Reports

Nonspreading Crustal Blocks at the Mid-Atlantic Ridge

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Science  24 Dec 1971:
Vol. 174, Issue 4016, pp. 1329-1331
DOI: 10.1126/science.174.4016.1329

Abstract

Transverse ridges consisting of protrusions into crustal fractures of ultramafic bodies derived from the upper mantle exist at the intersection of the Mid-Atlantic Ridge with equatorial fracture zones. Shallow-water limestones containing detrital grains of quartz, microcline, and orthoclase 1 millimeter in diameter were found on the summit of one such transverse ultramafic body at the Vema Fracture Zone; these findings are explained on the assumption that the limestones were deposited within a narrow, shallow proto-Atlantic and were left behind during the further opening of the Atlantic. Transverse ultramafic bodies from the offset zones of the Mid-Atlantic Ridge behave as nonspreading blocks plastered between spreading crustal plates.