Arid
DOI10.1016/j.lithos.2014.01.006
Banded iron formations of Urn Nar, Eastern Desert of Egypt: P-T-X conditions of metamorphism and tectonic implications
El-Shazly, A. K.1; Khalil, K. I.2
通讯作者El-Shazly, A. K.
来源期刊LITHOS
ISSN0024-4937
EISSN1872-6143
出版年2014
卷号196页码:356-375
英文摘要

Banded iron formations (BIF) in Um Nar, central eastern desert of Egypt, occur intercalated with schists of volcaniclastic and epiclastic origins within "ophiolitic-island arc rocks" of the Arabo-Nubian Shield. The BIF and its host rocks were affected by folding, thrusting, and regional metamorphism during the Pan-African Orogeny resulting in the development of north-verging overturned folds and E-W striking, S-dipping thrusts. Following the intrusion of granitoids, the entire sequence was refolded into south-plunging folds with NW-SE trending fold axes. Peak mineral assemblages of hornblende + plagioclase, and garnet + biotite + plagioclase + quartz in the host rocks, and andradite-rich garnet + epidote + hematite + magnetite + quartz in the BIF indicate metamorphism under epidote amphibolite facies conditions. Using the multiequilibrium approach of Thermocalc, and conventional thermobarometry, peak P-T conditions of metamorphism are estimated at 520 +/- 30 degrees C, 5 +/- 2 kbar. Fluids attending peak conditions in the oxide facies layers of the BIF were characterized by XCO2 similar to 0.03 and log fO(2) similar to -40. Textural and mineral chemical criteria suggest that, following peak conditions, the rocks underwent a stage of near-isobaric cooling or cooling and compression characteristic of a counter-clockwise P-T path.


These results are consistent with a model in which the BIFs formed by hydrothermal activity from off-axis submarine vents in several pulses during a protracted event of oceanic crust generation in an inter-arc basin. Concomitant arc volcanism supplied the basin with pyroclastic material that imposed suboxic conditions on the basin leading to increased concentrations of soluble Fe2+. During periods of arc quiescence, Fe2+ was likely oxidized, leading to deposition of several layers of BIF. During the Pan-African Orogeny, the BIFs, tuffs, oceanic crust and lithospheric mantle were deformed and metamorphosed while being emplaced onto the continental margin. (C) 2014 Elsevier B.V. All rights reserved.


英文关键词Banded iron formation Central Eastern Desert of Egypt Epidote amphibolite facies metamorphism Thermobarometry Fluid composition Tectonic evolution
类型Article
语种英语
国家USA ; Egypt
收录类别SCI-E
WOS记录号WOS:000336347800023
WOS关键词ARABIAN-NUBIAN SHIELD ; CORE COMPLEX ; NEOPROTEROZOIC TECTONICS ; CRUSTAL EVOLUTION ; GEOCHEMISTRY ; CONSTRAINTS ; BIF ; GEOTHERMOMETRY ; ASSEMBLAGES ; SPREADSHEET
WOS类目Geochemistry & Geophysics ; Mineralogy
WOS研究方向Geochemistry & Geophysics ; Mineralogy
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/183798
作者单位1.Marshall Univ, Dept Geol, Huntington, WV 25755 USA;
2.Univ Alexandria, Fac Sci, Dept Geol, Moharram Bey, Egypt
推荐引用方式
GB/T 7714
El-Shazly, A. K.,Khalil, K. I.. Banded iron formations of Urn Nar, Eastern Desert of Egypt: P-T-X conditions of metamorphism and tectonic implications[J],2014,196:356-375.
APA El-Shazly, A. K.,&Khalil, K. I..(2014).Banded iron formations of Urn Nar, Eastern Desert of Egypt: P-T-X conditions of metamorphism and tectonic implications.LITHOS,196,356-375.
MLA El-Shazly, A. K.,et al."Banded iron formations of Urn Nar, Eastern Desert of Egypt: P-T-X conditions of metamorphism and tectonic implications".LITHOS 196(2014):356-375.
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