Physical properties of basalts from the Galapagos, Leg 70.

Abstract

The physical properties of compressional and shear-wave velocity, bulk and grain density, porosity, eletrical resistivity, and fluid permeability were measured on basalt samples cored from the Galapagos during Leg 70. These basalts are fresh and have higher density and sonic velocity that do those from older ocean crust. In addition, basalts from Sites 506, 507, and 508(0.54-0.85Ma) have higher grain density and lower sonic velocity than do those from Site 510(2.73Ma), which is probably the result of the higher Fe and Ti content of the former. Mean fluid perimeability was estimated to be approx 1.3 X 10-16cm2 and the size of pores responsible for fluid flow was estimated by means of the relationships between permeability versus resistivity and permeability versus porosity to be approx 0.03mu m or more. The permeability of laboratory samples is much lower than the large-scale permeability (10-11 approx 10-10cm2) (Anderson et al, 1977; Karato and Becker, this volume), suggesting that hydrothermal circulation in basaltic layers may occur through larger-scale fissures whose width is about three orders of magnitude greater than that of laboratory samples.-Author