Oldest volcanic-hosted submarine iron ores in South China: Evidence from zircon U–Pb geochronology and geochemistry of the Paleoproterozoic Dahongshan iron deposit

The Dahongshan iron deposit is hosted in the Paleoproterozoic submarine metavolcanic rocks of the Dahongshan Group in the Yangtze Block, South China. LA-ICP-MS dating of hydrothermal zircon grains from the genetically associated albitite and dolomite albitite show ca. 2008 Ma ages that are consistent with the zircon ages from the host metavolcanic rocks (ca. 2012 Ma), and postdated the post-ore diabase dike (ca. 1724 Ma), marking the Dahongshan iron deposit as the oldest submarine volcanic-hosted deposit so far as known. The ore-hosting metavolcanic rocks in the Dahongshan deposit have low Ni (9.1–77.4 ppm), Cr (1.0–63.0 ppm) and Co contents (5.6–62.9 ppm), suggesting the fractionation of olivine, clinopyroxene and plagioclase within the magma chamber. The major and trace element features of the alkaline to tholeiitic metavolcanic rocks are consistent with high-degree partial melting of the mantle wedge metasomatized by melts enriched in high field strength elements (HFSEs), which were derived from the subducted slab in volcanic arc setting. Based on an evaluation of the morphology of orebody, ore fabrics, petrology and melt-fluid inclusions, as well as the geochemical characteristics of the major ore mineral (magnetite), we correlate the iron mineralization in the Dahongshan deposit with hydrothermal process induced by the high-temperature, high-salinity and Fe-rich brines derived through magmatic exsolution. The similar characteristic of Ce and Eu anomalies of the Dahongshan iron deposit and banded iron formations (BIFs) suggest that the Dahongshan deposit was formed in reducing environment, although the two types of iron ores were generated through distinct processes with hydrothermal processes dominating for the submarine volcanic-hosted iron deposits whereas the BIFs were formed through chemical precipitation.     

Mississippian volcanism in the south-central Andes: New U–Pb SHRIMP zircon geochronology and whole-rock geochemistry

In the northern extension of the Famatina and the southern Puna (NW Argentina) prominent rhyolitic volcanic rocks traditionally referred to as Ordovician are exposed, resting on metamorphic basement and covered by thick Late Paleozoic siliciclastic successions. We report new U–Pb SHRIMP ages from these rhyolites that show them to be of Mississippian (348–342 Ma) age, thus identifying a previously unknown volcanic event in this portion of western Gondwana. Whole-rock geochemistry and Sr–Nd isotopic analyses suggest a crustal source for these rocks but with a juvenile input (ε_Nd(t) between ? 2.91 and ? 0.3, and T_DM values between 1.09 and 1.1 Ga). This is different from the Early Paleozoic magmatism of western Argentina where crustal recycling took place without any involvement of mantle material. The Carboniferous magmatism is compatible with an extensional environment developed along the Terra Australis accretionary orogen as a result of tectonic switching processes. These rhyolites may be related to the coeval Mississippian A-type granites exposed to the east, in the Sierras Pampeanas, confirming the regional character of this magmatism.     

Early Paleozoic tectonic evolution of the Chinese South Tianshan Orogen: constraints from SHRIMP zircon U–Pb geochronology and geochemistry of basaltic and dioritic rocks from Xiate,NW China

Traditionally the Chinese South Tianshan has been regarded as a late Paleozoic orogenic belt. However, little is known about the early Paleozoic tectonic architecture of the region. This paper presents the first evidence of Cambrian–Ordovician MORB-type basalts and adakitic diorites on the southern margin of the Yili plate in China. Basalts from Xiate in southwestern Tianshan show a typical transitional (T-) MORB and ferrobasalt composition, which indicate a formation at a propagating spreading ridge. The basalts give a weighted mean ²⁰⁶Pb/²³⁸U crystallization age of 516.3 ± 7.4 Ma by SHRIMP U–Pb zircon dating and have experienced contact metamorphism due to the intrusion of a dioritic pluton. The dioritic pluton has a weighted mean ²⁰⁶Pb/²³⁸U crystallization age of 470 ± 12 Ma and geochemical characteristics resembling that of adakitic rocks. The pluton is considered to have been formed by partial melting of garnet amphibolites from thickened lower crust in arc or continental collision settings. The basalts and diorites are considered to outline the eastern extension of the early Paleozoic suture zone, the Nikolaev Line, which stretches east–west for hundreds of kilometers between the Northern Tianshan and Central Tianshan terranes of Kyrgyzstan. Our findings substantiate that the Yili and Central Tianshan plates were separated by the early Paleozoic Terskey ocean. The Terskey ocean probably closed during the early stage of the late Ordovician (Lomize et al. in Geotectonics 31(6):463–482, 1997), resulting in the final amalgamation of the Yili and Central Tianshan plates. Consequently, an early Paleozoic suture zone is documented in the Chinese Tianshan region, which is most likely represented by the North Nalati fault.     

Volcanism,mineralization and metamorphism at the Xitieshan Pb–Zn deposit,NW China: Insights from zircon geochronology and geochemistry

The footwall volcanic rocks of the Ordovician Tanjianshan Group in the world-class Xitieshan Pb–Zn deposit have experienced prolonged arc volcanism followed by strong metamorphism and deformation. This has resulted in a complex thermal history and led to ambiguity in interpretation of zircon geochronological results. An integrated study involving textural characterization, CL imaging, trace element analysis, Ti-in-zircon thermometry and LA-ICPMS U–Pb dating has provided tight constraints on the age and genesis of the zircon groups in the volcanic rocks. The temperature of metamorphism and deformation indicated by metacryst minerals and micro-structures in the volcanic rocks ranges from 550 to 650 °C, which partially overlaps with the lower temperature range of zircon crystallization (600–750 °C) calculated using the Ti-in-zircon thermometer. Cathodoluminescence images and trace element compositions confirm a magmatic origin for the zircons, which have also been variably altered by metamorphic fluids. Two ranges of U–Pb ages, 475–470 Ma and 460–450 Ma, have been obtained on typical magmatic zircons and are interpreted to represent pre-mineralization arc volcanism in the Xitieshan deposit. A younger age group of 440–430 Ma for the fluid-modified zircons is considered to record post-ore metamorphism during the North Qadaim Orogeny. Thus, we propose that the original exhalative ores at the Xitieshan Pb–Zn deposit formed at 450–440 Ma.     

Crustal stabilization:Evidence from the geochemistry and U–Pb detrital zircon geochronology of quartzites from Simlipal Complex,Singhbhum Craton,India

Cratonic stabilization was a critical crustal process during the Hadean to Archean for the formation of cratons.The understanding of how and where this process took place is significant to evaluate the architecture of continents.The Singhbhum Craton of eastern India has well preserved Precambrian volcanosedimentary sequences.The Simlipal volcano-sedimentary complex of Singhbhum Craton consists of circular bands of mafic volcanic rocks interlayered with quartzites/shales/phyllites.In the present study,we report petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U–Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton.The quartzites are texturally mature with sub-angular to sub-rounded quartz grains followed by feldspars embedded in a silty matrix.Based on modal compositions and major element ratios,these quartzites are categorized as quartz arenite and sub-lithic arenites.Trace element abundances normalized to Archean Upper Continental Crust(AUCC)display positive anomalies at U,Zr,Hf and negative anomalies at Nb.REE patterns are characterized by negative Eu anomalies(Eu/Eu^*=0.47–0.97)and flat HREE suggesting felsic provenance.These quartzites show depletion of LILE,enrichment of HFSE and transition metals relative to AUCC.High weathering indices such as CIA,PIA,and ICV are suggestive of moderate to intense chemical weathering.Low trace element ratios such as Th/Cr,Th/Sc,La/Sc,La/Co and Th/Co indicate a predominantly felsic source for these rocks.The overall geochemical signatures indicate passive margin deposition for these quartzites.Detrital zircons from the Simlipal quartzites yield U–Pb ages 3156±31 Ma suggesting Mesoarchean crustal heritage.The trace element geochemistry of detrital zircons suggests that the zircons are magmatic in origin and possibly derived from the 3.1 Ga anorogenic granite/granitoid provenance of Singhbhum Craton.These observations collectively indicate the Mayurbhanj Granite and Singhbhum Granite(SBG-III)provenance for these quartzites,thereby tracking the stabilization of the eastern Indian Shield/Singhbhum Craton back to Mesoarchean.     

Geochemistry and zircon U–Pb geochronology of the Pulang complex,Yunnan province,China

The Pulang complex is located tectonically at the southern margin of the Yidun–Zhongdian island arc belt in Yunnan province, China, and is closely related to formation of the Pulang copper deposit, which is the largest copper deposit in Asia. The Pulang complex can be divided into three intrusion stages based on contact relationships and petrological characteristics: (1) a first stage of quartz dioritic porphyry; (2) a second stage of quartz monzonitic porphyry; and (3) a third stage of granodioritic porphyry. The crystallization ages of these intrusion stages were determined by single-zircon U–Pb dating, yielding ages of 221.0 ± 1.0, 211.8 ± 0.5, and 206.3 ± 0.7 Ma for the first, second, and third stages, respectively. These dates, integrated with previous geochronological data and field investigations, indicate that the second-stage quartz monzonitic porphyry has a close spatial and temporal relationship with the large Pulang porphyry copper deposit. These age data, geochemical and Sr–Nd isotopic results suggest that the Pulang complex formed in the Indo-Chinese epoch (257 ～ 205 Ma) by multiphase intrusion of a mixture of mantle- and crust-derived magmas.     

Oligocene subduction-related plutonism in the Nodoushan area,Urumieh-Dokhtar magmatic belt: Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry

Geochemical data and Sr–Nd isotopes of the host rocks and magmatic microgranular enclaves (MMEs) collected from the Oligocene Nodoushan Plutonic Complex (NPC) in the central part of the Urumieh–Dokhtar Magmatic Belt (UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U–Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene (middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene (latest Chattian) for granodioritic and diorite porphyry units, respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite (SiO₂ = 47.73–57.36 wt.%; Mg# = 42.15–53.04); the host intrusions are mainly granite, granodiorite and diorite porphyry (SiO₂ = 56.51–72.35 wt.%; Mg# = 26.29–50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs) and heavy rare earth elements (HREEs). These features, combined with a relative depletion in Nb, Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display I_Sr = 0.705045–0.707959, ε_Nd(t) = −3.23 to +3.80, and the Nd model ages (T_DM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with I_Sr ranging from 0.705513 to 0.707275 and ε_Nd(t) from −1.46 to 4.62. The MMEs have T_DM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust- and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle (SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr–Nd isotope data indicate that ∼50% to 90% of the lower crust-derived melt and ∼10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast, ∼45%–65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma (∼35%–55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.     

The late Neoarchean transition from low- to high-K granitoids in western Liaoning Province,NE China: Clues from geochemistry and zircon U–Pb–Hf–O isotopes

High-K granitoids are among the most abundant rock types in many Archean cratons. Late Neoarchean monzogranitic to syenogranitic gneisses with high-K affinities are widely distributed in the Anshan, Suizhong, Qinhuangdao, and Aolaishan areas on the northeastern margin of the North China Craton (NCC). In this contribution, we present an integrated study of zircon U–Pb–Hf–O isotopic compositions and whole-rock elemental compositions of amphibolites and trondhjemitic and monzo–syenogranitic gneisses of the Jinzhou area in the metamorphic basement of eastern Hebei–western Liaoning, with the aim of constraining their petrogenesis and geodynamic setting. Emplacement ages of the amphibolites and trondhjemitic–monzogranitic gneisses are 2543 ± 27, 2532 ± 19, and 2513 ± 7 Ma, respectively. The amphibolites are tholeiitic in composition with SiO₂ contents of 49.7–50.8 wt%, variable degrees of light rare-earth-element (LREE) enrichment and high-field-strength element (HFSE) depletion, and high zircon εHf(t) values of +2.6 to +6.3, suggesting a depleted lithospheric mantle origin. The major- and trace-element compositions of the trondhjemitic gneisses are similar to those of the low-pressure tonalite–trondhjemite–granodiorite (TTG) suite. The zircon Hf (εHf(t) = +1.6 to +3.9) and O (δ¹⁸O = +3.76‰ to +5.73‰) isotopic compositions of the trondhjemitic gneisses indicate a juvenile basaltic source at the base of a thickened magmatic arc. The monzogranitic gneisses differ from their TTG counterparts in that they have lower SiO₂ and higher MgO, K₂O, and incompatible-element (especially Ba, Th, Sr, P, and LREE) contents. They also have slightly evolved zircon εHf(t) values (+0.6 to +3.8) and higher δ¹⁸O values (+4.69‰ to +6.13‰). These features suggest that the monzogranitic gneisses represent sanukitoid-type rocks, with a mantle source modified by crust-derived melts. The weakly deformed syenogranitic gneisses are characterized by high SiO₂ and K₂O, and very low MgO, Cr, and Ni contents, suggesting that they were formed by partial melting of local TTG rocks. Our results, together with those of previous investigations, suggest that the 2554–2513 Ma low- to high-K magmatism in the Jinzhou area most likely originated in an arc–back-arc tectonic setting on the northern margin of the NCC. The large volumes of high-K granitoids in eastern Hebei–western Liaoning are related to extensive mantle–crust interactions and crustal reworking in such a setting.     

The genesis of the ores and granitic rocks at the Hongshi Au deposit in Eastern Tianshan,China: Constraints from zircon U–Pb geochronology,geochemistry and isotope systematics

The Hongshi gold deposit is located in the southwestern margin of the Kanggur–Huangshan ductile shear zone in Eastern Tianshan, Northwest China. The gold ore bodies are predominantly hosted in the volcanogenic metasedimentary rocks of the Lower Carboniferous Gandun Formation and the Carboniferous syenogranite and alkali-feldspar granite. The syenogranite and the alkali-feldspar granite yield SHRIMP zircon U–Pb ages of 337.6 ± 4.5 Ma (2σ, MSWD = 1.3) and 334.0 ± 3.7 Ma (2σ, MSWD = 1.1), respectively, indicating that the Hongshi gold deposit is younger than 334 Ma. The granitoids belong to shoshonitic series and are relatively enriched in large ion lithophile elements (Rb, K, Ba, and Pb) and depleted in high field-strength elements (Nb, Ta, P, and Ti). Moreover, these granitoids have high SiO₂, Al₂O₃, and K₂O contents, low Na₂O, MgO, and TiO₂ contents, low Nb/Ta ratios, and slightly positive Eu anomalies. The ε_Hf(t) values of the zircons from a syenogranite sample vary from + 1.5 to + 8.8 with an average of + 5.6; the ε_Hf(t) values of the zircons from an alkali-feldspar granite sample vary from + 5.0 and + 10.1 with an average of + 7.9. The δ³⁴S values of 10 sulfide samples ranged from − 11.5‰ to + 4.2‰, with peaks in the range of + 1‰ to + 4‰. The above-mentioned data suggest that the Hongshi granitoids were derived from the melting of juvenile lower crust mixed with mantle components formed by the southward subduction of the paleo-Tianshan ocean plate beneath the Aqishan–Yamansu island arc during the Early Carboniferous. The Hongshi gold deposit was formed by post-collisional tectonism during the Permian. The granitoids most likely acted as impermeable barriers that prevented the leakage and runoff of ore-bearing fluids. Thus, the granitoids probably played an important role in controlling gold mineralization.     

Origin of the Alxa Block,western China: New evidence from zircon U–Pb geochronology and Hf isotopes of the Longshoushan Complex

The NW–SE trending Longshoushan is in the southwestern margin of the Alxa Block, which was traditionally considered the westernmost part of the North China Craton (NCC). Precambrian crystalline basement exposed in the Longshoushan area was termed the “Longshoushan Complex”. This complex's formation and metamorphism are significant to understand the geotectonics and early Precambrian crustal evolution of the western NCC. In this study, field geology, petrology, and zircon U–Pb and Lu–Hf isotopes of representative orthogneisses and paragneisses in the Longshoushan Complex were investigated. U–Pb datings reveal three Paleoproterozoic magmatic episodes (ca. 2.33, ca. 2.17 and ca. 2.04 Ga) and two subsequent regional metamorphic events (ca. 1.95–1.90 Ga and ca. 1.85 Ga) for metamorphic granitic rocks in the Longshoushan Complex. U–Pb dating of the detrital magmatic zircons from two paragneisses yields concordant ²⁰⁷Pb/²⁰⁶Pb ages between 2.2 Ga and 2.0 Ga, and a small number of metamorphic zircon rims provide a ca. 1.95 Ga metamorphic age, suggesting that the depositional time of the protolith was between 2.0 and 1.95 Ga and that the sedimentary detritus was most likely derived from the granitic rocks in the Longshoushan Complex itself. Zircon Lu–Hf isotopic analyses indicate that nearly all magmatic zircons from ca. 2.0 Ga to ca. 2.17 Ga orthogneisses have positive εHf(t) values with two-stage Hf model ages (T_DMC) ranging from 2.45 to 2.65 Ga (peak at ca. 2.5 Ga), indicating that these Paleoproterozoic granitic rocks were derived from the reworking of the latest Neoarchean–early Paleoproterozoic juvenile crust. Detrital magmatic zircons from two paragneisses yield scattered ¹⁷⁶Hf/¹⁷⁷Hf ratios, εHf(t) and T_DMC values, further indicating that the sedimentary detritus was not only derived from these plutonic rocks but also from other unreported or denuded Paleoproterozoic igneous rocks. The ca. 2.15 Ga detrital magmatic zircons from one paragneiss have negative εHf(t) values with T_DMC ranging from 2.76 to 3.04 Ga, indicating another important crustal growth period in the Longshoushan region. These data indicate that the Longshoushan Complex experienced Neoarchean–Early Paleoproterozoic crustal growth, approximately ca. 2.3–2.0 Ga experienced multiphase magmatic events, and approximately ca. 1.95–1.90 Ga and ca. 1.85 Ga experienced high-grade metamorphic events. The sequence of tectonothermal events is notably similar to that of the main NCC. Together with the datasets from an adjacent area, we suggest that the western Alxa Block was most likely an integrated component of the NCC from the Neoarchean to the Paleoproterozoic.     

Zircon U–Pb and Hf isotopic study of Mesozoic felsic rocks from eastern Zhejiang,South China: Geochemical contrast between the Yangtze and Cathaysia blocks

The Jiangshan–Shaoxing Fault Zone (JSFZ) in Zhejiang Province has been proposed to represent a suture between the Yangtze and Cathaysia blocks in South China. In this study, in-situ zircon U–Pb and Hf isotopic analysis and whole-rock major- and trace-element measurement of early to middle Cretaceous felsic rocks across the fault zone were conducted to constrain the nature of the fault zone. Twelve Cretaceous granitoid bodies were sampled from the NW and SE sides of the fault zone, respectively, with composition ranging from diorite to granite (SiO₂ = 56.2–76.6 wt.%). These granitoids yielded U–Pb ages ranging from 135–100 Ma, with a systematic variation in zircon Hf isotopic compositions (ε_Hf(t) = + 6.9 to –7.0 in the NW side vs. + 1.9 to ? 12.9 in the SE side). The T_DM2 values for the granitoids from the NW side are 0.34 to 1.33 Ga, with two peaks at ca. 876 and 1170 Ma respectively, whereas those from the SE side are 0.70 to 1.62 Ga, with a single peak at ca. 1126 Ma. The Hf isotopic disparity for the two sides may indicate a fundamental difference in the lower crustal compositions of the Yangtze and Cathaysia blocks, supporting that the JSFZ is possibly a suture zone between the two blocks. Our results together with the available geological data suggest that the Mesoproterozoic materials are important for both the Yangtze and Cathaysia basement and the Neoproterozoic magmatic activities were important in the Yangtze Block, possibly related to the break-up of the Rodinia supercontinent, but less significant in the Cathaysia Block. This may imply that the two blocks have not completely juxtaposed in the Neoproterozoic.     

The formation and rejuvenation of continental crust in the central North China Craton: Evidence from zircon U–Pb geochronology and Hf isotope

The Trans-North China Orogen (TNCO) along the central part of the North China Craton (NCC) is considered as a Paleoproterozoic suture along which the Eastern and Western Blocks of the NCC were amalgamated. Here we investigate the Precambrian crustal evolution history in the Fuping segment of the TNCO and the subsequent reactivation associated with extensive craton destruction during Mesozoic. We present zircon LA-ICP-MS U–Pb and Lu–Hf data on TTG (tonalite–trondhjemite–granodiorite) gneiss, felsic orthogneiss, amphibolite and granite from the Paleoproterozoic suite which show magmatic ages in the range of 2450–1900 Ma suggesting a long-lived convergent margin. The ε_Hf(t) values of these zircons range from −11.9 to 12 and their model ages suggest magma derivation from both juvenile components and reworked Archean crust. The Mesozoic magmatic units in the Fuping area includes granite, diorite and mafic microgranular enclaves, the zircons from which define a tight range of 120–130 Ma ages suggesting a prominent Early Cretaceous magmatic event. However, the ε_Hf(t) values of these zircons show wide a range from −30.3 to 0.2, indicating that the magmatic activity involved extensive rejuvenation of the older continental crust.     

Phanerozoic reactivation of the Archean North China Craton through episodic magmatism: Evidence from zircon U–Pb geochronology and Hf isotopes from the Liaodong Peninsula

The Archean lithospheric root of the North China Craton (NCC) has been considerably eroded and modified by Phanerozoic magmatic processes. Here we investigate the decratonization of the NCC through U–Pb and Hf isotopic analyses of zircons from Cenozoic basalts in the Liaodong Peninsula using ion-probe and MC-ICPMS techniques. The U–Pb zircon geochronology identifies three zircon populations: Precambrian, Paleozoic and Mesozoic. The Precambrian zircons yield ²⁰⁷Pb/²⁰⁶Pb ages of 2275–2567 Ma with a peak at around 2.5 Ga. They define a U–Pb discordia with upper intercept ages of 2447 ± 50 Ma to 2556 ± 50 Ma and a wide range of Hf T_DM ages with a mode at 2.7–2.8 Ga. Our results clearly demonstrate the presence of an Archean lower crust in the Liaodong region. The Paleozoic zircons from the Liaodong region lack the clear internal zoning and are subhedral to rounded in shape, and yield a narrow ²⁰⁶Pb/²³⁸U concordant ages of 419–487 Ma with a weighted mean age of 462 ± 16 Ma. The Mesozoic zircons predominantly show crystallization in the early Cretaceous and yield a relatively large range in ²⁰⁶Pb/²³⁸U ages from 100 to 138 Ma (n = 53) with a peak around 120 Ma. Three samples give indistinguishable weighted mean ²⁰⁶Pb/²³⁸U ages of 120 ± 5 Ma, 120 ± 4 Ma and 121 ± 2 Ma. These early Cretaceous zircons have enriched Hf isotope compositions with ε_Hf(t) values from ?26 to ?16. Our results provide important constraints on episodic magmatism during the Phanerozoic in the Liaodong region, which led to substantial reactivation of the Archean basement of the North China Craton.     

Timing of the initiation of the Jurassic Yanshan movement on the North China Craton: evidence from sedimentary cycles,heavy minerals,geochemistry, and zircon U–Pb geochronology

A series of significant geological changes indicated by deformation, magmatic–metallogenic systems, and the climate and environment occurred in East Asia during Late Jurassic to Early Cretaceous time, but the timing and development of the ‘Yanshan movement’ on the north margin of the North China Craton has not been well-established. Based on the evidence of tectonic deformation and magmatic activity, previous studies resulted in two views of the beginning of the Yanshan movement: Early Jurassic vs. late Middle Jurassic. In this work, the timing of the initial Yanshan movement was investigated by examining the Jurassic Chenjiabangou section in the Ningwu–Jingle basin overlying the north-central part of the North China Craton. The timing of the initial Yanshan movement was constrained by restoration of stream flow directions, determination of boundaries of sedimentary cycles, identification of heavy mineral assemblages in clastic rocks, quantification of changes in chemical compositions, and zircon U–Pb isotope dating. The results indicate that the basal conglomerates of the Middle Jurassic Yungang Formation (Bathonian) mark the beginning of the Yanshan movements. Evidence supporting this conclusion includes the following. (1) The switch from transgressive lacustrine deposition to regressive lacustrine deposition in the Yungang Formation sedimentary succession indicates a change from extension to compression, possibly reflecting uplift. (2) Early-stage clastic rocks rich in quartz and feldspar are replaced by feldspar detritus in late-stage clastic rocks; the heavy mineral assemblage dominated by zircon at the early stages changed to garnet-dominated assemblage upsection. Moreover, the concentrations of CaO, MgO, CO_2, and Fe₂O₃ + FeO and the Fe₂O₃/FeO ratio changed abruptly near the basal conglomerates of the Middle Jurassic Yungang Formation, suggesting increased denudation. (3) Conglomerates at the bottom of the Middle Jurassic Yungang Formation were deposited approximately 168 million years ago, as inferred from the age of zircons in tuffaceous micrite (160.6 ± 0.55 Ma) at the bottom of the Upper Jurassic Tianchihe Formation (Oxfordian) and the age of zircons in pyroclastic rocks (179.2 ± 0.79 Ma) in the Lower Jurassic Yongdingzhuang Formation (Toarcian). These lines of evidence indicate that initial Jurassic Yanshan movement began 168 million years ago during Middle Jurassic time.     

Phanerozoic amalgamation of the Alxa Block and North China Craton: Evidence from Paleozoic granitoids,U–Pb geochronology and Sr–Nd–Pb–Hf–O isotope geochemistry

The North China Craton (NCC) has been considered to be part of the supercontinent Columbia. The nature of the NCC western boundary, however, remains strongly disputed. A key question in this regard is whether or not the Alxa Block is a part of the NCC. It is located in the vicinity of the inferred boundary, and therefore could potentially resolve the issue of the NCC's relationship to the Columbia supercontinent. Some previous studies based on the Alxa Block's geological evolution and detrital zircon ages suggested that it is likely not a part of the NCC. The lack of evidence from key igneous rock units, however, requires further constraints on the tectonic affinity of the western NCC and Alxa Block and on the timing of their amalgamation.In this study, new zircon U–Pb age and Hf–O isotopes and whole-rock geochemical and Sr–Nd–Pb isotopic data for the Paleozoic granitoids in or near the eastern Alxa Block were used to constrain the petrogenesis of these rocks and the relationship between the Alxa Block and NCC. Secondary ion mass spectrometry (SIMS) U–Pb zircon dating indicates that the Bayanbulage, Hetun, Diebusige and South Diebusige granitoids were formed at ca. 423 Ma, 345 Ma, 345 Ma and 337 Ma, respectively. The Late Silurian (Bayanbulage) quartz diorites have variable SiO₂ (58.0–67.9 wt.%), and low Sr/Y (20–24) values, while the Early Carboniferous (Hetun, Diebusige and South Diebusige) monzogranites have high SiO₂ (71.5–76.7 wt.%) and Sr/Y (40–94) values. The Late Silurian quartz diorites display relatively homogeneous and high zircon δ¹⁸O (8.5–9.1‰) and ε_Hf(t) (− 8.6 to − 5.3) values, high whole-rock ε_Nd(t) values (− 9.2 to − 7.6) and highly radiogenic Pb isotopes (²⁰⁶Pb/²⁰⁴Pb = 18.13–18.25), whereas the Early Carboniferous monzogranites exhibit relatively low and variable zircon δ¹⁸O (5.7–7.2‰) and ε_Hf(t) (− 23.1 to − 7.4) values, low whole-rock initial ⁸⁷Sr/⁸⁶Sr (0.7043–0.7070) and ε_Nd(t) (− 19.1 to − 13.5) values and variable Pb isotopes (²⁰⁶Pb/²⁰⁴Pb = 16.06–18.22). The differences in whole rock Nd model ages and Pb isotope compositions of the Paleoproterozoic–Permian rocks in either side of the west fault of the Bayanwulashan–Diebusige complexes suggest that the Alxa Block is not a part of the NCC, and that the western boundary of the NCC is probably located on this fault. Furthermore, the linear distribution of the Early Paleozoic–Early Carboniferous granitoids, the high zircon δ¹⁸O values of the Late Silurian quartz diorites, the Early Devonian metamorphism and the foreland basin system formed during the collision between the Alxa Block and the NCC indicate that a Paleozoic cryptic suture zone likely existed in this area and records the amalgamation of the Alxa Block and North China Craton. Together with detrital zircon data, the initial collision was considered to have possibly occurred in Late Ordovician.     

Metallogeny of precious and base metal mineralization in the Murchison Greenstone Belt, South Africa: indications from U–Pb and Pb–Pb geochronology

The 3.09 to 2.97 Ga Murchison Greenstone Belt is an important metallotect in the northern Kaapvaal Craton (South Africa), hosting several precious and base metal deposits. Central to the metallotect is the Antimony Line, striking ENE for over 35?km, which hosts a series of structurally controlled Sb–Au deposits. To the north of the Antimony Line, hosted within felsic volcanic rocks, is the Copper–Zinc Line where a series of small, ca. 2.97 Ga Cu–Zn volcanogenic massive sulfide (VMS)-type deposits occur. New data are provided for the Malati Pump gold mine, located at the eastern end of the Antimony Line. Crystallizations of a granodiorite in the Malati Pump Mine and of the Baderoukwe granodiorite are dated at 2,964?±?7 and 2,970?±?7?Ma, respectively (zircon U–Pb), while pyrite associated with gold mineralization yielded a Pb–Pb age of 2,967?±?48?Ma. Therefore, granodiorite emplacement, sulfide mineral deposition and gold mineralization all happened at ca. 2.97?Ga. It is, thus, suggested that the major styles of orogenic Au–Sb and the Cu–Zn VMS mineralization in the Murchison Greenstone Belt are contemporaneous and that the formation of meso- to epithermal Au–Sb mineralization at fairly shallow levels was accompanied by submarine extrusion of felsic volcanic rocks to form associated Cu–Zn VMS mineralization.     

Palaeozoic polymetamorphism in the North Qinling orogenic belt,Central China: Insights from petrology and in situ titanite and zircon U–Pb geochronology

The Qinling orogenic belt experienced multiple phases of orogenesis during the Palaeozoic. Unraveling the timing and P–T conditions of these events is the key to understanding the convergence processes between the South China and the North China Blocks. The Songshugou Complex, located in the southern part of the North Qinling orogenic belt, has registered multistage metamorphism in Palaeozoic, and thus potentially provides insights into the tectonic evolution of the Qinling orogenic belt. In this study, three metabasic rocks (a garnet pyroxenite, a garnet amphibolite and a gneissic amphibolite) from the Songshugou Complex were selected for petrological study and zircon and titanite U–Pb dating. Our results show that the metabasic rocks experienced three metamorphic events during the Palaeozoic. The first metamorphic event (M1) is characterized by high pressure conditions. Two zircon grains in equilibrium with garnet and in absence of plagioclase were recognized from the garnet pyroxenite sample. They yielded Ti-in-zircon temperatures of 660–851 °C at ∼12.0 kbar and a weighted mean age of 498 ± 15 Ma, providing the constraints on the temperature and timing of prograde or peak metamorphism (M1-1). Zircons that are inequilibrium with garnet from the garnet pyroxenite and the garnet amphibolite gave U–Pb ages of 494 ± 9 Ma and 484 ± 4 Ma, and Ti-in-zircon temperatures of 793 ± 33 °C and 738 ± 18 °C, respectively. Thus, these zircons were formed on the retrograde amphibolite-facies conditions at ∼8.0 kbar (M1-2). Titanite inclusions were found in actinolite cores of zoned amphibole from the garnet amphibolite. They yielded a U–Pb age of ∼470 Ma and Zr-in-titanite temperature of 676 ± 23 °C at pressure of ∼7.0 kbar, suggesting that the amphibolite-facies retrogression perhaps persisted to ∼470 Ma.Weakly zoned zircons from the garnet amphibolite and inclusion-free titanites from the garnet pyroxenite gave consistent U–Pb ages of 418 ± 5 Ma and 423 ± 10 Ma, and Ti-in-zircon temperature of 742 ± 26 °C and Zr-in-titanite temperature of 764 ± 18 °C at ∼7.0 kbar, respectively. It is suggested that a heating event (M2) is registered by a subsequent phase of amphibolite-facies metamorphism. The ilmenite-bearing titanite crystals from the garnet pyroxenite yielded a U–Pb age of 352 ± 4 Ma, recording a late thermal event (M3).On the basis of combined petrological and geochronological results, we propose a revised tectonic model for the North Qinling orogeny in Palaeozoic. The high pressure granulites were formed by the northward subduction of the Shangdan oceanic slab and the arc-continent collision at ca. 500 Ma. Their exhumation happened at ca. 494–484 Ma as a result of slab breakoff. Subsequent amphibolite-facies metamorphism dated at ca. 440–420 Ma are coeval with the widespread magmatism in the North Qinling Terrane, which are likely caused by the reinitiation northward-subducted of Shangdan oceanic slab. At ca. 350 Ma, the North Qinling Terrane was likely affected by another thermal overprinting event.     

Late Palaeoproterozoic post-collisional magmatism in the North China Craton: geochemistry,zircon U–Pb geochronology,and Hf isotope of the pyroxenite–gabbro–diorite suite from Xinghe,Inner Mongolia

The North China Craton (NCC) witnessed a prolonged subduction–accretion history from the early to late Palaeoproterozoic, culminating with final collision at ca. 1.85 Ga and assembling the continental blocks into the cratonic framework. Subsequently, widespread post-collisional magmatism occurred, particularly along the Trans-North China Orogen (TNCO) that sutures the Eastern and Western blocks of the NCC. Here we present petrological, geochemical, and zircon U–Pb geochronological and Lu–Hf data from a pyroxenite (websterite)–gabbro–diorite suite at Xinghe in Inner Mongolia along the northern segment of the TNCO. The internal structures and high Th/U values of the zircons from the gabbro–diorite suite suggest magmatic crystallization. LA-ICP-MS U–Pb age data on three gabbros and one diorite from the suite yield emplacement ages of 1786.1 ± 4.8, 1783 ± 15 ,1754 ± 16 and 1767 ± 13 Ma, respectively. The ε_Hf(t) shows mostly positive values (up to 5.8), with the lowest value at –4.2, suggesting that the magma was derived from dominantly juvenile sources. The generally low SiO₂ and high MgO values, and other trace element features of the Xinghe suite are consistent with fractionation from a mantle-derived magma with a broadly E-MORB affinity, with no significant crustal contamination. Recent studies clearly establish that the major magmatic pulse associated with rifting of the NCC within the Columbia supercontinent occurred in the late Mesoproterozoic at ca. 1.3–1.2 Ga associated with mantle plume activity. This, together with the lack of robust geochemical imprints of rift-related magmatism in the Xinghe suite, prompts us to suggest a tectonic model that envisages magma genesis associated with post-collisional extension during slab break-off, following the westward subduction of the Eastern Block and its collision with the Western Block. The resulting asthenospheric upwelling and heat input might have triggered the magma generation from a heterogeneous, subduction-modified sub-lithospheric mantle source for the Xinghe rocks, as well as for similar late Palaeoproterozoic suites in the TNCO.     

Petrogenesis of the Late Jurassic Laomengshan rhyodacite (Southeast China): constraints from zircon U–Pb dating,geochemistry and Sr–Nd–Pb–Hf isotopes

Extensive magmatism occurred in southeast China during Late Jurassic time, forming large-scale granitic and volcanic rocks associated with non-ferrous, rare earth and rare, radioactive metal deposits. The Shuikoushan Pb–Zn–Au orefield is a typical example located in Hunan Province. This study reports LA-ICP-MS zircon U–Pb ages, whole-rock chemistry, and Sr–Nd–Pb isotopic compositions, and in situ Hf isotopic geochemistry of zircons from the Laomengshan rhyodacite in the Shuikoushan Pb–Zn–Au orefield. Zircon U–Pb dating yields a weighted average age of 156.7 ± 1.6 Ma for the intrusion of the rhyodacite. The rhyodacite samples are mainly shoshonitic series, having metaluminous to weakly peraluminous A/CNK values ranging from 0.96 to 1.09, with moderately high magnesium content (Mg# = 42.4–47.5). Samples display high (⁸⁷Sr/⁸⁶Sr)_i values (0.71165–0.71176), low ε_Nd(T) values (?10.7 to ?10.3), old Nd model ages (T_DM = 1.73–1.86 Ga), and relatively homogeneous Pb isotopic compositions [(²⁰⁶Pb/²⁰⁴Pb)_i = 18.365–18.412, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.663–15.680, and (²⁰⁸Pb/²⁰⁴Pb)_i = 38.625–38.666]. The zircons exhibit enriched ε_Hf(T) values (?16.22 to ?9.86) and old two-stage Hf model ages (T_DM2 = 1.82–2.22 Ga). All the above data indicate that the Laomengshan rhyodacite originated from melting Palaeoproterozoic basement, perhaps contaminated by subordinate mantle melts. Intense extension and thinning of the continental lithosphere during Late Jurassic time resulted in melting of upwelling asthenosphere, and mafic mantle melts interacted with and melted Palaeoproterozoic lower crust, thus forming the Laomengshan rhyodacite.