FORMATION AND EVOLUTION OF THE MASIRAH OPHIOLITE CONSTRAINED BY PALEOMAGNETIC STUDY OF VOLCANIC-ROCKS

The extrusive rocks of the lower ophiolitic nappe of Masirah Island (O man) were paleomagnetically studied. Four mean directions of magnetiza tion were isolated, one at low temperature, the others at high tempera ture, The low-temperature component, found in most samples, correspond s to a recent viscous and/or chemical remagnetization. ?he high-temper ature component, found at three sites in the Centre area, is interpret ed as a possible primary magnetization acquired during extrusion or, m ore probably, as an early remagnetization related to subsequent hydrot hermal alteration and indicates formation of the Masirah ophiolite aro und a paleolatitude of 40 degrees S, close to the present position of the West Somali basin, A second high-temperature component, found in t hree other sample sites in the Hakl and in the Thumi areas, is probabl y a chemical remagnetization related to the emplacement of the upper o phiolite nappe in late Maastrichtian to Paleocene times, Finally a las t high-temperature component, found only in the two sites from Naft ar ea, could be a post-tectonic remagnetization acquired in Oligocene or Miocene times or represents differential tilting of pillows and sedime ntary blocks. The high-temperature components are usually fairly scatt ered due to the very complex tectonic history of the area. Nevertheles s, the relation between the defined paleopoles and the Indian polar wa nder is unambiguous and the evolution of the Masirah ophiolite from fo rmation up to the emplacement of the second ophiolitic nappe is clearl y related to the northward movement of the Indian plate. This new pale omagnetic study rules out the possibility of a common or related origi n for the Masirah and the Semail ophiolites.