Rift-related sedimentation and volcanism of the north-Indian margin inferred from a Permian–Triassic exotic block at Lamayuru, Indus suture zone (Ladakh Himalaya) and regional comparisons

Abstract

Stratigraphical, petrographical and geochemical work on an important limestone exotic within the Indus suture zone, near Lamayuru, reveals the following history of events: (i) Late Permian deposition on a shallow-water carbonate platform open to the Neotethys Ocean; (ii) Late Permian–Early Triassic break-up, tilting, fissuring and subsidence; (iii) Early Triassic mantling by ammonite-bearing, pink pelagic carbonate and chlorite-rich volcaniclastic sediment; (iv) Deposition of Fe, Mn- and/or Mn-rich oxide-sediments, as crusts and fissure fills. The metal-rich oxides were precipitated from hydrothermal solutions related to nearby volcanism; (v) Late Triassic? eruption of pillowed and massive basalts of within-plate type on an irregular seafloor. Taking account of evidence from similar exotic units associated with Upper Cretaceous melange beneath the Spontang Ophiolite further south in the Zanskar Mountains (e.g. Photoskar unit), the Lamayuru exotic is interpreted as part of a small carbonate platform formed somewhere between the Zanskar/Lamayuru passive continental margin and a Permian–Triassic Neotethyan spreading axis to the north. The carbonates probably capped a volcanic seamount that later collapsed and was covered by pelagic sediments and basic extrusives. The Lamayuru exotic was later detached from its igneous basement and tectonically emplaced, probably in the latest Cretaceous, and was also influenced by Early Tertiary suturing of Neotethys, and mid–late Tertiary backthrusting.