ROLE OF POST-OROGENICEXTENSIONAL TECTONICS IN THE SUPERGIANT ANTIMONY MINERALIZATION IN CENTRAL HUNAN PROVINCE, SOUTH CHINA

The Xikuangshan antimony deposit in central Hunan, South China, is the largest antimony deposit ever known in the world. The ore bodies are strictly confined to the footwalls of mafor high-angle normal faults which transect the inclined folds in the flank;away from the fault planes,both the homogenization temperatures of inclusions in gangue minerals and the intensity of antimony mineralization decrease.These characteristics strongly demonstrate that the faults are used as the conduit for the metal-bearing fluid in mineralization.The normal faults,striking the NE to NNE,are interpreted to be generated by the postmgenic extension in the time from Cretaceous to Paleogene.Crustal or lithospheric thinning, directly resulting from regional extension inevitably increase the geothermal gradient, Which is likely to cause large-scale convection of underground water that may leach out and transport valuablemetals such as Sb from source rocks.Focussed discharge along the fault zones contributes to the formation of the supergiant antimony deposit in Xikuangshan under the appropriate sedimentary barrier.

Geochronological Significance of the Post-Orogenic Mafic-Ultramafic Rocks in the Hongqiling Area of Jilin Province, Northeast China

Mafic-uitramafic complexes are widespread in Hongqiling in central Jiulin Province, NE China. The Hongqiling complex comprises pyroxenite, olivine websterite, lberzolite, gabbro and leucogabbro. Based on the latest geochronological results, these intrusions yield a zircon U-Pb age of about 216 Ma, implying that they emplaced in the late Triassic period and that the mafic-uitramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the accumulated olivine crystallizing is basaltic with high MgO, and it comes from depleted or juvenile lithospheric mantle, according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source, implying that the mafic-uitramafic rocks originate from the mixing product of crust- and mantle-derived magma. Therefore, the magmatic source was contaminated by an amount of crustal material, and the subsequent crystal fractionation resulted in the Cu-Ni mineralization. Dynamic analyses indicate that, after the collision of the North China Craton and Jiamusi Massif, the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass and underplating of the mantle-derived magma, which led to the formation of the primary mafic-uitramafic magma due to the mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-uitramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes, and they were exposed as maficultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies that the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic-uitramafic complexes in the Xing＇an-Mongolia Orogenic Belt in NE China and in the Altay-Tianshan-Junggar Orogenic Belt in Northern Xinjiang indicates that mafic intrusions are an important magmatic suite that evolved during post-orogenic processes. Portions of this mafic magma could have underplated the lower crust, and served as a heat source for associated late-stage granitic magmas.

Early Yanshanian post-orogenic granitoids in the Nanling region——Petrological constraints and geodynamic settings

Early Yanshanian magmatic suites predominate absolutely in the Nanling granite beit. They consist mainly of monzogranite and K-feldspar granite. There occur associations of early Yanshanian A-type granitoids (176 Ma-178 Ma) and bimodal volcanic rocks (158 Ma-179 Ma) in southern Jiangxi and southwestern Fujian in the eastern sector of the granite belt and early Yanshanian basalts (177 Ma-178 Ma) in southern Hunan in the central sector of the belt. Both the acid end-member rhyolite in the bimodal volcanic rock association and A-type granitoids in southern Jiangxi have the geochemical characteristics of intraplate granitic rocks and the basic end-member basalt of the association is intraplate tholeiite, while the basaltic rocks in southern Hunan include not only intraplate tholeiite but also intraplate alkali basalt. Therefore the early Yanshanian magmatic suites in the Nanling region are undoubtedly typical post-orogenic rock associations. Post-orogenic suites mark the end of a post-collision or late orogenic event and the initiation of Pangaea break-up, indicating that a new orogenic Wilson cycle is about to start. Therefore it may be considered that the early Yanshanian geodynamic settings in the Nanling region should be related to post-orogenic continental break-up after the Indosinian orogeny and the break-up did not begin in the Cretaceous.

Middle Triassic post-orogenic extension on Hainan Island: Chronology and geochemistry constraints of bimodal intrusive rocks

This work studies new petrological and geochemical data and zircon U-Pb ages for bimodal intrusive rocks from Xinglong re- gion, Hainan Island. Zircon U-Pb dating yields mean 238U/26pb ages of 238 ± 2 Ma and 234±2 Ma for diabasic and granitic phases, respectively, representing the Middle Triassic emplacement. The diabase and granite bodies were formed from discrete mafic and acidic magma sources that experienced local mechanical mixing at their mutual contacts. Although SiO2 content of intrusions is bimodal, trace element ratios indicate that both were formed in a post-orogenic extensional setting. Sr-Nd isotopic composition reflects a shared EMII type enriched mantle source component, possibly influenced by subduction-fluid metaso- matism.

Origin and Tectonic Implications of Post-Orogenic Lamprophyres in the Sulu Belt of China

Lamprophyre dykes that crosscut different types of ultrahigh pressure(UHP)metamorphic rocks are widely distributed in the Triassic Sulu UHP orogenic belt.Although abundant studies have been performed on these dykes,their origin and petrogenesis remain topics of controversy.This study presents the results of a detailed field-based study of petrology,whole-rock geochemistry and zircon U-Pb and Lu-Hf isotopes on lamprophyre dykes exposed in the central Sulu UHP zone,aiming at shedding lights on their petrogenesis and providing clues on the geological evolution of eastern continental China during the Cretaceous.The lamprophyres are typically porphyritic,with phenocrysts dominantly composed of amphibole and clinopyroxene set in a lamprophyric matrix.The dykes have moderate Si O2(47.70 wt.%–60.44 wt.%),variably high Mg O(2.58 wt.%–8.28 wt.%)and Fe2 O3 T(4.88 wt.%–9.26 wt.%)contents with high Mg#of 49–66.Geochemically,they have enriched light rare earth element(REE)and flat heavy REE patterns((La/Gd)N=5.14–10.56;(Dy/Yb)N=1.43–1.54)with negligible Eu anomalies(Eu/Eu*=0.83–1.10),and they show enrichment in large ion lithophile elements(e.g.,Ba and K)but depletion in high-field strength elements(e.g.,Nb,Ti and P).In-situ zircon U-Pb geochronology reveals that the lamprophyres have concordant ages of 120–115 Ma,demonstrating that the dykes emplaced in the Early Cretaceous.These zircons have?Hf(t)values ranging from-26.0 to-11.0.Inherited zircons that occur in the dykes are dated to be Neoproterozoic,in line with the protolith ages of their host(i.e.,the UHP rocks).An integration of these data allows us to propose that the lamprophyres were generated during the Cretaceous,by melting of subcontinental lithospheric mantle-derived metasomatite with enriched chemical compositions underneath the North China Craton.The metasomatite was formed mainly by peridotite-fluid/melt reactions,with the fluids/melts mainly liberated from subducted Yangtze continental crust during the Triassic.Regional extension,lithospheric thinning and mantle upwelling caused by rollback of the subducted paleoPacific plate is considered to account for the generation of the lamprophyres as well as the extensive arc-like magmatic rocks in eastern continental China during the Early Cretaceous.

Phanerozoic Tectonic Evolution,Metallogenesis and Formation of Mineral Systems in China

The continental Asia is mainly composed of three major tectonic regimes,the Tethys,Paleo Asian Ocean,and West Pacific.It underwent multi-stage plate convergences,ocean-continent transformations,and subductions,collisions and/or collages,and post collisional(orogenic)extensions in Phanerozoic.Tectonic evolution of the Asia brings up a unique fault system and tectonic geomorphological features in the China's Mainland.Also,it provides a geodynamic background for the formation and evolution of metallogeneses and mineral systems,resulting in nonuniform distribution of tectono-metallogenic systems and metallogenic belts.The spatiotemporal distribution of mineral deposits in China and adjacent areas exhibits periodic variation under controlling of the full life Wilson cycle and tectonic evolution,forming the plate convergence-related mineral system in East Asia.Porphyry Cu deposits are mainly related to compressional systems in Paleozoic and early Mesozoic,and more closely related to post-collision extensional settings in late Mesozoic and Cenozoic.Orogenic Au deposits mainly formed in post-orogeny extensional setting.Alkaline rock related rare earth element deposits formed mainly at margins of the North China and Yangtze cratons.Granite-pegmatite Li and other rare metal deposits formed mainly in early Mesozoic,related to Indosinian post-orogeny extension.Tectono-metallogenic systems provide important basis for the prospecting of mineral resources.

Zircon SHRIMP Dating for the Weiya Pluton, Eastern Tianshan: Its Geological Implications

The timing of the emplacement of the Weiya pluton remains controversial due to the absence of systematic and precise dating. This paper reports zircon SHRIMP U-Pb dating of different lithologic phases in the Weiya pluton, and discusses the genesis and tectonic environment. The ages of gabbro, quartz syenite, diorite porphyrite and fine-grained granite are 236±6 Ma, 246±6 Ma, 233±8 Ma and 237±8 Ma, respectively. All these phases were formed in early-middle Indosinian （Triassic） in a post-orogenic environment. In addition to underplating, intraplating of mantle-derived magmas is also a substantial mechanism for magma generation and vertical accretion of the continental crust. Granitoid rocks are important products of vertical continental accretion as underplating evolves gradually to intraplating. The existence of post-orogenic Indosinian granites shows that the middle Tianshan orogenic belt underwent an important tectonic conversion from the Paleo-Asian ocean subduction-collision system to the Paleo-Tethys ocean regime.

Geochemical constraints on the origin of Early Cretaceous alkaline intrusions and its tectonic implication,Sulu Orogenic Belt,Eastern North China Craton

Post-orogenic alkaline intrusions from the Sulu Orogenic Belt of eastern North China Craton consist of A-type granites.In this study,we report U-Pb zircon ages,geochemical data,Sr-Nd-Pb,and zircon Hf isotopic data for these rocks.The LA-ICP-MS U-Pb zircon analyses yield consistent ages ranging from 127.1±2.4 to 119.5±4.8 Ma for four samples.The alkaline rocks are characterized by high total alkalis(K2 O+Na2 O=8.32-10.11 wt%),light rare-earth element enrichment,and heavy rare-earth element depletion,with a wide range(La/Yb)N values(20-48),moderate negative Eu anomalies(Eu/Eu*=0.50-0.74),enrichment in large-ion lithophile elements(LILEs,i.e.,Rb,Th,U and Pb),and depletion in Ba,Sr and high field strength elements(HFSEs,i.e.,Nb,Ta,and Ti),high(87Sr/86Sr)i ranging from 0.708 to 0.7089,low sNd(t)values from-19.4 to-16.8,(206Pb/204Pb)i=16.751-16.935,(207Pb/204Pb)i=15.381-15.535,(208-Pb/204Pb)i=37.472-37.838,negativeεHf(t)values between-21.3 and-25.7 for the magmatic zircons,and larger TDM2 model ages from 2.5 to 2.8 Ga.These results suggest that the rocks were derived from a common enriched lithospheric mantle source that was metasomatized by foundered lower crustal eclogitic materials before magma generation.Furthermore,the geochemical and isotopic feature implies that the primary magma of these rocks originated through partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from lower crust eclogite.These rocks in this study may have been generated by subsequent fractionation of potassium feldspar,plagioclase,ilmenite,and/or rutile.However,negligible crustal contamination occurred during the diagenesis process.

Characterization of a Post Orogenic A-Type Granite, Gabal El Atawi, Central Eastern Desert, Egypt: Geochemical and Radioactive Perspectives

The alkali feldspar granite of Gabal El Atawi is post orogenic granite originated from subalkaline magma in extensional suite. It is developed within plate tectonic setting and has A2-type character which generated from apparent crustal source. The petrographic, geochemical and radioactive characteristics of El Atawi granite meet and fulfill the requirements of being fertile granite and it can be considered as promising uraniferous granite. Fluid inclusion studies of the altered granite elucidated two different solutions acting on the host granitic pluton. The first is NaCl-CaCl low temperature fluid with a wide range of salinity. The second is high temperature and salinity Fe-Mg-Na chloride solution. Different fractures in the granite acted as good channels for the hydrothermal fluids that leached uranium from its bearing minerals disseminated all over the host granite and redeposited it in the alteration zones.

Tectonic Setting of the Cu-Ni Sulfide-Bearing Mafic-Ultramafic Complexes in Northern Jilin Province, NE China

There are series of Cu-Ni sulfide-bearing mafic-ultramafic intrusions widespread in north JilinProvince,Northeastern China. The intrusions formed in Xing’an-Mongolian Orogenic Belt near to the northeastern margin of North China Craton. The complexes were formed in almost same period according to the zircon U-Pb dating reported recently, which means that the complexes were formed in same tectonic period and belong to one tectonic magmatic event. The rock assemblages are different from the ophiolite type and Yidun type in orogenic belt. The mafic-ultramafic complexes formed in the range from 217 Ma to 232 Ma coeval with A-type granites in the area, which formed bimodal igneous rock assemblage. According to the regional angular unconformities, there were existed the orogenies of Caledonian, Hercynian, Early Indosinian, Late Indosinian and Yanshanian. The Early Indosinian coeval with orogenic I-type granites and sanukitie that suggesting the lithosphere thickening in the extrusion tectonic setting of orogenic processes, however the Late Indosinian coeval with bimodal igneous rock assemblage that suggesting the lithosphere thinning in the extension tectonic setting of post-orogenic processes in the Xing’an-Mongolian Orogenic Belt. Chemical composition of the mafic-ultramafic rocks has the characteristics of high-Mg and low-K tholeiites related with inter-continental post-orogenic tectonic setting. The trace elements indicate their formed in conditions of continental extension belt or initial rift and has the characteristics of revolution from oceanic island arc, volcanic arc of continental margin to continental extended belt. The low initial Sr isotopic ratios and positive εNd(t) values suggest that the initial magma of the complexes come from the parting melting of depleted lithospheric mantle. The depleted ithospheric mantle was new formed supported by zircon Hf isotope in Hongqiling complex. The depleted lithospheric mantle may be caused by the asthenosheric mantle upwelling and underplating in the tectonic setting of extension during the Late Indosinian post-orogenic processes.

Multi-isotope and geochemical approach to the magma source and tectonic setting of Proterozoic anorthosite massifs and AnorthositeMangerite-Charnockite-Granite(AMCG)suites

The occurrence of massif-type anorthosite intrusions is a widespread Proterozoic phenomenon.They are usually associated with gabbroic,charnockitic,and granitic rocks,comprising the so-called anorthositemangerite-charnockite-granite(AMCG)suite.Although these rocks have been extensively studied worldwide,several aspects concerning their formation remain unsettled.Among them,the magma source and the tectonic setting are the most important.To evaluate these issues,we first compiled geochemical and isotopic data of Proterozoic anorthosite massifs and AMCG suites worldwide and stored it in a database named datAMCG.This plethora of data allows us to make some important interpretations.We argue that the wide-ranging multi-isotopic composition of this group of rocks reflects varying proportions of juvenile mantle-derived melts and crustal components.We interpret that the precursor magmas of most massive anorthosite bodies and associated mafic rocks have a mantle-dominated origin.However,we highlight that a crustal component is indispensable to generate these lithologies.Adding variable amounts of this material during succeeding multi-stage assimilation-fractional crystallization(AFC)processes gives these intrusions their typical mantle-crustal hybrid isotopic traits.In contrast,a crustaldominant origin with a complementary mantle component is interpreted for most MCG rocks.In summary,the isotopic information in datAMCG indicates that both sources are necessary to generate AMCG rocks.Therefore,we suggest that hybridized magmas with different mantle-crust proportions originate these rocks.This interpretation might offer a more nuanced and accurate depiction of this phenomenon in future work instead of choosing a single-sourced model as in the past decades.Finally,tectonomagmatic diagrams suggest that the rocks under study were likely generated in a tectonic environment that transitioned between collision and post-collisional extension,sometimes involving subduction-modified mantle sources.This interpretation is supported by geological and geochronological information from most complexes,thus challenging the Andean-type margins as an ideal tectonic setting.

Age, Geochemistry, and Tectonic Implications of Dulaerqiao Granite, Inner Mongolia

Dulaerqiao granite is located at the Xinlin-Xiguitu-Toudaoqiao suture zone between the Erguna massif and the Xing＇an massif, northeast of Inner Mongolia. The rocks are mainly composed of K-feldspar, quartz, and plagioclase. Zircon LA-ICP-MS U-Pb data show that this granite was deposited in the Late Carboniferous Period （308.7±2.0 Ma）. The samples are rich in alkali, Fe, and AI and low in Mg, Ca, and P. Chondrite-normalized REEs exhibit right-inclined patterns with significant negative Eu anomalies. Additionally, the granite shows high quantities of trace elements such as Zr, Hf, Th, K, and Rb and decreased quantities of Sr, P, and Ti. The chemical characteristics identified herein and a series of diagrams that distinguish different types of granite show that Dulaerqiao alkali-feldspar granites belong to the aluminous A-type granite group. Meanwhile, the initial magma crystallizes under high- temperature, low-pressure conditions resulting from a tectonic extension setting. The formation of Du- laerqiao aluminous A-type granite is related to the rejuvenation of the ancient Xinlin-Xiguitu- Toudaoqiao suture zone, which was activated by the interaction between the combined Erguna-Xing＇an massif and the Songnen massif in the Late Paleozoic Era. This aluminous A-type granite was deposited about 30 Ma after the collision.

The First Discovery of a Tin Deposit Related to Hercynian A-Type Granites in China

This paper introduces the petrological, mineralogical and geochemical fea. tures of the rocks hosting the Sareshik tin deposit—an independent tin deposit related to Hercynian A-type granites discovered in China in 1987. A comparison with the features of A-type granites at home and abroad indicates that some of their petrological features are more typical than those of famous A-type granites of Nigeria. The geological features of the tin deposit are salient and notably different from those of some famous tin deposits in China, so the deposit may represent China’s deposits associated with anorogenic granites. This tin deposit was formed in the Hercynian Stage. This type of tin deposit was for the first time discovered in China and is also rare in the world. It is a new type of tin deposit in China.