Cr-poor megacrysts from the Shamah volcanic field, northwestern part of the Arabian Plate

Megacrysts are common in alkali basalt of Quaternary age in the northeastern Harrat Shamah basalt fields of Jordan. The dominant phases are Al-clinopyroxene, Al-bronzite, pleonaste spinel and kaersutite amphibole. The megacrysts differ in composition from analogous phases in associated lherzolite xenoliths, but are similar to those in associated Al-augite pyroxenite xenoliths. Major and trace element partioning indicates that most of the megacrysts may have been in equilibrium with their host magmas at high pressure.