Between 73 degrees and 74 degrees N in NE Greenland, a Lower Series of
quartz tholeiite lavas is overlain by an Upper Series which varies fr
om quartz tholeiitic to basanitic. The Lower Series basalts are attrib
uted to large melt fractions produced east of the present outcrop wher
e lithospheric thinning permitted the Iceland plume to ascend to shall
ow levels. Relocation of eruption sites up to 150 km (?) further west,
preceeded Upper Series activity. In this, small-degree melts, generat
ed principally from garnet-lherzolite facies sources, were followed by
products of more extensive, shallower melting which gave rise success
ively to the Upper Series lavas, a post-Upper Series basaltic dyke swa
rm and its associated caldera complex. Palaeomagnetic observations and
Ar-40/Ar-39 dating suggest that the Lower Series (and part of the Upp
er Series) erupted in C24r at 58-57Ma. Rejuvenescent activity at c. 32
Ma, marking the termination of volcanism, may relate to decompressive
mantle melting associated with late regional uplift.