Geochemistry of the basalts from DSDP Leg 42A

During DSDP Leg 42A, drilling at site 373A in the central Tyrrhenian Sea penetrated Miocene basaltic basement for 190 m and recovered basalt from up to 450 m below the sea floor. Despite mineralogical and chemical alteration due to hydrothermal processes under the high heat flow regime in the Tyrrhenian marginal basin, petrological analogies to high-Al abyssal basalts can be traced.
Two interlayered basalt groups have been recognized: (1) the lower-Ti group (core 5/1-2, core 7, 10), and (2) the higher-Ti group (core 5/3, core 6, core 11, core 12 and outer barrel), respectively.
We consider a distinction of two magma types: a more primitive magma leading to the plagioclase-bearing, lower-Ti basalts with affinities to high-Al abyssal tholeiites and a more differentiated magma leading to basalts with higher Ti.