Middle Permian plume-related volcanism of the Hawasina Nappes (Oman) and the Neo-Tethys opening
Abstract
According to palinspastic reconstructions, the Neo-Tethys opening took place during the Permian between the Cimmerian fragments in the north and the Indian-Arabian margin in the south. Igneous remnants of this opening are found nowdays in Oman where they belong mostly to the Hawasina nappes and consist of pillowed mafic flows interbedded with Middle Permian sediments. Three groups of rocks have been distinguished among the Middle Permian rocks from Oman which were emplaced either on the Arabian submerged platform or the neighbouring Hawasina basin. Group 1 is tholeiitic and characterized by low TiO_2 (< 1.5%) and incompatible (Th, La, Nb) trace element contents, and high ɛNdi values (+7.6 to +3.6). Group 1 volcanics are either (i) LREE-depleted, or (ii) with flat REE patterns or even (iii) slightly enriched in LREE. Group 1 plots at the boundary or within the MORB field in the Pb-Pb correlation diagrams and between the MORB and Bulk Silica Earth (BSE) fields in ɛNdi-(206Pb/204Pb)_i diagram. Group 2 is alkalic and differs from Group 1 by higher TiO_2, La and Nb contents, and lower and more homogeneous ɛNdi values (+3). Most of the Group 2 volcanics share with Group 1 similar initial Pb ratios.Group 3 differs from Groups 1 and 2 by low to negative ɛNdi (+1.6 to -2). It consists of tholeiitic (TiO_2-poor) and alkalic (TiO_2-rich) rocks which are either interbedded with carbonate-platform sediments from the Saih Hatat window or found with deep-sea sdiments from the Hawasina Nappes. Group 3 trace element chemistry is similar to that of Group 2. Thus, whatever the geological setting of the Oman Permian lavas, they belong to tholeiitic and alkalic magmas but differ by their Nd isotopic composition. A majority of the magmas emplaced in the Hawasina basin are characterized by ɛNd that fall within the range of OIB. In contrast, most of the volcanic rocks emplaced on the submerged Arabian platform and few samples from the Hawasina nappes have low to negative ɛNdi suggesting a contribution of continental crust.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....3713L