Orogenic versus extensional settings for regional metamorphism; Knoydartian events in the Moine Supergroup revisited

• Published in: Journal of the Geological Society Vol. 166; no. 2; pp. 201 - 204
• Main Authors: Cutts, Kathryn A, Hand, M, Kelsey, D. E, Strachan, R. A
• Format: Journal Article
• Language: English
• Published: London, UK Geological Society of London 01-03-2009; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: burial; compression; crustal thickening; crystal zoning; Crystalline rocks; Earth sciences; Earth, ocean, space; Europe; Exact sciences and technology; extension; fabric; folds; garnet group; Geology; geothermal gradient; Great Britain; igneous and metamorphic rocks; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Knoydartian; Metamorphic rocks; metamorphism; mineral assemblages; Moine Supergroup; Moinian; Neoproterozoic; nesosilicates; orogeny; orthosilicates; P-T conditions; P-T-t paths; Petrology; phase equilibria; Plate tectonics; Precambrian; Proterozoic; recumbent folds; regional metamorphism; Rodinia; Scotland; silicates; Structural geology; tectonics; thermodynamic properties; United Kingdom; upper Precambrian; Western Europe; United Kingdom; Scotland; Great Britain; Europe; Western Europe; extension; crustal thickening; burial; software; thickness; thermodynamics; P-T conditions; pressure; tectonics; geothermal gradient; regional metamorphism
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/0016-76492008-015

Considerable debate exists over the tectonic regimes associated with mid-Neoproterozoic metamorphism of the Moine Supergroup, NW Scotland. Published pressure conditions imply burial to 35-40 km, a potential doubling of crustal thickness, and hence a substantial collisional event. Re-evaluation using updated thermodynamic software suggests more modest peak pressures of c. 7.5 kbar implying burial to c. 21 km. The revised P-T path has a comparatively flat clockwise evolution from early high geothermal gradient conditions. The revised P-T conditions suggest that c. 800 Ma crustal thickening within the Moine Supergroup was less significant than previously envisaged and possibly preceded by extension.