The BGS Lexicon of Named Rock Units — Result Details
Beannach Metapicrite Subswarm
| Computer Code: | BMP | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Paleoproterozoic Era (AL) — Paleoproterozoic Era (AL) | ||
| Lithological Description: | The Beannach Picrite Subswarm comprises the Mg-rich members of the Scourie Dyke Swarm. The dykes of the subswarm are most abundant within the Lewisian Gneiss Complex in the Assynt region, where they are found to the north of the Canisp Shear Zone. They typically have a broadly east-west trend.The dykes of the subswarm are mostly coarse-grained, texturally hererogeneous and lacking in chilled margins.In composition they are picritic and have the primary mineralogy olivine - orthopyroxene - clinopyroxene - plagioclase - phlogopite - chromite. The dykes of the Beannach Metapicrite Subswarm clearly post-date the majority of the metadolerites of the Scourie Dyke Swarm, although they are cross-cut by some late dolerites. One dyke of the subswarm has been dated at 2418 +7/-4 Ma (Heaman and Tarney, 1989). | ||
| Definition of Lower Boundary: | N/a | ||
| Definition of Upper Boundary: | N/a | ||
| Thickness: | 1m -100m. | ||
| Geographical Limits: | The dykes of the Beannach Picrite Subswarm are part of the Lewisian Gneiss Complex and only occur within it. They have only been mapped as a separate subswarm in the Assynt area where they occur between Glen Canisp and Scourie. | ||
| Parent Unit: | Scourie Dyke Swarm (SCOUR) | ||
| Previous Name(s): | Assynt Metapicrite Subswarm [Obsolete Name And Code: Use BMP]
(AMP)
Bronzite picrite dykes of the Scourie Dyke Swarm [Obsolete Name and Code: Use BMP] (-4478) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Area | Dykes of the subswarm occur in the Lewisian Gneiss Complex of Assynt. The well-studied examples are at Lochs Beannach [NC145 264] and Leothaid [NC 144 227]. Tarney, 1973; Tarney and Weaver, 1987. | ||
| Reference(s): | |||
| Tarney, J. 1973. The Scourie Dyke Suite and the nature of the Inverian event in Assynt. 105-117 in Park, R G and Tarney, J (editors), The Early Precambrian of Scotland and related rocks of Greenland. [University of Keele.] | |||
| Weaver, B L and Tarney, J. 1981. The Scourie Dyke Suite: Petrogenesis and Geotechnical Nature of the Proterozoic Sub-Continental Mantle. Contributions to Mineralogy and Petrology, Vol.78, 175-188. | |||
| Heaman, L M and Tarney, J. 1989. U-Pb baddeleyite ages for the Scourie Dyke Swarm, Scotland; evidence for two distinct intrusion events. Nature, 340, 705-708. | |||
| Tarney, J. and Weaver, B L. 1987. Mineralogy, petrology and geochemistry of the Scourie dykes: petrogenesis and crystallization processes in dykes intruded at depth. p. 217-233 in Evolution of the Lewisian and Comparable Precambrian High Grade Terrains. Park, R.G. and Tarney, J. (eds.) Geological Society Special Publication No. 27. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||