The Gataia Pleistocene lamproite: A new occurrence at the southeastern edge of the Pannonian Basin, Romania
I. Seghedi, T. Ntaflos, Z. Pécskay, 2008. "The Gataia Pleistocene lamproite: A new occurrence at the southeastern edge of the Pannonian Basin, Romania", Metasomatism in Oceanic and Continental Lithospheric Mantle, M. Coltorti, M. Grégoire
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The petrological identity of the lamproite occurrence situated c. 5 km south of Gătaia (Banat, western Romania), until now considered to be an alkali basalt, has been revealed by exploration drilling. This drilling programme pierced a slightly vesicular lava flow inside the Şumiga hill (198 m above sea level), revealing a sequence of vesicular lava intercalated with fallout scoria deposits. The isolated lamproite volcano, dated at 1.32±0.06 Ma (whole-rock K/Ar method), is situated at the southeastern margin of the Pannonian Basin and at the western margin of the South Carpathians, along an important NE–SW fault system. The lamproite magma erupted through flat-lying Miocene sedimentary rocks, which overlie older crystalline basement that experienced intense lithospheric deformation and orogeny during Cretaceous times. The lamproite is associated with contemporaneous volcanic activity that lies 50–150 km to the NNE, along the South Transylvanian fault system (Lucareţ alkali basalts, Uroiu shoshonites); these rocks, however, are not consanguineous, and derive from different mantle sources. There are, however, similarities to Oligocene lamproites from Serbia (Bogovina), generated on similar basement. The lamproite is fresh and has a slightly porphyritic texture with phenocrysts of high-Mg olivine and microphenocrysts of euhedral leucite in a glassy matrix. The matrix also contains microcrysts of olivine, armalcolite, apatite, sanidine, low Al-diopside, fluorine-bearing titanium phlogopite, fluorine-bearing amphibole and accessory chrome spinels. Ba-sulphate aggregates fill small vesicles. Very rare clots of corroded Al-phlogopite surrounded by secondary spinels are enclosed by leucite aggregates, suggesting formation during an earlier event. Major and trace element geochemistry and Sr and Nd isotopes show that the rock is a typical lamproite, close to the compositions of Leucite Hills and Gaussberg lamproites. The source for the Gătaia lamproite was probably a garnet harzburgite lithospheric mantle, metasomatized by alkaline mafic melts, most probably active at the Cretaceous–Palaeogene boundary. Metasomatism by alkaline melts is indicated by high abundances of incompatible trace elements, such as Ba, Sr, Rb and Zr. The Gătaia lamproite probably had a limited available source volume for melting that reflects the ambient thermal regime in the typical post-collisional tectonic setting active during Late Neogene to Quaternary time. Emplacement of this lamproite was probably a result of surface uplift and erosion at the base of the lithosphere, marking the collapse of the Alpine orogen.
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Twenty years have passed since Menzies & Hawkesworth extended the concept of metasomatism to mantle processes. The aim of this book is to gather together progress made on this topic since then. Most of the 14 papers reported in the volume rely on in situ major and trace element analyses of minerals and glasses in mantle xenoliths, and deal with different kinds of metasomatic agents at variable fluid/rock ratios in tectonic settings as different as intra-plate, mid-ocean ridge (ophiolites) and supra-subduction. The book contributes to the wide debate on the nature of the fluids migrating into the mantle wedge, as well as on the different residential times of the subduction signature. In addition papers on intra-plate settings deal with the problem of relating various metasomatic signatures to one single metasomatic event through an infiltration-reaction process.