Emplacement of the giant Kunene AMCG complex into a contractional ductile shear zone and implications for the Mesoproterozoic tectonic evolution of SW Angola

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

Two Paleoproterozoic metamorphic events in the Zhujiafang ductile shear zone of the Hengshan Complex: Insights into the tectonic evolution of the North China Craton

2020 ◽  
Author(s):  
Jiahui Qian
Keyword(s):  
Shear Zone ◽  
North China Craton ◽  
Tectonic Evolution ◽  
North China ◽  
Shear Zones ◽  
Ductile Shear Zone ◽  
Garnet Amphibolite ◽  
Inclusion Type ◽  
Mineral Assemblages ◽  
Ductile Shear

<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>

Structural analysis of the Nanchang-Wanzai sinistral ductile shear zone (Jiangnan region, South China)

1991 ◽  
Vol 6 (1) ◽  
pp. 13-23 ◽  
Author(s):  
Liangshu Shu ◽  
Jacques Charvet ◽  
Yangshen Shi ◽  
Michel Faure ◽  
Dominique Cluzel ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Shear Zone ◽  
South China ◽  
Ductile Shear Zone ◽  
Ductile Shear

40Ar/ 39Ar laser dating of Zongwulong ductile shear zone in northeastern Tibetan Plateau ：Constrains on the closure time of the northmost Paleo-Tethys ocean

2021 ◽  
Author(s):  
Wanli Gao ◽  
Zongxiu Wang
Keyword(s):  
Shear Deformation ◽  
Shear Zone ◽  
Ductile Deformation ◽  
Low Grade ◽  
Ductile Shear Zone ◽  
The South ◽  
Oblique Collision ◽  
Ductile Shear ◽  
Tethys Ocean ◽  
Tectonic Belt

<p><strong><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.67d6c7216eff55356050161/sdaolpUECMynit/12UGE&app=m&a=0&c=5572aca4b392eef83f52919e1be673e9&ct=x&pn=gepj.elif&d=1" alt="">Abstract</strong>：The Zongwulong tectonic belt (ZTB) is located between the northern Qaidam tectonic belt and the south Qilian orogenic belt and contains Late Paleozoic and Early- Middle Triassic strata. Structural features and geochronology of Zongwulong ductile shear zone have key implications for the tectonic property of the ZTB. This study integrated field structure, microscopic structure and <sup>40</sup>Ar/<sup>39</sup>Ar laser probe analysis. The shear zone strikes ~NEE-SWW and dips at a high angle, with a NWW-SEE trending and WE stretching lineation, indicating the shear zone as a thrust- slip shear ductile shear. The asymmetric folds, rotating porphyroclast,structural lens and crenulation cleavage can be seen in the field. Mica fish, S − C fabrics, σ type quartz porphyroclastic and quartz wire drawing structure can also be observed under microscope, indicating that the strike- slip- related ductile deformation and mylonitization occurred under low- grade greenschist facies conditions at temperatures of <em>300° C − 400° C</em>.  The highly deformed<br>mylonite schist yielded <sup>40</sup>Ar/<sup>39</sup>Ar ages <em>(245.8±1.7)Ma </em>and <em>(238.5±2.6)</em>Ma for muscovite and biotite, respectively, indicating that the shear deformation occurred during the Early- Mid Triassic. Combined with comprehensive analysis of regional geology and petrology, the authors hold that the age of ductile shear deformation represents the time of Triassic orogeny in the ZTB. The oroginic activity was probably related to the oblique collision between the South Qilian block and the Oulongbuluke block after the closure of the northermost Paleo-Tethys ocean.</p>

Sign in / Sign up

Export Citation Format

Share Document