Miocene anatexis, cooling and exhumation in the Khumbu Himal, Nepal. Issue 14 (6th August 2022)

• Record Type: Journal Article
• Authors: Larson, Kyle P.; Cottle, John M.; Camacho, Alfredo; Piercey, Stephen; Grujic, Djordje
• Is Part Of: International geology review. Volume 64:Issue 14(2022)
• Page Start: 2008
• Page End: 2033
• Publication Date: 2022-08-06
• Subjects: Humbu Himalaya -- U(-Th)/Pb geochronology -- 40Ar/39Ar thermochronology -- U(-Th)/He thermochronology; Geology -- Periodicals; Electronic journals; 551.05
• DOI: 10.1080/00206814.2021.1969524
• Languages: English
• ISSNs: 0020-6814

Abstract

ABSTRACT: The Khumbu region of Nepal is host to numerous large leucogranite bodies that comprise some of the most iconic peaks in the Himalaya. These leucogranites occur throughout the high-metamorphic grade rocks exposed there in the immediate footwall of the orogen-scale South Tibetan detachment system. Previous work on leucogranites in the area has been limited spatially but has yielded U-Th/Pb ages between ~23 and 16 Ma. The current study expands upon that work with 522 new individual zircon, monazite and xenotime U-Th/Pb analyses across 10 leucogranite specimens collected from across the Khumbu. The dates returned outline the episodic crystallization of leucogranites at ~19 and 17 Ma, both of which contain significant inherited age components presumably from their source rocks. 40 Ar/ 39 Ar dating of muscovite from the same leucogranite bodies indicate rapid cooling through Ar closure (~510 °C) on the scale of ~500 kyr. The weighted mean of all 40 Ar/ 39 Ar dates, 16.48 ± 0.05 Ma, coincides with the timing of motion along the normal-sense Qomolangma detachment indicating a potential genetic relationship between the leucogranite cooling and extension. Finally, U(-Th)/He dating of apatite and zircon show that cooling slowed significantly post argon closure and that the rapid cooling may have been ephemeral.