Geologic Investigations in the Cayman Trough: Evidence for Thin Oceanic Crust along the Mid-Cayman Rise
The Mid-Cayman Rise is a 110 km long accreting plate boundary (~ 2cm/yr, full rate) characterized by a deep rift valley. Eighteen transponder-navigated dives were made by the submersible ALVIN along the rift valley walls in two areas on opposite sides of the rift valley. The relief of the walls is produced by a large number of inward facing small-throw fault escarpments with vertical displacements ranging from a few tens of meters to perhaps as much as 400 m. From these escarpments 142 samples were collected, and gabbroic rocks (116 samples), characterized by a wide range of compositions and a complex metamorphic history, predominate in number over other rock types (basalt, serpentinized ultramafic). We interpret the assemblage of rocks exposed on the escarpments to indicate that a shallow level magma reservoir exists beneath the axis of accretion at the Mid-Cayman Rise and creates anomalously thin oceanic crust with a carapace of only several hundreds of meters of diabase and basalt. This carapace is und...