6533b826fe1ef96bd1283b84

RESEARCH PRODUCT

Late proterozoic island arc volcanics from Gebeit, Red Sea Hills, north-east Sudan

subject

description

The area of Gebeit Mine in the northern Red Sea Hills, Sudan, is built up of voluminous volcanic rocks and minor volcaniclastic and clastic sequences. According to their chemical and modal compositions the Gebeit volcanics can be devided into four groups: (a) cpx-physic basalts with clinopyroxene and plagioclase as the dominant phenocrysts and minor opaques; (b) hbl-physic basalts with hornblende, clinopyroxene, plagioclase and subordinate magnetite including one rare dacite; (c) pl-phyric andesites with plagioclase phenocrysts in a matrix that is rich in magnetite; and (d) aphyric basalts. The compositional variation within the distinct volcanic groups can only partly be explained by fractional crystallization, and more than one magma source reservoir is required. Mineral and whole rock Sm/Nd data for the cpx-physic and hbl-physic basalts yield an isochron age of 832 ± 26 Ma (ɛNdT = 6.74 ± 0.19, MSWD = 0.12) which is interpreted as the age of eruption. The ɛNdt values for the aphyric basalts and pl-physic andesites range from 6.7 to 8.3, indicating the involvement of different depleted magma sources. The Nd and Sr isotopic data rule out any significant influence of older continental crust in the formation of the Gebeit volcanics and indicate an intraoceanic origin. This implies that the Gebeit terrane is a segment of juvenile crust that originated in a subduction-related environment and supports the arc accretion model for the Arabian-Nubian Shield.