Geochemistry,zircon U–Pb geochronology and Hf isotopes of Jurassic-Cretaceous granites in the Tengchong terrane,SW China: implications for the Mesozoic tectono-magmatic evolution of the Eastern Tethyan Tectonic Domain

ABSTRACT

Recently identified Early Jurassic, Early Cretaceous, and Late Cretaceous granites of the Tengchong terrane, SW China, help to refine our understanding of the Mesozoic tectonic-magmatic evolutionary history of the region. We present new zircon U–Pb geochronological, Lu–Hf isotopic and geochemical data on these rocks. The zircon LA-ICP-MS U–Pb ages of the Mangzhangxiang, Laochangpo, and Guyong granites, and Guyong granodioritic microgranular enclaves are 185.6, 120.7, 72.9, and 72.7 Ma, respectively. Geochemical and Hf isotopic characteristics suggest the Mangzhangxiang and Laochangpo S-type granites were derived from partial melting of felsic crust and that the Guyong I-type granite and associated MMEs were generated through magma mixing/mingling. Mesozoic magmatism in the Tengchong terrane can be divided into three episodes: (1) the Triassic syn- and post-collisional magmatic event was related to the closure of the Palaeo-Tethyan Ocean, as represented by the Changning-Menglian suture zone; (2) the Jurassic to Early Cretaceous magmatism was related to the subduction of the Meso-Tethyan oceanic crust, as represented by the Myitkyina ophiolite belt; and (3) the Late Cretaceous magmatism was related to the subduction of the Neo-Tethyan oceanic crust, as represented by the Kalaymyo ophiolite belt.     

U–Pb dating of zircon and cassiterite from the Early Cretaceous Jiaojiguan iron-tin polymetallic deposit,implications for magmatism and metallogeny of the Tengchong area,western Yunnan,China

The newly discovered Jiaojiguan deposit, a medium-scale skarn iron-tin polymetallic deposit on the Sino-Burma boundary of Yunnan Province (SW China), is spatially associated with the biotite monzonitic granite. Here, we report new in situ zircon LA-MC-ICP-MS U–Pb ages, trace element and Hf isotope data from the granite, and U–Pb dating ages of cassiterite from the ore bodies. In this study, we obtain a weighted mean ²⁰⁶Pb/²³⁸U age of 124.1 ± 1.4 Ma for the zircon and a ²⁰⁷Pb/²⁰⁶Pb-²³⁸U/²⁰⁶Pb intercept age of 123.8 ± 2.2 Ma for the cassiterite. The granite crystallized during the Early Cretaceous, with zircons exhibiting εHf(t) values from ?5.8 to ?0.6 and two-stage Hf model ages (T_DM2) of 1.21–1.54 Ga. The close temporal and spatial links between pluton emplacement and ore-forming events suggest that magmatic-hydrothermal events were the key factors that triggered the genesis of the iron-tin polymetallic deposits in the area. Regional geochronological data show that tin mineralization took place three times during the Cretaceous–Palaeogene in the Tengchong block due to re-melting of the underlying supposed Proterozoic (1.5 ± 0.5 Ga) Sn-rich strata/materials. Compared with those in the Bangong–Nujiang metallogenic belt (BNMB), we propose that the Cretaceous iron-tin polymetallic mineralization events in Tengchong–Baoshan closely resemble those of the Bangong–Nujiang belt in northern Tibet, both of which have experienced similar tectono-magmatic-metallogenic histories since the Mesozoic.     

Linking the Tengchong Terrane in SW Yunnan with the Lhasa Terrane in southern Tibet through magmatic correlation

New zircon U–Pb data, along with the data reported in the literature, reveal five phases of magmatic activity in the Tengchong Terrane since the Early Paleozoic with spatial and temporal variations summarized as Cambrian–Ordovician (500–460 Ma) to the east, minor Triassic (245–206 Ma) in the east and west, abundant Early Cretaceous (131–114 Ma) in the east, extensive Late Cretaceous (77–65 Ma) in the central region, and Paleocene–Eocene (65–49 Ma) in the central and western Tengchong Terrane, in which the Cretaceous–Eocene magmatism migrated from east to west. The increased zircon ε_Hf(t) of the Early Cretaceous granitoids from − 12.3 to − 1.4 at ca. 131–122 Ma to − 4.6 to + 7.1 at ca. 122–114 Ma, identified for the first time in this study, and the magmatic flare-up at ca. 53 Ma in the central and western Tengchong Terrane indicate increased contributions from mantle- or juvenile crust-derived components. The spatial and temporal variations and changing magmatic compositions over time in the Tengchong Terrane closely resemble those of the Lhasa Terrane in southern Tibet. Such similarities, together with the data of stratigraphy and paleobiogeography, enable us to propose that the Tengchong Terrane in SW Yunnan is most likely linked with the Lhasa Terrane in southern Tibet, both of which experienced similar tectonomagmatic histories since the Early Paleozoic.     

The giant tin polymetallic mineralization in southwest China:Integrated geochemical and isotopic constraints and implications for Cretaceous tectonomagmatic event

The Gejiu-Bozushan-Laojunshan W-Sn polymetallic metallogenic belt(GBLB) in southeast Yunnan Province is an important part of the southwestern Yangtze Block in South China.Tin polymetallic mineralization in this belt includes the Niusipo,Malage,Songshujiao,Laochang and Kafang ore fields in the Gejiu area which are spatially and temporally associated with the Kafang-Laochang and Songshujiao granite plutons.These granites are characterized by variable A/CNK values(mostly 1.1,except for two samples with 1.09),high contents of SiO_2(74.38-76.84 wt.%) and Al_2 O_3(12.46-14.05 wt.%) and variable CaO/Na_2 O ratios(0.2-0.65) as well as high zircon δ~(18)O values(7.74‰-9.86‰),indicative of S-type affinities.These rocks are depleted in Rb,Th,U,Ti,LREE[(La/Yb)N=1.4-20.51],Ba,Nb,Sr,and Ti and display strong negative Eu and Ba anomalies.The rocks possess high Rb/Sr and Rb/Ba ratios,relatively low initial ~(87)Sr/~(86)Sr ratios(0.6917-0.7101),and less radiogenic εNd(t)values(-8.0 to-9.1).The zircon grains from these rocks show negative ε_(Hf)(t) values in the range of-3.7 to-9.9 with mean T_(DM2)(Nd) and T_(DM2)(Hf) values of 1.57 Ga and 1.55 Ga.They show initial ~(207)Pb/~(204)Pb ranging from15.69 to 15.71 and ~(206)Pb/~(204)Pb from 18.36 to 18.70.Monazite from Songshujiao granites exhibits higher U and lower Th/U ratios,lower δ~(18)O values and higher ε_(Hf)(t) values than those of the zircon grains in the KafangLaochang granites.The geochemical and isotopic features indicate that the Laochang-Kafang granites originated by partial melting of Mesoproterozoic crustal components including biotite-rich metapelite and metagraywacke,whereas the Songshujiao granites were derived from Mesoproterozoic muscovite-rich metapelite crustal source.Most zircon grains from the Songshujiao,Laochang and Kafang granites have high-U concentrations and their SIMS U-Pb ages show age scatter from 81.6 Ma to 88.6 Ma,80.7 Ma to 86.1 Ma and 82.3 Ma to 87.0 Ma,suggesting formation earlier than the monazite and cassiterite.Monazite SIMS U-Pb ages and Th-Pb ages of three same granite samples are consistent and show yielded 206 Pb/~(238)U ages of 83.7 ± 0.6 Ma,83.7±0.6 Ma,and 83.4±0.6 Ma,and ~(208)Pb/~(232)Th ages of 83.2 ± 0.5 Ma,83.8 ± 0.4 Ma,and 83.5±0.9 Ma,which are within the range of the SIMS zircon U-Pb ages from these rocks.The data constrain the crystallization of the granites at ca.83 Ma.In situ U-Pb dating of two cassiterite samples from the cassiterite-sulfide ore in the Songshujiao ore field and Kafang ore field,and two from the cassiterite-oxide+cassiterite bearing dolomite in the Laochang ore field yielded weighted mean 206 Pb/~(238)U ages of 83.5±0.4 Ma(MSWD=0.6),83.5 ± 0.4 Ma(MSWD=0.5),83.6 ±0.4 Ma(MSWD=0.6) and 83.2 ±0.7 Ma(MSWD=0.6),respectively.Combined with geological characteristics,the new geochronological data indicate that the formation of the granites and Sn polymetallic deposits are coeval.We correlate the magmatic and metallogenic event with lithospheric thinning and asthenosphere upwelling in continental extension setting in relation to the eastward subduction of the Neo-Tethys beneath the Sanjiang tectonic domain during Late Cretaceous.     

Geochronology and geochemistry of the Donglufang porphyry-skarn Mo-Cu deposit in the southern Yidun Terrane and their geological significances

The newly-discovered Donglufang Moe Cu porphyry-skarn deposit is located in the southern Yidun Terrane, southeast Tibet, with more than 80 million tonnes(Mt) of reserves(grading 0.15 wt.% Mo and0.48 wt.% Cu) hosted in Triassic strata and Late Cretaceous granodiorite porphyry. Ree Os dating of molybdenum ore yielded a weighted mean age of 84.9 ± 1.0 Ma and an isochron age of 85.2 ± 0.6 Ma.LA-ICP-MS Ue Pb dating of zircons from the granodiorite porphyry yielded206 Pb/238 U ages ranging from 87.4 Ma to 84.2 Ma with a weighted mean206 Pb/238 U age of 85.1 ±0.5 Ma, indicating a temporal linkage between granitic magmatism and Moe Cu mineralization. Geochemical analyses show that the granodiorite porphyries are I-type granites with Si O_2 contents of 64.3 -66.7 wt.%. These rocks are typically metaluminous with high K_2 O/Na_2 O ratios, low Mg O(1.32 -1.56 wt.%), Cr(5.6 -12.9 ppm), Ni(3.79 -10.81 ppm), Mg#(43 -52) values, and high Sr(304 -844 ppm), Sr/Y(21.2 -50.8) and La/Yb ratios(37.0 -60.1). They are enriched in light rare-earth elements(LREE) relative to heavy rare-earth elements(HREE), with slightly negative Eu anomalies, and are enriched in Th, U and large ion lithophile elements(LILE, e.g., K and Rb), and depleted in high field strength elements(HFSE, e.g., Nb, Ta, P and Ti). They also show negative zircon εHf(t) values(-6.7 to -2.3) and negative whole rock εNd(t) values(à5.2 to-4.3), as well as old Hfe Nd model ages, indicating the magmas were derived from a thickened ancient lower crust within the garneteamphibolite facies. Considering the tectonic evolution of the Yidun Terrane, geochemical characteristics of granodiorite porphyry, and the ages of mineralization obtained in this study. We suggest that the Donglufang deposit was formed in a post-collisional setting, which has a genetic relationship with the emplacement of the granodiorite porphyry. The present study provide key information for the exploration of the Late Cretaceous metallogeny in the Yidun Terrane.     

Discovery of Paleozoic rocks at northern margin of Sambagawa terrane,eastern Kyushu,Japan: Petrogenesis,U–Pb geochronology and its tectonic implication

Ordovician diorite-quartz diorite mylonite (Saganoseki quartz diorite) was discovered in Sambagawa metamorphic terrane at the northern margin of Saganoseki Peninsula, Kyushu Island, Japan. The LA-ICP-MS zircon U–Pb geochronology revealed that the intrusion age of Saganoseki quartz diorite was 473.3 ​± ​3.6 ​Ma. These rocks show the volcanic arc affinity based on the trace element composition. On the basis of geochronological and geochemical results, Saganoseki quartz diorite is considered to be a member of the Early Paleozoic igneous rocks of the Kurosegawa tectonic zone. Saganoseki quartz diorite is located just south of the Median Tectonic Line (MTL) and is in close contact with the pelitic and psammitic schist without any brittle shear zone. U–Pb ages of detrital zircon grains from two psammitic schists show the estimated sedimentation age of early Late Cretaceous, indicate that these psammitic schists are the member of Sambagawa metamorphic rocks. Together with these results and the mode of occurrence in the field, we argue that the Early Paleozoic igneous rocks of the Kurosegawa tectonic zone existed as an upper structural unit of the Sambagawa terrane. This relationship is the key to reconstruct the Mesozoic tectonics of Japan as a part of East Asia, and its evolution through time.     

Detrital zircon constraints on late Paleozoic tectonism of the Bogda region(NW China) in the southern Central Asian Orogenic Belt

The Chinese North Tianshan(CNTS) in the southern part of the Central Asian Orogenic Belt(CAOB) has undergone multistage accretion-collision processes during Paleozoic time,which remain controversial.This study addresses this issue by tracing the provenance of Late Paleozoic sedimentary successions from the Bogda Mountain in the eastern CNTS through U-Pb dating and Lu-Hf isotopic analyses of detrital zircons.New detrital zircon U-Pb ages(N=519) from seven samples range from 261±4 Ma to 2827±32 Ma.The most prominent age peak is at 313 Ma and subordinate ages vary from 441 Ma to 601 Ma,with some Precambrian detrital zircon ages(～7%) lasting from 694 Ma to 1024 Ma.The youngest age components in each sample yielded weighted mean ages ranging from 272±9 Ma to 288±5 Ma,representing the maximum depositional ages.These and literature data indicate that some previously-assumed "Carboniferous"strata in the Bogda area were deposited in the Early Permian,including the Qijiaojing,Julideneng,Shaleisaierke,Yangbulake,Shamaershayi,Liushugou,Qijiagou,and Aoertu formations.The low maturity of the sandstones,zircon morphology and provenance analyses indicate a proximal sedimentation probably sourced from the East Junggar Arc and the Harlik-Dananhu Arc in the CNTS.The minor Precambrian detrital zircons are interpreted as recycled materials from the older strata in the Harlik-Dananhu Arc.Zircon E_(Hf)(t) values have increased since ～408 Ma,probably reflecting a tectonic transition from regional compression to extension.This event might correspond to the opening of the Bogda intraarc/back arc rift basin,possibly resulting from a slab rollback during the northward subduction of the North Tianshan Ocean.A decrease of zircon ε_(Hf)(t) values at ～300 Ma was likely caused by the cessation of oceanic subduction and subsequent collision,which implies that the North Tianshan Ocean closed at the end of the Late Carboniferous.     

Late Cambrian to Early Silurian Granitic Rocks of the Gemuri Area, Central Qiangtang, North Tibet: New Constraints on the Tectonic Evolution of the Northern Margin of Gondwana

The Paleozoic tectonic framework and paleo–plate configuration of the northern margin of Gondwana remain controversial. The South Qiangtang terrane is located along the northern margin of Gondwana and records key processes in the formation and evolution of this supercontinent. Here, we present new field, petrological, zircon U-Pb geochronological, and Lu-Hf isotopic data for granitic rocks of the Gemuri pluton, all of which provide new insights into the evolution of the northern margin of Gondwana. Zircon U-Pb dating of the Gemuri pluton yielded three concordant ages of 488.5 ± 2.1, 479.9 ± 8.9, and 438.5 ± 3.5 Ma. Combining these ages with the results of previous research indicates that the South Qiangtang terrane records two magmatic episodes at 502–471 and 453–439 Ma. These two episodes are associated with enriched zircon Hf isotopic compositions(εHf(t) =-10.1 to-3.9 and-16.6 to-6.5, respectively), suggesting the granites were formed by the partial melting of Paleoproterozoic–Mesoproterozoic metasedimentary rocks(Two–stage Hf model ages(TCDM) = 2094–1704 and 2466–1827 Ma, respectively). Combining these data with the presence of linearly distributed, contemporaneous Paleozoic igneous rocks along the northern margin of Gondwana, we suggest that all of these rocks were formed in an active continental margin setting. This manifests that the two magmatic episodes within the Gemuri area were associated with southward subduction in the Proto-(Paleo-) Tethys Ocean.     

Petrology,geochemistry and geochronology of the Zhongcang ophiolite,northern Tibet: implications for the evolution of the Bangong-Nujiang Ocean

Ophiolites are widespread along the Bangong-Nujiang suture zone, northern Tibet. However, it is still debated on the formation ages and tectonic evolution process of these ophiolites. The Zhongcang ophiolite is a typical ophiolite in the western part of the Bangong-Nujiang suture zone. It is composed of serpentinized peridotite, cumulate and isotropic gabbros, massive and pillow basalts, basaltic volcanic breccia, and minor red chert. Zircon SHRIMP Ue Pb dating for the isotropic gabbro yielded weighted mean age of 163.4 ± 1.8 Ma. Positive zircon ε Hf(t) values(+15.0 to +20.2) and mantle-like σ~(18)O values(5.29 ±0.21)% indicate that the isotropic gabbros were derived from a long-term depleted mantle source. The isotropic gabbros have normal mid-ocean ridge basalt(N-MORB) like immobile element patterns with high Mg O, low TiO_2 and moderate rare earth element(REE) abundances, and negative Nb,Ti, Zr and Hf anomalies. Basalts show typical oceanic island basalt(OIB) geochemical features, and they are similar to those of OIB-type rocks of the Early Cretaceous Zhongcang oceanic plateau within the Bangong-Nujiang Ocean. Together with these data, we suggest that the Zhongcang ophiolite was probably formed by the subduction of the Bangong-Nujiang Ocean during the Middle Jurassic. The subduction of the Bangong-Nujiang Tethyan Ocean could begin in the Earlye Middle Jurassic and continue to the Early Cretaceous, and finally continental collision between the Lhasa and Qiangtang terranes at the west Bangong-Nujiang suture zone probably has taken place later than the Early Cretaceous(ca. 110 Ma).     

The Late Cretaceous source-to-sink system at the eastern margin of the Tibetan Plateau: Insights from the provenance of the Lanping Basin

The surface uplift of the Tibetan Plateau(TP) and its geomorphology evolution has triggered aridification of Asia's interior and drainage development at the eastern margin of the plateau.However, how the pre-Cenozoic early growth histories of the TP impact the drainage system and climate is poorly constrained.The Late Mesozoic Lacustrine evaporite-bearing basins on the eastern margin of the TP record significant information on the uplift of the source terranes, source-to-sink system development and climate change.In this study, we presented detrital zircon U–Pb ages from the Upper Cretaceous Yunlong Formation in the Lanping Basin, as well as Hf isotopic, petrographic, direct statistical, and multidimensional scaling analyses, and use them to characterize the provenance and reconstruct the drainage system.All of the samples have five major age peaks at 200–290 Ma, 400–490 Ma,750–1000 Ma, 1750–1950 Ma, and 2400–2600 Ma with mostly negative ε_(Hf)(t) values(81%).We infer the sediments are primarily derived from recycled sediments of the Songpan-Garze terrane, and partly from the Sichuan Basin and the Southern Qiangtang terrane, as well as the exposed magmatic rocks of the Yidun Arc and SongpanGarze terrane.The provenance features of the contemporaneous sediments from the Sichuan, Xichang, Chuxiong,and Simao basins indicate a complex hierarchical drainage pattern on the eastern margin of the TP during the Late Cretaceous.The hierarchical drainage system exhibits a complete gradational cycle of lake-basin types from overfilled freshwater Sichuan Basin through balanced fill saline Xichang Basin and underfilled hypersaline Chuxiong, Lanping, Simao, and Khorat Plateau basins from proximal to distal.The early growth of the TP primarily controlled the drainage and lake-basin evolution by not only causing the uplift and exhumation of the source areas and providing large amounts of clastic material to the proximal sub-drainage areas but also intensifying the aridity and deposition of evaporites.     

Geochronology,petrogenesis and tectonic implications of the Zhongchuan granitic pluton in the Western Qinling metallogenic belt,China

The Zhongchuan district is an important component of the metallogenic belt in the Western Qinling. The Zhongchuan granite pluton occurring in the centre of the Zhongchuan metallogenic area has been poorly constrained, though the Triassic granite in Western Qinling has been well documented. In‐situ zircon U–Pb ages, Hf isotopic compositions and whole‐rock geochemical data are presented for host granite and mafic microgranular enclaves (MMES) from the Zhongchuan pluton, in order to constrain its sources, petrogenesis and tectonic setting of the pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMES and the host granitic rocks mainly due to interactions between coeval felsic host magma and mafic magma. The zircon U–Pb age of host granite (231.6 ± 1.5 to 235.8 ± 2.3 Ma) has overlapping uncertainty with that of the MMES (236.6 ± 1.3 Ma), establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the MMES (ε_Hf(t) = −13.4 to 4.0) is distinct from the host granite (ε_Hf(t) = −15.7 to 0.0), indicating that both enriched subcontinental lithosphere mantle (SCLM) and crustal sources contributed to their origin. The zircons have two‐stage Hf model ages of 1064 to 1798 Ma for the host granite and 858 to 1747 Ma for the MMES. This suggests that the granitic pluton was likely derived from partial melting of a Late Mesoproterozoic crust, with subsequent interaction with the SCLM‐derived mafic magmas in tectonic affinity to the South China Block. Copyright © 2012 John Wiley & Sons, Ltd.     

Late Mesozoic Huangbeiling S-type granite in the East Qinling Orogen,China: Geochronology,petrogenesis and implications for tectonic evolution

S-type granites are typical features of collisional orogenic belts and could provide insights into the tectonic process associated with the final phase of orogeny. The East Qinling Orogen, one of significant segments in the Central China Orogen, witnessed complex tectonic evolution during the Late Mesozoic. The rare S-type granites in this orogen can be used as important proxies to understand the Late Mesozoic tectonic processes. Although a few previous studies suggested that the Huangbeiling pluton in the East Qinling Orogen might be S-type granite, detailed studies are lacking. Thus, we report the results from a systematic petrological, whole-rock geochemical and zircon U-Pb-Lu-Hf isotopic studies on the Huangbeiling pluton, with a view to constrain the timing of magmatism, petrogenetic evolution and genetic type, and to evaluate the implications for Late Mesozoic tectonic evolution of the East Qinling Orogen. Zircon U-Pb analysis yield ²⁰⁶Pb/²³⁸U spot ages in the range of 156.7–132.2 Ma, with weighted ²⁰⁶Pb/²³⁸U mean ages varying from 146.8 to 141.9 Ma, suggesting the Huangbeiling pluton formed during the Late Jurassic to Early Cretaceous. Zircon Lu-Hf isotopic data show negative εHf(t) values of ?21.5 to ?14.9 and two-stage Hf model ages of 2546–2131 Ma, which are correlated with the Neoarchean to Paleoproterozoic (3.0–2.1 Ga) meta-sedimentary rocks from nearby Taihua Group, indicating that the magma was sourced from reworked ancient crustal components involving meta-sedimentary rocks. Whole-rock geochemical data display enrichment of LREEs, Pb, Hf and Y as well as depletion in HREEs, Ba and HFSEs (e.g., Ta, P, Ti), with weakly negative Eu anomalies. The Huangbeiling granitoids are identified as S-type granites, which generated through partial melting of lower-middle crust and upper crustal fractional crystallization in syn-collisional settings. In conjunction with published information related to the tectonic evolution of the East Qinling Orogen, we propose that the Late Mesozoic Huangbeiling S-type granites might response to the complex tectonic evolution related to extensional tectonics induced by multi-directional (intra-continental) subductions from the Yangtze and North China Cratons as well as the Paleo-Pacific Plate during the Late Mesozoic.     

Metallogenic Epoch of Nonferrous Metallic and Silver Deposits in the Jiaodong Peninsula, China and its Geological Significance

As China's most important gold-producing district,the Jiaodong Peninsula also contains copper,lead-zinc,molybdenum(tungsten),and other nonferrous metal ore deposits,but the space-time and genetic relationships with gold deposits remain uncertain.To investigate the temporal relationship between these nonferrous metal and gold ore deposits,We collected the samples from a number of nonferrous metallic and silver deposits and metallogenetic rock bodies in the eastern Jiaodong Peninsula for isotopic dating.The results show that the Re-Os isotopic model ages of the Lengjia molybdenum deposit in Rongcheng range from 114.5± 1.8 Ma to 112.6± 1.5 Ma,with an average age of 113.6± 1.6Ma;the LA-ICP-MS ~(206)Pb/~(238)U ages of 33 zircons in the sericitization porphyritic monzogranite that hosts the Tongjiazhuang silver deposit in Rongcheng range between 122 Ma and 109 Ma,with a weighted mean age of 116.04± 0.95 Ma;the LA-ICP-MS ~(206)Pb/~(238)U ages of 31 zircons in the copper metallogenic pyroxene monzodiorite that hosts the Kuangbei copper deposit in Rongcheng range from126 Ma to 106 Ma,with a weighted mean age of 116.6± 1.7 Ma;and the LA-ICP-MS ~(206)Pb/~(238)U ages of19 zircons in the pyroxene monzodiorite surrounding the Dadengge gold and multimetal deposit in Weihai range from 113 Ma to 110 Ma,with a weighted mean age of 111.7± 0.6 Ma.All these results indicate that the metallogenic ages of the silver and nonferrous metallic deposits in the Jiaodong Peninsula are in a limited range from 118 Ma to 111 Ma.Previous studies have demonstrated that the isotopic ages of gold deposits in the Jiaodong Peninsula range from 123 Ma to 110 Ma,while Weideshanian magmatism occurred between 126 Ma to 108 Ma.Both these ranges are grossly consistent with the metallogenic ages of silver and nonferrous metallic deposits in this study,suggesting that the large-scale mineralization occurred in the Early Cretaceous when magmatic activities were strong.This epoch may be linked to the lithosphere thinning and the thermo-upwelling extension in eastern China at that time.In addition,field investigation also shows that gold and nonferrous metallic deposits are distributed nearby the Weideshanian granite,with the nonferrous metallic deposits lying within or surrounding the granite pluton and the gold deposits outside the granite pluton.We propose the following mineralization scenario:In the Early Cretaceous,an intensive lithospheric extension induced partial melting and degassing of the metasomatized lithospheric mantle,which resulted in the formation of mantle-derived fluids enriched in metal elements.During the rapid process of magma ascent and intrusion,crust-derived fluids were activated by the magmatic thermal dome and served to further extract ore-forming materials from the crust.These fluids may have mixed with the mantle-derived fluid to form a crust-mantle mixing-type ore-forming fluid.The high-temperature conditions in the center or in contact with the granitic magmatic thermal dome would have been favorable for the formation of porphyry-type,skarn-type,and hydrothermal-vein-type ores,thus forming a series of Mo(W),Cu,and Pb-Zn deposits in the mid-eastern Jiaodong Peninsula.In contrast,the medium-to low-temperature conditions in the periphery of the magmatic thermal dome would have favored the deposition of gold(silver) ores under the appropriate physiochemical and structural conditions.The metallogenic epoch of the molybdenum,copper,and silver deposits,and their spatio-temporal and genetic relations to the gold deposits,as demonstrated in this study,not only provide important insights to the study of regional metallogeny,our understanding of the metallogenesis of the Jiaodong type gold deposit,and the geodynamic background of the large-scale mineralization in the Jiaodong Peninsula,but also have practical value in guiding the mineral exploration.     

Geologic and geochronologic data from the Guerrero terrane in the Tejupilco area,southern Mexico: new constraints on its tectonic interpretation

The eastern part of the Guerrero terrane contains two tectonically juxtaposed metavolcanic-sedimentary sequences with island arc affinities: the lower, Tejupilco metamorphic suite, is intensely deformed with greenschist facies metamorphism; the upper, Arcelia-Palmar Chico group, is mildly to moderately deformed with prehnite-pumpellyite facies metamorphism. A U–Pb zircon age of 186 Ma for the Tizapa metagranite, and Pb/Pb isotopic model ages of 227 and 188 Ma for the conformable syngenetic Tizapa massive sulfide deposit, suggest a Late Triassic–Early Jurassic age for the Tejupilco metamorphic suite. ⁴⁰Ar/³⁹Ar and K–Ar age determinations of metamorphic minerals from different units of the Tejupilco metamorphic suite in the Tejupilco area date a local early Eocene thermal event related to the emplacement of the undeformed Temascaltepec granite. The regional metamorphism remains to be dated. ⁴⁰Ar/³⁹Ar ages of 103 and 93 Ma for submarine volcanics support an Albian–Cenomanian age for the Arcelia-Palmar Chico group, although it may extend to the Berriasian. U–Pb isotopic analyses of zircon from the Tizapa metagranite, together with Nd isotopic data, reveal inherited Precambrian zircon components within units of the Tejupilco metamorphic suite, precluding the generation of Tejupilco metamorphic suite magmas from mantle- or oceanic lithosphere-derived melts, as was previously considered to be the case. Instead, these data, together with high-grade gneiss xenoliths with Grenvillian Nd isotopic affinity in Oligocene subvolcanics, indicate the presence of pre-Mesozoic continental crust beneath at least the eastern part of the Guerrero terrane. As a Late Triassic–Early Jurassic basement unit in the eastern part of the Guerrero terrane, the Tejupilco metamorphic suite may therefore represent an evolved volcanic arc developed on old crust with assimilated craton-derived sediment. This would imply a tectonic cycle of deformation, metamorphism and erosion during the Middle–early Late Jurassic that was probably related to the accretion and consolidation of part of the Guerrero terrane into the Acatlán Complex, the pre-Mississippian poly-deformed and metamorphosed basement of the Mixteco terrane.     

Geochemistry,zircon U–Pb and molybdenite Re–Os dating of the Taolaituo porphyry Mo deposit in the Central Great Hinggan Range: implications for the geodynamic evolution of northeastern China

The Taolaituo porphyry‐type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. The mineralization occurs mainly as veins, lenses and layers within the host porphyry. To better understand the link between the mineralization and the host igneous rocks, we studied samples from the underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Five molybdenite samples yield a Re–Os isochron weighted mean age of 133.0 ± 0.82 Ma, whereas the porphyry granitoids samples yield crystallization ages of 133 ± 1 Ma and 130.4 ± 1.3 Ma. The U–Pb and Re–Os ages are similar, suggesting that the mineralization is genetically related to the Early Cretaceous porphyry emplacement. Re contents of the molybdenites range from 21.74 to 42.45 ppm, with an average of 32.69 ppm, whereas δ³⁴S values vary between 3.7‰ and 4.2‰, which is typical of mantle sulphur. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/ ²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb vary in the ranges of 18.276–18.385, 15.566–15.580 and 38.321–38.382, respectively. The Taolaituo Early Cretaceous granitoids are A‐type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Taolaituo deposit occurred contemporaneously with the Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra‐continental extension in northeast China. Copyright © 2015 John Wiley & Sons, Ltd.     

Late Triassic Granites From the Quxu Batholith Shedding a New Light on the Evolution of the Gangdese Belt in Southern Tibet

The Gangdese magmatic belt formed during Late Triassic to Neogene in the southernmost Lhasa terrane of the Tibetan plateau. It is interpreted as a major component of a continental margin related to the northward subduction of the Neo-Tethys oceanic slab beneath Eurasia and it is the key in understanding the tectonic framework of southern Tibet prior to the India-Eurasia collision. It is widely accepted that northward subduction of the Neo-Tethys oceanic crust formed the Gangdese magmatic belt, but the occurrence of Late Triassic magmatism and the detailed tectonic evolution of southern Tibet are still debated. This work presents new zircon U-Pb-Hf isotope data and whole-rock geochemical compositions of a mylonitic granite pluton in the central Gangdese belt, southern Tibet. Zircon U-Pb dating from two representative samples yields consistent ages of 225.3±1.8 Ma and 229.9±1.5 Ma, respectively, indicating that the granite pluton was formed during the early phase of Late Triassic instead of Early Eocene(47–52 Ma) as previously suggested. Geochemically, the mylonitic granite pluton has a sub-alkaline composition and low-medium K calc-alkaline affinities and it can be defined as an I-type granite with metaluminous features(A/CNK1.1). The analyzed samples are characterized by strong enrichments of LREE and pronounced depletions of Nb, Ta and Ti, suggesting that the granite was generated in an island-arc setting. However, the use of tectonic discrimination diagrams indicates a continental arc setting. Zircon Lu-Hf isotopes indicate that the granite has highly positive εHf(t) values ranging from +13.91 to +15.54(mean value +14.79), reflecting the input of depleted mantle material during its magmatic evolution, consistent with Mg~# numbers. Additionally, the studied samples also reveal relatively young Hf two-stage model ages ranging from 238 Ma to 342 Ma(mean value 292 Ma), suggesting that the pluton was derived from partial melting of juvenile crust. Geochemical discrimination diagrams also suggest that the granite was derived from partial melting of the mafic lower crust. Taking into account both the spatial and temporal distribution of the mylonitic granite, its geochemical fingerprints as well as previous studies, we propose that the northward subduction of the Neo-Tethys oceanic slab beneath the Lhasa terrane had already commenced in Late Triassic(~230 Ma), and that the Late Triassic magmatic events were formed in an active continental margin that subsequently evolved into the numerous subterranes, paleo-island-arcs and multiple collision phases that form the present southern Tibet.     

Geochronology and geochemistry of early Mesozoic magmatism in the northeastern North China Craton: Implications for tectonic evolution

This paper reports geochronological, geochemical, zircon U–Pb and Hf–O isotopic data of the Late Triassic and Early Jurassic intrusive rocks in the northeastern North China Craton (NCC), with the aim of reconstructing the tectonic evolution and constraining the spatial–temporal extent of multiple tectonic regimes during the early Mesozoic. Zircon U–Pb ages indicate that the early Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Triassic (221–219 Ma) and Early Jurassic (180–177 Ma). Late Triassic magmatism produced mainly granodiorite and monzogranite, which occur as a NE–SW-trending belt parallel to the Sulu–Jingji Belt. Geochemically, they are classified as high-K calc-alkaline and metaluminous to weakly peraluminous granitoids, and are enriched in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high-field-strength elements (HFSEs; e.g., Nb, Ta, Ti, and P) and heavy rare earth elements (HREEs), indicating an affinity to adakite. Combined with their ε_Hf(t) values (−17.9 to −3.2) and two-stage model ages (2387–1459 Ma), we conclude that the Late Triassic granitoid magma in the northeastern NCC was derived from partial melting of the thickened lower crust of the NCC and was related to deep subduction and collision between the NCC and the Yangtze Craton (YC). The Early Jurassic magmatism is composed mainly of monzogranites, which are classified as metaluminous, high-K calc-alkaline, and I-type granite. Their ε_Hf(t) values and two-stage model ages are −16.7 to −4.2 and 2282–1491 Ma, respectively. Compared with the Late Triassic granitoids, the Early Jurassic granitoids have relatively high HREE contents, similar to calc-alkaline igneous rocks in an active continental margin setting. These Early Jurassic granitoids, together with the coeval calc-alkaline volcanic rocks and gabbro–diorite–granodiorite association in the northeastern (NE) Asian continental margin, comprise a NNE–SSW-trending belt parallel to the NE Asian continental margin, indicative of the onset of Paleo-Pacific Plate subduction beneath Eurasia.     

Neoproterozoic complexes of the shelf cover of the Dzabkhan terrane basement in the Central Asian Orogenic Belt

The formation stages of high-grade metamorphic complexes and the related granitoids of the Dzabkhan terrane basement are considered. The age data (U–Pb method, TIMS) of zircons from the trondhjemite block of the eastern part of the Dzabkhan terrane, which is directly overlain by the dolomite sequence of the Tsagaan Oloom Formation, are given. Trondhjemites yield the U–Pb zircon age of 862 ± 3 Ma. In their structural position, they are assigned to typical postmetamorphic formations that determine the formation and cratonization of rocks of the host block. The geochronological study of trondhjemites gives grounds to distinguish fragments of the continental crust in the Dzabkhan terrane basement, the formation of which occurred at different periods of time: ～860 and ～790 Ma. Geological–geochronological and Sm?Nd isotope–geochemical studies indicate that the Dzabkhan terrane basement is not a single block of the Early Precambrian continental crust, but a composite terrane, comprising Neoproterozoic ensialic and island-arc structural and compositional complexes. Correlation of Sr isotopic characteristics with the ⁸⁷Sr/⁸⁶Sr variation curve in the Neoproterozoic and Cambrian seawater shows that carbonate deposits accumulated at the eastern margin of the Dzabkhan terrane near the end of the Neoproterozoic, 700–550 Ma, and in the central part of the terrane in the Early Cambrian, 540–530 Ma.     

Incremental growth and origin of the Cretaceous Renjiayingzi pluton,southern Inner Mongolia,China: Evidence from structure,geochemistry and geochronology

The Renjiayingzi intermediate-acid pluton is located along a pre-existing ENE–WSW-trending dextral shear zone that forms part of the Xar Moron suture zone that marks the final closure of the Paleo-Asian Ocean. The pluton is composed of three small intrusions, which from northwest to southeast, are named the Shuangjianshan (SI), the Qianweiliansu (QI) and the Xingshuwabeishan (XI) intrusions. LA-ICPMS zircon U–Pb dating of a pyroxene diorite from the SI yields an age of 138 ± 1 Ma; the SHRIMP zircon U–Pb age of a tonalite from the QI records an age of 134 ± 2 Ma, whereas LA-ICPMS zircon U–Pb dating of a monzogranite from the XI has an age of 126 ± 1 Ma, suggesting the entire pluton was built up by three separate emplacement events that young to the ESE: this is further supported by the contact relations. Incremental growth of plutons by amalgamation of repeated small magma pulses is the most viable emplacement model. The pluton was probably emplaced by updoming of the roof along previous tensile fractures and by upward stacking of the three intrusions. The SI and QI have similar U–Pb ages and geochemical characteristics, and most likely had the same magma source and underwent similar petrogenetic processes. They have high MgO concentrations at low silica contents, are enriched in large ion lithophile elements, depleted in high field strength elements, have negative ε_Nd(t) values of −1.8 to −3.7, with Nd model ages of 1.07–1.19 Ga. Pyroxene diorites of the SI also have variable zircon ε_Hf(t) values (from −0.8 to +6.1), indicating that they were mainly derived from juvenile crust with minor crustal contamination and clinopyroxene-dominated fractional crystallization. The late monzogranites from the XI show weak negative ε_Nd(t) values of −2.3 to −2.5, young Nd model ages of 0.99–1.00 Ga, positive zircon ε_Hf(t) values (+1.3 to +4.6) and higher SiO₂ and K₂O contents, with strong depletion in Eu, P and Ti, indicating derivation from a distinct petrogenetic process from the two earlier intrusions. The monzogranites were the result of partial melting of juvenile crust in response to mantle-derived magma underplating, together with plagioclase-dominated fractional crystallization.     

Magma mixing revealed from in situ zircon U–Pb–Hf isotope analysis of the Muhuguan granitoid pluton, eastern Qinling Orogen, China: implications for late Mesozoic tectonic evolution

In this paper, we present zircon U–Pb age and Hf isotope data to document the significance of magma mixing in the formation of Late Jurassic granitoid intrusions in the eastern Qinling Orogen, China. The Muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite, all containing abundant hornblende-rich cumulates, dioritic xenoliths, and mafic magmatic enclaves (MMEs). The monzogranite and granodiorite are intruded by a number of lamprophyre dykes. Both a cumulate and a dioritic xenolith samples have concordant zircon U–Pb ages of ca. 161 ± 1 Ma, but possess contrasting Hf isotopic compositions. The cumulate has more radiogenic zircon Hf isotopes with negative ε _Hf(t) values (?7.9 to ?2.5) and T _DM1 ages of 0.9–1.1 Ga, indicating its derivation likely from basaltic rocks of the Neoproterozoic to early Paleozoic Kuanping Group in the area. The dioritic xenolith has much lower zircon ε _Hf(t) values of ?19.5 to ?8.8 and T _DM2 ages of 2.4–1.7 Ga, consistent with a juvenile Paleoproterozoic crust source presumably represented by the metabasic rocks of the Qinling Group in the area. Individual samples of the monzogranite, MME, and a lamprophyre dyke have U–Pb ages of 150 ± 1, 152 ± 1, and 152 ± 1 Ma, respectively, demonstrating coeval mafic and felsic magmatism in the Late Jurassic. The lamprophyre dyke has homogeneous, highly negative zircon ε _Hf(t) values (?29.8 to ?24.8) and Archean T _DM2 ages (3.0–2.7 Ga), and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source. Zircons from the fine-grained MME show a large range of ε _Hf(t) between ?29.1 and ?9.8, overlapping values of the monzogranite and lamprophyre dyke samples. Zircon U–Pb age and Hf isotopes of the MMEs are consistent with their formation by mixing of crustal- and enriched mantle-derived magmas. The main group of zircons from the monzogranite has ε _Hf(t) values (?17.9 to ?9.3) and T _DM2 ages (2.3–1.8 Ga) that are compatible with the dioritic xenoliths, indicating that the former was produced by partial melting of Paleoproterozoic crustal source with involvement of mantle-derived magmas. Mafic magmatism revealed from the Muhuguan pluton indicates that the eastern Qinling Orogen was dominated by lithospheric extension during the Late Jurassic. Compilation of existing geological and geochronological data suggests that this extensional event started in Late Jurassic (ca. 160 Ma) and persisted into the Early Cretaceous until ca. 110 Ma. The Jura-Cretaceous extension may have resulted from the late Mesozoic westward subduction of the Pacific plate beneath the East Asian continental margin.