Journal ArticleDOI
A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric criteria
TLDR
In this article, a simple general equation is presented for estimating the Fe 3 § concentrations in ferromagnesian oxide and silicate minerals from microprobe analyses, assuming that iron is the only element present with variable valency.Abstract:
A simple general equation is presented for estimating the Fe 3 § concentrations in ferromagnesian oxide and silicate minerals from microprobe analyses. The equation has been derived using stoichiometric criteria assuming that iron is the only element present with variable valency and that oxygen is the only anion. In general, the number of Fe 3 + ions per X oxygens in the mineral formula, F, is given by; F = 2X(1 - T/S) where T is the ideal number of cations per formula unit, and S is the observed cation total per X oxygens calculated assuming all iron to be Fe 2 § Minerals for which this equation is appropriate include pyralspite and ugrandite garnet, aluminate spinel, magnetite, pyroxene, sapphirine and ilmenite. The equation cannot be used for minerals with cation vacancies (e.g. micas, maghemite) unless, as in the case of amphiboles, the number of ions of a subset of elements in the formula can be fixed. Variants of the above equation are presented for some of the numerous published schemes for the recalculation of amphibole formulae. The equation is also inappropriate for minerals showing SP += 4H § substitution (e.g. staurolite, hydrogarnet), minerals containing an unknown proportion of an unanalysed element other than oxygen (e.g. boron-bearing kornerupine) and minerals containing two or more elements with variable valency.read more
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Geometry of a large-scale, low-angle, midcrustal thrust (Woodroffe Thrust, central Australia)
TL;DR: In this paper, the authors reconstructed the geometry of the Woodroffe Thrust and showed that basement-cored, thick-skinned, midcrustal thrusts can be very shallowly dipping on a scale of many tens of kilometers in the direction of movement.
Journal ArticleDOI
Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement
J. W. Dottin,Jabrane Labidi,James Farquhar,Philip M. Piccoli,Ming-Chang Liu,Kevin D. McKeegan +5 more
TL;DR: In this article, a combination of new sulfur isotope data, mineral composition and abundance data, and consideration of mineral textures is used to link assimilation of surface-derived Martian sulfate to oxidation of nakhlite melts.
Journal ArticleDOI
Volcanic geology and geochemistry of Motuhora (Whale Island), Bay of Plenty, New Zealand
R M Burt,Jim Cole,P. Z. Vroon +2 more
TL;DR: Motuhora (Whale Island) lies c. 11 km offshore from Whakatane in the Bay of Plenty, New Zealand, and comprises tuffaceous marine sediments of the Camp Bay and Motuhora Formations separated by lavas, volcanic breccias, and slope-wash deposits of the Whale Volcanics as mentioned in this paper.
Journal ArticleDOI
Mantle Xenoliths and Their Host Magmas in the Eastern Alkaline Province, Northeast Mexico
Adalberto Treviño-Cazares,Juan Alonso Ramírez-Fernández,Fernando Velasco-Tapia,Pedro Rodríguez-Saavedra +3 more
TL;DR: In this article, a partial melting model for REE was used to identify the source of mafic magnetites in the garnet P-T stability field, which was supported by an enrichment in light REE ([La/Yb]N = 10.8-27.1; chondrite-normalized ratios) and the behavior of relatively immobile trace elements.
Journal ArticleDOI
Estimation of pre-eruptive magmatic water fugacity in the Phlegrean Fields, Naples, Italy
TL;DR: In this article, the water fugacity of the trachytic Breccia Museo eruption, Naples, Italy, was estimated using the biotite-magnetite-sanidine equilibrium.
References
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Journal ArticleDOI
Origin of Basalt Magmas: An Experimental Study of Natural and Synthetic Rock Systems
H. S. Yoder,C. E. Tilley +1 more
Journal ArticleDOI
The iron-titanium oxides of salic volcanic rocks and their associated ferromagnesian silicates
TL;DR: In this article, the coexisting microphenocrysts of magnetite and ilmenite together with the ferromagnesian silicates in salic volcanic rocks have been analyzed with the electron microprobe.
Journal ArticleDOI
Omphacite in Californian metamorphic rocks
TL;DR: Omphacite is a common mineral in greenstones, metasediments and related Franciscan rocks of the glaucophane schist facies as discussed by the authors, and it also occurs in late veins cutting amphibolites, glaucaphane schists, eclogites, greenstones and occasionally metagraywackes.