ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉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 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar and 〈span〉in situ〈/span〉 zircon 〈sup〉238〈/sup〉U–〈sup〉206〈/sup〉Pb ages from its crustal and upper and lower mantle sequences. Major and trace elements from harzburgite minerals suggest that the ophiolite formed at a mid-ocean ridge-type spreading centre, whereas published spinel compositions from Spongtang dunites are consistent with a suprasubduction-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 that the mantle section of the ophiolite cooled at rates of 100° Ma〈sup〉−1〈/sup〉 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 centre with a spreading rate 〉2 cm a〈sup〉−1〈/sup〉 in the Neotethyan Ocean, possibly from the Late Triassic to Jurassic. By the Early Cretaceous, the ridge experienced increasing influence of subduction beneath the Spongtang oceanic lithosphere owing to a subduction polarity reversal. Based on 〈sup〉238〈/sup〉U–〈sup〉206〈/sup〉Pb ages of the youngest Cenozoic zircon grain, latest obduction occurred between 64.3 ± 0.8 and 42.4 ± 0.5 Ma, in accordance with 56.7 ± 5.2 Ma whole-rock 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar ages. 〈strong〉Supplementary material:〈/strong〉 Excel files with details of electron microprobe and inductively coupled plasma mass spectrometry (ICP-MS) analyses, argon isotopic whole-rock and secondary ion mass spectrometry (SIMS) analyses, and the 〈span〉T〈/span〉〈sub〉REE〈/sub〉 calculations, including an inversion diagram showing regression through measured REE distributions in cpx and opx (from 〈a href="https://pubs.geoscienceworld.org/jgs#C84"〉Liang 〈span〉et al.〈/span〉 2013〈/a〉), are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4261856"〉https://doi.org/10.6084/m9.figshare.c.4261856〈/a〉〈/span〉