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Showing 1 to 20 of 20 for “"Phenocryst"”.
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Order and chaos in the olivine underworld: two mechanisms for the formation of basal olivine layers
… could have formed by the emplacement of a single phenocryst bearing magma, followed by settling of the initial phenocryst load, and in-situ differentiation. Second, a high-resolution analysis of the internal ordering of the Palisades Sill olivine horizon, widely recognized as the result of an …
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Evidence From High Ni Olivine For Diverse Primitive Magmas In Cascade Volcanism
<p>Minor element abundances in olivine phenocrysts from primitive, high-Mg# lavas (Mg/Mg+Fe >0.60) are used to explore the nature of magma genesis in the Cascade subduction system. Electron-microprobe analyses were obtained for olivine phenocrysts in primitive basalt from central Oregon and …
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Geochemistry and petrogenesis of the Tsirub nephelinite-basanite intrusions, Aus, southern Namibia
… olivine is dominant, and sometimes the only, phenocryst/microphenochryst phase, and less commonly clinopyroxen; the groundmass consists of clinopyroxine, olivine, Fe-Ti oxides and secondary generation amphibole. Rare felsic xenoliths comprising alkali feldspar (orthoclase) and clinopyroxene …
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Aspects of the geochemistry of Onverwacht Group lavas from the Barberton Greenstone Belt
… facies mineral assemblages. Although original phenocryst phases are often pseudomorphed, they can still be identified from occasionally preserved relict grains and from the secondary mineral assemblages. In this way all the major phases that occur in the various lava types could be identified. …
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Silicate Melt Inclusions in Igneous Petrogenesis
Silicate melt inclusions are ubiquitous in quartz phenocrysts, yet there are few studies of such inclusions from porphyry copper systems. A melt inclusion forms when magma is trapped in a growing phenocryst. If a phenocryst is able to preserve the original parent magma, then accurate information …
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Petrology of the Roxboro metagranite, North Carolina
… microphaneritic granite, now metamorphosed. Phenocrysts of plagioclase, quartz, and perthite are accompanied by porphyroblasts of epidote. Relict igneous textural relationships suggest two possible fractional crystallization models, in which the order of crystallization was plagioclase, …
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Petrologic studies of the Robles Formation, south central Puerto Rico
… series.</p> <p>Plagioclase and olivine phenocrysts contain a series of metamorphic alteration phases as follows: (1) analcime, celadonite, chlorite, sericite; (2) laumontite and albite; (3) prehnite; (4) pumpellyite; (5) epidote; (6) actinolite. Assemblages containing analcime, …
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Geochemistry and mineralogy of selected Atlantic Ocean basalts
… with a detailed study of the chemistry of phenocryst minerals and associated melt inclusions are used to place constraints on the genetic relationships between the various lava types. The distribution of NiO in olivine and Cr-spinel phenocrysts distinguishes the picritic basalts, …
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Petrogenesis and evolution of alkalic basaltic magmas in a continental intraplate setting: the South Auckland Volcanic Field, New Zealand
… analyses. Forsteritic olivine is the dominant phenocryst phase in each rock group (group A: Fo₆₁ - Fo₈₂; group B: Fo₆₄ - Fo₉₂). Clinopyroxene is abundant and ranges from augite (Wo₃₅₋₄₇ En₃₆₋₅₀ Fs₁₁₋₂₃) in group A to diopside (Wo₄₂₋₅₂ En₃₂₋₄₆ Fs₁₀₋₂₀) in group B basalts. Plagioclase (An₄₀₋₇₀) …
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TEMPORAL AND SPATIAL VARIATIONS IN THE GEOCHEMISTRY AND MINERAOLOGY OF THE YOUNGER HISTORIC LAVAS OF MOUNT ETNA, SICILY
… by incompatible trace element chemistry, phenocryst compositions and petrographic textures. Mixing involves several end-member magma compositions, some of which can be related to earlier eruptions using geochemical and volcanological evidence. The effects of post-mixing crystal …
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The geochemistry and petrology of the Rodrigues Ridge (Western Indian Ocean)
… spinel. Only the most western site contained any phenocryst clinopyroxene. Phenocryst olivine was in the range Fo88-79 and plagioclase was in the range An79-60. Where present the clinopyroxene was titaniferous (2.0-3.7% TiO2) in the range Ca4852Mg30-19Fe 19.33. The Rodrigues Ridge lavas are …
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Geochemistry and geohydrology of the Deccan volcanic rocks of Akole Taluka, Ahmednagar District, Maharashtra State, India.
… Two suites were defined on the basis of phenocryst content: Suite No 1 with olivine, plagioclase, clinopyroxene assemblages, and Suite No 2 with olivine, plagioclase, clinopyroxene, and magnetite assemblages. Chemically the rocks are altered and show variation in compostion, with …
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Geology, Petrology, and Tectonic Setting of the Mafic Rocks of the 1480 MA Old Granite-Rhyolite Terrane of Missouri, USA
… fractional crystallization of the observed phenocryst phases—plagioclase + olivine + apatite—but trace element modelling indicates that the petrogenetic relationships are more complex. The metamorphic mafic rocks of the terrane are present as unexposed thick bodies. They are suggested to be …
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Primitive magmas of the Earth and Moon : a petrologic investigation of magma genesis and evolution
… may not have been whole moon. Chapter 3 uses phenocryst petrology, Os-isotopes, major and trace element geochemistry and petrography to argue for the formation of primitive magnesian andesites of Mt. Shasta and Mt. Lassen as primary mantle melts. Recent proposals that primitive magnesian …
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THE PETROLOGY AND GEOCHEMISTRY OF HIGH CASCADE VOLCANICS IN SOUTHERN WASHINGTON: MOUNT ST. HELENS VOLCANO AND THE INDIAN HEAVEN BASALT FIELD (TRACE ELEMENT, ISOTOPES, MINERALOGY)
… crystallization processes involving the observed phenocryst assemblages. However, the strontium and oxygen isotopic compositions of representative samples of the Mount St. Helens suite indicate that closed system processes cannot explain the isotopic variations. The isotopic ratios are positively …
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Geochemical and volcanological aspects of rhyolite eruptions from Taupo Volcanic Zone, New Zealand
… 5-7 km depth) and crystallise, as indicated by phenocryst and glass equilibrium. Geochemical and mineralogical heterogeneity in the OVC deposits, often on a clast-scale, suggests that the eruptions commonly tap several homogeneous, compositionally distinct magma batches. Temporal fractional …
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The geochemistry, kinematics and geodynamics of the Gannakouriep dyke swarm
… reconcilable in terms of fractionation of the phenocryst assemblage olivine, plagioclase, clinopyroxene, (ilmenite and Ti-magnetite). However an earlier phase of fractionation of essentially olivine and plagioclase at the base of the crust is suggested since constraints on the degree of partial …
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Petrogenesis of Mesoarchean high-K rocks in the Kaapvaal Craton: Investigating the Boesmanskop Alkaline Complex and Salisbury Kop batholith
… porphyritic textures that indicate K-feldspar phenocryst accumulation, with clinopyroxene and Ca-amphibole as intercumulus phases. Field observations indicate that the BAC magmas were emplaced at shallow levels along active shear zones. New U-Pb zircon dating of a quartz monzonite yielded a …
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Geochemical Evolution at White Island, New Zealand
… detailed studies of silicate melt inclusions, phenocrysts, and matrix glass contained in recent ejecta (1977-1991). Most melt inclusions contained only glass, however, daughter minerals present in multiphase melt inclusions in the 1991 sample indicate a different P-T history compared to the …
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Petrology and geochemistry of the Killdeer carbonates
… or dolomitizad clastic rock composed of phenocryst fragments and shards of rhyolitic composition. These clasts were transported by the wind to the drainage basin and admixed with other detritus before final deposition. Rhyolitic shards suggest a Pliocene age for the sediments.</p> …