Unroofing the Ladakh Batholith: constraints from autochthonous molasse of the Indus Basin, NW Himalaya

Abstract

The Indus Molasse records orogenic sedimentation associated with uplift and erosion of the southern margin of Asia in the course of ongoing India–Eurasia collision. Detailed field investigation clarifies the nature and extent of the depositional contact between this molasse and the underlying basement units. We report the first dataset on detrital zircon U–Pb ages, Hf isotopes and apatite U–Pb ages for the autochthonous molasse in the Indus Suture Zone. A latest Oligocene depositional age is proposed on the basis of the youngest detrital zircon U–Pb age peak and is consistent with published biostratigraphic data. Multiple provenance indicators suggest exclusively northerly derivation with no input from India in the lowermost parts of the section. The results provide constraints on the uplift and erosion history of the Ladakh Range following the initial India–Asia collision. Supplementary material: Method description, Sample locations, Figures S1 and S2 and Tables S1 to S3 are available at: https://doi.org/10.6084/m9.figshare.c.4858848

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

“…Despite the relatively limited scope of our data, this is the first regionally extensive multithermchronometric study from the IBSRs and reveals a postdepositional Miocene‐Pliocene cooling signal along the India‐Asia collision zone in NW India. Deposition continued regionally along the collision zone until Late Oligocene‐Early Miocene time (~26–23 Ma; Bhattacharya et al, 2020; Clift et al, 2002; Sinclair & Jaffey, 2001; Zhou et al, 2020), and there is no unequivocal evidence of cooling beginning in the IBSRs until ~22–20 Ma. Using the ZHe and AHe data sets, we calculate the amount of material removed since the onset of cooling at ~22–20 Ma.…”

“…The Tar Group consists of carbonate and siliciclastic rocks that are tectonically bounded to the south by the precollisional Dras-Lamayuru-Nidar Complexes and are juxtaposed in the north against the Indus Group. The Indus Group exhibits extreme along-strike variations in siliciclastic fluvial facies that unconformably overlie the Ladakh batholith (Bhattacharya et al, 2020;Brookfield & Andrews-Speed, 1984;Clift et al, 2002;Garzanti & Van Haver, 1988;Henderson et al, 2010Henderson et al, , 2011Searle et al, 1990;Sinclair & Jaffey, 2001;Singh et al, 2015;Steck, 2003;St-Onge et al, 2010;Tripathy-Lang et al, 2013;Wu et al, 2007;Zhou et al, 2020). The Indus Group is categorized into two subgroups: (i) the Early Eocene-Early Miocene Lower Indus Group and (ii) the Pliocene Upper Indus Group.…”

“…All ZHe ages from the Lower Indus Group are <20 Ma. Deposition in the Lower Indus Group ended by ~26–23 Ma, after which basin inversion and regional counterthrusting began at ~23–20 Ma (Bhattacharya et al, 2020; Clift et al, 2002; Zhou et al, 2020). Therefore, we interpret the ZHe and AHe ages from the Lower Indus Group formations as thermally reset.…”

“…Indus Basin sedimentation began in Late Cretaceous time with the deposition of the marine Tar Group, which continued until ~50 Ma (Henderson et al, 2010). After ~50 Ma, the continental facies of the Lower Indus Group were deposited until Late Oligocene‐Early Miocene time (Bhattacharya et al, 2020; Clift et al, 2002; Henderson et al, 2011; Sinclair & Jaffey, 2001; Zhou et al, 2020). 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.…”

“…Precollisional deposition of the IBSRs initiated in an arc-bounded or a forearc marine basin in Late Cretaceous time, and the depocenter evolved into a continental intermontane basin with the onset of India-Asia collision in Early Eocene time (Garzanti & Van Haver, 1988;Henderson et al, 2010). Regional IBSRs deposition largely ended by Late Oligocene-Early Miocene time (~26-23 Ma) when basin inversion began, although local-scale deposition continued in Pliocene time in patches of western and central Ladakh (Bhattacharya et al, 2020;Clift et al, 2002;Henderson et al, 2010Henderson et al, , 2011Mathur, 1983;Zhou et al, 2020).…”