Types and genesis of the enclaves in Central Anatolian granitoids

Central Anatolian granitoids range from tonalite–monzonite, through granodiorite, to alkali feldspar granite in composition, and typically have angular to oval‐shaped mafic magmatic and metamorphic enclaves. These enclaves range from millimetres up to metres in size. The mineral compositions, textural features and amphibole chemistry reveal that the enclaves can be genetically differentiated into three types as xenolithic enclaves, magma segregation enclaves and magma mixing/mingling enclaves. The xenolithic enclaves are observed at the contact of granitoids with the metamorphic basement and/or ophiolitic rocks in Ortaköy (Akdağmadeni), Murmano and Akçakent plutons, and also in the southern part of the Agaçören Intrusive Suite. Based on their texture and mineral composition, these enclaves are identified as amphibolite, calc‐schist and hornfels. The magma segregation enclaves, which are observed in almost all of the Central Anatolian granitoids, are monomineralic in composition and consist of accumulations of mafic minerals. They are small in size and best observed under the microscope. The magma mixing/mingling enclaves are the most abundant enclave type in Central Anatolian granitoids. 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 feldspar and acicular apatite. Analyses of the amphiboles by electron micro‐probe analysis reveal that the xenolithic enclaves have tremolitic–actinolitic hornblende compositions. The magma segregation and the magma mixing/mingling enclaves have mainly magnesio‐ and ferro‐hornblende compositions, similar to those found in their host rocks. This similarity in the amphibole compositions suggests thermal and chemical equilibrium between the respective enclaves and their host attained during the course of their crystallization. Copyright © 1999 John Wiley & Sons, Ltd.