The metamorphism of the Tibetan Series from the Manang area, Marsyandi Valley, Central Nepal

Geological Society Special Publication - Tập 74 Số 1 - Trang 357-374 - 1993
Christian Schneider1, L. Masch1
1Mineralogisch-Petrographisches Institut, Universität München Theresienstr. 41, 8000 München 2, Germany

Tóm tắt

Abstract In the Manang area a distinctive metamorphic zonation with grade increasing downward to deeper structural levels of the Tibetan Series can be observed. The first appearance of prograde biotite/phlogopite introducing the metamorphic zonation can be located in the Devonian Tilicho Pass Formation. The Silurian Dark Band Formation contains prograde titanite. Tremolite is not observed to the west of the Mutsog region (Nilgiri Limestone). In the lower parts of the Nilgiri Limestone, tremolite appears together with K-feldspar. Diopside only occurs in the lowest parts of the Nilgiri Limestone. Maximum temperatures for the prograde metamorphism, derived from carbonate solvus thermometry, are in the range of 510–530°C for the middle Nilgiri Limestone and 370–390°C for the Lower Carboniferous. The fluid composition during the prograde metamorphism at the base of the Tibetan Series was CO 2 rich ( X CO 2 between 0.4 and 0.7). A strong retrogressive phase with a fluid composition rich in H 2 O is documented by secondary growth of sphene, clinozoisite and amphibole. This retrograde phase is rare in formations above the Nilgiri Limestone and might be contemporaneous with detachment at the base of the Tibetan Series. The prograde mineral phases are related to a first deformation phase. A second deformation phase, most probably related to detachment movements between the Tibetan Series and the High Himalayan Crystalline, resulted in a partly developed crenulation cleavage unrelated to any metamorphic change. The formation of the dominating E-W-orientated syncline took place in a third deformation phase.

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Geological Society Special Publication

Tập 74 Số 1

357-374

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