الملخص الإنجليزي
The extrusive rocks of the lower ophiolitic nappe of Masirah Island (Oman) were paleomagnetically studied. Four mean directions of magnetization were isolated, one at low temperature, the others at high temperature. The low-temperature component, found in most samples, corresponds to a recent viscous and/or chemical remagnetization. The high-temperature component, found at three sites in the Centre area, is interpreted as a possible primary magnetization acquired during extrusion or, more probably, as an early remagnetization related to subsequent hydrothermal alteration and indicates formation of the Masirah ophiolite around a paleolatitude of 40°S, close to the present position of the West Somali basin. A second high-temperature component, found in three other sample sites in the Hakl and in the Thumi areas, is probably a chemical remagnetization related to the emplacement of the upper ophiolite nappe in late Maastrichtian to Paleocene times. Finally a last high-temperature component, found only in the two sites from Naft area, could be a post-tectonic remagnetization acquired in Oligocene or Miocene times or represents differential tilting of pillows and sedimentary blocks. The high-temperature components are usually fairly scattered due to the very complex tectonic history of the area. Nevertheless, the relation between the defined paleopoles and the Indian polar wander is unambiguous and the evolution of the Masirah ophiolite from formation up to the emplacement of the second ophiolitic nappe is clearly related to the northward movement of the Indian plate. This new paleomagnetic study rules out the possibility of a common or related origin for the Masirah and the Semail ophiolites.
