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MACROSCOPICAL AND MICROSCOPICAL EVIDENCES MAGMA MIXING/MINGLING TYPE INTERACTION IN KESTANBOL GRANITOID (SOUTH CANAKKALE), NORTHWEST ANATOLIA-TURKEY

S. Y. Sahin, Y. Gungor, F. Goker

Abstract

Kestanbol granitoid, one of the post-collision granitoids outcropping in Northwestern Anatolia, takes place as a pluton in the southern of \cCanakkale that approximately N-S trending and within a great tectonic belt. This tectonic belt, named Sakarya Continent, is bordered with Intra Pontide Suture in the NorthAern part and Izmir-Ankara Suture in the Southern part. Kestanbol granitoid intruded into crustal meta-sedimentary rocks by hot-contact and it is surrounded by contact metamorphic aureole. Kestanbol granitoid have a contact relation with volcanic and volcanosedimentary rocks formed in coeval plutonic rocks or younger ones. Kestanbol granitoids is composed of monzonite, quartz monzonite, monzogranite and granodiorite according to field and microscopical investigations. Due to interaction of felsic and mafic magmas syn-plutonic dykes, magma mingling and magma mixing processes are revealed in this pluton. It includes mafic magmatic enclaves (MME) and some mixing texture under the microscopy. Medium-coarse grained Kestanbol granitoids have commonly holocrystalline granular texture but sometimes it displays porphyritic texture due to the presence of K-feldspar megacrystalls. It includes plagioclase (An 8-14) + orthoclase + quartz + hornblende + biotite minerals and sphene+apatite+zircon and opaque minerals as accessory minerals. Mafic magmatic enclaves are darker than their host rocks and they are composed of diorite, quartz diorite, monzodiorite and quartz monzodiorite. The boundaries between MME and host rock commonly have sharp; seldom gradually contacts. MMEs have generally microgranular but sometimes-porphyritic textures due to the presence of plagioclase phenocrystalls. These enclaves are described as “composite enclaves” due to their different textures and rock-types. Surrounding chilled margin zones of MMEs are darker than their host rocks. Porphyritic textures are formed by plagioclase phenocrystalls and K-feldspar megacrystals that exist either in the host rocks or their MMEs. MMEs are mostly ovoidal-ellipsoidal and rarely cornered shaped. Some of them are elongated-ellipsoidal shaped. Size of long axises of MMEs are ranging from centimeter to meter. Cause of these elongated shapes is the intensive deformation of their host rocks. Mineralogically they are composed of plagioclase (An 18-22) + hornblend + biotite + sphene + apatite + zircon and opaque minerals. It rarely includes quartz, K-feldspar (ortoclase) and pyroxene. Acicular, lath-shaped mafic minerals are seen along fine-grained marginal zone around of MMEs. Kestanbol granitoid includes some mixing textures such as antirapakivi, lathshaped small plagioclase within large plagioclase, poicilitic K-feldspar and poicilitic plagioclase, rarely acicular apatite, appinitic and sphene-plagioclase ocellar textures. Also MMEs have some mixing textures such as commonly acicular apatite texture, blade-shaped biotite, poicilitic K-feldspar/plagioclase texture, hornblende/biotite zones in K-feldspar/plagioclase phenocrystals, Spongy cellular plagioclase and spike zone in plagioclase and dissolution melting in plagioclase texture.

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