Comparative study of oceanic plate and ophiolite based on accurate analyses of crustal and mantle material

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The results obtained from this research project are summarized as follows.Systematic mineral and bulk rock analyses for mantle harzburgites sampled from extensive area of the northern Oman ophiolite indicate that a highly depleted zone is present within the mantle section. The depleted zone is defined by the appearance of Cr-spinels with high Cr# (Cr/(Cr+Al), and traced along the shear zone trending NW-SE described by French group. Remelting of mantle sections caused by invasion of fluids expelled from the underling basement during oceanic thrusting movement would bring a such depleted zone.We have examined a regional variation of the mantle-crust transition zone. Lithologic column obtained from7 routes, located at different locations in a segment architecture, indicate a systematic variation of the mantle-crust transition zone depending on the segment structure, as follows. The thickness of the transition zone thickens toward the segment center, and become to thin at the segment margi … More n. However, abnormally thick transition zone was found from the northern tribute branch of Wadi Fizh, locating at the most margin of the segment. Systematic variations in structural features in the transition zone are also obvious, that is, intensive lineation and foliation are well observed at the segment center, while they are only poorly developed at the segment margin. These results suggest that mantle upwelling and magmatic flowage were more vigorous at the segment center. Also lithologic column for extrusive successions are studied at different localities in terms of segment structure. Systematic variations in respect to mode of occurrence of the extrusives were found, as follows: Massive flows are predominant at the segment center with numerous numbers of unit. Whereas, pillow lavas are predominant at the segment margin and are characterized by much thicker unit than the segment center. Thus, both extrusives in the uppermost level, and deeper section of the crust, were controlled by segmentation structure. Less