Paper Number: 2616
Sr, Nd isotopes and geochemistry of the western Nuba Mountains low-grade metavolcanics (Sudan): New evidence for Neoproterozoic arc magmatism on the eastern Saharan Metacraton
Ibinoof M. A.12, Bumby A. J.2and Grantham G.H.3
1Department of Geology, Faculty of Petroleum and Minerals, University of Al Neelain, Sudan
2Department of Geology, Faculty of Natural and Agricultural Sciences, University of Pretoria, South Africa
3Department of Geology, Faculty of Sciences, University of Johannesburg, South Africa
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Pillowed metabasalt in the Nuba Mountains of Sudan has a geochemical signature of HFSE-depleted tholeiitic basalt. Associated meta-andesite has calc-alkaline LILE-enriched, HFSE depleted patterns characteristic of arc-derived magma, a well-developed negative Nb-Ta troughand a negative Zr-Hf trough, all of whichare features of subduction-related arc magmas. This arc magmatism occurred at 751±47 Ma (the age of eight points Sm – Ndiscochron), well within the age of arc magmatism in the ANS.
The pillowed basalt has a geochemical signature of HFSE-depleted tholeiitic basalt, and the meta-andesite has calc-alkaline large ion lithophile element (LILE)-enriched, high field strength element (HFSE) depleted patterns characteristic of arc-derived magma, a well-developed negative Nb-Ta troughand a negative Zr-Hf trough, all of whichare features of subduction-related arc magmas. This arc magmatism occurred at 751±47 Ma (the age of eight points Sm – Ndiscochron), well within the age of arc magmatism in the ANS.
All of the metavolcanics have a homogenous Sr – Nd isotope composition: initial 87Sr/86Sr (0.703872±0.00040) and εNd (5.4±1.2) at 751 Ma. Metamorphic, isotopic, geochronological and geographical distribution characteristics of these metavolcanics identify them as a low-grade juvenile Neoproterozoic terrane to the west of medium-grade gneisses of presumably the pre-Neoproterozoic SmC of south central Sudan. This terrane, named the Abutulu terrane, is proposed to have formed as a result of opening and closing of a marginal basin that developed on the medium grade gneisses of the SmC. Whether or not this terrane represents a new location for the eastern boundary of the SmC in central Sudan is dependent on the age and nature of the medium to high-grade gneisses between the Kabus suture and the Abutulu terrane and hence more geological and geochronological investigations are needed in that region.