Sedimentary Serpentinites from the Mid-atlantic Ridge

Abstract

ABSTRACT Indurated sedimentary rocks with serpentine minerals as major components were recovered from the lower slopes of transverse ridges associated with the Romanche Fracture Zone in the equatorial Mid-Atlantic Ridge. In addition to serpentine minerals, sedimentary serpentinites from the Mid-Atlantic Ridge contain grains of diopside, enstatite, tremolite, chlorite, calcite and, frequently, calcareous microfossils; some samples display layering and graded bedding. These sedimentary serpentinites were emplaced by gravity sliding, slumping and turbidity current transport of serpentinite masses originating from the upper levels of ultramafic transverse ridges at the Romanche Fracture. Chemical and mineralogical differences between the sedimentary serpentinites and their ultramafic source rocks re discussed. The rocks in question are identical to sedimentary serpentinites common in alpine-type orogenic areas of the world.