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

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. This study aims to better understand the tectonostratigraphy and the structural evolution of the high- pressure low-temperature (HP-LT) rocks and their surroundings by examining data obtained from detailed geological mapping near Dağgüney, Orhaneli, Bursa. There are three main tectonostratigraphic units including 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 Tavşanlı 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
• Tavşanlı Zone
• Tectonostratigraphy

Orhaneli, Bursa İli, Batı Türkiye Yakınlarındaki Yüksek Basınçlı Düşük Sıcaklıklı Mavişist Fasiyesli Kayaçların Yapısal Yorumlanması ve Tektonostratigrafisi

Abstract

Kuzeyde Sakarya mikrokıtası (tavan bloğu) ile güneyde Anatolid-Torid bloğu (taban bloğu) arasında bir Neo-Tetis çarpışma bölgesi olan İzmir-Ankara sütur hattı, Bursa, Orhaneli, Dağgüney köyü yakınlarındaki mavişist fasiyes kayaları dahil, orta Kretase döneminde oluşmuştur. Bu çalışma, Bursa, Orhaneli, Dağgüney yakınlarındaki ayrıntılı jeolojik haritalamadan elde edilen verileri inceleyerek yüksek basınç düşük sıcaklık (HP-LT) kayaçlarının ve çevrelerinin tektonostratigrafisini ve yapısal evrimini daha iyi anlamayı amaçlamaktadır. Çalışma alanında (HP-LT) kayaçları, melanj ve subofiyolitik peridotitleri içeren üç ana tektonostratigrafik birim vardır. Lavsonit mavişist, grafitli mikaşist, beyaz mikaşist ve mermerin burada yoğun şekilde mostra vermesi, HP-LT oluşum koşullarına işaret etmektedir. Buna ek olarak, Tavşanlı Zonu dalma-batma-ilişkili etkileşim açısından önem taşıyan iki diğer kayaç birimini daha içermektedir. Bunlar, metamorizmaya uğramış radyolarit, greenstone, meta-volkanik-tüf, amfibolit, beyaz-mikaşist, mavişist ve serpantinit içeren melanj, ve okyanusal litosfer olarak oluştuğu düşünülen dünit, harzburjit ve gabro içeren peridotitlerdir. Bileşimsel katmanlanma ve şistozite ile tanımlanan metamorfik yapraklanma, genellikle DKD doğrultulu ve hafifçe kuzeye doğru eğimlidir. Yönlenmiş kalsit ve sodik amfibol mineralleri tarafından tanımlanan metamorfik lineasyon, BGB doğrultulu ve düşük açı ile dalım yapmaktadır. Mavişist fasiyes kayalarında mezoskopik izoklinal kıvrımlar yaygındır. Kıvrımların çoğu KKD-GGB doğrultulu ve doğuya doğru düşük açılarla dalmaktadır. Çalışma alanında yaşa, kesme ilişkisine ve doğrultu atımına bağlı olarak en az dört ana fay tipi tespit edilmiştir. HP-LT kayaçlarında mavişist fasiyes mineral topluluklarının kimyasal özellikleri korunmuştur, bu nedenle mavişistlerin yüzeylemesinin dalma-batma kanalı içinde kaldırma kuvveti kaynaklı v hızlı bir mekanizmayla gerçekleştiği yorumlanmıştır. Ayrıca melanj içinde mavişist, amfibolit ve beyaz mikaşist bulunması, yüzeylemenin dalma-batma sırasında meydana geldiğini açıklamaktadır.

Keywords

• Lavsonit mavişist
• Yapısal Jeoloji
• Tavşanlı Zonu
• Tektonostratigrafi

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