Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdise giant magmatic belt, within which the Qüxü batholith is the most typical MME-bearing pluton. Systematic sampl...Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdise giant magmatic belt, within which the Qüxü batholith is the most typical MME-bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U-Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±l Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions.Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge-scale magma mixing in the Gangdise belt took place 15-20 million years after the initiation of the India-Asia continental collision, genetically related to the underplating of subduction-collision-induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass-energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.展开更多
Whole-rock and mineral separate Ar-Ar dating was carried out for the Linzizong volcanic rocks at Linzhou Basin in Tibet to constrain the time span of volcanism and the corresponding stratigraphic sequence. Sampling wa...Whole-rock and mineral separate Ar-Ar dating was carried out for the Linzizong volcanic rocks at Linzhou Basin in Tibet to constrain the time span of volcanism and the corresponding stratigraphic sequence. Sampling was based on detailed geologic mapping and stratigraphic se-quence of Dianzhong, Nianbo, Pana Formations, systemati-cally from the bottom to near the top. The results indicate that the Linzizong volcanic rocks erupted from Paleocene to middle of Eocene (64.43—43.93 Ma). Among them, the Pana Formation formed from ca. 48.73 to 43.9 Ma, the Nianbo Formation around 54 Ma and the Dianzhong Formation from 64.4 to 60.6 Ma. In combination with evidence from the geochemical characteristics of the volcanic rocks, and from stratigraphy in southern Tibet, it is postulated that the age of the lowest member in the Dianzhong Formation of the Lin-zizong volcanic rock, which overlies unconformably the Late Cretaceous Shexing Formation, likely corresponds to the inception of the collision between Indian and Asian conti-nents in southern Tibet.展开更多
An analysis of trace elements and isotopic geochemistry suggest that the ore-forming materials of gold deposits in the Jiaodong granite-greenstone belt have multiple sources, especially the mantle source. Seismic wave...An analysis of trace elements and isotopic geochemistry suggest that the ore-forming materials of gold deposits in the Jiaodong granite-greenstone belt have multiple sources, especially the mantle source. Seismic wave, magnetic and gravity fields show that the crust-mantle structure and its coupling mechanism are the fundamental dynamic causes for the exchange and accumulation of materials and energy in the metallogenic system. Considering the evolution history of the structural setting, the tectono-metallogenic dynamics model of the area can be summarized as follows: (1) occurrence of the greenstone belt during the Archean-Proterozoic-the embryonic form of Au-source system; (2) stable tectonic setting in the Paleozoic-an intermittence in gold mineralization; (3) intensive activation and reformation of the greenstone belt in the Mesozoic-tectono-mineralization and tectono-diagensis; (4) posthumous structural activity in the Cenozoic-destruction of orebodies in the later stage. In the middle and late Indosinian, the Tancheng-Lujiang fault zone cut deeply into the upper mantle so that the ore-bearing fluids migrated to higher layers through the crust-mantle interaction, resulting in alteration and mineralization.展开更多
The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered th...The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest.The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle Tianshan to the south. It is part of a Hercynian orogen with three distinct E-W-trending tectonic belts: the Devonian-Early Carboniferous Tousuquan-Dananhu island arc on the north and the Carboniferous Aqishan -Yamansu rift basin to the south, which are separated by rocks of the Kanggurtag shear zone. The porphyry deposits, dated at 322 Ma, are related to the late evolutionary stages of a subduction-related oceanic or continental margin arc. In contrast, the skarn, gold, and magmatic Ni-Cu deposits are associated with post-colli-sional tectonics at ca. 290-270 Ma. These Late Carboniferous - Early Permian deposits are associated with large-scale emplacement and eruption of magmas possibly caused by lithosphere delamination and rifting within the East Tianshan.展开更多
The reported new U-Pb age by sensitive high-resolution ion microprobe (SHRIMP Ⅱ) on zircon was obtained from a tuff sample at the basal Doushantuo Formation in the Jiuqunao section, which situated at the western limb...The reported new U-Pb age by sensitive high-resolution ion microprobe (SHRIMP Ⅱ) on zircon was obtained from a tuff sample at the basal Doushantuo Formation in the Jiuqunao section, which situated at the western limb of the Huangling anticline in the Yangtze Gorges in Zigui, Hubei, South China. Eighteen spots of zircons were analyzed and they form two clusters: one includes three spots, with an inherited age of 784+ 15 Ma (MSWD=0.05); the other consists of 15 spots and gives a weighted mean ^206pb/^238U age of 628.3±5.8 Ma (MSWD=0.86). It is the first SHRIMP U-Pb zircon age obtained nearly the base of the Doushantuo Formation of Ediacaran and represents a maximum age of the Doushantuo Formation It also forms an age constraint on the upper limit age of the Nantuo (Marinoantype) glaciation.展开更多
Various shaped mafic microgranular enclaves (MMEs) together with several mafic massifs are developed within the Yuegelu granitoid pluton in the eastern part of the Eastern Kunlun. On the basis of detailed field geolog...Various shaped mafic microgranular enclaves (MMEs) together with several mafic massifs are developed within the Yuegelu granitoid pluton in the eastern part of the Eastern Kunlun. On the basis of detailed field geological surveying and of the results of the petrological and geo-chemical studies it is suggested that there must be some ge-netic relationship among the granodiorite host, the MMEs and the hornblende (Hb)-gabbro massifs. Magmatic zircon grains are extracted from samples of granodiorite host rock, Hb-gabbro and the MMEs for U-Pb dating. The U-Pb ages are determined by using SHRIMP Ⅱ technique, which yields the ages of 242±6 Ma, 239±6 Ma and 241±5 Ma, respectively. The overall correspondence in the U-Pb dating results of them excludes the possibility that the MMEs in the granitoids are solid refractory relics from the source region or that they are xenoliths from the wall rocks. It can also rule out the possibility of a later emplacement of basic magma after the solidification of the granitoids. This dating result indicates that they are the products of magma mixing in early-mid Triassic epoch. Among them the granitoid host is chemically akin to the acidic end member during the magma mixing process, the Hb-gabbro is akin to the basic ones while the MMEs are the incompletely mixed basic magma clots trapped in the acidic magma. Combined with the results from other researches on this pluton it is reasonable to con-sider that in the mid-Triassic the Eastern Kunlun granitoid belt had undergone a process of magma mixing between the mantle-derived basic magma and the crustal acidic magma which indicates that the injection of mantle materials and energy into the crust and the reactions between them played an important role in the formation of the granitoid rocks.展开更多
Calcimicrobialites, which could be correlated to the layer 27 in Meishan section according to the Hindeodus parvus, occur abruptly on the end-Permian mass extinction boundary in South China. Microbialites mainly distr...Calcimicrobialites, which could be correlated to the layer 27 in Meishan section according to the Hindeodus parvus, occur abruptly on the end-Permian mass extinction boundary in South China. Microbialites mainly distribute on the top of reef facies or shallow carbonate platforms, thin- ning into deep facies. All the microbialites discovered are composed of micrite and coarse crystal digitate carbonate or patch carbonate. Microfossils usually dominate in the micro- bialites, and small gastropods, bivalves and ostracodes can also be found. This fossil assemblage represents a simple but particular remanent biota after the end-Permian mass ex- tinction on the top of reefs or shallow carbonate platforms. Abrupt occurrence of microbialites above the mass extinction boundary is the ecological response to the end-Permian global event in reef or shallow carbonate facies. Many studies have been done on the Permian-Triassic boundary and event in deep water facies sections or middle to lower shelf facies sections. However, the calcimicrobialites in South China are mainly located above reef facies or shallow carbonate plat- form facies. It will surely be helpful for people to know more about the different responses in different depths of ancient marine environment during the transition between Permian and Triassic by the study of petrology, palaeontology and palaeoecology of the calcimicrobialites.展开更多
In the newly revised Regional Chronostrati-graphic (Geochronologic) Scale of China, the original bipar-tite division of the Neoproterozoic is changed to tripartite division. The three 搒ystem?rank chronostratigraphic ...In the newly revised Regional Chronostrati-graphic (Geochronologic) Scale of China, the original bipar-tite division of the Neoproterozoic is changed to tripartite division. The three 搒ystem?rank chronostratigraphic units are in ascending order of the Qingbaikou, Nanhua and Sin-ian Systems. This report presents SHRIMP zircon U-Pb dat-ing on volcanic tuffs from the candidate stratotype section of the Nanhua System at the Yangjiaping section that is geo-graphically located in Hupingshan Town, Shimen County, Hunan Province. Tuff from the upper part of the Xieshuihe Formation (equivalent to the Liantuo Formation) in the Lower Nanhua Series yields a zircon U-Pb age of 758 23 Ma, which may provide a constraint on the lower limit of the Gucheng glacial stage in the Nanhua System. Tuff from the Laoshanya Formation of its underlying Qingbaikou System (equivalent to the Banxi Group) gives a zircon U-Pb age of 809 16 Ma. The sampling locality lies 12 m from the upper boundary of the Qingbaikou System. According to the sedi-mentation rate it is estimated that the upper boundary age is about 800 Ma. The present studies also provide a resolution to the long-standing problems concerning stratigraphic cor-relation of the Late Precambrian in South China whether the Liantuo Formation is equivalent to the Banxi Group or not.展开更多
As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropaleontolog...As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropaleontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkable diagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ～3 Ma.展开更多
U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ...U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ages for the Kude and the Sajia leu- cogranite are 27.5±0.5 and 14.4±0.2 Ma,respectively. Combined with published U-Pb data from the North Himalayan leu- cogranites,the time-span for the formation of the North Himalayan leucogranites is updated from 27.5 to 10 Ma,instead of previous 15 to 10 Ma.According to the U-Pb ages,the petrogenesis for the North Himalayan leucogranites can be constrained.It is suggested that the North Himalayan leu- cogranites have variety in their petrogenesis.展开更多
Located in the East Qinling molybdenum metallogenic belt on the southern margin of the North China craton, the Nannihu Mo (-W) orefield comprising Nannihu, Sandaozhuang, and Shangfanggou deposits is a superlarge skarn...Located in the East Qinling molybdenum metallogenic belt on the southern margin of the North China craton, the Nannihu Mo (-W) orefield comprising Nannihu, Sandaozhuang, and Shangfanggou deposits is a superlarge skarn-porphyry Mo (-W) orefield in the world. Re-Os dating was performed of six molybdenite samples from the Mo deposits in the Nannihu Mo orefield with inductively coupled plasma mass spectrometry (ICP-MS). The results show that the Re-Os model ages are 145.8±2.1-141.8±2.1 Ma for the Nannihu deposit, 145.4±2.0-144.5±2.2 Ma (averaging 145.0±2.2 Ma) for the Sandaozhuang deposit and 145.8±2.1-143.8±2.1 Ma (averaging 144.8±2.1 Ma) for the Shangfanggou deposit; dating of the six samples yields an isochron age of 141.5±7.8 Ma (2σ), which accurately determines the timing of mineralization. The results also suggest that the ore-forming materials were mainly derived from the lower crust, mixed with minor mantle components. These Mo deposits were formed during the transition of the Mesozoic tectonic regime in eastern China, and its mineralization was a part of the Late Mesozoic large-scale mineralization in that region.展开更多
An isochron age of 282±20 (95% conf. limit) Ma of the sulfide ores in the Huangshandong Cu-Ni sulfide deposit, the East Tianshan Mountains has been obtained through Re-Os isotopic measurement. The age implies tha...An isochron age of 282±20 (95% conf. limit) Ma of the sulfide ores in the Huangshandong Cu-Ni sulfide deposit, the East Tianshan Mountains has been obtained through Re-Os isotopic measurement. The age implies that the Cu-Ni sulfide deposit and other related deposits in the same area occurred in a Permian extensional environment of post-collision instead of Devonian-Early Carboniferous ophiolite-related oceanic or island arc environments inferred before. It shares the same ages with the orogenic and epithermal gold deposit systems in the same area. An initial 187Os/188Os ratio of 0.25±0.04 (1σ) and a γos value of 99 on average display the participation of large quantities of crustal components into the rock-forming and ore-forming system during mineralization and magmatic emplacement.展开更多
Seventy-three large-superlarge deposits in China were formed in 4 metallogenic epochs, and located in 6 metallogenic domains. By combing their time-space distribution and the relevant data of crustal thickness, we dis...Seventy-three large-superlarge deposits in China were formed in 4 metallogenic epochs, and located in 6 metallogenic domains. By combing their time-space distribution and the relevant data of crustal thickness, we discuss the control conditions of deep tectonics on superlarge deposits. The various spatial variation of the crustal thickness where deposits locate is closely related to their different tectonic setting. The crustal thickness of the region where deposits are in the Precatnbrian metallogenic epoch is 37.1 km and shows double-peak distribution, which is related to the different tectonic-mineralization processes in the Tarim-North China and Yangtze metallogenic domains. The crustal thickness of the region where deposits are in the Paleoproterozoic metallogenic epoch is 43.4 km and shows normal distribution, which is the result of 'pure' mineralization setting. The crustal thickness of the region where deposits are in the Late Palaeozoic-Early Mesozoic metallogenic epoch is about 41.2 km and shows multi-peak distribution, which can be related with dispersing distribution in the metallogenic domain of these superlarge deposits. The crustal thickness of the region where deposits are in the post-Indosinian metallogenic epoch is 37.3 km, and shows skew distribution, which resulted from different tectonic settings in eastern and western China.展开更多
Occurrence of Cretaceous basalts in Fuxin County, Liaoning Province provides us an opportunity to understand Mesozoic mantle processes beneath the northern margin of the North China Craton (NNCC). Fuxin Jianguo basalt...Occurrence of Cretaceous basalts in Fuxin County, Liaoning Province provides us an opportunity to understand Mesozoic mantle processes beneath the northern margin of the North China Craton (NNCC). Fuxin Jianguo basalts occur as volcanic channel phases with well-developed columnar jointings and contain few spinel lherzolite and pyroxenite xenoliths. They are poor in silica and rich in alkalis, Ti and Al, belonging to alkaline basalts. In trace element compositions, Jianguo basalts are moderately enriched in LREE and LILE, but not depleted in HFSE. They have low Sr and high Nd and Pb isotopic ratios. These geochemical characteristics suggest that Jianguo basalts originated from the depleted asthenosphere, representing an undifferentiated and uncontaminated primitive magma. Presence of these basalts indicates that the lithosphere beneath the region had thickness less than 65 km at the time of basalt eruption and was mainly composed of fertile pargasite-bearing spinel lherzolite and plagioclase pyroxenite. The voluminous basaltic-andesitic magmatism during the early Jurassic-late Cretaceous time indicates that the commencement and accomplishment of lithosphere thinning in the NNCC was much earlier than that in the southern margin, since the mafic-intermediate volcanism only occurred at the Cretaceous time in the southern margin and the basalts with an asthenosphere isotopic signature at the Tertiary. This shows that highly spatial and temporal heterogeneity existed in the Mesozoic lithosphere evolution.展开更多
Unlike typical oceans such as the wide and 'clean' Atlantic, the Tethys has been showing an archipelagic pattern during all its evolutionary stages. Compared with the traditional, wedge-shaped and relatively &...Unlike typical oceans such as the wide and 'clean' Atlantic, the Tethys has been showing an archipelagic pattern during all its evolutionary stages. Compared with the traditional, wedge-shaped and relatively 'clean' ocean model, the archipelagic model is more suitable for the Tethys, especially the eastern Tethys. This paper demonstrates the eastern Tethys archipelagic system in terms of the subdivision, characteristics and evolutionary history of the Qinling-Qilian-Kunlun, South China and Xizang (Tibet)-Yunnan Regions of the eastern Eurasian Tethys.展开更多
In the Late Cambrian, the North China Platform was a typical carbonate ramp platform. The Upper Cambrian of the northern part of the North China Platform is famous for the development of bioherm limestones and storm c...In the Late Cambrian, the North China Platform was a typical carbonate ramp platform. The Upper Cambrian of the northern part of the North China Platform is famous for the development of bioherm limestones and storm calcirudites and can be divided from bottom to top into the Gushan, Changshan and Fengshan formations. In this set of strata, the deep-ramp mudstone and marls and the shallow-ramp packstones and grainstones constitute many carbonate meter-scale cycles of subtidal type. More tidal-flat dolomites are developed in the Upper Cambrian of the southern margin of the North China platform, in which limestone and dolomite beds also constitute many carbonate meter-scale cycles of the peritidal type. These cycles are marked by a variety of litho-facies successions. There are regularly vertical stacking patterns of meter-scale cycles in long-term third-order sequences, which is the key to discerning such sequences. Third- order sequence is marked by a particular sedimentary-facies succession that is the result of the environment-changing process of deepening and shoaling, which is genetically related to third-order sea level changes. Furthermore, four third- order sequences can be grouped in the Upper Cambrian of the North China Platform. The main features of these four third -order sequences in the northern part of the platform can be summarized as follows: firstly, sequence-boundaries are characterized by drowning unconformities; secondly, the sedimentary-facies succession is generally constituted by one from deep-ramp facies to shallow-ramp facies; thirdly, a succession of “CS (?)+HST” (i.e., “condensed section and high- stand system”) forms these four third-order sequences. The chief features for the third-order sequences in the southern part of the North China Platform comprises: more dolomites are developed in the HSTs of third-order sequences and also developed more carbonate meter-scale cycles of peritidal types; the sedimentary-facies succession of the third-order sequences is marked by “shallow展开更多
In this paper, oscillatory properties for solutions of certain nonlinear impulsive parabolic equations with several delays are investigated and a series of new sufficient conditions for oscillations of the equation ar...In this paper, oscillatory properties for solutions of certain nonlinear impulsive parabolic equations with several delays are investigated and a series of new sufficient conditions for oscillations of the equation are established.展开更多
Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample ...Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.展开更多
Petrology and SHRIMP U-Pb zircon chronol- ogy are reported for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya to the southeast of Yangzuoyong Co. Twenty-one measured zircon grains from ...Petrology and SHRIMP U-Pb zircon chronol- ogy are reported for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya to the southeast of Yangzuoyong Co. Twenty-one measured zircon grains from a dacite sample of the Sangxiu Formation can be divided into two groups, which include long columnar magmatic zircons of 133±3.0 Ma, representing the age of volcanism in the Sangxiu Formation, and inherited zircons consisting of core and overgrowth rim, in which ages of the three cores are 2244±16, 1153±33 and 492±25 Ma respectively; and the age of one overgrowth rim is 132.7±5.2 Ma. These ages are con- sidered to represent the remelting of accretionary crust at different periods resulting from the volcanism of Sangxiu Formation. These volcanic rocks in the Sangxiu Formation, for which age is close to that of Bunbury basalt in south- western margin of Australia, and older than that of Rajma- hal basalt in northeastern India, maybe considered as the products of early activity of the hotspot represented by the Rajmahal basalt.展开更多
The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is ju...The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Yangtze craton. Therefore we argue that these contemporary basalts all originated from the Emeishan mantle plume, and the ELIP could have a significant westward extension with an outcropped area of over 500,000 km2. This new scenario shows that the LT tholeiite occurs on the western margin of the Yangtze craton, while the HT tholeiite overlying the LT basalts occupies the whole area of the ELIP.展开更多
基金the grants of the National Key Project for Basic Research of China(No.2002CB412600)the National Natural Science Foundation of China(Nos.40172025,40103003,49802005,49772107,40473020)the key project on the Tibetan Plateau of the Ministryof Land and Resources of China(No.20010102401).
文摘Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdise giant magmatic belt, within which the Qüxü batholith is the most typical MME-bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U-Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±l Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions.Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge-scale magma mixing in the Gangdise belt took place 15-20 million years after the initiation of the India-Asia continental collision, genetically related to the underplating of subduction-collision-induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass-energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.
文摘Whole-rock and mineral separate Ar-Ar dating was carried out for the Linzizong volcanic rocks at Linzhou Basin in Tibet to constrain the time span of volcanism and the corresponding stratigraphic sequence. Sampling was based on detailed geologic mapping and stratigraphic se-quence of Dianzhong, Nianbo, Pana Formations, systemati-cally from the bottom to near the top. The results indicate that the Linzizong volcanic rocks erupted from Paleocene to middle of Eocene (64.43—43.93 Ma). Among them, the Pana Formation formed from ca. 48.73 to 43.9 Ma, the Nianbo Formation around 54 Ma and the Dianzhong Formation from 64.4 to 60.6 Ma. In combination with evidence from the geochemical characteristics of the volcanic rocks, and from stratigraphy in southern Tibet, it is postulated that the age of the lowest member in the Dianzhong Formation of the Lin-zizong volcanic rock, which overlies unconformably the Late Cretaceous Shexing Formation, likely corresponds to the inception of the collision between Indian and Asian conti-nents in southern Tibet.
基金This study is supported jointly by the National Natural Science Foundation of China(No.40172036)"the Key Project of Science and Technology Research"(No.01037)+1 种基金the“Trans-century Training Program for Outstanding Talents”Fund sponsored by the Ministry of Educationthe National Important Basic Research and Development Planning Program(No.1999043206).
文摘An analysis of trace elements and isotopic geochemistry suggest that the ore-forming materials of gold deposits in the Jiaodong granite-greenstone belt have multiple sources, especially the mantle source. Seismic wave, magnetic and gravity fields show that the crust-mantle structure and its coupling mechanism are the fundamental dynamic causes for the exchange and accumulation of materials and energy in the metallogenic system. Considering the evolution history of the structural setting, the tectono-metallogenic dynamics model of the area can be summarized as follows: (1) occurrence of the greenstone belt during the Archean-Proterozoic-the embryonic form of Au-source system; (2) stable tectonic setting in the Paleozoic-an intermittence in gold mineralization; (3) intensive activation and reformation of the greenstone belt in the Mesozoic-tectono-mineralization and tectono-diagensis; (4) posthumous structural activity in the Cenozoic-destruction of orebodies in the later stage. In the middle and late Indosinian, the Tancheng-Lujiang fault zone cut deeply into the upper mantle so that the ore-bearing fluids migrated to higher layers through the crust-mantle interaction, resulting in alteration and mineralization.
文摘The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest.The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle Tianshan to the south. It is part of a Hercynian orogen with three distinct E-W-trending tectonic belts: the Devonian-Early Carboniferous Tousuquan-Dananhu island arc on the north and the Carboniferous Aqishan -Yamansu rift basin to the south, which are separated by rocks of the Kanggurtag shear zone. The porphyry deposits, dated at 322 Ma, are related to the late evolutionary stages of a subduction-related oceanic or continental margin arc. In contrast, the skarn, gold, and magmatic Ni-Cu deposits are associated with post-colli-sional tectonics at ca. 290-270 Ma. These Late Carboniferous - Early Permian deposits are associated with large-scale emplacement and eruption of magmas possibly caused by lithosphere delamination and rifting within the East Tianshan.
文摘The reported new U-Pb age by sensitive high-resolution ion microprobe (SHRIMP Ⅱ) on zircon was obtained from a tuff sample at the basal Doushantuo Formation in the Jiuqunao section, which situated at the western limb of the Huangling anticline in the Yangtze Gorges in Zigui, Hubei, South China. Eighteen spots of zircons were analyzed and they form two clusters: one includes three spots, with an inherited age of 784+ 15 Ma (MSWD=0.05); the other consists of 15 spots and gives a weighted mean ^206pb/^238U age of 628.3±5.8 Ma (MSWD=0.86). It is the first SHRIMP U-Pb zircon age obtained nearly the base of the Doushantuo Formation of Ediacaran and represents a maximum age of the Doushantuo Formation It also forms an age constraint on the upper limit age of the Nantuo (Marinoantype) glaciation.
文摘Various shaped mafic microgranular enclaves (MMEs) together with several mafic massifs are developed within the Yuegelu granitoid pluton in the eastern part of the Eastern Kunlun. On the basis of detailed field geological surveying and of the results of the petrological and geo-chemical studies it is suggested that there must be some ge-netic relationship among the granodiorite host, the MMEs and the hornblende (Hb)-gabbro massifs. Magmatic zircon grains are extracted from samples of granodiorite host rock, Hb-gabbro and the MMEs for U-Pb dating. The U-Pb ages are determined by using SHRIMP Ⅱ technique, which yields the ages of 242±6 Ma, 239±6 Ma and 241±5 Ma, respectively. The overall correspondence in the U-Pb dating results of them excludes the possibility that the MMEs in the granitoids are solid refractory relics from the source region or that they are xenoliths from the wall rocks. It can also rule out the possibility of a later emplacement of basic magma after the solidification of the granitoids. This dating result indicates that they are the products of magma mixing in early-mid Triassic epoch. Among them the granitoid host is chemically akin to the acidic end member during the magma mixing process, the Hb-gabbro is akin to the basic ones while the MMEs are the incompletely mixed basic magma clots trapped in the acidic magma. Combined with the results from other researches on this pluton it is reasonable to con-sider that in the mid-Triassic the Eastern Kunlun granitoid belt had undergone a process of magma mixing between the mantle-derived basic magma and the crustal acidic magma which indicates that the injection of mantle materials and energy into the crust and the reactions between them played an important role in the formation of the granitoid rocks.
基金the National Natural Science Foundation of China(Grant Nos.40232025 and 40325004).
文摘Calcimicrobialites, which could be correlated to the layer 27 in Meishan section according to the Hindeodus parvus, occur abruptly on the end-Permian mass extinction boundary in South China. Microbialites mainly distribute on the top of reef facies or shallow carbonate platforms, thin- ning into deep facies. All the microbialites discovered are composed of micrite and coarse crystal digitate carbonate or patch carbonate. Microfossils usually dominate in the micro- bialites, and small gastropods, bivalves and ostracodes can also be found. This fossil assemblage represents a simple but particular remanent biota after the end-Permian mass ex- tinction on the top of reefs or shallow carbonate platforms. Abrupt occurrence of microbialites above the mass extinction boundary is the ecological response to the end-Permian global event in reef or shallow carbonate facies. Many studies have been done on the Permian-Triassic boundary and event in deep water facies sections or middle to lower shelf facies sections. However, the calcimicrobialites in South China are mainly located above reef facies or shallow carbonate plat- form facies. It will surely be helpful for people to know more about the different responses in different depths of ancient marine environment during the transition between Permian and Triassic by the study of petrology, palaeontology and palaeoecology of the calcimicrobialites.
基金jointly supported by the Ministry of Science and Technology of China for fundamental work(Grant No.2001DEA20020-1)the Natural Science Foundation of China(Grant No.40272015)China Commission on Stratigraphy(research on the stage establishment for China’s main chronostratigraphy).
文摘In the newly revised Regional Chronostrati-graphic (Geochronologic) Scale of China, the original bipar-tite division of the Neoproterozoic is changed to tripartite division. The three 搒ystem?rank chronostratigraphic units are in ascending order of the Qingbaikou, Nanhua and Sin-ian Systems. This report presents SHRIMP zircon U-Pb dat-ing on volcanic tuffs from the candidate stratotype section of the Nanhua System at the Yangjiaping section that is geo-graphically located in Hupingshan Town, Shimen County, Hunan Province. Tuff from the upper part of the Xieshuihe Formation (equivalent to the Liantuo Formation) in the Lower Nanhua Series yields a zircon U-Pb age of 758 23 Ma, which may provide a constraint on the lower limit of the Gucheng glacial stage in the Nanhua System. Tuff from the Laoshanya Formation of its underlying Qingbaikou System (equivalent to the Banxi Group) gives a zircon U-Pb age of 809 16 Ma. The sampling locality lies 12 m from the upper boundary of the Qingbaikou System. According to the sedi-mentation rate it is estimated that the upper boundary age is about 800 Ma. The present studies also provide a resolution to the long-standing problems concerning stratigraphic cor-relation of the Late Precambrian in South China whether the Liantuo Formation is equivalent to the Banxi Group or not.
基金supported by the National Natural Science Foundation of China(Grant No.4999560)the National Key Basic Research Special Foundation(Grant No.G2000078500).
文摘As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropaleontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkable diagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ～3 Ma.
文摘U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ages for the Kude and the Sajia leu- cogranite are 27.5±0.5 and 14.4±0.2 Ma,respectively. Combined with published U-Pb data from the North Himalayan leu- cogranites,the time-span for the formation of the North Himalayan leucogranites is updated from 27.5 to 10 Ma,instead of previous 15 to 10 Ma.According to the U-Pb ages,the petrogenesis for the North Himalayan leucogranites can be constrained.It is suggested that the North Himalayan leu- cogranites have variety in their petrogenesis.
文摘Located in the East Qinling molybdenum metallogenic belt on the southern margin of the North China craton, the Nannihu Mo (-W) orefield comprising Nannihu, Sandaozhuang, and Shangfanggou deposits is a superlarge skarn-porphyry Mo (-W) orefield in the world. Re-Os dating was performed of six molybdenite samples from the Mo deposits in the Nannihu Mo orefield with inductively coupled plasma mass spectrometry (ICP-MS). The results show that the Re-Os model ages are 145.8±2.1-141.8±2.1 Ma for the Nannihu deposit, 145.4±2.0-144.5±2.2 Ma (averaging 145.0±2.2 Ma) for the Sandaozhuang deposit and 145.8±2.1-143.8±2.1 Ma (averaging 144.8±2.1 Ma) for the Shangfanggou deposit; dating of the six samples yields an isochron age of 141.5±7.8 Ma (2σ), which accurately determines the timing of mineralization. The results also suggest that the ore-forming materials were mainly derived from the lower crust, mixed with minor mantle components. These Mo deposits were formed during the transition of the Mesozoic tectonic regime in eastern China, and its mineralization was a part of the Late Mesozoic large-scale mineralization in that region.
基金the National Natural Science Foundation of China(No.40172021)the Major State Basic Research Program of the People’s Republic of China(No.G1999043211)the New Round Geological Survey Project (DKD9902001,2001BA609A-07-04).
文摘An isochron age of 282±20 (95% conf. limit) Ma of the sulfide ores in the Huangshandong Cu-Ni sulfide deposit, the East Tianshan Mountains has been obtained through Re-Os isotopic measurement. The age implies that the Cu-Ni sulfide deposit and other related deposits in the same area occurred in a Permian extensional environment of post-collision instead of Devonian-Early Carboniferous ophiolite-related oceanic or island arc environments inferred before. It shares the same ages with the orogenic and epithermal gold deposit systems in the same area. An initial 187Os/188Os ratio of 0.25±0.04 (1σ) and a γos value of 99 on average display the participation of large quantities of crustal components into the rock-forming and ore-forming system during mineralization and magmatic emplacement.
基金the Chinese Academy of Sciences (No. KXCX2-109) National Natural Science Foundation of China (No. 40304007 ,No.40172036)+1 种基金"Key Project of Science and Technology Research”(No. 01037) China Postdoctoral Science Foundation (No. 2003033238).
文摘Seventy-three large-superlarge deposits in China were formed in 4 metallogenic epochs, and located in 6 metallogenic domains. By combing their time-space distribution and the relevant data of crustal thickness, we discuss the control conditions of deep tectonics on superlarge deposits. The various spatial variation of the crustal thickness where deposits locate is closely related to their different tectonic setting. The crustal thickness of the region where deposits are in the Precatnbrian metallogenic epoch is 37.1 km and shows double-peak distribution, which is related to the different tectonic-mineralization processes in the Tarim-North China and Yangtze metallogenic domains. The crustal thickness of the region where deposits are in the Paleoproterozoic metallogenic epoch is 43.4 km and shows normal distribution, which is the result of 'pure' mineralization setting. The crustal thickness of the region where deposits are in the Late Palaeozoic-Early Mesozoic metallogenic epoch is about 41.2 km and shows multi-peak distribution, which can be related with dispersing distribution in the metallogenic domain of these superlarge deposits. The crustal thickness of the region where deposits are in the post-Indosinian metallogenic epoch is 37.3 km, and shows skew distribution, which resulted from different tectonic settings in eastern and western China.
基金This work was supported by the National Natural Science Foundation of China(Grant No.40073004)the Chinese Academy of Sciences(KZCX1-07).
文摘Occurrence of Cretaceous basalts in Fuxin County, Liaoning Province provides us an opportunity to understand Mesozoic mantle processes beneath the northern margin of the North China Craton (NNCC). Fuxin Jianguo basalts occur as volcanic channel phases with well-developed columnar jointings and contain few spinel lherzolite and pyroxenite xenoliths. They are poor in silica and rich in alkalis, Ti and Al, belonging to alkaline basalts. In trace element compositions, Jianguo basalts are moderately enriched in LREE and LILE, but not depleted in HFSE. They have low Sr and high Nd and Pb isotopic ratios. These geochemical characteristics suggest that Jianguo basalts originated from the depleted asthenosphere, representing an undifferentiated and uncontaminated primitive magma. Presence of these basalts indicates that the lithosphere beneath the region had thickness less than 65 km at the time of basalt eruption and was mainly composed of fertile pargasite-bearing spinel lherzolite and plagioclase pyroxenite. The voluminous basaltic-andesitic magmatism during the early Jurassic-late Cretaceous time indicates that the commencement and accomplishment of lithosphere thinning in the NNCC was much earlier than that in the southern margin, since the mafic-intermediate volcanism only occurred at the Cretaceous time in the southern margin and the basalts with an asthenosphere isotopic signature at the Tertiary. This shows that highly spatial and temporal heterogeneity existed in the Mesozoic lithosphere evolution.
文摘Unlike typical oceans such as the wide and 'clean' Atlantic, the Tethys has been showing an archipelagic pattern during all its evolutionary stages. Compared with the traditional, wedge-shaped and relatively 'clean' ocean model, the archipelagic model is more suitable for the Tethys, especially the eastern Tethys. This paper demonstrates the eastern Tethys archipelagic system in terms of the subdivision, characteristics and evolutionary history of the Qinling-Qilian-Kunlun, South China and Xizang (Tibet)-Yunnan Regions of the eastern Eurasian Tethys.
文摘In the Late Cambrian, the North China Platform was a typical carbonate ramp platform. The Upper Cambrian of the northern part of the North China Platform is famous for the development of bioherm limestones and storm calcirudites and can be divided from bottom to top into the Gushan, Changshan and Fengshan formations. In this set of strata, the deep-ramp mudstone and marls and the shallow-ramp packstones and grainstones constitute many carbonate meter-scale cycles of subtidal type. More tidal-flat dolomites are developed in the Upper Cambrian of the southern margin of the North China platform, in which limestone and dolomite beds also constitute many carbonate meter-scale cycles of the peritidal type. These cycles are marked by a variety of litho-facies successions. There are regularly vertical stacking patterns of meter-scale cycles in long-term third-order sequences, which is the key to discerning such sequences. Third- order sequence is marked by a particular sedimentary-facies succession that is the result of the environment-changing process of deepening and shoaling, which is genetically related to third-order sea level changes. Furthermore, four third- order sequences can be grouped in the Upper Cambrian of the North China Platform. The main features of these four third -order sequences in the northern part of the platform can be summarized as follows: firstly, sequence-boundaries are characterized by drowning unconformities; secondly, the sedimentary-facies succession is generally constituted by one from deep-ramp facies to shallow-ramp facies; thirdly, a succession of “CS (?)+HST” (i.e., “condensed section and high- stand system”) forms these four third-order sequences. The chief features for the third-order sequences in the southern part of the North China Platform comprises: more dolomites are developed in the HSTs of third-order sequences and also developed more carbonate meter-scale cycles of peritidal types; the sedimentary-facies succession of the third-order sequences is marked by “shallow
基金This work is supported by National Natural Science Foundation of China (40373003 and 40372121).
文摘In this paper, oscillatory properties for solutions of certain nonlinear impulsive parabolic equations with several delays are investigated and a series of new sufficient conditions for oscillations of the equation are established.
文摘Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.
基金This study was financially supported by the National Key stone Basic Research Program of China(Grant No.2002CB412609)the Integrated Study of Basic Geology in the Blank Area of Southem Tibetan Plateau(Grant No.200313000025)the Key Laboratory of Lithospheric Tectonics and Exploration,China University of Geosciences,Ministry of Education,China(Grant No.2003004).
文摘Petrology and SHRIMP U-Pb zircon chronol- ogy are reported for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya to the southeast of Yangzuoyong Co. Twenty-one measured zircon grains from a dacite sample of the Sangxiu Formation can be divided into two groups, which include long columnar magmatic zircons of 133±3.0 Ma, representing the age of volcanism in the Sangxiu Formation, and inherited zircons consisting of core and overgrowth rim, in which ages of the three cores are 2244±16, 1153±33 and 492±25 Ma respectively; and the age of one overgrowth rim is 132.7±5.2 Ma. These ages are con- sidered to represent the remelting of accretionary crust at different periods resulting from the volcanism of Sangxiu Formation. These volcanic rocks in the Sangxiu Formation, for which age is close to that of Bunbury basalt in south- western margin of Australia, and older than that of Rajma- hal basalt in northeastern India, maybe considered as the products of early activity of the hotspot represented by the Rajmahal basalt.
文摘The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Yangtze craton. Therefore we argue that these contemporary basalts all originated from the Emeishan mantle plume, and the ELIP could have a significant westward extension with an outcropped area of over 500,000 km2. This new scenario shows that the LT tholeiite occurs on the western margin of the Yangtze craton, while the HT tholeiite overlying the LT basalts occupies the whole area of the ELIP.
