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- W2346875620 abstract "Over forty igneous horizons of Dinantian age are recorded. Themajor Lavas occur as 'scutulu~type' shields reaching diameters of 10 kmand thicknesses of 1-200 mwith central vents marked by boss-like tuffcones. Subordinate pyroclastic intercalations and discrete cones representphraeatomagmatic interactions but extrusive activity was predominantlysubaerial. 'Clay-wayboards' also associated with emergentsurfaces, represent air-fall ash of distal, acidic, origin. but alsoinclude local degraded tuffs.The basalts display a restricted petrography and all are microphyricwith olivine, augite and labradorite. Eight petrographic typesbased on phenocryst assemblage and textures are defined. Selectioncriteria were developed to avoid weathered or hydrothermally alteredsamples although deuteric affects are ubiquitous. Despite theirphyric-nature, geochemical variations encompass well defined trends.Geochemical evolution was controlled by restricted eutectic fractionationin a periodically replenished magma chamber. The basalts are of a 'transitional'nature between typical alkali or tholeiitic types.The basalts are not'barren' with regard to mineralisation but fundamentalchanges in the style of mineralisation within basalt hosts arenoted. Hydrothermal interactions result in zoned wall-rock alterationthe development of which correlates with the attainment of wall-rockdiffusion equilibrium, while geochemical variations correspond withfluid-inclusion data.K-Ar isotopic dating indicate complex relationships, with devitrificationand smectite replacement of interstitial phases resulting insystematic argon loss. Samples yielding true stratigraphic ages can only be selected on an empirical basis. Deuteric smectite phasespersist during incipient hydrothermal alteration and exert an older'contaminating' influence resulting in a spread of 'apparent' ages.This is negated during 'advanced' -alteration reflecting in relativepotassium saturations and resolves the spread of ages into twodistinct mineralising events at 240 ~ 5 m.y. and 170 ± 5 m.y. Thesecorrelate with widespread episodes of Mesozoic mineralisation in theUnited Kingdom.The Sills and Lavas are consanguineous, it is envisaged thatreplenishment of a number of shallow magma chambers was accompaniedby ascensive injections of magma which in places reached the surfaceas extrusive lavas, but elsewhere formed high-level Sills oftenlocalised by intrusion along the 'line of weakness' afforded by olderLava interfaces." @default.
- W2346875620 created "2016-06-24" @default.
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- W2346875620 date "1981-01-01" @default.
- W2346875620 modified "2023-09-27" @default.
- W2346875620 title "The igneous horizons of the South Pennine orefield and their interactions with mineralization." @default.
- W2346875620 hasPublicationYear "1981" @default.
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