TECTONIC RELATIONSHIPS BETWEEN VERY HIGH PRESSURE SUBDUCTION COMPLEX ASSEMBLAGES AND CO-EXISTING GRANITOIDS IN THE TAVSANLI ZONE, SIVRIHISAR MASSIF, TURKEY

The Sivrihisar Massif in western Anatolia exposes blueschist and eclogite facies metasedimentary and metabasaltic rocks in close association with granitoid plutons. The region is located within the Tavsanli Zone, considered the subducted and exhumed northern continental margin of the Anatolide-Tauride Platform. The timing relationship of the very high pressure assemblages to co-existing granitoid plutonic bodies (termed Kaymaz and Sivrihisar) is unclear as the region can be considered the type locality for the entrainment of excess argon in K-bearing minerals. To further understand the nature between the subduction zone assemblages and intrusive igneous bodies, samples from the Kaymaz and Sivrihisar granitoids and a subduction complex assemblage were collected, imaged with cathodoluminescence (CL), and dated using zircon U-Pb in situ (in thin section) ion microprobe methods. The granitoids are chemically heterogeneous as evidenced by CL images and significant variations in their major and trace elements. Finer-grained Sivrihisar samples can be considered syenite whereas coarser-grained samples are monzonite. Our samples of the Kaymaz granitoid are extremely Si rich (~82-97 wt% SiO₂) and have experienced sericitization. CL images of both granitoids show ample evidence for fluid interactions at both the subsolidus and lower temperature stages in their tectonic history. High-resolution CL images of zircons from the assemblages collected in this study help interpret the meaning of their U-Pb ages. Subduction along the Tavsanli Zone was ongoing during 116.4±8.6 Ma to 86.9±7.2 Ma (²³⁸U-²⁰⁶Pb ages. ±1σ), but entrained zircons with clear igneous zoning that crystallized as early as 1870±102 Ma to 1646±81Ma and during 565±32 Ma to 311±16 Ma. Sivrihisar Massif granitoids record zircon crystallization from 79.9±8.6 Ma to 33.3±2.0 Ma. Here we present a model in which we speculate the Sivrihisar and Kaymaz melts were largely sourced from a subducting slab along the Afyon zone further to the south, and likely have mixed with a component generated during decompression from the breakoff of the Tavsanli slab. The model speculates that the Tavsanli Zone is the northernmost segment of an amalgamation of stacked subduction zones that progressively transition from north to south over time.