Structures,kinematic analysis,rheological parameters and temperature-pressure estimate of the Mesozoic Xingcheng-Taili ductile shear zone in the North China Craton |
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| Institution: | 1. College of Earth Sciences, Jilin University, Jianshe Str. 2199, 13006 Changchun, Jilin, China;2. Department of Geography and Geology, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria;3. Planetary Science Institute, Faculty of Earth Sciences, China University of Geosciences (Wuhan), Wuhan, Hubei, China;1. Departamento de Geologia, Universidade Federal de Ouro Preto, Campus Morro do Cruzeiro, s/n, Ouro Preto CEP: 35400-000, MG, Brazil;2. Department of Geological Sciences, Brown University, Providence, RI 02912, USA;1. ICT – Instituto de Ciências da Terra, Pólo da Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal;2. Tectonophysics, Institute of Geoscience, University of Mainz, 55128 Mainz, Germany;3. ICT - Instituto de Ciências da Terra, Pólo da Universidade do Porto / Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal;4. School of Earth, Atmosphere and Environment, Monash University, 3800 Clayton, VIC, Australia |
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| Abstract: | The NE to ENE trending Mesozoic Xingcheng-Taili ductile shear zone of the northeastern North China Craton was shaped by three phases of deformation. Deformation phase D1 is characterized by a steep, generally E–W striking gneissosity. It was then overprinted by deformation phase D2 with NE-sinistral shear with K-feldspar porphyroclasts forming a subhorizontal low-angle stretching lineation on a steep foliation. During deformation phase D3, lateral motion accommodated by ENE sinistral strike-slip shear zones dominated. Associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle- to shallow crustal levels. In some parts, the older structures have been in turn overprinted by late-stage sinistral D3 shearing. Finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid (L-S tectonites) near plane strain. Simple shear-dominated general shear during D3 deformation is probably of general significance. The quartz c-axis textures indicate prism-gliding with a dominant rhomb <a> slip and basal <a> slip system formed mainly at low-middle temperatures. Mineral deformation behavior, quartz c-axis textures, quartz grain size and the Kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 °C. Dislocation creep is the main deformation mechanism at a shallow crustal level. Fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self-similarities. Differential stresses deduced from dynamically recrystallized quartz grain size are at around 20–39 MPa, and strain rates in the order of 10?12 to 10?14 s?1. This indicates deformation of granitic rocks in the Xingcheng-Taili ductile shear zone at low strain rates, which is consistent with most other ductile shear zones. Hornblende-plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca. 3–5 kbar and temperatures of 400–500 °C within greenschist facies conditions. The main D3 deformation of the ENE-trending sinistral strike-slip ductile shearing is related to the roll-back of the subducting Pacific plate beneath the North China Craton. |
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| Keywords: | Ductile shear zone EBSD analysis Quartz microfabrics Finite-strain determination Kinematic vorticity Hornblende-plagioclase thermobarometer Fractal dimension Paleo-piezometry North China Craton Xingcheng-Taili ductile shear zone |
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