Mesozoic magmatic and sedimentary development of the Tavşanlı Zone (NW Turkey): implications for rifting, passive margin development and ocean crust emplacement
Upper Ordovician–Upper Cretaceous high-pressure–low-temperature metasedimentary and meta-igneous rocks in the Dursunbey area provide insights into the Tavşanlı Zone (Anatolides) when compared to crustal units further south (e.g. Afyon Zone and Taurides). Schists near the base of the Tavşanlı Zone succession are cut by a small Upper Ordovician metagranite. This is covered by metaclastic sediments that are interbedded with bimodal rift-related basic-silicic volcanics of inferred Triassic age. Above this is a thick metacarbonate platform interpreted as the result of post-rift subsidence. Overlying metacarbonates, metapelites and metachert with metabasaltic intercalations (Upper Cretaceous?) reflect platform collapse. Overlying mélange contains blocks of ocean-derived intrusive and extrusive igneous rocks (e.g. ocean island-type basalt), metacarbonates and radiolarian chert, set in a low-grade metamorphosed shaly matrix. The Tavşanlı Zone was buried in a north-dipping subduction zone to 74–79 km at c. 88 Ma, exhumed and tectonically juxtaposed with accretionary mélange prior to the Late Palaeocene–Early Eocene. Geochemical studies of the meta-igneous rocks indicate the presence of ocean island basalt (OIB) and mid-ocean ridge basalt (MORB) sources modified by crustal contamination, evidenced by Th enrichment and fractional crystallization. A subduction chemical influence in the lower part of the succession (e.g. Nb depletion) was probably derived from subcontinental mantle lithosphere, modified during some previous subduction event (Panafrican?).