In this paper, we present a detailed description of the morphology and microstructure of fibrous and nonfibrous veins crosscutting basaltic cores recovered from Hole 896A. The nonfibrous veins consisting of spheroidal smectite aggregates and blocky carbonate crystals indicate that minerals crystallized in open spaces during single-stage crack opening. Fibrous veins (mainly smectite + carbonate-bearing) indicate that fibers crystallized by a crack-seal mechanism, involving repeated increments of microcrack openings, followed by displacement-controlled crystal growth. We report descriptions of diagnostic features of the crack-seal veins studied. Finally, composite veins consisting of both nonfibrous and fibrous mineral infill are interpreted to result from recrystallization of fibrous minerals into blocky minerals, or to indicate a decreasing crystallization rate with respect to the fracture opening rate.

Date of initial receipt: 16 August 1994
Date of acceptance: 28 February 1995

Return to Contents of Leg 148
Return to Contents of Scientific Results