Low-Temperature Alteration of Oceanic Basalts, DSDP Leg 49

Abstract

Alteration of ocean-floor rocks by seawater has been the subject of intensive study in the last four years, especially since the /eep Sea Drilling Project began large-scale penetration of hard rocks of the ocean floor (Andrews, 1977; Bass, 1976; Baragar et al., 1977; Robinson et al., Scarfe and Smith, 1977). Previously, dredged rocks wereused for study and the results of the work, summarized by Scott and Hajash (1976), are similar to those already described in the Initial Reports for Legs 34 and 37. Although our results are similar, we have been able to add significantly to the knowledge of the mineralogy of alteration processes, basalt glass-palagonite changes, and additionally, the chemistry of the alteration fronts which occur close to veins and fractures. Another alteration mineral, zeolite, occurring mainly as vein material and occasionally as centers of vesicles, has been examined in some detail and has proved to be of the phillipsite type. Carbonate, especially in veins, is calcite containing low MgO. Most of the MgO from seawater or olivine phenocryst alteration has gone to form clays.