Low Temperature Alteration of Oceanic Basalts, DSDP Leg 37

Secondary Minerals in Basalt from the Costa Rica Rift, Holes 501 and 504B, Deep Sea Drilling Project Legs 68, 69, and 70

“…The phillipsite associated with these minerals can form under oxidizing conditions, as it has in the recent pelagic sediment of the Pacific. This mineral association differs from that determined for the oxidizing diagenesis of either the recent basalt of the East Pacific and Atlantic mid-oceanic ridges (Bass, 1976;Robinson et al, 1977;Seyfried et al, 1976Seyfried et al, , 1978 or the ancient basalt from the Nauru Basin , where the chief minerals of oxidative diagenesis are hydrous ferric oxides and celadonite. It should also be noted that the oxidative diagenesis in the Costa Rica Rift basalts is not as great in importance as in some other mid-oceanic ridges (e.g., those drilled during Legs 34 and 37).…”

Mineral Assemblages and Processes of Alterations in Basalts at Deep Sea Drilling Project Sites 417 and 418

“…The composition of phillipsite was not quite common; its distinctive features are an extremely low CaO content and a predominance of Na2θ over K2O. This distinguishes it from the more common phillipsite of Leg 37 (Robinson et al, 1977).…”

“…The most intensely altered are the basalts from Hole 417A and the fine-grained basalt differentiates, irrespective of depth. The mineralogy of the alteration products is generally similar to that of the altered basalts from the drill holes of Leg 37 (Robinson et al, 1977) and from dredge samples of oceanic basalts taken at the Mid-Atlantic Ridge (Scott and Hayash, 1976;Hart, 1973). The aim of this paper is to discuss the mineralogy of the basalts from Legs 51 through 53, the distribution of alteration products at various depth intervals, and the mineral assemblages and conditions of formation.…”

“…For the basalts of Leg 37 (Robinson et al, 1977), an attempt was made to prove the dependence of chemical alteration in the rocks upon their degree of hydration by plotting various diagrams of their relationship. However, such diagrams, as well as chemical composition-versusdepth plots, are unsatisfactory for the basalts of Legs 51 through 53.…”

Smectite composition as a tracer of deep circulation: the case of the Northern North Atlantic

“…No amorphous components have been found at North Atlantic sites where smectites are dominant (Fagel et al, 1996); (2) hydrothermal alteration of basalt to smectites occurs only locally in active areas of Iceland and of the MidAtlantic Ridge (Chamley, 1989), yielding formation of nontronite and trioctahedral smectites (e.g. Robinson et al, 1977); dioctahedral smectites in the studied sites do not include nontronite; (3) in active areas of mid-oceanic ridges, volcanogenic clays (smectites, celadonite, ...) are observed in and above weathered basaltic beds, but rapidly decrease within a few tens of centimeters in the sedimentary column (e.g. Chamley, 1989); and (4) SmNd studies of the whole <2 µm fraction of surface sediments from the Reykjanes Ridge (site 063, Fig.…”