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Petrography of Northern Margin of Büyükorhan Granitoid And its Relationship with Country Rocks (West of Orhaneli, Bursa)
Geological evolution of the region of west and south of Orhaneli, Bursa were determined by petrogenic studies. Relations between Büyükorhan Granitoid and metamorphic rocks were decribed.
Metabasite, metapelite and high levels of calcschists were found in Sırıl Metamorphics. Existance of basal conglomerate that consists of limestone and quartz gravels in passage of calcschist-marble unit, proves that Çatalca Marble exist uncomformably above the metamorphic. Prior studies states metamorphics have Paleozoic age and Çatalca Marble has Mesozoic age (Lisenbee, 1972).
Above Sırıl Metamorphic and Çatalca Marble thrusts Orhaneli Ophiolites, of Upper-Cretaceous age. This unit consists of ultramafic-mafic rocks such as dunite, harzburgite and gabbro.
Büyükorhan Granitoid of Eocene age spreads through west of study field. Three different facies were identified: margin zone facies with small traces of porphyry around south of Sadağ village, the facies near Çakıryenice village consists of light coloured and large grained K-feldspar and the normal facies with large amphibole and biotite minerals that surfaces in a larger area in south.
Thick endoskarn facies found north of granitoid indicates Çatalca Marble was on granitoid earlier, then moved due to erosion. Mineralogical-petrographic and chemical analysis showed endoskarn rocks has syenite compound with alkali feldspar, pyroxen with Ca-Fe (Diopside-hedenbergite), garnet (andradite) minerals.
In contact zones between granitoid and metamorphic, hornfels rocks with pelitic sources were observed. These rocks were affected by conditions of pyroxen-hornfels facies and have sillimanite-andalusite-cordierite paragenesis. Diyopside-hedenbergite and hornblende paragenesis in hornblende-hornfels facies conditions exist in calcschist sourced xenolite pieces inside granitoid. Both hornfels samples have characteristics of inner contact zone.
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