Fabrics and geochronology of the Taibai ductile shear zone: Implications for tectonic evolution of the Qinling Orogenic Belt, central China

2019 ◽  
Vol 177 ◽  
pp. 1-16 ◽  
Author(s):  
Chao Cheng ◽  
Shengsi Sun ◽  
Yunpeng Dong
2020 ◽  
Author(s):  
Jiahui Qian

<p>Ductile shear zones <span>usually record mineralogical and isotopic changes that are not apparent in the surrounding host rocks and thus may preserve a complete evolutionary record in a single locale from relatively undeformed to highly deformed rocks. </span>The Zhujiafang ductile shear zone is situated in the central Hengshan Complex, a key area for understanding the Paleoproterozoic tectonic evolution of the Trans-North China Orogen, North China Craton. Detailed metamorphic and geochronological analyses were carried out on metapelite and garnet amphibolite from the Zhujiafang ductile shear zone. The metapelite preserves two phases of mineral assemblages: early kyanite-rutile-bearing assemblage and late chlorite-staurolite-bearing assemblage in garnet–mica schist, and inclusion-type muscovite (high-Si) + kyanite assemblage and late sillimanite-bearing assemblage in sillimanite–mica gneiss. Garnet in the metapelite occasionally exhibits pronounced two-stage zoning characteristic of a diffusion core with irregular pyrope (X<sub>py</sub>) and grossular (X<sub>gr</sub>) contents and a growth rim with X<sub>py</sub> and X<sub>gr</sub> increasing outwards. The isopleths of the maximum X<sub>gr</sub> in garnet core and Si content in inclusion-type muscovite in the P–T pseudosections suggest that the early mineral assemblages underwent medium-high-pressure type metamorphism with pressures up to 12–14 kbar at 700–750 °C. The late assemblages and the growth zoning of garnet rim predict a late separated clockwise P–T path with peak conditions of 6.5 ± 0.2 kbar/620 ± 10 °C (medium-low-pressure type). The garnet amphibolite is mainly composed of garnet, hornblende, plagioclase, ilmenite and quartz, without overprinting of late mineral assemblages except for localized corona textures. Phase modeling suggests that the rock has experienced high-amphibolite facies metamorphism with peak conditions of 10.5 ± 0.8 kbar/770 ± 50 °C, which is broadly consistent with the early-phase metamorphism of metapelite. Zircon U–Pb dating on metapelite yields two metamorphic age groups of 1.96–1.92 Ga and 1.87–1.86 Ga which are interpreted to represent the timing of the two separated phases of metamorphism. Two separated orogenic events may have occurred respectively at ~1.95 Ga and ~1.85 Ga in the Hengshan–Wutai area. The older orogeny was resulted from continental collision and the younger one may be caused by within-plate deformation. The final exhumation of the high-grade rocks formed in the older (i.e. 1.95 Ga) orogeny should be related with the younger deformation/metamorphic event. For more details, please refer to <span>https://doi.org/10.1016/j.lithos.2019.02.001.</span></p>


2020 ◽  
Vol 109 (4) ◽  
pp. 1463-1485 ◽  
Author(s):  
Jeremie Lehmann ◽  
Grant Michael Bybee ◽  
Ben Hayes ◽  
Trishya Margaret Owen-Smith ◽  
Georgy Belyanin

2014 ◽  
Vol 1010-1012 ◽  
pp. 1413-1416
Author(s):  
Hui Mei Guan ◽  
Zong Xiu Wang ◽  
Wei Feng Xiao

Kanggurtag-Yamansu ductile shear zone is the largest ductile shear zone in the East Tianshan orogenic belt. Deformation characteristics and structural associations of the shear zone suggest that the shear zone was formed by Nearly N-S compression duing late Carboniferous-early Permian. Which confirmed that the Eastern Tianshan mountains along the southern edge of the Turpan Basin were the results of plate interactions in Late Paleozoic.


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