Search results for "OLIVINE"

Neoproterozoic Ophiolites of the Arabian-Nubian Shield

2004

Publisher Summary Ophiolites of mid-Neoproterozoic age are abundant in the Arabian-Nubian Shield (ANS) of NE Africa and Arabia. The ANS ophiolitic mantle was mostly harzburgitic, containing magnesian olivines and spinels that have compositions consistent with extensive melting. Cumulate ultramafics transition upwards into layered gabbro. Several crystallization sequences are inferred from ANS transition zones and cumulate gabbro sections. In all samples studied, olivine and spinel crystallized first, followed by cpx-plag, cpxopx-plag, and opx-cpx-plag. The ANS in NE Africa and W. Arabia is the largest tract of juvenile continental crust of Neoproterozoic age on Earth. The best preserved oph…

Accretion of arc-oceanic lithospheric mantle in the Mediterranean: Evidence from extremely high-Mg olivines and Cr-rich spinel inclusions in lamproit…

2007

Abstract Si-rich Mediterranean type lamproites (48–56 wt.% SiO2) are olivine-phyric, mantle-derived volcanics, in which both phenocrystic and xenocrystic olivine are present. Here we demonstrate the phenocrystic origin of the most extremely NiO–MgO enriched olivine in lamproites with Mg# up to 0.95, that host Cr-rich (Cr# around 0.95) spinels. Our comprehensive study of olivine–spinel pairs from Mediterranean lamproites enables us to constrain the extent of depletion of their mantle source. Olivine–spinel pairs from primitive Mediterranean lamproites plot in the most refractory part of the olivine–spinel mantle array diagram, showing even more refractory character than mineral pairs from bo…

Noble-gas signature of magmas from a heterogeneous mantle wedge: The case of Stromboli volcano (Aeolian Islands, Italy)

2014

Abstract We report on the variation of the elemental (He, Ne, and Ar) and isotopic (He and Ar) compositions of olivine- and clinopyroxene-hosted fluid inclusions hosted in lavas, pyroclastics, and cumulate xenoliths from the last 60 ka of the eruptive history of Stromboli volcano, Italy. Samples belong to (i) the present-day activity as represented by shoshonitic (SHO) basalts, i.e., pumices with low porphyritic (LP) content and high porphyritic (HP) scoriae; (ii) the subalkaline versus alkaline products erupted at Stromboli during its subaerial history among the extreme magmatic series, i.e., calc-alkaline (CA) and potassic (KS); and (iii) the only known ultramafic cumulates (San Bartolo w…

Spectral, mineralogical, and geochemical variations across Home Plate, Gusev Crater, Mars indicate high and low temperature alteration

2009

Over the last ~3 years in Gusev Crater, Mars, the Spirit rover observed coherent variations in color, mineralogy, and geochemistry across Home Plate, an ~80 m-diameter outcrop of basaltic tephra. Observations of Home Plate from orbit and from the summit of Husband Hill reveal clear differences in visible/near-infrared (VNIR) colors between its eastern and western regions that are consistent with mineralogical compositions indicated by Mössbauer spectrometer (MB) and by Miniature Thermal Emission Spectrometer (Mini-TES). Pyroxene and magnetite dominate the east side, while olivine, nanophase Fe oxide (npOx) and glass are more abundant on the western side. Alpha Particle X-Ray Spectromet…

Geodynamic setting of Upper Miocene to Quaternary alkaline basalts from Harrat al ‘Uwayrid (NW Saudi Arabia): Constraints from K Ar dating, chemical …

2019

Highlights • Volcanic activity of Harrat Uwayrid (NW Arabia) lasted from 8.2 to 0.3 Ma. • Alkali olivine basalts are followed by basanites, tephrites and tephriphonolites. • Sr-Nd-Pb isotopic ratios of all volcanic rocks suggest a PREMA source. • Different degrees of partial melting of amphibole-garnet-spinel lherzolite • Lithospheric mantle source rather than asthenosphere or plume-type mantle Abstract The volcanic field of Harrat ar Rahah-’Uwayrid (NW Saudi Arabia) consists of an older plateau basalt sequence that overlies Cambrian sandstone and younger cinder cones with smaller flows that are concentrated in the central part of this field. Petrographic and whole rock geochemical data ind…

Petrography, mineralogy and geochemistry of a primitive pumice from Stromboli: implications for the deep feeding system

2011

We describe the field relations, petrographic, mineralogical and geochemical characteristics of an exceptional “ golden ” pumice belonging to a tephra layer exposed on the summit area of Stromboli volcano, Italy. Pumice sample PST-9 comes from a fallout deposit older than a spatter agglutinate sequence emplaced during the twentieth century. The eruption that produced it had a size exceeding that of intermediate paroxysms but was smaller than large-scale, spatter-forming, paroxysms from the sixteenth century and 1930 A.D. Lapilli are strongly vesicular and crystal-poor, similar to other “ golden ” pumices. Modal proportions include 89 vol% glass, 8 vol% clinopyroxene, 1–2 vol% olivine and 1–…

Coupled evolution of back-arc and island arc-like mafic crust in the late-Neoproterozoic Agardagh Tes-Chem ophiolite, Central Asia: evidence from tra…

2002

We report major-element, trace-element and isotopic data of volcanic rocks from the late-Neoproterozoic (570 Ma) Agardagh Tes-Chem ophiolite in Central Asia, south-west of Lake Baikal (50.5°N, 95°E). The majority of samples are high-alumina basalts and basaltic andesites having island-arc affinities. They were derived from an evolved parental magma (Mg#≥0.60, Cr~180 ppm, Ni~95 ppm) by predominantly clinopyroxene fractionation. The parental magma developed from a primary mantle melt by fractionation of about 12% of an olivine+spinel assemblage. The island-arc rocks have high abundances of incompatible trace elements (light rare-earth element abundances up to 100 times chondritic, chondrite-n…

Geochemistry and origin of ultramafic enclaves and their basanitic host rock from Kula Volcano, Turkey

2013

Abstract The Quaternary Kula Volcanic Province is located in western Anatolia, Turkey. This Na-alkaline anorogenic volcanism includes exposures of around 80 cinder cones, lava flows, and tuffs, representing one of the youngest volcanic activities in this region (1.9–0.026 Ma). The magmatism is related to an extensional regime and is interpreted as being derived predominantly from the asthenospheric mantle. The lava flows are mostly of a basanitic composition and host rare comagmatic enclaves. The enclaves are composed of two dominant lithologies: amphibolites and clinopyroxenites with and without olivine. Amphibole is usually resorbed and replaced by a rhoenite-rich breakdown corona. The mi…

Goldschmidt Abstracts 2010 – R

2010

Effect of High Pressure on the Crystal Structure and Vibrational Properties of Olivine-Type LiNiPO4

2018

In this work, we present an experimental and theoretical study of the effects of high pressure and high temperature on the structural properties of olivine-type LiNiPO4. This compound is part of an interesting class of materials primarily studied for their potential use as electrodes in lithium-ion batteries. We found that the original olivine structure (α-phase) is stable up to ∼40 GPa. Above this pressure, the onset of a new phase is observed, as put in evidence by the X-ray diffraction (XRD) experiments. The structural refinement shows that the new phase (known as β-phase) belongs to space group Cmcm. At room temperature, the two phases coexist at least up to 50 GPa. A complete conversio…