The petrology and geochemistry of the intraplate manwar volcanics, part of the Harrat Rahat, Saudi Arabia

Abstract EN

The centrally located Manwar volcanic chain is a recent addi¬tion to the c.

10 Ma old Harrat Rahat, a field of continental intraplate al- kalic volcanism generated contemporaneously with the opening of the Red Sea.

The volcanic chain consists mainly of scoria cones, domes and lava flows.

The lavas have compositions ranging from basalt through hawaiite, mugearite, and benmoreite to trachyte.

Basalts and hawaiite are either fine-grained or sparsely porphyritic.

The hawaiite shows weakly developed flow texture.

Mugearites are mainly aphyric and fine-grained with well-developed trachytic or fluidal flow tex¬ture.

Benmoreites are sparsely microporphyritic with well developed flui¬dal groundmass.

Trachytes are holocrystalline aphanitic lavas and display trachytic texture.

The Manwar lavas have alkalic character and show an alkalic differentia¬tion trend ranging from mugearite to benmoreite and trachyte.

The Harrat Rahat and Manwar lavas show broadly similar incompatible elements pat¬terns, suggesting a common source.

However, the Manwar benmoreite and trachyte display a stronger trough at Sr, P and Zr on the spider diagram and indicate a higher degree of fractionation.

The Manwar AOB (alkali olivine basalt) enriched in the incompatible elements relative to normal and en¬riched MORB (mid-oceanic ridge basalts) and is closely similar to other in¬traplate magmas.

Similarities between REE patterns of all Manwar mugearites suggest a common source as well as an analogous fractionation process.

The REE patterns are similar to other continental alkalic basalts provinces of Saudi Arabia and the Azores Islands.