Over the past two decades, several sites of hydrothermal circulation on mid-ocean-ridge flanks have been investigated. These include the Galapagos mounds, the southern flank of the Costa Rica Rift, the equatorial East Pacific Rise flank, the western flank of the East Pacific Rise near 20°S, the western flank of the Mid-Atlantic Ridge, and the flank of the Mariana Trough spreading axis. These sites represent a wide range in sediment thickness and continuity, sediment type, crustal age, and basement topography. Although these localities display a correspondingly wide range of hydrothermal conditions and processes, our understanding of the processes remains only semiquantitative.
As a result of a series of coordinated surface-ship and submersible studies that began with a reconnaissance survey in 1988, the eastern flank of the Juan de Fuca Ridge has become one of the most thoroughly studied ridge flanks. By providing critical hydrologic, geophysical, and geochemical samples and observations of three characteristic types of subseafloor fluid-flow systems (Hydrothermal Transition [HT] system from bare crust to sedimented crust; Rough Basement [RB] system with basement topography influencing fluid flow; and Buried Basement [BB] system with "flat" basement covered by sediment) that occur in simple form on this ridge flank, work conducted during Ocean Drilling Program (ODP) Leg 168 will greatly improve our understanding of ridge-flank hydrothermal circulation and crustal evolution.
To 168 Table of Contents