HR: 0800h
AN: T51A-0299    [Abstracts]
TI: Neo-Tethyan Ocean evolution of southwest Tibet inferred from a melange structurally beneath the Kiogar ophiolite
AU: * Chan, G H
EM: gavin.chan@earth.ox.ac.uk
AF: Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Aitchison, J
EM: jona@hku.hk
AF: Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, N/A, Hong Kong
AU: Chan, J S
EM: jackyhku@graduate.hku.hk
AF: Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, N/A, Hong Kong
AU: Searle, M
EM: mike.searle@earth.ox.ac.uk
AF: Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, United Kingdom
AB: Pre-collisional tectonic evolution of Neo-Tethyan Ocean is best recorded in the Yarlung Tsangpo suture zone (YTSZ) ophiolite complexes and associated melanges, one of which occurs in the Kiogar area of SW Tibet. Structural, sedimentological, palaeontological and geochemical work on a subophiolitic melange has been carried out in order to better constrain the tectonic evolution of this part of the Neo-Tethyan Ocean. The melange includes a series of south-verging dismembered thrust sheets and blocks, separated from the overlying ophiolite by a north-dipping thrust fault. The rocks include radiolarian cherts, pelagic limestones, reefal limetones, turbiditic sandstones and basaltic blocks. Biostratigraphic age data show that radiolarian cherts interbedded with basalts of a coherent succession were deposited in mid-Cretaceous time. Similar-age radiolarian cherts are depositionally associated with ophiolitic rocks elsewhere along the YTSZ in the Xigaze area of southeast Tibet. Extrusive rocks consists mainly of vesicular to highly vesicular, plagioclase-phyric and porphyritic-ankaramitic lavas. Geochemical evidence shows that the extrusive rocks, of inferred Cretaceous age, range from E-MORB to OIB, interpreted to be related off-axis seamount volcanism. MORB-type basaltic blocks, the ages of which remain unconstrained, were also found elsewhere. The melange was emplaced when the passive margin north of India collapsed, creating a foredeep ahead of advancing thrust sheets of ophiolitic rocks, prior to the closure of the Neo-Tethys.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8104 Continental margins: convergent
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting