Tertiary igneous activity at Giesecke Bjerge, northern East Greenland

The Tertiary igneous activity at Giesecke Bjerge, northern East Greenland, was initiated by the eruption of plagioclase--porphyritic hyaloclastic breccias and lavas with tholeiitic affinity. These were succeeded by transitional and mildly alkaline lavas, mainly ankaramites and pyroxene-olivine porphyritic basalts. Tholeiitic sills, possibly contemporaneous with the older lavas, were intruded in the sediments beneath the volcanic sequence. Both the lavas and the sills were cut by bas_altic dykes. The older lavas at Giesecke Bjerge are similar to the bulk of Tertiary lavas in East Greenland while the younger lavas show a resemblance to the Quaternary volcanic products of Jan Mayen. It is suggested that the formation and emplacement of the transitional and alkaline lavas were related to a WNW trending fracture system following Kejser Franz Josephs Fjord.