EARLY TERTIARY MAGMATISM IN NE GREENLAND

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 from quartz tholeiitic to basanitic. The Lower Series basalts are attributed to large melt fractions produced east of the present outcrop where lithospheric thinning permitted the Iceland plume to ascend to shallow levels. Relocation of eruption sites up to 150 km (?) further west, preceeded Upper Series activity. In this, small-degree melts, generated principally from garnet-lherzolite facies sources, were followed by products of more extensive, shallower melting which gave rise successively to the Upper Series lavas, a post-Upper Series basaltic dyke swarm and its associated caldera complex. Palaeomagnetic observations and Ar-40/Ar-39 dating suggest that the Lower Series (and part of the Upper Series) erupted in C24r at 58-57Ma. Rejuvenescent activity at c. 32Ma, marking the termination of volcanism, may relate to decompressive mantle melting associated with late regional uplift.