Search results for "OLIVINE"
showing 10 items of 82 documents
Eclogite xenoliths from the Kuruman kimberlites, South Africa: geochemical fingerprinting of deep subduction and cumulate processes☆
2004
The mineralogically diverse eclogite xenolith suite sampled by the >1.6 Ga Zero kimberlite in the Kuruman group, close to the western edge of the Kaapvaal craton consists of bimineralic eclogites, orthopyroxene-bearing eclogites with and without sanidine, and kyanite eclogites. Garnet exsolutions in clinopyroxene occur in all Zero eclogite types, and orthopyroxene and, where present, sanidine are also exsolved from clinopyroxene in orthopyroxene-bearing eclogites. Mineral thermobarometry indicates that the last P–T condition prior to the kimberlite eruption was 900–950 °C at 3.5–4.0 GPa. However, inclusions of quartz, rutile and rarely K-feldspar, plus former fluid inclusions in garnets, in…
Integrating Ultramafic Lamprophyres into the IUGS Classification of Igneous Rocks: Rationale and Implications
2005
RECEIVED JULY 16, 2004; ACCEPTED MARCH 16, 2005ADVANCE ACCESS PUBLICATION APRIL 29, 2005We introduce a modification to the current IUGS classificationsystem for igneous rocks to include ultramafic lamprophyres, whicharecurrentlyentirelyomitted.Thisisdonebyincludinganewstepinthe sequential system, after the assignment of pyroclastic rocks andcarbonatites, that considers ultramafic inequigranular textured rockswith olivine and phlogopite macrocrysts and/or phenocrysts. At thisstepultramaficlamprophyresareconsideredtogetherwithkimberlites,orangeites (former Group 2 kimberlites) and olivine lamproites.This proposal allows the correct identification and classificationof ultramafic lamprophyres w…
Cooling and crystallization recorded in trachytic enclaves hosted in pantelleritic magmas (Pantelleria, Italy): Implications for pantellerite petroge…
2015
Abstract This study focuses on the comenditic trachyte enclaves hosted in pantelleritic lava and pumices emplaced during one of the most recent eruptive events at Pantelleria (~ 6 ka). Enclaves range from mm-sized fragments to dm-sized blocks with spheroidal to amoeboid shapes and characteristic globular surfaces; they are crystal-rich with ~ 30 vol% large anorthoclase, less abundant Fe-rich olivine, clinopyroxene and Fe–Ti oxides. Vesicles ranging from a few mm to 1–2 cm in size are distributed throughout the enclave and are commonly filled with microlite-free vesicular glass. The groundmass presents spectacular textures, including fine to coarse spherulites and hopper and skeletal microli…
The lithium and magnesium isotope signature of olivine dissolution in soil experiments
2021
Abstract This study presents lithium and magnesium isotope ratios of soils and their drainage waters from a well-characterised weathering experiment with two soil cores, one with olivine added to the surface layer, and the other a control core. The experimental design mimics olivine addition to soils for CO2 sequestration and/or crop fertilisation, as well as natural surface addition of reactive minerals such as during volcanic deposition. More generally, this study presents an opportunity to better understand how isotopic fractionation records weathering processes. At the start of the experiment, waters draining both cores have similar Mg isotope composition to the soil exchangeable pool. …
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…
Relationship of Mediterranean type lamproites to large shoshonite volcanoes, Miocene of Lesbos, NE Aegean Sea
2014
Abstract Shoshonites, which are high-K trachyandesitic rocks, are found in many orogenic belts and are commonly of post-collisional origin. The petrogenesis of shoshonites has been widely debated. Small lava flows and dykes of lamproite and related lamproitic rocks of early Miocene age in Lesbos are coeval with voluminous shoshonite volcanoes. Their distinctive petrology and isotope geochemistry provide an exceptional opportunity to assess the petrogenetic relationship between lamproites and shoshonites. The lamproitic rocks contain phenocrysts of forsteritic olivine (as high as Fo93) and clinopyroxene, both with inclusions of chrome spinel (Cr# ~ 0.9 or ~ 0.6) and carbonate melt inclusions…
The kinetics of the olivine dissolution under the extreme conditions of nano-silica production
2015
Abstract This article addresses the kinetics of the dissolution of olivine for nano-silica production at extreme conditions. The extreme conditions are pH values between −0.7 and 1, temperature between 50 and 90 °C, solid content around 250 g/L and percentage dissolved between 80% and 99%. This work is structured in 3 parts: (1) chemical and mineralogical characterization of the dunites employed; (2) mechanism of the olivine dissolution focusing on the possible resistances to the transport; and (3) determination of the kinetic parameters kT and n. The results shown here demonstrate that: (1) the limiting step of this process is not the diffusion through a silica layer but the surface reacti…
Eclogite xenoliths from Kimberley, South Africa — A case study of mantle metasomatism in eclogites
2009
Abstract Eclogite xenoliths from the Kimberley diamond mine dumps were studied for major, trace elements and oxygen isotopes. The suite consists of typical garnet and clinopyroxene rocks as well as kyanite-eclogites and olivine- or orthopyroxene-bearing samples. All samples have Al[6]/Al[4] ratios > 2 which indicate high equilibration pressures, i.e. in the eclogite stability field as opposed to pyroxenites. Most samples are modally and cryptically metasomatized and contain up to 10 vol.% phlogopite plus ilmenite and rutile. Trace element geochemical characteristics of phlogopite and Ti-oxides are similar to those described for metasomatized peridotite xenoliths from the Kaapvaal craton, an…
Zirconolite-bearing ultra-potassic veins in a mantle-xenolith from Mt. Melbourne Volcanic Field, Victoria Land, Antarctica
1991
One mantle xenolith from a basanite host of the Mt. Melbourne Volcanic Field (Ross Sea Rift) is extraordinary in containing veins filled with leucite, plagioclase, clinopyroxene, nepheline, Mg-ilmenite, apatite, titaniferous mica, and the rare mineral zirconolite. These veins show extensive reaction with the dunitic or lherzolitic host (olivine+spinel+orthopyroxene+clinopyroxene). The reaction areas contain skeletal olivine and diopside crystals, plagioclase, phlogopite, aluminous spinel and ilmenite in a fine grained groundmass of aluminous spinel, clinopyroxene, olivine, plagioclase and interstitial leucite. The vein composition estimated from modal abundances and microprobe analyses is a…
Evidence from Antarctic mantle peridotite xenoliths for changes in mineralogy, geochemistry and geothermal gradients beneath a developing rift
2006
Abstract Garnet and spinel peridotite xenoliths associated with the Phanerozoic Lambert–Amery Rift in eastern Antarctica contain evidence for several stages in the development of the mantle beneath the rift. Despite the fact that equilibria were only partly attained, a combination of petrography, whole-rock geochemistry, mineral chemistry and thermobarometry can be used to decipher four stages prior to entrainment of the xenoliths in the host magma during the initial stages of the breakup of Antarctica, India and Madagascar. The first chronological stage is represented by harzburgitic protoliths represented by rare occurrences of low-Ca olivines and orthopyroxenes in spinel lherzolites: the…