Two-stage Hf Model Ages Research Articles

Widespread ca. 800 Ma granitoids in the southern Dabie Orogen: Petrogenesis and implications for Neoproterozoic accretion-type orogeny in the northern Yangtze Block

Large-scale Neoproterozoic granitoids occur widely in the Dabie Orogen of the northern Yangtze Block and provide significant clues to understanding the geological evolution of the Block within the Rodinia supercontinent. We present evidence for a prominent episode of granitoid intrusion at ca. 800 Ma in the southern Dabie Orogen (SDO), verified by new zircon LA-ICP-MS ages from four separate granitoid intrusions ranging from 807 Ma to 795 Ma in age. The granitoids are dominated by monzogranite and granodiorite with bulk-rock A/CNK and zircon δ18O values of 0.90–1.10 and 5.03–6.45‰, respectively, corresponding to I-type affinity. This is also supported by negative correlations of SiO2 vs. P2O5 and Sr vs. P2O5, and positive correlations of SiO2 vs. A/CNK, Rb vs. Y and Rb vs. Th. Low zircon εHf(t) values (−15.03 to −3.84) and relatively old two-stage Hf model ages (mainly between 1900 and 2200 Ma) for these granitoids are consistent with primary derivation of magma from partial melting of Paleoproterozoic metabasites. Relatively low Ga/Al ratios, Zr contents, and zircon saturation temperatures and consistently negative zircon εHf(t) and bulk-rock εNd(t) values are distinct from those of 780–720 Ma A-type granites in the Dabie Orogen that formed in a rift setting. We propose that the ca. 800 Ma granitoids in the SDO were products of variable degrees of partial melting of ancient mafic crust, promoted by heating of the upwelled asthenosphere due to oceanic slab breakoff in an accretion-type orogeny. Our observations suggest that the formation of the unified Yangtze Block was achieved by diachronous assembly of multiple micro-blocks during the Neoproterozoic, consistent with a peripheral location of the Yangtze Block in the Rodinia supercontinent.

Mesoproterozoic (∼1.4 Ga) magmatism in northern Alxa, China: Implications for tectonic affinity of microcontinents in the southern Central Asian Orogenic Belt

The origin and paleogeographic reconstruction of Precambrian microcontinents in the Central Asian Orogenic Belt (CAOB) are crucial for understanding continental crustal evolution, mechanisms of accretionary orogeny, and assemblage and breakup of the supercontinent during the Earth’s early history. The existence and basement nature of the South Gobi microcontinent within the central segment of the southern CAOB remain controversial. This study represents the first work to unveil the presence of Mesoproterozoic (∼1.4 Ga) intrusive rocks in the Zhusileng-Hangwula tectonic zone that is the central segment of the southern CAOB, and is distributed along the border areas between China and Mongolia. It offers pivotal evidence for the existence of the South Gobi microcontinent.Three alkali feldspar granites samples collected from the Zhusileng-Hangwula tectonic zone yielded crystallization ages ranging from 1371 ± 17 Ma to 1420 ± 29 Ma, while detrital zircons from a two-mica quartz schist xenolith yielded similar 206Pb/238U ages clustered around ∼1.4 Ga. The ∼1.4 Ga zircons display depleted Hf isotopic signatures (εHf(t) = 3.2–6.0) and relatively young two-stage Hf model ages (1.9–1.7 Ga), suggesting rapid reworking of juvenile mantle-derived materials. These findings indicate that the Zhusileng-Hangwula tectonic zone constitutes a microcontinental fragment with Mesoproterozoic basement, rather than a Paleozoic accretionary complex as previously postulated. Combining the contemporaneous magmatism data from the microcontinents in the southern CAOB, the 1.48–1.32 Ga arc-related magmatism exhibits a coherent trend of geochemical evolution, potentially indicating a geodynamic transition from a convergent to an extensional environment. Moreover, the temporal, tectonic evolution, and petrological similarities imply a tectonic affinity between these microcontinents and Fennoscandia, and they may have originated from an accretionary belt along the edge of Nuna during the Mesoproterozoic.

Provenance of the He 8 Member of the Upper Paleozoic Shihezi Formation, Ordos Basin, China: Insights from Heavy Minerals, Paleocurrents, Detrital Zircon Chronology, and Hf Isotopes

The Ordos Basin is located in the western part of the North China Craton. The Upper Paleozoic Shihezi Formation, particularly the He 8 Member, is one of the main gas-bearing strata. However, the source areas for the north and south sections have not been clearly distinguished, which has constrained oil and gas exploration to some extent. Therefore, understanding the source rock evolution of He 8 Member in both the south and north basins will provide a favorable theoretical basis for oil and gas exploration. The provenance of the He 8 Member of the Shihezi Formation in the Ordos Basin has not been well defined until now. Seven wellbore sandstone samples and three field outcrop sandstone samples from the He 8 Member in the Ordos Basin were analyzed. Based on zircon U–Pb dating and Lu–Hf isotope analyses, zircon assemblages of 520–386 Ma and 350–268 Ma in the southern Ordos Basin might have originated from the North Qinling Orogenic Belt (NQinOB) and the North Qilian Orogenic Belt (NQiOB); the 350–268 Ma age group of zircons from the NQinOB, and a large number of ~320–260 Ma detrital zircons supplied to the southern Ordos Basin by the NQinOB suggest that NQinOB magmatic and/or metamorphic events may have occurred in the NQinOB during the ~320–260 Ma period. From ~320–260 Ma, the NQinOB might have experienced significant tectonic activity that has not been fully revealed thus far. The zircons from 2600–2300 Ma, 2000–1600 Ma, and 450–300 Ma in the northern Ordos Basin might have been derived from the Trans-North China Orogenic Belt (TNCO), the Khondalite Belt, the Yinshan Belt, and the Alxa Belt. The paleocurrent and heavy mineral analyses determined that there are certain differences between the northern Ordos Basin and southern Ordos Basin, with unstable minerals such as barite and pyrite, as well as moderately stable minerals such as garnet, showing an increasing trend from south to north. There are also differences in the dominant paleocurrent directions between the south and north parts of the basin, and the Hf isotope data in the Ordos Basin show two-stage Hf model ages (TDM2) ranging from 918 Ma to 3574 Ma. As a result, the He 8 Member deposits in the southern Ordos Basin and northern Ordos Basin had different sources. The southern Ordos Basin might have derived from the NQinOB, the NQiOB, and the TNCO, and the northern Ordos Basin might have derived from the TNCO, the Khondalite Belt, the Yinshan Belt, and the Alxa Belt.

1.38 Ga magmatism and the extension tectonics in East Kunlun, northern Tibetan Plateau

Numerous Paleo- to Mesoproterozoic magmatic rocks were emplaced during the assembly, accretion and break-up of the Columbia supercontinent, and are keys to illustrating the supercontinent circle. The geological, petrological, geochronological and geochemical data of the newly discovered meta-felsic and meta-mafic magmatic rocks from the Wulonggou area are presented in this study to shed light on the Mesoproterozoic geodynamic setting of the Central Kunlun Belt and the Qaidam Block. Zircon U-Pb geochronological results indicate that the crystallization ages of the meta-felsic samples are 1385–1376 Ma, and the meta-mafic is 1379 ± 25 Ma (MSWD=0.17). Samples from the meta-felsic unit have SiO2 contents of 68.37–73.03 wt% and belong to the high-K calc-alkaline series. They exhibit similar REE distribution patterns and display enrichment in light rare earth elements (LREES) and negative Eu anomalies. Enrichments in Rb, Ba, Th, U and K, depletion in Nb, Ta, Sr, P and Ti are seen in the primitive mantle-normalized trace element pattern diagram. Magmatic zircons from different meta-felsic samples yield variable εHf(t) values of −8.14 to + 9.37 corresponding to ca. 1.7–2.0 Ga two-stage Hf model ages. Samples from the meta-mafic unit have low SiO2 concentrations of 49.87–50.43 wt%, high contents of Fe2O3T, MgO, CaO and TiO2, and Mg# values of 52–58. They show low total REE concentrations of 19.8–30.4 µg/g, and depletion in LREES, flat HREES distribution patterns with (La/Yb)N of 0.27–0.53 and insignificant Eu anomalies. Flat distribution pattern of high field strength elements (HFSEs) is observed in the primitive mantle-normalized trace element pattern diagram. They display similar immobile elements’ concentrations and distribution patterns, low Ti/Y, Nb/Y, La/Yb, and high Nb/La ratios, comparable with the present-day normal middle ocean ridge basalt. Zircons from the meta-mafic sample have mostly positive εHf(t) values ranging from −0.10 to + 4.10 with a single stage Hf model ages of ca. 1.7–2.0 Ga. The geochemical result implies that the meta-felsic unit was generated by partial melting of the Paleoproterozoic juvenile mafic lower-crustal material with mantle attributions, and the meta-mafic unit was probably from partial melting of the lithospheric mantle. Synthesizing the above evidences, Wulonggou Mesoproterozoic meta-magmatic rocks are a bimodal suite formed in a continental extensional tectonic setting which is probably related to the break-up of the Columbia supercontinent.

Constraints on the Growth and Evolution of Continental Crust in the Northeast Cathaysia Block: Insights from Detrital Zircon U-Pb Age and Hf-O Isotope Analysis in Tingjiang Sediments

Fluvial detrital zircons provide crucial insights into the early Precambrian crustal evolution. In this study, we utilize U-Pb geochronology and Hf-O isotopic compositions of detrital zircons from the Tingjiang River to comprehend the provenance and continental crustal evolution of the northeast Cathaysia Block. Zircon U-Pb ages display seven major populations at 105-177 Ma, 200-262 Ma, 376-520 Ma with a striking peak at ca. 422 Ma, 606-775 Ma, 836-1457 Ma, 1710-2042Ma, and 2300-2661Ma, corresponding to the documented tectonic-thermal events in the South China Block. Episodic magmatism was the response to the formation and breakup of the Columbia and Rodinia supercontinent. The episode of 422 Ma matches with the ages of widely spread early Paleozoic intraplate orogenic events in the South China Block. The isotopic signatures of Hf and O in the detrital zircons indicate that the majority of Precambrian zircons likely originated from the re-melted ancient continental crust, with contributions from juvenile mantle-derived magmas. Phanerozoic zircons, on the other hand, were formed through partial melting of recycled crustal material. Analysis of crustal growth rates, based on the two-stage Hf model ages, suggests a significant presence of juvenile crustal growth during the Paleoproterozoic era. Specifically, it is estimated that approximately 40% and 90% of the present crust within the northeastern Cathaysia Block were formed around 2.3 Ga and 1.6 Ga, respectively.

Geochronology, geochemistry, and isotope signatures of porphyries from the dabate Mo—Cu deposit, Western Tianshan, China: Implications for petrogenesis and geodynamic setting

The Dabate deposit in the West Tianshan Orogenic Belt is a large porphyry Mo-Cu deposit with obvious zoning feature. The Dabate pluton is closely related to mineralization associated with the rhyolite and granite porphyries. Copper (Cu) mineralization occurs on the margin of the rhyolite porphyry, and molybdenum (Mo) mineralization occurs in the interior of the rhyolite porphyry. Petrology, zircon U-Pb isotopic data, whole-rock geochemistry, and Sr-Nb-Hf-Pb isotopic data of the rhyolite and granite porphyries in the Dabate Mo-Cu mining zone and to discuss the properties, sources, evolution, and tectonic environment of the magma. Zircon U-Pb age dating shows that the rhyolite porphyry and granite porphyry were formed in 300.1 ± 1.3 Ma and 290.4 ± 5.2 Ma, respectively, and they are geochemically similar. Both are characterized by negative Eu anomalies (δEu = 0.09–0.15 and 0.10–0.11, respectively) and are slightly rich in light rare earth elements (LREE) but depleted in high-field-strength elements (HFSE), which indicates that they are both A2 type granites that underwent high differentiation. The Sr isotope (ISr) values for the rhyolite and granite porphyries range from 0.70564 to 0.70658 and 0.70833–0.70954, respectively. The Nd isotopic composition [εNd(t)] values for both are negative but close to zero (−0.25 to −0.46 and −0.65 to −1.10, respectively), and the two-stage depleted mantle Nd model ages (TDM2(Nd)) are 1.07–1.10 Ga and 1.11–1.14 Ga, respectively. Zircon εHf(t) values are 7.29–11.97 and 6.26–11.08 for rhyolite porphyry and granite porphyry, respectively, and the two-stage Hf model ages (TDM2(Hf)) are 550–848 Ma and 605–916 Ma, respectively. The initial Pb isotope ratios for the rhyolite and granite porphyry are close at (206Pb/204Pb)i = 18.26–18.65, (207Pb/204Pb)i = 15.54–15.64, and (208Pb/204Pb)i = 38.19–38.57. These results indicate that the two porphyries have a mixed source, likely originating from the partial melting of mantle blended with some recently formed lower crust material. The geochronology, geochemistry, and Sr-Nd-Hf-Pb isotope data of existing intrusions in the West Tianshan imply that the Late Carboniferous to Early Permian Dabate area was underplated in a post-collisional extensional setting, and A2-type granite intrusions with related Mo-Cu mineralization were formed.

Late Jurassic granitoids in Mufushan complex and their significance for the Mesozoic tectonic evolution of eastern South China

The Mesozoic tectono-thermal evolution of eastern South China plays an important role in forming the abundant magmatic rocks and associated giant polymetallic deposits. The middle-late Mesozoic granitoids in Mufushan and adjacent regions (e.g., Lianyunshan, Wangxiang, Taohuahsan, etc.) represent the western front of the southeast China magmatic province. However, the tectonic regimes and petrogenesis of the magmatic rocks are still elusive. Here, we report zircon UPb ages, geochemistry, and Sr-Nd-Hf-Pb isotopic data for the granitic rocks in the Mufushan region, in combination with data available from the literatures, to discriminate the middle-late Mesozoic tectono–magmatic history of the Mufushan complex in north-central South China Block. New zircon UPb dating suggests that the Mufushan two-mica monzogranites were emplaced at 149–144 Ma, a short time after the 153–151 Ma granodiorites. These late Jurassic felsic magmas share broad similarities in geochemical-isotopic characteristics, with significant enrichment in LREEs and LILEs (e.g., Ba, Rb, Th, and K), depletion in some HFSEs (e.g., Nb, Ta, Ti, and P) and positive Pb anomalies, similar to those of arc-type rocks. The common existence of Neoproterozoic zircons within the magmatic rocks indicates a certain amount of ancient material involved in the genesis of the magma. The two-mica monzogranites have εHf(t) values ranging from −13.4 to +3.5, overlapping with those of the granodiorites (−11.3 to +6.6), but both are lower than contemporaneous diorites (−2.4 to +0.59), suggesting a greater incorporation of enriched materials into the source for the granitoids. The two-mica monzogranites and granodiorites have εNd(t) values ranging from −7.9 to −8.8 and − 10 to −7.9, with corresponding two-stage Nd model ages of 1.7–1.6 Ga and 1.6 Ga, respectively, falling within their two-stage Hf model ages of 2.0–1.4 Ga and 1.8–1.4 Ga, respectively. Compared with the geochemical and isotopic compositions of the coeval magmatic rocks in eastern South China, we favor that the late Jurassic Mufushan granodiorites evolved from variable mixing and differentiation of the diorites and granitoids, accompanied by a continuous magma assimilation. The presence of late Jurassic highly fractionated granites suggests an extensive magma differentiation in eastern South China and the well-developed early Cretaceous A-type granites in eastern South China reflect a dominant extensional tectonic regime induced by slab roll-back of the Izanagi plate. The involvement of subduction-related melts facilitated the underplating of mantle-derived magma and crustal heating, triggering intensive partial melting of the lithosphere and magma enrichment, as well as the polymetallic deposits in eastern South China.

Geochemistry and Zircon LA–ICP–MS U–Pb Geochronology of the Shuangwang Au Deposit, Shaanxi Province: Implications for Tectonic Evolution and Metallogenic Age

The Shuangwang Au deposit (with a gold resource of approximately 70 t Au), is located in the Fenxian-Taibai fore-arc basin in the West Qinling Orogen of central China. Igneous intrusions in the region include the Xiba granitic pluton and granite porphyry and lamprophyre dykes. The Xiba pluton is composed of granodiorite and monzonite granite. The granodiorite is typical I-type granite, and it yields a crystallization age of 221.1 ± 1.2 Ma and a two-stage Hf model age of 1432–1634 Ma. The monzonite granite shows a transitional characteristic between I-type and A-type granite, and it yields a crystallization age of 214.8 ± 1.2 Ma and a two-stage Hf model age of 1443–1549 Ma. The granitoid was derived mainly from a crust–mantle mixed source. The ages indicate that the granodiorite and monzonite granite formed during two different stages. The REE distribution patterns of the Xiba granitoid exhibit significant fractionation between LREE and HREE, showing right-dipping curves, with an enrichment of LREE and a deficit of HREE. The granodiorite displays a light negative Eu anomaly, while the monzonite granite displays an obvious negative Eu anomaly. The granite porphyry dikes are distributed in the No. I breccia and Jiupinggou granite porphyry, and they yield crystallization ages of 219.9 ± 1.5 Ma and 213.1 ± 0.89 Ma, respectively, and two-stage Hf model ages of 1382–1501 Ma and 1373–1522 Ma, respectively. The lamprophyre dikes in the deposit yield a crystallization age of 214.4 ± 2.7 Ma. After the collision event between the Yangtze and the North China Plates along the Qinling orogenic belt, at approximately 220 Ma in the Late Triassic, the detachment of the slab produced the upwelling of the asthenosphere material. Under conditions of mantle heat and tectonic stress, widespread partial melting of the subducted continental crust and the upper lithosphere mantle occurred, forming granitoids with various degrees of adakite characteristics.

Subduction initiation of Paleo-Pacific Ocean and final closure of Paleo-Asian Ocean: constraints from Triassic granitoids in Jiamusi Block, NE China

ABSTRACT The process of transformation and superposition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean tectonic systems have been a critical scientific issue. However, the final closure of the Paleo-Asian Ocean and the initial subduction time of the Paleo-Pacific Ocean, together with the conversion between them in Northeast China, still remain controversial. The Triassic granites in the Jiamusi Block are located in the key position of Northeast China, recording the conversion process of two tectonic domains. Through systematic geochronology and geochemical studies, it can provide important constraints for revealing the superposition and conversion mechanism of the Paleo-Asian Ocean and the Paleo-Pacific Ocean and the early subduction history of the Paleo-Pacific Ocean plate. In this study, the granites in Jiamusi Block were formed in the Early–Middle Triassic (250–245 Ma), characterized by high Si, rich alkali, poor Mg, and are obviously enriched in light rare earth elements and large ion lithophile elements, depleting in high field strength elements such as Nb, Ta, and Ti. They have typical characteristics of continental magmatic arc, deriving from partial melting of amphibolite facies and garnet amphibolite facies mafic lower crust. Combined with zircon Hf isotope results, zircon εHf(t) values are −6.52 to + 9.79, and the two-stage Hf model ages are 0.6–1.7 Ga, indicating that the magma should be derived from a relative younger crustal source, and some ancient materials may be added. Moreover, based on the spatial-temporal framework and Hf isotope characteristics of magmatism in Northeast China, we believe that the Jiamusi Block belonged to an exotic block. Meanwhile, combined with geochronological and geochemical data of igneous rocks on the Jiamusi Block, we suggest that the evolution of Jiamusi Block was dominated by the Paleo-Pacific Ocean rather than Paleo-Asian Ocean during the Triassic, which means the subduction of Paleo-Pacific Ocean plate initiated at least in Early Triassic.

Genesis of the Yangyugou syenite-carbonatite complex-related REE deposit in the Qinling Orogenic Belt, Central China: Constraints from zircon U-Pb geochronology, Hf isotopes, and mineral geochemistry

The Qinling Orogenic Belt (Central China) is a world-class rare earth element (REE) metallogenic belt in which REE deposits are mainly hosted by alkaline rocks and/or carbonatites. The newly discovered Yangyugou REE deposit, hosted by alkaline complexes in this belt, is unusual because the REE mineralization mainly takes the form of Ba- and REE-bearing minerals, such as barytocalcite. In this study, we present whole-rock major and trace elements, zircon geochronology, Hf isotopes, and mineral geochemistry to investigate the enrichment of REE and Ba and origin of this deposit. The REE-bearing alkaline complex at the Yangyugou deposit consists of syenite and carbonatite. Carbonatite exhibits higher concentrations of REE and Ba compared to syenite. The concentrations of REE and BaO in the carbonatite can be up to 6214 ppm and 22.4 wt%, respectively, and exhibit a positive correlation. The carbonatite contains numerous Ba-rich minerals, primarily comprising barytocalcite and a smaller amount of bazirite. The REE concentrations of barytocalcite range from 3059 to 10032 ppm, and the Ba concentration can be as high as 37.4 wt%. The barytocalcite is the primary carrier of REE and Ba in the Yangyugou carbonatite. Zircons from the syenite have a 206Pb/238U weighted mean age of 438.9 ± 3.3 Ma (MSWD = 1.08). The εHf(t) values of these zircons range from −8.28 to −3.17, with two-stage Hf model ages of 1.61–1.93 Ga. Apatite from the syenite has initial 87Sr/86Sr ratios of 0.70906 to 0.70984. Our study indicates that syenite-carbonatite complex was probably derived from the enriched mantle that has been metasomatized by a Ba-rich fluid, and that the early Silurian alkaline magmatism may be related to the opening of the Erlangping back-arc basin.

Geology, geochronology, geochemistry and Hf-Sr-Nd isotopes of the ‘green-bean rocks’ (felsic tuffs) in the western Yangtze Block, China: Implications for genesis and enrichment mechanism of Li

The widespread ‘green-bean rocks’ (GBRs) in the western Yangtze Block (YZB) are traditionally considered to be originally felsic volcanic tuff. These greenish or yellowish green GBRs are characterized by the presence of bean-like grains. Although the GBRs are enriched in Li in addition to K, the enrichment mechanism of Li during the formation process of GBRs remains controversial. Detailed petrography, scanning electron microscopy, X-ray diffraction, whole-rock geochemistry, U-Pb dating and Hf-Sr-Nd isotopes have been conducted on the GBRs from the Longmendong section in the western YZB to shed light on the genesis of GBRs, Li enrichment mechanism, and further exploration.The zircon and apatite from Longmendong GBRs yielded U-Pb ages of 247.2 ± 0.6 Ma and 247.0 ± 11.0 Ma, respectively. Longmendong GBRs show bull-rock (87Sr/86Sr)i ratios ranging from 0.72602 to 0.72948 and εNd(t) values between −9.8 and −10.4. Zircons have low εHf(t) values and old two-stage Hf model ages (TDM2) ranging from −16.1 to −7.4 and 1741 to 2285 Ma, respectively. Apatite grains display high (87Sr/86Sr)i ratios and low εNd(t) values in the range of 0.72225–0.72461 and −9.93–−11.18, respectively. The combined evidence from textures, mineral compositions, whole-rock geochemistry and Sr-Nd-Hf isotopic compositions indicates that the GBRs originated from felsic volcanic ashes that erupted along the Sanjiang Orogen. The magma of volcanic ashes was sourced from the remelting of ancient crust in response to the initial collision of Indochina-Yangtze Blocks during the closure of the eastern Paleo-Tethys Ocean. The apatite grains separated from GBRs show significantly low Sr and Eu contents (136–223 ppm and 4.23–6.53 ppm, respectively) and low (La/Sm)N (0.97–1.11) and (Sm/Yb)N (3.49–4.56) ratios, indicating that apatite crystallized earlier than the plagioclase and the original magma are highly evolved. The magma of GBRs originated from ancient crust with significant differentiation, facilitating the initial enrichment of Li during the magma evolution. On the other hand, the GBRs have elevated levels of K2O, MgO and clay minerals (e.g., illite and illite/smectite mixed layer minerals), which are proportional to the Li concentrations. This suggests that Li in the GBRs is adsorbed by clay minerals in ionic form and experience additional enrichment during the transformation from volcanic ashes into clay minerals. Furthermore, the GBRs in the northeastern Sichuan basin under a limited sedimentary environment have relatively higher Li concentrations, suggesting that continuous evaporation also positively contributed to Li enrichment in GBRs. Geographically, GBRs in the Sichuan basin are closely related to underground Li-rich brines hosted within the adjacent strata. Therefore, the widespread Li-rich GBRs in the western YZB not only hold promise as a potential Li resource, but also serve as a marker layer for the prospecting Li brines in the Sichuan basin.

Petrogenesis of two episodes of Neoarchean TTG gneisses (∼2.72 Ga and 2.56–2.54 Ga) from the Zhongtiao Mountains, North China Craton: Implications for crustal evolution

The petrogenesis of tonalite-trondhjemite-granodiorite (TTG) suites can provide key clues for the formation and evolution of continental crust. Neoarchean TTG gneisses are widely distributed in the Zhongtiao Mountains (ZTM), North China Craton (NCC). In this contribution, to better understand Neoarchean crustal evolution of the NCC, two discrete episodes of TTG gneisses (∼2.72 Ga and ∼2.56–2.54 Ga) from the ZTM are investigated. New results approve that the two episodes of TTG gneisses are all characterized by high SiO2, Na2O contents, (La/Yb)N and Sr/Y values, but low K2O/Na2O ratios. These geochemical features are similar to the Archean TTG suites and Phanerozoic high-SiO2 adakites, suggesting that they were both derived from partial melting of mafic rocks. The characteristics of trace elements (e.g., La/Yb, Sr/Y, Y/Yb, (Ho/Yb)N and Nb/Ta ratios) imply that both of them correspond to MP-TTGs, and garnet-amphibole exist in the residue phase. The ∼2.72 Ga TTGs show high Mg# values (ave. = 51), Cr (4.87–104 ppm) and Ni (6.37–55.7 ppm) contents, and negative Nb, Ta anomalies. Some high Nb/Ta ratios (up to 17.6) imply that rutile might be involved in the residual phase, which should require a higher pressure. Zircons from these rocks yield positive εHf(t) values of +4.0 ∼ +6.8 (ave. = +5.6), with two-stage Hf model ages (TDM2) of ∼2.85–2.70 Ga, indicating a juvenile basaltic crustal source. Hence, we interpret that ∼2.72 Ga TTGs in the ZTM were derived from partial melting of mafic rocks, and more likely related to subduction process. In contrast, the ∼2.56–2.54 Ga TTGs have lower Mg# values (39–54, mostly <45), Cr (6.02–22.8 ppm) and Ni (4.93–15.7 ppm) contents. They exhibit more evolved zircon Hf (average εHf(t) = +3.21) and whole-rock Nd (εNd(t) = +1.87) isotopic compositions, and their TDM2 ages are concentrated at ∼2.85–2.68 Ga. These ∼2.5 Ga TTGs in the ZTM show similar geochemical features with contemporary TTGs in the XQL, DF and EZT of the southern NCC, identical to melts from partial melting of mafic rocks under a thickened lower crust. The ∼2.5 Ga TTGs, A-type granites and mafic rocks in the ZTM jointly indicate a complicated crust-mantle process at different depths related to mantle plume activity during the late Neoarchean. Based on comparison of the spatial-temporal distribution and geochemical features of ∼2.7 Ga and ∼2.5 Ga TTGs in the NCC, we propose that Neoarchean crustal evolution of the ZTM is similar to the whole NCC, which recorded a significant crustal growth event at ∼2.7 Ga, and an important crustal reworking event associated with some juvenile crustal growth at ∼2.5 Ga.

Magmatic controls on Pb-Zn and W-Sn metallogenic variations in the Nanling Metallogenic Belt, South China: Difference in sources, oxygen fugacity and differentiation degree

The Nanling Metallogenic Belt (NMB) in South China contains huge amounts of Middle to Late Jurassic granitoid-related polymetallic Pb-Zn and W-Sn deposits. Whether there is a link between granitoid genesis and mineral species and what specific factors control the metallogenic specialization remained unclear. Herein, we presented a systematic investigation on the Dafang Pb-Zn ore-causative intrusion, and then placed it into the compiled comprehensive dataset of the NMB ore-hosting granitoids aiming to reveal the magmatic control on the Pb-Zn and W-Sn metallogenic variations in South China. Our results illustrate that the Dafang granitoid is potassic, alkaline (Na2O + K2O: 5.84 % to 7.87 wt%) and meta-luminous (A/CNK: 0.75 to 1.01), with middle SiO2 content (60.59–65.15 wt%), displaying an analogous nature of I-type granitoids. Trace elements of all samples are characterized by a significant enrichment in LREEs, Pb, and K, and a strong depletion of HREEs, HFSEs as well as Ba. Further zircon U-Pb dating yields a concordant age of 157.0 ± 0.8 Ma (MSWD = 1.1), consisting with the Jurassic magmatic-hydrothermal activities in the NMB. Their negative εHf(t) values (−6.7 to −10.2) and two-stage Hf model ages (1.6 to 1.7 Ga) suggest that the Dafang granitoid intrusion was generated from the partial melting of a Paleoproterozoic middle-lower crust. By comparing the Dafang with other NMB ore-causative granitoids in the comprehensive dataset, we investigated two types of ore-causative granitoids, i.e., the Pb-Zn- and W-Sn-mineralized granitoids, with distinct magmatic source, redox state and evolution degree. The Pb-Zn-bearing granitoids predominantly generated from amphibolite with a high oxygen fugacity (Ce4+/Ce3+: average 104.8, n = 55) and low differentiation degree (Rb/Sr: average 0.8, n = 60; Nb/Ta: average 12.5, n = 62). In contrast, the W-Sn metallogenic granitoids originated from metasedimentary rocks with a relatively lower oxygen fugacity (Ce4+/Ce3+: average 46.7, n = 258) and higher differentiation degree (Rb/Sr: average 59.0, n = 139; Nb/Ta: average 5.3, n = 156). Collectively, we conclude the Pb-Zn and W-Sn metallogenic variations in the NMB (South China) are jointly determined by magmatic sources, oxygen fugacity and differentiation degree.

Strongly Peraluminous Highly Fractionated I-Type Granite from Bangong–Nujiang Metallogenic Belt, Tibet: Implications for Continental Evolution and Evaluation of Economic Potentiality

The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma’s evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits.

Characteristics of early Paleozoic granite-pegmatite and associated lithium-beryllium mineralization in the Tugeman area, Altun orogenic system, northwestern China

The Altun Orogenic Belt (AOB) is located on the northern margin of the Tibetan Plateau. We report the petrography, zircon U-Pb ages, Hf isotopic compositions, and whole-rock geochemistry of the Tugeman pegmatitic and granitic rocks from the AOB to constrain their petrogenesis and tectonic setting. Zircon U-Pb dating of the pegmatitic and granitic rocks yielded ages of 500–440 Ma, which we interpret as the emplacement ages of the granites and formation age of pegmatite. The granites are weakly peraluminous to peraluminous (A/CNK = 1.01–1.26), and they have high SiO2 (63.9–74.2 wt%) and Al2O3 (13.7–17.6 wt%) and low CaO (0.72–3.80 wt%) and P2O5 (0.06–0.44 wt%) contents. They show marked depletion in HREEs, enrichment in LREEs, and pronounced negative Eu anomalies, and they are enriched in Th, U, K, Pb, Nd, and Sm and depleted in Ba, Nb, Ce, Sr, P, and Ti. Zircon εHf(t) values vary from − 12.0 to + 3.3, with two-stage Hf model ages of 2.2–1.2 Ga, implying that the granites were derived mainly from ancient crust with a minor contribution from juvenile crust. Weakly peraluminous pegmatitic rocks have geochemistry characters of SiO2 (74.4–79.9 wt%) and Al2O3 (12.3–14.9 wt%) and low CaO (0.08–0.69 wt%) and P2O5 (0.05–0.33 wt%), depletion in HREEs, enrichment in LREEs, depletion in Ba, La, Ce and Ti, enriched in U, K, Pb and P. Granitic pegmatite can be formed at different stages of crystallization differentiation of granitic magma, but the pegmatite associated with highly differentiated granites is favorable to the Li and/or Be mineralization, while the pegmatite associated with low differentiated granites (such as biotite granites) is unfavorable to the Li and/or Be mineralization. Based on our findings, we propose that the Tugeman granitic magmas originated from partial melting of crustal metagreywacke and metabasalt. Furthermore, we suggest that the early Paleozoic magmatism in the Central Altun Block (CAB) can be categorized into three groups, which correspond to different tectonic events. These events include the northward subduction of the Central Altun Ocean (CAO) beneath the CAB around 520 Ma, the closure of CAO at 490–480 Ma, and post-collisional extension at 480–440 Ma induced by slab breakoff and delamination of the subducted CAO.

Petrogenesis of early Cretaceous granites in Mufushan complex, northeastern Hunan Province: Insights on middle-late Mesozoic tectonic evolution of eastern South China

We present new field observations, whole-rock major and trace elements, Sr-Nd-Pb-Hf isotopes and zircon UPb ages for the Mesozoic granites in the Mufushan complex, eastern South China. The age determinations by LA-ICP-MS UPb dating of zircons indicate that the porphyritic biotite granites and two-mica monzogranites have ages of ∼136 Ma and ∼ 130 Ma, respectively. These granites display highly evolved S-type granite geochemical characteristics, with high SiO2 (70–74 wt%) contents, high 10000*Ga/Al ratios (2.3–3.2, average of 2.8) and weakly peraluminous (A/CNK > 1.1). Both types of granites are enriched in large ion lithophile elements (LILEs, e.g., Rb, K, Ba, Sr) and depleted in high field strength elements (HFSEs, e.g., Nb, Ta, Ti), with negative anomalies of Eu and positive anomalies of Pb, which are akin to continental arc rocks. The two-mica monzogranites have high 87Sr/86Sr(i) (0.71355–0.71535), 206Pb/204Pb(i) (18.105–18.157), low εNd(t) (−9.1 to −9.6) and εHf(t) (−4.1 to −10.4), similar to those of the porphyritic biotite granites which are characterized by high 87Sr/86Sr(i) (0.717337–0.71692), 206Pb/204Pb(i) (18.134–18.580), low εNd(t) (−9.1 to −9.7) and zircon εHf(t) (−6.8 to −3.3). The similar emplacement ages and mineral assemblages as well as Sr-Nd-Hf isotopic signatures indicate their derivations were likely derived from a common magma source. These early Cretaceous granites yield two-stage Nd model ages of 1.6–1.7 Ga, similar to the two-stage Hf model ages of 1.3–1.8 Ga. The presence of Neoproterozoic and subordinate Mesoproterozoic zircons within the granitic rocks suggest a significant contribution of ancient crustal materials involved in the genesis of the magmas. In combination with comprehensive studies on the magmatic rocks, the early Cretaceous Mufushan granitic rocks may have experienced an extensive enrichment process, contemporaneously with partial melting of the Neoproterozoic volcanic-sedimentary sequences that produced the arc-like rocks. Almost simultaneously, an extensional event caused by the subduction and slab roll-back of the Paleo-Pacific plate (Izanagi plate) dominates the middle-late Mesozoic tectonics in eastern South China. This extensional regime was accompanied by the underplating of mantle-derived magma and crustal melting, producing the widespread early Cretaceous granites in adjacent regions. The development of coeval basin-and-range structures with the production of contemporaneous magmatic rocks and related polymetallic deposits in eastern South China are all related to slab roll-back tectonics.

Timescale of magma recharge for a crystal-rich mush: Perspectives from the compositional zoned quartz in Xiangshan caldera, SE China

Crystal-rich (>30 vol%) volcanic rocks, which are generally thought to be formed by the eruption of crystal-rich mush after its reactivation, have provided an important lens through which to view the connection of volcanic and plutonic rocks in the calderas worldwide. The crystal-rich rhyolitic porphyritic lava is widely exposed in Cretaceous calderas in the southeast China. However, the petrogenesis of crystal-rich porphyritic lava still remains controversial. Xiangshan caldera is a uranium mineralization related volcanic-plutonic complex, which is composed of first subcycle rhyodacite and second subcycle tuff, crystal-rich rhyolitic porphyritic lava, granite porphyry and quartz monzonitite porphyry. All the volcanic and plutonic rocks have consistent zircon U-Pb ages (135 to 133 Ma). Sr-Nd-Hf-O isotopic characteristics show that they all mainly originated from crust derived intermediate-silicic magma. Zircon εHf(t) values for inherited zircons from rhyolitic porphyritic lava and rhyodacite range from −6.9 to +9.5. Correspondingly, zircon Hf two-stage model ages of inherited zircons are 2.12 to 1.10 Ga, suggesting their derivation from the Neoproterozoic juvenile crust and the Archean to Paleoproterozoic ancient crust. The rhyolitic porphyritic lavas show higher SiO2 contents and Rb/Sr ratios, and more obvious negative anomalies of Eu/Eu*, Ba, Sr, P and Ti; The granite porphyry show lower SiO2 contents and Rb/Sr ratios, with weak negative anomalies of Eu/Eu*, Ba, Sr, P and Ti. Combined with similar Sr-Nd-Hf-O isotopic composition, they may be derived from the same magma reservoir. Lower εNd(t), εHf(t), δ18O values and older model ages of tuff indicate more contribution of older crustal material. The cathodoluminescence (CL) brightness is strongly correlated with Ti concentration in quartz. The CL of selected quartz grains from crystal-rich rhyolitic porphyritic lava and granite porphyry show brightness zoned mantles (Ti = 19 to 77 ppm) and bright rims (high-Ti; >70 ppm). Some grains have dark cores (low-Ti; <9 ppm). However, the Ti contents of the quartz in the tuff of the second subcycle are homogeneous. Resemble the crystal-rich rhyolitic porphyritic lavas, the rims of quartz phenocrysts in the granite porphyry have consistent CL-brightness with the quartz in groundmass and have small embayments caused by growth impediments in them, which is due to the pressure release. It indicates that the granite porphyry also migrated upward rather than in situ cumulate. The repeated rise of CL brightness and Ti contents in the mantle of quartz phenocrysts recorded the rise of temperature and/or the injection of more primitive magma, indicating several times of magma recharge in the magma reservoir. The timescale of Ti diffusion in the compositional zoned mantle of quartz documented an ephemeral reactivation and remobilization of the crystal-rich mush within several to 16 thousand years with at least 7 times of magma recharge which lasted for 17 years to >11 thousand years each time.

Geochronology, petrogenesis, and magmatic oxidation state of the Mangling intrusive complex, Northern Qinling Belt, Central China: Implications for magma fertility and tectonic setting

The Mangling intrusive complex has different dioritic to granitic phases and is spatially and temporally related to molybdenum deposits in the Qinling Orogen. Zircon U-Pb dating of the Mangling intrusive complex indicates that dioritic rocks (biotite diorite and biotite diorite enclave; ca. 150−147 Ma) formed earlier than granitic rocks (medium- to fine-grained and fine-grained monzogranite and K-feldspar granite; ca. 145−141 Ma). The Mangling dioritic rocks exhibit large ion lithosphere element (e.g., Rb) and light rare earth element enrichment and high field strength element (e.g., Nb, Ta, and Ti) depletion. They have low to moderate SiO2 (51.33−58.16 wt%), high MgO (3.10−4.75 wt%) and Mg# (48−60), and negative zircon εHf(t) values (−11.6 to −6.8), suggesting origination from the continental lithospheric mantle that may have been metasomatized by previous sediment-derived melts and slab-derived fluids constrained by high Nb/Y, Th/Yb, and Rb/Y ratios. The Mangling granitic rocks are I-type granites and have high SiO2 (67.90−81.88 wt%) and low MgO (0.16−0.74 wt%). They have low and negative zircon εHf(t) values (−18.7 to −1.9) and old zircon Hf two-stage model ages (2334−1287 Ma), as well as similar mineral fractionation (e.g., hornblende, biotite, sphene, and apatite) with the Mangling dioritic rocks, indicating that they were derived from the remelting of old crustal rocks (e.g., Xiong’er and Kuanping groups) by the evolved underplated mafic magma. Compared with the Taoguanping mineralized monzogranite in the Northern Qinling Belt, zircon geochemistry (e.g., Ce4+/Ce3+, Eu/Eu*, and ΔFMQ [relative fayalite-magnetite-quartz buffer]) indicates that magma of the Mangling intrusive complex (except the biotite diorite) has high oxygen fugacity and small fractionated granitic intrusions, which are coeval with the biotite diorite enclave or younger than the Mangling granitic rocks, may have potential for generating porphyry molybdenum mineralization. The combination of this study and previous studies corroborates that the Qinling Orogen underwent an intracontinental orogenic evolution in a post-collisional compression to extension transitional setting during the Late Jurassic to Early Cretaceous, affected by far-field Paleo-Pacific slab subduction.

Neoproterozoic amphibolite-facies metamorphism of the Douling complex in the northern Yangtze Craton and its tectonic implications: Constraints from petrology and zircon U-Pb-Hf-O isotopes

Neoproterozoic evolution of the Yangtze Craton has long been debated. The Douling complex, representing one of the oldest crystalline basements, records Neoproterozoic high-grade metamorphism and may provide pivotal clues into a reliable Neoproterozoic configuration of the Yangtze Craton. However, its metamorphic evolution and tectonic significance have not been well constrained. In this contribution, we conduct an integrated study of petrography, zircon U-Pb age and Hf-O isotopic compositions for two garnet amphibolites and one gneiss from the Douling complex. Phase equilibrium modeling and conventional geothermobarometry calculation define peak P-T conditions of 9–10 kbar and 670-690 °C, and shape a clockwise P-T path. Zircon grains from the gneiss mostly reveal core-rim structure. The cores display oscillatory zoning, high Th/U ratios and trace element contents, as well as HREE-enriched patterns, high 176Lu/177Hf ratios and δ18O values, consistent with a magmatic origin. They yield a weighted mean 206Pb/238U age of 868 ± 9 Ma, which is taken as the protolith age. The cores have strongly positive ƐHf(t) values of 7.0–15.6 and young two-stage Hf model ages of ca. 1310–760 Ma, indicating that the protolith was dominantly sourced from prompt reworking of Meso-Neoproterozoic juvenile crust. On the other hand, the zircon overgrowth rims in the gneiss exhibit no zoning patterns, low Th/U ratios and trace element contents, flat HREE patterns and pronouncedly negative Eu anomalies, variable 176Lu/177Hf ratios and comparable ƐHf(t) values to the magmatic cores, indicating their coeval formation with garnet and plagioclase under amphibolite-facies metamorphism and might be generated by dissolution-reprecipitation. Zircon crystals from the two amphibolites perform weak zoning patterns, low Th/U ratios and trace element contents, high formation temperatures, flat to weakly enriched HREE patterns, insignificantly and/or clear negative Eu anomalies, and low 176Lu/177Hf ratios and ƐHf(t) values, suggesting that they may form near the peak stage of amphibolite-facies metamorphism. Metamorphic zircon in the three samples yield homogeneously high δ18O values (10.81 ± 0.17‰, 11.45 ± 0.40‰, 10.92 ± 0.08‰), indicating the participation of external fluid originated from surrounding metasedimentary rocks. These metamorphic zircon grains together yield a weighted mean age of 817 ± 4 Ma (MSWD = 0.63), which is taken as the best estimated age for the upper amphibolite-facies metamorphism in the Douling complex. Considering the widespread contemporaneous magmatism in the northern Yangtze Craton, we propose that the Douling complex recorded a tectonic regime switch from compression to extension at ca. 830–820 Ma, in response to outboard oceanic subduction on the periphery of the Yangtze Craton and then tectonic extension and collapse of the thickened lithosphere.

Geochemical Characteristics of the Granodiorite Porphyry in Dongxiang W-Cu Deposit, SE China

The Dongxiang tungsten–copper deposit is a large W–Cu deposit located in the northeast of Jiangxi province in south China. Previous studies have mainly considered the geochemical and isotopic attributes of the ore deposit, but information is still lacking on the genesis and setting of Dongxiang W–Cu mineralization-related intrusive rocks. This paper presents systematic elements and Sr–Nd–Hf isotopic data of the Dongxiang granodiorite porphyry. The Dongxiang granodiorite porphyry is intermediate–acidic in composition, with SiO2 contents of 60.00–75.16 wt.%, Al2O3 contents of 10.15–18.53 wt.%, an K2O contents of 2.95–4.28 wt.%. The REEs content ranges from 64.2 to 198.1 ppm, with LREE/HREE ratios of 7.67–17.47. It is characterized by adakitic geochemical affinities with high Sr/Y and (La/Yb)N ratios but low Y and Yb contents. A slight Eu anomaly, extreme depletion in Y and Yb, relatively low MgO content, and relatively high 207Pb/204Pb ratios together indicate that the Dongxiang granodiorite porphyry was likely derived from partial melting of the thickened lower continental crust. Based on zircon εHf(t) values (−11.8–−4.5), two-stage Hf model ages (1.33–1.94 Ga), and the regional geological setting, it can be inferred that Dongxiang granodiorite porphyry magma is mainly derived from Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust.