Abstract
Problem statement: Al-Harida volcano is located in the Jordanian parts of the Harrat Al-Shaam plateau and contains considerable amounts of mantle xenoliths within its pyroclastic successions. Approach: These xenoliths are reported for the first time for this area. Mineralogical investigations show that they are composed of olivine, orthopyroxene, clinopyroxene, spinel and phlogopite. Results: The xenoliths range in size from 5-30 cm with an average of 10 cm. They are classified as Type I and belong to the Cr-diopside group and are characterized by high contents of MgO, Cr and Ni. The occurrence of hydrous mineral phases and the enrichment of incompatible elements such as Sr, Rb and Ba indicate a considerable mantle metasomatism. Conclusion/Recommendations: Thermobarometry of the studied xenoliths indicates a temperature ranging from 960-1040°C and pressure ranging from 11-13 Kbar which corresponds to a depth of origin of about 43 km.
Highlights
The term metasomatism usually refers to a solidstate transformation without or only marginal melting[1]
Metasomatic xenoliths are mostly found in host magmas of mantle origin that are enriched in incompatible elements[2] and other magmas like highly potassic mafic volcanic[3]; basanites and alkali olivine basalts[4]
In the last three decades, mantle metasomatism has been increasingly recognized as an important process[5,6,7]
Summary
The term metasomatism usually refers to a solidstate transformation without or only marginal melting[1]. Spinel lherzolite is considered to form the major part of the upper mantle[15,16] occurring at depths of 4060 km[17,18]. The existence of such xenoliths offers a direct insight into the lithosphere and the asthenosphere. The Harrat AlShaam (or Ash shaam) covers an area of 45 000 km and is the most northwestern basalt plateau of the Arabian plate. This plateau extends from Syria to Saudi.
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