Eskola (1921) published 65 years ago a classic treatise (M.A.2-313) which described several types of eclogites from the Western Gneiss region (WGR) of Norway. These occur in Proterozoic orthogneisses, but also in paragneisses, peridotites, anorthosites, gabbros and coarse-grained 'rapakivi granites'. Structural and isotopic data suggested that many of these rocks were juxtaposed by early Caledonian thrusting prior to eclogite formation at approx 425 m.y. Low-P protoliths can be demonstrated for many of the eclogites; prograde metamorphism to eclogite facies is shown by inclusion suites in garnets and by zoning in eclogite minerals. The high-P metamorphism occurred essentially in situ in a continental collision zone similar to the present Himalayas. The Baltic Shield was overriden from the W by the Greenland plate; maximum depths of approx 70-90 km were recorded by external eclogites near the present coast, with shallower depths (30-40 km) in the E and S parts of the WGR. Maximum pressures were reached at 100-200o>Tmax, this P-T-time path being consistent with the preservation of jadeite-rich clinopyroxene (and possible coesite) in the coastal region.-R.A.H.
|Number of pages||11|
|Publication status||Published - 1987|