Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Journal of the Geological Society

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Johnson, T.E. Articles by Droop, G.T.R. Search for Related Content GeoRef GeoRef Citation

Evidence for a genetic granite–migmatite link in the Dalradian of NE Scotland

^{1 1}Laboratory for Crustal Petrology, Department of Geology, University of Maryland, College Park, MD 20742, USA (e-mail: timj@geol.umd.edu)
^{2 2}Division of Earth Systems Science, University of Derby, Kedleston Road, Derby DE22 1GB, UK
^{3 3}Department of Earth Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK

The Inzie Head gneisses of the NE Dalradian are syntectonic metapelitic migmatites containing numerous sill-like bodies of granite. Leucosomes preserve evidence for efficient deformation-controlled segregation and interconnection of melt, from intergranular pockets to sheets of leucogranite hundreds of metres thick. Although the physico-chemical system is complex, the geochemistry of in situ decimetre-scale leucosomes and discrete metre- to decametre-scale leucogranite sheets within the migmatites suggests derivation from a common metapelitic source. A comparison with spatially and temporally related Grampian Granite plutons and garnet-bearing aplites that occur at shallower crustal levels supports a genetic granite–migmatite link. The compositions of the granitic rocks are interpreted to be linked via fractional crystallization of a parental magma and escape of the fugitive melt from a cumulate residue. Leucogranite sheets within the migmatites have compositions that are similar to experimentally determined first-formed melts at the appropriate P–T conditions, and are interpreted to approximate parental liquids. Smaller-scale leucosomes contain the accumulated products of fractional crystallization and variable quantities of entrained solids, principally biotite. The Grampian Granites and aplites represent evolved liquids that segregated from source. The evolution of Grampian Granite melts involved varying degrees of K-feldspar-dominated fractional crystallization that is consistent with magma ascent; removal of a maximum of 15–20% cumulate material is implied. The composition of the aplites suggests a multistage evolution that involved plagioclase-dominated fractionation of a fugitive melt batch.

KEYWORDS: Dalradian, migmatite, leucogranite, fractional crystallization

This article has been cited by other articles:

				G. STEINHOEFEL, E. HEGNER, and G. J.H. OLIVER Chemical and Nd isotope constraints on granitoid sources involved in the Caledonian Orogeny in Scotland Journal of the Geological Society, July 1, 2008; 165(4): 817 - 827. [Abstract] [Full Text] [PDF]

				M. Brown Crustal melting and melt extraction, ascent and emplacement in orogens: mechanisms and consequences Journal of the Geological Society, July 1, 2007; 164(4): 709 - 730. [Abstract] [Full Text] [PDF]