Nature, Age, and Emplacement of the Spongtang Ophiolite, Ladakh, NW India

The Spongtang ophiolite (Ladakh, NW India) constrains the nature of oceanic lithosphere before Indo–Asia collision and key stages in the development of the Himalayas. We report whole-rock ⁴⁰Ar/³⁹Ar and in-situ zircon ²³⁸U–²⁰⁶Pb ages from its crustal, upper and lower mantle sequences. Major and trace elements from harzburgite minerals suggest the ophiolite formed at a mid-ocean ridge-type spreading center, whereas published spinel compositions from Spongtang dunites are consistent with a supra-subduction zone setting. Rare Earth Element-in two-pyroxene thermometry for the harzburgite yields 1058±13°C whereas temperature from solvus-based two-pyroxene and olivine-spinel thermometry is lower (to 656°C). The distribution suggests the mantle section of the ophiolite cooled at rates of 100° Myr^-1 or slower. Based on ages, major and trace element geochemistry, and geospeedometric estimates, we model the origin of the Spongtang ophiolite as forming within a mid-ocean ridge-type spreading center with a spreading rate >2cm y^-1 in the Neo-Tethyan Ocean, possibly from the Late Triassic to Jurassic. By Early Cretaceous, the ridge experienced increasing influence of subduction beneath the Spongtang oceanic lithosphere owing to a subduction polarity reversal. Based on 238U–206Pb ages of the youngest Cenozoic zircon grain, latest obduction occurred between 64.3±0.8 Ma to 42.4±0.5 Ma, in accordance 56.7±5.2 Ma whole-rock ⁴⁰Ar/³⁹Ar ages.