Types and genesis of the enclaves in Central Anatolian granitoids

Central Anatolian granitoids range from tonalite-monzonite, through granodi orite, to alkali feldspar granite in composition, and typically have angula r to oval-shaped mafic magmatic and metamorphic enclaves. These enclaves ra nge from millimetres up to metres in size. The mineral compositions, textur al features and amphibole chemistry reveal that the enclaves can be genetic ally differentiated into three types as xenolithic enclaves, magma segregat ion enclaves and magma mixing/mingling enclaves. The xenolithic enclaves ar e observed at the contact of granitoids with the metamorphic basement and/o r ophiolitic rocks in Ortakoy (Akdagmadeni), Murmano and Akcakent plutons, and also in the southern part of the Agacoren Intrusive Suite. Based on the ir texture and mineral composition, these enclaves are identified as amphib olite, calc-schist and hornfels. The magma segregation enclaves, which are observed in almost all of the Central Anatolian granitoids, are monomineral ic in composition and consist of accumulations of mafic minerals. They are small in size and best observed under the microscope. The magma mixing/ming ling enclaves are the most abundant enclave type in Central Anatolian grani toids. They are microgranular in texture and rich in mafic minerals (mafic microgranular enclaves), and have characteristic petrographic features such as blade-shaped biotite, quartz ocelli, poikilitic ferdspar and acicular a patite. Analyses of the amphiboles by electron micro-probe analysis reveal that the xenolithic enclaves have tremolitic-actinolitic hornblende compositions. T he magma segregation and the magma mixing/mingling enclaves have mainly mag nesio- and ferro-hornblende compositions, similar to those found in their h ost rocks. This similarity in the amphibole compositions suggests thermal a nd chemical equilibrium between the respective enclaves and their host atta ined during the course of their crystallization. Copyright (C) 1999 John Wi ley & Sons, Ltd.