CALEDONIAN TERRANE ASSEMBLY ON SVALBARD - NEW EVIDENCE FROM AR-40 AR-39 DATING IN NY FRIESLAND/

Ar-40/Ar-39 dating of hornblendes and muscovites from the Atomfjella C omplex of northern Ny Friesland provides new evidence of Caledonian hi gh grade metamorphism, with uplift and cooling occurring during the Mi d to Late Silurian, prior to Old Red Sandstone deposition. Hornblende crystallized during transpressive orogeny, the latter characterized by lateral shortening and extensive axial elongation. Ny Friesland is a part of Svalbard's Eastern Terrane. The Atomfjella metamorphic complex is overlain by Late Proterozoic and Carnbro-Ordovician successions cl osely similar to those of the Laurentian margin of East Greenland. Thi s similarity, suggesting pre-Caledonian juxtaposition, contrasts with the markedly different tectono-stratigraphic evolution of terranes far ther west on Svalbard. The assembly of Svalbardian terranes by large t ranscurrent displacements on major north trending faults, first postul ated by W.B. Harland in the mid 1960s, finds support in the new invest igations. On Svalbard, these transpressive movements were largely of S ilurian age, simultaneous with Scandian collisional convergence betwee n Baltica and Laurentia farther south in the orogen. The transcurrent displacements of Svalbard Terranes may have been a direct response ('' escape'') to this Scandian collision. In northeastern Greenland, appar ently similar sinistral transpression occurred during the Devonian, su ggesting that deformation along the Laurentian margin progressed from the hinterland toward the foreland during the Mid Paleozoic.