NEW DATA ON THE STRUCTURE OF THE GORRINGE RIDGE

Abstract

The Gorringe Ridge, in the northwestern segment of the Azores-Gibraltar zone has long been a feature of great interest, primarily because bedrock exposures of the ophiolite association, i.e., serpentinite, gabbro, metadolerite, and what seem to be pillow lavas have been found on its summits, i.e., the Gettysburg and Ormond seamounts. The 16th cruise of the Akademik Mstislav Keldysh (June-August 1988) yielded additional data, which suggest ways in which the ridge could have formed as a morphostructure. The presence of granite and metamorphic rocks in xenoliths from alkalic basalt of the Ormond Seamount indicates rather convincingly that fragments of continental crust must be present at the base of the ridge. But in combination with charts of the subhorizontal tectonic zones and finds of jaspers on the lower parts of the slopes, these data indicate unambiguously that the Gorringe Ridge has a thrust-sheet structure, most probably involving thrust sheets dipping to the northeast and therefore displaced toward the southwest.