The Jingdezhen ductile shear zone is evolved from the Neoproterozoic Zhangyuan ophiolite melange belt in the eastern Jiangnan Orogen, South China. Comprehensive study of geometry, kinematics, quartz c-axis fabric, tem...The Jingdezhen ductile shear zone is evolved from the Neoproterozoic Zhangyuan ophiolite melange belt in the eastern Jiangnan Orogen, South China. Comprehensive study of geometry, kinematics, quartz c-axis fabric, temperature-pressure conditions and geochronology were conducted in this study. The Jingdezhen shear zone extends -180 km along the NE orientation with two groups of subvertical fo- liation and subhorizontal lineation. One group of foliation strikes NEN orientation whereas another one NEE orientation. Field investigation, microscopic observation and quartz c-axis fabric show that sinistral shearing along NEN-striking foliation occurred earlier than dextral shearing along NEE-striking foliation. Syn-tectonic staurolite porphyroblasts and deformation manner of feldspar imply that sinistral shearing occurred at 530-420 ℃ and 6-2 kbar. Deformation manner and c-axis fabric of quartz and pre-tectonic staurolite porphyroblasts indicate that dextral shearing took place at 420-300 ℃. LA-ICP-MS zircon U-Pb and mica ^40Ar/^39Ar dating indicate that the sinistral shearing occurred during Neoproterozoic oro- geny （830-800 Ma） whereas the dextral shearing at 447＋12 Ma. The sinistral shearing resulted from the Neoproterozoic final assembly between the Yangtze and Cathaysia blocks. The dextral shearing was caused by Early Paleozoic orogen parallel extension and clockwise rotation.展开更多
Strain analyses for the Shuanghe pluton show that the main strain planes suffered distinct deformation. The main strain value (XZ) is up to 1.59–2.18, and the value of Flinn index (K) ranges from 0.11 to 0.82. Anisot...Strain analyses for the Shuanghe pluton show that the main strain planes suffered distinct deformation. The main strain value (XZ) is up to 1.59–2.18, and the value of Flinn index (K) ranges from 0.11 to 0.82. Anisotropy of magnetic susceptibility (AMS) measurements reveal that the orientations of the magnetic foliation and lineation gently dip SE, consistent with the macroscopic foliation of the pluton. The value of anisotropy degree (P) ranges from 1.109 to 1.639, and the shape parameter (T) from 0.079 to 0.534. These studies prove that the pluton was deformed under strong compression. Quartz c-axis textures, defined by monoclinic or triclinic asymmetry, usually developed the high maxima paralleling the b-axis, which is defined by the prismatic slip (1010) under the high temperature. These fabrics are quite different from those developed in the high-ultrahigh pressure rocks (UHP) which were captured in the pluton or country rocks. It is concluded that the Shuanghe pluton emplaced under regional compression slightly after the formation of UHP, and it is characterized by synkinematic granitic deformation.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 Natural Science Foundation of China (Nos. 41402174, 41472166)the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan)+1 种基金China Scholarship Council (No. 201406415007)the Natural Sciences and Engineering Research Council of Canada
文摘The Jingdezhen ductile shear zone is evolved from the Neoproterozoic Zhangyuan ophiolite melange belt in the eastern Jiangnan Orogen, South China. Comprehensive study of geometry, kinematics, quartz c-axis fabric, temperature-pressure conditions and geochronology were conducted in this study. The Jingdezhen shear zone extends -180 km along the NE orientation with two groups of subvertical fo- liation and subhorizontal lineation. One group of foliation strikes NEN orientation whereas another one NEE orientation. Field investigation, microscopic observation and quartz c-axis fabric show that sinistral shearing along NEN-striking foliation occurred earlier than dextral shearing along NEE-striking foliation. Syn-tectonic staurolite porphyroblasts and deformation manner of feldspar imply that sinistral shearing occurred at 530-420 ℃ and 6-2 kbar. Deformation manner and c-axis fabric of quartz and pre-tectonic staurolite porphyroblasts indicate that dextral shearing took place at 420-300 ℃. LA-ICP-MS zircon U-Pb and mica ^40Ar/^39Ar dating indicate that the sinistral shearing occurred during Neoproterozoic oro- geny （830-800 Ma） whereas the dextral shearing at 447＋12 Ma. The sinistral shearing resulted from the Neoproterozoic final assembly between the Yangtze and Cathaysia blocks. The dextral shearing was caused by Early Paleozoic orogen parallel extension and clockwise rotation.
基金supported by the National Natural Science Foundation of China(Grant Nos.40334037 and 40172069).
文摘Strain analyses for the Shuanghe pluton show that the main strain planes suffered distinct deformation. The main strain value (XZ) is up to 1.59–2.18, and the value of Flinn index (K) ranges from 0.11 to 0.82. Anisotropy of magnetic susceptibility (AMS) measurements reveal that the orientations of the magnetic foliation and lineation gently dip SE, consistent with the macroscopic foliation of the pluton. The value of anisotropy degree (P) ranges from 1.109 to 1.639, and the shape parameter (T) from 0.079 to 0.534. These studies prove that the pluton was deformed under strong compression. Quartz c-axis textures, defined by monoclinic or triclinic asymmetry, usually developed the high maxima paralleling the b-axis, which is defined by the prismatic slip (1010) under the high temperature. These fabrics are quite different from those developed in the high-ultrahigh pressure rocks (UHP) which were captured in the pluton or country rocks. It is concluded that the Shuanghe pluton emplaced under regional compression slightly after the formation of UHP, and it is characterized by synkinematic granitic deformation.
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.
