130-10 Multi-stage crustal thickening, surface uplift, and collision in the western Himalaya-Karakoram-Tibet orogen revealed by chemical mohometry

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism, Part II

Presenting Author:

Authors:

Abstract:

The westernmost part of the Himalaya–Karakoram-Tibet (HKT) orogen is the result of collision between three terranes (the Indian continent, the Kohistan-Ladakh Arc, or KLA, and the Karakoram terrane of the southernmost Asian continent) and provides an unrivaled opportunity to study the dynamic linkages between deep and surface processes during collisional orogenesis. However, these efforts are hindered by conflicting interpretations on the number and timing of collisional events, and ambiguity in the timing of crustal thickening and associated surface uplift in the western HKT orogen. Here, we resolve this with quantitative paleo-crustal thickness estimates in the northwestern HKT orogen by applying chemical mohometry to a compilation of previously published geochemistry and geochronology from the northwestern HKT orogen.

Our results suggest that the paleo-Asian margin (Karakoram terrane) had thick crust (50–60 km) at least 65 Myr prior to terminal collision, consistent with a continental arc setting that has been inferred from geochemistry of the Karakoram Batholith. Importantly, our results show that crustal thickening to >60 km in the KLA occurred at ca. 60–50 Ma, and in the Karakoram Terrane by 40–25 Ma. These data suggest an initial collision between India and the KLA at 60-50 Ma, followed by a terminal collision between Asia and the composite India-KLA terrane by ~40 Ma, in support of other studies that advocate for a multi-stage collision in the western HKT orogen, and in agreement with the metamorphic rock record preserved in the Karakoram Terrane. Modern crustal thicknesses in the northwestern HKT have been sustained since ca. 40–25 Ma, suggesting broad attainment of orogenic steady-state on a regional scale in which crustal thickening, crustal flow, and surface uplift have been balanced by surface erosion. Additionally, despite myriad petrologic processes that can lead to misinterpretation of chemical mohometry, our study demonstrates that with sufficient data, the use of multiple mohometers, and statistical analysis, it is possible to obtain meaningful results with chemical mohometry to investigate the paleo-crustal thickness history of orogenic belts. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8104

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