Eocene seismogenic reactivation of a Jurassic ductile shear zone at Cap de Creus, Pyrenees, NE Spain

<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&#65306;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 40Ar/39Ar 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 &#8722; C fabrics, &#963; 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 300&#176; C &#8722; 400&#176; C.&#160; The highly deformed mylonite schist yielded 40Ar/39Ar ages (245.8&#177;1.7)Ma and (238.5&#177;2.6)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.

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New Aspects of Rotational Dynamics Within the North American-Pacific Ductile Shear Zone

Deep Structure and Past Kinematics of Accreted Terranes - Geophysical Monograph Series ◽

10.1029/gm050p0179 ◽

2013 ◽

pp. 179-201 ◽

Cited By ~ 2

Author(s):

Erik R. Ivins

Keyword(s):

Shear Zone ◽

North American ◽

Rotational Dynamics ◽

Ductile Shear Zone ◽

The North ◽

Ductile Shear

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Macro- and microstructural analysis of the Zhujiafang ductile shear zone, Hengshan Complex: Tectonic nature and geodynamic implications of the evolution of Trans−North China orogen

Geological Society of America Bulletin ◽

10.1130/b35672.1 ◽

2020 ◽

Author(s):

Lingchao He ◽

Jian Zhang ◽

Guochun Zhao ◽

Changqing Yin ◽

Jiahui Qian ◽

...

Keyword(s):

Shear Zone ◽

North China ◽

Shear Zones ◽

Crustal Thickening ◽

Slip Systems ◽

High Grade ◽

Ductile Shear Zone ◽

Crustal Rocks ◽

Ductile Shear ◽

Lower Crustal

In worldwide orogenic belts, crustal-scale ductile shear zones are important tectonic channels along which the orogenic root (i.e., high-grade metamorphic lower-crustal rocks) commonly experienced a relatively quick exhumation or uplift process. However, their tectonic nature and geodynamic processes are poorly constrained. In the Trans−North China orogen, the crustal-scale Zhujiafang ductile shear zone represents a major tectonic boundary separating the upper and lower crusts of the orogen. Its tectonic nature, structural features, and timing provide vital information into understanding this issue. Detailed field observations showed that the Zhujiafang ductile shear zone experienced polyphase deformation. Variable macro- and microscopic kinematic indicators are extensively preserved in the highly sheared tonalite-trondhjemite-granodiorite (TTG) and supracrustal rock assemblages and indicate an obvious dextral strike-slip and dip-slip sense of shear. Electron backscattered diffraction (EBSD) was utilized to further determine the crystallographic preferred orientation (CPO) of typical rock-forming minerals, including hornblende, quartz, and feldspar. EBSD results indicate that the hornblendes are characterized by (100) <001> and (110) <001> slip systems, whereas quartz grains are dominated by prism <a> and prism <c> slip systems, suggesting an approximate shear condition of 650−700 °C. This result is consistent with traditional thermobarometry pressure-temperature calculations implemented on the same mineral assemblages. Combined with previously reported metamorphic data in the Trans−North China orogen, we suggest that the Zhujiafang supracrustal rocks were initially buried down to ∼30 km depth, where high differential stress triggered the large-scale ductile shear between the upper and lower crusts. The high-grade lower-crustal rocks were consequently exhumed upwards along the shear zone, synchronous with extensive isothermal decompression metamorphism. The timing of peak collision-related crustal thickening was further constrained by the ca. 1930 Ma metamorphic zircon ages, whereas a subsequent exhumation event was manifested by ca. 1860 Ma syntectonic granitic veins and the available Ar-Ar ages of the region. The Zhujiafang ductile shear zone thus essentially record an integrated geodynamic process of initial collision, crustal thickening, and exhumation involved in formation of the Trans−North China orogen at 1.9−1.8 Ga.

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Progressive development of structures in a ductile shear zone

Journal of Structural Geology ◽

10.1016/0191-8141(87)90052-6 ◽

1987 ◽

Vol 9 (3) ◽

pp. 277-287 ◽

Cited By ~ 86

Author(s):

S.K Ghosh ◽

Sudipta Sengupta

Keyword(s):

Shear Zone ◽

Ductile Shear Zone ◽

Progressive Development ◽

Ductile Shear

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