Two main groups of basaltic rocks with slightly different chemical and petrological characteristics have been recognized among the Oligo-Miocene volcanics (30-18 Ma) of northern Yemen. The first group includes basalts from different parts of northern Yemen with low incompatible element abundances and moderate Ti02 (1-3%) contents. To this group belong all the studied transitional and alkali basalts from the Sa'dah area , north of San'a (Northern Yemen Trap Series) , the mafic dykes outcropping in the Yemen coastal plain (Tihama), together with some basalts from the region south of Sumara (Southern Yemen Trap Series). The second group is made by transitional basalts, characterized by high Ti02 (>4%) and incompatible element abundances from the central and southern portions of the Yemen Trap Series. The geochemical and isotopic data evidenced that the volcanics from the central and southern parts of the Yemen plateau were generated mostly by extensive AFC process, involving a Pan-African type crust ; the degree of contamination increases southwards. Although, the less differentiated volcanics (Si02< 52%) still show evidence of crustal contamination, the basic ones, with (87Sr/86Sr)i values lower than 0.7038 allow the recognition of two different geochemical reservoirs in the evolution of their mantle source . The source of high-Ti transitional basalts was characterized by the presence of a within plate type geochemical component. Conversely, the source of Tihama basaltic dykes has a strong MORB signature, tending to the Red Sea Type MORB end member.
Mantle domains beneath the Red Sea region: inferences from isotopic and geochemical characteristics of Oligo-Miocene magmatism in Yemen
POLI, Giampiero
1992
Abstract
Two main groups of basaltic rocks with slightly different chemical and petrological characteristics have been recognized among the Oligo-Miocene volcanics (30-18 Ma) of northern Yemen. The first group includes basalts from different parts of northern Yemen with low incompatible element abundances and moderate Ti02 (1-3%) contents. To this group belong all the studied transitional and alkali basalts from the Sa'dah area , north of San'a (Northern Yemen Trap Series) , the mafic dykes outcropping in the Yemen coastal plain (Tihama), together with some basalts from the region south of Sumara (Southern Yemen Trap Series). The second group is made by transitional basalts, characterized by high Ti02 (>4%) and incompatible element abundances from the central and southern portions of the Yemen Trap Series. The geochemical and isotopic data evidenced that the volcanics from the central and southern parts of the Yemen plateau were generated mostly by extensive AFC process, involving a Pan-African type crust ; the degree of contamination increases southwards. Although, the less differentiated volcanics (Si02< 52%) still show evidence of crustal contamination, the basic ones, with (87Sr/86Sr)i values lower than 0.7038 allow the recognition of two different geochemical reservoirs in the evolution of their mantle source . The source of high-Ti transitional basalts was characterized by the presence of a within plate type geochemical component. Conversely, the source of Tihama basaltic dykes has a strong MORB signature, tending to the Red Sea Type MORB end member.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
