کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4729421 | 1640261 | 2007 | 24 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
A-type volcanics in Central Eastern Sinai, Egypt
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موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
زمین شناسی
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
Alkaline rhyolitic and minor trachytic volcanics were erupted â¼580-530 Ma ago. They occur with their A-type intrusive equivalents in Sinai, southern Negev and southwestern Jordan. At Taba-Nuweiba district, these volcanics outcrop in three areas, namely, Wadi El-Mahash, Wadi Khileifiya and Gebel El-Homra. Mineralogically, they comprise alkali feldspars, iron-rich biotite and arfvedsonite together with rare ferro-eckermannite. Geochemically, the older rhyolitic volcanics are highly evolved, enriched in HFSE including REE and depleted in Ca, Mg, Sr and Eu. The rhyolitic rocks of Wadi El-Mahash and Gebel El-Homra are enriched in K2O content (5.3-10.1 wt.%) and depleted in Na2O content (0.08-2.97 wt.%), while the rhyolites of Wadi Khileifiya have normal contents of alkalis. Their REE patterns are uniform, parallel to subparallel, fractionated [(La/Yb)n = 5.4] and show prominent negative Eu-anomalies. They are classified as alkali rhyolites with minor comendites. The younger volcanics are classified as trachyandesite and quartz trachyte (56.6-62.9 wt.% SiO2). Both older and younger volcanics represent two separate magmatic suites. The overall mineralogical and chemical characteristics of these volcanics are consistent with within plate tectonic setting. It is suggested that partial melting of crustal rocks yielded the source magma. Lithospheric extension and crustal rupture occurred prior to the eruption of these volcanics. The rather thin continental crust (â¼35 km) as well as the continental upheaval and extensive erosion that preceded their emplacement favoured pressure release and increasing mantle contribution. The volatiles of the upper mantle were important agents for heat transfer, and sufficient for the anatexis of the crustal rocks. A petrogenetic hypothesis is proposed for the genesis of the recorded potassic and ultrapotassic rhyolitic rocks through the action of dissolved volatiles and their accumulation in the uppermost part of the magma chamber.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of African Earth Sciences - Volume 47, Issues 4â5, April 2007, Pages 203-226
Journal: Journal of African Earth Sciences - Volume 47, Issues 4â5, April 2007, Pages 203-226
نویسندگان
M.D. Samuel, H.E. Moussa, M.K. Azer,