Multi-chronometer dating of the Souter Head complex: Rapid exhumation terminates the Grampian Event of the Caledonian Orogeny

Darren F. Mark; Clive M. Rice; Malcolm Hole; Dan Condon

doi:10.1017/S1755691020000043

Multi-chronometer dating of the Souter Head complex: Rapid exhumation terminates the Grampian Event of the Caledonian Orogeny

Darren F. Mark^* (Corresponding Author)
, Clive M. Rice
, Malcolm Hole
, Dan Condon

^*Corresponding author for this work

Scottish Universities Environmental Research Centre (SUERC)
University of St Andrews
British Geological Survey

Research output: Contribution to journal › Article › peer-review

4 Citations (Scopus)

Abstract

The Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238-lead-206 (238U-206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U-Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium-osmium (Re-Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U-Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5-10 km Ma-1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50-100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.

Original language	English
Pages (from-to)	95-108
Number of pages	14
Journal	Earth and Environmental Science Transactions of the Royal Society of Edinburgh
Volume	111
Issue number	2
Early online date	8 Jul 2020
DOIs	https://doi.org/10.1017/S1755691020000043
Publication status	Published - 2020

Bibliographical note

Acknowledgements
Scottish Universities Environmental Research Centre (SUERC) would like to thank NERC for continued funding of the NERC Argon Isotope Facility. We would like to thank the following: Joyce Neilson/Natalie Farrell, John Still, Jenny Johnston/Jamie Bowie and the Lyon Bequest (University of Aberdeen) for discussion of CL data, assistance with the SEM, preparing figures and funding the work, respectively. Ross Dymock and Jim Imlach (SUERC) are thanked for their assistance with sample preparation. Martin Lee at the School of Geographical and Earth Sciences at the University of Glasgow for use of the SEM/CL equipment and Peter Chung for technical assistance. David Selby at the University of Durham for the Re–Os analyses and discussion of the data.

Keywords

granite
Ireland
KEY WORDS Ar/Ar
Re-Os
Scotland
U-Pb

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Multi-chronometer dating of the Souter Head complex: Rapid exhumation terminates the Grampian Event of the Caledonian Orogeny. / Mark, Darren F. (Corresponding Author); Rice, Clive M.; Hole, Malcolm et al.
In: Earth and Environmental Science Transactions of the Royal Society of Edinburgh, Vol. 111, No. 2, 2020, p. 95-108.

Research output: Contribution to journal › Article › peer-review

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abstract = "The Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238-lead-206 (238U-206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U-Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium-osmium (Re-Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U-Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5-10 km Ma-1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50-100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.",

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note = "Acknowledgements Scottish Universities Environmental Research Centre (SUERC) would like to thank NERC for continued funding of the NERC Argon Isotope Facility. We would like to thank the following: Joyce Neilson/Natalie Farrell, John Still, Jenny Johnston/Jamie Bowie and the Lyon Bequest (University of Aberdeen) for discussion of CL data, assistance with the SEM, preparing figures and funding the work, respectively. Ross Dymock and Jim Imlach (SUERC) are thanked for their assistance with sample preparation. Martin Lee at the School of Geographical and Earth Sciences at the University of Glasgow for use of the SEM/CL equipment and Peter Chung for technical assistance. David Selby at the University of Durham for the Re{\textendash}Os analyses and discussion of the data.",

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AU - Condon, Dan

N1 - Acknowledgements Scottish Universities Environmental Research Centre (SUERC) would like to thank NERC for continued funding of the NERC Argon Isotope Facility. We would like to thank the following: Joyce Neilson/Natalie Farrell, John Still, Jenny Johnston/Jamie Bowie and the Lyon Bequest (University of Aberdeen) for discussion of CL data, assistance with the SEM, preparing figures and funding the work, respectively. Ross Dymock and Jim Imlach (SUERC) are thanked for their assistance with sample preparation. Martin Lee at the School of Geographical and Earth Sciences at the University of Glasgow for use of the SEM/CL equipment and Peter Chung for technical assistance. David Selby at the University of Durham for the Re–Os analyses and discussion of the data.

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N2 - The Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238-lead-206 (238U-206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U-Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium-osmium (Re-Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U-Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5-10 km Ma-1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50-100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.

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Multi-chronometer dating of the Souter Head complex: Rapid exhumation terminates the Grampian Event of the Caledonian Orogeny

Abstract

Bibliographical note

Keywords

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