Sr and Pb isotopes exhibit global trends with the concentrations of major elements (SiO 2 , TiO 2 , FeO, Al 2 O 3 and K 2 O) and major elements ratios (CaO/Al 2 O 3 and K 2 O/TiO 2 ) in the shield-stage lavas from 18 oceanic hotspots (including Hawaii, Iceland, Galapagos, Cook-Australs, St. Helena, Cape Verde, Cameroon, Canary, Madeira, Comoros, Azores, Samoa, Society, Marquesas, Mascarene, Kerguelen, Pitcairn, and Selvagen). Based on the relationships between major elements and isotopes in ocean island basalts (OIBs), we find that the lavas derived from the mantle end members, HIMU (or high ‘μ’ =  238 U/ 204 Pb), EM1 (enriched mantle 1), EM2 (enriched mantle 2), and DMM (depleted MORB [mid-ocean ridge basalt] mantle) exhibit distinct major element characteristics: When compared to oceanic hotspots globally, the hotspots with a HIMU (radiogenic Pb-isotopes and low 87 Sr/ 86 Sr) component, such as St. Helena and Cook-Australs, exhibit high CaO/Al 2 O 3 , FeO T , and TiO 2 and low SiO 2 and Al 2 O 3 . EM1 (enriched mantle 1; intermediate 87 Sr/ 86 Sr and low 206 Pb/ 204 Pb; sampled by hotspots like Pitcairn and Kerguelen) and EM2 (enriched mantle 2; high 87 Sr/ 86 Sr and intermediate 206 Pb/ 204 Pb; sampled by hotspots like Samoa and Societies) exhibit higher K 2 O concentrations and K 2 O/TiO 2 weight ratios than HIMU lavas. EM1 lavas exhibit the lowest CaO/Al 2 O 3 in the OIB dataset, and this sets EM1 apart from EM2. A plot of CaO/Al 2 O 3 vs K 2 O/TiO 2 perfectly resolves the four mantle end member lavas. Melting processes (pressure, temperature and degree of melting) fail to provide an explanation for the full spectrum of major element concentrations in OIBs. Such processes also fail to explain the correlations between major elements and radiogenic isotopes. Instead, a long, time integrated history of various parent–daughter elements appears to be coupled to major element and/or volatile heterogeneity in the mantle source. End member lava compositions are compared with experimental partial melt compositions to place constraints on the lithological characteristics of the mantle end members.

Compositions of HIMU, EM1, and EM2 from Global Trends between Radiogenic Isotopes and Major Elements in Ocean Island Basalts

The Cenozoic magmatism of East-Africa: Part I — Flood basalts and pulsed magmatism

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015TC004000

Long‐term, deep‐mantle support of the Ethiopia‐Yemen Plateau

Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces, being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. In this paper, a review of the Yemen volcanic province and its relations with the Red Sea rifting are presented. Tertiary continental extension in Yemen resulted in the extrusion of large volumes of effusive rocks. This magmatism is divided in the Oligo-Miocene Yemen Trap Series (YTS) separated by an unconformity from the Miocene-Recent Yemen Volcanic Series (YVS). Magmas of the YTS were erupted during the synrift phase and correlate with the first stage of sea-floor spreading of the Red Sea and the Gulf of Aden (30 - 15 Ma), whereas the magmas of the YVS were emplaced during the post rift phase (10 - 0 Ma). A continental within plate character is recognized for both the YTS and YVS basalts. The YTS volcanic rocks are contemporaneous with, and geochemically similar to, the Ethiopian rift volcanism, just as the volcanic fields of the YVS are geochemically alike to most of the Saudi Arabian volcanics. YTS and YVS have analogous SiO2 ranges, but YVS tend to have, on average, higher alkalis and MgO contents than YTS. Fractional crystallization processes dominate geochemical variations of both series. Primitive magmas (MgO > 7.0%) are enriched in incompatible elements and LREEs with respect to primitive mantle, but YVS are more enriched than YTS. To first order, the different geochemical patterns agree with different degrees of partial melting of an astenospheric mantle source: 25% - 30% of partial melting for YTS and 10% - 3% for YVS. Secondly, the higher degree of enrichment in incompatible elements of YVS reflects also greater contribution of a lithospheric mantle component in their source region.

/pdf/continental-flood-basalts-and-rifting-geochemistry-of-594jdngos7.pdf

Continental Flood Basalts and Rifting: Geochemistry of Cenozoic Yemen Volcanic Province

Geodynamic setting of Upper Miocene to Quaternary alkaline basalts from Harrat al ‘Uwayrid (NW Saudi Arabia): Constraints from KAr dating, chemical and Sr-Nd-Pb isotope compositions, and petrological modeling

The Red Sea is part of the Afro-Arabian rift system, the world’s largest active continental rift system. The early opening phases of the Red Sea Rift were accompanied by continental flood magmatism. Large volumes of flood basalts emplaced in the Oligocene through to the present time at discrete eruptive centres along the western margin of the Arabian plate. Some of these rocks, in Southern Yemen, were investigated by geochemistry and K/Ar whole rock (WR) geochronology. In addition, the Jabal At-Tair (JAT) volcano, in the Red Sea trough, was investigated by geochemistry, with particular concern to the lavas of the last eruption of September 2007. The magmatism of Yemen is divided in: Oligocene–Early Miocene trap series (YOM), Tertiary intrusive rocks, and Late Miocene–recent volcanic series (YMR). YOM and Tertiary intrusions yielded K/Ar WR ages mostly in the range 31.6–16.6 Ma. Three older ages of 34.6, 35.4 and 49.0 Ma, if confirmed by further investigation, could suggest an Eocenic pre-trap phase of magmatic activity. YMR samples yielded K/Ar WR ages between 2.52 and 8.14 Ma. Both YOM and YMR basalts are alkaline, but YMR tend to be richer in alkalis than YOM. JAT basalts have subalkaline tholeiitic character, are geochemically homogeneous, and in the hygromagmaphile element spidergrams display increasing normalised concentrations from Cs to Ta, then decreasing up to Lu, with negative spikes of Nb, K and Pb. YOM have patterns almost identical to those of JAT, whereas YMR have higher normalized concentrations of all trace elements, but REE. The geochemical characteristics of JAT, YOM and YMR, framed in the broader context of the Red Sea Rift, are mostly consistent with a model of continental uplift and magmatism occurring across a linear, north–south axis of mantle upwelling, which intersects the Red Sea axis at the initiation site of axial seafloor spreading. The symmetrical propagation of the rift system to opposite sides of the N–S lineament, along the Red Sea axis, resulted in the observed symmetrical distribution of geochemical signatures of the Red Sea basalts and Yemen continental magmas.

M. N. Shawki

Papers

Continental Flood Basalts and Rifting: Geochemistry of Cenozoic Yemen Volcanic Province

Geochemical evolution of southern Red Sea and Yemen flood volcanism: evidence for mantle heterogeneity