The building of an Archean microcontinent: Evidence from the North China Craton

Continents on the early earth are considered to have been built through the accretion of microterranes, oceanic arcs and plateaus. The North China Craton (NCC), envisaged in recent models as a collage of several microblocks which were amalgamated along multiple zones of ocean closure during the late Neoarchean, provide a typical case to investigate the origin and amalgamation of microcontinents through convergent margin processes. Here we report a suite of magmatic rocks developed at the periphery of one of these microblocks, the Jiaoliao Block, that forms part of the composite Eastern Block of the NCC. We integrate our new data with those from various parts of this microblock to elucidate the mechanism of continent building in the Archean. We present petrological, geochemical and zircon U–Pb geochronological and Lu-Hf isotopic data from the magmatic suite that belongs to the Yishui Complex. Geochemically, the felsic units of the suite straddle from monzonite through granodiorite to granite with dominantly metaluminous affinity, magnesian composition and arc-related features. The metagranites, TTG gneisses and charnockites are characterized by negative Nb-Ta anomalies and positive K and Pb anomalies. The diorites and gabbros display negative anomalies of Th-U, Nb-Ta and Zr-Hf and positive anomalies at Ba, Pb and Sm with negative Eu anomalies and minor positive Ce anomalies, attesting to arc-related features. In the tectonic discrimination diagrams, the rocks plot in the volcanic arc field, indicating arc-related origin in subduction setting.Zircon grains from all the rocks display core–rim texture with the cores showing magmatic crystallization and the narrow structureless rims corresponding to metamorphic overgrowth. The magmatic zircons from the metagranites show upper intercept ages or ²⁰⁷Pb/²⁰⁶Pb weighted mean ages of 2505 ± 29 Ma and 2569 ± 20 Ma to 2513 ± 27 Ma, those from the TTG gneisses show 2535 ± 17 Ma to 2546 ± 39 Ma, from charnockites display 2543 ± 20 Ma–2555 ± 15 Ma, and diorite and gabbro show 2587 ± 15 Ma and 2516 ± 13 Ma respectively. The zircon rim ages of 2472 ± 23 Ma, 2457 ± 35 Ma, 2545 ± 30 Ma and 2511 ± 35 Ma suggest the timing of metamorphism (ca. 2.55–2.45 Ga). Magmatic zircons with slightly older ages of ca. 2.73 Ga, 2.64 Ga also occur suggesting multiple magmatic pulses. The Lu-Hf isotopic data show positive εHf(t) values ranging from 0.2 to 5.7 for metagranites, with Hf model ages of 2602–2815 Ma (T_DM) and 2658–3002 Ma (T_DM^C), whereas for TTG gneisses, the positive εHf(t) values are up to 6.5 and display dominant Mesoarchean Hf model ages with limited early Neoarchean Hf model ages. Charnockite samples show positive εHf(t) values 2.3–5.7 and display the Hf model ages ranging from 2601 Ma to 2772 Ma (T_DM) and 2658 Ma to 2904 Ma (T_DM^C). Diorite and gabbro also show positive εHf(t) (2.3–6.9) and yield Hf model ages of 2625–2788 Ma (T_DM) and 2647 Ma to 2903 Ma (T_DM^C). The Hf isotopic data indicate that the magmas were derived from Neoarchean-Mesoarchean juvenile sources.Integrating our data with those from the entire Jiaoliao microblock reveals vestiges of Hadean crust involved in building the Eoarchean nucleus of this microblock. Vigorous convergent margin processes ranging from Mesoarchean to late Neoarchean with multiple pules of arc magmatism associated with subduction tectonics led to further growth of continental crust, culminating in paired high temperature and high pressure metamorphism during late Neoarchean – early Paleoproterozoic transition.     

Early to late Neoproterozoic magmatism and magma mixing–mingling in Sri Lanka: Implications for convergent margin processes during Gondwana assembly

The Sri Lankan fragment of Gondwana preserves the records of Neoproterozoic tectonothermal events associated with the final assembly of the supercontinent. Here we investigate a suite of magmatic rocks from the Wanni, Kadugannawa and Highland Complexes through geological, petrological, geochemical and zircon U–Pb and Lu–Hf isotopic techniques. The hornblende biotite gneiss, charnockites, metagabbro and metadiorites investigated in this study show geochemical features consistent with calc-alkaline affinity and subduction-related signature including LILE enrichment relative to HFSE coupled with distinct Nb–Ta depletion and weak negative Zr–Hf anomalies. The felsic suite falls in the volcanic arc granites (VAGs) field and the mafic suite shows island arc basalt affinity in tectonic discrimination plots, suggesting that the protoliths of the rocks were derived from arc-related magmas in a convergent margin setting. LA-ICPMS zircon U–Pb analyses show crystallization of charnockite and dioritic mafic magmatic enclave from the Highland Complex during ca. 565 and 576 Ma corresponding to bimodal magmatism. The diorite also contains metamorphic zircons of ca. 525 Ma. Hornblende–biotite gneiss from the Kadugannawa Complex shows protolith emplacement age at 973–980 Ma, followed by new zircon growth during repeated thermal events through late Neoproterozoic. The dioritic enclaves in these rocks are much younger, and form part of a deformed and metamorphosed dyke suite with emplacement ages of 559 Ma, broadly coeval with the bimodal magmatism in the Highland Complex at that time. The youngest group of zircons in this rock shows ages of 508 Ma, corresponding to the latest thermal event. A charnockite from this locality shows oldest group of zircons at 962 Ma, corresponding to emplacement age similar to that of the magmatic protolith of the hornblende biotite gneiss. This rock also shows zircon growth during repeated thermal events at 832 Ma, 780 Ma, 721 Ma and 661–605 Ma. The lower intercept age of 543 Ma marks the timing of collisional metamorphism. Charnockite from the Wanni Complex shows emplacement age at 1000 Ma, followed by thermal event at 570 Ma, the latter correlating with the bimodal magmatic event in the Highland Complex. The dioritic enclave within this charnockite shows an age of ca. 980 Ma, suggesting intrusion of mafic magma into the felsic magma chamber. Zircons in the diorite also record multiple zircon events during 950 to 750 Ma. Zircons in the Highland Complex charnockite possess negative εHf(t) values in the range − 6.7 to − 12.6 with T_DM^C of 2039–2306 Ma suggesting magma derivation through melting of Paleoproterozoic source. In contrast, the εHf(t) range of − 11.1 to 1.6 suggests a mixed source of both of older crustal and juvenile material. The εHf(t) values of − 4.5 to 4.5 and T_DM^C of 1546–1962 Ma for the hornblende biotite gneiss also shows magma derivation from mixed sources that included Paleoproterozoic components. The younger dioritic intrusive, however, has a more juvenile magma source as indicated by the mean εHf(t) value of 1.3. The associated charnockite shows a tight positive cluster of εHf(t) from 0.6 to 5.1, suggesting juvenile input. Charnockite from the Wanni Complex shows clearly positive εHf(t) values of up to 13.1, and T_DM^C in the range 937–1458 Ma suggesting much younger and depleted mantle source. The diorite enclave also has positive εHf(t) values with an average value of 8.5 and T_DM^C in the range of 709–1443 Ma clearly suggesting younger juvenile sources. The early and late Neoproterozoic bimodal suites are correlated to convergent margin magmatism associated with the assembly of Sri Lanka within the Gondwana supercontinent.     

The Yanbian Terrane (Southern Sichuan Province,SW China): A Neoproterozoic arc assemblage in the western margin of the Yangtze Block

The magmatic and tectonic history of the Yangtze Block and its possible affinity with other Neoproterozoic arc terranes are important elements in the reconstruction of Neoproterozoic plate tectonics. The Yanbian Terrane in the western margin of the Yangtze Block is a typical arc assemblage composed of a flysch-type sedimentary sequence intruded by gabbroic and granodioritic plutons. The sedimentary sequence consists chiefly of tuffaceous material with interlayered chert, sandstone, and pillow basalts. Laser ablation ICP-MS U–Pb dating of detrital zircons from the sandstones yield ages as young as 840 Ma. The Gaojiacun and Lengshuiqing mafic intrusions are dated at 812 ± 3 Ma and 806 ± 4 Ma, respectively, using the SHRIMP zircon U–Pb technique. Geochemical data show that both the Gaojiacun and Lengshuiqing intrusions have arc signatures, with ɛNd(t) values of +1.5 to +6.0, initial ⁸⁷Sr/⁸⁶Sr ratios of 0.705–0.706 and pronounced negative Nb–Ta and Zr–Hf anomalies. Their geochemical variations are best explained by fractional crystallization without major crustal contamination. The Yanbian Terrane represents a typical arc assemblage formed on the western edge of the Yangtze Block during Neoproterozoic time. The sedimentary sequence was deposited in an oceanic setting, probably in a back arc basin environment. The depleted, subduction-modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized. This scenario suggests subduction of oceanic lithosphere eastward (present-day orientation) underneath the Yangtze Block.     

Neoarchean convergent margin tectonics associated with microblock amalgamation in the North China Craton: Evidence from the Yishui Complex

Archean tectonic history of the North China Craton (NCC) involved complex processes of amalgamation of microcontinents along multiple subduction zones prior to the consolidation of the major crustal blocks and their assembly into unified cratonic architecture. Here we report a suite of granitoids, diabase, metabasalts, volcanic tuff, banded iron formations and quartzite from the Yishui Complex along the southern margin of the Jiaoliao microblock within the Eastern Block of the NCC. The geochemical features of the magmatic suite are consistent with calc-alkaline magmatism in a convergent margin setting. In tectonic discrimination diagrams, the mafic suite shows variable IAB, MORB and OIB affinities typical of rocks formed in an arc-related subduction environment. Zircon grains in most of the rocks from Yishui Complex display core–rim texture with the cores showing magmatic crystallization and the narrow structureless rims corresponding to metamorphic overgrowth. The ²⁰⁷Pb/²⁰⁶Pb ages of magmatic zircons show 2504 ± 19 Ma for the volcanic tuff, 2581 ± 21 Ma for the granitoid, 2501 ± 19 Ma for the metavolcanics, 2537 ± 38 Ma for the pyroxenite, and 2506 ± 13 Ma for the diabase. Metamorphism is constrained from the 2451 ± 18 Ma and 2466 ± 23 Ma age groups in the metavolcanics and (meta-) pyroxenites. Zircons from BIF show multiple population with the oldest showing a spot age of 2503 Ma, followed by a number of distinct groups of Paleoproterozoic zircons corresponding to later thermal events. The oldest population of magmatic zircons from the quartzite shows ²⁰⁷Pb/²⁰⁶Pb mean age of 2495 ± 24 Ma. The dominantly positive εHf(t) values of the magmatic zircons from the Yishui suite are broadly consistent with a depleted mantle source with only minor input of crustal components. Their Hf crustal residence ages (T_DM^C) range from 2586 to 3181 Ma and Hf depleted mantle model ages (T_DM) are in the range of 2548–2927 Ma. The data indicate that magma production involved Meso- to Neoarchean juvenile sources within a continental arc setting, suggesting the Jiaoliao microblock as one of the ancient continental nuclei in the NCC. We trace the continuity of a Neoarchean subduction system along the western and southern margins of the Jiaoliao microblock with convergence of the Qianhuai and Xuhuai microblocks towards the Jiaoliao microblock with subduction–accretion–collision during the Archean–Proterozoic transition.     

Neoproterozoic magmatic events in the South Qinling Belt,China: Implications for amalgamation and breakup of the Rodinia supercontinent

Neoproterozoic magmatic rocks in the South Qinling Belt of China provide important clues for understanding the mechanism and timing of the amalgamation and breakup of the Rodinia supercontinent. Here we report new geochemical and high-precision LA-ICP-MS zircon U–Pb–Hf isotopic analyses on magmatic suites from the Liuba and Zhashui areas in the South Qinling Belt. Our data show that the crystallization ages of the granitic intrusions from Tiefodian and Tangjiagou in the Liuba area are 863 ± 22 Ma and 794 ± 11 Ma, respectively, whereas those of the dioritic and gabbroic intrusions at Chishuigou in the Zhashui area are 925 ± 28 Ma and 832.6 ± 4.0 Ma, respectively. The diorites at Chishuigou display arc-related geochemical affinity, characterized by strong depletion in Nb, Ta, P and Ti, and enrichment in large-ion lithophile elements (i.e., Rb, Ba, Th and U), indicating a subduction-related arc setting at ca. 925 Ma. The Tiefodian granitic rocks have high SiO₂ (68.46–70.98 wt.%), Na₂O (3.87–4.51 wt.%), and low K₂O (1.34–2.61 wt.%) contents with TTG affinity. However, their Cr, and Ni contents and Cr/Ni, Nb/Ta ratios are similar to those of continental crust, and together with high negative ε_Hf(t) values (− 4.87 to − 14.84), suggesting a continental margin arc at ca. 863 Ma. The gabbros at Chishuigou have high TiO₂ content (2.74–3.14 wt.%), Zr/Y (3.93–4.24), Ta/Yb (0.19–0.25) ratios and low Zr/Nb ratios (11.37–13.17), similar to the features of within-plate basalts, indicating an intra-continental rift setting at ca. 833 Ma. The granitoids at Tangjiagou exhibit enrichment of LREE, K and Pb, and depletion of Nb, Ta, P and Ti, suggesting an extensional tectonic environment at ca. 794 Ma.The results indicate that Neoproterozoic magmatic rocks in the South Qinling Belt formed before ca. 833 Ma and might represent the amalgamation of the Rodinia supercontinent in an arc-related subduction environment, whereas the magmatic events with the peak ages at ~ 740 Ma during ca. 833–680 Ma represent the breakup of Rodinia. Integrating our new data with those from previous works, we propose a new tectonic model for the evolutionary history of the South Qinling Belt in the Neoproterozoic, including four key stages: 1) an ocean that separated the South Qinling Belt and the Yangtze Block in the Early Neoproterozoic (ca.1000–956 Ma); 2) bidirectional subduction of the oceanic lithosphere during ca. 956–870 Ma; 3) subduction and collision between the South Qinling Belt and the Yangtze Block during ca. 870–833 Ma, thus suggesting that the South Qinling Belt was as a part of the Yangtze Block from this period; and 4) intra-continental rifting during ca. 833–680 Ma, although the blocks were not entirely rifted apart.     

Neoarchean suprasubduction zone arc magmatism in southern India: Geochemistry,zircon U-Pb geochronology and Hf isotopes of the Sittampundi Anorthosite Complex

The Sittampundi Anorthosite Complex (SAC) in southern India is one of the well exposed Archean layered anorthosite-gabbro-ultramafic rock associations. Here we present high precision geochemical data for the various units of SAC, coupled with zircon U-Pb geochronology and Hf isotopic data for the anorthosite. The zircon ages define two populations, the older yield a concordia age of 2541 ± 13 Ma, which is interpreted as the best estimate of the magmatic crystallization age for the Sittampundi anorthosite. A high-grade metamorphic event at 2461 ± 15 Ma is suggested by the upper intercept age of the younger zircon population. A Neoproterozoic event at 715 ± 180 Ma resulted in Pb loss from some of the metamorphic zircons. The magmatic age of the anorthosite correlates well with the timing of crystallization of the arc-related ~ 2530 Ma magmatic charnockites in the adjacent Salem Block, while the metamorphic age is synchronous with the regional metamorphic event. The geochemical data suggest that the rocks were derived from a depleted mantle source. Sub-arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous, aluminous basalt magma. The magma fractionated at depth to produce a variety of high-alumina basalt compositions, from which the anorthositic complex with its chromite-rich and amphibole-rich layers formed as cumulates within the magma chamber of a supra-subduction zone arc. The coherent initial¹⁷⁶Hf/¹⁷⁷Hf ratios and positive εHf values (1.7 – 4.5) of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source. Our study further confirms that the southern part of the Dharwar Craton was an active convergent margin during the Neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth.     

Zircon geochemistry of two contrasting types of eclogite: Implications for the tectonic evolution of the North Qaidam UHPM belt,northern Tibet

Compared to the extensively documented ultrahigh-pressure metamorphism at North Qaidam, the pre-metamorphic history for both continental crust and oceanic crust is poorly constrained. Trace element compositions, U–Pb ages, O and Lu–Hf isotopes obtained for distinct zircon domains from eclogites metamorphosed from both continental and oceanic mafic rocks are linked to unravel the origin and multi-stage magmatic/metamorphic evolution of eclogites from the North Qaidam ultrahigh-pressure metamorphic (UHPM) belt, northern Tibet.For continental crust-derived eclogite, magmatic zircon cores from two samples with U–Pb ages of 875–856 Ma have both very high δ¹⁸O (10.6 ± 0.5‰) and mantle-like δ¹⁸O (averaging at 5.2 ± 0.7‰), high Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, and steep MREE-HREE distribution patterns (chondrite-normalized) with negative Eu anomalies. Combined with positive ε_Hf (t) of 3.9–14.3 and T_DM (1.2–0.8 Ga and 1.3–1.0 Ga, respectively), they are interpreted as being crystallized from either subduction-related mantle wedge or recycled material in the mantle. While the metamorphic rims from the eclogites have U–Pb ages of 436–431 Ma, varying (inherited, lower, and elevated) oxygen isotopes compared with cores, low Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, and flat HREE distribution patterns with no Eu anomalies. These reflect both solid-state recrystallization from the inherited zircon and precipitation from external fluids at metamorphic temperatures of 595–622 °C (T_Ti-in-zircon).For oceanic crust-derived eclogite, the magmatic cores (510 ± 19 Ma) and metamorphic rims (442.0 ± 3.7 Ma) also show distinction for Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, and the REE patterns and Eu anomalies. Combined with the mantle-like δ¹⁸O signature of 5.1 ± 0.3 ‰ and two groups of model age (younger T_DM close to the apparent ages and older > 700 Ma), two possible pools, juvenile and inherited, were involved in mixing of mantle-derived magma with crustal components. The relatively high δ¹⁸O of 6.6 ± 0.3‰ for metamorphic zircon rims suggests either the protolith underwent hydrothermal alteration prior to the ~ 440 Ma oceanic crust subduction, or external higher δ¹⁸O fluid activities during UHP metamorphism at ~ 440 Ma.Therefore, the North Qaidam UHPM belt witnesses multiple tectonic evolution from Late Mesoproterozoic–Neoproterozoic assembly/breakup of the Rodinia supercontinent with related magmatic emplacement, then Paleozoic oceanic subduction, and finally transition of continental subduction/collision related to UHP metamorphism.     

Detrital zircon U-Pb-Hf isotopes and provenance of Late Neoproterozoic and Early Paleozoic sediments of the Simao and Baoshan blocks,SW China: Implications for Proto-Tethys and Paleo-Tethys evolution and Gondwana reconstruction

Early Paleozoic evolution of the northern Gondwana margin is interpreted from integrated in situ U-Pb and Hf-isotope analyses on detrital zircons that constrain depositional ages and provenance of the Lancang Group, previously assigned to the Simao Block, and the Mengtong and Mengdingjie groups of the Baoshan Block. A meta-felsic volcanic rock from the Mengtong Group yields a weighted mean ²⁰⁶Pb/²³⁸U age of 462 ± 2 Ma. The depositional age for the previously inferred Neoproterozoic Lancang and Mengtong groups is re-interpreted as Early Paleozoic based on youngest detrital zircons and meta-volcanic age. Detrital U-Pb zircon analyses from the Baoshan Block define three distinctive age peaks at older Grenvillian (1200–1060 Ma), younger Grenvillian (~ 960 Ma) and Pan-African (650–500 Ma), with εHf(t) values for each group similar to coeval detrital zircons from western Australia and northern India. This suggests that the Baoshan Block was situated in the transitional zone between northeast Greater India and northwest Australia on the Gondwana margin and received detritus from both these cratons. The Lancang Group yields a very similar detrital zircon age spectrum to that of the Baoshan Block but contrasts with that for the Simao Block. This suggests that the Lancang Group is underlain by a separate Lancang Block. Similar detrital zircon age spectra suggest that the Baoshan Block and the Lancang Block share common sources and that they were situated close to one another along the northern margin of East Gondwana during the Early Paleozoic. The new detrital zircon data in combination with previously published data for East Gondwana margin blocks suggests the Early Paleozoic Proto-Tethys represents a narrow ocean basin separating an “Asian Hun superterrane” (North China, South China, Tarim, Indochina and North Qiangtang blocks) from the northern margin of Gondwana during the Late Neoproterozoic-Early Paleozoic. The Proto-Tethys closed in the Silurian at ca. 440–420 Ma when this “Asian Hun superterrane” collided with the northern Gondwana margin. Subsequently, the Lancang Block is interpreted to have separated from the Baoshan Block during the Early Devonian when the Paleo-Tethys opened as a back-arc basin.     

Timing of metamorphism in the Paleoproterozoic Jiao-Liao-Ji Belt: New SHRIMP U–Pb zircon dating of granulites,gneisses and marbles of the Jiaobei massif in the North China Craton

The Paleoproterozoic Jiao-Liao-Ji Belt lies in the Eastern Block of the North China Craton, with its southern segment extending across the Bohai Sea into the Jiaobei massif. High-pressure pelitic and mafic granulites have been recently recognized in the Paleoproterozoic Jingshan Group (Jiaobei massif). New SHRIMP U–Th–Pb geochronology combined with cathodoluminescence (CL) imaging of zircon has been applied to the determination of the timing of the metamorphism of the high-temperature and high-pressure granulites and associated gneisses and marbles. Metamorphic zircons in these high-pressure granulites, gneisses and marbles occur as either single grains or overgrowth (or recrystallization) rims surrounding and truncating oscillatory-zoned magmatic zircon cores. Metamorphic zircons are all characterized by nebulous zoning or being structureless, with high luminescence and relatively low Th/U values. Metamorphic zircons from two high-pressure mafic granulites yielded ²⁰⁷Pb/²⁰⁶Pb ages of 1956 ± 41 Ma and 1884 ± 24 Ma. One metamorphic zircon from a garnet–sillimanite gneiss also gave an apparent ²⁰⁷Pb/²⁰⁶Pb age of 1939 ± 15 Ma. These results are consistent with interval of ages of c. 1.93–1.90 Ga already obtained by previous studies for the North and South Liaohe Groups and the Laoling Group in the northern segment of the Jiao-Liao-Ji Belt. Metamorphic zircons from a high-pressure pelitic granulite and two pelitic gneisses yielded weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 1837 ± 8 Ma, 1821 ± 8 Ma and 1836 ± 8 Ma respectively. Two diopside–olivine–phlogopite marbles yielded weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 1817 ± 9 Ma and 1790 ± 6 Ma. These Paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c. 1.85 Ga produced from the Ji'an Group in the northern segment of the Jiao-Liao-Ji Belt and c. 1.86–1.80 Ga obtained for the high-pressure pelitic granulites from the Jingshan Group in the southern segment. As this metamorphic event was coeval with the emplacement of A-type granites in the Jiao-Liao-Ji Belt and its adjacent areas, it is interpreted as having resulted from a post-orogenic or anorogenic extensional event.     

Geology and geochemistry of the Triassic Wenquan Mo deposit and Mo-mineralized granite in the Western Qinling Orogen,China

The recently-discovered Wenquan porphyry Mo deposit hosted in the Wenquan granite of the West Qinling Orogen has been recognized as a product of the Indosinian metallogenesis. Three generations of mineral assemblage for the deposit are identified as follows: (1) quartz–biotite–K-feldspar; (2) quartz–sulfide and (3) sulfide–calcite. Geochemical study shows that the mafic microgranular enclaves (MMEs) in the ore-bearing Wenquan granite have lower SiO₂, and higher Mg# and Nb/Ta ratios than the host granite itself. Different from the granite which have zircon ε_Hf(t) values of − 3.6–3.0 and T_DM2 of 1234–890 Ma, the MMEs are characterized by the ε_Hf(t) values of − 10.1–10.8 and T_DM1 of 865–441 Ma. This can be interpreted to indicate a mixture origin of the Meso- and Neoproterozoic crust-derived component and Neoproterozoic SCLM-derived materials for the formation of the Wenquan granite, which played an essential role in the Mo mineralization. Comparative Pb isotopic data between ores and K-feldspar suggest that the Wenquan granitic magma originated from the middle-lower crust of the South China Block and the ore-forming materials were incorporated by hydrothermal fluid differentiated from the Triassic magmatic system, with minor contribution of sedimentary rocks. The δ³⁴S values of 5.0–11.7‰ with a pronounced mode at 5.0 to 6.1‰ for the ores probably represent the sulfur incorporation of a typical magmatic hydrothermal fluid contaminated by heavy sulfur of Devonian sediments. The granite yielded the zircon U–Pb ages of 218 ± 2.4 Ma and 221 ± 1.3 Ma, as the same as the ages of 217 ± 2.0 Ma and 218 ± 2.5 Ma obtained for the MMEs. These ages are indistinguishable with the molybdenite Re–Os isochron age of 219 ± 5.2 Ma which is the timing for the Mo mineralization. Tectonically, the magmatic mixture processes of the Wenquan granite and the Mo mineralization to form the Wenquan Mo deposit contemporaneously occurred during the transition of tectonic regime from syn- to post-collision orogeny in the Qinling Orogen in the Late Triassic.     

Detrital zircon ages and geochronological constraints on the Neoproterozoic Puga diamictites and associated BIFs in the southern Paraguay Belt,Brazil

The Paraguay belt comprises a thick sedimentary succession deposited on the southwestern border of the Amazonian Craton and the Rio Apa Block. The base of the succession in the southern Paraguay belt is marked by a level of glacially derived deposits from the Puga Formation associated with banded iron formations, which has been assumed to be end-Cryogenian in age (635 Ma) by previous authors is spite of the lack of geochronological data. Here we present the first U–Pb SHRIMP ages on detrital zircon grains separated from the matrix of six samples of these diamictites two different localities (Puga Hill and Bodoquena area). U–Pb ages determined from two samples (ca. 130 grains) of Puga Hill show a large variation between 970 Ma and 2100 Ma. Rocks with these ages can be found in the Amazonian Craton suggesting that it is the most probable source of the sediments. Detrital zircons (ca. 230 grains) from the Bodoquena area (about 200 km south of Puga Hill) range from 706 to 1990 Ma. The 1760 Ma source is significantly more important in these samples, comprising more than 70% of analyzed grains, and indicates provenance from the adjacent Rio Apa Block. The youngest zircon was dated at 706 ± 9 Ma, thus constraining the maximum depositional age for the Puga Formation. Possible sources for this younger population could be either the juvenile Mara Rosa magmatic arc in the Brasilia belt, or the rocks from the Laurentian external fold belts located to the west of the sampled area in Neoproterozoic paleogeographic reconstructions. The maximum depositional age of the diamictites (and associated BIFs), together with cap carbonate carbon and strontium isotope data (δ¹³C = ? 5.0 and ⁸⁷Sr/⁸⁶Sr = 0.7077) in Puga Hill, indicate that they were deposited after 700 Ma, suggesting that they may represent the end-Cryogenian event.     

Postcollisional magmatism: Geochemical constraints on the petrogenesis of Mesozoic granitoids in the Sulu orogen,China

A combined study of zircon U–Pb ages and Lu–Hf isotopes, mineral O isotopes, whole-rock elements and Sr–Nd isotopes was carried out for Mesozoic granitoids from the Shandong Peninsula in east-central China, which tectonically corresponds to the eastern part of the Sulu orogen that formed by the Triassic continental collision between the South and North China Blocks. Four plutons were investigated in this region, with the Linglong and Guojialing plutons from the northwestern part (Jiaobei) and the Kunyushan and Sanfoshan plutons from the southeastern part (Jiaodong). The results show that these granitoids mostly have high Sr, low Yb and Y contents, high (La/Yb)_N and Sr/Y ratios with negligible to positive Eu anomalies (Eu/Eu* = 0.69–1.58), which are similar to common adakites. On the other hand, they have relatively low MgO, Cr, Ni contents and thus low Mg#. Zircon U–Pb dating yields Late Jurassic ages of 141 ± 3 to 157 ± 2 Ma for the Linglong and Kunyushan plutons, but Early Cretaceous ages of 111 ± 2 to 133 ± 3 Ma for the Guojialing and Sanfoshan plutons. Some zircon cores from the Linglong and Kunyushan granitoids have Neoproterozoic U–Pb ages. All the granitoids have variably negative zircon ε_Hf(t) values of ?39.6 to ?5.4, with Mesoproterozoic to Paleoproterozoic Hf model ages of 1515 ± 66 to 2511 ± 97 Ma for the Sanfoshan pluton, but Paleoproterozoic to Paleoarchean Hf model ages of 2125 ± 124 to 3310 ± 96 Ma for the other three plutons. These indicate that the Mesozoic granitoids formed in the postcollisional stage and were derived mainly from partial melting of the subducted South China Block that is characterized by Paleoproterozoic juvenile crust and Neoproterozoic magmatic rocks along its northern edge. However, there are some differences between the Jiaobei and Jiaodong plutons. Compared to the Jiaodong granitoids, the Jiaobei granitoids have very old zircon Hf model ages of 3310 ± 96 Ma suggesting the possible involvement of a Paleoarchean crust that may be derived from the North China Block. Therefore, the continental collision between the two blocks would bring crustal materials from both sides into the subduction zone in the Triassic, yielding subduction-thickened crust as the magma source for the adakite-like granitoids. While lithospheric extension and orogenic collapse are considered a major cause for postcollisional magmatism, anatexis of the subducted mafic crust is proposed as a mechanism for chemical differentiation of the continental crust towards felsic composition.     

Provenance of lateritic bauxite deposits in the Wuchuan–Zheng’an–Daozhen area,Northern Guizhou Province,China: LA-ICP-MS and SIMS U–Pb dating of detrital zircons

The provenance of the large and super-large scale bauxite deposits developed in the Wuchuan–Zheng’an–Daozhen (WZD) alumina metallogenic province in the Yangtze Block of South China is poorly understood. LA-ICP-MS and SIMS U–Pb dating of detrital zircons from bauxite ores and the underlying Hanjiadian Group in the WZD area provide new constrains on the provenance of the WZD bauxite and provide new insight on the bauxite ore-forming process. The ages of the detrital zircons in the bauxites and the zircons in the Hanjiadian Group are similar suggesting that the bauxites are genetically related to the Hanjiadian sediments. The detrital zircon populations of the four samples studied show four primary age peaks: 2600–2400 Ma, 1900–1700 Ma, 1300–700 Ma and 700–400 Ma. The age distribution of detrital zircons indicates that they are probably derived from various sources including Neoproterozoic, Mesoproterozoic, Paleoproterozoic, Archean and some minor Paleozoic sources. The most abundant age population contains a continuous range of ages from 1300 to 700 Ma, ages consistent with subduction-related magmatic activities (1000–740 Ma) along the western margin of the Yangtze Block and the worldwide Grenville orogenic events (1300–1000 Ma). Thus, it is suggested that the main provenances of the WZD bauxite and the Hanjiadian Group are the Neoproterozoic igneous rocks in the western Yangtze Block and the Grenville-age igneous rocks in the southern Cathaysia Block. In addition, this work verifies that the global Grenville orogenic events and subduction-related magmatic activities associated with the Yangtze Block had a significant influence on the formation of the WZD bauxite deposits.     

Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province,SW China): Implications for subduction-related metasomatism in the upper mantle

Metasomatism above subduction zones is an important process that produces heterogeneous mantle and thus a diversity of igneous rocks. In the Panzhihua district, on the western margin of the Yangtze Block (SW China), two Neoproterozoic mafic intrusions, one olivine gabbro and one hornblende gabbro, have identical ages of 746 ± 10 and 738 ± 23 Ma. Both of the gabbros are tholeiitic in composition and have arc-like geochemical compositions. The hornblende gabbros have K₂O concentrations ranging from 0.70 to 1.69 wt.% and show enrichment of Rb, Ba, U, Th and Pb and depletion of Nb,Ta and Ti. They have variable ⁸⁷Sr/⁸⁶Sr ratios (0.7045–0.7070) with constant ɛNd(t) values (−0.12 to −0.93). The olivine gabbros have relatively low K₂O (0.19–0.43 wt.%), are depleted in Rb and Th relative to Ba and U, and have obvious negative Nb–Ta and Zr–Hf anomalies on primitive mantle-normalized trace element diagrams. Their ɛNd(t) values range from −0.64 to −1.73 and initial ⁸⁷Sr/⁸⁶Sr ratios from 0.7070 to 0.7075. Both types of gabbro experienced fractional crystallization of clinopyroxene, plagioclase, amphibole and minor Fe–Ti oxide. The parental magmas of the olivine and hornblende gabbros were formed by about 20% partial melting of garnet–spinel lherzolite and spinel lherzolite, respectively. According to trace elemental ratios, the hornblende gabbros were probably derived from a source strongly modified by subducted slab fluids, whereas the olivine gabbros came from a mantle source modified by subducted slab melts. The close association of the olivine gabbros and hornblende gabbros suggests that a steep subduction zone existed along the western margin of the Yangtze Block during Neoproterozoic time. Thus, the giant Neoproterozoic magmatic event in South China was subduction-related.     

Zircon U–Pb age,Hf isotopic compositions and geochemistry of the Silurian Fengdingshan I-type granite Pluton and Taoyuan mafic–felsic Complex at the southeastern margin of the Yangtze Block

This work presents an integrated study of zircon U–Pb ages and Hf isotope along with whole-rock geochemistry on Silurian Fengdingshan I-type granites and Taoyuan mafic–felsic intrusive Complex located at the southeastern margin of the Yangtze Block, filling in a gap in understanding of Paleozoic I-type granites and mafic-intermediate igneous rocks in the eastern South China Craton (SCC). The Fengdingshan granite and Taoyuan hornblende gabbro are dated at 436 ± 5 Ma and 409 ± 2 Ma, respectively. The Fengdingshan granites display characteristics of calc-alkaline I-type granite with high initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7093–0.7127, low εNd(t) values ranging from −5.6 to −5.4 and corresponding Nd model ages (T_2DM) of 1.6 Ga. Their zircon grains have εHf(t) values ranging from −2.7 to 2.6 and model ages of 951–1164 Ma. The Taoyuan mafic rocks exhibit typical arc-like geochemistry, with enrichment in Rb, Th, U and Pb and depletion in Nb, Ta. They have initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7053–0.7058, εNd(t) values of 0.2–1.6 and corresponding T_2DM of 1.0–1.1 Ga. Their zircon grains have εHf(t) values ranging from 3.2 to 6.1 and model ages of 774–911 Ma. Diorite and granodiorite from the Taoyuan Complex have initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7065–0.7117, εNd(t) values from −5.7 to −1.9 and Nd model ages of 1.3–1.6 Ga. The petrographic and geochemical characteristics indicate that the Fengdingshan granites probably formed by reworking of Neoproterozoic basalts with very little of juvenile mantle-derived magma. The Taoyuan Complex formed by magma mixing and mingling, in which the mafic member originated from a metasomatized lithospheric mantle. Both the Fengdingshan and Taoyuan Plutons formed in a post-orogenic collapse stage in an intracontinental tectonic regime. Besides the Paleozoic Fengdingshan granites and Taoyuan hornblende gabbro, other Neoproterozoic and Indosinian igneous rocks located along the southeastern and western margin of the Yangtze Block also exhibit decoupled Nd–Hf isotopic systemics, which may be a fingerprint of a previous late Mesoproterozoic to early Neoproterozoic oceanic subduction.     

The Mesozoic tectono-magmatic evolution at the Paleo-Pacific subduction zone in West Borneo

Metamorphic and magmatic rocks are present in the northwestern part of the Schwaner Mountains of West Kalimantan. This area was previously assigned to SW Borneo (SWB) and interpreted as an Australian-origin block. Predominantly Cretaceous U-Pb zircon ages (c. 80–130 Ma) have been obtained from metapelites and I-type granitoids in the North Schwaner Zone of the SWB but a Triassic metatonalite discovered in West Kalimantan near Pontianak is inconsistent with a SWB origin. The distribution and significance of Triassic rocks was not known so the few exposures in the Pontianak area were sampled and geochemical analyses and zircon U-Pb ages were obtained from two meta-igneous rocks and three granitoids and diorites. Triassic and Jurassic magmatic and metamorphic zircons obtained from the meta-igneous rocks are interpreted to have formed at the Mesozoic Paleo-Pacific margin where there was subduction beneath the Indochina–East Malaya block. Geochemically similar rocks of Triassic age exposed in the Embuoi Complex to the north and the Jagoi Granodiorite in West Sarawak are suggested to have formed part of the southeastern margin of Triassic Sundaland. One granitoid (118.6 ± 1.1 Ma) has an S-type character and contains inherited Carboniferous, Triassic and Jurassic zircons which indicate that it intruded Sundaland basement. Two I-type granitoids and diorites yielded latest Early and Late Cretaceous weighted mean ages of 101.5 ± 0.6 and 81.1 ± 1.1 Ma. All three magmatic rocks are in close proximity to the meta-igneous rocks and are interpreted to record Cretaceous magmatism at the Paleo-Pacific subduction margin. Cretaceous zircons of metamorphic origin indicate recrystallisation at c. 90 Ma possibly related to the collision of the Argo block with Sundaland. Subduction ceased at that time, followed by post-collisional magmatism in the Pueh (77.2 ± 0.8 Ma) and Gading Intrusions (79.7 ± 1.0 Ma) of West Sarawak.     

Identification and isotopic studies of early Cambrian magmatism (El Carancho Igneous Complex) at the boundary between Pampia terrane and the Río de la Plata craton,La Pampa province,Argentina

We have identified late Early Cambrian metaigneous rocks very poorly exposed at the Estancia El Carancho, in central La Pampa province, Argentina. They comprise calc–alkaline metadiorite and metagranite, and tholeiitic metapyroxenite and metagabbro. They are jointly referred to as the El Carancho Igneous Complex, and regarded to pertain to the Pampean magmatic arc and backarc, respectively. Titanite U–Pb SHRIMP dating of the metapyroxenite yielded 528 ± 5 Ma, and zircon U–Pb SHRIMP dating of the metadiorite yielded 520 ± 1.4 Ma. Hafnium isotope determinations on the dated zircons show ¹⁷⁶Hf/¹⁷⁷Hf ratios corresponding to positive εHf values from + 7.18 to + 9.37; Hf model ages of the Cambrian zircons yielded 884 Ma. It is interpreted that the metadiorites of the Complex crystallized from an Early Neoproterozoic (Tonian) juvenile source. We argue that the inferred occurrence of juvenile Tonian magmatic rocks in the (otherwise, mostly Paleo-Mesoproterozoic) substratum of the southern Pampia terrane could indicate a zone of thinned basement possibly associated with the early stage of Rodinia's breakup. In addition, the studied segment of the Pampean magmatic arc is contaminated by also juvenile, Late Mesoproterozoic crust, as evidenced by the presence of xenocrystic cores of 1140–1194 Ma – T_DM-Hf 1720 Ma and εHf values of + 3.24 to + 4.85 – in the Cambrian zircons, hence suggesting that the studied segment of the Pampean magmatic arc was intruded into juvenile Late Mesoproterozoic magmatic arc rocks. The El Carancho Igneous Complex would be located at the tectonic boundary between the Pampia terrane and the Río de la Plata craton. This boundary stands out in the aeromagnetic data as a change in the structural orientation about a roughly N-S line located approximately at 65° W and representing the suture zone between the Pampia terrane and the Río de la Plata craton. Our geotectonic model envisages westward dipping subduction of oceanic crust beneath the Pampia terrane; the El Carancho Igneous Complex would, therefore, have been originated on the Pampia side (upper plate) of the suture. Slivers of the arc- and backarc-type rocks would have been tectonically imbricated in the suture zone during the Pampean orogeny.     

Peri-Amazonian,Avalonian-type and Ganderian-type terranes in the South Carpathians,Romania: The Danubian domain basement

The Danubian domain basement of the South Carpathians, Romania, comprises two Neoproterozoic continental crustal fragments, the Dr?g?an and Lainici-P?iu? terranes, which were sutured by the closure of an intervening oceanic domain, the Ti?ovi?a terrane. Magmatic and detrital zircons extracted from an orthogneiss, four granitoid plutons, two metasedimentary units, and a Liassic sandstone were dated by zircon U/Pb LA-ICP-MS. The F?ge?el augen gneiss from the Dr?g?an terrane basement yielded an age of 803.2 ± 4.4 Ma, the oldest well-constrained crystallization age reported from the Romanian Carpathians basement. The Tismana, ?u?i?a, Novaci and Olte? granitoid plutons, which intrude the Lainici-P?iu? terrane basement, yielded ages of 600.5 ± 4.4, 591.0 ± 3.5, 592.7 ± 4.9, and 588 ± 2.9 Ma, respectively. The Tismana granitoid age of 600 Ma and the youngest detrital zircon ages of 637–622 Ma from a metaquartzite within the Lainici-Paiu? terrane, constrain the deposition of the metaquartzite protolith to ca. 620–600 Ma. The 803 Ma age represents an old Pan-African age, whereas the younger Neoproterozoic ages suggest Pan-African/Cadomian thermotectonic events. Detrital and inherited zircon ages within the Dr?g?an and Lainici-Paiu? terranes attest to a peri-Amazonian, Avalonian-type provenance for the Dr?g?an terrane and possibly a Ganderian-type provenance for the Lainici-P?iu? terrane. The Lainici-P?iu? terrane rifted off Gondwana before the Dr?g?an terrane. Both terranes were attached to Moesia during the Early Paleozoic.     

U–Pb and Lu–Hf isotopes in detrital zircon from Neoproterozoic sedimentary rocks in the northern Yangtze Block: Implications for Precambrian crustal evolution

A combined study of Lu–Hf isotopes and U–Pb ages for detrital zircons from sedimentary rocks can provide information on the crustal evolution of sedimentary provenances, and comparisons with potential source regions can constrain interpretations of paleogeographic settings. Detailed isotopic data on detrital zircons from Neoproterozoic sedimentary rocks in the northern part of the Yangtze Block suggest that these rocks have the maximum depositional ages of ~ 750 Ma, and share a similar provenance. In their source area, units of late Archean (2.45 to 2.55 Ga) to Paleoproterozoic (1.9 to 2.0 Ga) U–Pb ages made up the basement, and were overlain or intruded by magmatic rocks of Neoproterozoic U–Pb ages (740 to 900 Ma). Hf isotopic signatures of the detrital zircons indicate that a little juvenile crust formed in the Neoarchean; reworking of old crust dominates the magmatic activity during the Archean to Paleoproterozoic, while the most significant juvenile addition to the crust occurred in the Neoproterozoic. Only the Neoproterozoic zircon U–Pb ages can be matched with known magmatism in the northern Yangtze Block, while other age peaks cannot be correlated with known provenance areas. Similar zircon U–Pb ages have been obtained previously from sediments along the southeastern and western margins of the Yangtze Block. Thus, it is suggested that an unexposed old basement is widespread beneath the Yangtze Block and was the major contributor to the Neoproterozoic sediments. This basement had a magmatic activity at ~ 2.5 Ga, similar to that in North China; but zircon Hf isotopes suggest significant differences in the overall evolutionary histories between the Yangtze and North China.     

40Ar–39Ar geochronology across Archean and Paleoproterozoic terranes from southeastern Guiana Shield (north of Amazonian Craton,Brazil): Evidence for contrasting cooling histories

A ⁴⁰Ar/³⁹Ar geochronological study was performed on amphibole and biotite from some representative units of distinct tectonic domains of the southeastern Guiana Shield, north of the Amazonian Craton, the Amapá Block and the Carecuru Domain. In the Amapá Block, an Archean continental block involved in the Transamazonian orogenesis (2.26–1.95 Ga), the investigated minerals, from rocks of the Archean high-grade basement assemblage, give only Paleoproterozoic ages, indicating their complete resetting during the Transamazonian orogenic event. Amphibole ages vary from 2087 ± 3 to 2047 ± 20 Ma, and biotite ages spread mainly between 2079 ± 18 and 2033 ± 13 Ma. In the Carecuru Domain, in which the geodynamic evolution is related to Paleoproterozoic magmatic arc setting during the Transamazonian event, calc-alkaline granitoids yield amphibole age of 2074 ± 17 Ma, and biotite ages of 1928 ± 19 Ma and 1833 ± 13 Ma.These data reinforce the importance of the Transamazonian orogenic cycle in the investigated area, and indicate that the rocks were not significantly affected by post-Transamazonian events. When coupled with available U–Th–Pb monazite and Pb–Pb zircon geochronological records and petro-structural observations, the new ⁴⁰Ar/³⁹Ar data delineate contrasting cooling and exhumation histories for the tectonic domains. In the Amapá Block, the data suggest nearly vertical T–t paths that reflect fast cooling rates, which indicate tectonically controlled exhumation, related to collisional stages of the Transamazonian event, between 2.10 and 2.08 Ga. Conversely, in the Carecuru Domain, low cooling rates suggest that the arc-related granitoids underwent slow and monotonous cooling since their emplacement until reaching the biotite isotopic closure temperature.