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The Tethyan plume: geochemical diversity of Middle Permian basalts from the Oman rifted margin |
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| Authors: | H Lapierre A Samper D Bosch R C Maury F Bchennec J Cotten A Demant P Brunet F Keller J Marcoux |
| Institution: | a Laboratoire Géodynamique des Chaînes Alpines, UMR-CNRS 5025, Université Joseoh Fourier, Géosciences, B.P. 53, 15 rue Gignoux, 38041, Grenoble cedex, France b Laboratoire de Tectonophysique, UMR-CNRS 5568, Institut des Sciences de la Terre, de l'Eau et de l'Espace de Montpellier, Université Montpellier 2, Place E. Bataillon, 34095, Montpellier cedex, 05, France c Laboratoire Domaines Océaniques, UMR-CNRS 6538, Université de Bretagne Occidentale, Place Nicolas Copernic, 29280, Plouzané, France d Bureau de Recherches Géologiques et Minières, SGR Pays de Loire, B.P. 92342, 44323, Nantes cedex 3, France e Laboratoire de Pétrologie Magmatique, Faculté des Sciences de St Jérôme, Université Aix-Marseille III, CC 441, 13397, Marseille cedex 20, France f Laboratoire Mécanismes de Transfert en Géologie, UMR-CNRS 5563, Université P. Sabatier, 38 rue des trente-six ponts, 31400, Toulouse, France g UMR-CNRS 7578, Institut de Physique du Globe de Paris, Université Paris VII, 4 Place Jussieu, 75252, Paris, France |
| Abstract: | According to palinspastic reconstructions, the Neo-Tethys opening took place during the Permian between the Cimmerian fragments in the north and the Indo-Arabian margin in the south. Igneous remnants of this opening are exposed in Oman within either the Hawasina nappes or the para-autochtonous Arabian platform exposed in the Saih Hatat tectonic window. They consist predominantly of pillowed basaltic flows among which three groups have been distinguished. Group 1 is tholeiitic and characterized by low TiO2 and incompatible trace element contents, and a large range of  Ndi values. Group 1 basalts are associated with distal sediments and plot near the boundary of or within the MORB field in the Pb–Pb correlation diagrams and between the MORB and Bulk Silica Earth (BSE) fields in Ndi–(206Pb/204Pb)i diagram. Group 2 basalts are alkaline and differ from Group 1 ones by their higher TiO2, La and Nb contents, and lower and more homogeneous Ndi values (+3 to +5). Group 2 volcanics are similar to alkali basalts from oceanic islands and share with Group 1 similar initial Pb ratios. Group 3 consists of tholeiitic and alkali basalts which are interbedded either with carbonate-platform sediments from the Saih Hatat window or with distal sediments from the Hawasina Nappes. This group differs from Groups 1 and 2 by its low to negative Ndi (+1.6 to ?2). Group 1 likely derived from the mixing of depleted and enriched sources while Group 2 derived exclusively from an enriched source. There is no indication that continental crust was involved in the genesis of both Groups 1 and 2. In contrast, the low to negative Ndi values of Group 3 suggest that the magmas of this group were contaminated by the Arabian continental crust during their ascent. The geochemical features of the Middle Permian plume-related basalts suggest thus that the basement of the Hawasina basin was not genuine oceanic crust but either the thinned Arabian rifted continental margin or the continent–ocean transition zone of the Neo-Tethys. |
| Keywords: | Plume-related basalts Middle Permian Neo-Tethys Arabian rifted margin Hawasina Nappes Oman Isotopic chemistry |
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