Deciphering the relationship between polyphase tectonic foliations and their associated mineral assemblages is significant in understanding the process from diagenesis to low-/medium-/high-grade metamorphism.It can pr...Deciphering the relationship between polyphase tectonic foliations and their associated mineral assemblages is significant in understanding the process from diagenesis to low-/medium-/high-grade metamorphism.It can provide information related to strain,metamorphic conditions and overprinting relationships and so help reveal the tectonic evolution of orogenesis.In this study,we predominately focus on the formation of foliations and their related minerals,as developed in two separate basins.First of all,two stages of axial plane cleavages(S1 and S2)were recognized in the Hongyanjing inter-arc basin,the formation of the S1 axial plane cleavage is associated with mica rotation and elongation in mudstones in the local area.The pencil structure of S2 formed during the refolding phase,the minerals in the sedimentary rocks not changing their shape and orientation.Secondly,in the Liao-Ji backarc basin,foliations include diagenetic foliation(bedding parallel foliation),tectonic S1 foliation(secondary foliation or axial plane cleavage of S0 folding)and crenulation cleavage(S2).The formation mechanism of foliation changes from mineral rotation or elongation and mineral solution transfer in S1 to crystal-plastic deformation,dynamic recrystallization and micro-folding in S2.Many index metamorphic minerals formed from low-grade to medium-grade consist of biotites,garnets,staurolite and kyanite,constituting a typical Barrovian metamorphic belt.Accordingly,a new classification of foliation is presented in this study.The foliations can be divided into continuous and disjunctive foliations,based on the existence of microlithons,detectable with the aid of a microscope.Disjunctive foliation can be further sub-divided into spaced foliation and crenulation cleavage,according to whether(or not)crenulation(micro-folding)is present.The size of the mineral grains is also significant for classification of the foliations.展开更多
Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous.It has been proposed that the preceding Jurassic-Earl...Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous.It has been proposed that the preceding Jurassic-Early Cretaceous extensional regime that resulted in a low-relief volcanic arc and the backarc Neuquén basin came to an end,giving way to shortening and Andean growth from the Late Cretaceous onward.Nevertheless,there are disagreements regarding the timing and nature of this transition to Andean orogenesis.To address these issues,we conducted geochronologic(U-Pb and^(40)Ar/&(39)Ar),sedimentologic,and structural studies on Mesozoic-Cenozoic sedimentary and volcanic rocks in the Río Maule area(Principal Cordillera,Chile,36°S).From our findings and prior analyses,we propose the following tectono-stratigraphic evolution of the region.(1)Marine deposition of the Tithonian-Hauterivian Baños del Flaco Formation took place in an extensional backarc basin.(2)After a~40 Myr hiatus,fluvial deposits of the Colimapu Formation and volcanic rocks of the Plan de los Yeuques Formation accumulated during the Cenomanian-Danian.Whereas the Colimapu Formation displays evidence of syndepositional shortening,the Plan de los Yeuques Formation exhibits synextensional growth strata.Contrary to other studies,our results suggest that the Chilean part of the Principal Cordillera was largely a zone of active deposition rather than an elevated fold-thrust belt during the Late Cretaceous.We propose that sedimentation occurred within a series of relatively stable intermontane subbasins generated by shortening,followed by extension.(3)After a~20 Myr hiatus,middle Eocene to early Miocene(Lutetian-Aquitanian)accumulation of a thick succession of andesitic lavas and minor clastic sediments of the Abanico Formation occurred in an intraarc extensional basin.(4)Finally,major shortening and uplift of previously deposited Mesozoic-Cenozoic rocks took place throughout the Neogene.This phase constituted the primary contractional deformation in the Andes of south-central Chile and Argentina.In terms of the transition to early Andean deformation,we propose that structural deformation did not generate a major,regional-scale fold-thrust belt during the late Albian-Santonian.Modest extension,tectonic quiescence,or low-magnitude shortening seem to have dominated during the early to middle Cenozoic.展开更多
Based on an analysis of full-cover multi-beam bathymetric data,seismic and sub-bottom profiling data,and other geological-geophysical data sets,the geomorphologic features of the Ryukyu trench-arc-backarc(T-A-BA)syste...Based on an analysis of full-cover multi-beam bathymetric data,seismic and sub-bottom profiling data,and other geological-geophysical data sets,the geomorphologic features of the Ryukyu trench-arc-backarc(T-A-BA)system are delineated,and a geomorphologic map of the system is compiled.The re-sults show that the evolution and spatial distribution patterns of the geomorphologic types of the Ryukyu T-A-BA system are controlled mainly by tectonic move-ments.The tectonic geomorphologic characteristics of the Ryukyu Arc(RA) differ distinctly from those of the East China Sea(ECS) continental shelf and slope.In term of geological structures,RA consists of the Tokara volcanic ridge,the Ryukyu folded ridge,the fore-arc accre-tion-wedge ridge and the Amami Depression and the fore-arc depressions between the ridges,which is com-posed of a complex of alternating island-slope ridges and fault basins.The slope of the ECS is a passive continental margin with stepwise faults.The Okinawa Trough (OT)is a backarc rift in which tectonic movements are inten-sive,with active volcanic and hydrothermjal eruptions and sea floor spreading.The development of geomorphic features of the OT is controlled by the central en echelon spreading axes,the faults along the ECS slope and the marginal faults to the west of the Tokara vol-canic ridge.The geomorphic complex of the OT is ar-ranged in the following pattern:the en echelon grabens and volcanic chains formed by rifting and spreading lie in the central part of the trough,the turbidite plains inclining eastwards-southeastwards from the slope foot of the ECS lie in the western-northwestern parts of the OT,and the volcaniclastic deposit plains inclining westward-northwestwards from the western slope foot of the RA lie in the eastern-southeastern parts of the OT. In term of tectonic geomorphology,the OT forms a natural division between the shelf of the ECS and the RA.展开更多
Different models have been proposed for the formation and tectonic evolution of the South China Sea （SCS）, including extrusion of the Indochina Peninsula, backarc extension, two-stage opening, proto-SCS dragging, ex...Different models have been proposed for the formation and tectonic evolution of the South China Sea （SCS）, including extrusion of the Indochina Peninsula, backarc extension, two-stage opening, proto-SCS dragging, extension induced by a mantle plume, and integrated models that combine diverse factors. Among these, the extrusion model has gained the most attention. Based on simplified physical experiments, this model proposes that collision between the Indian and Eurasian Plates resulted in extrusion of the Indochina Peninsula, which in turn led to opening of the SCS. The extrusion of the Indochina Peninsula, however, should have led to preferential open- ing in the west side of the SCS, which is contrary to observations. Extensional models propose that the SCS was a backarc basin, rifted off the South China Block. Most of the backarc extension models, however, are not compatible with observations in terms of either age or subduction direction. The two-stage extension model is based on extensional basins surrounding the SCS. Recent dating results indeed show two-stage opening in the SCS, but the Southwest Subbasin of the SCS is much younger, which contradicts the two-stage extension model. Here we pro- pose a refined backarc extension model. There was a wide Neotethys Ocean between the Australian and Eurasian Plates before the Indian-Eurasian collision. The ocean floorstarted to subduct northward at ~ 125 Ma, causing backarc extension along the southem margin of the Eurasian Plate and the formation of the proto-SCS. The Neotethys sub- duction regime changed due to ridge subduction in the Late Cretaceous, resulting in fold-belts, uplifting, erosion, and widespread unconformities. It may also have led to the subduction of the proto-SCS. Flat subduction of the ridge may have reached further north and resulted in another backarc extension that formed the SCS. The rollback of the fiat subducting slab might have occurred ~ 90 Ma ago; the second backarc extension may have initiated between 50 and 45 Ma. The opening of the Southwest Subbasin is roughly simultaneous with a ridge jump in the East Sub- basin, which implies major tectonic changes in the sur- rounding regions, likely related to major changes in the extrusion of the Indochina Peninsula.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.92062214,41430210 and 41888101)the NSFC Regional Science Foundation(Grant No.41962012)+3 种基金the Scientific Program of Jiangxi Educational Committee(Grant No.GJJ190586)the Chinese Geological Survey projects(Grant No.DD20190003)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(Grant No.XDB18020203)the Basic Scientific Research Foundations of the Institute of Geology,Chinese Academy of Geological Sciences(Grant No.J2030,J2009)。
文摘Deciphering the relationship between polyphase tectonic foliations and their associated mineral assemblages is significant in understanding the process from diagenesis to low-/medium-/high-grade metamorphism.It can provide information related to strain,metamorphic conditions and overprinting relationships and so help reveal the tectonic evolution of orogenesis.In this study,we predominately focus on the formation of foliations and their related minerals,as developed in two separate basins.First of all,two stages of axial plane cleavages(S1 and S2)were recognized in the Hongyanjing inter-arc basin,the formation of the S1 axial plane cleavage is associated with mica rotation and elongation in mudstones in the local area.The pencil structure of S2 formed during the refolding phase,the minerals in the sedimentary rocks not changing their shape and orientation.Secondly,in the Liao-Ji backarc basin,foliations include diagenetic foliation(bedding parallel foliation),tectonic S1 foliation(secondary foliation or axial plane cleavage of S0 folding)and crenulation cleavage(S2).The formation mechanism of foliation changes from mineral rotation or elongation and mineral solution transfer in S1 to crystal-plastic deformation,dynamic recrystallization and micro-folding in S2.Many index metamorphic minerals formed from low-grade to medium-grade consist of biotites,garnets,staurolite and kyanite,constituting a typical Barrovian metamorphic belt.Accordingly,a new classification of foliation is presented in this study.The foliations can be divided into continuous and disjunctive foliations,based on the existence of microlithons,detectable with the aid of a microscope.Disjunctive foliation can be further sub-divided into spaced foliation and crenulation cleavage,according to whether(or not)crenulation(micro-folding)is present.The size of the mineral grains is also significant for classification of the foliations.
基金founded by ANID,Fondecyt Regular projects 1151146,and 1200428founded by ANID,National Doctoral Scholarship.
文摘Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous.It has been proposed that the preceding Jurassic-Early Cretaceous extensional regime that resulted in a low-relief volcanic arc and the backarc Neuquén basin came to an end,giving way to shortening and Andean growth from the Late Cretaceous onward.Nevertheless,there are disagreements regarding the timing and nature of this transition to Andean orogenesis.To address these issues,we conducted geochronologic(U-Pb and^(40)Ar/&(39)Ar),sedimentologic,and structural studies on Mesozoic-Cenozoic sedimentary and volcanic rocks in the Río Maule area(Principal Cordillera,Chile,36°S).From our findings and prior analyses,we propose the following tectono-stratigraphic evolution of the region.(1)Marine deposition of the Tithonian-Hauterivian Baños del Flaco Formation took place in an extensional backarc basin.(2)After a~40 Myr hiatus,fluvial deposits of the Colimapu Formation and volcanic rocks of the Plan de los Yeuques Formation accumulated during the Cenomanian-Danian.Whereas the Colimapu Formation displays evidence of syndepositional shortening,the Plan de los Yeuques Formation exhibits synextensional growth strata.Contrary to other studies,our results suggest that the Chilean part of the Principal Cordillera was largely a zone of active deposition rather than an elevated fold-thrust belt during the Late Cretaceous.We propose that sedimentation occurred within a series of relatively stable intermontane subbasins generated by shortening,followed by extension.(3)After a~20 Myr hiatus,middle Eocene to early Miocene(Lutetian-Aquitanian)accumulation of a thick succession of andesitic lavas and minor clastic sediments of the Abanico Formation occurred in an intraarc extensional basin.(4)Finally,major shortening and uplift of previously deposited Mesozoic-Cenozoic rocks took place throughout the Neogene.This phase constituted the primary contractional deformation in the Andes of south-central Chile and Argentina.In terms of the transition to early Andean deformation,we propose that structural deformation did not generate a major,regional-scale fold-thrust belt during the late Albian-Santonian.Modest extension,tectonic quiescence,or low-magnitude shortening seem to have dominated during the early to middle Cenozoic.
文摘Based on an analysis of full-cover multi-beam bathymetric data,seismic and sub-bottom profiling data,and other geological-geophysical data sets,the geomorphologic features of the Ryukyu trench-arc-backarc(T-A-BA)system are delineated,and a geomorphologic map of the system is compiled.The re-sults show that the evolution and spatial distribution patterns of the geomorphologic types of the Ryukyu T-A-BA system are controlled mainly by tectonic move-ments.The tectonic geomorphologic characteristics of the Ryukyu Arc(RA) differ distinctly from those of the East China Sea(ECS) continental shelf and slope.In term of geological structures,RA consists of the Tokara volcanic ridge,the Ryukyu folded ridge,the fore-arc accre-tion-wedge ridge and the Amami Depression and the fore-arc depressions between the ridges,which is com-posed of a complex of alternating island-slope ridges and fault basins.The slope of the ECS is a passive continental margin with stepwise faults.The Okinawa Trough (OT)is a backarc rift in which tectonic movements are inten-sive,with active volcanic and hydrothermjal eruptions and sea floor spreading.The development of geomorphic features of the OT is controlled by the central en echelon spreading axes,the faults along the ECS slope and the marginal faults to the west of the Tokara vol-canic ridge.The geomorphic complex of the OT is ar-ranged in the following pattern:the en echelon grabens and volcanic chains formed by rifting and spreading lie in the central part of the trough,the turbidite plains inclining eastwards-southeastwards from the slope foot of the ECS lie in the western-northwestern parts of the OT,and the volcaniclastic deposit plains inclining westward-northwestwards from the western slope foot of the RA lie in the eastern-southeastern parts of the OT. In term of tectonic geomorphology,the OT forms a natural division between the shelf of the ECS and the RA.
基金supported by the NSFC(No.91328204,41421062)the Chinese Academy of Sciences(KZCX1-YW-15)
文摘Different models have been proposed for the formation and tectonic evolution of the South China Sea （SCS）, including extrusion of the Indochina Peninsula, backarc extension, two-stage opening, proto-SCS dragging, extension induced by a mantle plume, and integrated models that combine diverse factors. Among these, the extrusion model has gained the most attention. Based on simplified physical experiments, this model proposes that collision between the Indian and Eurasian Plates resulted in extrusion of the Indochina Peninsula, which in turn led to opening of the SCS. The extrusion of the Indochina Peninsula, however, should have led to preferential open- ing in the west side of the SCS, which is contrary to observations. Extensional models propose that the SCS was a backarc basin, rifted off the South China Block. Most of the backarc extension models, however, are not compatible with observations in terms of either age or subduction direction. The two-stage extension model is based on extensional basins surrounding the SCS. Recent dating results indeed show two-stage opening in the SCS, but the Southwest Subbasin of the SCS is much younger, which contradicts the two-stage extension model. Here we pro- pose a refined backarc extension model. There was a wide Neotethys Ocean between the Australian and Eurasian Plates before the Indian-Eurasian collision. The ocean floorstarted to subduct northward at ~ 125 Ma, causing backarc extension along the southem margin of the Eurasian Plate and the formation of the proto-SCS. The Neotethys sub- duction regime changed due to ridge subduction in the Late Cretaceous, resulting in fold-belts, uplifting, erosion, and widespread unconformities. It may also have led to the subduction of the proto-SCS. Flat subduction of the ridge may have reached further north and resulted in another backarc extension that formed the SCS. The rollback of the fiat subducting slab might have occurred ~ 90 Ma ago; the second backarc extension may have initiated between 50 and 45 Ma. The opening of the Southwest Subbasin is roughly simultaneous with a ridge jump in the East Sub- basin, which implies major tectonic changes in the sur- rounding regions, likely related to major changes in the extrusion of the Indochina Peninsula.
