New age constraints on the cooling and unroofing history of the Trans-Himalayan Ladakh Batholith (Kargil area), N. W. India

Abstract

Thermotectonic history of the Trans-Himalayan Ladakh Batholith in the Kargil area, N. W. India, is inferred from new age data obtained here in conjunction with previously published ages. Fission-track (FT) ages on apatite fall around 20 + 2 Ma recording cooling tM:ough temperatures of ~ 100~ and indicating an unroofing of 4 km of the Ladakh Range since the Early Miocene. Coexisting apatite and zircon FT ages from two samples in Kargil show the rocks to have cooled at an average rate of 5-6~ in the past 40 Ma. Zircon FT ages together with mica K-At cooling ages from the Ladakh Batholith cluster around 40-50 Ma, probably indicating an Eocene phase of uplift and erosion that affected the bulk of the batholith after the continental collision of India with the Ladakh arc at 55 Ma. Components of the granitoids in Upper Eocene-Lower Oiigocene sediments of the Indus Molasse in Ladakh supports this idea. Three hornblende K-Ar ages of 90 Ma, 55 Ma, and 35 Ma are also reported; these distinctly different ages probably reflect cooling through 500-550~ of three phases of I-type plutonism in Ladakh also evidenced by other available radiometric data: 102 Ma (mid-Cretaceous), 60 Ma (Palaeocene), and 40 Ma (Late Eocene); the last phase being Ioealised sheet injections. The geodynamic implications of the age data for the India-Asia collision are discussed.

Early–Middle Eocene Exhumation of the Trans-Himalayan Ladakh Batholith, and the India–Asia Convergence

“…New zircon FT ages (OWM = 43.0  0.5 Ma, Table 2) constrain its low-temperature cooling history (Figure 3 a). When ZFT ages from the Kargil pluton are taken into consideration 46 ( Supplementary Table 1), the batholiths yields an overall single uniform ZFT age population. 45 and published FT data, and zircon and apatite (U-Th)/He (ZHe, AHe) ages 21,22 of the LB and the Deosai Batholith in the west 20 .…”

Rapid early Miocene exhumation of the Ladakh batholith, western Himalaya

“…U-Pb crystallisation ages from the main Batholith range from 65 to 49 Ma , suggesting that magmatism was contemporaneous with the Gangdese Batholith (Scharer et al, 1984) and that magmatic activity ceased with the collision of India and Eurasia. Apatite fission track (AFT) ages of the Ladakh Batholith from Kargil to Chumatang range from 28 to 4.8 Ma (Choubey, 1987;Sorkhabi et al, 1994;Clift et al, 2002;Schlup et al, 2003). The young Pliocene ages are related to minor faulting (Choubey, 1987), however, there remains a spread in single AFT ages from 18 to 28 Ma (Sorkhabi et al, 1994;Clift et al, 2002).…”

“…Apatite fission track (AFT) ages of the Ladakh Batholith from Kargil to Chumatang range from 28 to 4.8 Ma (Choubey, 1987;Sorkhabi et al, 1994;Clift et al, 2002;Schlup et al, 2003). The young Pliocene ages are related to minor faulting (Choubey, 1987), however, there remains a spread in single AFT ages from 18 to 28 Ma (Sorkhabi et al, 1994;Clift et al, 2002). How these ages record the detailed history of exhumation of the Batholith is not clear due to the broad scatter of the samples.…”

“…This region has a vertical extent of just over 1.3 km, from 3921 to 5245 m.a.s.l., over a horizontal distance of 10 km. The profile is between sites of previous studies (Choubey et al, 1987;Sorkhabi et al, 1994;Clift et al, 2002;Schlup et al, 2003). Only sample KHARS 5245 from the top of the profile was analysed using all techniques.…”

40Ar–39Ar dating of volcanic rocks of the Shyok suture zone in north–west trans-Himalaya: Implications for the post-collision evolution of the Shyok suture zone

“…The pioneering geochronological studies by Honegger et al (1982) showed that the magmatism started at least 100 Ma ago and continued till the continent-continent collision. Later studies indicated that the span of the plutonic magmatism may range from 100 to 40 Ma ago (Reuber, 1989;Sharma, 1990;Sorkhabi et al, 1994;Weinberg and Dunlap, 2000;Kohn and Parkinson, 2002;Guillot et al, 2003). Recent studies reported Ar-Ar plateau-age of 29.8 ± 0.2 Ma of muscovite from a leucogranite in Ladakh batholith indicating younger post-collision magmatism due to intra-crustal melting at the base of thickened crust in otherwise subduction related batholith (Bhutani et al, 2004).…”