Phanerozoic granulites

Abstract

Granulites can form at every stage of the Wilson cycle: during plate accretion (Mid-Atlantic Ridge), in active plate margins of island-arc and Andean type (Ivrea Zone, main complex in Kohistan in the Karakorums), in the roots of Andean-type batholiths (Coast Range Complex, British Columbia; Santa Lucia Range of California), during the closure of a marginal basin (Aracena belt, Spain), during Himalayan-type collision (Jijal Complex in the Karakorums of N Pakistan and at I’Agly in the Pyrenees) and during post-tectonic intrusion at depth(Sä0 Paulo, Brazil). Himalayan-type orogenic belts may, in principle, contain any of such granulites. The majority of granulites form along active plate margins in the roots of magmatic arcs, which are the main sites of crustal growth in the Phanerozoic. Layered stratiform complexes, formed largely by cumulate processes, are common in Phanerozoic granulites (Kohistan, Ivrea, Calabria in Italy, Cabo Ortegal in NW Spain, Brittany and N Pyrenees). Their granulite-grade parageneses may have formed during cooling from an igneous temperature, or during superimposed metamorphism. Variations in the types of granulites may help in understanding how different types of lower continental crust are constructed.