Scandian-Acadian-Caledonian sensu strictu metamorphism in the age range 430–360 Ma

Abstract

S U M M A R Y: Metamorphism in the age range Wenlock to mid-Devonian, when it can be recognized, appears to have accompanied some of the most intense phases of convergent tectonics in the orogen. Very different styles of metamorphism in different regions suggest different tectonic settings. In Scandinavia deep subduction and imbrication of the Baltic continental margin beneath N America (?), with little or no plutonism, produced a regional pattern leading to high temperature eclogites and granulites. In the British Isles, Canada and Maine, broad greenschist, prehnite-pumpellyite and lower-grade metamorphism accompanied the closure of Iapetus, with local higher-grade punctuations associated with widespread plutonic activity. In France, locally in Newfoundland, in southern New England and in part of the southern Appalachians both plutonic heating and intense deformation were involved in metamorphism to the amphibolite and locally the granulite facies, complicated in France by eclogites and locally by glaucophane schists.

Blueschists and Eclogites of the World and Their Exhumation

“…This unit near Trondheim contains variably fragmented ophiolite associations (Gale and Roberts, 1974). The Koli nappes are weakly metamorphosed, including greenschist-facies assemblages (Robinson et al, 1988). Thus, the boundary must be a normal fault on the top and a reverse fault on the bottom of the Seve nappes, which include glaucophane-bearing eclogite.…”

“…The eclogite-bearing, highgrade gneiss zone extends eastward into the Massif Central, where eclogite with a U-Pb age of 318 to 320 Ma is widespread (Gebauer et al, 1981;Liegeois and Duchesne, 1981;Giraud et al, 1984;Demange, 1985;Piboule and Briand, BLUESCHISTS AND ECLOGUES OF THE WORLD 513 1985). The eclogite, which occurs as thin layers, pods, or lenses within high-grade gneiss, formed at P = 11 to 20 kbar and T = 900 to 1000° C (Robinson et al, 1988). The high-P/T belt extends northward to northeastern Bavaria in Germany , through the Bohemian Massif, and further eastward to the Polish Sudety (Smulikowski and Smulikowski, 1985).…”

Timing of strain partitioning and magmatism in the Scottish Scandian collision, evidence from the high Ba–Sr Orkney granite complex

“…Syn-to postcollisional magmatism, ranging from ultramafic to granitic (the Newer granites), was channeled through, and emplaced along, shear zones and accompanied by local metamorphism (e.g. Watson 1984;Robinson et al 1988;Jacques and Reavy 1994;Dewey and Strachan 2003). Atherton and Ghani (2002) proposed that the Scandian collision was accompanied by slab breakoff, providing a new framework for our understanding of the orogeny.…”