Search results for "Pyroxene"

Contrasting types of metasomatism in dunite, wehrlite and websterite xenoliths from Kimberley, South Africa

2008

Abstract Dunite, wehrlite and websterite are rare members of the mantle xenolith suite in the Kimberley kimberlites of the Kaapvaal Craton in southern Africa. All three types were originally residues of extensive melt extraction and experienced varying amounts and types of melt re-enrichment. The melt depletion event, dated by Re–Os isotope systematics at 2.9 Ga or older, is evidenced by the high Mg# (Mg/(Mg + Fe)) of silicate minerals (olivine (0.89–0.93); pyroxene (0.88–0.93); garnet (0.72–0.85)), high Cr# (Cr/(Cr + Al)) of spinel (0.53–0.84) and mostly low whole-rock SiO2, CaO and Al2O3 contents. Shortly after melt depletion, websterites were formed by reaction between depleted peridotit…

Detection of a Ca-rich lithology in the Earth's deep (>300 km) convecting mantle

2005

Earth's deep convecting upper mantle is believed to represent a rather homogenous geochemical reservoir of spinel or garnet lherzolite with primitive major element and moderately depleted trace element composition. Only where subduction occurs is this homogeneity disrupted by a suite of rocks ranging from eclogites/garnet pyroxenites (former oceanic crust) to residual harzburgites. In addition to these well documented peridotitic and metabasaltic rocks we have now discovered the presence of a chemically distinct reservoir in the deep convecting upper mantle. In situ structural analyses (micro X-ray diffraction and micro Raman spectroscopy) and three-dimensional trace element mapping (confoc…

Origin and crystallization history of Permian tholeiites from the Saar-Nahe trough, SW Germany

1973

The Hirschberg and Rodern diatremes, within the Permian Saar-Nahe trough, SW Germany, are composed chiefly of basaltic tuffs, with associated small intrusions of K-rich tholeiites. Several tholeiite bodies carry 2–20 mm crystals of magnesian clinopyroxene and orthopyroxene, the latter containing up to 5.5% Al2O3 and often extensively resorbed and rimmed by fine-grained olivine and clinopyroxene. Experimental duplication of these pyroxenes has been achieved under conditions of Pload=6–10 kb, T=1280–1080° C and 2–4 wt.-% H2O, confirming that they represent a rare occurence of high pressure phenocrysts in tholeiitic basalts. These conditions of pyroxene crystallization also place constraints o…

A new hydrous Al-bearing pyroxene as a water carrier in subduction zones

2011

Abstract A new Hydrous Al-bearing PYroxene (HAPY) phase has been synthesized at 5.4 GPa, 720 °C in the MgO–Al2O3–SiO2–H2O model system. It has the composition Mg2.1Al0.9(OH)2Al0.9Si1.1O6, a C-centered monoclinic cell with a = 9.8827(2), b = 11.6254(2) c = 5.0828(1) A and β = 111.07(1)°. The calculated density is 3.175 g/cm3 and the water content is 6.9% H2O by weight. Its structure has been solved in space group C2/c by the recently developed automated electron diffraction tomography method and refined by synchrotron X-ray powder diffraction. HAPY is a single chain inosilicate very similar to pyroxenes but with three instead of two cations in the octahedral layer, bonded to four oxygens and…

Raman-Mössbauer-XRD studies of selected samples from “Los Azulejos” outcrop: A possible analogue for assessing the alteration processes on Mars

2016

The outcrop of “Los Azulejos” is visible at the interior of the Cañadas Caldera in Tenerife Island (Spain). It exhibits a great variety of alteration processes that could be considered as terrestrial analogue for several geological processes on Mars. This outcrop is particularly interesting due to the content of clays, zeolite, iron oxides, and sulfates corresponding to a hydrothermal alteration catalogued as “Azulejos” type alteration. A detailed analysis by portable and laboratory Raman systems as well as other different techniques such as X ray diffraction (XRD) and Mössbauer spectroscopy has been carried out (using twin-instruments from Martian lander missions: Mössbauer spectrometer MI…

Origin of SiO2-rich components in ordinary chondrites

2006

Abstract Silica-rich objects are common minor components in ordinary chondrites (OC), occurring as fragments and as chondrules. Their typical paragenesis is orthopyroxene + SiO 2 (with bulk SiO 2 >65 wt%) and occasionally with additional olivine and/or spinel. Individual silica-rich components (SRC) have previously been studied in various types of OCs, although there is only one comprehensive study of these objects by Brigham et al. [Brigham, C.A., Murrell, M.T., Yabuki, H., Ouyang, Z., El Goresy, A., 1986. Silica-bearing chondrules and clasts in ordinary chondrites. Geochim. Cosmochim. Acta 50, 1655–1666]. Several different explanations of how SRCs formed have been published. The main ques…

Clinopyroxene-bearing garnet amphibolites from the Ferrà valley (northern Peloritani Mts., Sicily

2001

Elemental and isotope covariation of noble gases in mineral phases from Etnean volcanics erupted during 2001–2005, and genetic relation with peripher…

2008

Abstract During 2001–2005, Mount Etna was characterized by intense eruptive activity involving the emission of petrologically different products from several vents, which involved at least two types of magma with different degrees of evolution. We investigated the ratios and abundances for noble-gas isotopes in fluid inclusions trapped in olivines and pyroxenes in the erupted products. We confirm that olivine has the most efficient crystalline structure for preserving the pristine composition of entrapped gases, while pyroxene can suffer diffusive He loss. Both the minerals also experience noble gas air contamination after eruption. Helium isotopes of the products genetically linked to the …