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Spatial coupling between spilitization and carbonation ofbasaltic sills in SW Scottish Highlands: evidence of amineralogical control of metamorphic fluid flow
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.ORCID-id: 0000-0002-3732-7993
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.ORCID-id: 0000-0003-0847-9258
2011 (Engelska)Ingår i: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 11, nr 3, s. 245-259Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In a geochemical and petrological analysis of overprinting episodes of fluid–rock interaction in a well-studied metabasaltic sill in the SW Scottish Highlands, we show that syn-deformational access of metamorphic fluids and consequent fluid–rock interaction is at least in part controlled by preexisting mineralogical variations. Lithological and structural channelling of metamorphic fluids along the axis of the Ardrishaig Anticline, SW Scottish Highlands, caused carbonation of metabasaltic sills hosted by metasedimentary rocks of the Argyll Group in the Dalradian Supergroup. Analysis of chemical and mineralogical variability across a metabasaltic sill at Port Cill Maluaig shows that carbonation at greenschist to epidote–amphibolites facies conditions caused by infiltration of H2O-CO2 fluids was controlled by mineralogical variations, which were present before carbonation occurred. This variability probably reflects chemical and mineralogical changes imparted on the sill during premetamorphic spilitization. Calculation of precarbonation mineral modes reveals heterogeneous spatial distributions of epidote, amphibole, chlorite and epidote. This reflects both premetamorphic spilitization and prograde greenschist facies metamorphism prior to fluid flow. Spilitization caused albitization of primary plagioclase and spatially heterogeneous growth of epidote ± calcic amphibole ± chlorite ± quartz ± calcite. Greenschist facies metamorphism caused breakdown of primary pyroxene and continued, but spatially more homogeneous, growth of amphibole + chlorite ± quartz. These processes formed diffuse epidote-rich patches or semi-continuous layers. These might represent precursors of epidote segregations, which are better developed elsewhere in the SW Scottish Highlands. Chemical and field analyses of epidote reveal the evidence of local volume fluctuations associated with these concentrations of epidote. Transient permeability enhancement associated with these changes may have permitted higher fluid fluxes and therefore more extensive carbonation. This deflected metamorphic fluid such that its flow direction became more layer parallel, limiting propagation of the reaction front into the sill interior.

Ort, förlag, år, upplaga, sidor
2011. Vol. 11, nr 3, s. 245-259
Nyckelord [en]
carbonation;metamorphic fluids;mineralogical control;spilitization;SW Scottish Highlands
Nationell ämneskategori
Geologi Geofysik Geokemi
Identifikatorer
URN: urn:nbn:se:su:diva-65249DOI: 10.1111/j.1468-8123.2011.00335.xISI: 000293796800001OAI: oai:DiVA.org:su-65249DiVA, id: diva2:461841
Anmärkning
authorCount :3Tillgänglig från: 2011-12-05 Skapad: 2011-12-05 Senast uppdaterad: 2020-01-30Bibliografiskt granskad

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Alasdair, SkeltonPitcairn, Iain
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