Neoproterozoic zirconium-depleted boninite and tholeiitic series rocks from Adola, southern Ethiopia

Wolde, Begashaw; Asres, Zemene; Desta, Zerihun; Gonzalez, J.J.

doi:10.1016/s0301-9268(96)00018-6

Cited by 33 publications

(11 citation statements)

References 21 publications

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“…The abundance of immature and volcaniclastic sediments deposited on top of the ophiolites suggests formation at an intraoceanic convergent margin, either in a back-arc basin or a forearc during subduction initiation. Magmas with boninitic affinities are reported from the Neoproterozoic ANS (Wolde et al 1993;Yibas et al 2003;Katz et al 2004;Teklay 2006). Because Phanerozoic boninites appear to be restricted to a forearc setting (e.g., Hawkins et al 1984;Murton 1989;Johnson and Fryer 1990;Stern and Bloomer 1992;Bé dard 1999;Beccaluva et al 2004), it can be inferred that boninites in the ANS also formed in a forearc.…”

Section: Discussion: Tectonic Setting Of Formation Of Eastern Desert mentioning

confidence: 99%

Neoproterozoic (835–720 Ma) Serpentinites in the Eastern Desert, Egypt: Fragments of Forearc Mantle

Azer¹,

Stern²

2007

The Journal of Geology

142

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Most Neoproterozoic ophiolites of the Arabian-Nubian Shield show compositions consistent with formation in a suprasubduction zone environment, but it has not been clear whether this was in a forearc or back-arc setting. Ophiolitic serpentinites are common in the Eastern Desert of Egypt, but their composition and significance are not well understood. Here we report new petrographic, mineral, chemical, and whole-rock compositional data for serpentinites from Wadi Semna, the northernmost ophiolitic serpentinites in the Eastern Desert, and use these to provide insights into the significance of other Eastern Desert serpentinite locales. The Wadi Semna serpentinites are composed essentially of antigorite, chrysotile, and lizardite, with minor carbonate, chromite, magnetite, magnesite, and chlorite, and they were tectonically emplaced. The alteration of chrome spinel to ferritchromite was accompanied by the formation of chloritic aureoles due to the release of Al from spinel. Major-element compositions indicate that, except for the addition of water, the serpentinites have not experienced extensive element mobility; these were originally CaO-and Al 2 O 3-depleted harzburgites similar to peridotites from modern oceanic forearcs. High Cr# () Cr/(Cr ϩ Al) in the relict spinels () indicates that these are residual after extensive partial melting, similar to spinels average p 0.69 in modern forearc peridotites. These characteristics of Wadi Semna serpentinites also typify 22 other Eastern Desert serpentinite localities. We infer that Eastern Desert ophiolitic serpentinites, except perhaps Gebel Gerf, originated by forearc seafloor spreading during subduction initiation associated with the closing of the Neoproterozoic Mozambique Ocean.

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Section: Discussion: Tectonic Setting Of Formation Of Eastern Desert mentioning

confidence: 99%

Neoproterozoic (835–720 Ma) Serpentinites in the Eastern Desert, Egypt: Fragments of Forearc Mantle

Azer¹,

Stern²

2007

The Journal of Geology

142

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“…1). Geochemical studies on magmatic rocks from the Adola and Moyale areas have reported that low-K tholeiitic basalts to basaltic-andesites and calc-alkaline granitoids, which formed in island-arc setting, dominate these areas (Gichile, 1991;Gichile and Fyson, 1993;Worku, 1996;Wolde et al, 1996;Hussien, 1999;Yibas et al, 2000). Zr-depleted boninite and transitional MORB were reported to have occurred interspersed within the tholeiitic rocks of Adola and Moyale areas of southern Ethiopia (Worku, 1996;Wolde et al, 1996 and references therein;Yibas et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

Geochemistry of the Neoproterozoic metabasic rocks from the Negele area, southern Ethiopia: Tectonomagmatic implications

Yihunie

Adachi

Yamamoto

2006

Journal of African Earth Sciences

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“…They reflect deformational styles and tectonic features in the basement during the subduction/accretion processes between terranes of the East African Orogen in the Neoproterozoic (Gichile 1991;Wolde et al 1996;Worku 1996).…”

Section: Discussionmentioning

confidence: 96%

“…The Lower and Middle Complexes comprise high-grade gneisses, granitic migmatite, pelitic schist and associated granulites and are regarded to form northern extremities of the Mozambique Belt in southern Ethiopia (Kazmin et al 1978;de Wit and Chewaka 1981;Gichile 1991;Worku 1996). The Upper Complex consists of island arc associations and ophiolitic sequences that form southward terminated low-grade belts in the Precambrian basement of southern Ethiopia (Kazmin 1976;Wolde et al 1996;Worku 1996). These rocks are thought to represent southern extensions of arc/back-arc sequences of the Arabian-Nubian Shield (Kazmin 1976;de Wit and Chewaka 1981;Berhe 1990;Gichile 1991;Worku 1996).…”

Section: Regional Geologymentioning

confidence: 99%

Pan-African deformations in the basement of the Negele area, southern Ethiopia

Yihunie

2002

International Journal of Earth Sciences

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Polydeformed and metamorphosed Neoproterozoic rocks of the East African Orogen in the Negele area constituted three lithostructurally distinct and thrustbounded terranes. These are, from west to east, the Kenticha, Alghe and Bulbul terranes. The Kenticha and Bulbul terranes are metavolcano-sedimentary and ultramafic sequences, representing parts of the Arabian-Nubian Shield (ANS), which are welded to the central Alghe gneissic terrane of the Mozambique Belt affinity along N-S-trending sheared thrust contacts. Structural data suggest that the Negele basement had evolved through three phases of deformation. During D1 (folding) deformation, north-south upright and inclined folds with north-trending axes were developed. East and west-verging thrusts, right-lateral shearing along the north-oriented Kenticha and Bulbul thrust contacts and related structural elements were developed during D2 (thrusting) deformation. The pervasive D1 event is interpreted to have occurred at 620-610 Ma and the D2 event ended prior to 554 Ma. Right-lateral strikeslips along thrust contacts are interpreted to have been initiated during late D2. During D3, left-lateral strike-slip along the Wadera Shear Zone and respective strike-slip movements along conjugate set of shear zones were developed in the Alghe terrane, and are interpreted to have occurred later than 557 Ma. The structural data suggest that eastward thrusting of the Kenticha and westward tectonic transport of the Bulbul sequences over the Alghe gneissic terrane of the Mozambique Belt, during D2, were accompanied by right-lateral strike-slip displacements along thrust contacts. Right-lateral strike-slip movements along the Kenticha thrust contact, further suggest northward movement of the Kenticha sequence during the Pan-African orogeny in the Neoproterozoic. Left-lateral strike-slip along the orogen-parallel NNE-SSW Wadera Shear Zone and strike-slip movements along a conjugate set of shear zones completed final terrane amalgamation between the Arabian-Nubian Shield and the Mozambique Belt in Neoproterozoic southern Ethiopia.

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Neoproterozoic zirconium-depleted boninite and tholeiitic series rocks from Adola, southern Ethiopia

Cited by 33 publications

References 21 publications

Neoproterozoic (835–720 Ma) Serpentinites in the Eastern Desert, Egypt: Fragments of Forearc Mantle

Neoproterozoic (835–720 Ma) Serpentinites in the Eastern Desert, Egypt: Fragments of Forearc Mantle

Geochemistry of the Neoproterozoic metabasic rocks from the Negele area, southern Ethiopia: Tectonomagmatic implications

Pan-African deformations in the basement of the Negele area, southern Ethiopia

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