The geology of Ben Nevis, South-west Highlands, Scotland

[摘要] The Ben Nevis volcanic-plutonic Complex was intruded into garnet gradePrecambrian metasediments in the Southwest Highlands of Scotland towards the end of theCaledonian Orogeny. A variety of techniques have been applied to the Ben Nevis Complex inorder to model its volcanic and plutonic evolution; these include: field mapping,petrography, mineral chemistry, whole rock major and trace element geochemistry and acombined study of the isotopes of neodymium and strontium.Rocks of the volcanic pile are subdivided into the following formations; the Allt a'Mhuillin formation, the Coire na Ciste formation, the Ledge Route formation and the Summitformation, and these overlie a basement of Dalradian schist. Fine grained metasediments ofthe Allt a' Mhuillin formation were deposited in a lacustrine basin into which entered aseries of non-volcanic mass flow units. Non-volcanic deposition was terminated with theentry of the first volcaniclastic lahars of the Coire na Ciste formation into the Ben Nevisbasin. Block and ash flows, lava flows and sills are also found in this formation. The LedgeRoute formation testifies to a complex period of quiescence, airfall deposition and mass flowmovement after which localised flows of lava dominate the overlying Summit formation. Asingle felsite dyke is found intruding the volcanic pile and is correlated with early membersof the Ben Nevis dyke swarm in the northern area of the Ben Nevis Complex.Plutonic rocks of the Ben Nevis Complex are subdivided into the Fine Quartz Diorite,Sgurr Finnisg-aig Quartz Diorite, Coarse Quartz Diorite, Porphyritic Outer Granite andInner Granite; these were intruded to a high level in the crust. A dextral stress regimeoperated during the intrusion of the plutonic rocks. Each of the above units was intruded as aseries of pulses.Mass balance and qualitative trace element vector modelling (Rayleighcrystallisation) is able to model the geochemical evolution of the Porphyritic Outer Graniteusing plagioclase, amphibole, biotite and magnetite as the fractionating assemblage.Pyroxene is found as a phenocryst and as a groundmass phase in the quartz diorites withcalcic amphibole found mainly as a replacement mineral after pyroxene; however, traceelement modelling identifies amphibole as a fractionating phase.Isotopic modelling of the Ben Nevis Complex indicates the involvement of at leastthree components; these being a mantle source, a lower crustal source with similar isotopiccharacteristics to the Islay-Colonsay-Basement and, of lesser importance, Dalradianmetasediments. No single parental magma can explain the geochemical and isotopic variationof the Ben Nevis Complex.

[发布机构] University:University of St Andrews;Department:Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)

[效力级别] Scotland--Ben Nevis

[关键词] Geology--Scotland--Ben Nevis;Scotland--Ben Nevis