THE GOTHIAN AND LABRADORIAN OROGENS - VARIATIONS IN ACCRETIONARY TECTONISM ALONG A LATE PALEOPROTEROZOIC LAURENTIA-BALTICA MARGIN

Intermittent crustal growth characterised late Paleoproterozoic develo pment in western Baltica during Gothian orogenesis, and in eastern Lau rentia during Labradorian orogenesis. Both regions are inferred to hav e belonged to the same margin of a supercontinent, but they do not sho w identical tectonic histories. Long-lived convergent margin activity associated with successive, oceanward migrating stages of subduction c haracterized western Baltica during the late Paleoproterozoic, in cont rast to the development of a pre-Labradorian, ca. 1.71 Ga sedimentary depocentre close to the margin of pre-Labradorian Laurentia that gave way to Labradorian 1.68-1.65 Ga calc-alkaline magmatism associated wit h subduction away from cratonic Laurentia. Continued Gothian, ca. 1.62 -1.58 Ga continental-margin calc-alkaline magmatism and are accretion has no recognized counterpart in eastern Laurentia, where collision of the outboard microcontinents/arcs resulted in voluminous granitoid ma gmatism caused by crustal thickening. Subduction either ceased at 1.65 Ga or northward subduction was initiated much farther south. The cave at to all interpretations is that some of the apparent differences may reflect inadequate geochronological databases of western Baltica and southeasternmost Laurentia.