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Contrasting magma emplacement mechanisms within the Rogart igneous complex, NW Scotland, record the switch from regional contraction to strike-slip during the Caledonian orogeny

Published online by Cambridge University Press:  16 December 2013

H. KOCKS ,
R. A. STRACHAN ,
J. A. EVANS  and
M. FOWLER
H. KOCKS
Affiliation:
Kocks Consult GmbH, Stegemannstr.32–38, Koblenz, Germany
R. A. STRACHAN*
Affiliation:
School of Earth & Environmental Sciences, University of Portsmouth, Burnaby Rd, Portsmouth, PO1 3QL, UK
J. A. EVANS
Affiliation:
NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, UK
M. FOWLER
Affiliation:
School of Earth & Environmental Sciences, University of Portsmouth, Burnaby Rd, Portsmouth, PO1 3QL, UK
*
†Author for correspondence: [email protected]
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Abstract

The Rogart igneous complex is unique within the northern Scottish Caledonides because it comprises an apparent continuum of magma types that records a progressive change in emplacement mechanisms related to large-scale tectonic controls. Syn-D2 leucogranites and late-D2 quartz monzodiorites were emplaced during crustal thickening and focused within the broad zone of ductile deformation associated with the Naver Thrust. In contrast, emplacement of the post-D2 composite central pluton was controlled by development of a steeply dipping dextral shear zone along the Loch Shin Line, interpreted as an anti-Riedel shear within the Great Glen Fault system. The mantle-derived nature of the late-to-post-D2 melts implies that the Naver Thrust and the Loch Shin Line were both crustal-scale structures along which magmas were channelled during deformation. A U–Pb zircon age of 425±1.5 Ma for the outer component of the central pluton provides an upper limit on regional deformation and metamorphism within host Moine rocks. These findings are consistent with the view that a fundamental change in tectonic regime occurred in the Scottish Caledonides at c. 425 Ma, corresponding to the switch from regional thrusting that resulted from the collision of Baltica and Laurentia, to the development of the orogen-parallel Great Glen Fault system.

Keywords

granitegeochronologytectonicsCaledonides
Type
Original Articles
Information
Geological Magazine , Volume 151 , Issue 5 , September 2014 , pp. 899 - 915
Copyright
Copyright © Cambridge University Press 2013 

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