An east–west trending diabase dyke cuts a north–south dyke and therefore is clearly younger. Chemical, petrographic, and diffraction data suggest that the north–south dyke belongs to the tholeiite group and the east–west dyke to the alkali basalt group. Excess argon in pyroxene from the east–west dyke and the alkaline affinities are taken as evidence of a deeper genesis for the east–west than the north–south dyke.

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