The geology of the Shyok suture zone: evidence for Cretaceous extension of the southern Eurasian margin and Eocene India–Eurasia collision

This study discusses whether the Eurasian margin, before the onset of the India–Eurasia collision, was a Cordillera-style accretionary orogen or a more complex Japan–Mariana-style margin with extended back-arc basins and oceanic crust between the volcanic arc(s) and continental lithosphere. This distinction is critical to understanding the development of the India–Eurasia orogenic system because each of these scenarios has very different implications for the timing of the continental collision between India and Eurasia. We present new field mapping, U/Pb zircon dates and whole-rock geochemical results that constrain the tectonostratigraphic and structural development of the Shyok suture zone, which separates the Kohistan–Ladakh arc from the Karakoram terrane in northwestern India and Pakistan. Our results suggest that the Shyok suture comprises a Jurassic forearc ophiolite overlain by Eurasia-derived sedimentary strata interlayered with andesites, which accumulated throughout the Cretaceous in a back-arc basin that was under extension between 115 and 72 Myr ago. Closure of this back-arc basin post-dates the formation of the Indus suture zone between the Kohistan–Ladakh arc and India.