Metamorphism during Alpine Crustal Thickening and Extension in Central Anatolia, Turkey: the Nigde Metamorphic Core Complex

Abstract

The Nig ˘de massif, a metamorphic core complex in Central Anatolia high-temperature reactions can obliterate assemblages (Turkey), contains petrologic evidence for the transition from Alpine formed during earlier, lower-temperature phases of meta- crustal thickening to extension and exhumation of high-grade mid- morphism. This can hinder use of petrologic information crustal rocks. Sillimanite-potassium feldspar gneiss formed and to interpret tectonic processes. If reaction textures are partially melted during Barrovian metamorphism and records max- preserved, however, rocks may record a range of pres- imum conditions of 5-6 kbar, >700∞C. The two-mica Uckapili sure-temperature conditions from their prograde and/ granite and a related dike suite intruded the migmatitic metapelitic or retrograde paths and a more complete picture of the rocks, forming a contact aureole that contains andalusite and tectonic evolution of a terrane can be reconstructed. Of cordierite. These low-pressure minerals indicate that crustal thick- particular interest are the mechanisms and timing of ening was followed by exhumation of mid-crustal rocks to relatively transition from contraction to extension and the ac- shallow depths (<10 km) at lower temperatures before the em- companying exhumation of middle- to lower-crustal placement of granitic magma. Formation of andalusite was followed rocks. The present study describes a medium-pressure, by a second, prograde episode of sillimanite growth during low- high-temperature terrane (the Nig ˘de massif; Fig. 1) in pressure—high-temperature metamorphism in the central part of the central Anatolia, Turkey, that developed as a meta- massif, where magmatism was most extensive. A generalized P-T morphic core complex in response to Alpine crustal path for the highest grade rocks therefore consists of an initial thickening. Metamorphic rocks in the central, high-grade clockwise path with a late thermal spike and characterizes burial part of the massif record in their mineral assemblages, and subsequent exhumation accompanied by magmatism. reaction textures, and structures the processes of burial, exhumation, and accompanying magmatism.