Grenville age for rocks in the Moine of north-western Scotland

Brook, M.; Brewer, Martin; Powell, Derek

doi:10.1038/260515a0

Cited by 109 publications

(45 citation statements)

References 15 publications

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“…Early attempts to date these intrusions using the Rb-Sr wholerock isochron method gave ages around 1000 Ma (Brook et al 1976). Together with Rb-Sr isochrons yielding c. 1000 Ma ages from the country rocks, these results were interpreted as evidence that the Grenville orogeny had affected the Moine rocks (Brook et al 1977;Brewer et al 1979;Roberts et al 1987).…”

Section: West Highland Granite Gneissmentioning

confidence: 94%

Late Precambrian U–Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

Tanner

Evans²

2003

JGS

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There has been controversy over the number and timing of orogenies in the Precambrian Moine block in the Scottish Caledonides since the earliest radiometric dating in the 1960s. This work challenges a recent hypothesis, that this sector of the Laurentian margin was subjected to continuous crustal extension between .900 and 470 Ma. U-Pb dating (thermal ionization mass spectrometry) of titanite from a calcsilicate pod in the Moine (Morar Group) of the western Highlands gives an age of 737 AE 5 Ma. The titanite grew from Fe-Ti-bearing detrital minerals during the main progressive, syn-D 2 , amphibolite-facies (sillimanite zone) regional metamorphism, thus demonstrating that a Neoproterozoic contractional tectonothermal event (Knoydartian orogeny) affected the Moine block following the rift-related emplacement of the West Highland granite gneiss at 873 Ma. We conclude that the Sgurr Beag Thrust, a major tectonic break separating the Morar and Glenfinnan groups of the Moine, is mainly of Neoproterozoic, not Caledonian, age. The early tectonothermal event was succeeded by the Grampian Phase (Caledonian orogeny) at 460-470 Ma.

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Section: West Highland Granite Gneissmentioning

confidence: 94%

Late Precambrian U–Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

Tanner

Evans²

2003

JGS

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“…The Strontian Granodiorite intrudes Moinian metasediments, mainly pelites and semipelites of the Glenfinnan Division, which probably underwent metamorphism in the Grenville Orogeny about 1.0 Ga ago (Brook et al, 1976) but have suffered further, Caledonian regional metamorphism (Brook et al, 1977, Table 3). The area studied ( fig.…”

Section: Copyright the Mineralogical Societymentioning

confidence: 99%

Garnet zoning and re-equilibration in the Strontian area, Scotland

Tyler

Ashworth

1981

Mineral. mag.

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ABSTRACT. In Moinian metasediments regionally metamorphosed to sillimanite grade, garnet has subsequently been re-equilibrated in the inner (cordierite-potash feldspar) zone of the aureole of the Strontian Granodiorite. Zoning profiles of garnet from the aureole, and from surrounding regional assemblages, show retrograde Mnrich rims. Some regional garnets are also internally zoned. In the aureole as a whole, the partition measure for Fe and Mg between garnet and biotite shows a correlation with that for Ca between garnet and plagioclase. If interpreted in terms of a simple equilibrium model, this might suggest that pressure decreased with increasing temperature towards the granodiorite, but the trend can more plausibly be attributed to deviation from ideal solidsolution behaviour of Ca in garnet and plagioclase, with incomplete homogenization of garnet as a complicating factor in the outer parts of the aureole. From the difference in the temperature thresholds for garnet core equilibration, the timescale t2 of the thermal event relative to the regional t I is estimated as t2/t 1 ~-10 -1"1-+0"7, consistent with emplacement of the intrusion at an early stage of regional cooling.

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“…The demonstration of a Grenville age for the Morar Division (Brook et al 1977) shows that it is no longer valid to apply evidence from one area to the whole Moine tract. At least two sedimentary prisms must be represented, perhaps more than two.…”

Section: Discussionmentioning

confidence: 95%

“…The former has yielded a whole-rock Rb/Sr age of 1050 ± 46 Ma (Brook et al 1976) and the latter an age of 1024 ± 95 Ma by the same method (Brook et al 1977). These ages imply a pre-Morarian (Grenville) orogenic metamorphism which Brook et al (1977, table 3) associate with the D2 tectonic event in the Morar and Glenfmnan Moines.…”

Section: Introductionmentioning

confidence: 91%

Proterozoic folds on the Northwest Caledonian Foreland

Soper

Barber

1979

SJG

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Synopsis Recent isotopic studies have shown that parts of the Moine sedimentary sequence underwent orogenic metamorphism before 1000 Ma and this raises doubts as to the significance of the c. 730 Ma ‘Morarian’ ages yielded by pegmatites from the Moine tract. From evidence readily available from Geological Survey publications we show that the Torridonian rocks of the NW Caledonian foreland were folded and eroded in Precambrian time. This folding was coeval with emplacement of the Morarian pegmatites, supporting the view that the Morarian was a tectonothermal event of regional importance, and permitting (but not establishing) the stratigraphic equivalence of the Upper Torridonian with the Moine rocks in western Sutherland.

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Grenville age for rocks in the Moine of north-western Scotland

Cited by 109 publications

References 15 publications

Late Precambrian U–Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

Late Precambrian U–Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

Garnet zoning and re-equilibration in the Strontian area, Scotland

Proterozoic folds on the Northwest Caledonian Foreland

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