LATE CRETACEOUS EARLY TERTIARY CONVERGENCE BETWEEN THE INDIAN AND ARABIAN PLATES RECORDED IN OPHIOLITES AND RELATED SEDIMENTS

Remnants of ocean floor forming the Eastern Ophiolite Belt in Oman and the Western Ophiolite Belt in Pakistan have a common plate-tectonic h istory culminating in emplacement at the Cretaceous/Tertiary boundary. Fragments of ocean floor in these two belts have ages between 150 and 65 Ma and recorded tectonic events in the early Indian Ocean at 150 M a, 130-120 Ma, 110-100 Ma and 70-65 Ma. New radiometric and chronostra tigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving Indian Ocean , which was characterised by the stepwise breakup of Gondwana at 158 M a (East and West Gondwana), 130 Ma (Southern Atlantic, breakup of East Gondwana), 95-84 Ma (Madagascar and India/Seychelles), 65 Ma (India a nd Seychelles) and, finally, at 40 Ma, rifting between Africa and Arab ia. The 150-Ma-old oceanic rocks of Masirah Island in Oman originally formed the extension of the basins now preserved along the eastern edg e of the Afro-Arabian plate. Masirah drifted together with India-Seych elles when a new ridge formed at approximately 130 Ma separating micro plates (e.g., Kabul Block) from the northern edge of Greater India. Pa rts of this new ocean were later emplaced to form the western ophiolit e belt in Pakistan. Consumption of oceanic crust and emplacement of op hiolites during the closure of the Neotethys occurred not only north o f India (+/- Seychelles), but also along two or three subduction zones between the Afro-Arabian plate and India/Seychelles, documented by th e formation of metamorphic soles beneath ophiolites. Relies of ocean f loor formed approximately 65-70 Ma ago, now form the upper units in th e Western Ophiolite belt of Pakistan where they overlie an accretionar y prism of pillow lavas of dominantly (Aptistn-) Albian age and sedime ntary rocks. The breakup of India and the Seychelles at 65 Ma was asso ciated with the eruption of flood basalts (Deccan and Seychelles) and enhanced counter-clockwise movement of India. This breakup possibly ca used the Late Jurassic/Early Cretaceous fragments of ocean floor (e.g. , Masirah) to be thrust onto the eastern edge of Oman. The aphiolites, which were emplaced onto the western edge of India, drifted as part o f this plate farther north where collision with Eurasia and the accret ed microplates occurred in the Eocene( similar to 55 Ma).