Authors: CÜNEYT AKAL, CAHİT HELVACI
Abstract: Enclaves which are relicts of initial basic magma give important information on the origin and evolution of granitic magmas. The mafic microgranular enclaves from the l-type Kozak pluton are less than 1 m that are located at the margin of pluton and mostly less than 15 cm and are generally in sharp contact with the surrounding granodiorite. In some cases, several enclaves may occur close to each other, but they are not closely clustered to form swarms. Most of the enclaves are ellipsoidal in shape. The largest enclaves are less ellipsoidal with curved boundaries. The mafic microgranular enclaves contain same mineral species as the host granodiorite; however the proportions are different. In the mafic micragranular enclaves plagioclase, K-feldspar and hornblende are more abundant, quartz and biotite are less abundant. In some equigranular enclaves clinopyroxene and orthopyroxene are accessory minerals. The mafic microgranular enclaves are mostly intermediate in composition all contain more than 46% SiO 2 . The femic oxides (Fe 2 O 3 t, MgO and MnO) decrease systematically relative to SiO 2 ; most of mafic microgranular enclaves compositions cluster near the granodiorite trend line. Many trace elements do not show clear linear correlation with SiO 2 ; are scattered off the trends defined by related granodiorite. The petrographic and geochemical characteristics of the mafic enclaves and their host granodiorite indicate that the Kozak granodiorite is a product of partial melting and fractional crystallization of basic magma, and enclaves are trapped blobs of basic initial magma. Petrographic properties indicate that during magmatic evolution, the granodiorite and enclaves are effected by magma mingling and mixing processes.
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