Crustal melting during exhumation of the Menderes Core Complex: Insights from the mineral chemistry of the Güneşli granite (Western Türkiye)

The Güneşli Granite, located in the Gördes Submassif within the northern part of the Menderes Massif, represents one of the Early Miocene intrusions in the region. This high-K calc-alkaline, slightly peraluminous two-mica granite comprises two compositional members: granite and granodiorite, with some exhibiting adakitic signatures. This study investigates the intrusion's plagioclase, biotite, and muscovite chemistry. Plagioclases in the Güneşli granite predominantly consist of oligoclase, while the granodiorite exhibits anorthite contents ranging from An14 to An30, indicating oligoclase and occasionally andesine compositions. Black micas are classified as biotite, characterized by high Fe numbers and convergence toward annite composition due to low AlIV content. White micas are classified as muscovite based on their low Si and ferromagnesian content. Both mica types are of magmatic origin and show no evidence of post-magmatic alteration. Measured minerals are generally similar in adakitic and non-adakitic samples; however, adakitic rocks exhibit higher OH- compositions. The source rocks are predominantly crustal and closely resemble the peraluminous biotites found in S-type granites. The intrusion's oxygen fugacity (fO2), determined from biotite chemistry, indicates a slightly oxidizing state at FMQ+0.1 to +0.8 buffer. Thermobarometric calculations based on machine learning applied to biotite chemistry suggest that the magma crystallized at depths between 5.8 and 10.5 kbar, deeper than previously expected, with temperatures ranging from 723 to 779 °C. The integration of regional geology, field studies, and mineral chemistry indicates that the Güneşli granites originated from deep-crustal sections and were emplaced at mid-crustal depths within the Menderes Massif. These crustal-derived granites evolved through assimilation-fractional crystallization, indicating a crustal reworking during the development of the Gördes Dome in the Early Miocene.