Multiple syenite intrusions at Kærven, Kangerdlugssuaq, East Greenland: Evidence from the 1986 field work.

Abstract

Tue Kærven Syenite Complex is recognized as the earliest intrusive body in the Kangerdlugssuaq region associated with the opening of the proto-Atlantic Ocean in the Lower Tertiary. Earlier investigations of the geology of the Kærven Syenite Complex have interpreted the intrusion as a single igneous body, emplaced subsequent to the Kærven Gabbro and in turn cut by the Kangerdlugssuaq intrusion. Preliminary sampling on Kærven in 1977 revealed a relatively large range of rock types in the complex (syenite - alkali feldspar syenite - alkali feldspar granite). Tue field work conducted in 1986 has verified these findings and enabled the distinction of 8 intrusive events within the complex. Further, a preliminary geological map has been produced. An igneous breccia separates the complex from the earlier Kærven Gabbro along parts of the eastern and southern margins. The central part of the Kærven Syenite Complex include an hitherto unrecognized slice of Precambrian basement gneisses with numerous approximately N-S trending basaltic dykes. This is multiply intruded by syenite. Most notably in the eastern part of the complex, intimate associations of brecciated and remobilized basement gneiss and melts of syenitic through monzonitic to tonalitic composi­tions are found. The form of the intrusive bodies are more or less dyke-shaped and N-S trending. Toere is a general stratigraphic younging to the SW, which is matched by the tater adjacent Kangerdlugssuaq intrusion. Tue intrusive sequence and trend of the intrusions are thought to be closely related to an extentional tectonic regime present in this part of the fjord for a considerable period onwards from the earliest Tertiary magmatic activity in the area.