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

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

Ümit Yıldız

https://doi.org/10.29130/dubited.1273991

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

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

Thanks

Special thanks go to Dr. Nuri Uzunlar, Dr. Michael P. Terry, and the late Dr. Alvis L. Lisenbee for their help and support.

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