The BGS Lexicon of Named Rock Units — Result Details

Allt Crom Complex

Computer Code: ALCR Preferred Map Code: AC
Status Code: Pending Upgrade
Age range: Silurian Period (S) — Devonian Period (D)
Lithological Description: Composed of a grey, aphyric, biotite granodiorite, with a marginal zone of pink leucogranite up to 200m wide. The granodiorite is composed of oligoclase, quartz and microcline, partly chloritised biotite and minor hornblende. Abundant disorientated rafts of host rocks of psammite and semipelite up to 500m long occur in the southern part of the complex, preserving a disrupted ghost stratigraphy, mainly seen on Sheet 63E, Dalwhinnie. Elsewhere, the granodiorite includes an area where the rafts are predominantly composed of appinitic diorite. These rafts are penetrated by veins of granodiorite but otherwise generally intact, albeit thermally metamorphosed. Contact metamorphism is intense within the rafts, most noticeably affecting semipelites and any calc-silicate rocks, and recognised up to 1.4 km away from the external contacts of the intrusion. In the northern part of the complex, mainly Sheet 73E - Foyers, the metasedimentary rocks become progressively more coherent so that some areas may be regarded as intact metasedimentary formations permeated by granodiorite veins of a variety of scales and to varying degrees of intensity. Subdivisions of the complex are recognised on the basis of the character of the metasedimentary rocks enclosed.
Definition of Lower Boundary: none recorded or not applicable
Definition of Upper Boundary: none recorded or not applicable
Thickness: none recorded or not applicable
Geographical Limits: Southern Monadhliath Mountains in northern part of the Dalwhinnie district (Scotland sheet 63E) and southern part of the Foyers district (Scotland sheet 73E).
Parent Unit: Argyll And Northern Highlands Granitic Suite (ANHGR)
Previous Name(s): Allt Crom Pluton (-639)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Hilltops and river sections in the Coire Iain Oig area, upper Spey catchment [Sherramore Forest]. 
Reference(s):
Claybourn, J A P, 1981. Age and petrogenetic studies of some magmatic and metamorphic rocks in the Grampian Highlands. Unpublished PhD thesis, University of Oxford. 
Anderson, J G C. 1956. Moinian and Dalradian rocks between Glen Roy and the Monadhliath mountains, Inverness-shire. Transactions of the Royal Society of Edinburgh, Vol.63, 15-36. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S063 S073