Structural Interpretation and Tectonostratigraphy of High-Pressure Low-Temperature Blueschist Facies Rocks near Orhaneli, Bursa Province, Western Türkiye

Year 2024, Volume: 12 Issue: 1, 541 - 563, 26.01.2024

Ümit Yıldız

Abstract

The Izmir-Ankara suture, a Neo-Tethyan collision zone between the Sakarya microcontinent (hanging wall) to the north and the Anatolide-Tauride block (footwall) to the south, including blueschist facies rocks near Dağgüney village, Orhaneli in Bursa, Türkiye, formed during the mid-Cretaceous. There are three main tectonostratigraphic units including high-pressure/low-temperature (HP-LT) rocks, mélange, and subophiolitic peridotites. Extensive exposures of lawsonite blueschist, graphitic mica schist, white mica schist, and marble there indicate HP-LT conditions of formation. In addition, the Tavsanli Zone contains two other rock sequences of significance to subduction-related evolution. These are mélange, considered to have formed in an accretionary complex that includes metamorphosed radiolarian chert, greenstone, meta-volcanic-tuff, amphibolite, white-mica-schist, blueschist and serpentinite, peridotite which contains dunite, harzburgite, and gabbro, interpreted to have formed as the oceanic lithosphere. Metamorphic foliation, defined by compositional layering and schistosity, trends generally ENE and dips gently northerly. Metamorphic lineation, defined by elongate calcite and sodic amphibole grains, trends WSW and gently plunges. Mesoscopic isoclinal folds are common in the blueschist facies rocks. The majority of the folds trend NNE-SSW and plunge gently eastward in the HP-LT rocks. There are at least four major fault types based on age, cross-cutting relationships, and orientation. Blueschist facies mineral assemblages were preserved in the HP-LT rocks, thus a rapid exhumation mechanism of buoyancy-driven flow is interpreted to have taken place within the subduction channel. The presence of blueschist, amphibolite, and white mica schist within the mélange suggests that exhumation occurred during subduction.

Keywords

Lawsonite blueschist, Structural Geology, Tavsanli Zone, Tectonostratigraphy

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