Petrochemical and Geochemical Characteristics of the Dokhan Formation at the Type Locality, Jabal Dokhan, Eastern Desert, Egypt

Basta, E. Z.; Kotb, H.; Awadallah, M.F.

doi:10.1016/b978-0-08-024479-2.50014-6

Cited by 42 publications

(23 citation statements)

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“…The different models are dicussed as follows: 1. Based on the geochemical characteristics, Basta et al (1980), Ragab (1987), El Gaby et al (1989), and Abdel Rahman (1996) show that the Dokhan volcanics are calc-alkaline in nature and their trace element and REE contents resemble those of arcrelated orogenic suites and thus they were erupted during the final stages of active subduction beneath the Eastern Desert of Egypt. However, the younger granite intrusions in eastern Egypt are massive and undeformed postorogenic granitoids with typical Atype characteristics (Stern and Gottfried 1986;Sylvester 1989;Hassanen 1997;Moghazi 1999;Mohamed et al 1999).…”

Section: Tectonic Settingmentioning

confidence: 98%

“…Compared with the different types of volcanic rocks in eastern Egypt, Fig. 4 shows the fields of ophiolitic metavolcanics, island arc metavolcanics, and Dokhan volcanics, constructed based on data from Basta et al (1980), Stern (1981), Stern and Gottfried (1986), Moghazi (1994), andAbdel Rahman (1996). Geochemical variances on Fig.…”

Section: Chemical Characteristicsmentioning

confidence: 99%

“…The term "Dokhan volcanics" refers to varicolored thick sequence of lava flows and pyroclastics of predominantly andesitic to rhyodacitic composition in association with ignimbritic rhyolites (Gindy and Mohamed 1971;Basta et al 1980;Heikal et al 1980;Stern and Gottfried 1986;Abdel Rahman 1996). Although many geochemical studies have been done on the Dokhan volcanics, no consensus has been achieved regarding the tectonic setting for the genesis of their magmas.…”

Section: Introductionmentioning

confidence: 99%

“…Although many geochemical studies have been done on the Dokhan volcanics, no consensus has been achieved regarding the tectonic setting for the genesis of their magmas. They were interpreted by Basta et al (1980) as active continental margin volcanic rocks. Subsequent studies (Ragab 1987;El Gaby et al 1989Abdel Rahman 1996) show that the Dokhan volcanics were erupted during the final stages of active subduction beneath the Eastern Desert of Egypt.…”

Section: Introductionmentioning

confidence: 99%

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Geochemistry, petrogenesis and tectonic setting of late Neoproterozoic Dokhan-type volcanic rocks in the Fatira area, eastern Egypt

Mohamed¹,

Moghazi²,

Hassanen³

2000

International Journal of Earth Sciences

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The Neoproterozoic Dokhan volcanics of the Fatira area in eastern Egypt comprise two main rock suites: (a) an intermediate volcanic suite, consisting of basaltic andesite, andesite, dacite, and their associated pyroclastic rocks; and (b) a felsic volcanic suite composed of rhyolite and rhyolitic tuffs. The two suites display well-defined major and trace element trends and a continuum in composition with wide ranges in SiO 2 (54-76%), CaO (8.19-0.14%), MgO (6.96-0.04%), Sr (983-7 ppm), Zr (328-95 ppm), Cr (297-1 ppm), and Ni (72-1 ppm). They are enriched in LILEs (Rb, Ba, K, Th, Ce) relative to high field strength elements (Nb, Zr, P, Ti) and show strong affinity to calc-alkaline subduction-related rocks. However, their undeformed character, their emplacement temporally and spatially with post-orogenic A-type granite, and their high Zr/Y values suggest that their emplacement follow the cessation of subduction in eastern Egypt in an extensionalrelated within-plate setting. Major and trace element variations in the intermediate volcanics are consistent with their formation via partial melting of an enriched subcontinental lithospheric mantle source followed by a limited low-pressure fractional crystallization of olivine and pyroxene before emplacement. The LILE enrichment relative to HFSE is attributed to the inheritance of a subduction component from mantle material which constituted the mantle wedge during previous subduction events in eastern Egypt. The evolution of the whole volcanic spectrum was governed mainly by crystal/melt fractionation of amphibole, plagioclase, titanomagnetite, and apatite in the intermediate varieties and plagioclase, amphibole, biotite, Fe-Ti oxides, apatite, and zircon in the felsic varieties. At each stage of evolution, crystal fractionation was accompanied by variable degrees of crustal contamination.

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Section: Tectonic Settingmentioning

confidence: 98%

Section: Chemical Characteristicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geochemistry, petrogenesis and tectonic setting of late Neoproterozoic Dokhan-type volcanic rocks in the Fatira area, eastern Egypt

Mohamed¹,

Moghazi²,

Hassanen³

2000

International Journal of Earth Sciences

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“…Dokhan volcanic forms a successive sequence of acidic lava flows, ash tuffs, crystal lapilli tuffs and agglomerates. Many studies have been carried out on the petrography and geochemistry of the Dokhan volcanics, (Basta et al, (1980); Stern and Gottfried, (1986);El Gaby et al, (1989); Abdel Rahman, (1996); Mohamed et al, (2000); Eliwa, (2000); Moghazi, (2003); El Sayed et al, (2004) ; Eliwa et.al (2006) ; Khalaf (2010) and Alaabed and El Tokhi (2014).These authors show that the Dokhan volcanics have medium-to high-K calc-alkaline affinities. The geotectonic interpretation of the Dokhan volcanics is still controversial, especially whether they have been…”

Section: Introductionmentioning

confidence: 99%

Geology, Geochemistry and Radioactivity of Granitic and Volcanic Rocks at Hadarba Area, South Eastern Desert, Egypt

Shahin¹,

Masoud²,

Bayoumi³

2016

Int. Res. J. Geol. Min

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The present work deals with geology, geochemistry, radioactivity and tectonic environment of the granitic and volcanic rocks at Hadarba area, South Eastern Desert of Egypt. The granitic rocks comprise tonalite-granodiorite and monzogranite, while volcanic rocks include rhyolite, rhyodacite anddacite. These rocks are characterized by high concentrations of SiO2, Na2O, Fe2O3, K2O, Zr, Nb and Y but low in MgO, CaO, Cr, Ni, Sr, Ga and V. Field studies indicate that Dokhan volcanics extrude both tonalite-granodiorite and monzogranite with sharp contact forming a thick successive sequence of laminated acid lava flows, crystal lapilli tuffs and agglomerates. They range in composition from rhyolite, rhyodacite to dacite. Shear zone comprise lines-arranged intrusions trending NE-SW direction were recorded north Gabal Hadarba and extends for about 2.3 km in length with a width reaches up to 10 meter. These lines-arranged intrusions include quartz vein, microgranite and basic dykes. These shear zones cut through monzogranite. Petrochemical studies and tectonic discrimination diagrams for the monzogranite reveal that it is classified as granite developed in the within-plate tectonic environment, while Dokhan volcanics are classified as rhyolite and dacite developed in the immature island arcs and active continental margin environments.Field radiometric measurements of these granitic and volcanic rocks reveal low uranium and thorium contents. Uranium contents range from 1.2 to 2.7 ppm in the tonalite-granodiorite, from 1.1 to 8.5 ppm in the monzogranite, from 1.3 to 9.3 ppm in the Dokhan volcanic and from 1.4 ppm to 15.4 ppm in the felsite dyke.

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Late Pan‐African Magmatism and Crustal Development In Northeastern Egypt: Reply

Abdel‐Rahman

Martin

1989

Geological Journal

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Some of our interpretations on the nature of Pan-African magmatism and crustal development in northeastern Egypt (Abdel-Rahman and Martin 1987) have been challenged by Stern and Gottfried (1989), and we welcome this opportunity to respond to the three points raised.Point 1: a wide variety of <600 Ma igneous and sedimentary rocks occur in northeastern Egypt. Instead of reviewing the literature in an encyclopedic way, we deliberately (according to Stern and Gottfried) ignored evidence to make our point. Our interpretations concerning the tectonic setting of the area were based largely, but not exclusively, on a study of the Ras Gharib composite batholith (700 km2, 552 Ma). Information on this pluton was supplemented by data on other granitic complexes exposed in the same area and emplaced between 596 and 565 Ma (e.g. Fawakhir, Mons Claudianus, Abu-Kharif, Qena-Safaga, and Wadi Endiya,Figures 9 and 11 of our paper). Thus we do not consider our data base to be restricted, as claimed. On the contrary, the study area is considered quite representative of the crust of northeastern Egypt, where granitic rocks represent the major component (more than 70 per cent: Schurmann 1966).Points 2 and 3: geochemical data for <600 Ma igneous suites indicate the presecce of 'A-type' melts that formed in an extensional setting; active subduction younger than 600 Ma is inconsistent with accepted tectonic reconstructions. In fact, ours is not an iconoclastic interpretation, as almost all investigators of Late Proterozoic magmatism in the Arabian-Nubian Shield have concluded that Andean-type calc-alkaline magmas were involved in the period 600-550 Ma (cJ references quoted in Abdel-Rahman and Martin 1987, and those mentioned below). Hussein er al. (1982) proposed that most of the 'Younger' or 'Gattarian'granites of Egypt are subduction-related and of I type.As the example that was the focus of our investigation does not conform to the expected profile of an 'A-type complex', Stern and Gottfried suggested that it must therefore be older than 600 Ma, with its Rb-Sr system reset as a result of an indeterminate thermal event. The wide range of Rb/ Sr values and the relative absence of scatter along the %point isochron (Abdel-Rahman and Doig 1987), the agreement between our age and the K-Ar age of 550 Ma reported by Schurmann (1966), and the lack of evidence of thermal resetting, for example in the structural state of the K-feldspar in these rocks (Abdel-Rahman 1986), suggest to us that 552 Ma does represent the approximate age of crystallization of the pluton.The parallelism between <600 Ma magmatism in the Gharib block and in the Sinai Peninsula and Saudi Arabia is considered striking. Bielski (198 1) documented intensive calc-alkaline plutonism in the Sinai Peninsula between 600 and 580 Ma. Halpern and Tristan (1981) established ages between 588 and 552 Ma for several monzonite and calc-alkaline granitic complexes from the Sinai Peninsula. Segev (1987) showed that rhyodacitic rocks there (633-548 Ma) belong to the orogenic stage, whereas ...

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Petrochemical and Geochemical Characteristics of the Dokhan Formation at the Type Locality, Jabal Dokhan, Eastern Desert, Egypt

Cited by 42 publications

References 14 publications

Geochemistry, petrogenesis and tectonic setting of late Neoproterozoic Dokhan-type volcanic rocks in the Fatira area, eastern Egypt

Geochemistry, petrogenesis and tectonic setting of late Neoproterozoic Dokhan-type volcanic rocks in the Fatira area, eastern Egypt

Geology, Geochemistry and Radioactivity of Granitic and Volcanic Rocks at Hadarba Area, South Eastern Desert, Egypt

Late Pan‐African Magmatism and Crustal Development In Northeastern Egypt: Reply

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