Trace-element and isotopic characteristics of spinel peridotite xenoliths from Saudi Arabia

Clinopyroxenes separated from peridotite xenoliths from five localities in western Saudi Arabia (Al-Birk, Al-Kishb, Ithnayn, Uwayrid and Hutaymah) show large trace-element variations, for example, Sr ranges from 7 to 1040 ppm, Ti from 190 to 3800 ppm and Zr from 3 to 160 ppm. REE patterns range from LREE-depleted (IA group) to LREE-enriched (IB group). Type-IA samples have (Ce/Yb)n of 0.1–0.9, and tend to have higher Ti content, higher 143Nd144Nd (up to 0.51361) and lower 87Sr86Sr (down to 0.7021) than type-IB samples. Both type-IA and -IB xenoliths occur at each locality, regardless of the distance from the Red Sea rift. Geochemical data suggest that western Saudi Arabia is underlain by a long-term depleted mantle with characteristics indicating multi-event melting processes. Due to two-stage interaction with a mantle plume this depleted mantle was modified to different extent. The first stage took place sometime in the Proterozoic when the plume reached the base of the lithosphere, the second stage occurred during Red Sea rift formation.