Nature and Evolution of the Precambrian Lithosphere Beneath the Arabian Shield of Saudi Arabia Deduced from A Suite of Xenoliths from the Harrat Hutaymah Cenozoic Volcanic Field

摘要: Abstract Harrat Hutaymah is a Cenozoic small-volume volcanic field in the northeastern margin of Arabian Shield, Saudi Arabia. Mantle and lower-crustal xenoliths have been collected from various tuff ring maar deposits. Based on whole-rock mineral chemistry, there are two categories xenoliths: (1) fertile lherzolite moderately depleted harzburgite, (2) spinel-rich clinopyroxenite cumulates, lower crustal hornblendite, mid-crustal gabbro-diorite. The mantle peridotite high Mg# values (≥ 0.90), Fo NiO contents for olivines (91 0.37 wt% average), average clinopyroxene (0.93) orthopyroxene (0.92), low to intermediate Cr# spinels (0.1–0.4). show homogeneous unfractionated chondrite-normalized REE patterns, with slight enrichment LREE. compositional characteristics indicate that they came residual which experienced moderate degrees partial melting. estimated equilibration temperature peridotites 897 °C, corresponding an pressure 11 kbar, equivalent depth 37 km beneath relatively thin continental crust (~ 30 km) Shield. Clinopyroxenite (0.81), olivine (81), (0.85) (0.84), very (0.001). trace element compositions were cumulates formed early stage picritic melt within arc setting. P-T conditions cumulate gave 48 km, deeper below mantle-crust boundary. successive decrease bulk-rock (0.81) hornblendite (0.73) gabbro-diorite (0.44), LILE depletion HFSE characteristic negative Nb anomalies, La/Nb ratios, LREE suggests these rocks highly fractionated hydrous calc-alkaline parental subduction 6 kbar 20 km 4 kbar 14 km suite. Thus, could be earlier than xenoliths. proposed crystallization process produce layered decreasing amphibole increasing plagioclase upward shallower depth. Geochemical mineralogical lithospheric provide profile interpret lithosphere structure eastern