GEOCHEMISTRY, TECTONIC SETTING, AND POLY-OROGENIC HISTORY OF PALAEOPROTEROZOIC BASEMENT ROCKS FROM THE CALEDONIAN FOLD BELT OF NORTHEAST GREENLAND

Major and trace element chemistry and Rb-Sr isotope data are presented for Palaeoproterozoic basement gneisses within the Caledonian fold be lt of North-East Greenland. They indicate that these rocks represent r emnants of a Palaeoproterozoic collisional orogen formed near the marg in of an Archaean continent. Older tonalitic and granodioritic, gneiss es represent are granitoids. Granitic rocks (sensu stricto) of two dis tinct kinds can be recognised: (1) collision-type granites; and (2) po st-orogenic (''A-type'') granites, which may have formed during collap se of this orogen. It is suggested that the Palaeoproterozoic gneisses of North-East Greenland, together with coeval granitoid rocks in Scan dinavia and North America, form a T-shaped arrangement of orogenic bel ts. Similar patterns are also recognised for the later Grenvillian and Caledonian orogenic episodes. Orogenic activity of different ages in North-East Greenland overlaps in space, resulting in very complex geol ogical relationships.