The Ailaoshan-Red River（ASRR） shear zone is one of the major Southeast Asian tectonic discontinuities that have figured the present tectonic framework of the eastern Tibet.Several metamorphic massifs are distributed...The Ailaoshan-Red River（ASRR） shear zone is one of the major Southeast Asian tectonic discontinuities that have figured the present tectonic framework of the eastern Tibet.Several metamorphic massifs are distributed linearly along the shear zone,e.g.Xuelongshan,Diancangshan, Ailaoshan and Day Nui Con Voi from north to south.They bear a lot of lines of evidence for the tectonic evolution of the eastern Tibetan at different crustal levels in different tectonic stages.Controversy still exists on the deformation structures,microstructures and their relationship with metamorphisms along the ASRR.In this paper detailed microstructural and EBSD（Electron Backscattered Diffraction） fabric analysis of some highly sheared granitic rocks from different massifs along the ASRR are conducted.High temperature structures and microstructures are preserved in unsheared gneisses,in weakly sheared xenoliths or in some parts of the highly sheared rocks（mylonites）.Several types of high temperature quartz c-axis fabrics show symmetrical patterns or transitions from symmetrical to asymmetrical patterns.The former are attributed to coaxial deformation during regional shortening in an early stage of the Indian-Eurasian tectonic interaction and the latter are related to the transitions from coaxial compression to noncoaxial shearing during the post-collisional ASRR left lateral shearing.展开更多
The quartz fabric variation and the operation of slip systems were governed by the deformation flow. A new concept named quartz fabric slip flow pattern is to be considered thourgh this relation. On the other hand, st...The quartz fabric variation and the operation of slip systems were governed by the deformation flow. A new concept named quartz fabric slip flow pattern is to be considered thourgh this relation. On the other hand, strain path, quartz fabric variation and strain fabric development are inter related events which controlled by the deformation flow pattern. These events and related structures were analyzed in the Kazdag （IDA） stack antiform. The quartz fabric variation and the strain path analysis reveal mainly three distinct tectonic stages. These are initial vertical extrusion tectonic and following horizontal spreading tectonics. The beginning stage vertical extrusion represented by the quartz Y maxima fabric in rounded pattern and constructional strain and lengthening strain facies. The latest stage of the vertical extrusion also represented by the quartz fabric, constructional strain but proximating to plane strain and lengthening-widening strain facies. The vertical extrusions governed by the steeply dipping reverse faulting at the initial stage and then fallowed by the gently dipping thrusting at the latest stage. The flattening deformation was developed during the horizontal spreading stage. Typical incomplete single girdle quartz fabric, flattening type oblate strain and thinning--widening strain facies are characteristic features of the nappe tectonics.展开更多
The tectonic evolution of South Qinling, which is a main part of the Qinling orogenic belt, is still in dispute and deformation history of South Qinling is poorly studied. In this paper, detailed structural, microstru...The tectonic evolution of South Qinling, which is a main part of the Qinling orogenic belt, is still in dispute and deformation history of South Qinling is poorly studied. In this paper, detailed structural, microstructural, quartz c-axis fabric analysis, and geochronology results for the Madao gneiss in South Qinling are presented to characterize the deformation history. Results show that rocks in the northern part （Tiefodian-Laozhanggou） experience general shearing and deform at relative low temperature. The shear sense generally is south to north. In contrast, rocks in the southern part （Laozhanggou-Panjiahe） are weakly sheared with pure shear features and evidence of high- temperature deformation. Based on the analyses, we conclude that there exist two distinct deformation geometries in the Madao gneiss and accordingly we can divide the deformation into two stages. The early stage is represented by regional shortening, while the late stage features northward thrust shearing and evidence shows that it was a progressive process between them. LA-ICP MS U-Pb dating of zircons from pre-deformational migmatite veins yields age of 198.5 ±2.0 Ma. This result, in combination with the age of post-deformational granite, indicates that the northward thrust shearing of the Madao gneiss occurred in the Late Triassic. In view of these results and other reported data in South Qinling, we propose that deformation in Madao gneiss may result from the initial collision and subsequent northward accretion in Late Triassic.展开更多
基金supported by the National Key Basic Research and Development(973) Project (2009CB421001)National Natural Science Foundation of China(40872139)+2 种基金China Geological Survey (1212010661311)Ministry of Land and Resources (200811008)the Ministry of Education,Proiect 111 (B07011)
文摘The Ailaoshan-Red River（ASRR） shear zone is one of the major Southeast Asian tectonic discontinuities that have figured the present tectonic framework of the eastern Tibet.Several metamorphic massifs are distributed linearly along the shear zone,e.g.Xuelongshan,Diancangshan, Ailaoshan and Day Nui Con Voi from north to south.They bear a lot of lines of evidence for the tectonic evolution of the eastern Tibetan at different crustal levels in different tectonic stages.Controversy still exists on the deformation structures,microstructures and their relationship with metamorphisms along the ASRR.In this paper detailed microstructural and EBSD（Electron Backscattered Diffraction） fabric analysis of some highly sheared granitic rocks from different massifs along the ASRR are conducted.High temperature structures and microstructures are preserved in unsheared gneisses,in weakly sheared xenoliths or in some parts of the highly sheared rocks（mylonites）.Several types of high temperature quartz c-axis fabrics show symmetrical patterns or transitions from symmetrical to asymmetrical patterns.The former are attributed to coaxial deformation during regional shortening in an early stage of the Indian-Eurasian tectonic interaction and the latter are related to the transitions from coaxial compression to noncoaxial shearing during the post-collisional ASRR left lateral shearing.
文摘The quartz fabric variation and the operation of slip systems were governed by the deformation flow. A new concept named quartz fabric slip flow pattern is to be considered thourgh this relation. On the other hand, strain path, quartz fabric variation and strain fabric development are inter related events which controlled by the deformation flow pattern. These events and related structures were analyzed in the Kazdag （IDA） stack antiform. The quartz fabric variation and the strain path analysis reveal mainly three distinct tectonic stages. These are initial vertical extrusion tectonic and following horizontal spreading tectonics. The beginning stage vertical extrusion represented by the quartz Y maxima fabric in rounded pattern and constructional strain and lengthening strain facies. The latest stage of the vertical extrusion also represented by the quartz fabric, constructional strain but proximating to plane strain and lengthening-widening strain facies. The vertical extrusions governed by the steeply dipping reverse faulting at the initial stage and then fallowed by the gently dipping thrusting at the latest stage. The flattening deformation was developed during the horizontal spreading stage. Typical incomplete single girdle quartz fabric, flattening type oblate strain and thinning--widening strain facies are characteristic features of the nappe tectonics.
基金supported by the National Natural Science Foundation of China(41302080,41272220)the China Geological Survey Project(1212011121091,12120114009401)+1 种基金the Fundamental Research Funds for the Central Universities(53200959380)the Key Project of the National Twelve Five Year Research Program of China(2011BAB04B05)
文摘The tectonic evolution of South Qinling, which is a main part of the Qinling orogenic belt, is still in dispute and deformation history of South Qinling is poorly studied. In this paper, detailed structural, microstructural, quartz c-axis fabric analysis, and geochronology results for the Madao gneiss in South Qinling are presented to characterize the deformation history. Results show that rocks in the northern part （Tiefodian-Laozhanggou） experience general shearing and deform at relative low temperature. The shear sense generally is south to north. In contrast, rocks in the southern part （Laozhanggou-Panjiahe） are weakly sheared with pure shear features and evidence of high- temperature deformation. Based on the analyses, we conclude that there exist two distinct deformation geometries in the Madao gneiss and accordingly we can divide the deformation into two stages. The early stage is represented by regional shortening, while the late stage features northward thrust shearing and evidence shows that it was a progressive process between them. LA-ICP MS U-Pb dating of zircons from pre-deformational migmatite veins yields age of 198.5 ±2.0 Ma. This result, in combination with the age of post-deformational granite, indicates that the northward thrust shearing of the Madao gneiss occurred in the Late Triassic. In view of these results and other reported data in South Qinling, we propose that deformation in Madao gneiss may result from the initial collision and subsequent northward accretion in Late Triassic.
