U-Pb dating was conducted on different domains of zircons from metamorphosed leucosomes in Delingha （ 德令哈） complex, the lower basement rocks of the Olongbuluke （欧龙布鲁克 ） microcontinent, North Qaidam, in or...U-Pb dating was conducted on different domains of zircons from metamorphosed leucosomes in Delingha （ 德令哈） complex, the lower basement rocks of the Olongbuluke （欧龙布鲁克 ） microcontinent, North Qaidam, in order to review its complex tectonothermal history. The zircon core is comprised of highly-modified magmatic zircon relicts, the zircon mantle was produced in response to anatexis of a Late Protoproterozoic thermal event; age and isotopic composition of both the zircon core and the zircon mantle have been seriously disturbed due to the thermal event related with growth of the zircon overgrowth rim. The 207 PIV 206 Pb apparent age of the overgrowth rim was estimated to be - 1 030 Ma. This Late Mesoproterozoic thermal event has been interpreted as a response to the global Rodinia supercontinent assembly event in the Olongbuluke microcontinent, Northwest China.展开更多
The amalgamation and breakup mechanisms of the Rodinia supercontinent during the Meso- and Neoproterozoic have been the focus of much research. However, few studies have examined the response of Neoproterozoic tectoni...The amalgamation and breakup mechanisms of the Rodinia supercontinent during the Meso- and Neoproterozoic have been the focus of much research. However, few studies have examined the response of Neoproterozoic tectonics and magmatism along the northeastern margin of the Yangtze Plate to synchronous global events. The Qianliyan Uplift is located on the eastern margin of the Sulu orogenic belt in the ocean, but the tectonic affinity of the uplift and its relationship to the Sulu orogenic belt remains unclear. In this study, we investigated the formation age, geochemical characteristics, genesis type, and affinity of the granitic gneiss on Chaolian Island of the Qianliyan uplift and its tectonic significance.展开更多
The Tarim Craton is one of the major continental blocks in China.Mafic dykes,ultra-mafic–mafic–carbonatite complex and ultra-mafic–mafic pluton of 0.82–0.75 Ga widely occur in Kuluktage,Aksu and Tieklik area along
Early Cambrian and Mid--Late Neoproterozoic volcanic rocks in China are widespread on several Precambrian continental blocks, which had aggregated to form part of the Rodinia supercon- tinent by ca. 900 Ma. On the bas...Early Cambrian and Mid--Late Neoproterozoic volcanic rocks in China are widespread on several Precambrian continental blocks, which had aggregated to form part of the Rodinia supercon- tinent by ca. 900 Ma. On the basis of petrogeochemical data, the basic lavas can be classified into two major magma types： HT （Ti/Y 〉 500） and LT （Ti/Y 〈 500） that can be further divided into HT1 （Nb/La 〉 0.85） and HT2 （Nb/La ≤ 0.85）, and LT1 （Nb/La 〉 0.85） and LT2 （Nb/La ≤ 0.85） subtypes, respectively. The geochemical variation of the HT2 and LT2 lavas can be accounted for by lithospheric contamination of asthenosphere- （or plume-） derived magmas, whereas the parental magmas of the HT1 and LT1 lavas did not undergo, during their ascent, pronounced lithospheric contamination. These volcanics exhibit at least three characteristics： （1） most have a compositional bimodality; （2） they were formed in an intracontinental rift setting; and （3） they are genetically linked with mantle plumes or a mantle surperplume. This rift-related volcanism at end of the Mid-- Neoproterozoic and Early Cambrian coincided temporally with the separation between Australia-- East Antarctica, South China and Laurentia and between Australia and Tarim, respectively.展开更多
With the latest information on geology, isotop chronology, geochemistry and aerial geophysics, the structural enviroment, geological event characterists and evolution history of component units of Rodinia Supercontine...With the latest information on geology, isotop chronology, geochemistry and aerial geophysics, the structural enviroment, geological event characterists and evolution history of component units of Rodinia Supercontinent on a global scale are discussed. And some neo views and genetic pattern are provided. The East Eurppean Craton had a complex evolution history between 1.7 and 0.9 Ga. The arthors propose a new reconstruction of Laurentia acient land and Siberia at ca. 1 050～1 000 Ma. The largest litho-structural record of the Meso-Neoproterozoic orogenic collage in South America made up the western border of the South American Platform African Cratons are the result of convergence of Paleoproterozoic/Archaem Cratonic blocks. A part of Eastern Antarctica attached to southern Africa in Mesoproterozoic. Neoproterozoic felsic magmatic events in New India made the western border of Rodinia Pre-Grevoillian Laurentia was established as a major continental block by the end of the Paleoproterozoic. South China is geologically plausible to be between southern Laurentia and eastern Australia. Yangzi-Tarim connection or neighborhood is proposed. According to the abovementionded, the assembly and breakup paattern of Rodinia proposed by Pisarevsky is tested. It telles that primary break up is along the western border of Laurentia ancient land, which is similar to northern Atlantic. Another characteristic is that some continents are not considered as component parts of Rodinia, eg. India, Congo and San-Francisco.展开更多
The supercontinent cycle has had a profound effect on the Earth＇s evolution since the Late Archean but our understanding of the forces responsible for its operation remains elusive.Supercontinents appear to form by t...The supercontinent cycle has had a profound effect on the Earth＇s evolution since the Late Archean but our understanding of the forces responsible for its operation remains elusive.Supercontinents appear to form by two end-member processes：extroversion,in which the oceanic lithosphere surrounding the supercontinent（exterior ocean） is preferentially subducted（e.g.Pannotia）,and introversion in which the oceanic lithosphere formed between dispersing fragments of the previous supercontinent（interior ocean） is preferentially subducted（e.g.Pangea）.Extroversion can be explained by ＂top-down＂ geodynamics, in which a supercontinent breaks up over a geoid high and amalgamates above a geoid low. Introversion,on the other hand,requires that the combined forces of slab-pull and ridge push（which operate in concert after supercontinent break-up） must be overcome in order to enable the previously dispersing continents to turn inward.Introversion may begin when subduction zones are initiated along boundaries between the interior and exterior oceans and become trapped within the interior ocean.We speculate that the reversal in continental motion required for introversion may be induced by slab avalanche events that trigger the rise of superplumes from the core-mantle boundary.展开更多
The observation is made that there are very strong similarities between the supercontinents Columbia, Rodinia and Pangea. If plate tectonics was operating over the past 2.5 billion years of Earth history, and dominate...The observation is made that there are very strong similarities between the supercontinents Columbia, Rodinia and Pangea. If plate tectonics was operating over the past 2.5 billion years of Earth history, and dominated by extroversion and introversion of ocean basins, it would be unusual for three superconti-nents to resemble one another so closely. The term＇strange attractor＇ is applied to landmasses that form a coherent geometry in all three supercontinents. Baltica, Laurentia and Siberia form a group of＇strange attractors＇ as do the elements of East Gondwana （India, Australia, Antarctica, Madagascar）. The elements of ＂West Gondwana＂ are positioned as a slightly looser amalgam of cratonic blocks in all three super-continents and are referred to as ＇spiritual interlopers＇. Relatively few landmasses （the South China, North China, Kalahari and perhaps Tarim cratons） are positioned in distinct locations within each of the three supercontinents and these are referred to as＇lonely wanderers＇. 〈br〉 There may be several explanations for why these supercontinents show such remarkable similarities. One possibility is that modern-style plate tectonics did not begin until the late Neoproterozoic and horizontal motions were restricted and a vertical style of ＇lid tectonics＇ dominated. If motions were limited for most of the Proterozoic, it would explain the remarkable similarities seen in the Columbia and Rodinia supercontinents, but would still require the strange attractors to rift, drift and return to approximately the same geometry within Pangea. 〈br〉 A second possibility is that our views of older supercontinents are shaped by well-known connections documented for the most recent supercontinent, Pangea. It is intriguing that three of the four ＇lonely wanderers＇ （Tarim, North China, South China） did not unite until just before, or slightly after the breakup of Pangea. The fourth＇lonely wanderer＇, the Kalahari （and core Kaapvaal） craton has a somewhat unique Archean-age geology compared to its nearest neighbors in Gondwana, but very similar to that in western Australia.展开更多
A 〉1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton（SCC） consists of subduction mélange and extensional basin deposits. This belt is present under an uncon...A 〉1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton（SCC） consists of subduction mélange and extensional basin deposits. This belt is present under an unconformity of Devonian–Carboniferous sediments. Tectonic evolution of the Neoproterozoic rocks is crucial to determining the geology of the SCC and further influences the reconstruction of the Rodinia supercontinent. A subduction mélange unit enclosed ca.1000–850–Ma mafic blocks, which defined a Neoproterozoic ocean that existed within the SCC, is exposed at the bottom of the Jiangnan Orogen（JO） and experienced at least two phases deformation. Combined with new（detrital） zircon U–Pb ages from metasandstones, as well as igneous rocks within the metamorphic belt, we restrict the strongly deformed subduction mélange as younger than the minimum detrital age ca. 835 Ma and older than the ca. 815 Ma intruded granite. Unconformably overlying the subduction mélange and the intruded granite, an intra–continental rift basin developed 〈800 Ma that involved abundant mantle inputs, such as mafic dikes. This stratum only experienced one main phase deformation. According to our white mica ^40Ar/^（30）Ar data and previously documented thermochronology, both the Neoproterozoic mélange and younger strata were exhumed by a 490–400–Ma crustal–scale positive flower structure. This orogenic event probably induced the thick–skinned structures and was accompanied by crustal thickening, metamorphism and magmatism and led to the closure of the pre–existing rift basin. Integrating previously published data and our new results, we agree that the SCC was located on the periphery of the Rodinia supercontinent from the Neoproterozic until the Ordovician. Furthermore, we prefer that the convergence and dispersal of the SCC were primarily controlled by oceanic subduction forces that occurred within or periphery of the SCC.展开更多
This paper reports a newly discovered Late Mesoproterozoic-Early Neoproterozoic stromatolite assemblage, named here the ＂Jiawengmen stromatolite assemblage＂, represented by a Conophyton-Baicalia association in the J...This paper reports a newly discovered Late Mesoproterozoic-Early Neoproterozoic stromatolite assemblage, named here the ＂Jiawengmen stromatolite assemblage＂, represented by a Conophyton-Baicalia association in the Jiawenmen area in the southern belt of the Eastern Kunlun. This stromatolite assemblage is dominated by large-scale conical stromatolites and related elements, i.e., Conophyton garganicus var. inkeni, C. cf. ressoti Menchikov, Jacutophyton cf., Conicodomenia f., which commonly co-exist with elements of the group of Baicalia. This assemblage can be correlated with that of the middle Jixian-middle Qingbaikou System in North and Northwest China, but is different from that in South China. Correlation can also be made with that in the upper horizon of the Middle Riphean-lower horizon of the Upper Riphean in the South Ural Mountains and Siberia of Russia, in North Africa, and in the Alaskan Peninsula of North America. These facts suggest that the Jiawengmen stromatolite assemblage probably colonized during 1300-850 Ma ago. Accordingly, the stromatolite-bearing carbonate rocks are then proposed to correspond to the middle Jixian System-middle Qingbaikou System or the upper Middle Riphean-lower Upper Riphean. Our stromatolite data further suggest that a Precambrian microblock, named the Xialawen microblock here, occurred in the southern belt of Eastern Kunlun, the western part of the Maqên microblock. Similar stromatolite assemblages in the Maqên microblock and those blocks that occurred in North China, Siberia and North Africa point to similar paleogeographic and paleoenvironmental conditions. These microblock and blocks were probably located at low latitudes and on the continental margins of the Rodinian supercontinent, where warm epicontinental seas were favorable to widespread colonization of stromatolites during the Late Mesoproterozoic-Eady Neoproterozoic. However, these stromatolite assemblages are quite different from those of the South China block, which is suggestive of different paleogeographic contexts, and probably also of a different tectonic affinity.展开更多
The stratigraphic, structural and metamorphic features of the basal thrust belt of the ca. 1.0 Ga Miaowan （庙湾） ophiolite in the southern Huangling （黄陵） anticline, show that it can be divided into three tectono...The stratigraphic, structural and metamorphic features of the basal thrust belt of the ca. 1.0 Ga Miaowan （庙湾） ophiolite in the southern Huangling （黄陵） anticline, show that it can be divided into three tectono-lithostratigraphic units from north to south： mélange/wildflysch rock units, flysch rock units, and sedimentary rock units of the autochthonous （in situ） stable continental margin. The three units underwent thrust-related deformation during emplacement of the Miaowan ophiolitic nappe, with kinematic indicators indicating movement from the NNE to SSW, with the metamorphic grade reaching greenschist-amphibolite facies. LA-ICP-MS U-Pb geochronology of zircons from granite pebbles in the basal thrust-related wildflysch yield ages of 859±26, 861＋12 and 871±16 Ma; whereas monzonitic granite clasts yield an age of 813±14 Ma. This indicates that the formation age of the basal thrust belt is not older than 813±14 Ma, and is earlier than the earliest formation time of the majority of the Neoproterozoic Huangling granitoid intrusive complex, which did not experience penetrative ductile deforma-tion. These results suggest that the northern margin of the Yangtze craton was involved in collisional tectonics that continued past 813 Ma.This may be related to the amalgamation of the Yangtze craton with the Rodinia supercontinent. Through comparative study of lithology, zircon geochronology, REE patterns between granodiorite and tonalite pebbles in the basal thrust-zone conglomerate, it can be concluded that the pebbles are the most similar to the Huanglingmiao （黄陵庙） rock-mass （unit）, implying that they may have come from Huanglingmiao rock-mass. Zircon cores yield xenocrystic ages of 2 074±120 Ma, suggesting that the protolith of the Neoproterozoic Huangling granitoid intrusive complex may have originated from par-tial melting of older basement rocks, that is to say there may be Paleoproterozoic crystalline basement in the southern Huangling anticline. The ages of xenocrystic zircons in the granite pebbles in the basal-thrust congiomerate/wildflysch show a correlation with the age spectra from Australia, implying that the terrain that collided with the northern margin of the Yangtze craton and emplaced the Miaowan ophiolite at ca. 813 Ma may have been derived from the Australian segment of Rodinia.展开更多
基金The paper is supported by Key Project ( No .104039) and Special Doc-toral Project (No .20050491506) from the Ministry of Education , China ,the Open Research Program of the Key Laboratory of Continental Dynamics , Northwest University ,and NSFC Special Grant for National Education Base of Geology (No .J0530147) .
文摘U-Pb dating was conducted on different domains of zircons from metamorphosed leucosomes in Delingha （ 德令哈） complex, the lower basement rocks of the Olongbuluke （欧龙布鲁克 ） microcontinent, North Qaidam, in order to review its complex tectonothermal history. The zircon core is comprised of highly-modified magmatic zircon relicts, the zircon mantle was produced in response to anatexis of a Late Protoproterozoic thermal event; age and isotopic composition of both the zircon core and the zircon mantle have been seriously disturbed due to the thermal event related with growth of the zircon overgrowth rim. The 207 PIV 206 Pb apparent age of the overgrowth rim was estimated to be - 1 030 Ma. This Late Mesoproterozoic thermal event has been interpreted as a response to the global Rodinia supercontinent assembly event in the Olongbuluke microcontinent, Northwest China.
基金funded by the National Natural Science Foundation of China(grants No.41406080,41273066 and 41106060)China Geological Survey(grant No.DD20160155)
文摘The amalgamation and breakup mechanisms of the Rodinia supercontinent during the Meso- and Neoproterozoic have been the focus of much research. However, few studies have examined the response of Neoproterozoic tectonics and magmatism along the northeastern margin of the Yangtze Plate to synchronous global events. The Qianliyan Uplift is located on the eastern margin of the Sulu orogenic belt in the ocean, but the tectonic affinity of the uplift and its relationship to the Sulu orogenic belt remains unclear. In this study, we investigated the formation age, geochemical characteristics, genesis type, and affinity of the granitic gneiss on Chaolian Island of the Qianliyan uplift and its tectonic significance.
基金supported by the National Science Foundation of China (Nos. 41172069 and 41372075)the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan)
文摘The Tarim Craton is one of the major continental blocks in China.Mafic dykes,ultra-mafic–mafic–carbonatite complex and ultra-mafic–mafic pluton of 0.82–0.75 Ga widely occur in Kuluktage,Aksu and Tieklik area along
基金financial support from the Land and Resources Survey Project of China(Grants # 1212010611804, 121201120133)the National Natural Science Foundation of China(Grant # 40472044)
文摘Early Cambrian and Mid--Late Neoproterozoic volcanic rocks in China are widespread on several Precambrian continental blocks, which had aggregated to form part of the Rodinia supercon- tinent by ca. 900 Ma. On the basis of petrogeochemical data, the basic lavas can be classified into two major magma types： HT （Ti/Y 〉 500） and LT （Ti/Y 〈 500） that can be further divided into HT1 （Nb/La 〉 0.85） and HT2 （Nb/La ≤ 0.85）, and LT1 （Nb/La 〉 0.85） and LT2 （Nb/La ≤ 0.85） subtypes, respectively. The geochemical variation of the HT2 and LT2 lavas can be accounted for by lithospheric contamination of asthenosphere- （or plume-） derived magmas, whereas the parental magmas of the HT1 and LT1 lavas did not undergo, during their ascent, pronounced lithospheric contamination. These volcanics exhibit at least three characteristics： （1） most have a compositional bimodality; （2） they were formed in an intracontinental rift setting; and （3） they are genetically linked with mantle plumes or a mantle surperplume. This rift-related volcanism at end of the Mid-- Neoproterozoic and Early Cambrian coincided temporally with the separation between Australia-- East Antarctica, South China and Laurentia and between Australia and Tarim, respectively.
文摘With the latest information on geology, isotop chronology, geochemistry and aerial geophysics, the structural enviroment, geological event characterists and evolution history of component units of Rodinia Supercontinent on a global scale are discussed. And some neo views and genetic pattern are provided. The East Eurppean Craton had a complex evolution history between 1.7 and 0.9 Ga. The arthors propose a new reconstruction of Laurentia acient land and Siberia at ca. 1 050～1 000 Ma. The largest litho-structural record of the Meso-Neoproterozoic orogenic collage in South America made up the western border of the South American Platform African Cratons are the result of convergence of Paleoproterozoic/Archaem Cratonic blocks. A part of Eastern Antarctica attached to southern Africa in Mesoproterozoic. Neoproterozoic felsic magmatic events in New India made the western border of Rodinia Pre-Grevoillian Laurentia was established as a major continental block by the end of the Paleoproterozoic. South China is geologically plausible to be between southern Laurentia and eastern Australia. Yangzi-Tarim connection or neighborhood is proposed. According to the abovementionded, the assembly and breakup paattern of Rodinia proposed by Pisarevsky is tested. It telles that primary break up is along the western border of Laurentia ancient land, which is similar to northern Atlantic. Another characteristic is that some continents are not considered as component parts of Rodinia, eg. India, Congo and San-Francisco.
基金the continuing support of the Natural Sciences and Engineering Research Council,Canada through Discovery and Research Capacity grantsRDN is supported by National Science Foundation grant EAR-0308105+1 种基金a Baker Award from Ohio Universitya contribution to the International Geoscience Program,IGCP Project 597
文摘The supercontinent cycle has had a profound effect on the Earth＇s evolution since the Late Archean but our understanding of the forces responsible for its operation remains elusive.Supercontinents appear to form by two end-member processes：extroversion,in which the oceanic lithosphere surrounding the supercontinent（exterior ocean） is preferentially subducted（e.g.Pannotia）,and introversion in which the oceanic lithosphere formed between dispersing fragments of the previous supercontinent（interior ocean） is preferentially subducted（e.g.Pangea）.Extroversion can be explained by ＂top-down＂ geodynamics, in which a supercontinent breaks up over a geoid high and amalgamates above a geoid low. Introversion,on the other hand,requires that the combined forces of slab-pull and ridge push（which operate in concert after supercontinent break-up） must be overcome in order to enable the previously dispersing continents to turn inward.Introversion may begin when subduction zones are initiated along boundaries between the interior and exterior oceans and become trapped within the interior ocean.We speculate that the reversal in continental motion required for introversion may be induced by slab avalanche events that trigger the rise of superplumes from the core-mantle boundary.
基金supported in part by grants from the National Science Foundation EAR09-10888 and EAR11-19038
文摘The observation is made that there are very strong similarities between the supercontinents Columbia, Rodinia and Pangea. If plate tectonics was operating over the past 2.5 billion years of Earth history, and dominated by extroversion and introversion of ocean basins, it would be unusual for three superconti-nents to resemble one another so closely. The term＇strange attractor＇ is applied to landmasses that form a coherent geometry in all three supercontinents. Baltica, Laurentia and Siberia form a group of＇strange attractors＇ as do the elements of East Gondwana （India, Australia, Antarctica, Madagascar）. The elements of ＂West Gondwana＂ are positioned as a slightly looser amalgam of cratonic blocks in all three super-continents and are referred to as ＇spiritual interlopers＇. Relatively few landmasses （the South China, North China, Kalahari and perhaps Tarim cratons） are positioned in distinct locations within each of the three supercontinents and these are referred to as＇lonely wanderers＇. 〈br〉 There may be several explanations for why these supercontinents show such remarkable similarities. One possibility is that modern-style plate tectonics did not begin until the late Neoproterozoic and horizontal motions were restricted and a vertical style of ＇lid tectonics＇ dominated. If motions were limited for most of the Proterozoic, it would explain the remarkable similarities seen in the Columbia and Rodinia supercontinents, but would still require the strange attractors to rift, drift and return to approximately the same geometry within Pangea. 〈br〉 A second possibility is that our views of older supercontinents are shaped by well-known connections documented for the most recent supercontinent, Pangea. It is intriguing that three of the four ＇lonely wanderers＇ （Tarim, North China, South China） did not unite until just before, or slightly after the breakup of Pangea. The fourth＇lonely wanderer＇, the Kalahari （and core Kaapvaal） craton has a somewhat unique Archean-age geology compared to its nearest neighbors in Gondwana, but very similar to that in western Australia.
基金financially supported by Post–doctoral Scientific Foundation of China(No.2016M601084)Basic research funds of the Chinese Academy of Geological Sciences(No.JYYWF20182103)+1 种基金Geological Survey of China(No.DD20160022–01)a grant from the Ministry of Land and Resources of China(No.201511022)
文摘A 〉1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton（SCC） consists of subduction mélange and extensional basin deposits. This belt is present under an unconformity of Devonian–Carboniferous sediments. Tectonic evolution of the Neoproterozoic rocks is crucial to determining the geology of the SCC and further influences the reconstruction of the Rodinia supercontinent. A subduction mélange unit enclosed ca.1000–850–Ma mafic blocks, which defined a Neoproterozoic ocean that existed within the SCC, is exposed at the bottom of the Jiangnan Orogen（JO） and experienced at least two phases deformation. Combined with new（detrital） zircon U–Pb ages from metasandstones, as well as igneous rocks within the metamorphic belt, we restrict the strongly deformed subduction mélange as younger than the minimum detrital age ca. 835 Ma and older than the ca. 815 Ma intruded granite. Unconformably overlying the subduction mélange and the intruded granite, an intra–continental rift basin developed 〈800 Ma that involved abundant mantle inputs, such as mafic dikes. This stratum only experienced one main phase deformation. According to our white mica ^40Ar/^（30）Ar data and previously documented thermochronology, both the Neoproterozoic mélange and younger strata were exhumed by a 490–400–Ma crustal–scale positive flower structure. This orogenic event probably induced the thick–skinned structures and was accompanied by crustal thickening, metamorphism and magmatism and led to the closure of the pre–existing rift basin. Integrating previously published data and our new results, we agree that the SCC was located on the periphery of the Rodinia supercontinent from the Neoproterozic until the Ordovician. Furthermore, we prefer that the convergence and dispersal of the SCC were primarily controlled by oceanic subduction forces that occurred within or periphery of the SCC.
基金This work was supported by the KIP Key Project of the Chinese Academy of Sciences(KZCX3-SW-143)the KIP Key Project of the Chinese Academy of Sciences(KZCX2-SW-119)+3 种基金the Key Project of the National Natural Science Foundation of China(Grant No.40334044)the Chinese National Key Basic Research Project(2002CB4 12600)the National Natural Science Foundation of China(Grant No.49872077)the Lu Jiaxi Foundation of the Chinese Academy of Sciences.
文摘This paper reports a newly discovered Late Mesoproterozoic-Early Neoproterozoic stromatolite assemblage, named here the ＂Jiawengmen stromatolite assemblage＂, represented by a Conophyton-Baicalia association in the Jiawenmen area in the southern belt of the Eastern Kunlun. This stromatolite assemblage is dominated by large-scale conical stromatolites and related elements, i.e., Conophyton garganicus var. inkeni, C. cf. ressoti Menchikov, Jacutophyton cf., Conicodomenia f., which commonly co-exist with elements of the group of Baicalia. This assemblage can be correlated with that of the middle Jixian-middle Qingbaikou System in North and Northwest China, but is different from that in South China. Correlation can also be made with that in the upper horizon of the Middle Riphean-lower horizon of the Upper Riphean in the South Ural Mountains and Siberia of Russia, in North Africa, and in the Alaskan Peninsula of North America. These facts suggest that the Jiawengmen stromatolite assemblage probably colonized during 1300-850 Ma ago. Accordingly, the stromatolite-bearing carbonate rocks are then proposed to correspond to the middle Jixian System-middle Qingbaikou System or the upper Middle Riphean-lower Upper Riphean. Our stromatolite data further suggest that a Precambrian microblock, named the Xialawen microblock here, occurred in the southern belt of Eastern Kunlun, the western part of the Maqên microblock. Similar stromatolite assemblages in the Maqên microblock and those blocks that occurred in North China, Siberia and North Africa point to similar paleogeographic and paleoenvironmental conditions. These microblock and blocks were probably located at low latitudes and on the continental margins of the Rodinian supercontinent, where warm epicontinental seas were favorable to widespread colonization of stromatolites during the Late Mesoproterozoic-Eady Neoproterozoic. However, these stromatolite assemblages are quite different from those of the South China block, which is suggestive of different paleogeographic contexts, and probably also of a different tectonic affinity.
基金supported by the Postdoctoral Science Foundation (No. 20100471203)the Ministry of Land and Resources of China (No. 1212010670104)+1 种基金the National Natural Science Foundation of China (Nos. 91014002, 40821061, 41272242)Ministry of Education of China (Nos. B07039,TGRC201024)
文摘The stratigraphic, structural and metamorphic features of the basal thrust belt of the ca. 1.0 Ga Miaowan （庙湾） ophiolite in the southern Huangling （黄陵） anticline, show that it can be divided into three tectono-lithostratigraphic units from north to south： mélange/wildflysch rock units, flysch rock units, and sedimentary rock units of the autochthonous （in situ） stable continental margin. The three units underwent thrust-related deformation during emplacement of the Miaowan ophiolitic nappe, with kinematic indicators indicating movement from the NNE to SSW, with the metamorphic grade reaching greenschist-amphibolite facies. LA-ICP-MS U-Pb geochronology of zircons from granite pebbles in the basal thrust-related wildflysch yield ages of 859±26, 861＋12 and 871±16 Ma; whereas monzonitic granite clasts yield an age of 813±14 Ma. This indicates that the formation age of the basal thrust belt is not older than 813±14 Ma, and is earlier than the earliest formation time of the majority of the Neoproterozoic Huangling granitoid intrusive complex, which did not experience penetrative ductile deforma-tion. These results suggest that the northern margin of the Yangtze craton was involved in collisional tectonics that continued past 813 Ma.This may be related to the amalgamation of the Yangtze craton with the Rodinia supercontinent. Through comparative study of lithology, zircon geochronology, REE patterns between granodiorite and tonalite pebbles in the basal thrust-zone conglomerate, it can be concluded that the pebbles are the most similar to the Huanglingmiao （黄陵庙） rock-mass （unit）, implying that they may have come from Huanglingmiao rock-mass. Zircon cores yield xenocrystic ages of 2 074±120 Ma, suggesting that the protolith of the Neoproterozoic Huangling granitoid intrusive complex may have originated from par-tial melting of older basement rocks, that is to say there may be Paleoproterozoic crystalline basement in the southern Huangling anticline. The ages of xenocrystic zircons in the granite pebbles in the basal-thrust congiomerate/wildflysch show a correlation with the age spectra from Australia, implying that the terrain that collided with the northern margin of the Yangtze craton and emplaced the Miaowan ophiolite at ca. 813 Ma may have been derived from the Australian segment of Rodinia.
