Structural relationships between the Neoproterozoic rock complexes of a continental massif, island arc and back-arc basin geodynamic affinities are described and considered in this work based on field observations wit...Structural relationships between the Neoproterozoic rock complexes of a continental massif, island arc and back-arc basin geodynamic affinities are described and considered in this work based on field observations within the northeastern segment of the Central Taimyr tectonic zone distinguished in the late Hercynian fold- thrust belt of Taimyr Peninsula. As is established for the first time, rock complexes of the continental massif with the early Late Riphean （Tonian-Cryogenian） volcanogenic-sedimentary cover occur in the study region as the allochthonous syn- and post-sedimentary thrust sheets buried in or thrust over deposits of a back-arc basin, which accumulated in the terminal Late Riphean （Cryogcnian）-initial Vendian （Ediacaran）. These and other results of the large-scale structural observations elucidate important details of the region tectonic development in the Late Precambrian, when two lateral ensembles of the Neoproterozoic structures originated in the region. In the first half of the Neoproterozoic, the regional tectonic ensemble included the oceanic plate abut on the continental massif with a primitive volcano-plutonic belt. The subsequent system of an island arc and marginal back- arc basin originated in the second half of the Neoproterozoic and existed approximately till the mid-Vendian （Ediacaran） phase of the intense formation of thrust sheets in the region.展开更多
Recent mapping and seismic survey reveal that intensive compression during the Early Cenozoic in the Qiangtang block of the central Tibetan Plateau formed an extensive complex of thrust sheets that moved relatively so...Recent mapping and seismic survey reveal that intensive compression during the Early Cenozoic in the Qiangtang block of the central Tibetan Plateau formed an extensive complex of thrust sheets that moved relatively southward along several generally north-dipping great thrust systems. Those at the borders of the ~450 km wide block show it overrides the Lhasa block to the south and is overridden by the Hohxil-Bayanhar block to the north. The systems are mostly thin-skinned imbricate thrusts with associated folding. The thrust sheets are chiefly floored by Jurassic limestone that apparently slid over Triassic sandstone and shale, which is locally included, and ramped upward and over Paleocene-Eocene red-beds. Some central thrusts scooped deeper and carried up Paleozoic metamorphic rock, Permian carbonate and granite to form a central uplift that divides the Qiangtang block into two parts. These systems and their associated structures are unconformably overlain by little deformed Late Eocene-Oligocene volcanic rock or capped by Miocene lake beds. A thrust system in the northern part of the block, as well as one in the northern part of the adjacent Lhasa block, dip to the south and appear to be due to secondary adjustments within the thrust sheets. The relative southward displacement across this Early Cenozoic mega thrust system is in excess of 150 km in the Qiangtang block, and the average southward slip-rate of the southern Qiangtang thrusts ranged from 5.6 mm to 7.4 mm/a during the Late Eocene-Oligocene. This Early Cenozoic thrusting ended before the Early Miocene and was followed by Late Cenozoic crustal extension and strike-slip faulting within the Qiangtang block. The revelation and understanding of these thrust systems are very important for the evaluation of the petroleum resources of the region.展开更多
A contact zone sandwiched between an arc and an oceanic crust was discoveredin the Laohushan area in the present study. It consists of a series of north-dipping imbricatedthrust sheets and is exposed on the surface as...A contact zone sandwiched between an arc and an oceanic crust was discoveredin the Laohushan area in the present study. It consists of a series of north-dipping imbricatedthrust sheets and is exposed on the surface as a narrow arcuate belt, which extends for about 30 kmin an E-W direction and measures about 1-3 km wide. Lithologically, it can be divided into foursubzones. Subzone 1 consists of meta-andesite and metasandstone; subzone 2, psammitic schists;subzone 3, psammitic and pelitic schists, quartz diorite and hornfelses; and subzone 4, metagabbro,epidote amphibolite and pelitic schists. The metamorphism has the following grading sequence: lowgreenschist facies in subzone 1 - > high greenschist facies in subzone 2 - > low amphibolite fadesin subzone 3 - > epidote amphibolite facies in subzone 4. Petrographic and geochemical evidenceshows that rocks in subzones 1, 2 and 3 are arc rocks, whereas those of subzone 4 are oceaniccrustal rocks. The metamorphic mineral assemblages and especially mineral chemistry of the bluishgreen amphibole from the pelitic schists and epidote amphibolite of subzone 4 suggest that the rocksof the contact zone were metamorphosed at a pressure of up to 0.69 GPa. It is thought that theLate-Mid Ordovician oceanic lithosphere of a back-arc basin was underthrust northerly beneath an arcto a depth of 20-23 km, where the basaltic rocks and gabbro were converted to epidote amphiboliteand metagabbro respectively. Then, the root rocks of the arc and these metamorphosed oceanic rockswere brought up to shallower depths by thrust faults to form a contact zone between the arc and theoceanic crust in the Laohushan area.展开更多
We present an overview of the internal structure of the ophiolite massifs along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet with a focus on the geochemical character and tectonic evolution of the Ocean Islan...We present an overview of the internal structure of the ophiolite massifs along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet with a focus on the geochemical character and tectonic evolution of the Ocean Island Basalt(OIB)and mafic alkaline rock assemblages associated with these ophiolites.The Jurassic–early Cretaceous lavas,massive diabase and gabbroic rocks are either tectonically intercalated with the early Cretaceous,subduction-influenced ophiolitic units,or occur as thrust sheets or blocks with an early Cretaceous mélange and in a Jurassic-Cretaceous flysch unit structurally beneath these ophiolites.They display uniform chondrite-normalized REE patterns with light rare earth element(LREE)enrichment and heavy rare earth element(HREE)depletion,no obvious Eu anomalies or negative Nb,Ta and Ti anomalies,and primitive mantle normalized trace element patterns with significant large-ion lithophile element(LILE)enrichment,similar to those of modern OIB and the Hawaiian alkaline basalts.These mafic alkaline rock assemblages represent OIB-and Plume-type(P-type)oceanic crustal rocks(with no subduction influence)that formed from magmas produced by partial melting of plume–metasomatized asthenospheric mantle source during the early stages of the opening of a Neotethyan seaway between Proto-India and Eurasia.展开更多
The Nagaland–Manipur Hill ophiolite belt in NE India represents the southern extension of the Neotethyan Yarlung-Zhangbo suture zone in Southern Tibet,and connects this on-land exposure of the late Mesozoic collision...The Nagaland–Manipur Hill ophiolite belt in NE India represents the southern extension of the Neotethyan Yarlung-Zhangbo suture zone in Southern Tibet,and connects this on-land exposure of the late Mesozoic collision front in the north with a modern trench-arc system in the Andaman Sea region in the south.Ophiolitic subunits in the Nagaland–Manipur Hill area in the Indo-Myanmar Ranges occur as blocks or thrust sheets within a mélange with a serpentinite or fine-grained greywacke matrix,and are spatially associated with eclogitic and blueschist rock assemblages.This ophiolitic mélange zone is tectonically sandwiched between an older(Triassic–Cretaceous)accretionary prism complex(Nimi Flysch)to the east and a younger(Late Cretaceous–Miocene)accretionary wedge(Disang Flysch)to the west.The Nagaland–Manipur Hill ophiolitic mélange is thus part of a progressively westward migrated subduction-accretion complex,and it represents a typical subduction channel mélange evolved during the fast subduction of the Neotethyan oceanic lithosphere beneath Asia–Sundaland.展开更多
文摘Structural relationships between the Neoproterozoic rock complexes of a continental massif, island arc and back-arc basin geodynamic affinities are described and considered in this work based on field observations within the northeastern segment of the Central Taimyr tectonic zone distinguished in the late Hercynian fold- thrust belt of Taimyr Peninsula. As is established for the first time, rock complexes of the continental massif with the early Late Riphean （Tonian-Cryogenian） volcanogenic-sedimentary cover occur in the study region as the allochthonous syn- and post-sedimentary thrust sheets buried in or thrust over deposits of a back-arc basin, which accumulated in the terminal Late Riphean （Cryogcnian）-initial Vendian （Ediacaran）. These and other results of the large-scale structural observations elucidate important details of the region tectonic development in the Late Precambrian, when two lateral ensembles of the Neoproterozoic structures originated in the region. In the first half of the Neoproterozoic, the regional tectonic ensemble included the oceanic plate abut on the continental massif with a primitive volcano-plutonic belt. The subsequent system of an island arc and marginal back- arc basin originated in the second half of the Neoproterozoic and existed approximately till the mid-Vendian （Ediacaran） phase of the intense formation of thrust sheets in the region.
基金financially supporting the research under grants No.1212011221111,Sinoprobe-02-01 and 2006DFB21330 respectively
文摘Recent mapping and seismic survey reveal that intensive compression during the Early Cenozoic in the Qiangtang block of the central Tibetan Plateau formed an extensive complex of thrust sheets that moved relatively southward along several generally north-dipping great thrust systems. Those at the borders of the ~450 km wide block show it overrides the Lhasa block to the south and is overridden by the Hohxil-Bayanhar block to the north. The systems are mostly thin-skinned imbricate thrusts with associated folding. The thrust sheets are chiefly floored by Jurassic limestone that apparently slid over Triassic sandstone and shale, which is locally included, and ramped upward and over Paleocene-Eocene red-beds. Some central thrusts scooped deeper and carried up Paleozoic metamorphic rock, Permian carbonate and granite to form a central uplift that divides the Qiangtang block into two parts. These systems and their associated structures are unconformably overlain by little deformed Late Eocene-Oligocene volcanic rock or capped by Miocene lake beds. A thrust system in the northern part of the block, as well as one in the northern part of the adjacent Lhasa block, dip to the south and appear to be due to secondary adjustments within the thrust sheets. The relative southward displacement across this Early Cenozoic mega thrust system is in excess of 150 km in the Qiangtang block, and the average southward slip-rate of the southern Qiangtang thrusts ranged from 5.6 mm to 7.4 mm/a during the Late Eocene-Oligocene. This Early Cenozoic thrusting ended before the Early Miocene and was followed by Late Cenozoic crustal extension and strike-slip faulting within the Qiangtang block. The revelation and understanding of these thrust systems are very important for the evaluation of the petroleum resources of the region.
基金financially supportedby National Science Council.
文摘A contact zone sandwiched between an arc and an oceanic crust was discoveredin the Laohushan area in the present study. It consists of a series of north-dipping imbricatedthrust sheets and is exposed on the surface as a narrow arcuate belt, which extends for about 30 kmin an E-W direction and measures about 1-3 km wide. Lithologically, it can be divided into foursubzones. Subzone 1 consists of meta-andesite and metasandstone; subzone 2, psammitic schists;subzone 3, psammitic and pelitic schists, quartz diorite and hornfelses; and subzone 4, metagabbro,epidote amphibolite and pelitic schists. The metamorphism has the following grading sequence: lowgreenschist facies in subzone 1 - > high greenschist facies in subzone 2 - > low amphibolite fadesin subzone 3 - > epidote amphibolite facies in subzone 4. Petrographic and geochemical evidenceshows that rocks in subzones 1, 2 and 3 are arc rocks, whereas those of subzone 4 are oceaniccrustal rocks. The metamorphic mineral assemblages and especially mineral chemistry of the bluishgreen amphibole from the pelitic schists and epidote amphibolite of subzone 4 suggest that the rocksof the contact zone were metamorphosed at a pressure of up to 0.69 GPa. It is thought that theLate-Mid Ordovician oceanic lithosphere of a back-arc basin was underthrust northerly beneath an arcto a depth of 20-23 km, where the basaltic rocks and gabbro were converted to epidote amphiboliteand metagabbro respectively. Then, the root rocks of the arc and these metamorphosed oceanic rockswere brought up to shallower depths by thrust faults to form a contact zone between the arc and theoceanic crust in the Laohushan area.
基金supported by the National Nature Science Foundation of China(41303027)Special Fund for Basic Scientific Research of Central Colleges,Chang’an University(310827153506,310827153407)to G.-X.Yang.Y.Dilek’s research in Tibet and on the Yarlung-Zangbo suture zone ophiolites has been funded by the Chinese Academy of Geological Sciences(Beijing,China).
文摘We present an overview of the internal structure of the ophiolite massifs along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet with a focus on the geochemical character and tectonic evolution of the Ocean Island Basalt(OIB)and mafic alkaline rock assemblages associated with these ophiolites.The Jurassic–early Cretaceous lavas,massive diabase and gabbroic rocks are either tectonically intercalated with the early Cretaceous,subduction-influenced ophiolitic units,or occur as thrust sheets or blocks with an early Cretaceous mélange and in a Jurassic-Cretaceous flysch unit structurally beneath these ophiolites.They display uniform chondrite-normalized REE patterns with light rare earth element(LREE)enrichment and heavy rare earth element(HREE)depletion,no obvious Eu anomalies or negative Nb,Ta and Ti anomalies,and primitive mantle normalized trace element patterns with significant large-ion lithophile element(LILE)enrichment,similar to those of modern OIB and the Hawaiian alkaline basalts.These mafic alkaline rock assemblages represent OIB-and Plume-type(P-type)oceanic crustal rocks(with no subduction influence)that formed from magmas produced by partial melting of plume–metasomatized asthenospheric mantle source during the early stages of the opening of a Neotethyan seaway between Proto-India and Eurasia.
文摘The Nagaland–Manipur Hill ophiolite belt in NE India represents the southern extension of the Neotethyan Yarlung-Zhangbo suture zone in Southern Tibet,and connects this on-land exposure of the late Mesozoic collision front in the north with a modern trench-arc system in the Andaman Sea region in the south.Ophiolitic subunits in the Nagaland–Manipur Hill area in the Indo-Myanmar Ranges occur as blocks or thrust sheets within a mélange with a serpentinite or fine-grained greywacke matrix,and are spatially associated with eclogitic and blueschist rock assemblages.This ophiolitic mélange zone is tectonically sandwiched between an older(Triassic–Cretaceous)accretionary prism complex(Nimi Flysch)to the east and a younger(Late Cretaceous–Miocene)accretionary wedge(Disang Flysch)to the west.The Nagaland–Manipur Hill ophiolitic mélange is thus part of a progressively westward migrated subduction-accretion complex,and it represents a typical subduction channel mélange evolved during the fast subduction of the Neotethyan oceanic lithosphere beneath Asia–Sundaland.
