(U-Th)/He Thermochronology of the Indus Group, Ladakh, Northwest India: Is Neogene Cooling a Continental-Scale Thermal Event in the India-Asia Collision Zone?

D. A. Orme,D. M. Robinson,G. Bhattacharya,Andreas Wöfler

doi:10.2113/2021/3321949

Abstract

Abstract The India-Asia continental collision zone archives a sedimentary record of the tectonic, geodynamic, and erosional processes that control the thermal history of the Himalayan orogenic interior since the onset of collision in early Paleogene time. In this paper, we present new (U-Th)/He thermochronometric cooling age data from 18 detrital zircons (ZHe) and 19 detrital apatites (AHe) of the early Eocene–early Miocene (ca. 50–23 Ma) continental facies of the Indus Group along the India-Asia collision zone in Ladakh, northwest (NW) India. This along-strike regional-scale low-temperature thermochronometric data set from the Indus basin is the first report of ZHe and AHe cooling ages from western and eastern Ladakh. Thermal modeling of our ZHe and AHe cooling ages indicates a postdepositional Neogene cooling signal in the Indus Group. Cooling initiated at ca. 21–19 Ma, was operational along the ~300 km strike of the collision zone in NW India by ca. 11 Ma, and continued until ca. 3 Ma. The Miocene cooling signal, also present along the India-Asia collision zone in south Tibet, is a continental-scale cooling event likely linked to increased erosional efficiency by the Indus and Yarlung Rivers across an elevated region resulting from the subduction dynamics of the underthrusting Indian plate.

Highlights

The India-Asia collision zone records the largest intercontinental collision of Earth’s Cenozoic history and continues to provide new geological and geophysical data that improve our understanding of evolution of the Himalayan orogenic system
The apatite (U-Th)/He (AHe) ages are between 9:57 ± 0:11 and 3:23 ± 0:11 maximum depositional age (Ma) with majority of the ages between ca. 7 and 3 Ma
The new ZHe and AHe cooling ages together with the thermal modeling reveal a postdepositional Miocene–Pliocene cooling phase initiated in the Indus Group by ca. 21–19 Ma and by 11 Ma was in operation along the ~300 km strike of the India-Asia collision zone from western to eastern Ladakh in NW India

Summary

Introduction

The India-Asia collision zone records the largest intercontinental collision of Earth’s Cenozoic history and continues to provide new geological and geophysical data that improve our understanding of evolution of the Himalayan orogenic system. Indus suture after the onset of India-Asia collision and is currently at elevations of >4-5 km along with rest of the Indus basin sedimentary rocks [4,5,6,7,8,9,10,11]. Knowing the timing of burial, exhumation, and uplift of the Indus Group is critical in determining the tectonothermal, geodynamic, and erosional processes that governed regional exhumation and uplift of the India-Asia collision zone in NW India after the onset of collision. Previous low-temperature thermochronometric studies in the Indus Group as well as the overall Indus basin are restricted mostly to central Ladakh. Low-temperature thermochronometry in the central part of the Indus basin, using zircon fission-track (ZFT), apatite fission-track (AFT), zircon (U-Th/He) (ZHe), and apatite (U-Th)/He (AHe) data, indicates burial to >200°C and unveils a postdepositional Miocene–Pliocene cooling signal from ca. AFT ages from two samples in central Ladakh and one sample

Results

Discussion

Conclusion