59 research outputs found
The Petrology, Geochemistry And Genesis Of Sulphide-related Alteration At The Temagami Mine, Ontario
Complex subvolcanic magma plumbing system of an alkali basaltic maar-diatreme volcano (Elie Ness, Fife, Scotland)
Alkali basaltic diatremes such as Elie Ness (Fife, Scotland) expose a range of volcanic lithofacies that points to a complex, multi-stage emplacement history. Here, basanites contain phenocrysts including pyrope garnet and sub-calcic augites from depths of ~60km. Volcanic rocks from all units, pyroclastic and hypabyssal, are characterised by rare earth element (REE) patterns that show continuous enrichment from heavy REE (HREE) to light REE (LREE), and high Zr/Y that are consistent with retention of garnet in the mantle source during melting of peridotite in a garnet lherzolite facies. Erupted garnets are euhedral and unresorbed, signifying rapid ascent through the lithosphere. The magmas also transported abundant pyroxenitic clasts, cognate with the basanite host, from shallower depths (~35–40km). These clasts exhibit wide variation in texture, mode and mineralogy, consistent with growth from a range of compositionally diverse melts. Further, clinopyroxene phenocrysts from both the hypabyssal and pyroclastic units exhibit a very wide compositional range, indicative of polybaric fractionation and magma mixing. This is attributed to stalling of earlier magmas in the lower crust — principally from ~22 to 28km — as indicated by pyroxene thermobarometry. Many clinopyroxenes display chemical zoning profiles, occasionally with mantles and rims of higher magnesium number (Mg#) suggesting the magmas were mobilised by juvenile basanite magma. The tuffs also contain alkali feldspar megacrysts together with Fe-clinopyroxene, zircon and related salic xenoliths, of the ‘anorthoclasite suite’ — inferred to have crystallised at upper mantle to lower crustal depths from salic magma in advance of the mafic host magmas. Despite evidence for entrainment of heterogeneous crystal mushes, the rapidly ascending melts experienced negligible crustal contamination. The complex association of phenocrysts, megacrysts and autoliths at Elie Ness indicates thorough mixing in a dynamic system immediately prior to explosive diatreme-forming eruptions.Clough and Mykura Fund of the Geological Society of Edinburgh; Timothy Jefferson Fund of the Geological Society of Londo
J. R. Craig and D. J. Vaughan Ore Microscopy and Ore Petrography, 2nd Edition, Chichester and New York (John Wiley and Sons, Ltd). 1995 xiv + 434 pp. Price £18.95. ISBN 0471115991.
Kd interactions at 1.45 and 1.65 GeV/c and a regge pole analysis of the reaction Kn [lamda][pi]
J.R. Craig and D.J. Vaughan Ore Microscopy and Ore Petrography, 2nd Edition, Chichester and New York (John Wiley and Sons, Ltd). 1995 xiv + 434 pp. Price s ISBN 0-471-115991.
(J. D.) Ridge. Annotated bibliographies of mineral deposits in Africa, Asia (exclusive of the USSR) and Australasia. Oxford and New York (Pergamon Press), 1976 viii+545 pp., 8 figs. Price £16.50.
Regional Geochemistry of the Lake District and adjacent areas. Geochemistry Group of the British Geological Survey, Keyworth, Nottingham (British Geological Survey), 1993. viii + 98 pp, 46 coloured maps + 1:250 000 geological map. Price £50.00. ISBN 0 85272 2257.
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