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Major thrust faults and fold belts in the Great Basin of Nevada and Utah (Oldow et al. 1989; McQuarrie and Chase 2000; see also DeCelles 2004) and hypothetical contours (in km) of early Tertiary crustal thickness (Coney and Harms 1984).
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Uncertainty surrounds the fate of the orogenic plateau in what is now the Great Basin in western Utah and Nevada, which resulted from the Mesozoic and earliest Cenozoic contractile deformations and crustal thickening. Although there is some consensus regarding the gravitational collapse of the plateau by extensional faulting and consequent crustal...
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... a widely cited paper, Coney and Harms (1984) reconstructed the crustal thickness in the Great Basin area after late Palaeozoic and Mesozoic contractile orogenic deformations, showing the crust to be as much as 50 -60 km along a thickened welt, mostly in eastern Nevada (Figure 1). Although admitting 'circularity' (p. ...
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... analogies between the western US Cordillera and the Tibetan Plateau are flawed in that the latter lies inboard of a continent - continent collision, whereas the US Cordillera resulted from subduction of oceanic lithosphere studded with island arcs and oceanic plateaus. McQuarrie and Chase (2000) referred to the elevated thick crust in the hinterland of the Sevier fold-thrust belt in western Utah and eastern Nevada (Figure 1) as the 'Sevier Plateau'. In a review of the Cordilleran thrust belt, (DeCelles 2004, p. 147; see also DeCelles and Coogan 2006) referred to this hinterland as the 'Nevadaplano' whose crustal thickness was 50-60 km and palaeo-elevation was more than 3 km. ...
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... tectonic setting and ignimbrite flareup of the central Andean plateau during the late Cenozoic bear significant similarities to the middle Cenozoic Great Basin area (Best and Christiansen 1991, pp. 13,522-13,525, Figure 14; Maughan et al. 2002, pp. 150 -154, Figure 18a). ...
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... Figure 14; Maughan et al. 2002, pp. 150 -154, Figure 18a). Especially noteworthy is the occurrence in both of several thousands of cubic kilometres of crystal-rich, calc-alkaline high-K dacite ignimbrite -the monotonous intermediates of Hildreth (1981) and Maughan et al. (2002) -together with lesser, but still prodigious, volumes of rhyolite ash-flow tuff. ...
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... these are two of the most commonly analysed trace elements in the global data set, thus facilitating comparisons. Because Ba and Rb concentrations in calc-alkaline arc volcanic rocks are a function of silica content, we present plots against this oxide (Figures 9-12). ...
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... plotted in Figure 9 are the Ba contents of rocks in the central American arc (Carr et al. 2003), which are shown separately, for the sake of clarity, in Figure 10. Comparing the two figures it is immediately obvious that virtually all of the central America rocks lie above the main trend defined by other western hemisphere rocks. ...
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... the plot of Rb (Figure 11), 'Other western hemisphere' arc rocks again define a main differentiation trend and rocks sited on 50 -69 km crust lie above it. However, Andean rocks on the thickest crust (70 km) are not the highest in Rb and many analyses for rocks sited on crust 40 -49 km thick also lie well above this trend. ...
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... a hilly depositional surface, non- horizontal compaction foliations would have increased the between-site variations and adversely affected the success of palaeomagnetic correlations. Evidence for this fortunate circumstance consists of the positive results of the palaeomagnetic tilt tests -commonly known as fold tests -for nearly all of the regionally extensive ignimbrites surrounding the central Nevada caldera complex (Figure 2; see also Figure 14) with sufficient sites, as well as for the Nine Hill Tuff, for the most part east of the Carson Sink. ...
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... this smoothed ignimbrite terrain was interrupted by numerous effusions of lava that today are generally less than 1 km thick and range in composition from rhyolite to andesite (Best et al. 1989a, Fig. 3). Few major composite volcanoes on the scale of the modern Cascades formed in the smoothed terrain during the ignimbrite flareup. ...
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... location of the source from which two large outflow cooling-unit members of the 35 Ma Stone Cabin Formation were derived has not been ascertained so we cannot tell how these sheets are distributed around their source. Of the remaining 12 sheets for which the locations of seven sources are known, nine are distributed asymmetrically, more to the east than the west of their sources; that is, their eruptive sources are eccentrically offset toward the west within their corresponding outflow sheets ( Figure 13). Three sheets are distributed essentially symmetrically east and west of their sources, namely, one of four members of the 26 Ma Shingle Pass Formation and two of three members of the 27 Ma Monotony Tuff. ...
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... and Hardyman 1987;John 1992) Nevada ash flows could not always surmount a NS-trending topographic barrier positioned just east of Tonopah and Austin (Figure 2). In a symmetric manner, little or none of the outflow from sources west of the barrier (Figure 14) is known for certain east of it. The 22 Ma outflow tuff of Toiyabe (John 1992), whose caldera source is located about 20 km south of the south end of the Reese River Valley, extends at least 200 km to the west near the Nevada-California state line. ...
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... location of the barrier is constrained to lie essentially in Monitor Valley between the Monitor and the Toquima Ranges but to the south swings west roughly through Tonopah (Figures 2, 13, and 14). Lunar Cuesta and Big Ten Peak ash flows erupted about 25.6 Ma were dispersed eastward from their sources at the south end of the Monitor Range and 35 Ma Pancake Summit ash flows eastward from their source at the north end of the range. ...
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... 25 Ma tuff of Arc Dome that erupted from a source west of the barrier is tentatively correlated with tuff to the east of it. Comparison of the distribution of tuffs that are less than 27 Ma with that of older tuffs ( Figure 13) suggests that with time the ash flows from eastern sources advanced farther west (one cooling unit of the Monotony Tuff excepted), partially surmounting the topographic barrier. Although no exposed source for the 24 Ma Clipper Gap ash-flow tuff has been found, thickest sections of the tuff in the Toquima and Monitor Ranges suggest the source may lie concealed beneath northern Monitor Valley. ...
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... the Great Basin Altiplano its western margin was exposed to storms coming inland from the Pacific.) Because of the focused denudation along the margin and consequent isostatic uplift, a topographic high develops at the lip or break in slope between the plateau interior and the sloping margin (Figure 15(a)). Numerical modelling of precipitation, erosion, and isostatic uplift by Masek et al. (1994) simulated development of the topographic profile observed in the Tibetan and Andean plateau margins (Figure 15(b)). ...
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... of the focused denudation along the margin and consequent isostatic uplift, a topographic high develops at the lip or break in slope between the plateau interior and the sloping margin (Figure 15(a)). Numerical modelling of precipitation, erosion, and isostatic uplift by Masek et al. (1994) simulated development of the topographic profile observed in the Tibetan and Andean plateau margins (Figure 15(b)). If such a ridge had evolved on the western margin of the Great Basin Altiplano, its position would have been near that of our postulated topographic barrier to ash flow dispersal. ...
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... topographic barrier lies near and parallels the western edge of the Precambrian basement as well as the Toiyabe uplift zone (Figure 14) that is postulated by Speed et al. (1988) to consist of a chain of domical uplifts, at least some of which are thermal and diapiric. North of Austin, the zone is manifest by three domical uplifts that expose deep- seated rocks of moderate metamorphic grade; the dome at Austin is cored by a Jurassic (1994). ...
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... pluton. However, Speed et al. (1988) do not specify how the zone is expressed south of Austin and only note that the uplift zone as a whole lies along the Precambrian basement edge that was overrun by Palaeozoic -Mesozoic thrust sheets (Figure 1). ...
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... 34 Ma tuff of Cove Mine is draped over a roughly NS-trending topographic high in the northern Fish Creek Mts. and the southern and eastern parts of Battle Mountain (Figure 2; Doebrich 1995, Figure 19; S. Gromme, H.C. Palmer, and W.D. MacDonald unpublished data 1968John et al. 2008). To the east, the tuff of Cove Mine, which may have erupted from the Caetano caldera to the south, evidently filled a broad NS palaeovalley. ...
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... one example of such palaeovalleys, they (p. 217) cite the occurrence of the Guild Mine Member of the Mickey Pass Tuff, which was first described in the Yerington district by Proffett and Proffett (1976), in the ancestral Yuba River drainage in the Sierra Nevada and indicate its correlation with the intracaldera lower tuff of Mt Jefferson in the Toquima Range (Figures 2 and 14). The out-flow length in this palaeovalley is about 210 km, after compensating for subsequent crustal extension (C.D. Henry Written Communication, December 2008). ...
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... is well known that the ancient Pacific shoreline in Late Cretaceous through Miocene time coincided approximately with the present eastern margin of the Sacramento and San Joaquin valleys (i.e. the western margin of exposed Sierra Nevada bedrock). In Figure 16, we show two schematics depicting the implications of two different models for the history of the Sierra Nevada structural block (mostly a Cretaceous batholith). In the traditional model (Figure 16(a)), the main uplift occurred in two stages. ...
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... Figure 16, we show two schematics depicting the implications of two different models for the history of the Sierra Nevada structural block (mostly a Cretaceous batholith). In the traditional model (Figure 16(a)), the main uplift occurred in two stages. The first stage occurred between about 85 Ma to about 50 Ma, represented by exhumation of the batholithic rocks and terminating at the time of deposition of the Eocene Auriferous Gravels. ...
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... model dates back at least to the time of Waldemar Lindgren (1911) and is based almost entirely on geomorphologic evidence, reinforced lately by potassium-argon ages of overlying late Cenozoic volcanic rocks ( Wakabayashi and Sawyer 2001, and comprehensive references therein). Part A of Figure 16 is an attempt to show how this particular uplift history might connect with the western part of the Great Basin Altiplano; the figure involves a gross (more than sixfold) linear extrapolation of the slopes of Eocene Auriferous Gravel calculated and projected by ...
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... et al. (2006) concluded that Eocene elevations in the northern Sierra Nevada were 1.7 -1.8 km, with highest bedrock peaks up to 2.2 km. In constructing Part B of Figure 16, we have taken the 1.7-1.8 km elevation inferred by Mulch et al. (2006) and have applied it to Donner Summit, again using a linear extrapolation from ancient sea level. ...
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... adjustments imply overall slopes less than that of the present Sierra Nevada result and result in a rather even gradient from sea level to nearly 4 km elevation in middle Cenozoic time. Although the construction of Figure 16(b) involves a circular argument it is our intent to show the much greater plausibility of the newer model for timing of uplift of the Sierra Nevada in the context of a middle Cenozoic Great Basin Altiplano. Moreover, the form of Figure 16(b) is not entirely different from the Andean Pilcomayo profile displayed in Figure 15(a), with due allowance for the difference between a hypothetical profile and one based on real topography. ...
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... the construction of Figure 16(b) involves a circular argument it is our intent to show the much greater plausibility of the newer model for timing of uplift of the Sierra Nevada in the context of a middle Cenozoic Great Basin Altiplano. Moreover, the form of Figure 16(b) is not entirely different from the Andean Pilcomayo profile displayed in Figure 15(a), with due allowance for the difference between a hypothetical profile and one based on real topography. Figure 17 portrays our concept of the Great Basin Altiplano or orogenic plateau in a west-east cross-section near 38.58 N Latitude. ...
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... the construction of Figure 16(b) involves a circular argument it is our intent to show the much greater plausibility of the newer model for timing of uplift of the Sierra Nevada in the context of a middle Cenozoic Great Basin Altiplano. Moreover, the form of Figure 16(b) is not entirely different from the Andean Pilcomayo profile displayed in Figure 15(a), with due allowance for the difference between a hypothetical profile and one based on real topography. Figure 17 portrays our concept of the Great Basin Altiplano or orogenic plateau in a west-east cross-section near 38.58 N Latitude. ...
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... the form of Figure 16(b) is not entirely different from the Andean Pilcomayo profile displayed in Figure 15(a), with due allowance for the difference between a hypothetical profile and one based on real topography. Figure 17 portrays our concept of the Great Basin Altiplano or orogenic plateau in a west-east cross-section near 38.58 N Latitude. The topographic barrier to dispersal of ash flows lies at the crest of and between the western slope of the Altiplano and its smoothed interior. ...
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The evolution of the South China continental crust and its linkage to the assembly and rifting of eastern Gondwana are key issues in the understanding of the early Paleozoic evolution of eastern Asia. We report U-Pb zircon ages and geochemical and Lu-Hf isotopic data for the South Fufang and Yingshang granitoids and the Mayuan diabases from the Wuy...
Citations
... 525 We attribute the anomalously high mud fraction in sampled cross-bedded strata from BCCM 526 channels (~60%; Fig. 6B) to a combination of high fine-grained sediment loads and post-depositional 527 chemical alteration of sand-sized pyroclastic material in bed material load. As this floodplain-dominated 528 stratigraphic interval coincides with significant pyroclastic volcanism in the Great Basin (Larson and Evanoff, 1998); (Sato and Denson, 1967;Lipman and McIntosh, 2008;Best et al., 2009Best et al., , 2013, it is 530 possible that easily weathered fragments of pyroclastic material contributed a significant fraction of fine 531 sand-sized particles originally present in bed material. We emphasize this hypothesis is challenging to test 532 with chemically weathered, pyroclastically-sourced, floodplain sediment, as the original grain-size of 533 particles in transport cannot be determined by the measurement methods used in this study. ...
Rivers drive geomorphic change at Earth’s surface by transporting sediment from mountains to sedimentary basins. They are sensitive to changes in water and sediment flux driven by tectonism, climatic perturbation and or volcanism. We characterized changes in fluvial landscapes during a major Cenozoic cooling event, the Eocene-Oligocene Transition (EOT) at 33.9 Ma. The EOT is characterized by a long term ~4-5°C decrease in global mean annual temperature, punctuated by short, intense climatic fluctuations. In the Great Plains region of central North America, the temperature decreased by ~7°C and mean annual precipitation declined by ~50% across the EOT. Preceding the EOT, renewed Cordilleran uplift near northeastern Nevada began at ~39 Ma and extensive volcanism in the Great Basin region occurred at ~36 Ma. We reconstruct characteristics of rivers and floodplains through the Late Eocene-Early Oligocene deposits of White River Group (WRG), exposed at Toadstool Geologic Park in northwestern Nebraska, U.S.A., and evaluate how river landscapes responded to these events. We identified five stages of change in the paleo-rivers and -floodplain strata of the White River Group: (1) Following the Laramide uplift, the rivers of the Late Eocene Chamberlain Pass Formation adjusted from steep gradients (~10-3) to gentler ones (~10-4), and transitioned from shallow, mobile channels to deeper, stable channels and floodplains. (1) The transition from the Chamberlain Pass Formation to the Late Eocene Chadron Formation saw a shift from a relatively coarse-grained fluvial system with mobile channels to an extremely fine-grained, aggradational, floodplain-dominated system influenced by high volcanogenic sediment loads. (3) The transition from the Late Eocene Chadron Formation to the Early Oligocene Orella Member of the Brule Formation is associated with the onset of the Eocene-Oligocene Transition (EOT) and is marked by coarse floodplains and ephemeral river deposits that display evidence of significant, likely seasonality-driven, discharge variability. (4) Early Oligocene strata (33.9 - 31.6 Ma) also show compelling evidence of recurrent episodes of sustained channel incision and fill that we connect to climate fluctuations associated with the early phase of relatively rapid EOT cooling. (5) Early Oligocene strata deposited from 33.4 to 31.6 Ma show no significant erosional surfaces and continue to reflect discharge variability, high volcanogenic sediment loads, and a relatively stable climate system after the end of the initial phase of rapid cooling.
... In the BFVA the thick ignimbrites were most likely confined to broad, deep valleys or basins, hence, regional correlation (e.g., based on topographic elevation levels) will always have some uncertainty (cf. Lebti et al., 2006;Best et al., 2009). ...
... The Late Eocene (~35 Ma; McKee et al., 1971) felsic ash-flow tuffs of the Indian Well Formation and the Oligocene (~32 Ma; Smith and Ketner, 1976) shallow intrusive rocks in the map area are related to the Late Eocene-Oligocene 'Great Basin ignimbrite flare-up', a north to south sweep of felsic magmatism that affected most of Nevada (e.g., Best et al., 2009;Henry and John, 2013). This migration of volcanism is hypothesized to have been generated by the steepening of the subduction angle of the Farallon slab (e.g., Humphreys, 1995;Smith et al., 2014). ...
1:20k scale geologic map of the eastern flank of the northern Cortez Mountains, Nevada.
... 40 Ar/ 39 Ar geochronology from plagioclase yielded an emplacement age of 36.16 ± 0.07 Ma for this unit (Long et al., 2014). The Pancake Summit Tuff (Tps) is a porphyritic rhyolite ash-flow tuff with disseminated smoky quartz and lesser abundant sanidine phenocrysts, and is interpreted to be sourced from the Allison Creek caldera in the northeastern Monitor Hills, ~40 km west of the map (Best et al., 2009). 40 Ar/ 39 Ar geochronology from sanidine yielded and age range of 35.36 ± 0.07 to 35.40 ± 0.06 Ma for this unit (Long et al., 2014). ...
1:24k scale geologic map of the southern Diamond Mountains, Nevada.
... Between the late Eocene and middle Miocene, felsic volcanism of the Great Basin ignimbrite flareup swept southwestward across Nevada (e. g., Best et al., 2009;Henry and John, 2013) and has been attributed to Lee et al., 2017). The map traces of the Northern Snake Range dècollement (NSRD) and the basal fault of the Schell Creek Range detachment system (SCRDS) are shown in purple and red, respectively. ...
... Nevertheless, we acknowledge that estimates of the thickness of continental arc crust using geochemical indices are problematic due to the multiple petrogenetic processes that occur in this setting (Ducea et al., 2015), and these should perhaps only be used as qualitative indicators (e.g. Kay & Mpodozis, 2001;Best et al., 2009;Oliveros et al., 2018). The trace element compositions of Cretaceous igneous rocks to the north of Beagle Peninsula Andesites) yield similar compositions with respect to those present on Navarino Island (Figs. 8,9,11), and thus likely also formed under the influence of an active margin setting. ...
Navarino Island is located in the southernmost part of the Fuegian Andes, south of the Beagle Channel. It geological record documents the complex tectonic history of Tierra del Fuego that includes the opening and closure of the Rocas Verdes basin, Cordillera arc collision and subsequent subduction processes. The geology of the island is mostly comprised of the Cretaceous Yahgán Formation, a marine meta-sedimentary sequence, which is intruded by diverse plutons that are mostly exposed on the northwestern tip of the island. We herein present a new dataset that shows the presence of three Cretaceous-earliest Paleocene magmatic suites of active margin magmatism emplaced during the early stage of the Fuegian Andes, which are referred to as (i) the Dientes de Navarino Microdioritic Sills, a suite of pre-tectonic microdioritic sills that formed during ∼101-97 Ma; (ii) the Castores Plutonic Complex, a series of pre- to syn-tectonic gabbroic to tonalitic plutons emplaced during ∼90-87 Ma and (iii) the Samantha Monzonites, a suite of isolated monzonitic to monzodioritic post-tectonic plutons that formed at ∼66-65 Ma. These distinct magmatic episodes are recognised by field observations, geological mapping, petrography and whole-rock geochemistry integrated with amphibole and biotite ⁴⁰ Ar/ ³⁹ Ar and U-Pb zircon LA-ICP-MS geochronology. The geochemical compositions of these rocks are consistent with a continental arc setting that formed during the interval ∼101-65 Ma. While the three pulses spatially overlap in Navarino Island, the arc magmatism shows a migration (or expansion) throughout the Late Cretaceous. The locus of the arc then migrates at ∼68-66 Ma towards the southwest. We suggest that this trench-ward migration at ∼68-66 Ma may be associated with a change in the subduction angle. The three Cretaceous- earliest Paleocene plutonic pulses recorded in Navarino Island formed during the early stages of development of the Fuegian Andes, and are pre-, syn-and post-tectonic with respect to a major compressional event caused by the collision and obduction of the back-arc Rocas Verdes oceanic floor.
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6675416
... Magmatism and faulting allow for the transfer of deeply-sourced CO 2 to more shallow aquifers (Earman et al., 2005). Rollback of the shallowly subducting Farallon plate during the late Cretaceous and early Eocene would have exposed large portions of the overlying hydrated North American lithosphere to hot asthenosphere, triggering widespread regional magmatism (Best et al., 2009;Humphreys, 2009;Smith et al., 2014). The GGRB is located near several volcanic and plutonic provinces that were active during the early Eocene Epoch, including the Absaroka Volcanic Province, the Challis Volcanic Province, and the Colorado Mineral Belt, each of which could have supplied alkalinity to the GGRB if a riverine connection had existed ( Fig. 1) (Lowenstein et al., 2017). ...
Chemical sediments of the lacustrine Wilkins Peak Member of the Eocene Green River Formation potentially preserve detailed paleoclimate information relating to the conditions of their formation and preservation within the lake basin during the Early Eocene Climatic Optimum. The Green River Formation comprises the world’s largest sodium-carbonate evaporite deposit in the form of trona (Na2CO3⋅NaHCO3⋅2H2O) in the Bridger Basin and nahcolite (NaHCO3) in the neighboring Piceance Creek Basin. Modern analogues suggest that these minerals necessitate the existence of an alkaline source water. Detrital provenance geochronometers suggest that the most likely source for volcanic waters to the Greater Green River Basin is the Colorado Mineral Belt, connected to the basin via the Aspen paleoriver.
Here, we test the hypothesis that magmatic waters from the Colorado Mineral Belt could have supplied the Greater Green River Basin with the alkalinity needed to precipitate sodium-carbonate evaporites that are pre- served in the Wilkins Peak Member by numerically simulating the evaporation of modern soda spring waters from northwestern Colorado at various temperature and atmospheric pCO2 conditions. The resulting simulated evaporite sequence is then compared to the mineralogy and textures preserved within the Wilkins Peak Member. Simulated evaporation of Steamboat Springs and Mineral Spring waters produce a close match to core obser- vations and mineralogy. These simulations provide constraints on the salinities at which various minerals precipitated in the Wilkins Peak Member as well as insights into the regional temperature (>15 ◦C for gaylussite and trona; >27◦ for pirssonite and trona) and pCO2 conditions (<1200 ppm for gaylussite and trona) during the Early Eocene Climatic Optimum.
... This decoupling requires efficient lateral and vertical strain partitioning across the crustal column. The presence of decoupled extension-departing from the vertically coherent pure-shear hypothesis (Best et al., 2009;Coney & Harms, 1984)-suggests that the crustal thinning calculations based solely on the upper-crustal strain may not be valid (Say & Zuza, 2021). ...
Long‐standing debates exist over the mechanism of continental lithospheric extension and, more specifically, over the strain distribution across the lithosphere in intraplate settings. The Cretaceous extensional system in South China extends up to ∼800 km inboard of the Paleo‐Pacific convergent margin and enables investigation of the mechanism(s) of intraplate lithospheric extension. Here we use high‐resolution seismic reflection data to image the crustal and upper‐mantle architecture of the central segment of the extensional system. We identify a compositionally stratified upper lithosphere that has undergone depth‐dependent extension, expressed by heterogeneous normal faulting in the upper crust, widely distributed ductile stretching in the lower crust, mantle influx into the crust, a broadly smooth Moho with localized uplift, and mantle shear‐zone generation. We detect, beneath the center of the Ganzhou Rift, the thinnest crust (28–30 km thick) in South China. It spatially correlates with the locus of strong lithospheric thinning and asthenospheric upwelling. We suggest that the generation of the thinnest crust was assisted by lower‐crustal ductile stretching, mantle shearing, and exhumation during depth‐dependent extension. Our study provides insights into the partitioning of depth‐dependent extensional strain into an intraplate stratified lithosphere and the feedback between crustal and mantle processes that shaped the thinnest crust at a position ∼300 km inboard of the convergent margin during continental extension.
... However, we acknowledge that estimates of the thickness of continental arc crust using geochemical indices are problematic owing to the multiple petrogenetic processes that occur in such settings , and these should perhaps only be used as qualitative indicators (e.g. Kay and Mpodozis 2001;Best et al. 2009;Oliveros et al. 2019). ...
Periods of cessation, resumption and enhanced arc activity are recorded in the Cretaceous igneous rocks of the Antarctic Peninsula. We present new geochronological (LA-ICP-MS zircon U-Pb) analyses of 36 intrusive and volcanic Cretaceous rocks, along with LA-ICP-MS apatite U-Pb analyses (a medium-temperature thermochronometer) of 28 Triassic–Cretaceous igneous rocks of the Antarctic Peninsula. These are complemented by new zircon Hf isotope data along with whole-rock geochemistry and isotope (Nd, Sr and Pb) data. Our results indicate that the Cretaceous igneous rocks of the Antarctic Peninsula have geochemical signatures consistent with a continental arc setting and were formed during the interval ∼140–79 Ma, while the main peak of magmatism occurred during ∼118–110 Ma. Trends in εHft (zircon) combined with elevated heat flow that remagnetised rocks and reset apatite U-Pb ages suggests that Cretaceous magmatism formed within a prevailing extensional setting that was punctuated by periods of compression. A noteworthy compressive period probably occurred during ∼147–128 Ma, triggered by the westward migration of South America during opening of the South Atlantic Ocean. Cretaceous arc rocks that crystallised during ∼140–100 Ma define a belt that extends from southeastern Palmer Land to the west coast of Graham Land. This geographic distribution could be explained by (i) a flat slab with east-dipping subduction of the Phoenix Plate, or (ii) west-dipping subduction of the lithosphere of the Weddell Sea, or (iii) an allochthonous origin for the rocks of Alexander Island. A better understanding of the geological history of the pre-Cretaceous rocks of Alexander Island and the inaccessible area of the southern Weddell Sea is required.
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6089274
... Nonetheless, the age of onset of post-orogenic extension in the western North American Cordillera is debated (e.g., Best and Christiansen, 1991;Best et al., 2009;Canada et al., 2019;Zuza et al., 2021;Lund Snee and Miller, 2022). Although there may have been local extension during the emplacement of granitoids ca. ...
... Instead, most regional reconstructions place the shallow oceanic lithosphere of the Farallon slab beneath this region at the time of pluton construction (e.g., Best et al., 2009;Yonkee and Weil, 2015;Smith et al., 2017). Thus, the Wasatch igneous belt and the Little Cottonwood stock are expected to be genetically related to subduction. ...
Many porphyry molybdenum deposits are hosted in multi-phase plutons, but it is unclear in some deposits how these magmas originated and whether the pluton intruded as it fractionated or was intruded by new batches of magma. New mapping has clarified field relationships between units in the White Pine porphyry Mo system hosted in the Little Cottonwood stock, Utah (western United States), including the White Pine intrusion, the Red Pine porphyry, rhyolite dikes, and phreatomagmatic pebble dikes. Geologic relations and geochemistry show the system formed in a continental arc setting during rollback of the subducting Farallon slab rather than during extension related to orogenic collapse. Whole-rock geochemistry shows distinct fractionation trends for each of the major intrusive units in the composite pluton, suggesting they formed separately, which is supported by new U-Pb zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) ages of ca. 30 Ma for the Little Cottonwood stock, 27 Ma for the White Pine intrusion, and 26 Ma for the previously undated Red Pine porphyry. Mineral textures, cross-cutting relationships, and alteration mineralogy indicate that intrusion of the youngest phase led to a fluid-saturated magmatic system and triggered venting, including emplacement of pebble dikes. In the adjacent east Traverse Mountains, pebble dikes contain clasts that have similar mineral assemblages, textures, and ages as the major igneous units in the White Pine deposit. This indicates that the pebble dikes in east Traverse Mountains and in the pluton are the upper and lower parts of the same magmatic-hydrothermal system, which was decapitated by a mega-landslide that was likely facilitated by alteration in the Oligocene hydrothermal system and by later Basin and Range faulting.
