A Comparative Example of Multi-Level Mafic Magma Emplacement Along The South Shetland Arc (West Antarctica): The Dee and Cecilia Intrusions

Öz

This study presents a comparative investigation of the emplacement conditions for gabbroic intrusions exposed on Dee and Cecilia islands, located along the South Shetland Islands to the north of the Antarctic Peninsula in Western Antarctica. Crystallization temperatures and emplacement pressures were calculated using two-pyroxene geothermobarometry, and oxygen fugacity conditions were additionally constrained based on Fe–Ti oxide pairs. Petrographically, the Dee intrusions are characterized by fine-grained, holocrystalline porphyritic textures composed of plagioclase, clinopyroxene, orthopyroxene, olivine, and opaque minerals. The Cecilia intrusion displays broadly similar mineral assemblage but coarser-grained holocrystalline granular textures. Plagioclase in the Dee intrusions predominantly exhibits normal zoning, whereas plagioclase crystals in the Cecilia intrusion commonly show oscillatory and locally reverse zoning, together with sieve textures and embayment structures. Two-pyroxene geothermobarometric calculations suggest that the Dee intrusions crystallized at temperatures of approximately 1,030–1,090 ℃ and pressures of 2.5–3.5 kbar, corresponding to relatively shallow upper-crustal emplacement. In contrast, the Cecilia intrusion yields crystallization temperatures of 1,000–1,170 ℃ and pressures of 4.5–6.5 kbar, consistent with deeper emplacement at mid- to lower-crustal levels. Fe–Ti oxide barometry indicates that both intrusions crystallized under oxidizing redox conditions, with the Cecilia intrusion recording systematically higher oxygen fugacity values relative to the Dee intrusions. When field, petrographic, and mineral chemistry data are evaluated together, the Dee and Cecilia intrusions are interpreted to represent mafic magmatic bodies emplaced at different crustal levels within the South Shetland Arc magmatic system. Future geochronological studies will lead the investigation of the timing of emplacement and further assess the relationship between the crustal evolution of these mafic intrusions and the regional tectonic framework.

Anahtar Kelimeler

• South Shetland Islands
• Gabbro
• Petrography
• Mineral Chemistry
• Geothermobarometry

Proje Numarası

125Y065

Güney Shetland Yayı (Batı Antarktika) Boyunca Çok Seviyeli Mafik Magma Yerleşimine Karşılaştırmalı Bir Örnek: Dee ve Cecilia İntrüzyonları / A Comparative Example of Multi-Level Mafic Magma Emplacement Along The South Shetland Arc (West Antarctica): The Dee and Cecilia Intrusions

Öz

Bu çalışma, Batı Antarktika’da Antarktik Yarımada’nın kuzeyinde yer alan Güney Shetland Adaları boyunca konumlanan Dee ve Cecilia adalarında yüzeyleyen gabroik intrüzyonların yerleşim koşullarını karşılaştırmalı olarak incelemektedir. İntrüzyonların kristallenme sıcaklıkları ve yerleşim basınçları, iki-piroksen jeotermobarometresi kullanılarak hesaplanmış ve bununla beraber Fe–Ti oksit çiftlerinden oksijen fugasitesi koşulları belirlenmiştir. Petrografik olarak Dee intrüzyonları, plajiyoklaz, klinopiroksen, ortopiroksen ve olivin ve opak minerallerden oluşan, ince taneli ve holokristalen porfrik dokular ile temsil edilmektedir. Buna karşılık Cecilia İntrüzyonu, benzer mineralojik bileşime sahip olmakla birlikte, daha iri taneli holokristalen granüler dokular sergilemektedir. Dee intrüzyonlarında plajiyoklazlar baskın olarak normal zonlanma gösterirken, Cecilia İntrüzyonu’nda plajiyoklaz kristallerinde osilasyonlu ve yer yer ters zonlanmalar ile birlikte elek dokuları ve körfez yapıları izlenmektedir. Yapılan iki-piroksen jeotermobarometre hesaplamaları, Dee intrüzyonlarının yaklaşık 1030–1090 ℃ kristallenme sıcaklıkları ve 2,5–3,5 kbar basınç aralığı ile üst kabuk seviyelerinde görece sığ yerleşimine işaret etmektedir. Buna karşılık Cecilia İntrüzyonu, 1000–1170 ℃ aralığındaki kristallenme sıcaklıkları ve 4,5–6,5 kbar basınç değerleri ile orta–alt kabuk seviyelerinde daha derin bir sokuluma karşılık gelmektedir. Fe–Ti oksit barometresi sonuçları, her iki intrüzyonun da oksitleyici redoks koşulları altında kristallendiğini; Cecilia İntrüzyonu’nun Dee’ye kıyasla daha yüksek oksijen fugasitesi değerleri sergilediğini göstermektedir. Saha, petrografi ve mineral kimyası verileri birlikte değerlendirildiğinde, Dee ve Cecilia intrüzyonlarının Güney Shetland Yayı boyunca gelişen mafik magmatizmanın kabukta farklı seviyelere yerleşmiş olan üyelerini temsil ettikleri görülmektedir. İleride yapılacak olan yaşlandırma çalışmaları ile bu mafik intrüzyonların kabuk içerisindeki evriminin bölge tektonizması ile ilişkisinin araştırılması mümkün olabilecektir.

Anahtar Kelimeler

• Güney Shetland Adaları
• Gabro
• Petrografi
• Mineral Kimyası
• Jeotermobarometre

Destekleyen Kurum

TÜBİTAK

Proje Numarası

125Y065

Teşekkür

Bu çalışma T.C. Cumhurbaşkanlığı himayelerinde, Sanayi ve Teknoloji Bakanlığı uhdesinde, TÜBİTAK MAM KARE’nin koordinasyonunda TAE VIII. bünyesinde gerçekleştirilmiştir. Çalışmada elde edilen veriler yazarın yürütücülüğünü yaptığı 125Y065 numaralı TÜBİTAK projesi kapsamında üretilmiştir. Mineral kimyası çalışmaları sırasındaki destekleri sebebiyle sayın İbrahim Uysal ve Dirk Mueller’e teşekkürlerini sunmaktayım. Özellikle örnek hazırlama esnasındaki yardımları için Gökçenur Bayram ve Nisa Nur Sevinç’e de destekleri için teşekkür ederim. Bununla beraber, bu çalışma sırasında faydalı bilimsel fikir alışverişi ve desteği nedeniyle sayın Şafak Altunkaynak’a minnetlerimi sunarım.

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