Zircon Hf Isotope Research Articles

Geochronology, Geochemistry, and Sr–Nd–Hf Isotopes of the Balazha Ore‐Bearing Porphyries: Implications for Petrogenesis and Geodynamic Setting of Late Cretaceous Magmatic Rocks in the Northern Lhasa Block, Tibet

AbstractThe study of Late Cretaceous magmatic rocks, developed as a result of magmatism and related porphyry mineralization in the northern Lhasa block, is of significance for understanding the associated tectonic setting and mineralization. This paper reports zircon chronology, zircon Hf isotope data, whole‐rock Sr–Nd isotope data, and geochemistry data of Balazha porphyry ores in the northern Lhasa block. Geochemical features show that Balazha ore‐bearing porphyries in the northern Lhasa block belong to high‐Mg# adakitic rocks with a formation age of ~90 Ma; this is consistent with the Late Cretaceous magmatic activity that occurred at around 90 Ma in the region. The age of adakitic rocks is similar to the molybdenite Re–Os model age of the ore‐bearing porphyries in the northern Lhasa block, indicating that the diagenesis and mineralization of both occurred during the same magmatism event in the Late Cretaceous. The Hf and Sr–Nd isotope data indicate that these magmatic rocks are the product of crust–mantle mixing. Differing proportions of materials involved in such an event form different types of medium‐acid rocks, including ore‐bearing porphyries. Based on regional studies, it has been proposed that Late Cretaceous magmatism and porphyry mineralization in the northern Lhasa block occurred during collision between the Lhasa and Qiangtang blocks.

Early Cretaceous volcanic and sub-volcanic rocks in the Erlian Basin and adjacent areas, Northeast China: new geochemistry, geochronology and zircon Hf isotope constraints on petrogenesis and tectonic setting

ABSTRACTEarly Cretaceous volcanic rocks are widely distributed in northeast China and being extensively observed recently. However, petrogenesis and tectonic setting of these volcanic rocks are still on debate. We present zircon U–Pb ages, whole-rock geochemistry and zircon Hf isotope for these volcanic and sub-volcanic rocks surrounding the Erlian Basin including basic-intermediate volcanic rocks, intermediate-felsic volcanic rocks, and dacites and trachyandesite from dikes. The zircon U–Pb dating results indicate that these rocks formed in the Early Cretaceous (146–129 Ma). The basic-intermediate volcanic rocks mainly consist of basaltic andesite, which are featured by low SiO2 concentrations (49.96–58.34 wt. %), high Mg# values (54–37) and Co contents (17.85–25.98 ppm), and positive εHf(t) values (+7.11 to +13.87). Moreover, they show high La/Nb (1.79–2.87) and low La/Ba (0.02–0.08) ratios. Such features indicate that they were derived from partial melting of lithospheric mantle that had been modified by fluids. The intermediate-felsic volcanic rocks consist of trachydacite and andesite, which show medium SiO2 concentrations (58.31–66.44 wt. %), a wide range of Mg# values (28–53) and with A1-type granites affinities. These features, along with slightly positive to negative εHf(t) values (+0.53 to −17.71), indicate that they originated from mixed magma of melted lower crust and mantle substances. Dacites from dikes are distinguished by high SiO2 concentrations (65.72–67.2 wt. %), negative εHf(t) values (−2.55 to −6.72) and old zircon Hf TDM2 ages (1453–1653 Ma), suggesting they were generated by melting of Mesoproterozoic and Palaeoproterozoic crustal material. All of the investigated volcanic and sub-volcanic rocks exhibit geochemical signatures of extension setting. In combination with previous studies, we suggest the Early Cretaceous extension in northeast China is related to the collapse of thickened lithosphere after closure of the Mongol–Okhotsk Ocean and to the slab break off of the Mudanjiang Ocean.

Petrogenesis of Triassic granite from the Jintan pluton in Central Jiangxi Province, South China: implication for uranium enrichment

Numerous Triassic biotite granites and two-mica granites crop out in the interior of South China, and some of them possess high U contents, which have been regarded as the sources for later hydrothermal mineralization. Their petrogenesis is therefore crucial for constraining the possible origins of the U enrichment. Here we report new LA-ICPMS zircon UPb ages, mineral geochemistry of biotite and muscovite, whole rock geochemical results and SrNd and zircon Hf isotope data from the Jintan pluton in Central Jiangxi Province, South China. LA-ICPMS zircon UPb dating indicates that both biotite granite (BG) and two-mica granite (TMG) in the Jintan pluton crystallized at ~220 Ma. The TMG have higher U contents (7.85 to 48.90 ppm, average18.44 ppm) than theBG (4.99 to 17.72 ppm, average 8.64 ppm). Both BG and TMG show negative whole-rock εNd(t)and zircon εHf(t)values and contain some inherited zircons. The TMG are strongly peraluminous (A/CNK = 1.13–1.33), contain abundant primary muscovite, and display S-type affinity on plots of Yvs Rb and Th vs Rb, suggesting that they are S-type granites. The BG also display S-type granite affinities on plots of Yvs Rb and Th vs Rb. The suites display similar SrNd isotope compositions (BG initial 87Sr/86Sr values = 0.711389 to 0.714225 and εNd(t) = −9.91 to −9.16, TMG initial 87Sr/86Sr values = 0.711832 and εNd(t) = −10.02) and are spatially associated, suggesting that the BG should also be classified as S-type granites. The TMG have higher zircon εHf(t)values (−6.4 to −1.1) than the BG (−8.7 to −3.7), indicating the TMG and BG might be derived from similar sediments but possibly with some distinct characteristics in their sources. The BG exhibit linear covariations in chemical compositions with relatively high total REE and light REE contents and MgO contents, while the TMG displays broader compositional variations but with relatively low total REE, light REE and MgO contents. Biotite geochemistry indicates the TMG formed in a more reduced magmatic system than the BG. The temperatures estimated by zircon saturation thermometry indicate the BG had distinctly higher magmatic temperatures than the TMG. The TMG display relatively high Al2O3/TiO2 ratios and low CaO/Na2O ratios than the BG but have higher Sr/Y and La/Yb ratios. The geochemical and petrological data suggest the BG were derived from clay-poor psammite sources at deeper levels with higher temperatures and higher oxygen fugacity, and underwent an extensive fractional crystallization, while the TMG was derived from clay-rich pelitic sources at higher levels and lower temperatures and oxygen fugacity with only limited fractional crystallization. We conclude that the combination of U-rich sources, physical-chemical conditions such as low partial melting temperature or low degrees of partial melting, a reduced environment and low REE and LREE contents of magmas controlled the U enrichment in TMG.

U–Pb ages and Hf isotopes of detrital zircons from pre-Devonian sequences along the southeast Yangtze: a link to the final assembly of East Gondwana

AbstractThe Early Palaeozoic geology of the South China Craton (SCC) is characterized by an Early Palaeozoic intracontinental orogen with folded pre-Devonian strata and migmatites, MP/MT metamorphic rocks and Silurian post-orogenic peraluminous magmatic rocks in both the Yangtze and the Cathaysia blocks. In this contribution, we present new zircon U–Pb ages and Hf isotope data for detrital zircons from the Neoproterozoic to Silurian sedimentary sequences in the southeastern Yangtze Block. Samples from Neoproterozoic rocks generally display a major peak at 900–560 Ma, whereas samples from Lower Palaeozoic rocks are characterized by several broader peaks within the age ranges 600–410 Ma, 1100–780 Ma, 1.6–1.2 Ga and 2.8–2.5 Ga. Provenance analysis indicates that the 900–630 Ma detritus in Cryogenian to Ediacaran samples was derived from the Late Neoproterozoic igneous rocks in South China that acted as an internal source. The occurrence of 620–560 Ma detritus indicates the SE Yangtze was associated with Late Neoproterozoic arc volcanism along the north margin of East Gondwana. The change of provenance resulted in the deposition of 550–520 Ma and 1.1–0.9 Ga detrital zircons in the Cambrian–Ordovician sedimentary rocks. The εHf(t) values of these detrital zircons are similar to those of zircons from NW Australia–Antarctica and South India. This change of provenance in the Cambrian can be attributed to the intracontinental subduction between South China and South Qiangtang, and the convergence of India and Australia when East Gondwana finally amalgamated.

New Insights into the Late Triassic Nadigangri Formation of Northern Qiangtang, Tibet, China: Constraints from U‐Pb Ages and Hf Isotopes of Detrital and Magmatic Zircons

AbstractWe report here U‐Pb age and in situ Hf isotopic results for detrital and magmatic zircons from one conglomerate and four tuffite samples from the Late Triassic Nadigangri Formation across the North Qiangtang depression, Tibet. Coupled with previously published data in the region, this paper proposes new insights into the geochronological framework for the Nadigangri Formation. The deposition ages of tuffite from top to bottom in the Woruo Mountain, Quem Co and Dongqu River, are 203 Ma, 226 Ma, 221.5 Ma and 221.1 Ma, respectively. The detrital zircons yield a younger cluster of ages of 201.5–225 Ma from the conglomerate of the Quem Co Formation. The Late Triassic Nadigangri Formation defines a temporal range approximately between 201 and 225 Ma (Norian‐Rhaetian), including three predominant groups of 220–225 Ma, 210–217 Ma and 201–205 Ma, which correspond with the three main rifting episodes of initial rifting, further rifting and final rifting. Positive εHf(t) value and low model ages in younger detrital zircons suggests a juvenile character. However, the Hf isotopes of magmatic zircons display the presence of reworked ancient crust with 1.1–1.8 Ga. These results provide strong constraints not only on the temporal range of the Late Triassic Nadigangri Formation, but also on the onset of the Qiangtang Mesozoic rift basin.

New Discovery and Zircon Hf Isotopic Composition of the Early Yanshannian Monzogranite in the Yingyangguan Group of Eastern Guangxi, China

New Discovery and Zircon Hf Isotopic Composition of the Early Yanshannian Monzogranite in the Yingyangguan Group of Eastern Guangxi, China

Petrogenesis and tectonic implications of Late Carboniferous continental arc high-K granites in the Dongwuqi area, central Inner Mongolia, North China

Central Inner Mongolia is located in the southeastern segment of the Central Asian Orogenic Belt (CAOB), and controversy has long surrounded its late Paleozoic tectonic evolution. Here, we present an integrated study of zircon U-Pb ages, whole rock major and trace elements, and zircon Hf isotopes for five less studied alkali feldspar granitic plutons in the Dongwuqi area to the north of the Erenhot-Hegenshan-Heihe suture zone. Zircon U–Pb dating by laser ablation-inductively coupled plasma–mass spectrometry (LA–ICP–MS) indicates that these granitic plutons were emplaced in the Late Carboniferous (315–300 Ma). The Late Carboniferous alkali feldspar granites belong to high-K calc-alkaline series and are evolved I-type granites. They are high in SiO2 (73.22–77.36%), and low in MgO (0.07–0.49%) with enrichments in light rare earth elements (LREEs), Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. The Dongwuqi granitic rocks are characterized by high positive zircon εHf(t) values (+7.6 to +15.1), and relatively young two-stage Hf model (TDM2) ages (364–835 Ma). These geochemical data, together the common miarolitic texture, indicate that they were derived from partial melting of juvenile arc-related mafic to intermediate rocks in the lower crust, and eventually emplaced in low-pressure conditions or at shallow crustal levels, with involvement of extensive fractional crystallization during magma evolution. Our new results, along with the published regional data, delineate a NE-trending Carboniferous continental arc belt (more than 1700 km) in the northern accretionary zone of the Erenhot-Hegenshan-Heihe suture. Accordingly, we invoke that the Dongwuqi Late Carboniferous high-K granites were emplaced in an active continental margin setting, which was probably related to the northwestward subduction of the Hegenshan oceanic plate beneath the Xing'an-Uliastai-Nuhetdavaa block.

Sources of Magmatic Rocks from the Deep-Sea Floor of the Arctic Ocean and the Central Atlantic: Evidence from Data on the U–Pb Age, Hf Isotopes, and REE Geochemistry of Zircons

The results of geochronological (U–Pb), isotope–geochemical (Lu–Hf), and geochemical (REEs) studies of young (MZ, KZ) and xenogenic (AR, PR) zircons from magmatic rocks of the Central Arctic rises of the Arctic Ocean (AO) and the crest zone of the Mid-Atlantic Ridge (MAR) are presented. The data obtained show that the depleted mantle could be a source of young (KZ) zircons of the MAR, whereas young (MZ) zircons of the MAR and all xenogenic (AR, PR) zircons of the AO and MAR are from crustal rocks of the continental lithosphere.

Crustal architecture and its controls on mineralisation in the North China Craton

Knowledge of the history of the Earth’s continents and the genesis of mineral deposits is poorly understood on a crustal-scale. This contribution combines geological and zircon Hf-isotopic data collected from igneous rocks associated with mineralisation to gain a better understanding of the nature of the growth of, and mineral genesis in the North China Craton. The new zircon U–Pb dates reported here are 2587 ± 62 Ma for syenogranite at Zanhuang in the northeast part of craton, 2552 ± 24 Ma for trondhjemitic gneiss and 2554 ± 29 Ma for metadiorite at Dengfeng in the eastern and central part of, and 2820 ± 6 and 2821 ± 32 Ma for tonalite at Lushan in the southeast part of the craton. Lu-Hf isotopic data collected from granitic rocks for this study yield εHf(t) values and Hf crustal model ages (TDMc) of 3–5.8 and 2580–2600 Ma for the syenogranite at Zanhuang, 1.9–7.4 and 2550–2580 Ma for trondhjemitic gneiss and metadiorite at Dengfeng, and 0.5–5.2 and 3120–2840 Ma for tonalite at Lushan. Six major magmatic events have been recognised throughout the region. The crustal growth and reworking of the craton includes Eo- to Mesoarchean, early Neoarchean, and Paleoproterozoic events. The consistency in the evolution of Neoarchean magmatism coupled with zircon Hf isotope systematics indicate that similar crustal growth and reworking were in action in the Eastern, Trans-North China, and Western blocks. The crust architecture indicated by Hf isotopic mapping of the North China Craton constrains the distribution of mineral deposits. The BIF-hosted Fe deposits are spatially related to juvenile or reworked crustal domains, with groups of deposits located internal to and at the margins of Archean terranes, and orogenic Au deposits are spatially associated with juvenile crustal domains.

A newly Found Biotite Syenogranite in the Huangshaping Polymetallic Deposit, South China: Insights into Cu Mineralization

The W-Sn-Mo-Cu-Pb-Zn polymetallic mineralization in the Huangshaping Deposit is associated with different types of Jurassic granitic intrusions such as quartz porphyry, granophyre and granite porphyry. In this study, we carried out detailed mineralogical, petrological, geochemical, zircon U-Pb geochronological and Hf isotopic studies on a newly found, Cu-mineralization-related fine-grained biotite syenogranite at Huangshaping. This syenogranite is mainly composed of quartz (40%), K-feldspar (30%), plagioclase (15%) and biotite (5%), enriching in SiO2 (75.58 wt.%–76.02 wt.%), K2O (5.24 wt.%–5.78 wt.%), Al2O3 (12.23 wt.%–12.46 wt.%), Rb (405 ppm–504 ppm), U (18.5 ppm–40.7 ppm), Th (47 ppm–52.3 ppm), Nb (49.6 ppm–57.5 ppm), and Cu (54 ppm–288 ppm) whereas depleting in P2O5 (0.01 wt.%), TiO2 (0.05 wt.%–0.06 wt.%), Ba (5 ppm–13.1 ppm), Sr (6.8 ppm–23.9 ppm) and Eu (0.04 ppm–0.05 ppm), with A1-type alkaline granite characteristics. Magmatic and hydrothermal zircons were separated from a Cu-mineralized syenogranite sample and yielded the 206Pb/238U concordant ages of 156.5±1.8 and 154.4±2.9 Ma, representing the intrusive age of the pluton and probable Cu-mineralization time at the Huangshaping Deposit, respectively. Zircon Hf isotopes suggest a crust-derived (partial melting of Paleoproterozoic basement) magma for the syenogranite, with some degree of crust-mantle interaction. We infer that the syenogranite is a transitional phase between the granophyre and the granite porphyry, not only contributed greatly to the Cu mineralization but also provided W-Sn polymetallic ore-forming metals for the Huangshaping Deposit.

Indian-derived sediments deposited in Australia during Gondwana assembly

Sedimentary exchanges across continents during the collisional assembly and lifespan of supercontinents provide a powerful way of testing the assembling process and configuration of supercontinents. The Ord Basin in north-western Australia contains mid-Cambrian shallow marine and deltaic sedimentary successions that post-date the ca. 650–520 Ma Paterson-Petermann Orogeny (PPO) but are synchronous with the ca. 530–470 Ma Kurgiakh Orogeny in north India. We report new U-Pb ages and Hf isotopes of detrital zircons from the mid-Cambrian Ord Basin that suggest Indian-derived sedimentary input to Australian Cambrian basins. Compilations of published Ediacaran-Ordovician samples from the Centralian Superbasin indicate that during the ca. 650–520 Ma PPO, the 1200–1100 Ma Musgrave province in central Australia was exhumed and fed sediments to the syn-PPO Centralian Superbasin. Soon after the PPO termination, the Musgrave province likely remained a topographic high and continued to supply detritus to the Amadeus and Officer basins that were fragmented from the Centralian Superbasin, supplemented by the ∼630 Ma granites of the Paterson orogen. Conversely, we conclude that the mid-Cambrian Ord Basin did not record similar sedimentary provenance from the Musgrave province. Rather, Indian-derived detritus travelled along the northeastern Gondwanan continental margin via longshore currents, and in turn incorporated Paterson granitic detritus, during the assembly of Gondwana (including the Kurgiakh Orogeny in north India). A broad provenance comparison between potential eastern Gondwanan source regions and relevant Asian neighbours suggests that South China and South Qiangtang are affiliated with northern India, but Lhasa appears to have had a mixed affiliation between India and Australia.

Zircon U-Pb geochronology, Hf isotopes and geochemistry of intrusive rocks in the Simorgh prospecting area, Lut Block, eastern Iran: petrogenesis and geological implications

The Simorgh prospecting area is located in the central part of the Lut Block in eastern Iran. The Lut Block, the eastern part of the Central Iranian Microcontinent (CIM), has a complex tectonic evolution and is characterized by extensive magmatic activities with a range of geochemical signatures. The Simorgh intrusions have features typical of calc-alkaline to high-K calc-alkaline rocks, metaluminous to slightly peraluminous and formed in a volcanic arc setting. Mineralization in the area is believed to be related to these intrusions. To better understand the petrogenesis of these intrusions, we report zircon U-Pb dating and Hf isotopes and whole rock geochemistry of two granites and one diorite. Age dating using Zircon U-Pb method on pyroxene diorite porphyry stock and two granite porphyry dikes revealed 24.85 ± 0.51 Ma, 25.37 ± 0.56 Ma and 25.94 ± 0.76 Ma ages respectively (late Oligocene, Chattian). Field observations and U-Pb dating indicate that there are at least two stages of emplacement: pre-mineralization intrusions (diorite porphyry) and syn-mineralization intrusions (granite porphyry, granodiorite porphyry and pyroxene diorite porphyry). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements (LILE) and light rare earth elements ((La/Yb)N = 9.26–14.48), and depletion in high field strength elements (HFSE) and heavy rare earth elements, as well as negative Eu anomalies (Eu/Eu* = 0.49–0.91). Zircon Hf isotope data from the Simorgh intrusive rocks show largely positive eHf(t) (average = 3.6 ± 2.0). Hf model ages are ranging from 720 to 1320 Ma, indicating its derivation from a relatively juvenile source. The presence of zircon xenocrysts may prove its contamination by older continental crust (Siderian).

Late Cretaceous granitic magmatism and mineralization in the Yingwuling W–Sn deposit, South China: Constraints from zircon and cassiterite U–Pb geochronology and whole-rock geochemistry

Numerous Late Cretaceous W–Sn deposits associated with granitic rocks were developed in the southern part of South China. However, the relationship among granitic magma, mineralization and tectonic setting remains disputed. The Yingwuling W–Sn deposit is spatially associated with K-feldspar granite and biotite granite in the southwestern part of Guangdong province, South China. LA-ICP-MS zircon U–Pb dating of K-feldspar granite, biotite granite and weathered ore-bearing granites yielded ages of ∼79 Ma, which agree well with the LA-ICP-MS cassiterite U–Pb age of 79.6 ± 0.9 Ma, indicating a close genetic link between the Yingwuling pluton and W–Sn mineralization. Geochemically, both K-feldspar granite and biotite granite show high SiO2, Na2O + K2O and low CaO, P2O5 contents, and they belong to shoshonitic series and high-K calc-alkaline series, respectively. High Rb/Sr ratios and low Nb/Ta and Zr/Hf ratios of the Yingwuling pluton indicate strong magmatic differentiation. Compared with K-feldspar granite, biotite granite experienced a higher degree of fractional crystallization as indicated by lower Fe2O3, TiO2, LREE, Sr, Eu, Ba and Zr contents and higher SiO2, HREE, Rb, Cs and Y contents. Their Sr and Nd isotope compositions (initial 87Sr/86Sr = 0.7027 and 0.7097; εNd(t) = −5.6 and −5.7) are less radiogenic than that of the South China basement. Thus, it is likely that some juvenile materials were involved in the formation of these granitic intrusions. This is also favored by the wide range of zircon Hf isotope values (εHf(t) = −6.6 to 0.8), which indicates mixing processes. A-type granite affinity of the Yingwuling pluton shows that it was possibly formed in an extensional setting. Late Cretaceous W–Sn deposits constitute an EW-trending belt from Guangdong to Yunnan provinces, which was compatible with the northward subduction of the Neo-Tethys plate rather than the northwestward subduction of the Pacific plate during Late Cretaceous. Combined with previous studies on magmatic rocks and tectonic activities during Late Cretaceous in South China, this study suggests that the subduction of the Neo-Tethys plate was most possibly responsible for the Late Cretaceous Yingwuling granitic intrusion and associated W–Sn mineralization.

Crustal Accretion and Reworking within the Khanka Massif: Evidence from Hf Isotopes of Zircons in Phanerozoic Granitoids

This paper presents a synthesis and analysis of geochronological, geochemical, and zircon Hf isotopic data of Phanerozoic granitoids within the Khanka massif, with the aim of revealing the accretion and reworking processes of continental crust within the massif. Zircon U-Pb dating indicates that Phanerozoic granitic magmatism within the Khanka massif can be subdivided into eight stages: Late Cambrian, Middle–Late Ordovician, Middle Silurian, Late Carboniferous, Early Permian, Middle–Late Permian to Early Triassic, Late Triassic–Early Jurassic, and Early Cretaceous. The zircon Hf isotopic compositions reveal that crustal accretionary events took place mainly in the Mesoproterozoic and Neoproterozoic. Through time, the zircon eHf(t) values gradually increase, indicating that the Phanerozoic granitic magmas were derived from the melting of progressively less ancient and more juvenile crust. The zircon eHf(t) values exhibit a gradual decrease with the increases in latitude, which implies that the amounts of ancient crustal components within the lower continental crust of the Khanka massif increased from south to north. At the same latitude range, the zircon Hf isotopic compositions also display some variations. We conclude, therefore, that significant horizontal and vertical heterogeneities existed in the lower continental crust of the Khanka massif during the Phanerozoic.

Petrogenesis and tectonic implications of early Paleozoic granitoids in East Kunlun belt: Evidences from geochronology, geochemistry and isotopes

The East Kunlun Orogenic Belt (EKOB) provides an important link to reconstruct the evolution of the Proto-Tethys and Paleo-Tethys realm. The EKOB is marked by widespread Early Paleozoic magmatism. Here we report the petrology, bulk geochemistry, zircon U–Pb dating and, Lu–Hf and Sr–Nd isotopic data of the Early Paleozoic granitic rocks in Zhiyu area of the southern EKOB. Based on the zircon U–Pb dating, these granitoids, consisting of diorite, granodiorite and monzogranite, were formed during 450–430 Ma the Late Ordovician to Middle Silurian. The diorite and granodiorite are high Sr/Y ratio as adakitic affinities, and the monzogranite belongs to highly fractionated I-type. Their (87Sr/86Sr)i values range from 0.7059 to 0.7085, εNd(t) values from –1.6 to –6.0 and the zircon εHf(t) values show large variations from +9.1 to –8.6 with Hf model ages (TDM2) about 848 Ma and 1970 Ma. The large variations of whole-rock Nd and zircon Hf isotopes demonstrate strong isotopic heterogeneity of the source regions which probably resulted from multi-phase underplating of mantle-derived magmas. Geochemical and isotopic studies proved that the diorite and granodiorite had been derived from partial melting of heterogeneous crustal source with variable contributions from ancient continental crust and juvenile components, and the monzogranites were representing fractional crystallization and crustal contamination for arc magma. The Early Paleozoic adakitic rocks and high-K calc-alkaline granitoids in the southern EKOB were likely emplaced in a continental marginal arc setting possibly linked to the southwards subduction of the Paleo Kunlun Ocean and the magma generation is linked to partial melting of thickened continental crust induced by underplating of mantle-derived magmas.

Triassic alkaline magmatism and mineralization in the Xiong'ershan area, East Qinling, China

The Qinling orogenic belt is a complex subduction–accretion–collision orogen that welded the North China Craton and the Yangtze Craton during the final continental collision in the Triassic. The Xiong'ershan area, located in east Qinling, exposes a typical Triassic syenite pluton and several contemporaneous Mo, Au, and Cu deposits. The aegirine–augite syenites and syenites from the Mogou pluton are characterized by alkalic to peralkalic (total alkali Na2O + K2O = 13.95–14.63 wt.%, CaO = 0.06–2.87 wt.%), and shoshonitic features (K2O = 11.86–14.34 wt.%). Zircon LA–ICP–MS U–Pb dating of the aegirine–augite syenite and syenite yield emplacement ages of 232.5 ± 0.6 and 221.8 ± 0.7 Ma, indicating multiple pulses of magmatism. Evidence from zircon Hf isotopes; occurrence of mafic microgranular enclaves; heterogeneous peralkaline composition; and wide ranges of MgO, Ni, and other trace elements suggest that the parental magma was mainly sourced from partial melting of Archean to Paleoproterozoic crustal sources, mixed with juvenile mantle‐derived mafic magmas. The Mogou pluton was probably emplaced in the tectonic transition from syn‐collision to post‐collision settings and accompanying slab break‐off process, from the commencement of collision at approximately 245 Ma and post‐collisional extension at approximately 210 Ma. Gold, molybdenum, and copper deposits formed during the interval of 255–208 Ma, and the close temporal and spatial relationship between these Triassic polymetallic deposits and the Mogou alkaline pluton invokes a genetic linkage. The heat source for magmatism and related metallogeny is correlated to a hot upwelling asthenospheric mantle that caused partial melting of the Archean to Paleoproterozoic crustal basement, resulting in magma mixing between the two end‐members.

Anorthosites from an Archean continental arc in the Dharwar Craton, southern India: Implications for terrane assembly and cratonization

Anorthositic rocks have attracted attention in terms of their possible role as the primordial crust of our planet, and also as markers of Archean-Paleoproterozoic plate tectonic regimes. Here we investigate the Konkanhundi gabbro-anorthosite suite from Peninsular India, adjacent to the major collisional suture between the Western and Eastern Dharwar cratonic blocks. The anorthosites display high Al2O3 contents with negative correlation against MgO, high CaO and Sr contents, and positive Eu anomalies indicating plagioclase flotation in the magma chamber. The pyroxenite and gabbroic rocks of the suite show high Ni, Cr, Co contents and geochemical features typical of pyroxene cumulation. LA-ICPMS U-Pb analyses of magmatic zircon grains yield weighted mean 207Pb/206Pb ages of 2601 ± 12 Ma for pyroxenite, 2616 ± 12 Ma for gabbro, 2615 ± 13 Ma and 2627 ± 14 Ma for anorthositic gabbro, 2594 ± 16 Ma for anorthosite, and 2605 ± 27 Ma for microgabbro. The age data from the different rock types in the anorthosite suite are broadly consistent, marking the emplacement time as ca. 2.6 Ga, and providing insights on one of the oldest anorthosite complexes in Peninsular India. Zircon grains in the surrounding TTG gneisses into which the gabbro-anorthosite suite was emplaced show weighted mean 207Pb/206Pb age of 3321 ± 11 Ma suggesting Mesoarchean basement. The zircon grains display high Th/U values and REE patterns typical of magmatic crystallization with enriched HREE, positive Ce and Sm anomalies, and negative Pr, Nd, Eu anomalies. Zircon Lu-Hf analysis yield negative εHf(t) values of −4.9–−0.7 with TDMC (two stage model ages) of 3123–3376 Ma for pyroxenite, −4.5–−1.7 and 3192–3366 Ma for gabbro, −5.3–0.9 and 3034–3410 Ma for anorthositic gabbro, and −3.9–-2.4 and 3221–3311 Ma respectively, suggesting the incorporation of Mesoarchean components within the Neoarchean magmatic suite. However, zircon grains in the TTG gneiss possess more ‘juvenile’ εHf(t) values in the range of −0.2–1.3 with TDMC in the range of 3554–3646 Ma. The zircon Hf isotopes and trace element data, together with the whole rock geochemical features suggest that the parent magma of the Konkanhundi gabbro-anorthosite suite was derived from subduction-related depleted mantle source that also incorporated continental crustal components. The time of emplacement of the gabbro-anorthosite complex broadly correlates with widespread arc magmatism and crust production as well recycling in other domains of the Dharwar Craton. We envisage multiple convergence of microblocks during craton assembly at the end of Archean in Dharwar, with the greenstone belts marking zones of paleo-ocean closure.

Origin of the ca. 50 Ma Linzizong shoshonitic volcanic rocks in the eastern Gangdese arc, southern Tibet

The origin of the Eocene shoshonitic rocks within the upper part of the extensive Linzizong volcanic succession (i.e., the Pana Formation) in the Gangdese arc, southern Tibet remains unclear, inhibiting the detailed investigations on the crust-mantle interaction and mantle dynamics that operate the generation of the coeval magmatic flare-up in the arc. We report mineral composition, zircon U–Pb age and zircon Hf isotope, whole-rock element and Sr–Nd–Hf isotope data for the Pana Formation volcanic rocks from Pangduo, eastern Gangdese arc in southern Tibet. The Pana volcanic rocks from Pangduo include basalts, basaltic andesites, and dacites. SIMS and LA-ICPMS zircon U–Pb dating indicates that the Pangduo dacites were erupted at 50 ± 1 Ma, representing the volcanic equivalent of the coeval Gangdese Batholith that define a magmatic flare-up at 51 ± 1 Ma. The Pangduo volcanic rocks are exclusively shoshonitic, differing from typical subduction-related calc-alkaline volcanic rocks. The basalts have positive whole-rock ƐNd(t) (+1.7) and ƐHf(t) (+3.8) with high Zr abundances (121–169 ppm) and Zr/Y ratios (4.3–5.2), most likely derived from the partial melting of an enriched garnet-bearing lithospheric mantle that was metasomatized by subduction-related components with input from asthenosphere. Compared to the basalts, similar trace elemental patterns and decreased whole-rock ƐNd(t) (−3.5 to −3.3) and ƐHf(t) (−2.5 to −1.6) of the basaltic andesites can be attributed to the input of the ancient basement-derived material of the central Lhasa subterrane into the basaltic magmas. The coherent whole-rock Sr–Nd–Hf isotopic compositions ((87Sr/86Sr)i = 0.7064–0.7069, ƐNd(t) = −6.0 to −5.2, ƐHf(t) = −5.6 to −5.0) and varying zircon ƐHf(t) (−6.0 to +4.1) of the dacites can be interpreted by the partial melting of a hybrid lower crust source (juvenile and ancient lower crust) with incorporation of basement-derived components. Calculations of zircon-Ti temperature and whole-rock zircon saturation temperature of the dacites, and clinopyroxene crystallization temperature of the basalts suggest that the Pangduo volcanic rocks are most likely derived from the high-temperature melting of the lithosphere (including lithospheric mantle and overlying continental crust) as a result of the slab breakoff of the Neo-Tethyan oceanic lithosphere.

Convergent continental margin volcanic source for ash beds at the Permian-Triassic boundary, South China: Constraints from trace elements and Hf-isotopes

Volcanic activity around the time of the Permian-Triassic boundary (PTB) has been proposed as a trigger for the associated biocrisis. Multiple claystone beds are prominent near the PTB sections in South China. Twenty one PTB ash beds from three sections at Shangsi, Jianshi and Meishan in South China were sampled and analyzed. Volcanic ash geochemistry indicate dacite and rhyolite compositions. Zircons from the ash layers yield comparatively low Nb/Hf and high Th/Nb ratios, falling in the range of arc/orogenic-related settings. Zircon Hf-isotope compositions show that εHf(t) values vary from −11.7 to 1.8, indicating involvement of both juvenile and ancient crustal components. The ash beds (SS27a, JS129, JS130, JS133,MS25, MS26) near the biotic extinction horizon display a large variation in εHf (t) and relatively positive average values, indicating input of juvenile mantle or crust, and implying rapid transit through the older basement of the South China Craton. Spatial and temporal distribution of ash beds from thirty one PTB sections worldwide reveal that volcanic ash beds occur mainly in, or proximal to, the Tethys region and were sourced locally. Integration of Hf-isotope and trace-element compositions from magmatic zircons suggests that the PTB volcanism occurred along the convergent continent margin in, or near, southwestern South China as a result of the closure of the Paleo-Tethys Ocean.

Identification of ca. 850 Ma high-temperature strongly peraluminous granitoids in southeastern Guizhou Province, South China: A result of early extension along the southern margin of the Yangtze Block

Strongly peraluminous granites are characterized by high A/CNK values (>1.1) and are important for understanding the regional tectonic regime. Here, we present integrated studies of zircon U–Pb ages, trace elements and Lu–Hf isotopes, whole-rock major and trace elements, and Nd isotope compositions for the newly discovered Nage granite porphyry in southeastern Guizhou Province. The porphyry has a crystallization age of 852 ± 5 Ma and shows wide ranges in SiO2 (64.5–72.51 wt%) and Al2O3 (13.08–19.34 wt%) contents, with low TiO2 (0.41–0.84 wt%) and P2O5 (<0.15 wt%) contents. All the samples are strongly peraluminous with A/CNK >1.1, and they have similar trace element patterns with depletion in high field strength elements (HFSE, e.g., Nb and Ta) and enrichment in large-ion lithophile elements (LILE, e.g., Rb, Th and U). Initial zircon Hf isotopes of the porphyry vary from εHf(t) = −7.6 to −0.6, whereas whole-rock Nd isotopes are relatively uniform with εNd(t) = −6.0 to −6.7. They record high zircon saturation temperatures (Tzr) (786–842 °C, mostly >810 °C), but low oxygen fugacity (logfO2 = −16 to −25, corresponding to ΔFMQ −3 to ΔFMQ −7) and emplacement pressure of <0.5 GPa. Major and trace elements, 10,000 Ga/Al ratios and Zr + Nb + Ce + Y values, show good correlations with Tzr, indicating that fractional crystallization may have played an important role. Although these granites show low P2O5 contents that decrease with increasing Rb, the high A/CNK (>1.1), K2O/Na2O (0.7–2.6; average 1.4) and CaO/Na2O (0.2–0.8; mostly >0.5) ratios suggest that clay-poor metasedimentary rock were dominant in the source. Combined with the Nd–Hf isotopes, we suggest that the Nage granite porphyry formed by anatexis of an immature arkose and greywacke source, which was a mixture of weathered juvenile igneous materials and minor recycled ancient crustal components. The ca. 850 Ma strongly peraluminous granites, along with coeval extension-related magmatism along the southwestern margin of the Yangtze Block, indicate an extensional environment started as early as ca. 850 Ma.