Structure and composition of the lithosphere beneath Mount Carmel, North Israel.

A suite of mantle-derived xenoliths and xenocrysts in Cretaceous volcanic rocks from Mount Carmel, North Israel has been investigated to establish the regional paleo-geotherm and constrain the evolution of the lower crust and lithospheric mantle. Garnet pyroxenite xenoliths can be subdivided into low-MgO (MgO < 15%) and high-MgO (MgO > 15%) types. The low-MgO garnet websterites, with high equilibration pressures and temperatures (P = 20–23 kb, T = 1143–1192 ℃) and convex-upward REE patterns, are inferred to be cumulates from partial melts derived from a sub-lithospheric, fossilized plume head that impinged on the pre-existing lithospheric base during the early Mesozoic. In contrast, high-MgO pyroxenites, with lower T estimates, P defined by extrapolation to the inferred geotherm (1012–1046 ℃ and ~ 14–15 kb) and mantle-like geochemical compositions, are deduced to represent cumulates from mafic magmas extracted from asthenospheric peridotitic mantle during late Proterozoic continental crustal growth in the region. Granulite xenoliths are mainly plagioclase-rich and equilibrated at depths of ~ 18–34 km. They have lower MgO contents but trace-element patterns similar to those of the low-MgO garnet pyroxenites, and probably originated as cogenetic crystallized melts and cumulates intruded around the Moho. U–Pb dating of apatite indicates ages around ~ 250 Ma, consistent with major magmatism dated by zircon xenocrysts. The lithospheric mantle has a two-layered structure, comprising a shallow (and relatively ancient) layer dominated by spinel peridotite and high-MgO garnet pyroxenites, and a deeper layer with fertile garnet-bearing peridotites intercalated with the low-MgO garnet pyroxenites. [ABSTRACT FROM AUTHOR]