Geochemical Characteristics of the Pan-African Basement Rocks at Atud Area, Central Eastern Desert, Egypt

Year 2022, , 944 - 962, 31.08.2022

Demet Kıran Yıldırım , Amr Abdelnasser

https://doi.org/10.35414/akufemubid.1111229

Abstract

This paper reports the geochemical characteristics of the Precambrian Pan-African basement rocks of the Atud area (Central Eastern Desert of Egypt) to clarify their geological setting, field relationships, and petrographic and geochemical characteristics to define their tectonic setting and petrogenesis. The Atud area is made up of serpertinites and their derivatives and metatuffs that intruded by metagabbro-diorite complex and later intruded by olivine gabbronorite rocks. The serpentinites, talc-carbonate, and calc-silicate rocks refer to be metamorphic peridotites. Their rare earth elements (REE) behavior is characterized by enrichment in LREE and flat HREE with positive Eu-anomaly. This suggests to the oceanic serpentinization in nature occurred with the plagioclase circulation/dissolution of the hydrothermal fluids. The metatuffs were mostly derived from basic to intermediate magmatic suites pointing to have highest K/Rb ratio. They are, therefore, similar to the metasediments of the oceanic island arc having tholeiitic to calc-alkaline affinities and negative Eu-anomalies, HREE-depleted, and LREE-enriched patterns. Moreover, their source rocks originated from a magma contaminated by components added to the mantle source along the subduction zone that is back to their negative Eu-, Sr-, and Zr- anomalies. The metagabbro-diorite complex rocks show calc-alkaline gabbro and gabbro/diorite and diorite and gabbro/diorite, respectively. They are comparable with the calc-alkaline basalt (CAB) occurred in island arc setting indicating clinopyroxene and amphibole fractionation for the metagabbros and diorites, respectively. On the other hand, the olivine gabbronorite rocks are low-K tholeiitic gabbroic rocks having enrichment in the LREE and flat HREE. In addition, their REE pattern show negative anomalies of P and Ti and positive anomalies of Eu, Pb, Sr, Th, and Zr. It concluded that the gabbronorite rocks display low-pressure fractionation of olivine and plagioclase.

Keywords

Geochemical Characteristics, Atud Area, Central Eastern Desert, Egypt

Atud (Mısır) Bölgesi’nde Bulunan Pan-African Temel Kayaçlarının Jeokimyasal Karakteristikleri

Abstract

Bu çalışmada, Atud bölgesi’ndeki (Mısır'ın Orta Doğu Çölü) Prekambriyen Pan-Afrikan temel kayaçlarının jeolojik yerleşimlerini, jeokimyasal özelliklerini, saha ilişkilerini, tektonik yerleşimlerini ve petrojenezlerini belirlemek için petrografik ve jeokimyasal özellikleri ortaya konulmuştur. Atud Bölgesi’nde serpantinitler, bunların türevleri ve metatüfler, metagabro-diyorit kompleksi tarafından kesilmektedir. Metagabro-diyorit kompleksi ise olivin gabronoritik kayaçlar tarafından kesilmektedir. Serpantinitler, talk-karbonat ve kalk-silikat kayaçları metamorfik peridotitler olarak adlandırılmıştır. Nadir toprak elementleri (NTE) davranışları, HNTE ve pozitif Eu-anomalisi ile ANTE zenginleşmeleri ile karakterize edilir. Bu durum, hidrotermal akışkanların plajiyoklaz çözünmesi ve/veya sirkülasyonu ile doğada meydana gelen okyanus serpantinleşmesine işaret etmektedir. Metatüfler çoğunlukla en yüksek K/Rb oranına sahip olan bazik ile ortaç dereceli magma odalarından türetilmiştir. NTE paternleri, HNTE açısından zenginleşmiş, ANTE'den yoksun ve negatif Eu anomalilerine sahip genelde toleyitik ve kalk-alkalin kayaçlarla okyanus ada yayının metasedimentlerine benzemektedir. Ayrıca, dalma-batma zonu boyunca manto kaynağına eklenen bileşenler tarafından kirlenmiş bir magmadan kaynak kayaçlarının oluştuğunu ifade etmektedir, yani negatif Eu-, Sr- ve Zr- anomalileri göstermektedir. Metagabro-diyorit kompleksi kayaçlarının sırasıyla kalk-alkalin gabro ve gabro/diyorit ve diyorit ve gabro/diyorit olduğunu ortaya koymaktadır. Bu kayaçlar, sırasıyla metagabrolar ve diyoritler için klinopiroksen ve amfibol fraksiyonasyonuna işaret eden ada yayı ortamlarında meydana gelen kalk-alkali bazalt (CAB) ile karşılaştırılabilir. Öte yandan, olivin gabronorit kayaçları, K toleyitik magmatik afinitelere sahip gabroik kayaçlar olarak sınıflandırılır. NTE paternleri, HNTE ile zenginleşmeyi ve pozitif Eu-, Th-, Pb-, Sr- ve Zr-anomalileri ve plajiyoklaz ve olivin düşük basınçlı fraksiyonasyonunu ima eden negatif P- ve Ti-anomalileri ile ANTE açısından tüketilmeyi ortaya koymaktadır.

Keywords

Jeokimyasal Özellikler, Atud Bölgesi, Orta Doğu Çölü, Mısır

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