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Stratigraphic and sedimentary records of the rift to drift evolution of the northern North China craton at the Paleo- to Mesoproterozoic transition [查看] Qing-RenMeng、Hong-HongWei、Yong-QiangQu、Shou-XianMa

This paper presents a stratigraphic and sedimentary study of late Paleoproterozoic to early Mesoproterozoic successions of the northern margin of the North China craton, including the Changcheng and Nankou Groups.A reconstruction of the tectono-sedimentary history of these two groups demonstrates that the northern North China craton experienced a two-stage evolution. As recorded by the Changcheng Group, early synrift subsidence and sedimentation were controlled by normal faults and accompanied by volcanism. In contrast, a late postrift stage was characterized by broad subsidence and widespread occurrence of shallow-marine clastic and carbonate rocks. A transgressive unconformity is identified, and together with its time-equivalent conformable contact, clearly separates the synrift and postrift sequences. The diachronous unconformity can be related to continental rifting and the separation of the North China craton from the adjacent India craton at roughly 1600 Ma, and is thus interpreted as a breakup unconformity. This age of ca. 1600 Ma is constrained by newly reported precise SHRIMP U–Pb zircon ages of transgressive deposits in the overlying Mesoproterozoic Dahongyu and Gaoyuzhuang Formations, just coincident with the Paleoproterozoic to Mesoproterozoic transition. The 1600 Ma time estimate for the tectonic departure of the North China craton from the India craton is comparable with the timing for the breakup of Columbia, a pre-Rodinia supercontinent containing almost all of the earth's continental blocks.

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.

SHRIMP U–Pb (zircon), Ar–Ar (muscovite) and Re–Os (molybdenite) isotopic dating of the Taoxikeng tungsten deposit, South China Block [查看] ChunliGuo、JingwenMao、FrankBierlein、ZhenghuiChen、YuchuanChen、ChuanbiaoLi、ZailinZeng

The Taoxikeng tungsten deposit is located in the Jiangxi Province in the southern part of China, and is one of the largest wolframite quartz-vein type tungsten deposits in the country. The deposit is situated in Sinian(Neoproterozoic) to Permian strata at the contact with the buried Taoxikeng Granite. Sensitive High Mass Resolution Ion Microprobe (SHRIMP) zircon U–Pb analysis of the granite has yielded dates of 158.7±3.9 and 157.6±3.5 Ma, which are interpreted as the emplacement age of the granite. Molybdenite separated from ore-bearing quartz-veins yields a Re–Os isochron age of 154.4±3.8 Ma, and muscovite separated from greisen between the granite and country rocks yields 40Ar/39Ar plateau ages of 153.4±1.3 and 152.7±1.5 Ma.These dates obtained from three independent geochronological techniques constrain the ore-forming age of the Taoxikeng deposit and link the ore genesis to that of the underlying granite. The Taoxikeng deposit is an example of a Jurassic regional-scale tungsten–tin ore-forming event between 160 and 150 Ma in the Nanling region of the South China Block. The deposit's strikingly low rhenium contents (4.9 to 13.0×10−3 μg/g) in molybdenite suggests that the ore was derived from a crustal source. This conclusion is consistent with previously published constraints from S, D and O stable isotopes, Sr–Nd systematics, and petrogenetic interpretations of spatially related granites.

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.

Provenance of Meso- to Neoproterozoic cover sediments at the Ming Tombs, Beijing,North China Craton An integrated study of U–Pb dating and Hf isotopic measurement of detrital zircons and whole-rock geochemistry [查看] YushengWan、DunyiLiu、WeiWang、TianruiSong、AlfredKröner、ChunyanDong、HongyinZhou、XiaoyanYin

The North China Craton (NCC)was subjected to an extensional regime after the Lüliangmovement at ~1.8 Ga and then was covered by an extensive Meso- to Neoproterozoic sedimentary succession, namely the Changcheng,Jixian and Qingbaikou Groups in ascending order. We report age spectra for detrital zircons and monazites, Hf isotopic systematics of detrital zircons, and whole-rock chemical and Nd isotopic compositions for sediments from the succession in the Ming Tombs area, Beijing, one of the typicalMeso- to Neoproterozoic areas in the NCC.Detrital zircons of six sedimentary samples have two distinct age peaks at ~2.52 Ga and ~1.85 Ga. There are some detrital zircons at 2.4–2.0 Ga but none at 2.3 Ga and only a few N2.7 Ga. The detrital zircon age spectra change with time. Sediments in the lower succession (Changcheng Group) and in the upper successions (Jixian and Qinbaikou Groups) are dominated by significant detrital zircon populations of late Neoarchean and late Paleoproterozoic ages, respectively. The ~2.5 Ga detrital zircons of the ChangchengGroup have εHf(2.5 Ga) values and tDM(Hf) model ages mainly ranging from −2 to +7 and 2.8 to 2.7 Ga, respectively. Detrital monazites of a sample fromthe JixianGroup exhibit amajor age peak between 1.95 and 1.80 Ga with somedata between 2.0 and 1.95 Ga. The sedimentary rocks of the Changcheng Group are characterized by high K2O contents (mostly 7.09–15.20%) and insignificant Eu anomalies (Eu/Eu*=0.71–1.16). They have tDM(Nd) model ages ranging from 2.70 to 2.43 Ga, being older than the tDM(Nd) ages (2.11 and 1.99 Ga) of sedimentary samples from the Qingbaikou Group. Based on a comparison with ages for the early Precambrian (N1.8 Ga) basement of the NCC, it can be concluded that (1) the sediments of theMeso- to Neoproterozoic coverwere undoubtedly derived fromthe NCC itself or once neighboring terranes; (2) variations in the detrital zircon age spectra from the lower to the upper successions reflect provenance evolution in that the lower crustal late Paleoproterozoic rockswere exposed at the surface after the upper crustal late Neoarchean rocks had already been eroded.

Prolonged magmatism, juvenile nature and tectonic evolution of the Chinese Altai,NW China Evidence from zircon U–Pb and Hf isotopic study of Paleozoic granitoids [查看] KedaCai、MinSun、ChaoYuan、GuochunZhao、WenjiaoXiao、XiaopingLong、FuyuanWu

Paleozoic granitoid magmatism played an important role in the tectonic evolution of the Chinese Altai,and zircon U–Pb and Hf isotopic compositions have been determined for samples from eleven granitic plutons/batholiths. The Jiadengyu gneissic granitic pluton yielded a zircon U–Pb age of 479 Ma, and thus it does not represent Precambrian basement as suggested previously. Our results and published data demonstrate that voluminous granitoids were continuously emplaced over more than 30% area of the Chinese Altai during the period from 447 Ma to 368 Ma with a climax at ca. 400 Ma. Ages for zircon overgrowth rims demonstrate additional thermal events at ca. 360 and 280 Ma, respectively. Positive eHf(t) values (0 to +9) of normal magmatic zircons suggest that the granitoid magmas were derived from juvenile sources. Xenocrystic zircon cores are 543–421 Ma old and also give positive eHf(t) values (+2.5 to +12), suggesting their origin as early crystallized minerals in the magma chambers or as inherited cores from newly-accreted meterials. The strong magmatism at ca. 400 Ma significantly changed the Hf isotopic composition of the magma source by substantial input of juvenile material in a relatively short period.Geophysical, geological and geochemical data support that ridge subduction was a possible mechanism for the strong magmatism ca. 400 Ma and the above mentioned change of Hf isotopic composition in the magma source.

Precisely dating Paleozoic kimberlites in the North China Craton and Hf isotopic constraints on the evolution of the subcontinental lithospheric mantle [查看] Qiu-LiLi、Fu-YuanWu、Xian-HuaLi、Zhi-LiQiu、YuLiu、Yue-HengYang、Guo-QiangTang

Kimberlite, a deep-sourced ultramafic potassic rock, carries not only diamond, but also invaluable mantle xenoliths and/or xenocrysts,which are important for tracking the evolution of subcontinental lithosphericmantle(SCLM). However, it is challenging to accurately determine the emplacement age of kimberlite and its compositions of primary magma because of modifications by crustal and/or mantle contamination and postemplacement alteration. This paper reports emplacement ages of diamondiferous kimberlites in Mengyin and Fuxian of the North China Craton (NCC) using three different dating methods. For Mengyin kimberlite, singlegrain phlogopite Rb–Sr dating yields an isochron age of 485±4 Ma, U–Th–Pb analyses on perovskite give a 238U–206Pb age of 480.6±2.9 Ma and a 232Th–208Pb age of 478.9±3.9 Ma, and baddeleyite yields a 207Pb–206Pb age of 480.4±3.9 Ma. For Fuxian kimberlite, baddeleyite gives a 207Pb–206Pb age of 479.6±3.9 Ma, indicating that the Paleozoic kimberlites in the NCC were emplaced at ~480Ma. Numerous lines of evidence indicate that the studied baddeleyites are xenocrysts fromthe SCLM, and can be used to constrain Hf isotope compositions (εHf(t)~−6) of the SCLM when kimberlite erupted. Combined with data from Mesozoic–Cenozoic mantle-derived rocks and xenoliths, the Hf isotope evolution trend of the SCLM beneath NCC before craton destruction was tentatively constructed, which suggested that the Archean SLCM was enriched by metasomatism at ~1.3 Ga.Further Hf isotope investigations on additional SCLM-derived materials could be used to compare with the constructed Hf isotope evolution trend before craton destruction to determine when lithospheric thinning occurred.

Post-collisional granitoids from the Dabie orogen New evidence for partial melting of a thickened continental crust [查看] YongshengHe、ShuguangLi、JochenHoefs、FangHuang、Sheng-AoLiu、ZhenhuiHou

The geological implications of granitoid magmas with high Sr/Y and La/Yb are debated because these signatures can be produced by multiple processes. This study presents comprehensive major and trace element compositions and zircon SHRIMP U–Pb age data of 81 early Cretaceous granitoids and 4 mafic enclaves from the Dabie orogen to investigate partial melting of the thickened lower continental crust (LCC). On the basis of Sr/Y ratios, granitoids can be grouped into two magma series: (i) high Sr/Y granitoids (HSG) and (ii) normal granitoids with low Sr/Y. Relative to normal granitoids, HSG display the following distinct chemical features: (1) at given SiO2 and CaO contents, the HSG have significantly higher Sr than normal granitoids, defining two different trends in Sr versus SiO2, CaO diagrams; (2) highly depleted heavy rare earth element (REE) relative to middle and light REE with (Dy/Yb)N and (La/Yb)N up to 3.2 and 151, respectively; (3) variable and higher Nb/Ta; and (4) positive correlations among Sr/Y, (Dy/Yb)N, (La/Yb)N, and Nb/Ta. High Sr/Y, (La/Yb)N, (Dy/Yb)N, and Sr/CaO of HSG do not correlate with major elements (e.g., SiO2). Large variations in these ratios at a given SiO2 content indicate that these features do not reflect magma mixing or fractionation. HSG have higher Sr at a given CaO content and larger variation of (Dy/Yb)N than old crustal rocks (including exposed basement, global mafic LCC xenoliths, high Sr/Y TTG suites, and adakites in modern arcs). This precludes inheritance of the HSG chemical features from these source rocks. Instead, the chemical features of the HSG are best explained by partial melting of the thickened LCC with garnet-dominant, plagioclase-poor, and rutile-present residual lithologies. The coupled chemical features of the HSG are not observed in post-collisional granitoids younger than ca.130 Ma, indicating removal of the eclogitic source and/or residuum of HSG underneath the orogen. These characteristic chemical relationships in the Dabie HSG may be applied to distinguish partial melts of thickened LCC from high Sr/Y intermediate-felsic magmatic rocks which do not show clear indications for melting depth.

Petrogenesis and tectonic implications of Early Cretaceous S- and A-type granites in the northwest of the Gan-Hang rift, SE China [查看] Yao-HuiJiang、PengZhao、QingZhou、Shi-YongLiao、Guo-DongJin

The Gan-Hang rift, trending at least 450 km in a NE–SW direction, is a part of a Mesozoic Basin and Range Province in southeastern China. Detailed SHRIMP zircon U–Pb chronology, major and trace element, and Sr-Nd-Hf isotope data of three granitic plutons and a diabasic dike in the northwest of the Gan-Hang rift, are used to explore the origin of these granites and their relationship to the evolution of the Gan-Hang rift.SHRIMP zircon U–Pb dating shows that the granitic plutons and diabasic dike were emplaced in the Early Cretaceous (122–129 Ma). The Tongshan and Damaoshan plutons, close to the Gan-Hang rift, consist mainly of weakly peraluminous granitic rocks, which show A2 subtype affinity. These granites have initial 87Sr/86Sr ratios of 0.7080–0.7103, εNd (T) values of−1.4 to−5.6 and εHf (T) (in-situ zircon) values of −3.8 to +1.2. Detailed elemental and isotopic data suggest that they were formed by partial melting of granulitized Mesoproterozoic metamorphic basement (including metasedimentary and metaigneous rocks) in the shallow (b30 km) crust at a high temperature (~823 °C). These pure crustal melts underwent crystal fractionation of biotite, plagioclase and K-feldspar, forming the more felsic end-member of granitic rocks. The Ehu pluton,more distant from the Gan-Hang rift, is composed of two-mica granites, which are strongly peraluminous and are S-type granites. These granites have higher initial 87Sr/86Sr ratios (0.7162−0.7191) and lower εNd (T)(−7.1 to −7.4) and εHf (T) (−6.8; in-situ zircon) values than the Tongshan and Damaoshan granites.Detailed elemental and isotopic data suggest that the Ehu granites were formed by partial melting of Paleoproterozoic metasedimentary basement in the deep (~40–50 km) crust at a relatively low temperature(~757 °C), with no fractional crystallization and mantle-derived magma mixing in their evolution. The coeval diabasic dike is calc-alkaline and has initial 87Sr/86Sr ratio of 0.7085, εNd (T) value of+0.9 and εHf (T) (in-situ zircon) value of −7.1, suggesting that it was derived from the asthenospheric mantle wedge that had been metasomatised via addition of subducted sediment-derived melt with monazite in the residual phase. The association of Early Cretaceous (122–129 Ma) S- and A-type granites in the northwest of the Gan-Hang rift marks the onset of back-arc extension or intra-arc rift. With ongoing extension the crust and lithospheric mantle became progressively thinned. The upwelling of asthenosphere triggered partial melting of both metasedimentary and metaigneous rocks in the more thinned crust close to the Gan-Hang rift, forming the A-type granitic magmas such as Tongshan and Damaoshan, whereas partial melting of metasedimentary rocks in the less thinned crust farther from the Gan-Hang rift formed the S-type granitic magmas such as Ehu. The red sediments with the total thickness more than 10,000 mhave been successively deposited in the Gan-Hang rift valley since the late Early Cretaceous (~105 Ma), suggesting that this region experienced the most backarc extension.

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.

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