvillian collision between Laurentia and Amazonia around 1.2–1.0 Ga caused widespread mylonitisation and mica age resetting in the basement.
... Ga have been obtained for the Fig. 12; see below). In the Kanuku Belt one single 2.04 Ga U-Pb zircon age has been found for a garnet-sillimanite gneiss, with all other ages between 1.99 and 1.96 Ga (Nadeau et al., 2013). Also the two-phase anticlockwise metamorphic history of the three belts is similar (see below), although only in the Bakhuis Granulite Belt up to UHT conditions. ...
... This enormous magmatic province continues westwards into Guyana (Iwokrama metavolcanics and granites; Berrangé, 1977;Nadeau et al., 2013;Nadeau, 2014), Brazil (Surumu volcanics, Pedra Pintada granites; Reis et al., 2003Reis et al., , 2004Fraga & Dreher, 2010) and Venezuela (Caicará metavolcanics, Cuchivero granites; Cox et al., 1993;Wynn, 1993;Hackley et al., 2005), all with ages around 1.99-1.98 Ga (see Fig. 2). ...
... The charnockites are coeval with the widespread felsic magmatism surrounding the Bakhuis Granulite Belt. However, the charnockites have a juvenile composition whereas the felsic metavolcanics may contain inherited Archean zircons (Nadeau et al., 2013) and show rather high Nd T DM model ages of 2.43-2.44 Ga (De Roever et al., 2015), which may indicate that they were derived from a different source (Klaver et al., 2015). ...
Abstract
The Proterozoic basement of Suriname consists of a greenstone-TTG belt in the NE of the country,
two high-grade belts in the NW and SW respectively, and a large granitoid - felsic volcanic terrain in
the central part of the country, punctuated by numerous gabbroic intrusions. The basement is
overlain by the subhorizontal Proterozoic Roraima sandstone formation and transected by two
Proterozoic and one Jurassic dolerite dyke swarms. Late Proterozoic mylonitization affected large
parts of the basement. Almost 50 new U-Pb and Pb-Pb zircon ages and geochemical data have been
obtained in Suriname, and many new data are also available from the neighbouring countries. This
has led to a considerable revision of the geological evolution of the basement. The main orogenic
event is the Trans-Amazonian Orogeny, resulting from southwards subduction and later collision
between the Guiana Shield and the West-African Craton. The first phase between 2.18-2.09 Ga
shows ocean floor magmatism, volcanic arc development , sedimentation, metamorphism, anatexis
and plutonism in the Marowijne Greenstone Belt and the adjacent older granites and gneisses . The
second phase encompasses the evolution of the Bakhuis Granulite Belt and Coeroeni Gneiss Belt
through rift-type basin formation, volcanism, sedimentation and, between 2.07-2.05 Ga, high-grade
metamorphism. The third phase between 1.99-1.95 Ga is characterised by renewed high-grade
metamorphism in the Bakhuis and Coeroeni belts at higher pressures than in Phase II, and
ignimbritic volcanism and extensive and varied intrusive magmatism in the western half of the
country. An alternative scenario is also discussed, implying an origin of the Coeroeni Gneiss Belt as an
active continental margin, recording northwards subduction and finally collision between a magmatic
arc in the south and an older northern continent. The Grenvillian collision between Laurentia and
Amazonia around 1.2-1.0 Ga caused widespread mylonitization and mica age resetting in the
basement
... Ga have been obtained for the Fig. 12; see below). In the Kanuku Belt one single 2.04 Ga U-Pb zircon age has been found for a garnet-sillimanite gneiss, with all other ages between 1.99 and 1.96 Ga (Nadeau et al., 2013). Also the two-phase anticlockwise metamorphic history of the three belts is similar (see below), although only in the Bakhuis Granulite Belt up to UHT conditions. ...
... This enormous magmatic province continues westwards into Guyana (Iwokrama metavolcanics and granites; Berrangé, 1977;Nadeau et al., 2013;Nadeau, 2014), Brazil (Surumu volcanics, Pedra Pintada granites; Reis et al., 2003Reis et al., , 2004Fraga & Dreher, 2010) and Venezuela (Caicará metavolcanics, Cuchivero granites; Cox et al., 1993;Wynn, 1993;Hackley et al., 2005), all with ages around 1.99-1.98 Ga (see Fig. 2). ...
... The charnockites are coeval with the widespread felsic magmatism surrounding the Bakhuis Granulite Belt. However, the charnockites have a juvenile composition whereas the felsic metavolcanics may contain inherited Archean zircons (Nadeau et al., 2013) and show rather high Nd T DM model ages of 2.43-2.44 Ga , which may indicate that they were derived from a different source (Klaver et al., 2015). ...
The Proterozoic basement of Suriname consists of a greenstone-TTG belt in the NE of the country,
two high-grade belts in the NW and SW respectively, and a large granitoid - felsic volcanic terrain in
the central part of the country, punctuated by numerous gabbroic intrusions. The basement is
overlain by the subhorizontal Proterozoic Roraima sandstone formation and transected by two
Proterozoic and one Jurassic dolerite dyke swarms. Late Proterozoic mylonitization affected large
parts of the basement. Almost 50 new U-Pb and Pb-Pb zircon ages and geochemical data have been
obtained in Suriname, and many new data are also available from the neighbouring countries. This
has led to a considerable revision of the geological evolution of the basement. The main orogenic
event is the Trans-Amazonian Orogeny, resulting from southwards subduction and later collision
between the Guiana Shield and the West-African Craton. The first phase between 2.18-2.09 Ga
shows ocean floor magmatism, volcanic arc development , sedimentation, metamorphism, anatexis
and plutonism in the Marowijne Greenstone Belt and the adjacent older granites and gneisses . The
second phase encompasses the evolution of the Bakhuis Granulite Belt and Coeroeni Gneiss Belt
through rift-type basin formation, volcanism, sedimentation and, between 2.07-2.05 Ga, high-grade
metamorphism. The third phase between 1.99-1.95 Ga is characterised by renewed high-grade
metamorphism in the Bakhuis and Coeroeni belts at higher pressures than in Phase II, and
ignimbritic volcanism and extensive and varied intrusive magmatism in the western half of the
country. An alternative scenario is also discussed, implying an origin of the Coeroeni Gneiss Belt as an
active continental margin, recording northwards subduction and finally collision between a magmagmatic
arc in the south and an older northern continent. The Grenvillian collision between Laurentia and
Amazonia around 1.2-1.0 Ga caused widespread mylonitization and mica age resetting in the
basement.
... Ga have been obtained for the Fig. 12; see below). In the Kanuku Belt one single 2.04 Ga U-Pb zircon age has been found for a garnet-sillimanite gneiss, with all other ages between 1.99 and 1.96 Ga (Nadeau et al., 2013). Also the two-phase anticlockwise metamorphic history of the three belts is similar (see below), although only in the Bakhuis Granulite Belt up to UHT conditions. ...
... This enormous magmatic province continues westwards into Guyana (Iwokrama metavolcanics and granites; Berrangé, 1977;Nadeau et al., 2013;Nadeau, 2014), Brazil (Surumu volcanics, Pedra Pintada granites; Reis et al., 2003Reis et al., , 2004Fraga & Dreher, 2010) and Venezuela (Caicará metavolcanics, Cuchivero granites; Cox et al., 1993;Wynn, 1993;Hackley et al., 2005), all with ages around 1.99-1.98 Ga (see Fig. 2). ...
... The charnockites are coeval with the widespread felsic magmatism surrounding the Bakhuis Granulite Belt. However, the charnockites have a juvenile composition whereas the felsic metavolcanics may contain inherited Archean zircons (Nadeau et al., 2013) and show rather high Nd T DM model ages of 2.43-2.44 Ga , which may indicate that they were derived from a different source (Klaver et al., 2015). ...
The Proterozoic basement of Suriname consists of a greenstone–tonalite–trondhjemite–granodiorite belt in the northeast of the country, two high-grade belts in the northwest and southwest, respectively, and a large granitoid–felsic volcanic terrain in the central part of the country, punctuated by numerous gabbroic intrusions. The basement is overlain by the subhorizontal Proterozoic Roraima sandstone formation and transected by two Proterozoic and one Jurassic dolerite dyke swarms. Late Proterozoic mylonitisation affected large parts of the basement. Almost 50 new U–Pb and Pb–Pb zircon ages and geochemical data have been obtained in Suriname, and much new data are also available from the neighbouring countries. This has led to a considerable revision of the geological evolution of the basement. The main orogenic event is the Trans-Amazonian Orogeny, resulting from southwards subduction and later collision between the Guiana Shield and the West African Craton. The first phase, between 2.18 and 2.09 Ga, shows ocean floor magmatism, volcanic arc development, sedimentation, metamorphism, anatexis and plutonism in the Marowijne Greenstone Belt and the adjacent older granites and gneisses. The second phase encompasses the evolution of the Bakhuis Granulite Belt and Coeroeni Gneiss Belt through rift-type basin formation, volcanism, sedimentation and, between 2.07 and 2.05 Ga, high-grade metamorphism. The third phase, between 1.99 and 1.95 Ga, is characterised by renewed high-grade metamorphism in the Bakhuis and Coeroeni belts along an anticlockwise cooling path, and ignimbritic volcanism and extensive and varied intrusive magmatism in the western half of the country. An alternative scenario is also discussed, implying an origin of the Coeroeni Gneiss Belt as an active continental margin, recording northwards subduction and finally collision between a magmatic arc in the south and an older northern continent. The Grenvillian collision between Laurentia and Amazonia around 1.2–1.0 Ga caused widespread mylonitisation and mica age resetting in the basement.
... Fraga et al. (2008 Fraga et al. ( , 2009 ) identified a similar two-phase metamorphic evolution in the Cauarane Group, but they considered that the second phase represents the effects of nearby granite emplacement. The metamorphic age of the Kanuku Complex was determined by zircon LA-ICP-MS dating of paragneiss , migmatite, granulite and S-type granite as ranging from 1956 ± 12 Ma to 1979 ± 14 Ma (Nadeau et al., 2013). SHRIMP U-Pb zircon dating established an age of 2.04 Ga for detrital zircon in Cauarane paragneiss, giving a minimum age for, at least, part of its sedimentation (Santos, 2003). ...
... The zircon Pb-evaporation ages of 1987 ± 4 Ma and 1980 ± 4 Ma respectively obtained for a felsic metavolcanic rock and a hypabyssal granite from SW Surinam well agree with the 1.99–1.97 Ga ages of Guyana, Roraima and Venezuela felsic metavolcanics (Schobbenhaus et al., 1994; Brooks et al, 1995; Santos et al, 2003; Nadeau et al, 2013). At the greenstone belt / metavolcanics contact, the felsic metavolcanics rest unconformably on folded and metamorphosed rocks of the greenstone belt and show only large open folds themselves. ...
... Ga age for granites with volcanics. For a 1.99– 1.98 Ga age of the metavolcanic rocks (this study; Santos et al, 2003; Nadeau et al., 2013) the time difference of collision and volcanism is less significant. In addition, the open folding of the metavolcanics does not suggest a post-collisional nature. ...
Abstract: Felsic metavolcanic rocks and associated hypabyssal granites and biotite granites form a large Paleoproterozoic belt from Venezuela and central Guyana across the Bakhuis belt to southwestern Surinam and Northern Brazil. A metarhyolite and a coarse hypabyssal leucogranite from the Sipaliwini region, SW Surinam, near the Brazilian border furnished zircon Pb-evaporation
ages of 1987 ± 4 Ma and 1980 ± 4 Ma, respectively. A biotite granite from NW Surinam yielded a zircon Pb evaporation age of 1949 ± 12 Ma. These ages constrain the age of the magmatic belt in western Surinam, in agreement with 1.99–1.97 Ga ages of metavolcanic rocks from Brazil (Roraima State), Venezuela and Guyana. TDM model ages of 2.43-2.44 Ga (–2.41< ƐNd(t) <-1.54) show that the volcanism was derived from reworking of a Paleoproterozoic crust with minor Archean contribution.
South of the magmatic belt, the Cauarane-Coeroeni belt is represented in Surinam by the Coeroeni gneiss. U-Th-Pb dating of a monazite from a cordierite tonalite from the Coeroeni River gave an age of 2009 ± 14 Ma for the migmatization and high-grade metamorphism of the Coeroeni gneiss. Pb-evaporation ages of 2.72 and 2.89 Ga for two zircons from the cordierite tonalite point to
the presence of Archean inherited components in the protolith. In the border zone of the Coeroeni gneiss, zircon Pb-evaporation and titanite Pb-Pb ages of, respectively, 1976 ± 5 Ma and 1961 ± 17 Ma were obtained for a tonalitic gneiss, probably indicating gneiss emplacement during a second phase of high-grade metamorphism. The Orosirian metamorphism is substantially younger than the late Rhyacian UHT metamorphism in the Bakhuis belt (2.07-2.05 Ga). This indicates that the Bakhuis belt cannot be grouped together with the Cauarane-Coeroeni belt.
... These ages are perfectly consistent with Nd model ages (Dantas et al., 2004(Dantas et al., , 2013Peucat et al., 2011;Barbosa et al., 2012;Santos-Pinto et al., 2012), thus demonstrating the occurrence in South America of crustal terrains older than 3.4 Ga. This was confirmed in the Guiana shield, where a Hadean zircon xenocryst with a U-Pb zircon age of 4219 ± 19 Ma has already been reported (Nadeau et al., 2013). In this contribution, we present new LA-ICPMS U-Pb zircon dating results which significantly increase as well the age limit for the oldest South American proto-crust into Hadean times. ...
... However, the lack of any concordant point around 2 Ga in the Fig. 4 does not support this view. A similar major frequency peak at about 1.95 Ga was interpreted as metamorphic age or intrusion age as well in the different complexes from Guiana shield (Nadeau et al., 2013), where another Hadean zircon core was reported. ...
... Ga in Brazil compared to 2.65 Ga and 3.7 Ga in Argentina. All these differences suggest that at least two distinct nuclei of primitive basement are recorded in South America, in addition to that reported in Guiana Shield (Nadeau et al., 2013). These results should be confirmed by further U-Pb dating combined with Hf isotopes on additional zircon crystals in order to better characterize their magmatic source, as well as the number and extent of Hadean crustal nuclei. ...
... The BGB is surrounded to the W, S and E by subvolcanic granites and metavolcanic rocks of the Cuchivero-Surumu-Iwokrama-Dalbana (CSID) belt that intruded the Guiana Shield during the late-Transamazonian phase at 1.99-1.98 Ga Delor et al., 2003a;Nadeau et al., 2013;Reis et al., 2000). The subvolcanic granites and metavolcanic rocks of the CSID-belt were subsequently intruded by biotite granite in W Suriname, which is probably equivalent to the ∼1.97-1.95 ...
... Ga and the younger phase at 1.97-1.96 Ga Fraga et al., 2009;Nadeau et al., 2013). Extensive post-collisional <1.90 Ga granitoid magmatism is present to the southwest of the CCB in Guyana and Brazil (Kroonenberg and de Roever, 2010;Santos et al., 2004;Valério et al., 2009). ...
... MKS 40) do not show highly negative ε Nd (t) values. Recent zircon dating of CSID-belt volcanic rocks and the Cauarane-Coeroeni belt revealed the presence of a small (∼2% of the grains analysed) pre-Transamazonian detrital zircon population Nadeau et al., 2013). The oldest detrital grain encountered yielded a concordant Hadean age of 4219 Ma. ...
The Bakhuis Granulite Belt in western Suriname is an ultrahigh-temperature (UHT) metamorphic terrain in the centre of the Paleoproterozoic (Transamazonian) Guiana Shield. Next to the UHT granulites, the belt contains a 30 by 30 km body of orthopyroxene-bearing granitoids: the Kabalebo charnockites. This setting offers an excellent opportunity to investigate the source and origin of charnockite magmatism and the common association of charnockites with (ultra)high-temperature metamorphic terrains. We present a detailed geochemical dataset and LA-ICPMS zircon U/Pb ages with the aim to investigate the geochemical and geochronological relationship between charnockite magmatism and UHT metamorphism in the Bakhuis Granulite Belt. The Kabalebo charnockites have a characteristic trace element signature with elevated K2O, P2O5, Zr, REE and Ba coupled with mobile element depletion that is a consequence of high-temperature melting of anhydrous but fertile granulitic crust. Field and geochemical evidence indicates that the intermediate granulites in the Bakhuis Granulite Belt are the source of the Kabalebo charnockites. The new U/Pb zircon ages indicate that charnockite magmatism (1993-1984 Ma) postdates UHT metamorphism (2.07-2.05 Ga) by at least 60 Myr. We argue that it is not possible to maintain a thermal anomaly >200 °C in excess of a normal geothermal gradient for such a prolonged period and hence conclude that the Bakhuis Granulite Belt has experienced two distinct periods in which temperatures >950 °C were reached in the lower crust.
... Another proposed emplacement scenario is arc environment linked to the late phase of the Transamazonian Orogeny (1.99-1.95 Ga, Kroonenberg et al., 2016), as supported by several authors (e.g., Delor et al., 2003;Nadeau et al., 2013;Mahabier and De Roever, 2019). The ages close to 1968 Ma of the Orocaima volcano-plutonism are also correlated to the rocks formed during the Creporizão orogeny (ca. ...
... Volcanic rocks of the Dalbana Formation, at the border of Suriname and Brazil, show more frequent intermediate compositions than in Roraima, although acid sets are still dominant. Intermediate and/or more distal pyroclastic facies are suggested for the Dalbana Formation, given the evidence of reworking of tuff material in a Nadeau et al. (2013) subaqueous environment and less regular presence of lithic-rich facies (Fraga et al., 2017b). Regardless of the alternatives for the Orocaima volcano-plutonism emplacement scenario, the important participation of this thermal event in the evolution of the Guiana Shield is clear. ...
The Orocaima SLIP consists of an association of acid-intermediate volcanic-plutonic rocks. The volcanic rocks were generated in explosive eruptions through low eruptive columns, probably associated with fissural volcanism in the north of the Amazonian Craton, Brazil, between 2.0 and 1.98 Ga. It generated ignimbrites, whose facies (volcanic breccia rich in lithic, lapilli-tuff and lithic lapilli-tuff) show the proximity of the source. The extensive area of ca. 200.000 km² of ignimbrite, rhyolite and dacite deposits, as well as the age range (2.0–1.98 Ga) and geochemical signatures suggest that the Orocaima volcano-plutonism may correspond to one of the oldest silicic LIPs in the world. The silicic volcanism is essentially subaerial and characterized by high-grade ignimbrites (densely welded) and subordinate lava, the ages of which indicate the longevity of the volcanic event in the Orosirian. They are included in the Surumu Group and comprise rocks with high-K calc-alkaline affinities and were emplaced in a subduction-related setting, similar to the rocks that extend through Venezuela, Guyana and Suriname (Cuchivero-Surumu-Iwokrama-Dalbana metavolcanic belt - CSID). The occurrence of mafic fragments disseminated in volcanic and granitic rocks in the north of Roraima, Brazil and in other segments of the CSID belt suggests the coexistence of acid and basic magmas. Except for one sample (εNd(t) = -2.3), the Nd isotopic data of analyzed Surumu Group volcanic rocks yielded positive εNd(t) values (0.5–4.48; TDM = 2.0–2.47 Ga), suggesting generation from magmas derived from the mantle or from the melting of new juvenile crust. The Orocaima volcanism bears no evidence of involvement of Archean sources in the generation of the rocks. Thus, the Orocaima volcano-plutonism may represent one of the most significant ignimbrite eruption events during the Palaeoproterozoic in the world.
... These metamorphic/metasomatic events were responsible for the precipitation/crystallization of Ilmenite (up to 37 wt% TiO 2 ) and phlogopite (up to 2.87 wt% TiO 2 ) within the São Tomé intrusion as well as the crystallization of the emeralds (< 1.70 wt% Cr 2 O 3 ) near the phlogopite levels of the Serra Verde Mine (Ruiz et al., 2018;Santiago, 2017;Santiago et al., 2018). This mineralogy explains the relatively lower (McDonough and Sun, 1995) patterns of the studied rocks. F.G. Santos, et al. ...
... Ga, with some T DM model ages a little bit older (Martin et al., 1997;Dantas et al., 2004). Older (Hadean) ages have only been obtained from two detrital zircon grains from the Guiana shield (4219 ± 19 Ma) and São Francisco Craton (4096 ± 23 Ma) (Nadeau et al., 2013;Paquette et al., 2015). The Archean period in the RGND was characterized by a complex magmatic and deformational history, involving several episodes of magmatism between 2.7 and 3.4 Ga, related to melting of enriched mantle sources in the context of convergent margin (Dantas et al., 2013;Souza et al., 2015). ...
... the TTG-greenstone belt, the Bakhuis granulites, at 2.07– 2.05 Ga in the BGB (De Roever et al. 2003b; Klaver et al. 2015) postdates the amalgamation by at least 10 Myr and marks the end of the main Transamazonian phase. Northeast to northward subduction during the late Transamazonian phase is proposed to have been the cause of amphibolite-to granulite-facies metamorphism in the Cauarane-Coeroeni Belt at 2.01– 1.99 Ga (Fraga et al. 2009; Nadeau et al. 2013; De Roever et al. in press), charnockite magmatism in the BGB at 1.99 Ga (Klaver et al., 2015) and the development of a belt of felsic metavolcanic rocks and subvolcanic granites, the Cuchivero-Surumu-Iwokrama- Dalbana (CSID) belt, at 1.99– 1.98 Ga (Reis et al. 2000; Delor et al. 2003a; Nadeau et al. 2013; De Roever et al. in press). The CSID-belt was subsequently intruded by biotite granite and Stype granites at 1.96 – 1.95 Ga (Fraga et al. 2009; De Roever et al. in press). ...
... the TTG-greenstone belt, the Bakhuis granulites, at 2.07– 2.05 Ga in the BGB (De Roever et al. 2003b; Klaver et al. 2015) postdates the amalgamation by at least 10 Myr and marks the end of the main Transamazonian phase. Northeast to northward subduction during the late Transamazonian phase is proposed to have been the cause of amphibolite-to granulite-facies metamorphism in the Cauarane-Coeroeni Belt at 2.01– 1.99 Ga (Fraga et al. 2009; Nadeau et al. 2013; De Roever et al. in press), charnockite magmatism in the BGB at 1.99 Ga (Klaver et al., 2015) and the development of a belt of felsic metavolcanic rocks and subvolcanic granites, the Cuchivero-Surumu-Iwokrama- Dalbana (CSID) belt, at 1.99– 1.98 Ga (Reis et al. 2000; Delor et al. 2003a; Nadeau et al. 2013; De Roever et al. in press). The CSID-belt was subsequently intruded by biotite granite and Stype granites at 1.96 – 1.95 Ga (Fraga et al. 2009; De Roever et al. in press). ...
The Bakhuis Granulite Belt (BGB) is a metamorphic terrain within the Guiana Shield that experienced ultrahigh-temperature (UHT) metamorphism at 2.07–2.05 Ga. In the southwest of the BGB, the Kabalebo charnockites were emplaced at ca. 1.99 Ga and thus postdate UHT metamorphism by at least 60 Myr. Two generations of gabbroic intrusions have been recognized within the BGB, which could act as a heat source for the two UHT events. A younger generation of tholeiitic “Charlie” gabbros yields a baddeleyite U/Pb age of 1971 ± 15 Ma. The presence of a metamorphic overprint indicates that the hornblende-bearing “Moi–Moi” metagabbros predate the Charlie gabbros. Large zircons with complex zoning patterns are found in a Moi–Moi metagabbro sample. The main growth domains of these zircons give an age of 1984 ± 4 Ma, which is indistinguishable from the surrounding charnockites. Matching trace element and Hf isotope characteristics indicate that the complex zircons are derived from the charnockites. We argue that the emplacement of the metagabbros and charnockite magmatism were contemporaneous and that zircon grains from the charnockitic melt were mechanically transferred to the gabbroic bodies during magma mingling. The new ages for the gabbroic bodies in the BGB confirm that they are contemporaneous with, and the likely heat source for, charnockite magmatism, but that they are not associated with the 2.07–2.05 Ga UHT event. Furthermore, the new ages and recognition of the Moi–Moi metagabbros as an Alaskan-type complex provide the first direct evidence for late Transamazonian subduction zone magmatism in the Guiana Shield.
... The oldest (Hadean-Archaean) portion of the Amazonian Craton (Central Amazonia Province) consists of granite-greenstone terrains and high-grade metamorphic rocks exposed on the Brazil-Central and Guyana shields (Tassinari and Macambira, 2004;Nadeau et al., 2013). These are bounded by the Maroni-Itacaiunas Province developed around 2250-2050 Ma ( Fig. 1a; Ledru et al., 1994). ...
... Ga from the Amapá block. However, these evidences of the Archean crust are rare in both the Bakhuis belt (De Roever et al. 2015) and the Cauarane-Coeroeni belt in the Central Guiana shield (Nadeau et al. 2013). The occurrence of reworked Archean crust during the Paleoproterozoic is greater in the southeastern MIP (Bacajá domain), probably due to its proximity to the Archean crust of the CAP. ...
... Continental zircon grains in Galápagos lavas could indicate the presence of a component of recycled continental crust in the mantle below the islands, in line with geochemical evidence (Blichert-Toft & White, 2001;Hoernle et al., 2000), and similar to Hawai'i where old subcontinental lithospheric mantle zircon below Oahu has been recently reported (Greenough et al., 2021). The inherited zircon population in Galápagos matches, in terms of age and isotope systematics, (a) zircons from exposed basement regions of northern South America and Central America (Heilbron et al., 2017;Nadeau et al., 2013;Noguera et al., 2011), and (b) the inherited zircon grains reported from Cretaceous suprasubduction magmatic arc and mantle rocks of Cuba and Hispaniola recycled in the mantle by subduction of detritus shed from North and South America into nearby oceanic basins Rojas-Agramonte et al., 2016;Torró et al., 2018). A major Permian-Triassic age peak in the latter, corresponding to a prominent age of magmatic/metamorphic rocks in southwestern Mexico and Colombia, is also recorded in the old zircons of Galápagos. ...
In this contribution we report the first systematic study of zircon U-Pb geochronology and δ18O-εHf(t) isotope geochemistry from ten islands of the hot-spot related Galapagos Archipelago. The data extracted from the zircons allow them to be grouped into three types: 1) young zircons (0 – ~4 Ma) with εHf(t) (~5 – 13) and δ18O (~4 – 7) isotopic mantle signature with crystallization ages dating the islands, 2) zircons with εHf(t) (~5 – 13) and δ18O (~5 – 7) isotopic mantle signature (~4 to 164 Ma) which are interpreted to date the time of plume activity below the islands (~164 Ma is the minimum time of impingement of the plume below the lithosphere), and 3) very old zircons (~213 to 3000 Ma) with mostly continental (but also juvenile) εHf(t) (~ -28 – 8) and δ18O (~5 – 11) isotopic values documenting potential contamination from a number of sources. The first two types with similar isotopic mantle signature define what we call the Galápagos Plume Array (GPA). Given lithospheric plate motion, this result implies that GPA zircon predating the Galápagos lithosphere (i.e., >14 – 164 Ma) formed and were stored at sublithospheric depths for extended periods of time. In order to explain these observations, we performed 2D and 3D thermo-mechanical numerical experiments of plume-lithosphere interaction which show that dynamic plume activity gives rise to complex asthenospheric flow patterns and results in distinct long-lasting mantle domains beneath a moving lithosphere. This demonstrates that it is physically plausible that old plume-derived zircons survive at asthenospheric depths below ocean islands.
... U-Pb dating of hydrothermal zircons from the mineralized zone yielded an intercept age of 1.99 Ga, interpreted as the minimum age of mineralization, allowing a tentative age match with the OSL. The Eagle Mountain deposit, some 230 km southeast of Georgetown (Guyana), is of the porphyry gold type (Voicu et al. 2001) and the mineralization is related to granitoids at 1.98 Ga (Nadeau et al. 2013), in turn, hosted by metavolcanic rocks of the Barama-Mazaruni greenstone belt (Kroonenberg and de Roever 2010). The ore is widespread in the saprolitic rock or as stockworks, where it forms a bimetallic association with Mo and Cu. ...
This paper overviews the Proterozoic Large Igneous Provinces of the Amazonian Craton, characterized by large volumes of extrusive and intrusive magmatic rocks. We reassess the geologic, geochronologic and geochemical information to stablish three intracontinental felsic volcanic-plutonic igneous belts (i.e., SLIPs), namely: Orocaima (1.98-1.96 Ga), Uatumã (1.88-1.87 Ga) and Alta Floresta (1.80-1.79 Ga). The Avanavero LIP (1.79-1.78 Ga), as well as the Rincón del Tigre-Huanchaca LIP (1.11 Ga) are also revisited. The relationships of these events with intraplate settings through time and space are apparent. We examine the main characteristics of each magmatic event in light of the U-Pb zircon and baddeleyite ages and coupled isotopic-geochemical constraints, the geodynamic significance, and metallogenetic potential. The Uatumã and Alta Floresta SLIPs host the most important mineral resources within the Amazonian Craton. Global barcode matches of the Proterozoic SLIPS/LIP events of Amazonia are also addressed, as well as their possible links with geologic time-scale periods: the Orosirian, Statherian and Stenian boundaries. We also evaluate the available paleomagnetic data to address issues related to the barcode match of such SLIP/LIP events in the context of supercontinent cycles.
... 3.0-3.3 Ga sandstone and quartzose clastic rocks (Froude et al., 1983;Compston and Pidgeon, 1986;Wilde et al., 2001;Cavosie et al., 2007;Nebel et al., 2014;Valley et al., 2014;Nelson, 2002;Wyche et al., 2004;GSWA;2005;Wyche, 2007;Paquette et al., 2015;Byerly et al., 2018), even though many odd localities have been reported (Mojzsis and Harrison, 2002;Iizuka et al., 2006;Martel et al., 2008;Diwu et al., 2013;Nadeau et al., 2013;Cui et al., 2013;Xing et al., 2014;Li et al., 2016). ...
The size of continents is an essential parameter to understand the growth of the continental crust and the evolution of the solid Earth because it is subject to tectonism and mantle convection and affects the preservation of the crust. This article reviews the secular change in the size of continents on the early Earth, focusing on terrigenous clastic rocks, especially quartzose sandstones occurring on relatively large continents. The earliest continental crust in the Hadean or early Archean was produced with a width of ∼200–500 km, similar to modern oceanic island arcs along subduction zones or oceanic islands in hot spot regions by mantle plume heating. Through the collision and amalgamation of such primitive continental crusts, continental blocks over 500 km in width and length evolved and appeared by ca. 3.5 Ga. Through further amalgamation, during ca. 3.3–2.5 Ga, the Archean continents emerged with widths and lengths greater than 1,000 km, which were still smaller than those of modern continents. Continents with widths and lengths of nearly 10,000 km have existed since ca. 2.4 Ga (early Proterozoic). Further analyses of the composition and formation mechanism of clastic rocks will help reveal more quantitative secular changes in the sizes of continents.
... The most direct and effective solutions to the above-mentioned questions are derived from zircons (Cavosie et al. 2006;Kemp et al. 2010;Mojzsis et al. 2001;Valley et al. 2014;Whitehouse et al. 2017;Wilde et al. 2001). Hadean zircons outside China have been reported, for examples, from the Itsaq Gneiss Complex in West Greenland (Mojzsis and Harrison 2002), the Jack Hill Greenstone Belt in Western Australia (Harrison et al. 2005;Kemp et al. 2010;Wilde et al. 2001), the Acasta Gneiss in the Slave Province of Canada (Iizuka et al. 2006), the Quad Creek Quartzite in the USA (Maier et al. 2012), the Paleoproterozoic volcanic in Brazil (Nadeau et al. 2013) and the Paleoarchean TTGs of the Singhbhum Craton in Eastern India (Chaudhuri et al. 2018). ...
A fragment of Hadean continental crust has been postulated to underlie the North China Craton based on the discovery of >3.8 Ga detrital zircons, but these detrital zircons may be transported from a lateral source. Here we report new UPb ages of 3823 to 230 Ma for zircon xenocrysts directly from Cretaceous granites (129 Ma), which rules out a lateral source. Our results for the first time demonstrate the existence of 3.85 Ga crustal precursors beneath the southern North China Craton based on the Hf isotopic compositions of the 3.82 Ga zircon. The crustal precursors might be a granitic source that was produced by the wet melting of ancient continental crust. We further show that the southern North China Craton has experienced the global Columbia, Gondwana, and Pangaea supercontinent events, based on the inherited zircon age groups of 2017–1896 Ma, 1792–1776 Ma, 584–570 Ma and 251–230 Ma. These Eoarchaean to Triassic UPb ages document the evolution of the early continental crust and the geological process in the development of the North China Craton.
... There are Hadean zircons from Jack Hills (JH) (Compston and Pidgeon, 1986), Mt. Narryer and other locations in Australia, Canada (Iizuka et al., 2006), Tibet (Duo et al., 2007), multiple locations in China (Wang et al., 2007;Diwu et al., 2010Diwu et al., , 2013Cui et al., 2013;Xing et al., 2014) and South America (Nadeau et al., 2013;Paquette et al., 2015). More recently some Hadean zircons have been discovered in South Africa (Byerly et al., 2018). ...
... These mafic-dominated supracrustal belts are thought to represent segments of the ancient oceanic crust and their isotopic characters provide information about the Hadean and Eoarchean mantle (Furnes et al., 2009;O'Neil et al., 2012). Evidence is also accumulating about the existence of continental crust in Hadean times (4.0-4.5 Ga) from study of zircon grains in Archean sediments and xenocrystic zircon grains in granitic gneisses (Compston and Pidgeon, 1986;Nelson et al., 2000;Wilde et al., 2001;Wyche et al., 2004;Iizuka et al., 2006;Duo et al., 2007;Harrison, 2009;Nadeau et al., 2013). In recent years more refined isotopic studies of Pb, Sm, Nd, Lu, Hf, and particularly of short lived isotopes and oxygen isotopes have provided new information on the processes of crustal growth during the Hadean time and on the physical and chemical conditions existing on the surface of the early Earth (Bowring and Housh, 1995;Moorbath and Whitehouse, 1996;Kemp et al., 2010). ...
... Narryer quartzite by Froude et al. (1983) and subsequently in greater abundance by Compston and Pidgeon (1986) in a quartz pebble metaconglomerate at the Jack Hills -both in the Narryer Gneiss Complex of the Yilgarn Craton, western Australia. Zircons with Hadean (> 4 Ga) 207 Pb/ 206 Pb ages have subsequently been reported from most other continents including North America (Bowring and Williams, 1999;Mojzsis and Harrison, 2002;Iizuka et al., 2006), South America (Nadeau et al., 2013;Paquette et al., 2015), Eurasia (Wang et al., 2007;Duo et al., 2007;Xu et al., 2012;Xing et al., 2014), India (Miller et al., 2018), and Africa (Byerly et al., 2018), suggesting a widely distributed occurrence of zirconbearing crust by at least the late Hadean. Nonetheless, both the antiquity (Valley et al., 2014) and quantity (Holden et al., 2009) of Hadean zircon from the Jack Hills far exceed that yet analyzed from any other locality; as such, the Jack Hills zircon record predominates our understanding of the Hadean eon on Earth. ...
The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high-spatial-resolution high-throughput in situ isotopic and elemental analysis techniques, such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision (
... s in some of the drill holes at Mazoa. The sub-vertical dykes strike easterly across the quartzite. The age is unknown. The Marudi Granite intrudes these rocks (2.22 Ga, Nadeau, 2014), partly via a migmatitic contact. The Southern Guyana Granite Complex surrounds almost all the enclaves of Kwitaro Group rocks, and has been dated at 1.93-1.98 Ga by Nadeau et. al. (2013). ...
A brief update is given of the stratigraphy of Guyana, especially that of the greenstone belts. An updated stratigraphical table and
geological map are presented, including the geochronology. The Kwitaro Group is believed to be older, and can not be correlated
with the Barama-Mazaruni Supergroup. The Barama and Mazaruni groups both appear to have similar stratigraphy, though the
Mazaruni Group has a much greater thickness of mafic metavolcanics at the base. Felsic rocks from the central part of the sequence
in both groups are of a similar age. Both groups have sediments such as phyllites high in the sequence. Only the Barama Group
has manganiferous zones and regionally anomalous arsenic drainage geochemistry. Both areas have possibly unconformable
greywackes and conglomerates as the youngest rocks, which have been deformed and metamorphosed with the rest of the sequence.
I believe that folding and thrusting has juxtaposed a distal area with less sedimentation against a sediment rich area.
The Haimaraka Formation greywackes was originally considered to be the upper part of the Mazaruni Group. On the basis of it’s
much lower level of metamorphism, characteristic two phases of open folding, as well as field relationships to the Muruwa
Formation I consider this to be part of the younger Burro Burro Group, which explains the lack of primary gold occurrences.
... 2.51e3.81 Ga) were identified in felsic volcanics and comagmatic granitic intrusions of the Paleoproterozoic Iwokrama Formation in southern Guyana (Nadeau et al., 2013). According to these authors, it demonstrates the existence of an underlying "Lost Hadean Crust". ...
The southeastern Guyana Shield, northeast Amazonian Craton, in the north of Brazil, is part of a widespread
orogenic belt developed during the Transamazonian orogenic cycle (2.26e1.95 Ga) that includes a
large Archean continental landmass strongly reworked during the Transamazonian orogeny, named
Amapá Block. It consists mainly of a high-grade metamorphic granulitic-migmatitic-gneiss complex, of
Meso- to Neoarchean age and Rhyacian granitoids and supracrustal sequences. For the first time, coupled
U-Pb and Lu-Hf isotope data were obtained on zircon by LA-ICP-MS from five tectono-stratigraphic units
of the Archean basement and one Paleoproterozoic intrusive rock, in order to investigate the main episodes
of crustal growth and reworking. Whole-rock Sm-Nd isotope data were compared to the zircon
Lu-Hf data. Three main magmatic episodes were defined by U-Pb zircon dating, two in the Mesoarchean
(w3.19 Ga and 2.85 Ga) and one in the Neoarchean (w2.69e2.65 Ga). Subchondritic ƐHf(t) values obtained
for almost all investigated units indicate that crustal reworking processes were predominant
during the formation of rocks that today make up the Amapá Block. Hf-TDM
C model ages, ranging from
2.99 Ga to 3.97 Ga, indicate that at least two important periods of mantle extraction and continental crust
formation occurred during the Archean in southeastern Guyana Shield, an older one in the Eoarchean
(w4.0 Ga) and a younger one in the Mesoarchean (w3.0e3.1 Ga). The latter is recognized as an important
period of crustal accretion worldwide. The recognition of an Eoarchean episode to the southeastern most
part of the Guyana Shield is unprecedented and was not recorded by whole-rock Sm-Nd data, which
were restricted to the MesoePaleoarchean (2.83 Ga to 3.51 Ga). This finding reveals that continental crust
generation in the Amazonian Craton began at least 500 Ma earlier than previously suggested by the Sm-
Nd systematics.
... This discovery of Hadean zircons within the Kaapvaal craton adds to a growing list of known Hadean zircon-bearing localities (Bowring and Williams, 1999;Chaudhuri et al., 2018;Compston and Pidgeon, 1986;Cui et al., 2013;Duo et al., 2007;Froude et al., 1983;Nadeau et al., 2013;Nelson et al., 2000;Paquette et al., 2015;Wang et al., 2007;Xing et al., 2014). Further examination of the GSB within the context of findings from these other regions can add to our understanding of the early Earth. ...
Hadean zircons hold the promise of providing a rare window into the crustal development and surface evolution of early Earth. To date, the only known sources of abundant Hadean zircons are sedimentary units in the Jack Hills and Mount Narryer regions of Western Australia. Here we describe a sedimentary layer, termed the Green Sandstone Bed, dated at ca. 3306 Ma, in the Barberton greenstone belt, South Africa, that contains abundant zircons ranging from 3300 to 4100 Ma, many of which predate the oldest known rocks in the greenstone belt at ca. 3550 Ma. This adds to a very small number of known Hadean zircon-bearing localities and is particularly important due to its low degree of thermal metamorphism (lower greenschist facies) and negligible strain. There is a high probability that primary mineral compositions of zircon and other heavy minerals present in this bed are well preserved.
... Charnockite and anorthosite intrusions in the Bakhuis Mountains and gabbroic plutons elsewhere in Suriname (Lucie Gabbro, formerly De Goeje Gabbro) show similar ages, together testifying of an important magmatic pulse in the whole northern Guiana Shield in an Andean-type setting, called Orocaima event by Reis et al. (2000). Inherited zircons from the Iwokrama rocks in Guyana gave the highest ages so far found in South America of 4.2 Ga (Nadeau et al. 2013). ...
Proterozoic metamorphic and igneous rocks belonging to the Guiana Shield form the basement of the Colombian territory from its eastern borders westwards to at least the eastern flanks of the Central Cordillera. A small part of the Amazonian basement underlain by felsic metavolcanics records the Trans-Amazonian Orogeny (2.26–1.98 Ga), the major orogenic event that shaped most of the Guiana Shield. The main part of the Colombian Amazonian and Orinoquian basement and of the adjacent Venezuelan and Brazilian territories consists of high-grade, largely supracrustal metamorphic rocks which accreted onto the Trans-Amazonian basement during the Querarí Orogeny (1.86–1.72 Ga) and was intruded by Mesoproterozoic anorogenic plutons around 1.59–1.51 Ga. The Andean Precambrian basement crops out in upthrust blocks all along the Eastern and eastern Central Cordillera, from the Garzón Massif in the south to the Guajira Peninsula in the north, and continues further northeast into Venezuela and eastwards into the Subandean basins. The Andean basement consists mainly of granulites and other high-grade metamorphic rocks, mainly of supracrustal origin, as well as minor plutons, formed during the Grenvillian Orogeny (1.1–0.9 Ga) caused by the collision of Amazonian and Laurentia. Echos of this collision are also discernable in the adjacent Amazonian basement as large shear faults, folding and low-grade metamorphism of Mesoproterozoic sandstone sequences, thermal mineral age resetting and minor alkaline magmatism.
... Given the poor preservation of Hadean rocks, much of our very limited knowledge of the Hadean Earth comes from zircon > 4.0 Ga, found exclusively by U-Pb geochronology of detrital or xenocrystic zircons in younger rocks. So far, Hadean zircons have been found in the Acasta Gneiss [Bowring and Williams, 1999b;Iizuka et al., 2006] (see above); the Eoarchean Itsaq Gneiss, Greenland [Mojzsis and Harrison, 2002]; Ordovician volcanics of the Caotangou Group in the North Qinling Orogenic Belt, China [Wang et al., 2007;Diwu et al., 2013); metapelites within the Changdu Block of North Qiangtang, Tibetan Plateau, with a preliminary age of Meso-to Neoproterozoic [He et al., 2011]; Neoproterozoic to Paleozoic metasediments from the Cathaysia Block of Southern China [Xing et al., 2014]; Mesoarchean paragneisses and quartzites in the Beartooth Mountains, Wyoming Craton, USA [Mueller et al., 1992;Maier et al., 2012); orthoand paragneisses of the Napier Complex, Antarctica [Black et al., 1986;Belyatsky et al., 2011); felsic magmatic rocks of the Iwokrama Formation, Guyana shield [Nadeau et al., 2013]; and most recently from orthogneisses in the Sao Francisco craton in northeast Brazil [Paquette et al., 2015]. Typically only one or two grains of hundreds analyzed yielded such old ages; these discoveries are largely due to the ability of LA-ICPMS and SIMS U-Pb geochronology to screen a huge amount of zircon from a variety of rock types. ...
This book is a welcome introduction and reference for users and innovators in geochronology. It provides modern perspectives on the current state-of-the art in most of the principal areas of geochronology and thermochronology, while recognizing that they are changing at a fast pace. It emphasizes fundamentals and systematics, historical perspective, analytical methods, data interpretation, and some applications chosen from the literature. This book complements existing coverage by expanding on those parts of isotope geochemistry that are concerned with dates and rates and insights into Earth and planetary science that come from temporal perspectives. Geochronology and Thermochronology offers chapters covering: Foundations of Radioisotopic Dating; Analytical Methods; Interpretational Approaches: Making Sense of Data; Diffusion and Thermochronologic Interpretations; Rb-Sr, Sm-Nd, Lu-Hf; Re-Os and Pt-Os; U-Th-Pb Geochronology and Thermochronology; The K-Ar and 40Ar/39Ar Systems; Radiation-damage Methods of Geo- and Thermochronology; The (U-Th)/He System; Uranium-series Geochronology; Cosmogenic Nuclides; and Extinct Radionuclide Chronology.
... enous sources (Compston and Pidgeon 1986;Mueller et al. 1998;Wilde et al. 2001;Wyche et al. 2004;Iizuka et al. 2006Iizuka et al. , 2007Iizuka et al. , 2009Cavosie et al. 2007;Harrison 2009;Mueller and Wooden 2012;Thern and Nelson 2012;Nebel et al. 2014;Valley et al. 2014). In other areas, Hadean zircons are present in Proterozoic and younger units as either constituents of sedimentary rocks or xenocrysts in volcanic assemblages and so are of less certain cratonic origins (e.g., Wang et al. 2007;Nadeau et al. 2013). Data presented here suggest that the Singhbhum craton may also be a cratonic source for Hadean zircons. ...
The Singhbhum craton is one of five Archean cratons constituting the Indian subcontinent. It consists of four major
lithotectonic units with broadly defined ages from Eoarchean to Neoarchean: the Older Metamorphic Group (3.7–
3.2 Ga), Older Metamorphic Tonalite Gneisses (3.8–3.1 Ga), Singhbhum Granite (3.5–3.0 Ga), and Iron Ore Group
(3.51–2.55 Ga). In this study, 270 zircons were separated from modern sediment of the Baitarani River, which is wholly
contained within the craton. Zircons were analyzed with laser ablation ICP-MS for their U-Pb systematics; 150%
were less than 5% discordant. Three primary age groupings account for ∼98% of analyses: 3.62–3.55 Ga (5%), 3.50–
3.22Ga (87%), and 3.10–3.06Ga (6%). The preponderance of 3.50–3.22Ga zircons is consistent with the local basement
that includes a 3.47 Ga tonalite gneiss enclave within a 3.35–3.30 Ga outcrop of the Singhbhum Granite near Keonjhar.
Lu-Hf systematics of zircons yielded 67% with positive initial εHf scattered above and below the mantle growth curve
and 33%with negative initial εHf, indicating contributions from both depleted mantle and older crustal sources. Singlestage model ages range from 4.29 to 3.10 Ga. Of note is a single zircon with a
207
Pb/
206
Pb age of 4015 5 9 Ma (1.3%
discordant), which is the first Hadean zircon documented from any of the Indian cratons. This grain yielded an initial εHf
of 25.30, which indicates an episode of Hadean felsic crust formation in the Singhbhum craton comparable to that
proposed for the Jack Hills of the Yilgarn craton (Australia).
... Elsewhere in the world, Hadean-aged zircons are exceptionally rare, despite extensive searching. The known examples are a single xenocrystic grain encased in biotite (and hence protected from dissolution in the host tonalite magma) from Akilia Island, west Greenland (Mojzsis and Harrison, 2002), two grains from South America (Guyana and Brazil: Paquette et al., 2015;Nadeau et al., 2013) and eight from China (summarized in Li et al., 2016). These exceptional grains occur in a variety of sedimentary and metamorphic rocks of Archaean to Paleozoic age, and are challenging to put into a global context. ...
... enous sources (Compston and Pidgeon 1986;Mueller et al. 1998;Wilde et al. 2001;Wyche et al. 2004;Iizuka et al. 2006Iizuka et al. , 2007Iizuka et al. , 2009Cavosie et al. 2007;Harrison 2009;Mueller and Wooden 2012;Thern and Nelson 2012;Nebel et al. 2014;Valley et al. 2014). In other areas, Hadean zircons are present in Proterozoic and younger units as either constituents of sedimentary rocks or xenocrysts in volcanic assemblages and so are of less certain cratonic origins (e.g., Wang et al. 2007;Nadeau et al. 2013). Data presented here suggest that the Singhbhum craton may also be a cratonic source for Hadean zircons. ...
... In Guyana the volcanic rocks (Iwkorama Formation) and the associated granitoids are collectively designated as Burro-Burro Group (Gibbs & Barron, 1993;Berrangé, 1977), while in Suriname the volcanites are named Dalbana Formation and the associated granitoids received various names. Nadeau et al (2013) reports the presence of inherited Hadean zircon xenocrysts in the Iwokrama volcanic rocks, which show ages around 1.99-1.96 Ga. ...
... Estudos sismológicos, de comprimento e forma de ondas Rayleigh e S (Lloyd et al. 2010;Chulick et al. 2013;Corrêa Rosa et al. 2016), sugerem uma estrutura crustal para o CA composta por duas regiões de crosta mais espessa (> 50 km), que correspondem geotectonicamente a dois núcleos arqueanos: (1) Blocos Imataca e Amapá no Escudo das Guianas (Kroonenberg et al. 2016). Na divisa Brasil-Guiana ressalta-se a obtenção de uma idade de 4,2 Ga em zircão herdado de uma rocha vulcânica félsica do Grupo Surumu (Nadeau et al. 2013), registrando a presença de um paleo-núcleo hadeano, e; (2) Bloco Carajás, onde encontra-se crosta arqueana aflorante bem estabelecida (Cordani et al. 2009) com idades entre 2.6 e 3.2 Ga (Tassinari et al. 2000;Dal'Agnol et al. 2001;Santos 2003). Uma extensa faixa de orientação NNW-SSE cuja área corresponde às províncias Ventuari-Tapajós + Amazônia Central ou Tapajós-Parima possui uma espessura crustal em torno de 40 -45 km. ...
RESUMO: No sudeste do estado do Amazonas, as rochas vul-cânicas do Grupo Colíder (1,82-1,76 Ga) são caracterizadas por dois tipos composicionais relacionados a diferentes estilos erup-tivos. Lápili-tufos riolíticos ricos em cristais, lápili-tufos com baixo grau de soldagem e lápili-tufos ricos em púmice com textu-ra eutaxítica compõem a primeira associação. Estas vulcânicas são ricas em fenocristais e cristaloclastos de quartzo, indicando um magma supersaturado em SiO2. Feno-latitos porfiríticos, além de tufos vítreos e tufos reomórficos formam outra associa-ção e são relacionados a depósitos hipabissais e piroclásticos de magmas pobres em quartzo. A presença de texturas reomórficas indica soldagem de alta temperatura nas litologias subaéreas. Litofácies com lápili-acrescionário e gas pipes também foram identificadas nesse grupo e associadas a eventos piroclásticos. O Grupo Beneficente (1,76-1,74 Ga) é composto por associações de litofácies deltaicas (pró-delta, frente deltaica e planície deltaica) que, juntamente com conglomerados aluviais vulcanogênicos, quartzo arenitos costeiros e fluxos coesivos subaquosos de leques deltaicos indicam que a sedimentação ocorreu em ambientes del-taico e marinho. A continuidade do magmatismo nos estágios de maior aporte sedimentar é demonstrada pela intercalação entre tufos vítreos e as rochas sedimentares. ABSTRACT: In southeastern Amazonas state, the volcanic rocks of Colíder Group (1.82-1.76 Ga) are characterized by two compositional types related to different eruptive styles. Crystal-rich rhyolitic lapilli-tuffs, low-grade welded lapilli-tuffs and pumice-rich lapilli-tuffs with eutaxitic textures compose the first association. Pheno-latites in addition to vitric tuffs and rheomor-phic tuffs forms another association and are related to hypabyssal and pyroclastic deposits of quartz-poor magmas. The presence of rheomorphic textures indicate high-temperature welding in the subaerial litholo-gies. Accretionary-lapilli with gas pipes lithofacies were also identified and associated to pyroclastic events. The Beneficente Group (1.76-1.74 Ga) is composed by del-taic lithofacies associations (pro-delta, delta front and delta plain) which, together with volcanogenic alluvial conglomerates, coastal quartz sandstones and cohesive subaqueous flows, indicate deltaic and marine settings to the sedimentation. The magmatism continuity during major sediment supply stages is demonstrated by the in-tercalation between sedimentary rocks and vitric tuffs.
... The oldest zircon found in the Trinidad sediments was 3253 ± 16 Ma (Xie and Mann, 2014). Nadeau et al. (2013) reported several Paleoarchaean as well as one Hadean zircon xenocryst from Paleoproterozoic felsic volcanic rocks of the Kanuku Complex in the southern Guyana Shield and postulated the existence of a Hadean-to Archean crustal domain at depth. It is possible that our two oldest zircon grains also reflect derivation from this ancient basement. ...
The Lesser Antilles arc is one of the best global examples in which to examine the effects of the involvement of subducted sediment and crustal assimilation in the generation of arc crust. Most of the zircon recovered in our study of igneous and volcaniclastic rocks from Grenada and Carriacou (part of the Grenadines chain) is younger than 2 Ma. Within some late Paleogene to Neogene (~ 34–0.2 Ma) lavas and volcaniclastic sediments however, there are Paleozoic to Paleoarchean (~ 250–3469 Ma) xenocrysts, and Late Jurassic to Precambrian zircon (~ 158–2667 Ma) are found in beach and river sands. The trace element characteristics of zircon clearly differentiate between different types of magmas generated in the southern Lesser Antilles through time. The zircon population from the younger arc (Miocene, ~ 22–19 Ma, to Present) has minor negative Eu anomalies, well-defined positive Ce anomalies, and a marked enrichment in heavy rare earth elements (HREE), consistent with crystallization from very oxidized magmas in which Eu2 + was in low abundance. In contrast, zircon from the older arc (Eocene to mid-Oligocene, ~ 30–28 Ma) has two different REE patterns: 1) slight enrichment in the light (L)REE, small to absent Ce anomalies, and negative Eu anomalies and 2) enriched High (H)REE, positive Ce anomalies and negative Eu anomalies (a similar pattern is observed in the xenocrystic zircon population). The combination of positive Ce and negative Eu anomalies in the zircon population of the older arc indicates crystallization from magmas that were variably, but considerably less oxidized than those of the younger arc. All the igneous zircon has positive εHf(t), reflecting derivation from a predominantly juvenile mantle source. However, the εHf(t) values vary significantly within samples, reflecting considerable Hf isotopic heterogeneity in the source. The presence of xenocrystic zircon in the southern Lesser Antilles is evidence for the assimilation of intra-arc crustal sediments and/or the recycling and incorporation of sediments into the magma sources in the mantle wedge. Most likely however, primitive magmas stalling and fractionating during their ascent through the Antilles crust entrained ancient zircon. This is evidence by the geochemistry of the study samples, which is inconsistent with any involvement of partially melted subducted sediment. Paleogeographic reconstructions show that the old zircon could derive from distant regions such as the Eastern Andean Cordillera of Colombia, the Merida Andes, and the northern Venezuela coastal ranges, transported for example by the Proto-Maracaibo River precursor of the Orinoco River.
... A xenocrystic zircon from a felsic volcanic unit of the Iwokrama Formation, Guyana Shield (Fig. 11), yielded a concordant LA-ICP-MS U-Pb age of 4.22 ± 0.02 (Nadeau et al. 2013). No other geochemical analyses of this zircon have been reported. ...
... The oldest portion (Hadean-Archean) of the Amazonian Craton (Central Amazonian Province) consists of granite-greenstone terrains and high-grade metamorphic rocks exposed in the Brazil-Central and Guiana shields (Tassinari & Macambira 2004, Nadeau et al. 2013. The Maroni-Itacaiúnas Belt separates these landmasses, and it is dated around 2250-2050 Ma (Ledru et al. 1994). ...
In the last decade, the participation of the Amazonian Craton on Precambrian supercontinents has been clarified thanks to a wealth of new paleomagnetic data. Paleo to Mesoproterozoic paleomagnetic data favored that the Amazonian Craton joined the Columbia supercontinent at 1780 Ma ago, in a scenario that resembled the South America and BAltica (SAMBA) configuration. Ten, the mismatch of paleomagnetic poles within the Craton implied that either dextral transcurrent movements occurred between Guiana and Brazil-Central Shield after 1400 Ma or internal rotation movements of the Amazonia-West African block took place between 1780 and 1400 Ma. The presently available late-Mesoproterozoic paleomagnetic data are compatible with two different scenarios for the Amazonian Craton in the Rodinia supercontinent. The first one involves an oblique collision of the Amazonian Craton with Laurentia at 1200 Ma ago, starting at the present-day Texas location, followed by transcurrent movements, until the final collision of the Amazonian Craton with Baltica at ca. 1000 Ma. The second one requires drifting of the Amazonian Craton and Baltica away from the other components of Columbia after 1260 Ma, followed by clockwise rotation and collision of these blocks with Laurentia along Grenvillian Belt at 1000 Ma. Finally, although the time Amazonian Craton collided with the Central African block is yet very disputed, the few late Neoproterozoic/Cambrian paleomagnetic poles available for the Amazonian Craton, Laurentia and other West Gondwana blocks suggest that the Clymene Ocean separating these blocks has only closed at late Ediacaran to Cambrian times, after the Amazonian Craton rifted apart from Laurentia at ca. 570 Ma.
... The oldest portion (Hadean-Archean) of the Amazonian Craton (Central Amazonian Province) consists of granite-greenstone terrains and high-grade metamorphic rocks exposed in the Brazil-Central and Guiana shields (Tassinari & Macambira 2004, Nadeau et al. 2013. The Maroni-Itacaiúnas Belt separates these landmasses, and it is dated around 2250-2050 Ma (Ledru et al. 1994). ...
The Amazon Craton is a key unit in Proterozoic supercontinents (Columbia, Rodinia and Gondwana), but few paleomagnetic poles were available to constraint its paleogeographic position. Here we review the paleomagnetic record for the Amazon Craton between 1800 and 520 Ma, including seven new paleomagnetic poles obtained on sedimentary, volcanic and plutonic rocks. These poles are compared to those of other cratons thought to have interacted with Amazonia in the Proterozoic, such as Baltica and Laurentia. The oldest assemblage of continents to be addressed is the Paleoproterozoic Columbia (~1800 Ma), for which our data support a configuration aligning Laurentia, Baltica and Amazonia through their Paleo-Mesoproterozoic belts. For Neoproterozoic times (~1200-1000 Ma) a connection between Laurentia and Amazonia in an evolving configuration (with sinistral movement between the two units) is supported by a pole-to-pole comparison. According to our compilation, the assembly of Gondwana has probably occurred in different steps, comprising first (~630 Ma) the connection between Sao Francisco, Rio de la Plata, other minor blocks and the African cratons, followed by the collision of these central Gondwanan blocks with the Amazon craton by mid-Cambrian times (~530 Ma), after the opening of the Iapetus ocean basin.
The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high spatial resolution, high throughput in situ isotopic and elemental analysis techniques such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision (
Hadean zircons have been documented from fifteen terrestrial localities in Australia, Asia, Africa, and North and South America, in stony and martian meteorites, and in lunar rocks. Extraterrestrial zircons are characterized by the absence of the positive Ce anomaly, seen in virtually all terrestrial zircons, much higher formation temperatures, and a unique suite of mineral inclusions. Remarkably little effort has been directed toward characterizing the geochemical nature of Hadean zircons from terrestrial localities beyond the Jack Hills region and thus it remains unclear how representative it is of the Hadean world. A massive analysis campaign is indicated to better understand Earth’s last true ‘dark age’.
Zircon is the only candidate of Hadean terrestrial material that can be collected because it can survive physically and chemically, as well as maintain its U–Pb age system during omnigenous geological events. However, Hadean zircons are rare, so many age analyses of zircons are required to isolate Hadean zircon grains. There are two ways to improve the analyses; decrease the time required for pre-analyzing processes and decrease the time required for age analysis. New equipment, high-voltage pulse power fragmentation device and automatic zircon pick-up system are effective for crushing rock sample and separating zircon grains, respectively, in a short time. Another potential age analysis, the ²⁰⁷Pb/²⁰⁶Pb age screening analysis, shows good performance in selecting old zircons quickly. Integrative operation of equipment and methods will result in successfully finding numerous Hadean zircons.
Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Pb analyses of zircons from Paleoarchean (~3.4 Ga) tonalite-gneiss called the Older Metamorphic Tonalitic Gneiss (OMTG) from the Champua area of the Singhbhum Craton, India, reveal 4.24-4.03 Ga xenocrystic zircons, suggesting that the OMTG records the hitherto unknown oldest precursor of Hadean age reported in India. Hf isotopic analyses of the Hadean xenocrysts yield unradiogenic ¹⁷⁶Hf/¹⁷⁷Hfinitial compositions (0.27995 ± 0.0009 to 0.28001 ± 0.0007; ɛHf[t] = −2.5 to −5.2) indicating that an enriched reservoir existed during Hadean eon in the Singhbhum cratonic mantle. Time integrated ɛHf[t] compositional array of the Hadean xenocrysts indicates a mafic protolith with ¹⁷⁶Lu/¹⁷⁷Hf ratio of ∼0.019 that was reworked during ∼4.2-4.0 Ga. This also suggests that separation of such an enriched reservoir from chondritic mantle took place at 4.5 ± 0.19 Ga. However, more radiogenic yet subchondritic compositions of ∼3.67 Ga (average ¹⁷⁶Hf/¹⁷⁷Hfinitial 0.28024 ± 0.00007) and ~3.4 Ga zircons (average ¹⁷⁶Hf/¹⁷⁷Hfinitial = 0.28053 ± 0.00003) from the same OMTG samples and two other Paleoarchean TTGs dated at ~3.4 Ga and ~3.3 Ga (average ¹⁷⁶Hf/¹⁷⁷Hfinitial is 0.28057 ± 0.00008 and 0.28060 ± 0.00003), respectively, corroborate that the enriched Hadean reservoir subsequently underwent mixing with mantle-derived juvenile magma during the Eo-Paleoarchean.
The decays of U and Th to Pb were fundamental in the discovery of radioactivity and the subsequent exploitation of this process for dating geologic materials and determining the age of the Earth and solar system. A fundamental benefit of the U-Th-Pb decay schemes is that all three parent isotopes (238U, 235U, and 232Th) each decay to the stable daughter isotopes of Pb (206Pb, 207Pb, and 208Pb, respectively) via completely independent decay chains involving numerous intermediate isotopes. In the U-Th-Pb system, the presence of minerals with very high parent to daughter ratio presents the opportunity to perform somewhat ad hoc corrections for common Pb while introducing minimal age uncertainty. This chapter outlines the various approaches to the common Pb correction. Once the correction is done and uncertainties in this correction are accounted for, it is common to plot data on what are commonly called concordia diagrams.
New geological data allied to a review of the information made available by pioneering work on the shield led to the proposition of the Cauarane-Coeroeni belt, a sinuous NW-SE/NE-SW/NW-SE mega structure connecting amphibolite to granulite facies metamorphic supracrustal rocks of the Coeroeni Group (Surinam), Kanuku Complex (Guyana) and Cauarane Group (Roraima State, Brazil). The belt divides the shield into two contrasting domains and represents a major tectonic feature evolved in response to the amalgamation of Orosirian magmatic arcs and pre-existing Rhyacian juvenile continental blocks at around 1.995 Ga (?). The Cauarane-Coeroeni belt is bordered to north by post-collisional 1.98-1.96 Ga high-K calc-alkaline I-type and also A-type volcano-plutonic rocks, and to south by 1.95-1.93 Ga A-type foliated granites and charnockites and high-K, calc-alkaline, I-type granitoids and augen-gneisses. Introduction -The Guyana Shield, northern Amazonian Craton, is one of the least studied Precambrian areas in the world and its tectonic evolution remains a matter of discussion. New geological mapping and geochemical and geochronological data allied to a review of the information made available by pioneering work on the shield, led to the proposition of the Cauarane-Coeroeni belt, a sinuous NW-SE/NE-SW/NW-SE mega structure characterized by high grade supracrustal rocks (Fraga et al., 2008) (Fig.1). The belt divides the shield into two contrasting domains. Preserved juvenile Rhyacian (2.22-2.08 Ga) granite-greenstone terrains and Archean blocks and Rhyacian terrains partially recycled at around 2.07-2.03 Ga, occur in the northern domain. In the southern domain, basement either consists of rock units younger than 1.88 Ga, or has been significantly obliterated by extensive felsic magmatism in the 1.89-1.81 Ga interval during the Uatumã Event (Fraga et al., 2009 and references therein). Part of the Cauarane-Coeroeni belt has already been proposed by Kroonenberg (1976) as Central Guyana Granulitic Belt (CGGB) and confirmed by Berrangé (1977). However, as pointed out by Delor et al. (2003), Gibbs & Barron (1993) did not considered the link between the Kanuku and Coeroeni units as proposed by Kroonenberg (1976), and reinterpreted the CGGB as a straight NE-SW structure extending from Suriname to Roraima State in Brazil. The CGGB (Fig.1, inset) has been prolonged to southwest in the northern part of Amazonas State, Brazil (Lima et al., 1982) and interpreted as a major Paleoproterozoic tectonic feature of the shield (Gibbs & Barron, 1993; Fraga et al., 1998; Reis et al., 2003). However, Fraga (2002) pointed out that the basement rocks and the high temperature foliations that define the belt along its north-eastern, central, and south-western part, were developed during different periods of the Paleoproterozoic evolution of the shield, indicating that the CGGB is not a coherent structure. Fraga (2002) presented a geological sketch map of the Guyana Shield illustrating a sinuous belt of high grade supracrustal rocks (named Cauarane-Coeroeni belt by Fraga et al., 2008) corresponding to the main tectonic feature of the central part of the shield. Delor et al. (2003) has also mentioned a sinuous structure, named Roraima-Kanuku-Coeroene belt, including not only high grade supracrustal rocks, but also charnockites. However, the use of the term Roraima to denominate the belt as proposed by Delor et al. (2003) is not recommended as it refers to the Roraima Supergroup, including Paleoproterozoic sedimentary rocks.
One hadean zircon from the Cambrian sandstone in the southern part of South China has a U-Pb age of 4107±29 Ma with ɛ
Hf(t) value similar to that of the homochronous depleted mantle and Hf model age of 4102±21 Ma. This demonstrates the existence of hadean crustal remnant in South China. A close match between the U-Pb age and Hf model age with the highly position ɛ
Hf(t) value indicates the growth and immediate reworking of juvenile crust from the depleted mantle at ca 4.1 Ga. The prominent “Pan-African” and Grenville zircons derived from the exotic sources were also found in the sample, which indicates a linking between South China and Gondwana in the Cambrian period. The southern part of South China has complex histories of crustal growth and tectonic evolution.
Quad Creek Paleoarchean (≤ 3250 Ma) quartzites in southern Montana host Hadean (pre-3850 Ma) detrital zircons. Although an accessible resource for investigating early Earth processes distinct from other better known ancient zircon localities, the outcrop-scale geological and geochemical context of these rocks has not previously been well documented. New (1:250) mapping reveals a varied suite of isoclinally folded, sheared and variably deformed chromite-bearing banded and massive quartzites, garnetiferous siliceous (migmatitic) paragneisses, amphibolite, quartz–biotite schists and quartz + magnetite rocks (banded iron-formation; BIF). Conventional ion microprobe U–Pb zircon ages of populations from different quartzites and a paragneiss show outgrowth rim ages on older inherited detrital igneous zircon cores that match documented regional metamorphic events evidenced elsewhere in the Wyoming Craton. Weighted mean 207Pb/206Pb ages for the youngest concordant zircon cores of igneous derivation indicate the Quad Creek sediments were deposited by about 3250 Ma. Coupled with a large zircon 207Pb/206Pb age survey (n = 1274), and an extended U–Th–Pb depth-profile of the oldest grain in our sample set, these data support the notion that the oldest crust tapped by these sediments was comparable in age to the ca. 4000 Ma Acasta Gneiss Complex. This similarity is suggestive of both of a linkage between the Wyoming Craton and the Western Slave Province, and the lingering influence of Hadean crust well into the Archean.
A comprehensive interpretation of the crustal evolution of the South American Platform is made, based on sev- eral hundred Sm-Nd determinations from granitoid rocks of Brazil and part of the neighbouring countries. The histogram of the TDM model ages indicates small amounts of continental crust older than 3.3 Ga surviv- ing within Archean terrains formed between 3.1 and 2.7 Ga. The main period of crust formation was between 2.2 and 2.0 Ga, corresponding to the Transamazonian oro- genic cycle, and accretion of juvenile material contin- ued until Neoproterozoic times, but at much slower rates. The Transbrasiliano megasuture separates a large northwestern continental mass, including the Amazon- ian and São Luis cratons, from a southeastern mass, formed by a collage of cratonic fragments, of which the São Francisco and Rio de La Plata are the largest, which took part in the agglutination of the West Gond- wana supercontinent in the Neoproterozoic. On both continental masses, crustal evolution was similar between 3.0 and 1.7 Ga, suggesting that they were pos- sibly contiguous, within a Paleoproterozoic superconti- nent.
Evidence for the existence of continental crust older than 4.06 Ga has so far been obtained only from zircons in the Yilgarn Craton of Western Australia. In this paper we report the first occurrence of a very old zircon with a U-Pb age of 4.2 Ga in the Acasta Gneiss Complex of northwestern Canada, based on a laser ablation-inductively coupled plasma-mass spectrometry and sensitive high-resolution ion microprobe study. The U-Pb data reveal that the 4.2 Ga zircon occurs as a xenocryst in a 3.9 Ga granitic rock. Trace element compositions of the xenocryst suggest that it crystallized from a granitic magma. Our results, suggesting the existence of granitic rocks outside the Yilgarn Craton at 4.2 Ga, imply that granitic continental crust was more widespread than previously thought, and that it was reworked into Early Archean continental crust.
Detrital zircon crystals from the Jack Hills metasedimentary belt, Western Australia, are the only surviving vestiges of Hadean crust and represent an extraordinary archive into the nature of the early Earth. We report the results of an in situ isotopic study of 68 Jack Hills zircons in which the Hf and Pb isotope ratios were measured concurrently, allowing a better integration of isotope tracer information (176Hf/177Hf) with crystallization age (207Pb/206Pb). These data are augmented by Hf isotope data from zircons of the surrounding Narryer gneisses (3.65–3.30 Ga) and from Neoarchaean granites that intrude the Jack Hills belt. The detrital zircons define a subchondritic εHf–time array that attests to a far simpler evolution for the Hadean Earth than claimed by recent studies. This evolution is consistent with the protracted intra-crustal reworking of an enriched, dominantly mafic protolith that was extracted from primordial mantle at 4.4–4.5 Ga, perhaps during the solidification of a terrestrial magma ocean. There is no evidence for the existence of strongly depleted Hadean mantle, or for juvenile input into the parental magmas to the Jack Hills zircons. This simple Hf isotope evolution is difficult to reconcile with modern plate tectonic processes. Strongly unradiogenic Hf isotope compositions of zircons from several Archaean gneiss terranes, including the Narryer and Acasta gneisses, suggest that Hadean source reservoirs were tapped by granitic magmas throughout the Archaean. This supports the notion of a long-lived and globally extensive Hadean protocrust that may have comprised the nuclei of some Archaean cratons.
Magmatic outgassing of volatiles from Earth's interior probably played a critical part in determining the composition of the earliest atmosphere, more than 4,000 million years (Myr) ago. Given an elemental inventory of hydrogen, carbon, nitrogen, oxygen and sulphur, the identity of molecular species in gaseous volcanic emanations depends critically on the pressure (fugacity) of oxygen. Reduced melts having oxygen fugacities close to that defined by the iron-wüstite buffer would yield volatile species such as CH(4), H(2), H(2)S, NH(3) and CO, whereas melts close to the fayalite-magnetite-quartz buffer would be similar to present-day conditions and would be dominated by H(2)O, CO(2), SO(2) and N(2) (refs 1-4). Direct constraints on the oxidation state of terrestrial magmas before 3,850 Myr before present (that is, the Hadean eon) are tenuous because the rock record is sparse or absent. Samples from this earliest period of Earth's history are limited to igneous detrital zircons that pre-date the known rock record, with ages approaching ∼4,400 Myr (refs 5-8). Here we report a redox-sensitive calibration to determine the oxidation state of Hadean magmatic melts that is based on the incorporation of cerium into zircon crystals. We find that the melts have average oxygen fugacities that are consistent with an oxidation state defined by the fayalite-magnetite-quartz buffer, similar to present-day conditions. Moreover, selected Hadean zircons (having chemical characteristics consistent with crystallization specifically from mantle-derived melts) suggest oxygen fugacities similar to those of Archaean and present-day mantle-derived lavas as early as ∼4,350 Myr before present. These results suggest that outgassing of Earth's interior later than ∼200 Myr into the history of Solar System formation would not have resulted in a reducing atmosphere.
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