TDM Ages Research Articles

Tracing multiple sources of sediments using trace element and Nd isotope geochemistry: provenance of the Mesozoic succession in the Kutch Basin, western India

AbstractAn integrated approach involving Sr–Nd isotope, trace and rare earth element analyses tracks multiple sources of the Mesozoic sediments of the Kutch Basin at the western continental margin of India. High (87Sr/86Sr)t (ratio at time of deposition), negative εNd and high concentrations of large-ion lithophile elements (LILEs) indicate the upper continental source. Ratios of Nb/Ta and Zr/Hf suggest sedimentary and felsic igneous sources of sediments. The moderate to high concentration of La, Th and Sc, light rare earth elements (LREE-) enrichment, weak negative Eu anomalies and the relationship between εNd(0) and Th/Sc indicate the dominantly felsic composition of source rocks. However, low contents of Th, low values of (87Sr/86Sr)t and depleted mantle model age TDM < 1600 Ma indicate input from a younger mafic source. Increasing concentrations of Zr, Hf and Nd isotopes and a gradual increase in mean TDM from the older to the younger formations indicate erosional unroofing at the source terrain. The increasing (87Sr/86Sr)t through time relates to increased weathering of the source rock. The overwhelmingly southwesterly palaeocurrent direction of current-generated sedimentary structures, and the mean TDM ages trace suggest source areas of the Kutch Basin to Precambrian rocks in the north and NE of this basin. The TDM ages highlight the dominance of late Palaeoproterozoic source rocks. Nd isotope composition indicates that Proterozoic rocks of Marwar Supergroup and Erinpura Granite, in particular, served as main sediment contributors for the Mesozoic sediments in Kutch. We therefore conclude that the Mesozoic sediments in the Kutch Basin are predominantly of late Palaeoproterozoic age with lesser inputs from rocks of early Mesoproterozoic and early Palaeoproterozoic age.

Geochronology and sedimentology of the Huashan Group in the northern Yangtze Block: implications for the initial breakup of the South China

Middle Neoproterozoic sedimentary sequences are widespread in South China and provide crucial insights into the geological evolution of sedimentary basins related to the breakup of the Rodinia supercontinent. The Huashan Group is a key Neoproterozoic stratigraphic unit in the northern Yangtze Block, South China; however, its depositional age and tectonic setting of deposition are debated. Here, we report zircon U–Pb geochronology and Hf isotope data for a tuff from the second section of the Hongshansi Formation near the bottom of the Huashan Group. Zircon U–Pb geochronology yields a 206Pb/208U age of 836 ± 4 Ma (MSWD = 0.74, n = 29). Zircon Hf isotope ratios have eHf(t) values of + 3.1 to + 5.4 and TDM2 ages range from ca. 1.5 to 1.4 Ga, which indicates that juvenile materials derived from the mantle were involved in their host magmas. Combined with previous research, the Huashan Group was deposited from ca. 830 to 800 Ma from bottom to top, and it contains alluvial fan, fan delta, and semideep to deep lacustrine facies, which represent early sedimentation into a continental rift basin. Rifting and basin formation began at ca. 830 Ma in South China, which is coeval with the initial breakup of the Adelaidean Rift in southeastern Australia. The Huashan Group was deposited during the first and the second episodes of a superplume associated with the breakup of the Rodinia supercontinent.

Late Paleozoic igneous rocks in the Xing’an Massif and its amalgamation with the Songnen Massif, NE China

We present new zircon U–Pb–Hf isotopic and whole-rock geochemical data for late Paleozoic igneous rocks from the Xing’an Massif, Northeast China, to further our understanding of the amalgamation of the Xing’an and Songnen massifs. Zircon laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb ages indicate that late Paleozoic magmatism occurred in the Xing’an Massif over three stages: during the early Carboniferous (359–352 Ma), early late Carboniferous (327–320 Ma), and late Carboniferous–early Permian (307–295 Ma). The early Carboniferous igneous rocks are mainly quartz diorite, granodiorite, monzogranite, syenogranite, and rhyolite, and formed in an active continental margin setting related to the westward subduction of the Heihe–Nenjiang oceanic plate. The early late Carboniferous monzogranites are medium-K calc-alkaline I-type granitoids, with zircon εHf(t) values of +5.6 to +13.0 and TDM2 ages of 973–502 Ma, suggesting that the primary magma was derived from the partial melting of newly-accreted crust. The early late Carboniferous igneous rocks formed in collisional setting, marking the amalgamation of the Xing’an and Songnen massifs. The late Carboniferous–early Permian intrusive rocks are dominated by diorite, monzogranite, syenogranite, alkali-feldspar granite, and granite porphyry. The large volume of alkali feldspar granites and A-type granites suggested that they formed in a post-collisional extensional environment.

Petrogenesis of Late Carboniferous A-type granites and Early Cretaceous adakites of the Songnen Block, NE China: Implications for the geodynamic evolution of the Paleo-Asian and Paleo-Pacific oceans

The petrogenesis of Late Carboniferous A-type granites and Early Cretaceous adakites in NE China offers new insights into the geodynamic evolution of the Paleo-Asian and Paleo-Pacific oceans. This study reports new LA–ICP–MS zircon UPb ages, geochemical data, and zircon Hf isotopic compositions of syenogranites and quartz diorite porphyries exposed on the northern margin of the Songnen Block, NE China. Zircon UPb age data indicate that the syenogranites and quartz diorite porphyries were emplaced at ca. 319 and 120 Ma, respectively. The syenogranites have high K2O contents of 4.15–4.79 wt% and (K2O + Na2O)/CaO ratios of 33–102, and low MgO (0.06–0.20 wt%) and P2O5 (0.01–0.02 wt%) contents. Their remarkably high HREE contents and Y/Nb ratios (2.07–2.40), significantly negative Eu anomalies (Eu/Eu⁎ = 0.15–0.28), and low Sr contents (29.7–85.8 ppm) indicate that the syenogranites are A-type granites. They have positive zircon εHf(t) values of 8.4–12.1 and Neoproterozoic Hf TDM2 ages of 795–561 Ma, suggesting a juvenile lower crustal source. The quartz diorite porphyries have relatively high Na2O and MgO, and moderate K2O contents. Their A/CNK values (0.95–1.18) indicate a transition from being metaluminous to weakly peraluminous. They are enriched in LILEs (e.g., Rb, K, and Ba) and depleted in HFSEs (e.g., Nb, Ta, Ti, and P). Their low Y (11.1–14.4 ppm) and Yb (0.98–1.34 ppm) contents and high Sr (589–1131 ppm), Cr, and Ni contents and Sr/Y ratios indicate that they were generated by partial melting of oceanic crust. Based on these data and regional geological investigations, we propose that the syenogranites on the northern margin of the Songnen Block were formed in a post-collision extensional setting, likely due to closure of the Paleo-Asian Ocean between the Xing'an and Songnen blocks. Formation of the Early Cretaceous quartz diorite porphyries may have been triggered by partial melting of the Paleo-Pacific flat slab. Apart from rollback of the Paleo-Pacific oceanic slab, the main reason for the eastward migration of magmatism during the Cretaceous was the trench-ward dehydration, eclogitization, and sinking of the residual Paleo-Pacific flat slab.

Petrogenesis and geodynamic implications of Early Cretaceous highly fractionated leucogranites in the northern Lanping–Simao terrane, Eastern Tibetan Plateau

A felsic intrusion in the Guaguazi Cu mining district in the northern Lanping–Simao terrane, Eastern Tibetan Plateau was revealed through drill holes and is composed of highly fractionated leucogranites. In this paper, we report zircon U–Pb ages and whole-rock compositions to constrain the petrogenesis and geodynamic setting of this intrusion. Zircon grains separated from two leucogranite samples have identical U–Pb ages of 123.9 ± 2.0 Ma and 123.6 ± 1.9 Ma, indicating that the crystallization age of the intrusion is Early Cretaceous (ca. 124 Ma). Leucogranites from the intrusion have SiO2 contents from 74.3 to 77.6 wt% with differentiation index values of 96.3–97.6, indicative of highly fractionated nature. They are weakly peraluminous (A/CNK = 1.01–1.10) and have light REE enrichment ((La/Yb)N = 5.4–8.5) and negative Eu anomalies (Eu/Eu* = 0.26–0.45). The primitive-mantle-normalized spider diagram indicates strong enrichment in large-ion lithophile elements (Rb, Th, U, K, and Pb) relative to high-field-strength elements (Nb, Ta, P, and Ti). The high initial 87Sr/86Sr ratios (0.7070–0.7094) and negative εNd(t) values (−8.18 to −7.20) and TDM2 ages of 1.58–1.51 Ga of the rocks, suggest that their source was predominantly Mesoproterozoic lower continental crust with insignificant mantle contribution. High initial 207Pb/204Pb (15.74–15.75) and 206Pb/204Pb (18.51–18.63) ratios further confirm their crustal source and highly evolved nature. Considering the petrogenetic similarity of Early Cretaceous granitoids in the Guaguazi area and the Gaoligong tectonic belt, we propose that the eastern Bangong–Nujiang Tethyan Ocean was closed at least no later than the Early Cretaceous, and that the Guaguazi granitic intrusion formed in a crustal thickening setting in response to the Lhasa–Qiangtang collision.

Constraining provenance for the uraniferous Paleoproterozoic Francevillian Group sediments (Gabon) with detrital zircon geochronology and geochemistry

The Paleoproterozoic sandstones of the ca. 2.1 Ga Francevillian Group, southeast Gabon, host the oldest known redox-controlled high-grade uranium (U) deposits. Uranium-bearing detrital minerals (e.g., monazite) in the Francevillian Group sediments were derived by erosion of Archean basement rocks from the East Gabonian block of the northwestern Congo craton surrounding the Francevillian Basin. They are viewed as primary sources for U, but the nature of these sources remains poorly constrained. Here, U-Pb ages and Hf isotope data for detrital zircon grains are combined with literature geochemical data for igneous rocks from the Archean basement, to characterize the nature, age, and origin of the provenance for the Francevillian Basin and the ultimate source of U for the high-grade uranium deposits.Detrital zircon ages range from ca. 3.1 to 2.6 Ga with a dominant population between ca. 2.90 and 2.80 Ga, suggesting a major contribution from ca. 2.88 to 2.81 Ga high-K granitoids with a limited contribution from ca. 3.1 to 2.84 Ga TTGs and 2.75 to 2.7 Ga granitoids of the East Gabonian block. Most detrital zircon grains share similar depleted-mantle Hf model ages between ca. 3.08 and 3.30 Ga, indicating significant recycling of a Paleoarchean to Mesoarchean crust. We suggest that ca. 2.9 to 2.8 Ga high K, U, and Th granitoids, which reflect hybrid melts of both mantle and crustal parentage were the major detrital sources of U to the Francevillian Basin and, ultimately, for the U deposits. We propose that ca. 2.9 to 2.8 Ga detrital zircons with Hf TDM ages between ca. 3.1 and 3.3 Ga may thus allow for vectoring U deposits in sedimentary basins across the Congo craton.

Petrogenesis and Mo prospecting significance of Sadaigoumen granites on the northern margin of the North China Craton

The Sadaigoumen porphyry Mo deposit lies on the northern margin of the North China Craton. Molybdenum mineralization occurs mainly as veins and veinlets, or is disseminated within alkali feldspar granite and granite porphyry, which yield weighted-mean 206Pb/238U ages (±2σ) of 243.7 ± 1.6 to 242.2 ± 2.0 Ma and 240.0 ± 1.7 Ma, respectively. ReOs dating of molybdenite from Stage 3 mineralization yields an isochron age of 238.0 ± 1.9 Ma. The Sadaigoumen ore-related granites have petrological, mineralogical, and geochemical characteristics of I-type granite. Ore-related granites exhibit low (87Sr/86Sr)i ratios of 0.710256–0.711463, negative εNd(t) values of −16.4 to −15.4 with corresponding TDM2 (Nd) ages of 2061–1870 Ma, and negative εHf(t) values of −21.2 to −11.2 with corresponding TDM2 (Hf) ages of 2614–1983 Ma, indicating that the primary magma was derived by partial melting of ancient lower crust. In chondrite- and primitive-mantle-normalized trace element diagrams, the Sadaigoumen ore-related granites are characterized by moderate enrichment of light rare earth elements (REE) relative to heavy REE, moderate to strong negative Nb, Ta, Zr, Hf, and Ti anomalies, and increasing Rb/Sr ratios with decreasing Sr content, all attributed to fractional crystallization. Fractionation of amphibole, muscovite, and possibly minor biotite and garnet (and/or zircon) produced the variations in most elements. Together with the regional geology, the data imply that the Sadaigoumen ore-related granites and corresponding mineralization formed in a syn-collision to post-collision transitional setting during the Early–Middle Triassic. These fractionated Triassic alkaline granites or syenogranites potentially contain new porphyry Mo deposits.

Geochronology, Geochemistry and Hf Isotope of the Late Mesozoic Granitoids from the Lushi Polymetal Mineralization Area: Implication for the Destruction of Southern North China Craton

The North China Craton (NCC) is the best example of an Archean craton that has lost its stability in the Late Mesozoic. Although the cratonic destruction is generally considered to have occurred in the Eastern Block and reached a peak in the Early Cretaceous, the exact areal extent of cratonic destruction is debated, especially the southern and northern margin of the NCC. Here we report geochronology, geochemical and Hf isotopic data of the Late Mesozoic granitoids from Lushi polymetal mineralization area (LPMA) in the southern margin of NCC. These results provide new insights into the destruction in the southern margin of the NCC during the Late Mesozoic. Zircon U-Pb dating indicates that eight granitoids intruded in the Late Jurassic to Early Cretaceous (136.8-154.1 Ma), respectively. Geochemical signatures define these granitoids being A-type or I-type granite that formed in an extension setting. In addition, Hf isotopic compositions of zircons from these granitoids vary in a relatively large range, with eHf(t) values and TDM2 ages ranginge from -26.1 to +15.2 and 215 to 2 849 Ma, respectively. The parental magmas were likely derived from diverse sources, including materials of the partial melting of ancient lower crust and mantle-derived mafic magmas in various proportions. Combining with previous studies on the contemporaneous magma-tectonic activities in circum of NCC, we suggest that the rim of NCC was already unstabilized from the Late Jurassic in the LPMA. The subduction of the Paleo-Pacific Plate was the main trigger to the destruction of the southern margin of NCC, which was responsible for the lithospheric extension and thinning, extensive magmatism and mineralization.

Late Neoarchean granites in the Qixingtai region, western Shandong: Further evidence for the recycling of early Neoarchean juvenile crust in the North China Craton

The Neoarchean basement rocks of the Qixingtai region in the northwest of western Shandong, eastern North China Craton are divided into western and eastern domains, separated by a ductile shear zone. The western domain is mainly composed of early Neoarchean tonalitic and supracrustal rocks, and the eastern domain is composed of late Neoarchean crustally‐derived granite with diverse early Neoarchean enclaves up to several kilometres long of supracrustal and gneissic TTG‐diorite rocks. This study reports an integrated field, whole‐rock geochemistry and zircon U–Pb‐Hf study on the granites and their enclaves in the eastern domain. The supracrustal enclaves are mainly composed of meta‐basaltic and meta‐ultramafic rocks and are the same in lithological association and formation time as the 2,750–2,700 Ma Liuhang “Formation” in the western area. The TTG‐diorite enclaves can be divided into early and late groups. Magmatic zircons from early TTG‐diorite samples have U–Pb ages of 2,731 ± 17 to 2,748 ± 13 Ma and εHf(t) values of +2.7 to +9.5, whereas trondhjemite samples of the late group have U–Pb zircon ages of 2,588 ± 18 to 2,606 ± 12 Ma and εHf(t) values of +0.6 to +6.5. The Hf isotopic signatures on magmatic zircon from the >2,700 Ma diorite‐tonalites indicate that they are predominantly juvenile crustal additions, probably with minor involvement of older crust in their genesis, as given by tDM (Hf) ages ranging back to 2.92 Ga. The eastern granites range from monzogranite to syenogranite in composition and commonly have negative Eu anomalies, indicating residual plagioclase in the source region. Magmatic zircons from two granite samples have U–Pb ages of 2,516 ± 24 and 2,527 ± 18 Ma and εHf(t) values of +1.0 to +7.0. A fine‐grained syenogranite dyke contains inherited early Neoarchean zircons with εHf(t) values of +1.6 to +7.4. The isotopic signatures of the late Neoarchean granites that dominate the eastern domain show that they were derived from partial melting recycling of older continental crust recognized in the region – early Neoarchean rocks formed as a result of juvenile crustal additions. This is a common signature for late Archean crustal evolution throughout much of the North China Craton, and is the hallmark of some other Archean terranes, such as the Dharwar Craton of south India. The geodynamic explanations for the formation globally of vast amounts of crustally‐derived late Neoarchean granite are discussed.

Geochemical characteristics of igneous host rocks of Lubin-Zardeh Au-Cu deposit, NW Iran

The Lubin-Zardeh Au-Cu ± Pb ± Zn deposit is located in the Azerbaijan-Western Alborz zone, 45 km NE of Zanjan, Iran. It is situated within the Eocene-Oligocene volcanic-plutonic belt of the Tarom subzone of the Alborz mountains range. Quartz monzonite and tuffs are the main host rock of the Lubin-Zardeh Au-Cu ± Pb ± Zn deposit. Granitoid rocks are predominantly high- K, calc-alkaline with shoshonitic affinities. They are I-type, metaluminous, magnesian and are characterized by LILE, LREE and Th enrichment relative to HFSE, depletion in Nb, Ta, Ti and weak depletion in HREE and Y. These granitoids show some affinities with adakites, e.g., high Sr/Y and La/Yb ratios coupled with low Yb and Y, and enrichment in LREE and LILE with weak Eu anomalies. Their relatively low to moderate initial 87Sr/86Sr values (0.7047–0.7051), positive Nd (t = 36 Ma) values (0.39–2.1) and TDM ages of 0.69 to 1.06 Ga, with Pb isotopic ratios of initial 206Pb/204Pb = 18.49–18.68, initial 207Pb/204Pb = 15.58–15.61 and initial 208Pb/204Pb = 38.33–38.77, are consistent with a phlogopite-bearing, amphibole-rich, and enriched lithospheric mantle source metasomatized by earlier subducted sediments. The geochemical and isotopic compositions of the granitoids are similar to the host rocks of porphyry and epithermal deposits in the Urumieh–Dokhtar zone.

New U[sbnd]Pb, Hf and O isotope constraints on the provenance of sediments from the Adelaide Rift Complex – Documenting the key Neoproterozoic to early Cambrian succession

The Adelaide Rift Complex is arguably one of the most complete and best studied Neoproterozoic to early Cambrian successions worldwide, preserving evidence of the breakup of Rodinia, two Cryogenian glaciations and the interglacial phase, and one of the best documented Ediacaran to early Cambrian biotic transitions. However, the complex and protracted tectono-sedimentary history of this 0.8–0.5 Ga province is still being debated. We present new and published UPb ages and Hf and O isotope data for detrital zircons from the Adelaide Rift Complex, representing the most complete assembly of such data for this succession. Deposition during initial mid-Tonia extension was largely sourced locally from rift shoulders. As the basin evolved from rift- to sag-phase following continental breakup in the Cryogenian the provenance regions extended to more distal late Mesoproterozoic terranes to west and northwest. New data from Sturtian Glacial Epoch deposits are consistent with termination of this event at 0.66 Ga, with most deposition during deglaciation. Uplift of the Musgrave region during the Ediacaran to early Cambrian Petermann Orogeny led to dominant sediment supply from that terrane at that time in the north. In the south, earliest Cambrian deposition followed local tectonism, initially revitalising local proximal basement sources. An abrupt change in provenance occurred at the base of the Cambrian Kanmantoo Group, the youngest sediment package in the south. Paleocurrent data indicates transports from the south, probably from formerly contiguous Antarctica, possibly reflecting the onset of convergent tectonics and deposition in a foreland basin, consistent with the near depositional age of the dominant detrital zircon population. Whilst several episodes of significant crustal reworking are identified in the Hf and O isotope data, many of the zircon TDM ages lie within 0.5 Ga of the UPb ages indicating that new additions from the mantle were common in the provenance regions.

Neoarchean suprasubduction zone ophiolite discovered from the Miyun Complex: Implications for Archean–Paleoproterozoic Wilson cycle in the North China Craton

The North China Craton (NCC) offers a window to Archean–Paleoproterozoic crustal evolution. Following the amalgamation of microblocks during Neoarchean, the NCC witnessed another protracted Wilson cycle in the Paleoproterozoic with subduction-accretion-collision process. Here we report a newly identified suprasubduction zone ophiolite suite from the Miyun complex in the NCC where a rare and near-complete ophiolite succession is preserved including serpentinite, lherzolite, olivine clinopyroxenite, websterite, gabbro, dolerite, diorite, monzonite, metabasalts and trondhjemite, in association with Banded Iron Formation (BIF). The geochemical features of the suite are consistent with those of suprasubduction ophiolite complexes, with the mafic and intermediate members displaying Island Arc Tholeiite (IAT) and Mid-Ocean Ridge Basalt (MORB) affinity. Zircon grains from lherzolite define three groups of 207Pb/206Pb weighted mean ages at 2500 ± 12 Ma marking the formation age, and 2237 ± 47 Ma, and 1843 ± 30 Ma representing subsequent thermal events. The majority of zircon grains in olivine clinopyroxenite, gabbro, and quartz monzonite yield 207Pb/206Pb weighted mean ages of 2510 ± 19 Ma, 2495 ± 10 Ma, and 2486 ± 21 Ma respectively. Those from the trondhjemite show weighted mean age of 2476 ± 9.4 Ma. The compiled age data from all the rock types in the Miyun suite show two distinct age peaks at ca. 2486 Ma and 1832 Ma, corresponding to the timing of magma differentiation and subsequent metamorphism. The zircon Lu-Hf isotope data display distinct positive ɛHf(t) values in the range 0.35–7.05, suggesting magma derived from Neoarchean to Paleoproterozoic depleted mantle (juvenile) source. The zircon TDM ages show a peak at 2670 Ma, confirming Neoarchean components. The timing of magma formation in the Miyun ophiolite is broadly identical to those of the other rare Neoarchean – early Paleoproterozoic ophiolite suites described from the NCC including those from Yishui and Zunhua. Furthermore, evidence from the recently reported Alaskan-type intrusions and arc root mafic-ultramafic complexes around Miyun complex with ages in the range of 2.4–2.0 Ga suggest continued subduction-related magmatic processes, with final collision in latest Paleoproterozoic at around 1.84 Ga. We propose that following the assembly of ancient microblocks along multiple zones of ocean closure marked by major greenstone belts of 2.6–2.5 Ga, and high-grade metamorphism along the margins of the microblocks during Archean–Paleoproterozoic transition, the NCC went through another major Wilson cycle from early to late Paleoproterozoic involving prolonged subduction, accretion and collision of larger crustal blocks and intervening arc complexes, leading to final cratonization.

Geochronology, Geochemistry, and Pb–Hf Isotopic Composition of Mineralization-Related Magmatic Rocks in the Erdaohezi Pb–Zn Polymetallic Deposit, Great Xing’an Range, Northeast China

Late Mesozoic intermediate–felsic volcanics and hypabyssal intrusions are common across the western slope of the Great Xing’an Range (GXAR). Spatiotemporally, these hypabyssal intrusions are closely associated with epithermal Pb–Zn polymetallic deposits. However, few studies have investigated the petrogenesis, contributions and constraints of these Pb–Zn polymetallic mineralization-related intrusions. Therefore, we examine the representative Erdaohezi deposit and show that these mineralization-related hypabyssal intrusions are composed of quartz porphyry and andesite porphyry with concordant zircon U–Pb ages of 160.3 ± 1.4 Ma and 133.9 ± 0.9 Ma, respectively. These intrusions are peraluminous and high-K calc-alkaline or shoshonitic with high Na2O + K2O contents, enrichment in large ion lithophile elements (LILEs; e.g., Rb, Th, and U), and depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Zr, and Hf), similar to continental arc intrusions. The zircon εHf(t) values range from 3.1 to 8.0, and the 176Hf/177Hf values range from 0.282780 to 0.282886, with Hf-based Mesoproterozoic TDM2 ages. No differences exist in the Pb isotope ratios among the quartz porphyry, andesite porphyry and ore body sulfide minerals. Detailed elemental and isotopic data imply that the quartz porphyry originated from a mixture of lower crust and newly underplated basaltic crust, while the andesite porphyry formed from the partial melting of Mesoproterozoic lower crust with the minor input of mantle materials. Furthermore, a magmatic–hydrothermal origin is favored for the Pb–Zn polymetallic mineralization in the Erdaohezi deposit. Integrating new and published tectonic evolution data, we suggest that the polymetallic mineralization-related magmatism in the Erdaohezi deposit occurred in a back-arc extensional environment at ~133 Ma in response to the rollback of the Paleo-Pacific Plate.

Petrogenesis and tectonic setting of the Bolong ore-bearing granodiorite porphyry in the Bangongco–Nujiang metallogenic belt, northwestern Tibet: Evidence from geochemistry, zircon U[sbnd]Pb ages, and Sr–Nd–Pb–Hf isotopes

The giant Bolong porphyry Cu deposit (with proven Cu resources of 2.08 Mt. and 0.9 t Au) is located in the Bangongco–Nujiang metallogenic belt, northwestern Tibet. Copper mineralization has a genetic relationship with the granodiorite porphyry. Zircon laser ablation inductively coupled plasma mass spectrometry UPb dating gives crystallization ages of 124.5 ± 1.1 and 121.4 ± 0.6 Ma (Early Cretaceous) for the first and second stages, respectively, of the Bolong ore-bearing granodiorite porphyry. Geochemical analysis indicates that the Bolong ore-bearing granodiorite porphyry samples exhibit obvious light rare earth element enrichment, high initial ratios of 87Sr/86Sr (0.7076–0.7098) and low values of εNd(t) (−7.7 to −3.5), with TDM2(Nd) ages of 1.21 to 1.55 Ga. Ratios of (206Pb/204Pb)t, (207Pb/204Pb)t, and (208Pb/204Pb)t are 16.96–17.79, 15.48–15.52, and 36.72–37.74, respectively. Zircons yield εHf(t) values of −1.3 to 9.1 and 2.7 to 10.5 and TDM2(Hf) ages of 0.59–1.26 Ga. These isotopic signatures suggest that the primary magma of the Bolong ore-bearing granodiorite porphyry originated mainly from mixing of crust-derived felsic and metasomatized mantle-wedge-derived mafic melts. The Bolong ore-bearing granodiorite porphyry rocks have high logfO2 values ranging from −14.56 to −11.3 and −14.19 to −11.4 respectively, corresponding to △FMQ +1.7 to △FMQ +2.6 and △FMQ +2.2 to △FMQ +2.8, respectively. The Bolong porphyry CuAu deposit formed in a continental arc tectonic setting, during the northward subduction of the Bangongco–Nujiang Ocean in the Early Cretaceous.

Origin of the Triassic Lincang granites in the southeastern Tibetan Plateau: Crystallization from crystal mush

The crustal generation of the Paleo-Tethys orogenic belt in the southeastern Tibetan Plateau is a major unresolved geological problem. The Changning-Menglian suture in the southeastern Tibetan Plateau represents a remnant of the Paleo-Tethys Ocean. The Lincang batholith and associated volcanic rocks (the Manghuai rhyolites and Xiaodingxi basalts) are located to the east of the Changning-Menglian suture, and represent important constraints for the abovementioned geological problem. New zircon UPb ages, together with previously published results, indicate that the Manghuai rhyolites were emplaced at 229–239 Ma and the Lincang batholith yielded longer age span (211–239 Ma). Broad age span of zircons (to 28 million years) from these rocks record a long-lived crustal magmatic system in the Changning-Menglian Paleo-Tethys orogenic belt. These intrusive and associated volcanic rocks have significant differences between them in terms of geochemistry. In this study, these rocks are geochemically classified into three groups: (1) Group 1 comprises biotite granite and granodiorite rocks; (2) Group 2 includes alkali feldspar granite, two-mica granite, and rhyolite, which are high-silica (generally >70 wt%) rocks that have low TiO2, Al2O3, FeOtot, MgO, CaO, P2O5, Eu, and Sr contents, compared to those of Group 1. Based on their geochemical relationships and mineral textures, Groups 1 and 2 include cumulative- and fractionated-type granitoids, respectively; (3) while Group 3 is comprised of dioritic enclaves and the Xiaodingxi basalts. Based on more robust evidence, dioritic enclaves are derived from a mantle source magma. The Lincang granites have high and variable initial 87Sr/86Sr ratios (0.703122–0.728476), significantly negative εNd (t = 220 Ma) values (−13.4 to −7.5), negative εHf (t) values (−17.7 to −6.8), and old TDM2 ages. The Manghuai rhyolites and Xiaodingxi basalts have lower initial 87Sr/86Sr ratios (0.695970–0.709398), and higher εNd (t) values (−3.4 to −0.6) and εHf (t) values (−1.2 to +3.7) than those of the Lincang granites. Geochemical data suggest that the Manghuai rhyolites could be seen as fractionated and erupted melts from crystal mush reservoirs, which later crystallized to form the Lincang granites. The Manghuai rhyolites provide an instantaneous snapshot of the state of the crystal mush at the time of eruption. The Lincang granites are interpreted to record prolonged histories of open-system magmatic evolution, involving magma mixing, wall-rock assimilation, and multiple cycles of crystallization from the crystal mush reservoirs. Magmatic evolution was likely related to mantle upwelling in a post-collisional setting, forming large-volume granites and volcanics in the Changning-Menglian Paleo-Tethys orogenic belt. Thus, this crystal mush model provides an integrated picture of the Triassic silicic magmatism, linking the evolution of the Lincang batholith and Manghuai rhyolites before storage in the Changning-Menglian Paleo-Tethys orogenic belt.

Magmatic evolution and related W–Mo mineralization in the Larong deposit, eastern Tibet: Evidence from zircon U–Pb ages, geochemistry and Sr–Nd–Hf isotopes

The Late Cretaceous (ca. 92 Ma) Larong porphyry W–Mo deposit (39.44 Mt WO3 @ 0.1541%) is the first-discovered giant W–Mo deposit in the Leiwuqi-Zogang metallogenic belt, Sanjiang region. Multi-stage granitoids including the dacite porphyry (DP), granodiorite porphyry (GP), biotite granite porphyry (BGP), monzogranite porphyry (MP), biotite granite (BG), and granite aplite (GA) have been identified in the Larong deposit. However, the magmatic evolution and related W–Mo mineralization in this deposit are still poorly understood. LA–ICP–MS zircon U–Pb dating of the DP, GP, BGP, MP, BG, and GA yield weighted mean 206Pb/238U ages of 214.0 ± 0.7 Ma, 213.8 ± 1.3 Ma, 104.4 ± 0.9 Ma, 93.9 ± 1.3 Ma, 91.7 ± 0.5 Ma, and 36.2 ± 0.6 Ma, respectively. The Late Triassic DP and GP should be classified as peraluminous (A/CNK values of 0.95–1.57) S-type granitoids. They are characterized by pronounced negative εNd(t) values (−10.01 to −13.92) and εHf(t) values (−8.5 to −16.6) with old TDM2(Nd) and TDM2(Hf) ages (1.81–2.12 Ga and 1.79–2.30 Ga, respectively), indicating that the DP and GP were mainly derived from partial melting of ancient crustal materials after break-off of the Paleo-Tethyan oceanic slab. The Late Cretaceous BGP, MP, and BG and Late Eocene GA have low A/CNK ratios (0.92–1.06), but high SiO2 (70.57%–77.34%) and differentiation index (DI = 87.55–98.06), similar to the characteristics of highly fractionated I-type granite. Detailed elemental (e.g., depletion in Nb, Ta, Ti, Sr, Ba, Eu, and P) and isotopic data (87Sr/86Sr(i) = 0.71192–0.72932; εNd(t) = −11.81 to −9.11; εHf(t) = −10.4 to 1.4) demonstrate that they were the result of magma mixing between ancient crust-derived melts and mantle-derived melts. The BGP was produced during the final stage of Bangong–Nujiang Tethyan ocean (BNTO) subduction, the MP and BG were formed under a post-collisional tectonic setting related to slab break-off of the BNTO, and the GA was likely associated with delamination of the thickened eclogitic lower crust together with lithospheric mantle. The W–Mo mineralization in the Larong deposit is genetically associated with the MP, with four favorable factors that can account for the formation of this deposit: (1) high W background, (2) multi-stage magmatism, (3) highly evolved, relatively oxidized, and F-rich magmatic system, and (4) sufficient calcium obtained by intense fluid-rock interaction.

Crust–mantle interaction during subduction zone processes: Insight from late Mesozoic I-type granites in eastern Guangdong, SE China

Zircon U–Pb dating and in-situ Hf–O isotopic compositions, combined with whole-rock geochemical and Sr–Nd isotope data, are systematically presented to constrain the timing and petrogenesis of the late Mesozoic granitoids in eastern Guangdong Province, SE China. Zircon U–Pb chronology shows that two intrusions were emplaced from the Middle Jurassic to Early Cretaceous (166–144 Ma). All the granitoids are classified as calc-alkaline I-type granites with highly diverse elemental and isotopic compositions. The systematic variations in zircon Hf–O isotopes show that the granites can be categorized into three groups. The Donggang granitic porphyries (166 Ma) have the highest zircon δ18O values of 6.3–8.2‰ (average of 7.7‰) but the lowest εHf(t) values of −8.0 to −1.4, with the oldest Hf model ages of 1.30–1.70 Ga. The Liuzhoushan monzogranites (144 Ma) have intermediate zircon δ18O values of 6.0–6.9‰ (average of 6.4‰) and εHf(t) values of −5.0 to 0.3, with Hf model ages of 1.17–1.51 Ga. The late Early Cretaceous granitoids have the lowest δ18O values of 4.9–6.6‰ (average of 5.5‰) but the highest εHf(t) values of −3.2 to 3.3, with the youngest Hf model ages of 0.95–1.36 Ga. Zircon saturation temperatures of the Donggang, Liuzhoushan, and Xinwei (Sanrao) intrusions are calculated to be 642 °C, 722 °C, and 748 °C, respectively. Together with the variations in Sr–Nd isotopes, it appears that these granitoids were derived from the mixing of different proportions of mantle-derived components with Paleoproterozoic basement crust-derived magmas. The underplating of mantle-derived magmas into the continental crust, which supplied both heat and material contribution, was likely responsible for the generation of the most late Mesozoic I-type granites in eastern Guangdong. From Middle Jurassic to late Early Cretaceous, the increasing εHf(t) and εNd(t) values as well as the decreasing δ18O values and TDM2 ages indicate a progressive role of the crust–mantle interaction, corresponding to a gradually enhanced extensional tectonic environment. The northeast (NE)-ward younging trend and the enhanced crust–mantle interaction along coastal SE China were probably induced by the changing direction of the subducted plate from oblique to parallel to the continental margin.

Generation and maturation of Mesoarchean continental crust in the Anshan Complex, North China Craton

The mechanisms underlying the generation of tonalite–trondhjemite–granodiorite suites and the transition to K-rich granitoids, which marks the most profound stage of Archean intracrustal differentiation, remain controversial. The Archean Anshan Complex (AAC) of the North China Craton (NCC) preserves diverse 3.8–2.5 Ga granitoids, providing an excellent opportunity to address these problems. We conducted a detailed field, petrological, geochemical, and zircon isotopic study on AAC units, demonstrating that: (1) the Li–Dong–Ying trondhjemite intrudes and encloses ca. 3.3 Ga gneiss–migmatite complex across the Anshan, and crystallized at ca. 3.14 Ga; and (2) the porphyritic and fine-grained Chentaigou monzogranites were emplaced contemporaneously with the trondhjemite, both at ca. 3.14 Ga.The Li–Dong–Ying trondhjemites show high SiO2, Na2O, low MgO, significant variations in Sr, Y, and Yb, REE fractionation (LaN/YbN = 9–140), and variable Eu anomalies (Eu/Eu* = 0.4–1.3). The magmatic zircons yield δ18O of +4.8 ± 0.2‰ to +6.9 ± 0.4‰ and initial εHf of −1.1 ± 0.7 to +4.4 ± 0.9, which translate to TDM ages of 3.6–3.3 Ga. The Chentaigou monzogranites have higher SiO2 and K2O, lower Na2O and CaO, similar δ18O of +5.1 ± 0.3‰ to +7.0 ± 0.3‰, and more negative Eu anomalies as compared with the trondhjemites. The Hf–O isotopes, geochemistry, particularly considerable variations in pressure-sensitive proxies of the trondhjemites, suggest that they were derived by melting of low-temperature altered basaltic rocks at 1.0–1.5 GPa and 900–950 °C, leaving a garnet amphibolite residue with variable amounts of plagioclase but no rutile; the most plausible source is ca. 3.3 Ga basaltic rocks. Polybaric melting of basaltic sources and fractionation of hornblende and plagioclase from trondhjemitic magmas account for the chemical variability of AAC granitoids, providing a mechanism for the coeval emplacement of diverse Archean granitoids. Secular compositional changes in AAC trondhjemites imply that the depth and interval of melting of basaltic sources increased from the Eoarchean to Mesoarchean. Changes in the nature of the source and melting depth characterized the early stage of Archean intracrustal differentiation in the NCC.

Late Mesozoic tectonic evolution of the southern Great Xing'an Range, NE China: Evidence from whole-rock geochemistry, and zircon U[sbnd]Pb ages and Hf isotopes from volcanic rocks

The large-scaled Mesozoic volcanic activities in the Great Xing'an Range, northeastern (NE) China, have received extensive attention recently. However, the details of the tectonic setting and geodynamic processes of the Late Mesozoic time are still controversial. In this paper, we examined the geochronology and geochemistry of the Late Mesozoic volcanic rocks collected from the southern Great Xing'an Range, in order to constrain the tectonic evolution of the Great Xing'an Range in the Late Mesozoic time. The compiled data show that the Late Mesozoic volcanic rocks can be divided into three stages: Middle-Late Jurassic felsic volcanic rocks (174–148 Ma), Early Cretaceous intermediate and intermediate-felsic volcanic rocks (142–125 Ma, peak at 138 Ma) and Early Cretaceous felsic volcanic rocks (140–120 Ma, peak at 125 Ma). The Middle-Late Jurassic felsic volcanic rocks in the southern Great Xing'an Range are geochemically similar to A-type granite or highly fractionated granite, which have εHf(t) values of (−0.7 to +12.1) and Hf two-stage model (TDM2; 549–1714 Ma), indicating they are derived from the magma generated by partial melting of thickened juvenile lower crust and formed in a post-collisional extensional setting related to subduction of the Mongol–Okhotsk oceanic plate. The Early Cretaceous intermediate and intermediate-felsic volcanic rocks have the characteristics of active continental margin arc, which have εHf(t) values of −11.6 to +13.0 and TDM2 ages of 449–2670 Ma, suggesting that these rocks are the product of partial melting of lithospheric mantle. They are metasomatized by subduction-derived fluids or melts and related to the flat-slab subduction of the Mongol-Okhotsk oceanic plate beneath the Great Xing'an Range after the rapid closure of the Mongol-Okhotsk Ocean. The Early Cretaceous felsic volcanic rocks in the study are dominated by A-type rhyolite, which are associated with coeval A-type granites, metamorphic core complexes and rift basins, suggesting they formed in an extensional environment related to either the subduction of the Paleo-Pacific oceanic plate beneath the Eurasian continent or the massive upwelling of the asthenosphere following the collapse of the Mongol–Okhotsk oceanic plate.

Geochemistry, geochronology and Hf isotope of granitoids in the northern Alxa region: Implications for the Late Paleozoic tectonic evolution of the Central Asian Orogenic Belt

The tectonic setting of the northern Alxa region during the Late Paleozoic is highly controversial. The key to resolve this controversy is to recognize the Late Paleozoic magmatic processes in the northern Alxa. In this paper, we present new zircon U–Pb ages, Hf-isotopic compositions and whole-rock geochemical data of four granitoids along the Zhusileng-Hangwula Tectonic Belt in the northern Alxa region that could provide critical information about the tectonic evolution of this region. The zircon U–Pb data could be grouped as two phases: Late Devonian granite and diorite (ca. 373–360 ​Ma), and Late Carboniferous granodiorite (ca. 318 Ma). The Late Devonian granites and diorites are metaluminous to slightly peraluminous, with A/CNK and A/NK ratios of 0.90–1.11 and 0.95–2.19, respectively. The Late Devonian diorites are characterized by high MgO, Cr and Ni contents and MgO# values, together with variable εHf(t) values from –1.0 to +1.3 and old TDM2 ages varied from 1283 ​Ma to 1426 ​Ma, indicating the primary magma was potentially derived from magma mixing of depleted mantle with Mesoproterozoic continental crust. Even though the Late Devonian granites yielded most positive and minor negative εHf(t) values between –1.1 to +5.7 (three grains are negative) with two-stage model ages (TDM2) of 1003–1438 Ma, they display low MgO, Cr and Ni contents and MgO# values, suggesting that they were mainly derived from juvenile crustal materials, mixed with a small amount of ancient crust. The Late Carboniferous granitoids are metaluminous and medium-K calc-alkaline series, with A/CNK and A/NK ratios ranging from 0.88 to 0.95 and 1.75 to 1.90, respectively. These rocks were potentially derived from juvenile crustal materials mixed with depleted mantle, as evidenced by their high εHf(t) values (+11.6 to +14.1) and young TDM2 ages (427 ​Ma to 586 ​Ma), as well as high Mg# values, and MgO, Ni and Cr contents. Our data, along with available sedimentary evidence and previous researches, indicate that the Late Devonian and Late Carboniferous rocks are arc-related granitoids under the subduction setting. The identification of arc-related granitoids in the northern Alxa region not only reveals the Late Paleozoic magmatic process in response to the subduction of Paleo Asian Ocean, but also provide significant constrains to the tectonic evolution of the Central Asian Orogenic Belt.