Metamorphic history and tectonic evolution of the Himalayan UHP eclogites in Kaghan valley, Pakistan

• REHMAN Hafiz Ur

  Department of Earth and Environmental Sciences, Faculty of Science, Kagoshima University

• YAMAMOTO Hiroshi

  Department of Earth and Environmental Sciences, Faculty of Science, Kagoshima University

• KHALIL M. Ayub Khan

  Geological Survey of Pakistan

• NAKAMURA Eizo

  The Pheasant Memorial Laboratory, Institute for Study of the Earth's Interior, Okayama University

• ZAFAR Muhammad

  Faculty of Earth and Environmental Sciences, Bahria University

• KHAN Tahseenullah

  Geoscience Laboratory, Geological Survey of Pakistan

抄録

Eclogites of the Kaghan valley, Pakistan Himalaya were investigated petrographically and geochemically. Based on petrography, geochemistry and mineral compositions, metamorphic history and a reasonable tectonic model are proposed. Eclogites exposed in the Kaghan valley are classified into two groups. Group I eclogites appear as massive and Group II are lens-type. Group I eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, quartz, symplectite with rare epidote and phengite. Accessory minerals include abundant zircon, rutile, ilmenite, and rare apatite. Group II eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, phengite, quartz/coesite, epidote, and symplectite. In accessory minerals rutile and ilmenite are common while zircon and apatite are rare. Different types of protolith are proposed for these eclogites. Group I eclogites have higher FeO and TiO₂ contents and trace element contents, and seem to be derived from gabbroic protolith. Group II eclogites have lower FeO and TiO₂ and trace element contents and were derived from basalts. Pressure-temperature-time path was constructed for the Kaghan valley eclogites using various mineral assemblages along with textural relationship and inclusions study. At least three distinct metamorphic stages were identified. The first stage is the prograde garnet growth stage deduced from the inclusion paragenesis in garnet core. The second stage records the ultrahigh-pressure metamorphic stage deduced from the presence of coesite inclusions in omphacitic clinopyroxene. The third stage is the decompression stage and is deduced from the quartz-albite-amphibole symplectite portions. These petrological and geochemical results combined with isotopic ages reported elsewhere indicate that basalts and associated gabbroic dikes were emplaced at about 267 Ma when the Indian plate was moving northward and passing above an unknown hot spot. The closure of the Tethys and initiation of collision of the Indian plate with the Kohistan-Ladakh Island Arc is reported from 65-50 Ma. After that the leading-edge of the Indian plate underwent eclogite facies metamorphism at 49 Ma and when it reached to depths of about 100 km, the ultrahigh-pressure metamorphic event took place at 46 Ma.

収録刊行物

• Journal of Mineralogical and Petrological Sciences

  Journal of Mineralogical and Petrological Sciences 103 (4), 242-254, 2008

  一般社団法人　日本鉱物科学会

キーワード

• Kaghan valley
• Pakistan Himalaya
• Ultrahigh-pressure eclogites
• Tectonic model

詳細情報

• CRID: 1390282681523519488
• NII論文ID: 10021369864
• NII書誌ID: AA11460926
• DOI: 10.2465/jmps.080222
• COI: 1:CAS:528:DC%2BD1cXhtFOju7%2FJ
• ISSN: 13493825
• ISSN: 13456296
• 本文言語コード: en
• データソース種別:
  • JaLC
  • Crossref
  • CiNii Articles
• 抄録ライセンスフラグ: 使用不可