CATHODOLUMINESENCE (CL) EVIDENCE FOR THE TECTONIC HISTORY OF THE EGRIGOZ PLUTON, NORTHERN MENDERES MASSIF, WESTERN TURKEY

The Egrigoz pluton is a relatively well-studied pluton in the Northern Menderes Massif of western Turkey. Although much attention has focused on its geochemical and geochronological history, its relationship to major structures and other large plutons in the region are still debated. Some geologic maps show the Egrigoz pluton bounded by the low-angle Simav detachment fault. In contrast, other regional maps show no offsets between the Egrigoz pluton and surrounding metamorphic rocks or adjacent granites. Yet other studies indicate thrust faults may be present near the Egrigoz pluton, between Menderes metamorphic rocks and a meta-rhyolite unit. To gain a better understanding of the tectonic history of the Egrigoz pluton, cathodoluminesence (CL) images of samples from the granite and ArcGIS digital elevation data from the region were obtained to search for effects of micro- to macro-scales of deformation.

The Egrigoz pluton lies near the Alacam and Koyunoba plutons, within the Northern Menderes Massif, between the Simav graben and Afyon-Izmir-Ankara-Erzincan suture. Relief images of the Northern Menderes Massif were produced using 3 arc second (~90m) Shutter Radar Topographical Mission (SRTM) data. We observed numerous E-W trending lineations in the images that parallel the Simav graben and cut the plutons. These lineations may reflect large-scale extension. The Simav graben and its associated high-angle fault are evident in the SRTM data, but no other significant detachment-related basins or structures are shown, including the low-angle Simav detachment. The plutons lack noticeable elevation differences from surrounding areas.

The early Miocene Egrigoz pluton is speculated to have been emplaced syn-extensionally into Oligocene metamorphic rocks. However, reported mineral ages from the pluton range from Late Archean to early Miocene, with other ages between these extremes. The composition of the pluton ranges from calc-alkaline to shoshonitic and interpretations of the tectonic setting varies accordingly. Samples from the Egrigoz pluton plot within the Volcanic Arc Granite (VAG) field (Ozgenc and Ilbeyli, 2008; Ilbeyli and Kibici, 2009) or between VAG and syn-collisional granites (Akay, 2009) on the Rb-(Y+Nb) discriminant diagram. On the Nb-Y discrimination diagram, Egrigoz samples plot within the VAG and syn-collisional fields (Akay, 2009) or between within plate granite and VAG + syn-collisional granite fields (Ozgenc and Ilbeyli, 2008; Ilbeyli and Kibici, 2009). Samples from the granite are metaluminous or peraluminous (Ozgenc and Ilbeyli, 2008; Ilbeyli and Kibici, 2009) but others report only peraluminous rocks (Akay, 2009; Dilek et al., 2009). Both I-type and S-type granites have been reported from the pluton (Ozgenc and Ilbeyli, 2008; Dilek et al., 2009; Ilbeyli and Kibici, 2009).

To document microstructures that might help explain these heterogeneities, CL images were obtained from samples of the Egrigoz pluton. The pluton is comprised of Qtz + Pl + Kfs + Bt + Ms + Ap + Zr + Mnz + FeO + Rt + Ttn. Minerals that show CL in these rocks are predominantly Pl (brown/green) and Kfs (blue/red). Blue-CL is patchy in Kfs grains, consistent with fluid alteration. Some Pl grains show distinct color differences between the cores and rims, indicating either igneous zoning during magmatic evolution, or in some cases, response to late-stage fluids. Many plagioclase grains show significant alteration along outer rims. The CL images also show a range of microcrack and microvein types that cut grains and presumably allowed fluid-access during alteration. Many Pl grains appear to have been in part replaced by Kfs, a common feature of low-T alteration in plutons. The CL images constitute evidence of a complex, multi-stage tectonic history for the region that includes water-mediated brittle deformation.

Akay, E. (2009) Int J Earth Sci (Geol Rundsch), 98, 1655–1675. Dilek, Y., Altunkaynak, S., Oner, Z (2009) GSA Spec Pub, 321, 197-223. Ilbeyli N., Kibici, Y. (2009) Int Geol Rev, 51, 252-278. Ozgenc, I., Ilbeyli, N. (2008) Int Geol Rev, 50, 375-391.