ABSTRACT

Arid Arabia, where chemical weathering and anthropic modifications are negligible, is a huge natural laboratory for the study of sediment provenance. Mafic and ultramafic detritus from ophiolite belts is found along the Oman Mountains and on Masirah Island ("obduction-orogen provenance"). Dominant cellular serpentinite grains from residual mantle harzburgites of the Sama'il ophiolite contrast with gabbroic, diabase, and basaltic grains from igneous crustal rocks of the Masirah ophiolite. Detritus from autochthonous basement and cover rocks is found along the Arabian Sea margin ("rift-shoulder provenance"). Transition from carbonate-dominated lithic sands ("undissected stage") to hornblende-rich plagioclase arkoses ("dissected stage") is best documented at the northern edge of the Gulf of Aden. Along the older, strike-slip Owen-basin margin, only locally are feldspars, hornblende, and garnet derived from small outcrops of Pan-African basement. Modern eolian sands from Yemen to the Arabian (Persian) Gulf display marked enrichment in quartz, low plagioclase/feldspar ratios, and depleted dense-mineral assemblages with rounded epidotes, hornblende, garnet, and ultrastables, pointing to extensive recycling also fostered by Quaternary changes. The Rub'-Al-Khali and Wahibah sand seas have distinct quartz/feldspar ratios, reflecting largely separate transport pathways. Dune fields, fed chiefly from rift highlands in the west and south, mix with orogenic detritus in the northeast. Carbonate-dominated sands in coastal UAE are mostly derived from the Zagros Mountains, blown by northerly Shamal winds across the Gulf during Pleistocene lowstands to reach the backbulge depozone and the foreland beyond. Contributions from the Oman Mountains reach only 5-10% of bulk sediment along their southern apron, and mostly indirectly through deflation of Plio-Pleistocene fans. The Sama'il ophiolite supplies enstatite and diopside to the eastern UAE and Wahibah sands; the Masirah ophiolite supplies amphiboles and clinopyroxenes locally along the Batain coast. The composition of desert sediments faithfully mirrors tectonic history of source terranes, deformation style during orogeny, and unroofing level during extension. Bulk petrography coupled with dense-mineral analysis thus represents a powerful tool to investigate not only provenance and sediment transport but also crustal dynamics and geologic evolution at continental scale.