A PETROLOGIC AND STRUCTURAL EVOLUTION RELATED TO SUBDUCTION AND EXHUMATION PROCESSES ALONG THE CRETACEOUS IZMIR-ANKARA SUTURE ZONE NEAR ORHANELI, TURKEY

Detailed mapping and petrologic modeling combined with previous work provides new insights into the production and exhumation of HP-LT metamorphic rocks in subduction zones. Detailed mapping focussed on four major tectonic units are interpreted to represent the subophiolite, the metamorphic sole, the accretionary complex, and the HP unit. The structurally lowest HP unit contains continental and continental margin rocks including marble, phyllite and metagranitoid, and oceanic rocks including blueschist. All HP unit rocks appear to have similar peak metamorphic conditions (~420 C, 2.1 GPa). The metamorphic sole is an amphibolite that locally contains the peak assemblage garnet, phengite, paragonite, zoisite, Na-amphibole, plagioclase (An_2-8), quartz, titanite and rutile. Geothermobarometry and petrologic modeling of a fixed bulk composition indicates conditions of (~550 C, 1.0 GPa). Late growth of pumpellyite indicates overprinting at ~250 C and 0.5 GPa. These conditions are similar to reported conditions for overprinting in other parts of the metamorphic sole and similar to prograde conditions in accretionary complex (~200 C, 0.6 GPa). The accretionary complex is a tectonic melange of greenstone, serpentinite, phyllite with radiolarian chert, marble and amphibolite (similar to the metamorphic sole). The early contact between the HP unit and the accretionary complex is gently dipping and marked by highly-strained serpentinite. The structurally highest unit is composed of dunite and hartzburgite that contain structural fabrics that are oriented at a high angle to the underlying units. Combined with available geochronologic data these results indicate: 1) Early imbrication and juxtaposition of oceanic and continental rocks and subduction to about ~80 km depth. 2) Formation of the metamorphic sole at ~35 km depth that was followed by exhumation along the slab interface to ~20 km depth. 3) Exhumation of HP rocks initially by flow adjacent to gently dipping shear zones.