Drilling through Mount Everest would reveal sedimentary limestone at the peak overlying metamorphic and igneous core rocks.
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Peer-reviewed geological studies confirm that Mount Everest's summit is composed of limestone (the Qomolangma Formation), which overlies metamorphosed core rocks such as the Yellow Band.
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 40Ar–39Ar 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 87Rb–86Sr 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 (15.5–14.4 Ma).
New samples collected from a transect across the summit limestone of Mount Everest (Qomolangma Formation) show that multiple distinct deformational events are discretely partitioned across this formation. Samples from the highest exposures of the Qomolangma Formation (Everest summit) preserve a well-developed mylonitic foliation and microstructures consistent with deformation temperatures of ≥250 °C. Thermochronologic and microstructural results indicate these fabrics were ingrained during initial contractile phases of Himalayan orogenesis, when crustal thickening was accommodated by folding and thrusting of the Tethyan Sedimentary Sequence. In contrast, samples from near the base of the Qomolangma Formation (South Summit) preserve extensional shear deformation, indicate metasomatism at temperatures of ∼500 °C, and contain a synkinematic secondary mineral assemblage of muscovite + chlorite + biotite + tourmaline + rutile. Shear fabrics preserved in South Summit samples are associated with activity on the Qomolangma detachment, while the crystallization of secondary phases was the result of reactions between the limestone protolith and a volatile, boron-rich fluid that infiltrated the base of the Qomolangma Formation, resulting in metasomatism. The 40 Ar/ 39 Ar dating of synkinematic muscovite indicates the secondary assemblage crystallized at ca. 28 Ma and that shear fabrics were ingrained at ≥18 Ma. This paper presents the first evidence that Everest’s summit limestone records multiple phases of deformation associated with discrete stages in Himalayan orogenesis, and that the structurally highest strand of the South Tibetan detachment on Everest was initially active as a distributed shear zone before it manifested as a discrete brittle detachment at the base of the Qomolangma Formation.
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