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

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.

Spatial variations in chemical weathering and CO2 consumption in Nepalese High Himalayan catchments during the monsoon season

“…3 could be calcite itself and not necessarily silicates. Schneider and Masch (1993) reported up to 5 mol% MgCO 3 ($7 mol% Mg) in calcite grains of this study area. Taking into account the predominantly silicate lithology in the GHS (A sil /A tot ratios between 71 and 86%, cf.…”

Calcium and magnesium isotope systematics in rivers draining the Himalaya-Tibetan-Plateau region: Lithological or fractionation control?

“…The headwaters of the Marsyandi and its tributaries drain a 50 km transect of variably metamorphosed limestones and siliclastic rocks (Bordet et al, 1971;Schneider and Masch, 1993) known as the Tethyan Sedimentary Series (TSS). These limestones are impure, and pyritic black shales are common.…”

Temperature and age constraints on the metamorphism of the Tethyan Himalaya in Central Nepal: A multidisciplinary approach

“…In the Thakkhola graben, paleotemperature estimates are very low: 70°C in Cretaceous to 290°C in Carboniferous strata. For the Manang area and the Marsyandi valley, paleotemperatures of 250-360°C in Upper Triassic and Jurassic, 270-370°C in Permo-Carboniferous and 335-530°C in Cambrian to Devonian are reported (Garzanti et al, 1994;Schneider and Masch, 1993). The highest metamorphic temperatures occurred at the deepest structural levels together with the highest intensity of deformation in the Cambrian-Ordovician limestones (Colchen et al, 1986;Schneider and Masch, 1993;Garzanti et al, 1994).…”

“…Apart from the studies of Schneider and Masch (1993), Garzanti et al (1994) and Bollinger et al (2004), the pressure-temperature-time regime of the Himalayan orogeny (upper diagenesis to greenschist facies metamorphism) is still poorly constrained mainly due to the absence of indicative mineralogical assemblages.…”