Journal ArticleDOI
Chromite-bearing spessartites from Kasuga-mura, Japan, and their bearing on possible mantle origin andesite
Kazuhiro Suzuki,Keiichi Shiraki +1 more
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An unusual association of chromite and hornblende was found in the spessartites of andesite composition, occurring as a dike swarm associated with a Cretaceous granite batholith.Abstract:
An unusual association of chromite and hornblende was found in the spessartites of andesite composition, occurring as a dike swarm associated with a Cretaceous granite batholith. The spessartites are largely porphyritic with phenocrysts of either hornblende or augite. One dike, comprising a finegrained spessartite, exhibits distinct chilled selvages of aphanitic facies. The chromites in the fine-grained and augite-spessartites are significantly higher in Cr/ (Cr+Al) than those occurring rarely as inclusions in the phenocrystic hornblendes in the hornblende spessartite, although both are similar in Mg/ (Mg+Fe), Fe2O3, and TiO2. The phenocrystic hornblendes are titaniferous pargasite with high Mg/ (Mg+Fe), and differ in their higher octahedral Al from the groundmass hornblendes including those in the fine-grained spessartite. The crystallization sequence in the phenocrystic hornblende-bearing spessartites is Al-rich chromite, phenocrystic hornblende, and plagioclase without pyroxene, suggesting a high water content in the magma and the start of the crystallization at relatively high pressures. The finegrained spessartite from which the porphyritic spessartites have been derived by fractionation of dominant mafic minerals, has the high Mg-value and Cr content equivalent to those in primitive, undifferentiated basalts, although still andesitic in SiO2 content. Chemically similar magnesian andesites, although uncommon, found in some orogenic calc-alkalic suites may represent a magma composition in equilibrium with mantle peridotite under the condition of high water pressures.read more
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The nature and origin of lamprophyres: an overview
TL;DR: The lamprophyre family as mentioned in this paper is a family of mineral types that carry high alkalis at a given percentage of SiO2, together with one or more of normative elements such as ne, lc or ac, modal foids, and Na-K-Ti-rich amphiboles.
Journal ArticleDOI
High-Mg diorites derived from sanukitic HMA magmas, Kyushu Island, southwest Japan arc: evidence from clinopyroxene and whole rock compositions
TL;DR: In this article, the authors considered the source of Early Cretaceous high-Mg diorites on Kyushu Island, southwest Japan arc, based on their clinopyroxene and whole rock compositions.
Journal ArticleDOI
Nature and origin of calc-alkaline lamprophyres: minettes, vogesites, kersantites and spessartites
TL;DR: Calc-alkaline lamprophyres are porphyritic dyke-rocks, richer in amphibole, biotite, ultramark elements (Mg, Cr, Ni) and incompatible elements (K, F, P, Rb, Sr, Zn, Nb, Ba, REE, Th, U) than other rocks of comparable colour index (35-67) or % SiO2 (46-57) as discussed by the authors.
Journal ArticleDOI
Do lamprophyres carry gold as well as diamonds
TL;DR: The average gold abundance in lamprophyres seems to be at least an order of magnitude higher than in 'common' igneous rocks, and many individual values are 100-1,000 times higher as mentioned in this paper.
Journal ArticleDOI
Tectonic reconstruction of batholith formation based on the spatiotemporal distribution of Cretaceous–Paleogene granitic rocks in southwestern Japan
Kazuya Iida,Hikaru Iwamori,Hikaru Iwamori,Yuji Orihashi,Taeho park,Yong Joo Jwa,Sung Tack Kwon,Tohru Danhara,Hideki Iwano +8 more
TL;DR: In this paper, the authors examined two plausible models to explain the pattern of magmatic activity: (i) a segmented spreading ridge and subsequent slab melting (ridge-subduction model), and (ii) subduction with a temporally variable subduction angle and corresponding spatial distribution of normal arc magmatism (subduction angle model).
References
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Journal ArticleDOI
Aleutian magnesian andesites: Melts from subducted Pacific ocean crust
TL;DR: In this article, a small amount of partial melting of subducted Pacific ocean crust (basalt) consisting mainly of garnet and clinopyroxene (eclogite or garnet websterite) is proposed.
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Chromian spinel as a petrogenetic indicator: part 2. petrologic applications
TL;DR: In this article, the crystallization of chromium-bearing spinel from silicate magmas is examined, and then an attempt is made to apply the theory developed in Irvine (1965) to the principal occurrences of the...
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Atlantic ocean floor: Geochemistry and petrology of basalts from legs 2 and 3 of the Deep-Sea Drilling Project
TL;DR: Basalts cored on legs 2 and 3 of the Deep-Sea Drilling Project (DSDP) range in sea floor spreading age from 18 to 67×106 yr as discussed by the authors.
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The petrological evolution of island arc systems: Twenty-seventh William Smith Lecture
TL;DR: In this article, amphibole-controlled fractionation, eclogite controlled fractionation and direct partial melting of mantle pyrolite under conditions of high water vapour pressure are reviewed.