The Garabal Hill-Glen Fyne Igneous Complex

Abstract

I. Introduction The Garabal Hill-Glen Fyne igneous complex lies just west of the head of Loch Lomond and stretches westward into Glen Fyne. The complex occupies an area of some 12½ square miles embraced by sheets 37, 38, 45 and 46 of the one-inch Geological Survey map of Scotland. It breaks through various Dalradian schists already folded and regionally metamorphosed and these suffered thermal metamorphism when the rocks of the complex were intruded. The age of the complex is generally accepted as Lower Old Red Sandstone, owing to its close resemblance to other igneous masses of that age in Scotland. The earliest account of the area is given by Dakyns and Teall (1892) in a paper which has since become classical. The boundaries of the massif were accurately delineated, some of the rock types were mapped, briefly described and chemically analysed, and the hypothesis put forward that they had been derived from some parent magma by a process of differentiation operating at depth. A description of part of the western portion of the mass and of the thermal metamorphism induced there in the surrounding schists was published in the Cowal Geological Survey memoir (1897, pp. 96–101) and in the mid-Argyll memoir (1905, pp. 92–3). Finally, a paper by Wyllie and Scott appeared in 1913, dealing mainly with the ultrabasic rocks of the complex but including some data on the basic and intermediate rocks. The variation in the ultrabasic and dioritic rocks was ascribed to local variation

Peraluminous I-type granites

“…pointed out that in many intrusive and extrusive calc-alkaline rock suites there is a continuum from di-normative mafic compositions to felsic rocks that are C-normative. Both in that paper and in this was illustrated graphically for several rock suites, including granites of the Sierra Nevada Batholith (Bateman et al, 1963;Presnall and Bateman, 1973) and the Garabal Hills (sic) complex of Scotland (Nockolds, 1940). listed several models that had previously been proposed to account for the development of C-normative compositions, including secondary alteration, vapour phase transfer, assimilation or contamination with argillaceous material, crustal melting leaving an amphibolerich residue, melting of hydrous peridotite, and fractional crystallisation of clinopyroxene.…”

“…also plotted data from the Garabal HillGlen Fyne complex (32 km 2 ) of Scotland. The classic use of fractional crystallisation as a mechanism to account for the production of a series of granitic rocks for that complex was that of Nockolds (1940). Atherton (1993) has described that paper as "a geochemical confirmation of Bowen's belief in the importance of closed-system fractional crystallisation in the differentiation of plutonic rocks".…”

“…Such a dominance of felsic rocks is not uncommon among Caledonian plutonic rock suites. Phemister, in the printed account of the discussion after Nockolds presentation to The Geological Society, pointed out that over 80% of the complex is granodiorite (see Nockolds, 1940). He noted that this is far more than could have been produced by fractional crystallisation from Nockolds' parental pyroxene-mica diorite magma.…”

Hornblende-rich gabbro-diorite sequence in the Oura Igneous Complex, Maizuru City, Japan, part II: Hydrothermal events and genesis of igneous albite.

“…In the silicic differentiates from most mafic intrusions plagioclase is not albitic: andesine in the Skaergarrd intrusion (Wager and Deer, 1939), and oligoclase in the Gua dalupe igneous complex (Best, 1963) and Garabal Hill-Glen Fyne igneous complex (Nockolds, 1941). Unlike these differentiated rocks, the Oura appinitic rocks contain abundant igneous hornblende and rarely other mafic minerals.…”

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

“…There have been relatively few published accounts of the petrology of the Arrochar and Garabal Hill-Glen Fyne intrusions since the work of Anderson (1935) on Arrochar and the pioneering study of Nockolds (1941), which addressed the origin of the Garabal Hill-Glen Fyne complex. Johnston and Wright (1957) described the geology of the tunnels of the Loch Sloy hydroelectric scheme.…”