Dokhan volcanics of Gabal Monqul area,North Eastern Desert,Egypt: geochemistry and petrogenesis |
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| Authors: | Adel A A Abdel Wahed Khaled G Ali Magdy M A Khalil Ahmed E Abdel Gawad |
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| Institution: | (1) Nuclear Materials Authority, P.O. Box 530, Maadi, Cairo, Egypt;(2) Faculty of Science, Damietta Branch, Mansoura University, Mansoura, Egypt; |
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| Abstract: | The Dokhan volcanics are represented by a thick stratified lava flows succession of basalt, andesite, imperial porphyry, dacite,
rhyodacite, rhyolite, ignimbrites, and tuffs. These lavas are interbanded with their pyroclastics in some places including
banded ash flow tuffs, lithic tuffs, crystal lapilli tuffs, and agglomerates. They are typical calc–alkaline and developed
within volcanic arc environment. All rocks show moderate enrichment of most large ion lithophile elements relative to high
field strength elements (HFSE). The incompatible trace elements increase from basalt through andesite to rhyolite. The felsic
volcanics are characterized by moderate total rare earth elements (REE) contents (162 to 392 ppm), less fractionated patterns
{(Ce/Yb)N = (1.24 to 10.93)}, and large negative Eu anomaly {(Eu/Eu*) = (0.15 to 0.92)}. The mafic volcanics have the lowest REE contents
(61 to 192 ppm) and are relatively steep {(Ce/Yb)N = (3.2 to 8.5)}, with no negative Eu anomalies {(Eu/Eu*) = (0.88 to 1)}. The rhyolite displays larger negative Eu anomaly
(Eu/Eu* = 0.28) than those of other varieties, indicating that the plagioclase was an early major fractionating phase. The
mineralogical and chemical variations within volcanics are consistent with their evolution by fractional crystallization of
plagioclase and clinopyroxene. |
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