HR: 09:50h
AN: T21E-08    [Abstracts]
TI: Emplacement of the Western Tethyan Ophiolites and Atlantic Spreading
AU: * Smith, A G
EM: ags1@esc.cam.ac.uk
AF: Department of Earth Sciences, Sedgwick Museum Downing Street, Cambridge, CB3 2EQ United Kingdom
AB: This contribution shows that the cessation of emplacement of the 'Tethyan' supra-suduction zone (SSZ) ophiolites of the circum-Mediterranean region, and Oman, is contemporaneous with a marked drop in the relative velocities between Africa and Eurasia. It is argued that this contemporaneity is to be expected from plate theory. The Hellenic-Dinaric SSZ ophiolites in Greece, Albania and former Yugoslavia, range in age from ~173-168 Ma (mid-Jurassic). They were emplaced, eroded and covered by younger sediments by ~140 Ma, or possibly earlier, on the plate margin between northwest Gondwana and southwest Laurasia (=Africa/Eurasia). During emplacement, a passive continental margin was partially subducted, but because large-scale subduction of a continent appears to be precluded by the low density of continental crust, the subduction zone eventually ceased to exist and moved elsewhere. The SSZ ophiolites of Turkey, Cyprus, Syria, Iran and Oman are of mid-Cretaceous age. The initial setting of the mid-Cretaceous ophiolites is clearest in Oman. The Oman ophiolite appears to have formed during roll-back of Triassic (or possibly Permian) ocean-floor from the Iranian margin at ~95 Ma and to have been emplaced by early Maastrichtian time, ~70 Ma, after which the Arabian passive margin could not undergo further subduction. Despite the complexities and uncertainties in the Atlantic spreading data, the relative motion of Africa to stable Europe in the region of the Tethyan ophiolites is quite simple. A major slowing of the relative motion from ~40-50 mm yr-1 to less than 5 mm yr--1 took place at ~140 Ma, broadly synchronous with the cessation of Hellenic-Dinaric ophiolite emplacement. Slow motion lasted from ~140-125 Ma and is attributed to the failure to subduct the passive continental margin; to the destruction of the Africa-Eurasian margin of that time; and to its eventual reestablishment elsewhere, ~15 m.y. later, after which the relative motion speeded up to ~20 mm yr-1. A second phase of very slow motion to ~4 mm yr-1, from 75 Ma to 55 Ma, is broadly synchronous with the cessation of emplacement of the mid-Cretaceous ophiolites. Like the first phase, the slowing down is attributed to the failure to subduct a continental margin (in the case of Oman, the NE Arabian margin) and the requirement to re-position the margin; processes that took some 20 m.y. to complete. Thus both slow phases of Africa to Europe motions are dictated by the tectonic setting of ophiolite emplacement. In this setting, subduction zone processes influence the spreading history of the parts of the Atlantic, rather than the other way round. There is no evidence that any large igneous provinces (LIPs) played a role in the emplacement of these western Tethyan ophiolites.
DE: 8139 Obduction tectonics
DE: 8140 Ophiolites (3042)
DE: 8157 Plate motions: past (3040)
DE: 9305 Africa
DE: 9335 Europe
SC: Tectonophysics [T]
MN: Fall Meeting 2005