Harrats Volcanic Activity and Evolution of the Lithosphere-Asthenosphere Boundary beneath Western Saudi Arabia

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This project looks at the causes of volcanic activity within an enigmatic region of the Arabian Peninsula in Saudi Arabia. This region, known as the Makkah-Madinah-Nafud line (MMN) is a series of small to moderate size volcanic fields (known as 'harrats') that extend north from the Read Sea in Saudi Arabia, Jordan and Syria. Volcanism in this region has occurred in Neogene to recent times, with the oldest activity occurring starting more than 10 million years ago and the youngest occurred in 1256 (an eruption that threatened the culturally important city of Madinah. This project seeks to investigate the ultimate causes of the magmatic activity that lead to volcanism by use of geochronological, geochemical and petrological studies of erupted lavas. The team is specifically interested in the role of the continental lithosphere (the upper rigid portion of the mantle that directly underlies the crust) and asthenosphere (the underlying hotter portion of the mantle that convects) in producing erupted magmas and how these two regions might vary through time and space. The results of the study will have important implications for the tectonic development of this region and for the hazards represented by volcanic activity.The Saudi Arabian harrats are extensive Neogene to recent continental volcanic fields located in western portion of the Arabian Peninsula. Although most workers agree that Harrat volcanism is related to extension and sea floor spreading in the Red Sea in some way, the actual causes of magmatism remain uncertain. The key issues that this team will address via the study of selected harrats are: (i) the role of asthenosphere vs. lithosphere in the production of continental magmas; (ii) whether systematic changes in the depth and extent of melting occur in space and time, and the relation of these changes to geodynamic setting; and (iii) the potential role of mantle plume material in harrat volcanism. Little modern geochemical, petrological or geochronological study has been made of these areas. Thus their primary focus is to obtain 40Ar-39Ar ages, major and trace element concentrations, Sr-Nd-Pb-He isotope compositions and data for melt inclusions for well dated and representative samples suites from selected harrats that represent a ESE-WNW traverse across the north-south trending Makkah-Madinah-Nafud (MMN) volcanic line. They will also use a range of geochemical modeling techniques to investigate the conditions and sources of magmas along their traverse, and to study temporal changes in melting processes. The researchers' ultimate goal is to provide data that can allow harrat volcanism to be better understood in terms of broader geodynamic evolution of the Afro-Arabian region.