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Petrographic and geochemical characteristics of dolomites in the Devonian Shogram Formation, Karakorum Ranges, North Pakistan


Affiliations
1 Department of Earth and Environmental Sciences, Bahria University, Islamabad, Pakistan
2 Department of Earth Sciences, Quaid-i-Azam University Islamabad, Islamabad 45320, Pakistan
3 Department of Geology, Abdul Wali Khan University, Mardan, Pakistan
 

Excellent outcrops of Devonian carbonate rocks are present in the Karakorum Ranges of North Pakistan that are highly dolomitized. The Devonian Shogram Formation comprises both matrix and cement dolomite. Petrographic studies revealed the texture of matrix dolomite as fine-grained anhedral dolomite (D1), medium-grained subhedral to anhedral dolomite (D2), medium-grained euhedral dolomite (D3) and coarse-grained anhedral dolomite (D4). The saddle cement dolomite phase of hydrothermal origin precipitated in vugs and fractures. The origin of various dolomitization phases has been interpreted based on petrographic associations, elemental and stable isotopes signatures of each phase. The first two phases of dolomitization are affiliated with the compaction flow of overlying shales based on evidence of low Fe and Mn content and isotopically light signatures of d 18O. The increase in burial resulted in the third phase of dolomite showing signatures of redox conditions and high depleted d 18O compared to the original marine signatures. The final phases of matrix dolomite and saddle dolomite cement are associated with tectonic activity in the Karakorum region, which brought the deep-source Mg-rich fluids along the Reshun Fault.
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  • Petrographic and geochemical characteristics of dolomites in the Devonian Shogram Formation, Karakorum Ranges, North Pakistan

Abstract Views: 260  |  PDF Views: 141

Authors

Maryam Saleem
Department of Earth and Environmental Sciences, Bahria University, Islamabad, Pakistan
Faisal Rehman
Department of Earth Sciences, Quaid-i-Azam University Islamabad, Islamabad 45320, Pakistan
Abbas Ali Naseem
Department of Earth Sciences, Quaid-i-Azam University Islamabad, Islamabad 45320, Pakistan
Emadullah Khan
Department of Geology, Abdul Wali Khan University, Mardan, Pakistan
Syed Wasim Sajjad
Department of Earth Sciences, Quaid-i-Azam University Islamabad, Islamabad 45320, Pakistan
Zubair Ahmed
Department of Earth Sciences, Quaid-i-Azam University Islamabad, Islamabad 45320, Pakistan

Abstract


Excellent outcrops of Devonian carbonate rocks are present in the Karakorum Ranges of North Pakistan that are highly dolomitized. The Devonian Shogram Formation comprises both matrix and cement dolomite. Petrographic studies revealed the texture of matrix dolomite as fine-grained anhedral dolomite (D1), medium-grained subhedral to anhedral dolomite (D2), medium-grained euhedral dolomite (D3) and coarse-grained anhedral dolomite (D4). The saddle cement dolomite phase of hydrothermal origin precipitated in vugs and fractures. The origin of various dolomitization phases has been interpreted based on petrographic associations, elemental and stable isotopes signatures of each phase. The first two phases of dolomitization are affiliated with the compaction flow of overlying shales based on evidence of low Fe and Mn content and isotopically light signatures of d 18O. The increase in burial resulted in the third phase of dolomite showing signatures of redox conditions and high depleted d 18O compared to the original marine signatures. The final phases of matrix dolomite and saddle dolomite cement are associated with tectonic activity in the Karakorum region, which brought the deep-source Mg-rich fluids along the Reshun Fault.

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DOI: https://doi.org/10.18520/cs%2Fv123%2Fi4%2F583-591