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[HCG21-12] Provenance of the Pleistocene in the Kali Gandaki River, Central Nepal
The Himalayas were formed by the collision of the Indian subcontinent with the Eurasian plate about 50 Ma (Besse et al., 1984), and its uplift has continued to the present (Klootwijk, 1984). The Bengal Fan is the largest submarine fan in the world, and most of the sediments composing the fan were derived from the Himalayas (Curray and Moore, 1971). Therefore, the sediments that have formed the Bengal Fan are likely to record the uplift and denudation history of the Himalayas, and there have been many examples of studies about it. Yokoyama et al. (1990) and Amano and Taira (1992) pointed out the possibility of a two-phase of uplift of Higher Himalayas after 17 Ma: 10.9-7.5 Ma and 0.9 Ma~, based on changes in sedimentation rates of the cores from Bengal Fan (ODP 717-719). Especially the change in sedimentation rate from 0.9 Ma is remarkable and may reflect some changes in the uplift activity of the Himalayas during the Quaternary, however, the details are unclarified. In this study, the provenance of the Sammargaon Formation, Marpha Formation, and Kaligandaki Formation (middle to upper Pleistocene) in the upper Kali Gandaki River, central Nepal, is examined to understand the details of uplift activities of the Himalayas during the Quaternary period.
The heavy mineral assemblages of Sammargaon, Marpha, and Kaligandaki Formations are predominantly tourmaline, epidote, staurolite, garnet, allanite, and zircon. Particularly, tourmalines are abundant in all formations. In addition, minerals such as pyroxene, amphibole, sillimanite and kyanite are included in small quantities. These heavy mineral assemblages suggest an influence from multiple geological units, including Higher Himalaya Metamorphic Rocks and Himalayan Leucogranites. The chemical compositions of the tourmalines in the sand samples from Sammargaon, Marpha, and Kaligandaki Formations were analyzed and plotted on the diagram by Henry and Guidotti (1985). As a result, most of the tourmalines in the sand samples are plotted in the Li-poor granitoids and associated pegmatites and aplites region. This result suggests that the provenance of the tourmalines in the sand is granitic rocks. Moreover, the chemical compositions of the tourmalines in the sand samples in this study were compared with those of the High Himalayan Metamorphic Rocks and the Himalayan Leucogranites analyzed by Rai (2007). Consequently, the chemical compositions of the tourmalines in the Himalayan Leucogranites and the tourmalines in the sand samples are mostly correlatable.
Based on the above, one of the main provenances of Sammargaon, Marpha, and Kaligandaki Formations could be Himalayan Leucogranites. However, it is difficult to determine the provenance of minerals such as epidote, staurolite, and garnet only from the Himalayan Leucogranites, and it is possible that they were supplied from xenoliths in the Himalayan Leucogranites and from the northern slope of the High Himalaya Metamorphic Rocks. In addition, significant changes in heavy mineral assemblages are not observed in the Sammargaon, Marpha, and Kaligandaki Formations. This result suggests that the provenance area had not been experienced changes significantly at least from the Middle Pleistocene to the Late Pleistocene.
References
Amano, K. and Taira, A., 1992, Two-phase uplift of Higher Himalayas since 17 Ma. Geology, 20, 391-394.
Besse J, Courtillot V, Pozzi JP, Westphal M, Zhou YX (1984) Palaeomagnetic estimates of crustal shortening in the Himalayan thrusts and Zangbo suture. Nature, 311, 621-626.
Curray, R.J. and Moore, G.D. 1971, Growth of the Bengal Deep-Sea Fan and Denudation in the Himalayas. GSA Bulletin 82 (3), 563–572.
Henry, D.J. and Guidotti, C.V., 1985, Tourmaline as a petrogenetic indicator mineral: an example from the staurolite-grade metapelites of NW Maine. American Mineralogist, 70,1-15.
Klootwijk, C., 1984, A review of the Indian Phanerozoic collision. Tectonophysics 105, 331-353.
Rai, M.S., 2004, Tourmaline chemistry in the Miocene and Paleozoic granites, Central Nepal Himalaya. Journal of Nepal Geological Society, 29,23-34.
Yokoyama, K., Amano, K., Taira, A., Saito, Y., 1990, Proceedings of the Ocean Drilling Program, Scientific Results, 116.
The heavy mineral assemblages of Sammargaon, Marpha, and Kaligandaki Formations are predominantly tourmaline, epidote, staurolite, garnet, allanite, and zircon. Particularly, tourmalines are abundant in all formations. In addition, minerals such as pyroxene, amphibole, sillimanite and kyanite are included in small quantities. These heavy mineral assemblages suggest an influence from multiple geological units, including Higher Himalaya Metamorphic Rocks and Himalayan Leucogranites. The chemical compositions of the tourmalines in the sand samples from Sammargaon, Marpha, and Kaligandaki Formations were analyzed and plotted on the diagram by Henry and Guidotti (1985). As a result, most of the tourmalines in the sand samples are plotted in the Li-poor granitoids and associated pegmatites and aplites region. This result suggests that the provenance of the tourmalines in the sand is granitic rocks. Moreover, the chemical compositions of the tourmalines in the sand samples in this study were compared with those of the High Himalayan Metamorphic Rocks and the Himalayan Leucogranites analyzed by Rai (2007). Consequently, the chemical compositions of the tourmalines in the Himalayan Leucogranites and the tourmalines in the sand samples are mostly correlatable.
Based on the above, one of the main provenances of Sammargaon, Marpha, and Kaligandaki Formations could be Himalayan Leucogranites. However, it is difficult to determine the provenance of minerals such as epidote, staurolite, and garnet only from the Himalayan Leucogranites, and it is possible that they were supplied from xenoliths in the Himalayan Leucogranites and from the northern slope of the High Himalaya Metamorphic Rocks. In addition, significant changes in heavy mineral assemblages are not observed in the Sammargaon, Marpha, and Kaligandaki Formations. This result suggests that the provenance area had not been experienced changes significantly at least from the Middle Pleistocene to the Late Pleistocene.
References
Amano, K. and Taira, A., 1992, Two-phase uplift of Higher Himalayas since 17 Ma. Geology, 20, 391-394.
Besse J, Courtillot V, Pozzi JP, Westphal M, Zhou YX (1984) Palaeomagnetic estimates of crustal shortening in the Himalayan thrusts and Zangbo suture. Nature, 311, 621-626.
Curray, R.J. and Moore, G.D. 1971, Growth of the Bengal Deep-Sea Fan and Denudation in the Himalayas. GSA Bulletin 82 (3), 563–572.
Henry, D.J. and Guidotti, C.V., 1985, Tourmaline as a petrogenetic indicator mineral: an example from the staurolite-grade metapelites of NW Maine. American Mineralogist, 70,1-15.
Klootwijk, C., 1984, A review of the Indian Phanerozoic collision. Tectonophysics 105, 331-353.
Rai, M.S., 2004, Tourmaline chemistry in the Miocene and Paleozoic granites, Central Nepal Himalaya. Journal of Nepal Geological Society, 29,23-34.
Yokoyama, K., Amano, K., Taira, A., Saito, Y., 1990, Proceedings of the Ocean Drilling Program, Scientific Results, 116.