Geology of the summit limestone of Mount Qomolangma (Everest) and cooling history of the Yellow Band under the Qomolangma detachment

Abstract

Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The 40 Ar-39 Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock 87 Rb-86 Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period .

New constraints on the timing of partial melting and deformation along the Nyalam section (central Himalaya): implications for extrusion models

“…Near the Chomolangma summit (C, Fig.1b), apatite and zircon fission track ages from the Yellow Band Formation suggest that the STD was still active at c. 14.4 Ma because fast cooling was taking place at that time in the footwall (Sakai et al 2005). Further east, in the Saer area (S, Fig.…”

Stratigraphic correlation of Cambrian–Ordovician deposits along the Himalaya: Implications for the age and nature of rocks in the Mount Everest region

“…The entire upper part of Everest, above the Yellow Band, has been mapped as the Mount Qomolangma Formation, a succession of gray, dominantly fi ne-grained Ordovician limestone (Sakai et al, 2005). Most of these strata consist of highly recrystallized sandy limestone ; Fig.…”

“…Samples taken from 6 m below the summit of Everest consist of a variety of generally fi negrained marine carbonate deposits with variable amounts of land-derived silt and clay (Sakai et al, 2005). Grains in the limestone include fragments of crinoids and trilobites, as well as peloids (sand-sized fossilized fecal pellets).…”

Emplacement of hot Lesser Himalayan nappes from 15 to 10 Ma in the Jumla–Surkhet region, western Nepal, and their thermal imprint on the underlying Early Miocene fluvial Dumri Formation

“…This exposure age also coincides with the timing of rapid cooling in the Yellow Band at the top of the metamorphic belt beneath the Qomolangma detachment in the Mt Everest area (Sakai et al . ). These facts suggest that frontal and surface parts of the Kuncha and the Lesser Himalayan Crystalline nappes cooled rapidly below about 100°C at 15–14 Ma (Fig.…”

“…Cooling rate of the nappe and zircon FT ages of HHC nappe (**) are after S akai et al . (, ) and S akai (). (b) Conceptual cooling model of the nappe.…”