Petrogenesis of the Land's end granites

Abstract

Land's end granite is a serokinematic-post-kinematic, magmatic pluton which discordantly cuts the Mylor series and associated basic intrusives, the shallow slope of the granite is reflected in the narrow thermal metamorphic-metasomatlc aureole which does not exceed the grade of the amphibolite facies.
The granitic magma originated by differential anatexis of a deep-seated granite, granodiorite or granite-gneisse to produce a milieu mobilise corresponding in composition to the natural ternary field. This essentially quartzo-feldspathic liquid ascended in the crust by density difference, overhead stoping and assimilation. Towards the end of its emplacement history the magma consisted of a crystalline mash of both feldspars, micas & quartz, all lubricated by an interstitial fluid phase. Cooling was accompanied by autometasomatian.
Variations in the granite are due to contamination, while differentiation and filter pressing produced leucogranites and aplites which ascended through fractures in the essentially solid crust. This period was postdated by extensive potassium metasomatiam along a theme-chemical gradient with the production of the coarse porphyritic envelope surrounding the finer grained non-porphyritic core, the feldspar megacrysts arose by metasomatic, endoblastic growth upon nuclei (seed crystals) orientated by a regional stress gradient field.