Discussion of exhumation history of eastern Ladakh revealed by ⁴⁰ Ar/ ³⁹ Ar and fission track ages: the Indus River–Tso Morari transect, NW Himalaya

Low‐Temperature Thermochronology of the Indus Basin in Central Ladakh, Northwest India: Implications of Miocene‐Pliocene Cooling in the India‐Asia Collision Zone

“…This basin heating resulted in partial resetting of the Tar and Lower Indus Group rocks with respect to the ZFT system. Our ZFT age interpretations are consistent with the 280°C and 240°C maximum burial temperatures of the Tar and Lower Indus Group rocks determined using illite crystallinity and/or vitrinite reflectance (Clift et al, 2004;Schlup et al, 2003;Van Haver et al, 1986). Although best fit (U-Th)/He t-T model paths from the Lower Indus Group suggest burial temperatures of~170-190°C, this might be a consequence of relative extent of burial in the sampled sections.…”

“…Illite crystallinity estimates by Clift et al (2002) in central Ladakh suggests temperatures did not exceed 200°C in the Indus Group. Another paleo-geotemperature study in eastern Ladakh by Schlup et al (2003), which is also discussed in Clift et al (2004), reveals an illite crystallinity index of 0.36 (°Δ2θ) from a single Lower Indus Group sandstone sample. This illite crystallinity value translates to a lower anchizone grade burial temperature of~239°C using the index-temperature equation of Zhu et al (2016).…”

“…The Indus Basin was inverted at ~23–20 Ma (Clift et al, 2002), and there is no evidence of postdepositional basin cooling prior to that time. Burial temperatures largely remained below 240°C in the Indus Basin except the Tar Group, where maximum temperatures reached 280°C (Clift et al, 2004; Van Haver, 1984). In our first approach, to fit the ZHe and AHe data in the context of known regional geologic information, we allow individual models to explore the t ‐ T space younger than 23 Ma and colder than 240°C or 280°C (Figures 4a–4e).…”

“…Our ZFT results indicate that the Lower Indus Group is partially reset with respect to the ZFT system, indicating peak burial temperatures >185–200°C. In addition, paleo‐geotemperature estimates from the Lower Indus Group based on illite crystallinity also suggest maximum burial temperatures of ~239°C (Clift et al, 2004; Schlup et al, 2003). Hence, we allow the model to cool through 0–240°C after ~23 Ma.…”

(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?

“…Tripathy-Lang et al [10] determined ca. 52-28 Ma unreset predepositional ZHe ages from the late Oligocene Basgo Formation in central Ladakh and suggest that the ages reflect cooling of Indian plate [38], the illite crystallinity analyses of Clift et al [39] from eastern Ladakh yields a maximum basin temperature estimate of 239°C. Overall, there is limited evidence that suggests Miocene cooling along the India-Asia collision zone in NW India might have been regional in scale.…”