P-T evolution of subophiolitic amphibolites beneath the Kınık Ophiolite (İAESZ, Türkiye): Insights from garnet and amphibole chemistry

Öz

The metamorphic sole rocks at the base of the Kınık Ophiolite in the İzmir-Ankara-Erzincan Suture Zone provide important insights into the tectonothermal evolution of the northern Neotethys. Field and petrographic observations reveal a sequence of amphibolites, garnet-amphibolites, amphibole schists, and quartz schists, displaying granoblastic to nematoblastic textures with retrograde overprinting by chlorite and epidote. Mineral chemical data show that garnets are dominated by almandine with subordinate pyrope and grossular, and very low spessartine, consistent with basaltic protoliths. Amphiboles are mainly calcic types, such as magnesiohornblende and tschermakite, preserving magmatic affinities but partly modified during metamorphism. Geothermobarometric calculations indicate peak conditions of ~640-790 °C and ~4-5 kbar, corresponding to medium- to upper-amphibolite facies at mid-crustal depths of ~14-20 km. The higher temperatures recorded in one sample suggest a low-pressure/high-temperature regime, typical of metamorphic soles. These findings demonstrate that the Kınık amphibolites originated from basaltic precursors and underwent LP-HT metamorphism during intra-oceanic subduction and subsequent ophiolite emplacement.

Anahtar Kelimeler

• Kınık Ophiolite
• Subophiolitic metamorphic sole
• Amphibolite facies
• Garnet-hornblende geothermometry
• Al-in-hornblende barometry
• Neotethys closure

Kınık Ofiyoliti (İAESZ, Türkiye) altındaki subofiyolitik amfibolitlerin P-T evrimi: Granat ve amfibol kimyasından bulgular

Öz

İzmir-Ankara-Erzincan Sütur Zonu’nda yer alan Kınık Ofiyoliti’nin tabanındaki metamorfik taban kayaçları, kuzey Neotetis’in tektono-termal evrimi hakkında önemli bilgiler sunmaktadır. Arazi ve petrografik gözlemler; amfibolit, granat-amfibolit, amfibolşist ve kuvarsşistlerden oluşan bir diziyi ortaya koymakta olup, bu kayaçlar granoblastik ve nematoblastik dokular sergilemekte ve klorit ile epidot tarafından temsil edilen retrograd etkilerle değişim göstermektedir. Mineral kimyası verileri granatların baskın olarak almandin, daha az oranda pirop ve grossular, çok düşük oranda ise spessartin içerdiğini ve bazaltik protolitlerle uyumlu olduğunu göstermektedir. Amfiboller ise çoğunlukla kalsik tiplerdir (magnezyohornblend ve çermakit) ve kısmen metamorfizma ile yeniden dengelenmiş olsalar da magmatik özelliklerini büyük ölçüde korumaktadır. Jeotermobarometrik hesaplamalar, yaklaşık 640-790 °C sıcaklık ve 4-5 kbar basınç koşullarını işaret etmektedir. Bu değerler orta-üst amfibolit fasiyesi koşullarına ve yaklaşık 14-20 km derinliklere karşılık gelmektedir. Özellikle bir örnekte kaydedilen daha yüksek sıcaklıklar, metamorfik tabanlara özgü düşük basınç-yüksek sıcaklık (LP-HT) rejimine işaret etmektedir. Bu bulgular, Kınık amfibolitlerinin bazaltik protolitlerden türediğini ve okyanus içi dalma-batma sırasında, ofiyolit yerleşimi esnasında LP-HT metamorfizmasına uğradığını ortaya koymaktadır.

Anahtar Kelimeler

• Kınık Ofiyoliti
• Subofiyolitik metamorfik taban
• Amfibolit fasiyesi
• Granat-hornblend jeotermometresi
• Al-in-hornblend jeobarometresi
• Neotetis’in kapanışı

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