Tectonic Imprints of the Hazara Kashmir Syntaxis on the Mesozoic Rocks Exposed in Munda, Mohmand Agency, Northwest Pakistan
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We acknowledge financial support from the Department of Geology, University of Peshawar, and some logistical support and garnetiferous NZ samples from BAK Consulting Engineers. Ali appreciates the thin section preparation facilities provided by Department of Geology, University of Peshawar and petrographic facilities provided by the University of British Columbia, Canada and National Center of Excellence in Geology.


Tectonic Imprints of the Hazara Kashmir Syntaxis on the Mesozoic Rocks Exposed in Munda, Mohmand Agency, Northwest Pakistan
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    摘要:

    Two well-developed mesoscopic folds, D2 and D3, which postdate the middle amphibolite metamorphism, were recognized in the western hinterland zone of Pakistan. NW–SE trending D2 folds developed during NE–SW horizontal bulk shortening followed by NE–SW trending D3 folds, which developed during SE–NW shortening. Micro- to mesoscopically the NW–SE trending S2 crenulation cleavage, boudins and mineral stretching lineations are overprinted by D3. The newly established NW–SE trending micro- to mesoscopic structures in Munda termed D2, which postdated F1/F2, is synchronously developed with F3 structures in the western hinterland zone of Pakistan. We interpret that D2 and D3 folds are counterclockwise rotated in the tectonic event that has evolved the Hazara Kashmir Syntaxis after the main phase Indian plate and Kohistan Island Arc collision. Chlorite replacement by biotite in the main matrix crenulation cleavages indicates prograde metamorphism related with D2. The inclusion of muscovite and biotite in garnet porphyroblasts and the presence of staurolite in these rocks indicate that the Barrovian metamorphic conditions predate D2 and D3. We interpret that garnet, staurolite and calcite porphyroblasts grew before D2 because the well developed S2 crenulation cleavage wraps around these porphyroblasts.

    Abstract:

    Two well-developed mesoscopic folds, D2 and D3, which postdate the middle amphibolite metamorphism, were recognized in the western hinterland zone of Pakistan. NW–SE trending D2 folds developed during NE–SW horizontal bulk shortening followed by NE–SW trending D3 folds, which developed during SE–NW shortening. Micro- to mesoscopically the NW–SE trending S2 crenulation cleavage, boudins and mineral stretching lineations are overprinted by D3. The newly established NW–SE trending micro- to mesoscopic structures in Munda termed D2, which postdated F1/F2, is synchronously developed with F3 structures in the western hinterland zone of Pakistan. We interpret that D2 and D3 folds are counterclockwise rotated in the tectonic event that has evolved the Hazara Kashmir Syntaxis after the main phase Indian plate and Kohistan Island Arc collision. Chlorite replacement by biotite in the main matrix crenulation cleavages indicates prograde metamorphism related with D2. The inclusion of muscovite and biotite in garnet porphyroblasts and the presence of staurolite in these rocks indicate that the Barrovian metamorphic conditions predate D2 and D3. We interpret that garnet, staurolite and calcite porphyroblasts grew before D2 because the well developed S2 crenulation cleavage wraps around these porphyroblasts.

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Asghar ALI*, Umer HABIB, Atta Ur REHMAN, Noor ZADA, Zain Ul ABIDIN and Muhammad ISMAIL.2016. Tectonic Imprints of the Hazara Kashmir Syntaxis on the Mesozoic Rocks Exposed in Munda, Mohmand Agency, Northwest Pakistan[J]. ACTA GEOLOGICA SINICA(English edition),90(2):440~455

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  • 收稿日期:2015-01-08
  • 最后修改日期:2015-08-10
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  • 在线发布日期: 2016-04-15
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