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1
Gao, Peng, Chris Yakymchuk, Jian Zhang, Changqing Yin, Jiahui Qian, and Yanguang Li. "Preferential dissolution of uranium-rich zircon can bias the hafnium isotope compositions of granites." Geology 50, no. 3 (December 1, 2021): 336–40. http://dx.doi.org/10.1130/g49656.1.
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Abstract Hafnium (Hf) isotopes in zircon are important tracers of granite petrogenesis and continental crust evolution. However, zircon in granites generally shows large Hf isotope variations, and the reasons for this are debated. We applied U-Pb geochronology, trace-element, and Hf isotope analyses of zircon from the Miocene Himalayan granites to address this issue. Autocrystic zircon had εHf values (at 20 Ma) of–12.0 to–4.3 (median =–9). Inherited zircon yielded εHf values (at 20 Ma) of–34.8 to +0.3 (median =–13); the majority of εHf values were lower than those of autocrystic zircon. The εHf values of inherited zircon with high U concentrations resembled those of autocrystic zircon. Geochemical data indicates that the granites were generated during relatively low-temperature (<800 °C) partial melting of metasedimentary rocks, which, coupled with kinetic hindrance, may have led to the preferential dissolution of high-U zircon that could dissolve more efficiently into anatectic melt due to higher amounts of radiation damage. Consequently, Hf values of autocrystic zircon can be biased toward the values of U-rich zircon in the source. By contrast, literature data indicate that granites generated at high temperatures (>820–850 °C) generally contain autocrystic and inherited zircons with comparable Hf isotope values. During higher-temperature melting, indiscriminate dissolution of source zircon until saturation is reached will result in near-complete inheritance of Hf isotope ratios from the source. Our results impose an extra layer of complexity to interpretation of the zircon Hf isotope archive that is not currently considered.
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Vezinet, Adrien, Emilie Thomassot, Yan Luo, Chiranjeeb Sarkar, and D. Graham Pearson. "Diachronous Redistribution of Hf and Nd Isotopes at the Crystal Scale—Consequences for the Isotopic Evolution of a Poly-Metamorphic Crustal Terrane." Geosciences 12, no. 1 (January 12, 2022): 36. http://dx.doi.org/10.3390/geosciences12010036.
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In metamorphic rocks, mineral species react over a range of pressure–temperature conditions that do not necessarily overlap. Mineral equilibration can occur at varied points along the metamorphic pressure–temperature (PT) path, and thus at different times. The sole or dominant use of zircon isotopic compositions to constrain the evolution of metamorphic rocks might then inadvertently skew geological interpretations towards one aspect or one moment of a rock’s history. Here, we present in-situ U–Pb/Sm–Nd isotope analyses of the apatite crystals extracted from two meta-igneous rocks exposed in the Saglek Block (North Atlantic craton, Canada), an Archean metamorphic terrane, with the aim of examining the various signatures and events that they record. The data are combined with published U–Pb/Hf/O isotope compositions of zircon extracted from the same hand-specimens. We found an offset of nearly ca. 1.5 Gyr between U-Pb ages derived from the oldest zircon cores and apatite U–Pb/Sm–Nd isotopic ages, and an offset of ca. 200 Ma between the youngest zircon metamorphic overgrowths and apatite. These differences in metamorphic ages recorded by zircon and apatite mean that the redistribution of Hf isotopes (largely hosted in zircon) and Nd isotopes (largely hosted in apatite within these rocks), were not synchronous at the hand-specimen scale (≤~0.001 m3). We propose that the diachronous redistribution of Hf and Nd isotopes and their parent isotopes was caused by the different PT conditions of growth equilibration between zircon and apatite during metamorphism. These findings document the latest metamorphic evolution of the Saglek Block, highlighting the role played by intra-crustal reworking during the late-Archean regional metamorphic event.
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Huang, Chao, Hao Wang, Jin-Hui Yang, Lie-Wen Xie, Yue-Heng Yang, and Shi-Tou Wu. "Further Characterization of the BB Zircon via SIMS and MC-ICP-MS for Li, O, and Hf Isotopic Compositions." Minerals 9, no. 12 (December 11, 2019): 774. http://dx.doi.org/10.3390/min9120774.
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In this contribution, we report the results for the characterization of the BB zircon, a newly developed zircon reference material from Sri Lanka, via secondary ion mass spectrometry (SIMS) and multiple-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). The focus of this work was to further investigate the applicability of the BB zircon as a reference material for micro-beam analysis, including Li, O, and Hf isotopes. The SIMS analyses reveal that BB zircon is characterized by significant localized variations in Li concentration and isotopic ratio, which makes it unsuitable as a lithium isotope reference material. The SIMS-determined δ18O values are 13.81‰ ± 0.39‰ (2SD, BB16) and 13.61‰ ± 0.40‰ (2SD, BB40), which, combined with previous studies, indicates that there is no evidence of conspicuous O isotope heterogeneity within individual BB zircon megacrysts. The mean 176Hf/177Hf ratio of BB16 determined by solution MC-ICP-MS is 0.281669 ± 0.000012 (2SD, n = 29) indistinguishable from results achieved by laser ablation (LA)-MC-ICP-MS. Based on the SIMS and MC-ICP-MS data, BB zircon is proposed as a reference material for the O isotope and Hf isotope determination.
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Viehmann, Sebastian. "Hf-Nd Isotopes in Archean Marine Chemical Sediments: Implications for the Geodynamical History of Early Earth and Its Impact on Earliest Marine Habitats." Geosciences 8, no. 7 (July 16, 2018): 263. http://dx.doi.org/10.3390/geosciences8070263.
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The Hf-Nd isotope systems are coupled in magmatic systems, but incongruent Hf weathering (‘zircon effect’) of the continental crust leads to a decoupling of the Hf-Nd isotope systems in low-temperature environments during weathering and erosion processes. The Hf-Nd isotope record was recently dated back from the Cenozoic oceans until the Archean, showing that both isotope systems were already decoupled in seawater 2.7 Ga ago and potentially 3.4 Ga and 3.7 Ga ago. While there might have existed a hydrothermal pathway for Hf into Archean seawater, incongruent Hf weathering of more evolved, zircon-bearing uppermost continental crust that was emerged and available for subaerial weathering accounts for a significant decoupling of Hf-Nd isotopes in the dissolved (<0.2 µm) and suspended (>0.2 µm) fractions of Early Earth’s seawater. These findings contradict the consensus that uppermost Archean continental crust was (ultra)mafic in composition and predominantly submerged. Hence, Hf-Nd isotopes in Archean marine chemical sediments provide the unique potential for future research to trace the emergence of evolved continental crust, which in turn has major implications for the geodynamical evolution of Early Earth and the nutrient flux into the earliest marine habitats on Earth.
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Du, Bin, Zian Yang, Lifei Yang, Qi Chen, Jiaxuan Zhu, Kangxing Shi, Gao Li, Lei Wang, and Jia Lu. "Zircon Hf-Isotopic Mapping Applied to the Metal Exploration of the Sanjiang Tethyan Orogenic Belt, Southwestern China." Applied Sciences 12, no. 8 (April 18, 2022): 4081. http://dx.doi.org/10.3390/app12084081.
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Zircon Hf-isotopic mapping can be regarded as a useful tool for evaluating the coupling relationship between lithospheric structure and metallic mineralization. Hence, this method shows important significance for mineral prediction. To explore this potential, the published granite zircon Hf isotope data from the Sanjiang Tethyan Orogen were systematically compiled. This study uses the Kriging weighted interpolation in the Mapgis software system to contour Hf isotopes, revealing a relation between the crustal structure and metallogenesis. The mapping results suggest that the Changning–Menglian suture zone is the boundary between ancient and juvenile crust, viz., the western terranes have ancient crust attributes, whereas the eastern terranes exhibit the properties of new juvenile crust. In addition, this study also found that the mineralization and element types in the Sanjiang Tethyan Orogen have a coupling relationship with the crustal structure. The distribution of porphyry Cu-Mo-Au deposits is mainly controlled by the new juvenile crust, whereas the magmatic-hydrothermal Sn-W and porphyry Mo-W(-Cu) deposits are closely related to the reworked ancient crust. The results of zircon Hf isotope mapping prove that the formation and spatial distribution of deposits are related to the composition and properties of the crust. Hf isotope mapping can reveal the regional metallogenic rules and explore metallogenic prediction and metallogenic potential evaluation.
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van Schijndel, V., G. Stevens, C. Lana, T. Zack, and D. Frei. "De Kraalen and Witrivier Greenstone Belts, Kaapvaal Craton, South Africa: Characterisation of the Palaeo-Mesoarchaean evolution by rutile and zircon U-Pb geochronology combined with Hf isotopes." South African Journal of Geology 124, no. 1 (March 1, 2021): 17–36. http://dx.doi.org/10.25131/sajg.124.0011.
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Abstract The formation and evolution of Palaeoarchaean De Kraalen and Witrivier Greenstone Belts (DKGB and WGB) of the Kaapvaal Craton are poorly known. Here we report zircon and rutile in situ U-Pb ages and zircon Hf isotopic data from a variety of supracrustal rocks. The zircon cores from a metamafic amphibole-bearing gneiss from the DKGB give a protolith age of 3 441 ± 5 Ma, whereas the zircon mantle domains give a metamorphic age of 3 211 ± 16 Ma. The 176Hf/177Hft values for all zircon domains give a tight cluster around 0.280596 ± 0.00006 (2 SD). U-Pb analyses of zircon for an amphibolite intercalated with thin calc-silicate layers from the WGB give a single crystallisation age of 3 230 ± 3 Ma, but the Hf isotope ratios of these zircon grains define two different populations. The first population yields 176Hf/177Hf~3.23 Ga = 0.28064 ± 0.00004, corresponding to εHf~3.23 Ga = 2.4 ± 1.9 (2SD) and Hf model ages between ca. 3.51 to 3.30 Ga. These are Hf isotope characteristics for zircons from a relatively juvenile source extracted from a depleted mantle source ca. 0.28 to 0.07 Ga prior zircon crystallisation. The second population yields 176Hf/177Hf~3.23 Ga = 0.28093 ± 0.00004 with εHf~3.23 Ga = 8.1 ± 1.3 (2SD). These Hf data combined with the 206Pb/207Pb ages lead to isotope ratios that lie above those of Depleted Mantle. The unusually high Hf isotope signature for the cores of the zircons from the WGB amphibolite most likely represent a contribution from an early highly depleted mantle source. A rutile in situ U-Pb age of 3.085 Ga from a recrystallised quartzite indicate that the rocks from the DKGB experienced slow cooling following the 3.21 Ga metamorphic event or (partial) resetting due to elevated geothermal gradient caused by the ca. 3.1 Ga intrusions of the Vrede Granitiod Suite. The latter interpretation is preferred because ~145 Ma of slow cooling from the amphibolite facies conditions of peak metamorphism to the blocking temperature for mass diffusion of Pb in rutile is unlikely. While the Zr-in-rutile temperature of ca. 710°C at 7 kbar for DKGB most likely records the peak temperature of the ~3.23 to 3.21 Ga event. The trace element concentrations of the metamorphic rutile grains within the quartzite of the DKGB indicate that the source rock was enriched in Cr. Either due to silification during hydrothermal alteration of the (ultra)mafic country rock or during deposition in an atmosphere that allowed for chromite grains to be part of the sediment.
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Andersen, T., M. A. Elburg, and J. Lehmann. "Enigmatic provenance signature of sandstone from the Okwa Group, Botswana." South African Journal of Geology 123, no. 3 (September 1, 2020): 331–42. http://dx.doi.org/10.25131/sajg.123.0022.
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Abstract Detrital zircon grains from three samples of sandstone from the Tswaane Formation of the Okwa Group of Botswana have been dated by U-Pb and analysed for Hf isotopes by multicollector LA-ICPMS. The detrital zircon age distribution pattern of the detrital zircons is dominated by a mid-Palaeoproterozoic age fraction (2 000 to 2 150 Ma) with minor late Archaean – early Palaeoproterozoic fractions. The 2 000 to 2 150 Ma zircon grains show a range of epsilon Hf from -12 to 0. The observed age and Hf isotope distributions overlap closely with those of sandstones of the Palaeoproterozoic Waterberg Group and Keis Supergroup of South Africa, but are very different from Neoproterozoic deposits in the region, and from the Takatswaane siltstone of the Okwa Group, all of which are dominated by detrital zircon grains younger than 1 950 Ma. The detrital zircon data indicate that the sources of Tswaane Formation sandstones were either Palaeoproterozoic rocks in the basement of the Kaapvaal Craton, or recycled Palaeoproterozoic sedimentary rocks similar to the Waterberg, Elim or Olifantshoek groups of South Africa. This implies a significant shift in provenance regime between the deposition of the Takatswaane and Tswaane formations. However, the detrital zircon data are also compatible with a completely different scenario in which the Tswaane Formation consists of Palaeoproterozoic sedimentary rock in tectonic rather than depositional contact with the other units of the Okwa Group.
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Zhang, Wei, David R. Lentz, and Kathleen G. Thorne. "Petrogenesis of the Nashwaak Granite, West-Central New Brunswick, Canada: Evidence from Trace Elements, O and Hf Isotopes of Zircon, and O Isotopes of Quartz." Minerals 10, no. 7 (July 9, 2020): 614. http://dx.doi.org/10.3390/min10070614.
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The petrogenesis of the Pridoli to Early Lochkovian granites in the Miramichi Highlands of New Brunswick, Canada, is controversial. This study focuses on the Pridoli Nashwaak Granite (biotite granite and two-mica granite). In situ trace elements and O and Hf isotopes in zircon, coupled with O isotopes in quartz, are used to reveal its magmatic sources and evolution processes. In the biotite granite, inherited zircon cores have broadly homogenous δ18OZrc ranging from +6.7‰ to 7.4‰, whereas magmatic zircon rims have δ18OZrc of +6.3‰ to 7.2‰ and εHf(t) of −0.39 to −5.10. The Hf and Yb/Gd increase with decreasing Th/U. Quartz is isotopically equilibrated with magmatic zircon rims. The biotite granite is interpreted to be solely derived by partial melting of old basement rocks of Ganderia and fractionally crystallized at the fO2 of 10−21 to 10−10 bars. The two-mica granite has heterogeneous inherited zircon cores (δ18OZrc of +5.2‰ to 9.9‰) and rims (δ18OZrc of +6.2‰ to 8.7‰), and εHf(t) of −11.7 to −1.01. The two-mica granite was derived from the same basement, but with supracrustal contamination. This open-system process is also recorded by Yb/Gd and Th/U ratios in zircon and isotopic disequilibrium between magmatic zircon rims and quartz (+10.3 ± 0.2‰).
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LIU, YU, KUNGUANG YANG, ALI POLAT, and XIAO MA. "Reconstruction of the Cryogenian palaeogeography in the Yangtze Domain: constraints from detrital age patterns." Geological Magazine 156, no. 07 (August 20, 2018): 1247–64. http://dx.doi.org/10.1017/s0016756818000535.
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AbstractDetrital zircons are often used to constrain the maximum sedimentary age of strata and sedimentary provenance. This study aimed at reconstructing the Cryogenian palaeogeography of the Yangtze Domain based on U–Pb ages and Lu–Hf isotopic signatures of detrital zircons from sandstones in the southeastern part of the Yangtze Domain. U–Pb ages of the youngest detrital zircon grains from the Niuguping, Gucheng and Datangpo formations yielded average ages of 712±24 Ma, 679.2±6.2 Ma and 665.1±7.4 Ma, respectively, which are close to the depositional ages of their respective formations. An integrated study of detrital zircon Lu–Hf isotopes and U–Pb ages from three samples revealed six main peak ages in the samples from the Anhua section atc. 680 Ma,c. 780 Ma,c. 820 Ma,c. 940 Ma,c. 2000 Ma andc. 2500 Ma. The characteristics of the U–Pb ages and Hf isotopes indicate a link between the north and southeast margins of the Yangtze Domain as early asc. 680 Ma, and the provenance of the coeval sedimentary sequences in the SE Yangtze Domain was the South Qinling Block on the northern margin of the Yangtze Domain. The provenance analysis on thec. 680 Ma detritus composing upper Neoproterozoic strata in the Yangtze Domain revealed that the detritus was transported southward from South Qinling to the southeast margin of the Yangtze Domain through the Exi Strait, but was hindered by the Jiangnan Orogenic Belt.
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Sun, Xiang, Yongjun Lu, Qiang Li, and Ruyue Li. "A Downgoing Indian Lithosphere Control on Along-Strike Variability of Porphyry Mineralization in the Gangdese Belt of Southern Tibet." Economic Geology 116, no. 1 (November 23, 2020): 29–46. http://dx.doi.org/10.5382/econgeo.4768.
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Abstract The E-trending Gangdese porphyry copper belt in southern Tibet is a classic example of porphyry mineralization in a continental collision zone. New zircon U-Pb geochronological, zircon Hf-O, and bulk-rock Sr-Nd isotope data for the Miocene mineralizing intrusions from the Qulong, Zhunuo, Jiru, Chongjiang, and Lakange porphyry copper deposits and Eocene igneous rocks from the western Gangdese belt, together with literature data, show that both Paleocene-Eocene igneous rocks and Miocene granitoids exhibit coupled along-arc isotopic variations, characterized by bulk-rock ɛNd(t) and zircon ɛHf(t) values increasing from ~84° to ~92°E and then decreasing toward ~95°E. These are interpreted to reflect increasing contributions of subducted Indian continental materials from ~92° to ~84°E and from ~92° to ~95°E, respectively. The Miocene mineralizing intrusions were derived from subduction-modified Tibetan lower crust represented isotopically by the Paleocene-Eocene intrusions, with contributions from Indian plate-released fluids and mafic melts derived from mantle metasomatized by subducted Indian continental materials. Involvement of isotopically ancient Indian continental materials increased from east (Qulong) to west (Zhunuo), which is interpreted to reflect an increasingly shallower angle of the downgoing Indian slab from east to west, consistent with geophysical imaging. Exploration of Gangdese Miocene porphyry copper deposits should focus on the Paleocene-Eocene arc where the subarc mantle was mainly enriched by fluids from the subducted Neo-Tethyan oceanic slab. Neodymium-Hf isotope data for mineralizing igneous rocks from porphyry copper deposits globally show no obvious correlations with Cu endowment. Although Nd-Hf isotopes are useful for imaging lithospheric architecture through time, caution must be taken when using Nd-Hf isotopes to evaluate the potential endowment of porphyry copper deposits, because other factors such as tectonic setting, crustal thickening, magma differentiation, fluid exsolution, and ore-forming processes all play roles in determining Cu endowments and grades.
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Martin, Erin L., William J. Collins, and Christopher J. Spencer. "Laurentian origin of the Cuyania suspect terrane, western Argentina, confirmed by Hf isotopes in zircon." GSA Bulletin 132, no. 1-2 (June 12, 2019): 273–90. http://dx.doi.org/10.1130/b35150.1.
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Abstract The proto-Andean margin of Argentina consists of several suspect terranes, the origins of which are disputed. The Cuyania (greater Precordillera) suspect terrane was originally interpreted to be of southeast Laurentian affinity, but more recently a southwestern Gondwanan provenance has been argued. Both potential source regions comprise Mesoproterozoic rocks, but we show they are isotopically distinct, using previously published zircon Lu-Hf data. Detrital zircon εHf data from southwestern Gondwana (Namaqua-Natal belt) show no correlation with new zircon U-Pb and Lu-Hf data from Cuyania, suggesting that Gondwana was not the source of these sediments. Rather, detrital zircons from Cambrian strata in Cuyania yield Mesoproterozoic zircons with depleted εHf that correlate to the Grenville margin of Laurentia, and a ca. 535 Ma zircon population sourced directly from rift-related rocks of the Ouachita Embayment, thus recording rifting and drifting of Cuyania from Laurentia. By contrast, zircons from Middle to Late Ordovician strata of Cuyania record a larger range of εHf values, correlated with Western Sierras Pampeanas Mesoproterozoic basement inliers of Argentina. These synorogenic clastic deposits record the Ordovician arrival of Cuyania at the proto-Andean margin of Gondwana. The new data require the terrane boundaries of Cuyania to be redefined, thereby excluding Western Sierras Pampeanas basement inliers. The results verify the Laurentian microcontinent model for the origin of Cuyania.
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Huang, Hui, Yaoling Niu, Fang-Zhen Teng, and Shui-Jiong Wang. "Discrepancy between bulk-rock and zircon Hf isotopes accompanying Nd-Hf isotope decoupling." Geochimica et Cosmochimica Acta 259 (August 2019): 17–36. http://dx.doi.org/10.1016/j.gca.2019.05.031.
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Zhang, Shao-Hua, Wei-Qiang Ji, Hao Zhang, Guo-Hui Chen, Jian-Gang Wang, Zhong-Yu Meng, and Fu-Yuan Wu. "Identification of Forearc Sediments in the Milin-Zedong Region and Their Constraints on Tectonomagmatic Evolution of the Gangdese Arc, Southern Tibet." Lithosphere 2020, no. 1 (November 2, 2020): 1–20. http://dx.doi.org/10.2113/2020/8835259.
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Abstract The Xigaze forearc sediments revealed the part of the tectonomagmatic history of the Gangdese arc that the bedrocks did not record. However, the sediments’ development is restricted to the region around and west of Xigaze City. Whether the eastern segment of the arc had a corresponding forearc basin is yet to be resolved. In this study, a field-based stratigraphic study, detrital zircon U-Pb geochronology (15 samples), and Hf isotopic analyses (11 of the 15 samples) were carried out on four sections in the Milin-Zedong area, southeast Tibet. The analytical results revealed the existence of three distinct provenances. The lower sequence is characterized by fine-grained sandstone, interbedded mudstone, and some metamorphic rocks (e.g., gneiss and schist). The detrital zircon U-Pb age distribution of this sequence is analogous to those of the Carboniferous-Permian strata and metasediments of the Nyingtri group in the Lhasa terrane. The middle and upper sequences are predominantly composed of medium- to coarse-grained volcaniclastic/quartzose sandstones, which are generally interbedded with mudstone. The detrital zircon U-Pb ages and Hf isotope signatures indicate that the middle sequences are Jurassic to Early Cretaceous in age (~200–100 Ma) and show clear affinity with the Gangdese arc rocks, that is, positive εHft values. In contrast, the upper sequences are characterized by Mesozoic detrital zircons (150–100 Ma) and negative εHft values, indicative of derivation from the central Lhasa terrane. The overall compositions of the detrital zircon U-Pb ages and Hf isotopes of the middle to upper sequences resemble those of the Xigaze forearc sediments, implying that related forearc sediments may have been developed in the eastern part of the Gangdese arc. It is possible that the forearc equivalents were eroded or destroyed during the later orogenesis. Additionally, the detrital zircons from these forearc sediments indicate that this segment of the Gangdese arc experienced more active and continuous magmatism from the Early Jurassic to Early Cretaceous than its bedrock records indicate.
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Bikramaditya, R. K., A. Krishnakanta Singh, Sun-Lin Chung, Rajesh Sharma, and Hao-Yang Lee. "Zircon U–Pb ages and Lu–Hf isotopes of metagranitoids from the Subansiri region, Eastern Himalaya: implications for crustal evolution along the northern Indian passive margin in the early Paleozoic." Geological Society, London, Special Publications 481, no. 1 (November 22, 2018): 299–318. http://dx.doi.org/10.1144/sp481.7.
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AbstractWe studied the zircon U–Pb ages, Hf isotopes, and whole-rock and mineral chemistry of metagranitoids from the Subansiri region of the Eastern Himalaya to constrain their emplacement age, origin and geodynamic evolution. The investigated metagranitoids have high SiO2, Na2O + K2O, Rb, Zr and low Fe2O3, Nb, Ga/Al ratios with fractionated rare earth element patterns [(Ce/Yb)N = 6.46–42.15] and strong negative Eu anomalies (Eu/Eu* = 0.16–0.44). They are peraluminous (molar A/CNK = 1.04–1.27) and calc-alkaline in nature, with normative corundum (1.04–3.61) and relatively high FeOt/MgO ratios in biotite (c. 3.38), indicating their affinity with S-type granites. The time of emplacement of the Subansiri metagranitoids is constrained by zircon U–Pb ages between 516 and 486 Ma. The zircon grains have negative εHf(t) values ranging from −1.4 to −12.7 and yield crustal Hf model ages from 1.5 to 2.2 Ga, suggesting the occurrence of a major crustal growth event in the Proterozoic and re-melting of the crust during the early Paleozoic. The geochemical data in conjunction with the U–Pb ages and Hf isotope data suggest that the Subansiri metagranitoids were produced by partial melting of older metasedimentary rocks in the Indian passive margin.Supplementary material: Hf isotope results for the Mud Tank zircon standard acquired during the experimental period are available at https://doi.org/10.6084/m9.figshare.c.4299830
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Chen, Xiao-Dong, Bin Li, Chong-Bo Sun, and Hong-Bing Zhou. "Protracted Storage for Calc-Alkaline Andesitic Magma in Magma Chambers: Perspective from the Nageng Andesite, East Kunlun Orogen, NW China." Minerals 11, no. 2 (February 13, 2021): 198. http://dx.doi.org/10.3390/min11020198.
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Calc-alkaline andesitic rocks are a major product of subduction-related magmatism at convergent margins. Where these melts are originated, how long they are stored in the magma chambers, and how they evolved is still a matter of debate. In this study, we present new data of whole-rock elemental and Sr-Nd-Pb isotope compositions, and zircon U-Pb-Th isotopes and trace element contents of Nageng (basaltic-)andesites in the East Kunlun Orogen (NW China). The similar age and whole-rock elemental and Sr-Nd-Pb isotope contents suggest that the Nageng andesite and basaltic andesite are co-magmatic. Their low initial 87Sr/86Sr (0.7084–0.7086) but negative εNd(t) values (−10.61 to −9.49) are consistent with a magma source from the juvenile mafic lower crust, possibly related to the mantle wedge with recycled sediment input. The U-Pb age gap between the zircon core (ca. 248 Ma) and rim (ca. 240 Ma) reveals a protracted magma storage (~8 Myr) prior to the volcanic eruption. When compared to the zircon rims, the zircon cores have higher Ti content and Zr/Hf and Nb/Ta ratios, but lower Hf content and light/heavy rare earth element ratios, which suggests that the parental magma was hotter and less evolved than the basaltic andesite. The plagioclase accumulation likely resulted in Al2O3-enrichment and Fe-depletion, forming the calc-alkaline signature of the Nageng (basaltic-)andesites. The magma temperature, as indicated by the zircon saturation and Ti-in-zircon thermometry, remained low (725–828 °C), and allowed for the magma chamber to survive over ~8 Myr. The decreasing εHf(t) values from zircon core (avg. 0.21, range: −1.28 to 1.32) to rim (avg. −3.68, range: −7.30 to −1.13), together with the presence of some very old xenocrystic zircons (268–856 Ma), suggest that the magma chamber had undergone extensive crustal contamination.
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O’Connor, Liam, Dawid Szymanowski, Michael P. Eddy, Kyle M. Samperton, and Blair Schoene. "A red bole zircon record of cryptic silicic volcanism in the Deccan Traps, India." Geology 50, no. 4 (January 5, 2022): 460–64. http://dx.doi.org/10.1130/g49613.1.
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Abstract Silicic magmas within large igneous provinces (LIPs) are understudied relative to volumetrically dominant mafic magmas despite their prevalence and possible contribution to LIP-induced environmental degradation. In the 66 Ma Deccan LIP (India), evolved magmatism is documented, but its geographic distribution, duration, and significance remain poorly understood. Zircons deposited in weathered Deccan lava flow tops (“red boles”) offer a means of indirectly studying potentially widespread, silicic, explosive volcanism spanning the entire period of flood basalt eruptions. We explored this record through analysis of trace elements and Hf isotopes in zircon crystals previously dated by U–Pb geochronology. Our results show that zircon populations within individual red boles fingerprint distinct volcanic sources that likely developed in an intraplate setting on cratonic Indian lithosphere. However, our red bole zircon geochemical and isotopic characteristics do not match those from previously studied silicic magmatic centers, indicating that they must derive from yet undiscovered or understudied volcanic centers associated with the Deccan LIP.
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Kinny, P. D., G. J. Love, and N. J. Pearson. "Hf isotopes and zircon recrystallization: A case study." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A319. http://dx.doi.org/10.1016/j.gca.2006.06.645.
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Røhr, Torkil S., Tom Andersen, Henning Dypvik, and Ashton F. Embry. "Detrital zircon characteristics of the Lower Cretaceous Isachsen Formation, Sverdrup Basin: source constraints from age and Hf isotope data." Canadian Journal of Earth Sciences 47, no. 3 (March 2010): 255–71. http://dx.doi.org/10.1139/e10-006.
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Detrital zircons from the Lower Cretaceous Isachsen Formation of the Sverdrup Basin, Canadian Arctic Archipelago, have been dated by the U–Pb method and analyzed for Hf isotopes by laser ablation microprobe – inductively coupled plasma – mass spectrometry (LAM–ICP–MS). Five samples from four locations on Ellesmere and Axel Heiberg islands display similar ranges of U–Pb ages, with significant zircon populations at 2.8–2.6, 1.9–1.8, 1.7–1.6, and 1.2–1.0 Ga. Major hiatuses occur between 2.4 and 2.0 Ga and from 0.96 to 0.5 Ga. Low initial εHfvalues indicating recycled crust components are significant in Palaeoproterozoic (1.9–1.8 Ga) and Neoarchaean (2.8–2.6 Ga) zircon populations. Other U–Pb age populations in the studied samples are dominated by zircon with positive εHfvalues, indicating a significant contribution from mantle-derived protoliths. The εHfvalues seen within a given U–Pb age population are generally consistent, with only minor scatter among the different samples. U–Pb and Hf data closely resemble previously published data from Lower Cretaceous rocks in northern Greenland, suggesting they have the same origin. The data are also largely consistent with the East Greenland Caledonides and the Precambrian basement of Greenland and northern Canada as predominant sources of zircon for the studied sandstones. However, based on the level of similarity between data from the Wandel Sea Basin and Sverdrup Basin sediments and on previous Nd isotope work in the Sverdrup Basin, it is likely that the sediments represent redeposited lower and middle Palaeozoic sediments.
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Attia, Snir, John M. Cottle, and Scott R. Paterson. "Erupted zircon record of continental crust formation during mantle driven arc flare-ups." Geology 48, no. 5 (February 14, 2020): 446–51. http://dx.doi.org/10.1130/g46991.1.
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Abstract Coupled zircon U-Pb age, trace-element, and Lu-Hf isotope analyses from central Sierra Nevada (eastern California, USA) metavolcanic strata reveal the expression of three Mesozoic arc flare-ups in the volcanic record over ∼150 m.y. of magmatic activity. Zircon εHf(i) values vary up to 20 epsilon units within individual samples and coeval sample populations but show no clear links with other geochemical indices, requiring both mixing and fractionation for arc magma genesis. Zircon compositions show repeated temporal trends across flare-ups: Hf isotopes spanning evolved to juvenile values converge to more juvenile compositions, middle rare earth element (MREE) depletion and heavy REE slopes increase during flare-up main phases, and highly variable U/Yb values converge to low values as flare-ups conclude. Despite pervasive contamination, juvenile source magmas dominate magmas erupted throughout the entirety of high-magma-addition episodes. Arc flare-ups thus represent ∼30 m.y. of increased mantle magma input that represents significant continental crust formation in Cordilleran arcs.
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Zheng, Binsong, Chuanlong Mou, Renjie Zhou, Xiuping Wang, Zhaohui Xiao, and Yao Chen. "Nature and origin of the volcanic ash beds near the Permian–Triassic boundary in South China: new data and their geological implications." Geological Magazine 157, no. 4 (December 3, 2019): 677–89. http://dx.doi.org/10.1017/s001675681900133x.
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AbstractPermian–Triassic boundary (PTB) volcanic ash beds are widely distributed in South China and were proposed to have a connection with the PTB mass extinction and the assemblage of Pangea. However, their source and tectonic affinity have been highly debated. We present zircon U–Pb ages, trace-element and Hf isotopic data on three new-found PTB volcanic ash beds in the western Hubei area, South China. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of zircons yields ages of 252.2 ± 3.6 Ma, 251.6 ± 4.9 Ma and 250.4 ± 2.4 Ma for these three volcanic ash beds. Zircons of age c. 240–270 Ma zircons have negative εHf(t) values (–18.17 to –3.91) and Mesoproterozoic–Palaeoproterozoic two-stage Hf model ages (THf2) (1.33–2.23 Ga). Integrated with other PTB ash beds in South China, zircon trace-element signatures and Hf isotopes indicate that they were likely sourced from intermediate to felsic volcanic centres along the Simao–Indochina convergent continental margin. The Qinling convergent continental margin might be another possible source but needs further investigation. Our data support the model that strong convergent margin volcanism took place around South China during late Permian – Early Triassic time, especially in the Simao–Indochina active continental margin and possibly the Qinling active continental margin. These volcanisms overlap temporally with the PTB biocrisis triggered by the Siberian Large Igneous Province. In addition, our data argue that the South China Craton and the Simao–Indochina block had not been amalgamated with the main body of Pangea by late Permian – Early Triassic time.
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Shi, Yu, Xi Jun Liu, and Zuo Hai Feng. "Formation Age of the Qinling Complex and the early Paleozoic Tectonic Event." Advanced Materials Research 734-737 (August 2013): 60–70. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.60.
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The Qinling orogenic belt (QOB) located between the North China Craton (NCC) and the South China Craton (SCC) is composed of the Northern Qinling Belt (NQB) and the Southern Qinling Belt (SQB). This study presents new geochemical data, zircon U-Pb ages and Hf isotopes from two rocks from the Qinling complex in the NQB. LA-ICP-MS zircon U-Pb dating results suggest that the Qinling complex was formed in early Neoproterozoic and experienced the early Paleozoic metamorphism. HighεHf(t) values of 9.0-12.0 for the early Paleozoic zircons indicated that there is mantle-derived magma intruding into the Qinling complex in the early Paleozoic.
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Cecil, M. Robinson, George E. Gehrels, Margaret E. Rusmore, Glenn J. Woodsworth, Harold H. Stowell, Intan N. Yokelson, Emily Homan, Kouki Kitajima, and John W. Valley. "Mantle control on magmatic flare-ups in the southern Coast Mountains batholith, British Columbia." Geosphere 17, no. 6 (October 12, 2021): 2027–41. http://dx.doi.org/10.1130/ges02361.1.
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Abstract The southern Coast Mountain batholith was episodically active from Jurassic to Eocene time and experienced four distinct high magmatic flux events during that period. Similar episodicity has been recognized in arcs worldwide, yet the mechanism(s) driving such punctuated magmatic behavior are debated. This study uses zircon Hf and O isotopes, with whole-rock and mineral geochemistry, to track spatiotemporal changes in southern Coast Mountains batholith melt sources and to evaluate models of flare-up behavior and crust formation in Cordilleran arc systems. Zircon Hf isotope analysis yielded consistently primitive values, with all zircon grains recording initial εHf between +6 and +16. The majority (97%) of zircons analyzed yielded δ18O values between 4.2‰ and 6.5‰, and only five grains recorded values of up to 8.3‰. These isotopic results are interpreted to reflect magmatism dominated by mantle melting during all time periods and across all areas of the southern batholith, which argues against the periodic input of more melt-fertile crustal materials as the driver of episodic arc magmatism. They also indicate that limited crustal recycling is needed to produce the large volumes of continental crust generated in the batholith. Although the isotopic character of intrusions is relatively invariant through time, magmas emplaced during flare-ups record higher Sr/Y and La/Yb(N) and lower zircon Ti and Yb concentrations, which is consistent with melting in thickened crust with garnet present as a fractionating phase. Flare-ups are also temporally associated with periods when the southern Coast Mountains batholith both widens and advances inboard. We suggest that the landward shift of the arc into more fertile lithospheric mantle domains triggers voluminous magmatism and is accompanied by magmatic and/or tectonic thickening. Overall, these results demonstrate that the magmatic growth of Cordilleran arcs can be spatially and temporally complex without requiring variability in the contributions of crust and/or mantle to the batholith.
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Song, Jiaxuan, Hujun Gong, Jingli Yao, Huitao Zhao, Xiaohui Zhao, Yunxiang Zhang, and Biao Chen. "U–Pb Dating and Hf Isotopes Analysis of Detrital Zircons of the Shanxi Formation in the Otuokeqi Area, Northwestern Ordos Basin." Geofluids 2021 (February 25, 2021): 1–14. http://dx.doi.org/10.1155/2021/6693005.
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The Paleozoic strata are widely distributed in the northwest of the Ordos Basin, and the provenance attributes of the basin sediments during this period are still controversial. In this paper, the detrital zircon LA-MC-ICPMS U-Pb age test was conducted on the drilling core samples of the Shanxi Formation of the Upper Paleozoic in the Otuokeqi area of the Ordos Basin, and the provenance age and the characteristic of the Shanxi formation in the Otuokeqi area in the northwest were discussed. The cathodoluminescence image shows that the detrital zircon has a clear core-edge structure, and most of the cores have clear oscillatory zonings, which suggests that they are magmatic in origin. Zircons have no oscillatory zoning structure that shows the cause of metamorphism. The age of detrital zircon is dominated by Paleoproterozoic and can be divided into four groups, which are 2500~2300 Ma, 2100~1600 Ma, 470~400 Ma, and 360~260 Ma. The first two groups are the specific manifestations of the Precambrian Fuping Movement (2.5 billion years) and the Luliang Movement (1.8 billion years) of the North China Craton. The third and fourth groups of detrital zircons mainly come from Paleozoic magmatic rocks formed by the subduction and collision of the Siberian plate and the North China plate. The ε Hf t value of zircon ranges from -18.36 to 4.33, and the age of the second-order Hf model T DM 2 ranges from 2491 to 1175 Ma. The source rock reflecting the provenance of the sediments comes from the material recycling of the Paleoproterozoic and Mesoproterozoic in the crust, combined with the Meso-Neoproterozoic detrital zircons discovered this time, indicating that the provenance area has experienced Greenwellian orogeny.
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Sheikh, Lawangin, Wasiq Lutfi, Zhidan Zhao, and Muhammad Awais. "Geochronology, trace elements and Hf isotopic geochemistry of zircons from Swat orthogneisses, Northern Pakistan." Open Geosciences 12, no. 1 (June 25, 2020): 148–62. http://dx.doi.org/10.1515/geo-2020-0109.
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AbstractIn this study, zircon grains are applied for U–Pb dating, Hf isotopes and trace elements to reveal the origin of magmatism and tectonic evolution of Late Paleozoic rocks of the Indian plate, Northern Pakistan. Most of the zircons are characterized by oscillatory zoning, depletion of light rare earth elements (LREE) and enrichment of heavy rare earth elements (HREE) with Ce and Eu anomalies. The yielded ages for these rocks are 256 ± 1.9 Ma and are plotted in the zones defined for the continental setting with few deviated toward the mid-oceanic ridge and the oceanic arc setting. Deviated zircons are recognized as inherited zircons by displaying a high concentration of normalized primitive La and Pr values, while others are plotted in the continental zones. Rare earth elements (REE) and trace elements including Th, Hf, U, Nb, Sc and Ti discriminate Swat orthogneisses into the within plate setting and the inherited zircons are plotted in the orogenic or the arc-related setting. The LREE discriminated these zircons into a magmatic zone with inherited zircons deviated toward the hydrothermal zone. The temperature calculated for these rocks based on the Ti content in zircon ranges from 679 to 942°C. The εHf(t) ranging from −11.1 to +1.4 reveals that the origin is the continental crust with the minute input of the juvenile mantle.
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Zhang, Hong, Fang An, Mingxing Ling, Xiaolin Feng, and Weidong Sun. "Metallogenesis of Porphyry Copper Deposit Indicated by In Situ Zircon U-Pb-Hf-O and Apatite Sr Isotopes." Minerals 12, no. 11 (November 19, 2022): 1464. http://dx.doi.org/10.3390/min12111464.
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The origin of the Dexing porphyry Cu deposit is hotly debated. Zircon and apatite are important accessory minerals that record key information of mineralization processes. SHRIMP zircon U-Pb analyses of granodiorite porphyries yield ages of 168.9 ± 1.2 Ma, 168.0 ± 1.0 Ma, and 172.8 ± 1.3 Ma, whereas zircons in the volcanic rocks of the Shuangqiaoshan Group have Neoproterozoic ages of 830 ± 7 Ma, 829 ± 8 Ma, and 899 ± 12 Ma. The porphyry displays zircon in situ δ18O of mantle values (5.5 ± 0.2‰), low apatite 87Sr/86Sr ratios (0.7058 ± 0.0005), and high εHf values (5.1 ± 1.5), which are consistent with mantle-derived magmatic rocks. Apatite from the porphyries has relatively high total rare earth elements (REEs) and negative Eu anomalies, with relatively high Cl and As contents. These features are distinctly different from apatite in the Shuangqiaoshan Group, which shows lower total REE, Cl, and As contents but higher F content and positive Eu anomalies. Zircon in porphyries yields a relative high oxygen fugacity of ∆FMQ + 1.5 based on zircon Ce4+/Ce3+. Apatite in porphyries also shows high oxygen fugacity based on its SO3 and Mn compositions, reaching ∆FMQ + 2, which is different from that of the lower continental crust in general, but similar to subduction-related magmas. In contrast, the oxygen fugacity of the Shuangqiaoshan Group is much lower, suggesting a different origin for its wall rock. Therefore, the Dexing porphyries were not derived from the lower crust but derived from partial melting of the subducting Paleo-Pacific plate.
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Wang, Hu, Tang, and Li. "Geochemistry, Zircon U-Pb Geochronology and Hf-O Isotopes of the Banzhusi Granite Porphyry from the Xiong’ershan Area, East Qinling Orogen, China: Implications for Petrogenesis and Geodynamics." Minerals 9, no. 9 (September 5, 2019): 538. http://dx.doi.org/10.3390/min9090538.
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The Banzhusi granite porphyry is located in the Xiong’ershan area, East Qinling orogenic belt (EQOB). This study presents an integrated whole-rock geochemistry and zircon U-Pb-Hf-O isotope analysis of the Banzhusi granite porphyry. These rocks have metaluminous, high-K alkali-calcic and shoshonitic features and show significant enrichment in light rare earth elements (LREEs) over heavy rare earth elements (HREEs) with negative Eu anomalies. These samples are also greatly enriched in Rb, Ba, K, Pb, Th and U and depleted in Nb, Ta, P and Ti, and they mostly overlap the ranges of the Taihua Group tonalite–trondhjemite–granodiorite (TTG) gneiss. Magmatic zircons from three samples of the Banzhusi granite porphyry yield U-Pb ages of 125.1 ± 0.97 Ma, 128.1 ± 1.2 Ma and 128.2 ± 1.3 Ma. The Hf-O isotope features of zircons from the three samples are very similar (δ18Ozircon = 4.84‰ to 6.51‰, εHf(t) = −26.9 to −14.4). The co-variations of geochemical and isotopic data in these granite porphyries imply that the Banzhusi granite porphyry resulted from the mixing of the partially melted Taihua Group and mantle-derived material in a post-collisional setting from 128–125 Ma.
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Inácio Alves, Márcio, Bruna Saar de Almeida, Letícia Muniz da Costa Cardoso, Anderson Costa dos Santos, Ciro Appi, Anelise Losangela Bertotti, Farid Chemale, Armando Dias Tavares Jr, Maria Virginia Alves Martins, and Mauro César Geraldes. "ISOTOPIC COMPOSITION OF Lu, Hf AND Yb IN GJ-01, 91500 AND MUD TANK REFERENCE MATERIALS MEASURED BY LA-ICP-MS: APPLICATION OF THE Lu-Hf GEOCHRONOLOGY IN ZIRCON." Journal of Sedimentary Environments 4, no. 2 (June 23, 2019): 220–48. http://dx.doi.org/10.12957/jse.2019.43877.
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The Lu-Hf method has been used in the investigation of geological samples in order to understand processes and sources of magmatic rocks. This paper discusses the reference materials GJ-01, 91.500 and Mud Tank isotopic composition by LA-ICP-MS to investigate how suitable they are for the zircon analysis through this technique. The results show that the three zircons have homogeneous compositions for the proposed objectives. Considering that relatively high Yb contents produce isobaric interference, the results of this work have shown that the Mud Tank is the best reference material, since it has lower values of this element. Thus, the Mud Tank allows to obtain more reliable results due to lower correction requirements. In addition, it should be emphasized that the presented data corroborate the application of Hf isotopes for geological evolution and characterization of magmatic sources. The high abundances of Hf in the zircon grains allow to preserve the isotopic signatures of its crystallization from magmatic sources, allowing to characterize the isotopic signatures of the reservoir (s) that gave origin to that rocks, and in case studies of paleoclimate and paleoceanographic records and/or of sedimentary basins evolution, it allows to identify the origin of the sediments or temporal and spatial changes of the source of sedimentary particles. COMPOSIÇÃO ISOTÓPICA DE Lu, Hf e Yb ANALISADA POR LA-ICP-MS DOS MATERIAIS DE REFERÊNCIA “GJ-01”, “91.500” e “MUD TANK”: APLICAÇÃO DA GEOCRONOLOGIA Lu-Hf EM ZIRCÃO ResumoO método Lu-Hf tem sido utilizado para entender processos de formação e fontes de rochas magmáticas. Este artigo analisa a composição isotópica por LA-ICP-MS dos materiais de referência GJ-01, 91.500 e Mud Tank para investigar quão adequados eles são para a análise de zircônio através desta técnica. Os resultados mostram que os três zircões possuem composições homogêneas podendo ser usados com materiais de referência para as pesquizas referidas. Considerando que teores relativamente altos de Yb produzem interferência isobárica, os resultados deste trabalho mostraram que o Mud Tank é o melhor material de referência, uma vez que possui os menores valores deste elemento. O Mud Tank permite obter resultados mais confiáveis por requerer menor correção dos valores obtidos. Além disso, deve-se ressaltar que os dados apresentados corroboram a aplicação de isótopos de Hf para a evolução geológica e caracterização de fontes magmáticas. As altas abundâncias de Hf nos grãos de zircão permitem preservar as assinaturas isotópicas de sua cristalização a partir de fontes magmáticas, permitindo caracterizar as assinaturas isotópicas do (s) reservatório (s) que deram origem a essas rochas. Têm também utilidade em estudos de paleoclima e paleoceanográficos e/ou da evolução das bacias sedimentares, permitindo identificar a origem dos sedimentos ou mudanças temporais e espaciais da fonte das partículas sedimentares. Palavras-chave: Método Isotópico Lu-Hf. Interferência isobárica. Análise de Alta Resolução Espacial. Zircão. Calibração de materiais de georeferenciamento. Pesquisa analítica.
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Ogasawara, Masatsugu, Mayuko Fukuyama, Rehanul Haq Siddiqui, and Ye Zhao. "Origin of the Ordovician Mansehra granite in the NW Himalaya, Pakistan: constraints from Sr–Nd isotopic data, zircon U–Pb age and Hf isotopes." Geological Society, London, Special Publications 481, no. 1 (October 23, 2018): 277–98. http://dx.doi.org/10.1144/sp481.5.
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AbstractThe Mansehra granite in the NW Himalaya is a typical Lesser Himalayan granite. We present here new whole-rock geochemistry, Rb–Sr and Sm–Nd isotope data, together with zircon U–Pb ages and Hf isotope data, for the Mansehra granite. Geochemical data for the granite show typical S-type characteristics. Zircon U–Pb dating yields 206Pb/238U crystallization ages of 483–476 Ma. The zircon grains contain abundant inherited cores and some of these show a clear detrital origin. The 206Pb/238U ages of the inherited cores in the granite cluster in the ranges 889–664, 1862–1595 and 2029 Ma. An age of 664 Ma is considered to be the maximum age of the sedimentary protoliths. Thus the Late Neoproterozoic to Cambrian sedimentary rocks must be the protolith of the Mansehra granitic magma. The initial Sr isotope ratios are high, ranging from 0.7324 to 0.7444, whereas the εNd(t) values range from −9.2 to −8.6, which strongly suggests a large contribution of old crustal material to the protoliths. The two-stage Nd model ages and zircon Hf model ages are Paleoproterozoic, indicating that the protolith sediments were derived from Paleoproterozoic crustal components.
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Popeko, Ludmila I., Yulia N. Smirnova, Victor A. Zaika, Andrey A. Sorokin, and Sergey I. Dril. "Provenance and Tectonic Implications of Sedimentary Rocks of the Paleozoic Chiron Basin, Eastern Transbaikalia, Russia, Based on Whole-Rock Geochemistry and Detrital Zircon U–Pb Age and Hf Isotopic Data." Minerals 10, no. 3 (March 19, 2020): 279. http://dx.doi.org/10.3390/min10030279.
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The Chiron Basin extends along the southern periphery of the Siberian Craton and the western margin of the Mongol–Okhotsk Belt. Here, we present whole-rock geochemical data (major and trace elements and Sm–Nd isotopes) along with zircon U–Pb geochronology and Lu–Hf isotopic data from Paleozoic sedimentary rocks within the Chiron Basin to investigate their provenance and tectonic history. εNd(t) values of the siliciclastics rocks of the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations vary from −17.8 to −6.6, with corresponding two-stage Nd model ages (tNd(C)) ranging from 2.56 to 1.65 Ga. Detrital zircon grains from these rocks are predominantly Archean, Paleoproterozoic, and Carboniferous–Devonian in age. The data suggest that the southern flank of the Siberian Craton is the only viable source area for Archean and Paleoproterozoic zircon grains with Hf model ages (tHf(C)) of >2.20 Ga. The majority of zircon grains from sandstones from the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations are Devonian–Carboniferous in age. With respect to their Hf model ages, the zircon grains can be subdivided into two groups. The first group of Devonian–Carboniferous zircon grains is characterized by relatively old (mainly Paleoproterozoic) tHf(C) model ages of 2.25–1.70 Ga and the source was the southern margin of the Siberian Craton. The second group of Devonian–Carboniferous zircon grains is characterized by significantly younger (mainly Neoproterozoic) tHf(C) model ages of 1.35–0.36 Ga, which are consistent with a juvenile source, most likely eroded island arcs. Our data, show that sedimentary rocks of the Chiron Basin likely formed in a back-arc basin on the southern periphery of the Siberian Craton facing the Paleozoic Mongol–Okhotsk Ocean.
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Cheong, Albert Chang-sik, Youn-Joong Jeong, Shinae Lee, Keewook Yi, Hui Je Jo, Ho-Sun Lee, Changkun Park, Nak Kyu Kim, Xian-Hua Li, and Sandra L. Kamo. "LKZ-1: A New Zircon Working Standard for the In Situ Determination of U–Pb Age, O–Hf Isotopes, and Trace Element Composition." Minerals 9, no. 5 (May 27, 2019): 325. http://dx.doi.org/10.3390/min9050325.
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This study introduces a new zircon reference material, LKZ-1, for the in situ U–Pb dating and O–Hf isotopic and trace element analyses. The secondary ion mass spectrometric analyses for this gem-quality single-crystal zircon yielded a weighted mean 206Pb/238U age of 572.6 ± 2.0 Ma (2σ, n = 22, MSWD = 0.90), with moderately high U concentrations (619 ± 21 ppm, 1 SD), restricted Th/U ratios (0.146 ± 0.002, 1 SD), and negligible common Pb content (206Pbc < 0.2%). A comparable 206Pb/238U age (570.0 ± 2.5 Ma, 2σ) was produced by the isotope dilution-thermal ionization mass spectrometry. The secondary ion mass spectrometric and laser ablation-assisted multiple collector inductively coupled plasma mass spectrometer analyses respectively showed that LKZ-1 had little variation in O (δ18OV-SMOW = 10.65 ± 0.14‰; laser fluorination value = 10.72 ± 0.02‰; 1 SD) and Hf (176Hf/177Hf = 0.281794 ± 0.000016, 1 SD) isotopic compositions. LKZ-1 was also fairly homogeneous in its chemical composition (RSD of laser ablation ICPMS data ≤ 10%), displaying a relatively uniform chondrite-normalized rare earth element pattern ((Lu/Gd)N = 31 ± 3, Eu/Eu* = 0.43 ± 0.17, Ce/Ce* = 44 ± 32; 1 SD). These consistencies suggest that the LKZ-1 zircon is a suitable working standard for geochronological and geochemical analyses.
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Zhu, Yu-Sheng, Jin-Hui Yang, Hao Wang, and Fu-Yuan Wu. "A Palaeoproterozoic basement beneath the Rangnim Massif revealed by the in situ U–Pb ages and Hf isotopes of xenocrystic zircons from Triassic kimberlites of North Korea." Geological Magazine 156, no. 10 (January 9, 2019): 1657–67. http://dx.doi.org/10.1017/s0016756818000900.
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AbstractIn situ U–Pb and Hf analyses were used for crustal zircon xenocrysts from Triassic kimberlites exposed in the Rangnim Massif of North Korea to identify components of the basement hidden in the deep crust of the Rangnim Massif and to clarify the crustal evolution of the massif. The U–Pb age spectrum of the zircons has a prominent population at 1.9–1.8 Ga and a lack of Archaean ages. The data indicate that the deep crust and basement beneath the Rangnim Massif are predominantly of Palaeoproterozoic age, consistent with the ages of widely exposed Palaeoproterozoic granitic rocks. In situ zircon Hf isotope data show that most of the Palaeoproterozoic zircon xenocrysts have negative ϵHf(t) values (−9.7 to +0.7) with an average Hf model age of 2.86 ± 0.02 Ga (2σ), which suggests that the Palaeoproterozoic basement was not juvenile but derived from the reworking of Archaean rocks. Considering the existence of Archaean remanent material in the Rangnim Massif and their juvenile features, a strong crustal reworking event is indicated at 1.9–1.8 Ga, during which time the pre-existing Archaean basement was exhausted and replaced by a newly formed Palaeoproterozoic basement. These features suggest that the Rangnim Massif constitutes the eastern extension of the Palaeoproterozoic Liao–Ji Belt of the North China Craton instead of the Archaean Liaonan Block as previously thought. A huge Palaeoproterozoic orogen may exist in the eastern margin of the Sino-Korean Craton.
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Liu, Qian, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang, and Toshiaki Tsunogae. "Detrital Zircon U-Pb-Hf Isotopes of Middle Neoproterozoic Sedimentary Rocks in the Altyn Tagh Orogen, Southeastern Tarim: Insights for a Tarim-South China-North India Connection in the Periphery of Rodinia." Lithosphere 2020, no. 1 (September 30, 2020): 1–10. http://dx.doi.org/10.2113/2020/8895888.
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Abstract The location of the Tarim craton during the assembly and breakup of the Rodinia supercontinent remains enigmatic, with some models advocating a Tarim-Australia connection and others a location at the heart of the unified Rodinia supercontinent between Australia and Laurentia. In this study, our new zircon U-Pb dating results suggest that middle Neoproterozoic sedimentary rocks in the Altyn Tagh orogen of the southeastern Tarim craton were deposited between ca. 880 and 760 Ma in a rifting-related setting slightly prior to the breakup of Rodinia at ca. 750 Ma. A compilation of existing Neoproterozoic geological records also indicates that the Altyn Tagh orogen of the southeastern Tarim craton underwent collision at ca. 1.0-0.9 Ga and rifting at ca. 850-600 Ma related to the assembly and breakup of Rodinia. Furthermore, in order to establish the paleoposition of the Tarim craton with respect to Rodinia, available detrital zircon U-Pb ages and Hf isotopes from Meso- to Neoproterozoic sedimentary rocks were compiled. Comparable detrital zircon ages (at ca. 0.9, 1.3-1.1, and 1.7 Ga) and Hf isotopes indicate a close linkage among rocks of the southeastern Tarim craton, Cathaysia, and North India but exclude a northern or western Australian affinity. In addition, detrital zircons from the northern Tarim craton exhibit a prominent age peak at ca. 830 Ma with minor spectra at ca. 1.9 and 2.5 Ga but lack Mesoproterozoic ages, comparable to the northern and western Yangtze block. Together with comparable geological responses to the assembly and breakup of the Rodinia supercontinent, we offer a new perspective of the location of the Tarim craton between South China and North India in the periphery of Rodinia.
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Vlach, Silvio R. F. "On the Morphology and Geochemistry of Hydrothermal Crypto- and Microcrystalline Zircon Aggregates in a Peralkaline Granite." Minerals 12, no. 5 (May 14, 2022): 628. http://dx.doi.org/10.3390/min12050628.
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Singular crypto- and microcrystalline hydrothermal zircon aggregates occur in peralkaline granites from the Corupá Pluton of “A-type” granites and syenites in Graciosa Province, Southern Brazil, and are herein characterized for their morphological, textural and geochemical (major, minor and trace elements, and Lu-Hf isotopes) properties. The aggregates were found to present a variety of habits, such as dendritic, oolitic, botryoidal and spherulitic, and they are associated with typical hydrothermal minerals (alkali-feldspars, quartz, fluorite, epidote-group minerals, phyllosilicates and Fe oxides) in micro-fractures and small miarolitic cavities in the host rock. They precipitated directly from a hydrothermal fluid and, compared to magmatic zircon crystals from the host, were found to contain relatively high abundances of the “non-formula” elements (e.g., Fe, Al, and Ca) and HFSEs (High-Field-Strength Elements), particularly the L- and MREEs (Light and Medium Rare Earth Elements), features most typical of hydrothermal zircon, as well as high Th/U ratios, whereas the Lu-Hf isotopic signatures were found to be similar. The formation of the zircon aggregates and the associated epidote-groups minerals was probably due to the interaction between an orthomagmatic, F-bearing, aqueous fluid transporting the HFSEs with the host-rock and/or with an external meteoritic fluid from the country rocks. The preservation of an amorphous-like Zr-silicate compound and crypto-to-microcrystalline zircon varieties is arguably related to the inefficient fluid flux and/or elemental diffusion in a low-temperature oxidizing environment.
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Zeng, Renyu, Jianqing Lai, Xiancheng Mao, Bin Li, Jiandong Zhang, Richard BAYLESS, and Lizhi Yang. "Paleoproterozoic Multiple Tectonothermal Events in the Longshoushan Area, Western North China Craton and Their Geological Implication: Evidence from Geochemistry, Zircon U–Pb Geochronology and Hf Isotopes." Minerals 8, no. 9 (August 21, 2018): 361. http://dx.doi.org/10.3390/min8090361.
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The Alxa block is located in the southwestern margin of the North China Craton. The Paleoproterozoic tectonic evolution, crustal growth and tectonic affinity of the block remain unknown or controversial. The Longshoushan (LS) area is one of the few areas that outcrop Paleoproterozoic to crystalline basement rocks in the Alxa Block. In this study, we preset whole-rock geochemistry, zircon U–Pb geochronology and Lu–Hf isotope data from metagabbro, metadiorite, quartz syenite, granitic leucosome and pegmatoid leucosome in the LS area. These rocks all are enriched in LREE and LILE, and depleted in HREE and HFSE. Eight new LA-ICP-MS zircon U–Pb ages yielded three magmatic ages of 2044 Ma, 2029 Ma and 1940 Ma, and three metamorphic ages of 1891 Ma, 1848 Ma and 1812 Ma. Lu–Hf analyses reveal that the magmatic zircons and anatectic/metamorphic zircons from all the rock types are characterized by positive εHf(t) (−0.16 to 10.89) and variable εHf(t) (−11.21 to 6.24), respectively. Based on the previous studies and our new data, we conclude that the LS area experienced three magmatic events (2.5–2.45 Ga, ~2.1–2.0 Ga and ~1.95–1.91 Ga) and three regional metamorphism/anataxis events (~1.93–1.89 Ga, ~1.86–1.84 Ga and ~1.81 Ga) in Paleoproterozoic. The age–Hf isotope data establishes two main crustal growth events at ~2.9–2.5 Ga and ~2.2–2.0 Ga in the LS area. These data indicate that the LS area experienced intraplate extensional setting in the middle Paleoproterozoic, and continental subduction, collision and exhumation in the late Paleoproterozoic. Combining the geochronological framework and tectonic evolution, we suggest that the Alxa Block is part of the Khondalite Belt.
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Hannon, Jeffrey S., Craig Dietsch, Warren D. Huff, and Davidson Garway. "Tracking 40 Million Years of Migrating Magmatism across the Idaho Batholith Using Zircon U-Pb Ages and Hf Isotopes from Cretaceous Bentonites." Minerals 11, no. 9 (September 17, 2021): 1011. http://dx.doi.org/10.3390/min11091011.
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Cretaceous strata preserved in Wyoming contain numerous large bentonite deposits formed from the felsic ash of volcanic eruptions, mainly derived from Idaho batholith magmatism. These bentonites preserve a near-continuous 40 m.y. chronology of volcanism and their whole-rock and mineral chemistry has been used to document igneous processes and reconstruct the history of Idaho magmatism as emplacement migrated across the Laurentian margin. Using LA-ICP-MS, we analyzed the U-Pb ages and Hf isotopic compositions of nearly 700 zircon grains from 44 bentonite beds from the Bighorn Basin, Wyoming. Zircon populations contain magmatic autocrysts and antecrysts which can be linked to the main pulses of the Idaho batholith and xenocrysts ranging from approx. 250 Ma to 1.84 Ga from country rocks and basement source terranes. Initial εHf compositions of Phanerozoic zircons are diverse, with compositions ranging from −26 to nearly +12. Based on temporal trends in zircon ages and geochemistry, four distinct periods of plutonic emplacement are recognized during the Mid- to Late Cretaceous that follow plutonic emplacement across the Laurentian suture zone in western Idaho and into western Montana with the onset of Farallon slab shallowing. Our data demonstrate the utility of using zircons in preserved tephra to track the regional-scale evolution of convergent margins related to terrane accretion and the spatial migration of magmatism related to changes in subduction dynamics.
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Iizuka, Tsuyoshi, Takao Yamaguchi, Keita Itano, Yuki Hibiya, and Kazue Suzuki. "What Hf isotopes in zircon tell us about crust–mantle evolution." Lithos 274-275 (March 2017): 304–27. http://dx.doi.org/10.1016/j.lithos.2017.01.006.
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Petersson, Andreas, Karolina Bjärnborg, Anders Scherstén, Axel Gerdes, and Tomas Næraa. "Tracing Proterozoic arc mantle Hf isotope depletion of southern Fennoscandia through coupled zircon U–Pb and Lu–Hf isotopes." Lithos 284-285 (July 2017): 122–31. http://dx.doi.org/10.1016/j.lithos.2017.04.010.
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Tang, Yu-Wei, Long Chen, Zi-Fu Zhao, and Yong-Fei Zheng. "Geochemical evidence for the production of granitoids through reworking of the juvenile mafic arc crust in the Gangdese orogen, southern Tibet." GSA Bulletin 132, no. 7-8 (November 7, 2019): 1347–64. http://dx.doi.org/10.1130/b35304.1.
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Abstract Although continental crust is characterized by the widespread occurrence of granitoids, the causal relationship between continental crust growth and granitic magmatism still remains enigmatic. While fractional crystallization of basaltic magmas (with or without crustal contamination) and partial melting of mafic lower crust are two feasible mechanisms for the production of granitoids in continental arc regions, the problem has been encountered in discriminating between the two mechanisms by whole-rock geochemistry. This can be resolved by an integrated study of zircon U-Pb ages and Hf-O isotopes together with whole-rock major-trace elements and Sr-Nd-Pb isotopes, which is illustrated for Mesozoic granitoids from the Gangdese orogen in southern Tibet. The results provide geochemical evidence for prompt reworking of the juvenile mafic arc crust in the newly accreted continental margin. The target granitoids exhibit high contents of SiO2 (65.76–70.75 wt%) and Na2O + K2O (6.38–8.15 wt%) but low contents of MgO (0.19–0.98 wt%), Fe2O3 (0.88–3.13 wt%), CaO (2.00–3.82 wt%), Ni (<5.8 ppm), and Cr (≤10 ppm). They are enriched in large ion lithophile elements, Pb, and light rare earth elements but depleted in high field strength elements. The granitoids are relatively depleted in whole-rock Sr-Nd isotope compositions with low (87Sr/86Sr)i ratios of 0.7043–0.7048 and positive εNd(t) values of 0.5–2.6, and have relatively low 207Pb/204Pb and 208Pb/204Pb ratios at given 206Pb/204Pb ratios. Laser ablation–inductively coupled plasma–mass spectrometry and secondary ion mass spectrometry U-Pb dating on synmagmatic zircons yield ages of 77 ± 2–81 ± 1 Ma in the Late Cretaceous for their emplacement. Relict zircons have two groups of U-Pb ages in the late Mesozoic and the late Paleozoic, respectively. The whole-rock Sr-Nd isotopes in the granitoids are quite similar to those of Late Cretaceous mafic rocks in the Gangdese batholith. In addition, both synmagmatic zircons and relict zircons with Late Cretaceous U-Pb ages exhibit almost the same Hf-O isotope compositions to those of the slightly earlier mafic rocks. All these observations indicate that the granitoids were mainly derived from partial melting of the juvenile mafic arc crust. Therefore, reworking of the juvenile mafic arc crust is the mechanism for the origin of isotopically depleted granitoids in southern Tibet. It is this process that leads to differentiation of the juvenile mafic arc crust toward the felsic lithology in the continental arc. In this regard, the granitoids with depleted radiogenic isotope compositions do not necessarily contribute to the crustal growth at convergent plate boundaries.
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Xing, En Yuan, Yong Sheng Zhang, Mian Ping Zheng, Su Juan Wu, Bao Ling Gui, and Yuan Peng. "Geochemistry, U-Pb Zircon Ages and Hf Isotopes of Basement Rocks Beneath the Northeastern Margin of the Ordos Basin: Constraints on the Paleoproterozoic Evolution of the Western North China Craton." Minerals 12, no. 7 (July 7, 2022): 865. http://dx.doi.org/10.3390/min12070865.
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SHRIMP zircon ages, Hf-in-zircon isotopic compositions and whole rock geochemistry were analyzed on basement metamorphic rocks from drill cores collected from the northeastern margin of the Ordos Basin. Geochemical data from four metasedimentary rocks show large varia-tions in major element compositions, but have similar REE patterns and trace element compositions, with ΣREE = 161.80 × 10−6 ~ 341.82 × 10−6, δEu = 0.26~0.63 and LaN/YbN = 3.44~25.38. SHRIMP zircon U-Pb dating of granitic gneiss yielded the magmatic zircon ages between 1856 ± 14 Ma and 2188 ± 11 Ma, with the upper intercept age of 2,229 ± 88Ma. The cores have εHf(t) values of −5.46 to +6.57, and Hf model ages vary from 2869 Ma to 2300 Ma. The analyses of metamorphic overgrowths on zircon grains yield an average metamorphic age of 1865 ± 17Ma (MSWD = 3.5). The zircon cores have εHf(t) values of −3.98 to 1.95, and Hf model ages vary from 2782 to 2416 Ma. Combined with data from earlier studies, we draw the conclusion that the metamorphic rocks in the borehole were formed during middle Paleoproterozoic time and were involved in a major late Paleoproterozoic tectono-thermal event which might be attributable to the collision between the Western and Eastern Block along the TNCO (the Trans-North China Orogen). The basement rocks are petrologically, geochronologically and geochemically comparable with rocks from the Khondalite series. The fact that the material properties of basement rocks beneath the northeastern Ordos Basin are different from those of the Western Block indicates that the extent and exact boundaries of the Ordos Block need to be refined.
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Shardakova, G. Yu, and A. V. Korovko. "Vendian-Cambrian granites of the Salatim suture zone (the Northern Urals): Geochemistry of zircons, source composition, geochronological and geodynamical consequences." LITHOSPHERE (Russia) 21, no. 1 (March 4, 2021): 32–54. http://dx.doi.org/10.24930/1681-9004-2021-21-1-32-54.
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Research subject. The composition and isotope systems of zircons and their host granites from the Krutorechensky complex (western part of the Main Uralian fault zone, Northern Urals) were investigated. Methods. The U-Pb age, trace element contents and Lu-Hf isotopes in the zircons under study were determined by LA-ICP-MS (Ulan-Ude, Ekaterinburg). TIMS was used to determine Sm-Nd isotopes in the rocks. Results and Discussion. It was shown that the morphology and composition of the main zircon group from granites confirm their magmatic origin and the absence of alteration. It means that the previously defined Vendian-Cambrian (542 Ma) age of the granites remains valid. The relics ancient (1043–122 Ma) cores were probably inherited from Isherim suite rocks. The source of such detrital grains could have been the rocks from the East-European platform basement. Young zircons (400 Ma) differing strongly from others in composition could have been formed around the already existing grains produced by a fluid generated under the action of plume activity. The source for granite melting was mainly of a crust nature: εNd(t) = –6, εHf(t) = –6…–9, initial ratio (87Sr/86Sr)i = 0.796943. In terms of lithology, the source rocks correspond to sandstones with a small admixture of clay components. The obtained information confirms the necessity to further investigate questions concerning the area of distribution and the age of the Sarankhapnorsk suite within the Krutorechensky complex, as well as the position of the eastern boundary of the Isherim block. Conclusion. The obtained results can be used in geological mapping.
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Couzinié, Simon, Oscar Laurent, Jean-François Moyen, Armin Zeh, Pierre Bouilhol, and Arnaud Villaros. "Post-collisional magmatism: Crustal growth not identified by zircon Hf–O isotopes." Earth and Planetary Science Letters 456 (December 2016): 182–95. http://dx.doi.org/10.1016/j.epsl.2016.09.033.
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Qiu, Zhili, Fuyuan Wu, Qingyuan Yu, Liewen Xie, and Shufeng Yang. "Hf isotopes of zircon megacrysts from the Cenozoic basalts in eastern China." Chinese Science Bulletin 50, no. 22 (November 2005): 2602–11. http://dx.doi.org/10.1007/bf03183658.
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QIU, Zhili. "Hf isotopes of zircon megacrysts from the Cenozoic basalts in eastern China." Chinese Science Bulletin 50, no. 22 (2005): 2602. http://dx.doi.org/10.1360/982005-686.
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Xia, Xiao-Ping, Jian Xu, Chao Huang, Xiaoping Long, and Meiling Zhou. "Subduction polarity of the Ailaoshan Ocean (eastern Paleotethys): Constraints from detrital zircon U-Pb and Hf-O isotopes for the Longtan Formation." GSA Bulletin 132, no. 5-6 (October 7, 2019): 987–96. http://dx.doi.org/10.1130/b35294.1.
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Abstract The Paleotethys Ailaoshan Ocean separated the South China and Indochina blocks during the late Paleozoic. Uncertainty remains regarding subduction of this ocean—whether it was subducted eastward beneath the South China block or westward beneath the Indochina block. In this study, we present new detrital zircon U-Pb age, and Hf and O isotope data from the Longtan Formation, which was recognized to be deposited before the ocean closed. Our results show that the formation can be divided into three units: Unit 1 is distributed west of the suture and dominates the area; it contains major age peaks at 290–250 Ma and minor multiple old age peaks. Unit 2 consists of a minor distribution west of the suture, and it shows a dominant 250 Ma age peak; old zircons are very few or not present. Their Hf and O isotopic signatures are similar to those of unit 1. Unit 3 is distributed east of the suture and is characterized by a single distinct ca. 240 Ma age peak with almost no Precambrian zircons. We interpret that units 1 and 2 were likely deposited in a back-arc and forearc basin, respectively, and a volcanic arc developed on the eastern margin of the Indochina block, similar to the present-day northeastern Japan arc. Meanwhile, unit 3 was likely deposited in a forearc basin on the western margin of the South China block. Therefore, the Ailaoshan Ocean may undergone bipolar subduction both westward and eastward beneath the Indochina and South China blocks, respectively.
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Li, Min, Houtian Xin, Bangfang Ren, Yunwei Ren, and Wengang Liu. "Early–Middle Permian post-collisional granitoids in the northern Beishan orogen, northwestern China: evidence from U–Pb ages and Sr–Nd–Hf isotopes." Canadian Journal of Earth Sciences 57, no. 6 (June 2020): 681–97. http://dx.doi.org/10.1139/cjes-2019-0088.
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The geochemistry and Sr–Nd isotope, zircon U–Pb, and zircon Hf isotope compositions are reported for monzogranites and granodiorites from the Hazhu area in the northern Beishan orogen, northwestern China. Zircon U–Pb dating yielded ages of 270.1 ± 1.1 and 277.4 ± 1.2 Ma for the monzogranites and 263.6 ± 1.2 and 262.2 ± 1.1 Ma for the granodiorites. These monzogranites and granodiorites are metaluminous to weakly peraluminous I-type and belong to mid-K calc-alkaline and high-K calc-alkaline series. They exhibit high Mg# values and moderate degrees of differentiation (D.I. = 70.7–88.1). They are enriched in large-ion lithophile elements and light rare earth elements and depleted in high field strength elements. They show high (87Sr/86Sr)i ratios of 0.6995–0.7070 and high εNd(t) values of 4.37–5.70 with Nd model ages (TDM) of 522–789 Ma, suggesting a juvenile crustal origin. Furthermore, their εHf(t) values are all positive, and Hf isotopic crustal model ages ([Formula: see text] = 394–1097 Ma) also indicate a juvenile crustal origin. According to the data obtained in this study and other regional geological data acquired recently, the Hazhu granitoids were derived from common sources of melting from the Neoproterozoic to late Paleozoic juvenile crusts. The younger intrusions (granodiorites) are more basic, likely as a result of more juvenile lower crust being melted along with asthenospheric upwelling, which led to the addition of more basic components. These granitoids formed in a post-collisional setting. The tectonic regime transformed from an arc-related compressional setting to post-collisional extension, likely as a result of lithospheric extension and thinning in response to oceanic lithospheric delamination. These granitoids in the northern Beishan orogen were probably emplaced in a post-collisional extensional setting and suggest vertical continental crustal growth in the southern Central Asian Orogenic Belt.
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Wu, Li-Guang, Xian-Hua Li, Weihua Yao, Xiao-Xiao Ling, and Kai Lu. "Insights into Polyphase Phanerozoic Tectonic Events in SE China: Integrated Isotopic Microanalysis of Detrital Zircon and Monazite." Lithosphere 2020, no. 1 (October 5, 2020): 1–17. http://dx.doi.org/10.2113/2020/8837978.
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Abstract Widespread Paleozoic and Mesozoic granites are characteristics of SE China, but the geodynamic mechanisms responsible for their emplacement are an issue of ongoing debate. To shed new light on this issue, we present an integrated geochronological and isotopic study of detrital zircon and monazite from Cambrian metasandstones and modern beach sands in the Yangjiang region, SE China. For the Cambrian metasandstone sample, detrital zircon displays a wide age range between 490 and 3000 Ma, while monazite grains record a single age peak of 235 Ma. The results suggest that a significant Triassic (235 Ma) metamorphic event is recorded by monazite but not zircon. For the beach sand sample, detrital zircon ages show six peaks at ca. 440, 240, 155, 135, 115, and 100 Ma, whereas detrital monazite yields a dominant age peak at 237 Ma and a very minor age peak at 435 Ma. Beach sand zircon displays features that are typical of a magmatic origin. Their Hf–O isotopes reveal two crustal reworking events during the early Paleozoic and Triassic, in addition to one juvenile crustal growth event during the Jurassic–Cretaceous. The beach sand monazite records intense Triassic igneous and metamorphic events with significant crustal reworking. Such early Paleozoic and Triassic geochemical signatures of detrital zircon and monazite suggest they were derived from granitoids and metamorphic rocks which formed in intraplate orogenies, i.e., the early Paleozoic Wuyi–Yunkai Orogeny and Triassic Indosinian Orogeny. The Jurassic–Cretaceous signature of detrital zircon may reflect multistage magmatism that was related to subduction of the Paleo-Pacific Plate beneath SE China.
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Yang, Gang, Juan Zhang, Hongfu Zhang, Zhian Bao, and Abing Lin. "Petrogenesis and Tectonic Implications of the Neoproterozoic Peraluminous Granitic Rocks from the Tianshui Area, Western Margin of the North Qinling Terrane, China: Evidence from Whole-Rock Geochemistry and Zircon U–Pb–Hf–O Isotopes." Minerals 12, no. 7 (July 20, 2022): 910. http://dx.doi.org/10.3390/min12070910.
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The source and petrogenesis of peraluminous granitic rocks in orogenic belts can provide insights into the evolution, architecture, and composition of continental crust. Neoproterozoic peraluminous granitic rocks are sporadically exposed in the Tianshui area of the western margin of the North Qinling Terrane (NQT), China. However, the source, petrogenesis, and tectonic setting of these rocks still remain unclear, which limits our understanding of the Precambrian tectonic and crustal evolution of the Qinling Orogenic Belt (QOB). Here, we determined the whole-rock geochemical compositions and in situ zircon U–Pb ages, trace-element contents, and Hf–O isotopic compositions of a series of peraluminous granitic mylonites and granitic gneisses in the Tianshui area at the west end of North Qinling. Zircon U–Pb dating revealed that the protoliths of the studied granitic mylonites and granitic gneisses crystallized at 936–921 Ma. The granitic rocks displayed high A/CNK values (1.12–1.34) and were enriched in large-ion lithophile elements (e.g., Rb, Ba, Th, U, and K) and light rare earth elements, and they were depleted of high-field-strength elements (e.g., Nb, Ta, and Ti). These rocks showed variable zircon εHf(t) (−12.2 / 9.7) and δ18O (3.56‰ / 11.07‰) values, suggesting that they were derived from heterogeneous crustal sources comprising predominantly supracrustal sedimentary rocks and subordinate igneous rocks. In addition, the U–Pb–Hf isotopic compositions from the core domains of inherited zircons were similar to those of detrital zircons from the Qinling Group, suggesting that the Qinling Group was an important crustal source for the granitic rocks. The lithological and geochemical features of these granitic rocks indicate that they were generated by biotite dehydration melting of heterogeneous sources at lower crustal depths. Combining our results with those of previous studies, we suggest that the NQT underwent a tectonic transition from syn-collision to post-collision at 936–874 Ma in response to the assembly and breakup of the Rodinia supercontinent.
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SU, YUPING, JIANPING ZHENG, LILI LIANG, HONGKUN DAI, JUNHONG ZHAO, MING CHEN, XIANQUAN PING, ZIQI LIU, and JIAN WANG. "Derivation of A1-type granites by partial melting of newly underplated rocks related with the Tarim mantle plume." Geological Magazine 156, no. 3 (November 20, 2017): 409–29. http://dx.doi.org/10.1017/s0016756817000838.
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AbstractThe granitic rocks of the Tarim large igneous province (LIP) are temporally and spatially related to mafic intrusions. However, their tectonic setting and genetic relationship are debated. Here, we report geochemical, and zircon U–Pb–Hf isotopic results for three alkali feldspar granitic plutons in the Halajun area, western margin of the Tarim Block. Zircon U–Pb ages suggest these plutons were emplaced at 268–275 Ma, coeval with the neighbouring mafic–ultramafic complexes and syenitic rocks. These granitic rocks have high contents of SiO2, alkalis, Rb, Th, Zr and REE (except Eu), and high ratios of FeO*/MgO and Ga/Al, and show strong depletions in Ba, Sr, Eu, which are commonly observed in the A1-type granites. Zircon Hf isotopes reveal a limited range ofεHf(t) values from −1.0 to +3.5 for different samples from three granitic plutons, obviously higher than those (mostly <0) of the mafic rocks. This distinct difference, along with a Daly gap and small volume of mafic rocks, argues against extreme fractionation of mafic magma as the main origin of the A1-type granites. Instead the A1-type granites were most likely derived from partial melting of newly underplated rocks triggered by the upwelling asthenosphere, followed by extensive fractionation. These A1-type granites were emplaced within an anorogenic setting during the late stage of the Tarim LIP, which possibly lasts for more than 30 Ma. The Piqiang mafic–ultramafic complex directly stemmed from asthenospheric mantle and Halajun A1-type granites represent two manners of vertical crustal growth.
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Gan, Chengshi, Yuejun Wang, Yuzhi Zhang, Xin Qian, and Aimei Zhang. "The assembly of the South China and Indochina blocks: Constraints from the Triassic felsic volcanics in the Youjiang Basin." GSA Bulletin 133, no. 9-10 (February 1, 2021): 2097–112. http://dx.doi.org/10.1130/b35816.1.
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Abstract The Youjiang Basin is usually regarded as an important foreland basin in the southern part of the South China Block that is related to the convergence of the South China and Indochina blocks during the Permian-Triassic. However, the nature of the basin remains controversial due to questions about the subduction polarity and suture boundary between these two blocks. Permian-Triassic felsic volcanics across the Dian-Qiong and Song Ma suture zones could offer new insights into the convergent processes of the South China and Indochina blocks. This study presents detailed petrological, zircon U-Pb dating, and Hf-O isotope and whole-rock geochemical analyses for the Triassic felsic volcanics of the Youjiang Basin (northeast of the Dian-Qiong). The dacites and rhyolites from the Beisi and Baifeng Formations were dated at ca. 240–245 Ma. All of the felsic volcanics are characterized by high SiO2 (69.40–73.15 wt%), FeOt/MgO, 10000*Ga/Al, and TZr, δ18O (9.7–11.8‰) and negative εNd(t) (from −9.6 to −12.3) and zircon εHf(t) (from −6.2 to −14.5) with A-type granitoid geochemical affinities, suggesting the reworking of crustal rocks in an extensional setting. Permian-Triassic felsic igneous rocks display similar geochemical signatures across the Dian-Qiong suture zone, whereas they show distinctive Sr-Nd and zircon Hf-O isotopes across the Song Ma suture zone. The felsic igneous rocks to the northeast of the Song Ma suture zone have much lower εNd(t) and higher δ18O with negative zircon εHf(t) than those to the southwest, which have positive zircon εHf(t). Combined with other geological and geophysical features, it is inferred that the Song Ma suture zone was probably the suture boundary between the South China and Indochina blocks, and the Youjiang Basin was likely a peripheral foreland basin in response to the southwestward convergence of the South China Block toward the Indochina Block.
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Meng, Yuanku, Zhongbo Wang, Baoping Gan, and Jinqing Liu. "Petrogenesis and Tectonic Implications of the Early Cretaceous Granitic Pluton in the Sulu Orogenic Belt: The Caochang Granitic Pluton as an Example." Minerals 10, no. 5 (May 11, 2020): 432. http://dx.doi.org/10.3390/min10050432.
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The Sulu orogenic belt is the source of information on important magmatic events associated with the collision of the Yangtze craton and North China craton (NCC) and the destruction of the NCC during the Mesozoic in eastern China. In this study, we have, for the first time, identified a monzonitic granitic pluton. We hereby present petrological, geochemical, and zircon U-Pb-Hf-O isotopic data, shedding new light on the petrogenesis and tectonic implications for the granitic pluton in the Sulu belt. LA-ICP-MS and SHRIMP II analyses of zircon grains suggest that the monzonitic granitic pluton was crystallized in the Early Cretaceous (ca. 120 Ma). Geochemically, the granitic pluton shows sub-alkaline, high-K calc-alkaline, and metaluminous signatures, and is genetically of I-type granite, excluding the possibility of S-type granite, as evidenced by mantle-like zircon oxygen isotopic features. In addition, the pluton is enriched in light REE and large-ion lithophile elements (LILE) (e.g., La, Cs, Ba, K, and Pb), but depleted in high-field-strength elements (HFSE) (e.g., Nb, Ta, P, and Ti), suggesting an arc-related affinity. Zircon Hf isotopes (εHf(t) = −27.51~−32.35; TDM2 = 2979~3175 Ma) and mantle-like δ18O values (5.12–6.24‰) together indicate that the identified granitic pluton is derived from the partial melting (reworking) of the ancient mafic lower crustal material, with no supra-crustal material participation. Moreover, high Magnesium number (Mg# = 42–49) values and mafic micro-granular enclaves suggest that mantle-derived magma participated in the evolution of the granitic pluton in this study. Integrating the findings of this study and previous work, we propose that the Caochang granitic pluton is derived from the partial melting of the deep Yangtze basaltic lower crust during the Early Cretaceous, and that the large-scale thinning of the lithospheric mantle was the main factor that led to Early Cretaceous magmatic flare-up in the Sulu orogenic belt.