文档共享_Beijing SHRIMP Center

你好,请

SHRIMP U-Pb zircon Geochronology of the Xiaotongguanshan and Shatanjiao Intrusions and Its Petrological Implications in the Tongling Aear,Anhui [查看] DIYongjun、WUGanguo、ZHANGDa、SONGBiao、ZANGWenshuan、ZHANGZhongyi、LIJinwen

Abstract This paper determines the crystallization ages of the Xiaotongguanshan quartz monzodiorite and Shatanjiao quartz monzonite porphyry from the Tongling area using the SHRIMP zircon U-Pb method. The crystallization age of the former is 142.8±1.8 Ma; that of the latter is 151.8±2.6 Ma. These data indicate that they were formed during the Late Jurassic (142.8 to 151.8 Ma). Zoned magma chamber was formed because of double diffusive convection. Therefore, the intrusive sequence of magma is generally from quartz monzonite through quartz monzodiorite to pyroxene monzodiorite, i.e. an inverted sequence.

Petrogenesis and dating of the Kangding complex,Sichuan Province [查看] CHENYuelong、LUOZhaohua、ZHAOJunxiang、LIZhihong、ZHANGHongfei、SONGBiao

Abstract An analysis of major and trace element geochemistry and SHRIMP U-Pb zircon dating of mafic, intermediate, and felsic rocks from the Mianning metamorphic complex of Sichuan Province was conducted. One of our conclusions is that a majority of the zircons crystallized between 721 and 773 Ma in a magmatic regime. The complexes contain early to late Paleo- proterozoic relict zircons from ancient continental crust. The oldest age, 2468 Ma, may represent the basement of the Yangtze block. Overgrowth zircon rims and palingenetic zircons have been observed and dated, and are believed to have formed after crystallization, during Paleozoic and Mesozoic metamorphic-anatexis. We also conclude that depletion of Nb, Ta, HREE, in a spider-diagram normalized to primitive mantle and calc-alkaline association, implies that they formed in island-arc or under-plating settings.

Opening of the Tethys in southwest China and its significance to the breakup of East Gondwanalang in late PaleozoicEvidence from SHRIMP U-Pb zircon analyses for the Garze ophiolite block [查看] YANQuanren、WANGZongqi、LIUShuwen、LIQiugen、ZHANGHongyuan、WANGTao、LIUDunyi、SHIYuruo、JIANPing、WANGJianguo、ZHANGDehui、ZHAOJian

Abstract SHRIMP U-Pb zircon analyses for a gabbro sample from the Garzê ophiolite block yielded a mean 206Pb/238U age of 292±4 Ma, which indicated that the spreading time of the Garzê-Litang Tethys was most likely at the earliest Permian. Combined with previous studies, we suggest that the opening of the Tethys in southwest China was derived from breakup of the East Gondwanaland in the late Paleozoic.

U–Pb ages and Hf–O isotopes of zircons from Late Paleozoic mafic–ultramafic units in the southern Central Asian Orogenic Belt Tectonic implications and evidence for an Early-Permian mantle plume [查看] Ben-XunSu、Ke-ZhangQin、PatrickAsamoahSakyi、Xian-HuaLi、Yue-HengYang、HeSun、Dong-MeiTang、Ping-PingLiu、Qing-HuaXiao、SanjeewaP.K.Malaviarachchi

U–Pb age and Hf–O isotope data of zircons fromthe mafic–ultramafic complexes and their related rhyolites and granites in the Eastern Tianshan and Beishan regions were obtained by SIMS and LA-ICPMS. The Hf–O isotopic composition and Hf model age of the zircons are closely related to their tectonic setting and formation age. The zircons from the mafic–ultramafic complexes in the Bogeda–Haerlike and Jueluotage belts have higher εHf(t)(+8–+17) and lower δ18O (+4‰–+6‰), whereas most of the zircons in the gabbros, granites and rhyolite from theMiddle TianshanMassif and Beishan Rift display lower εHf(t) (0–+8) and higher δ18O (+5‰–+8‰).The positive εHf(t) and relatively lower δ18O values suggest that thesemafic–ultramafic complexes were derived from depleted mantle which was subjected to subduction-related modification processes. The Hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the Central Asian Orogenic Belt during the Paleozoic. The Hf model ages of the analyzed zircons, together with the regional geology suggest that the Beishan area had a northward subduction, possibly fromca. 900 Ma to ca. 400 Ma,whereas the Eastern Tianshan had a south-directed subductionmost likely fromca.600 Ma to ca. 310 Ma. Additionally, zircons with ca. 280 Ma U–Pb ages display wider and more scattered εHf(t) and δ18O variations than the relatively older and younger ones, which further support the Early Permian mantle plume model.

Timing of initiation of extension in the Tianshan, based on structural, geochemical and geochronological analyses of bimodal volcanism and olistostrome in the Bogda Shan (NW China) [查看] LiangshuShu、BoWang、WenbinZhu、ZhaojieGuo、JacquesCharvet、YuanZhang

This paper describes an olistostrome formation and accompanied bimodal volcanic rocks occurring in the Baiyanggou area, south of Bogda Shan. The main lithotectonic units consist of olistostrome, volcanic rocks and turbidite. The olistostrome is tectonically underlain by Upper Carboniferous limestone and sandstone along a NEE-trending detachment fault. Paleo-growth fault is locally observed. The olistostrome unit includes plenty of blocks of limestone, sandstone, rhyolite and volcaniclastic rocks, and a matrix of graywacke. Limestone blocks are dated as Pennsylvanian-Bashkirian in age by the coral and brachiopod fossils that are extensively recognized in the Upper Carboniferous strata. The volcanic unit consists of pillowed and massive basalt and rhyolite, the latter occur as an 8- to 10-meter-thick layer above the olistostrome unit.The turbidite unit is mainly composed of chert, siliceous mudstone and sandstone, within which the Bouma sequence can be locally recognized. Meter-wide gabbro and diabase dykes intrude these three units. Geochemically,rhyolites are characterized by high ACNK value of[1.1,depletion of Ba, Nb and Sm, and enrichment in Rb, Th and Zr. Basaltic rocks are rich in K2O, they show a LREE-enriched pattern and depletion in Ba, Nb and Zr, and enrichment in Ti, Ce and Hf, similar to continental rift-type tholeiite series. A gabbro porphyrite intruding the olistostrome was dated at 288 ± 3 Ma by a sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb method, and a rhyolite at 297 ± 2 Ma by a laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) zircon U–Pb method. The Baiyanggou olistostrome and accompanying bimodal volcanic series are linked to an extensional setting that developed in the south of the Bogda Shan.Several lines of evidence, e.g. occurrence of large-scale strike-slip shear zones, large number of mantle-derived magmatic rocks and available geochronological data,demonstrate a significant geodynamic change from convergence to extension in the Chinese Tianshan belt, even in the whole Central Asian Orogenic Belt. The extension in the Chinese Tianshan belt is initiated at ca. 300 Ma, i.e. around Carboniferous–Permian boundary times, and the peak period of intra-plate magmatism occurred in the interval of 300–250 Ma.

SHRIMP zircon U-Pb and molybdenite Re-Os isotopic dating of the tungsten deposits in the Tianmenshan-Hongtaoling W-Sn orefield, southern Jiangxi Province, China,and geological implications [查看] ChengyouFeng、ZailinZeng、DequanZhang、WenjunQu、AndaoDu、DaxinLi、HongquanShe

The southern Jiangxi Province is a major part of the Nanling W–Sn metallogenic province of southern China,where all W–Sn ore deposits are temporally and spatially related to Mesozoic granitic intrusions. The Tianmenshan–Hongtaoling orefield is a recently explored territory endowed by several styles of W–Sn mineralization. The orefield comprises three composite granitic plutons: Tianmenshan, Hongtaoling and Zhangtiantang associated with several tens ofW–Sn-polymetallic ore deposits (Maoping, Baxiannao, Niuling,Zhangdou, Yaolanzhai and others) along their contacts. In this study, four new SHRIMP zircon U–Pb ages were determined for three composite granitic plutons, and 33 molybdenite samples from fiveW–Sn deposits were analysed by ICP-MS Re–Os isotopic method. SHRIMP zircon U–Pb ages for both medium to coarse-gained biotite granite and porphyritic biotite monzogranite from the Tianmenshan composite pluton are 157.2±2.2 Ma and 151.8±2.9 Ma, respectively. Molybdenite Re–Os isochron ages for the related Baxiannao fracturecontrolled tungsten deposits are 157.9±1.5 Ma. Maoping greisens-type tungsten deposits were emplaced at 155.3±2.8 Ma and the Maoping wolframite–quartz veins at 150.2±2.8 Ma, respectively. The SHRIMP U–Pb age of zircons from the Hongtaoling biotite granite is 151.4±3.1 Ma whereas the molybdenite Re–Os isochron ages of the genetically related Niuling endocontact tungsten quartz veins and Zhangdou exocontact tungsten quartz veins are 154.9±4.1 to 154.6±9.7 Ma and 149.1±7.1 Ma, respectively. The SHRIMP zircon U–Pb age of the Zhangtiantang fine-grained muscovite granite is 156.9±1.7 Ma, whereas the molybdenite Re–Os isochron age for the related Yaolanzhai greisens-type tungsten deposit is 155.8±2.8 Ma. These new age data,combined with those available from the literature, indicate that the ages ofW–Sn ores and related granites are Late Jurassic with a peak at 150 to 160 Ma, which corresponds to the widespread Mesozoic metallogenic event in southern China. Molybdenites from this group of tungsten deposits have quite low Re contents (29.1 to 2608 ppb), suggesting continental crustal provenance of the ore metals.

Pyrrhotite Re–Os and SHRIMP zircon U–Pb dating of the Hongqiling Ni–Cu sulfide deposits in Northeast China [查看] LinsuLü、JingwenMao、HongboLi、FrancoPirajno、ZuohengZhang、ZhenhuaZhou

The Hongqiling (HQL) magmatic Ni–Cu sulfide deposits (Jilin Province, NE China) are located at the southern margin of the eastern Xing'an–Mongolian Orogenic Belt (XMOB) of the eastern Central Asian orogenic belt(CAOB), situated between the Siberian Craton (SC) and the North China Craton (NCC). The HQL ore-bearing mafic–ultramafic intrusions intrude into the metamorphic rocks of the lowermost Huangyingtun Formation of the Hulan Group (HLG), whose lithology is herein identified as a hornblende–zoisite gneiss. SHRIMP zircon U–Pb dating for the HLG, country rock of the HQL deposits, indicated a maximum deposition age of 272.2±4.3 Ma (95% confidence level, MSWD=2.6, n=14).Six pyrrhotite samples separated from massive Ni–Cu sulfide ores of the Fujia (No. 7) deposit yielded a Re–Os isotopic isochron age of 208±21 Ma (95% confidence level, MSWD=2.4, n=6), indicating that the oreformation age was Late Triassic. Re–Os isotope analyses showed an initial 187Os/188Os ratio of 0.315±0.050.The γOs values ranged from+137 to+161 with an average of+151, indicating that its ore-forming materials were mainly derived from mantle with possibly b30% crustal Os contamination. Large scale magmatic Ni–Cu mineralization in eastern Jilin occurred in post-collisional tectonic setting in the Late Triassic.Our new results suggest that the ages of the Ni–Cu sulfide deposits in the CAOB within China tended to become younger from west to east, as manifested by the Late Caledonian (~440 Ma), through the Late Hercynian (300–265 Ma) to the Late Indosinian (225–200 Ma). Such variation could reflect the gradual closure and post-collisional orogeny between the SC and the NCC from west to east.

Permo-Triassic arc magmatism in central Tibet， Evidence from zircon U-Pb geochronology,Hf isotopes,rare earth elements,and bulk geochemistry [查看] T.N.Yang、H.R.Zhang、Y.X.Liu、Z.L.Wang、Y.C.Song、Z.S.Yang、S.H.Tian、H.Q.Xie、K.J.Hou

There is hot debate on whether there is a Paleo-Tethyan suture within Qiangtang and on how the suture extends in central Tibet. In situ Hf and U–Pb isotopes, and rare earth element (REE) analyses of zircons, together with bulk chemistry, have helped us identify a significant, and previously unknown stage of subduction-related magmatism along the southern part of the eastern Qiangtang block, north of the Shuanghu suture, central Tibet. SHRIMP and LA-ICP-MS zircon U–Pb data demonstrate that the magmatism started as early as 275 Ma, lasted until 248 Ma, and took place at the same time as blueschist and eclogite were forming in the central Qiangtang high- to ultrahigh-pressure metamorphic belt (QMB). The positive εHf(t) values of the magmatic zircons range from 9.71 to 16.73, and indicate derivation of magma from a relatively uncontaminated, depleted mantle. Variations in εHf(t) values and the REE patterns of magmatic zircons,combined with substantial heterogeneities in the whole-rock chemistry, suggest that the arc-related magmatism occurred in pulses, and was long-lived. The present data can be interpreted in terms of a history of progressive subduction during the Early Permian and Early Triassic, during which time continental fragments of EQ affinity were tectonically eroded and subducted into the mantle, along with the subducted oceanic slab.The temporal and spatial correlations between the arc-like volcanic belt and the high-pressure metamorphic belt suggest a Late Paleozoic ocean (Paleo-Tethys) existed between the western and eastern Qiangtang blocks, and that the ocean was closed by northwards subduction.

Neoproterozoic (~900 Ma) Sariwon sills in North Korea Geochronology,geochemistry and implications for the evolution of the south-eastern margin of the North China Craton [查看] PengPeng、Ming-GuoZhai、QiuliLi、FuyuanWu、QuanlinHou、ZhongLi、TieshengLi、YanbinZhang

The Sariwon sills are distributed in the Pyongnam basin at the center of the Korean peninsula, eastern part of the North China Craton. These sills are up to 150 m in thickness and up to more than 10 km in length. Baddeleyite grains separated from a ~50 m thick sill give a SIMS 206Pb–207Pb age of 899±7 Ma(MSWD=0.34, n=14), which is interpreted to be the crystallization age of this sill. Zircon grains from the same sill gives a lower intercept U–Pb age of ~400 Ma, which is likely a close estimation of the greenschistfacies metamorphism of this sill. The Sariwon sills are dolerites and have tholeiitic compositions. They show enrichment of light rare earth element concentrations (La/YbN=1.4–2.8) and are slightly depleted in high field strength elements (e.g. Nb, Zr, and Ti), in comparison to neighboring elements on the primitive-mantle normalized spidergram. The whole rock εNdt (t=900 Ma) values are around −2, whereas in-situ εHft(t=900 Ma) values from zircon grains vary from−25 to+8. They are similar to the coeval sills in other parts of the North China Craton, e.g., the Chulan sills (Xu-Huai basin, Shandong peninsula) and the Dalian sills (Lv–Da basin, Liaodong peninsula). These sills possibly originated from a depleted mantle source (e.g., asthenosphere), rather than from the ancient lithospheric mantle of the North China Craton, and have experienced significant assimilation of lithospheric materials. The strata and sills in the Xu-Huai, Lv–Da and Pyongnam basins are comparable; moreover the three basins are geographically correlatable based on Neoproterozoic geographical reconstruction. We therefore propose that there is a Xu-Huai–Lv–Da–Pyongnam rift system along the south-eastern edge of the North China Craton during Neoproterozoic (~900 Ma), with the closure of the rift at ~400 Ma as a result of a continent-margin process. It is possible that this southeastern margin of the NCC did not face the inland in the configuration of the supercontinent Rodinia.

Magmatic-hydrothermal evolution of the Cretaceous Duolong gold-rich porphyry copper deposit in the Banggongco metallogenic belt,tibet,evidence from U-Pb and 40Ar-39Ar geochronology [查看] JinxiangLi、KezhangQin、GuangmingLi、BoXiao、JunxingZhao、LeiChen

The Duolong gold-rich porphyry copper deposit was recently discovered and represents a giant prospect(inferred resources of 4–5 Mt fine-Cu with a grade of 0.72% Cu; 30–50 t fine-gold with a grade of 0.23 g/t Au) in the Bangongco metallogenic belt, Tibet. Zircon SHRIMP and LA-ICP-MS U–Pb geochronology shows that the multiple porphyritic intrusions were emplaced during two episodes, the first at about 121 Ma (Bolong mineralized granodiorite porphyry (BMGP) and barren granodiorite porphyry (BGP)) and the second about 116 Ma (Duobuza mineralized granodiorite porphyry (DMGP)). Moreover, the basaltic andesites also have two episodes at about 118 Ma and 106 Ma, respectively. One andesite yields an U–Pb zircon age of 111.9 ± 1.9 Ma, indicating it formed after the multiple granodiorite porphyries. By contrast,the 40Ar/39Ar age of 115.2 ± 1.1 Ma (hydrothermal K-feldspar vein hosted in DMGP) reveals the close temporal relationship of ore-bearing potassic alteration to the emplacement of the DMGP. The sericite from quartz-sericite vein (hosted in DMGP) yields a 40Ar/39Ar age of 115.2 ± 1.2 Ma. Therefore, the ore-forming magmatic-hydrothermal evolution probably persisted for 6 m.y. Additionally, the zircon U–Pb ages (106–121 Ma) of the volcanic rocks and the porphyries suggest that the Neo-Tethys Ocean was still subducting northward during the Early Cretaceous.