Caledonian ductile thrusting in a Precambrian metamorphic complex: The Moine of northwestern Scotland

Barr, David; Holdsworth, R. E.; Roberts, Alan

doi:10.1130/0016-7606(1986)97<754:cdtiap>2.0.co;2

Cited by 106 publications

(95 citation statements)

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“…However, such thickness variations can also be explained by variable amounts of thickening by folding, or by original stratigraphic facies changes. Barr et al (1986) suggested that the Knoydart Slide was marked by a jump in metamorphic grade from relatively low-grade in the east (c. 500 ± 30C°) to higher grade (580 ± 30C°) in the Morar Pelite. However, data points are sparse and it is unclear whether this represent a real jump or a more gradual change.…”

Section: Discussionmentioning

confidence: 99%

“…In eastern Knoydart, a major thrust termed the 'Knoydart Slide' has been interpreted along the contact between the Barrisdale Psammite and the Morar Pelite Formation (Poole & Spring 1974;Powell 1974;Barr et al 1986;Soper et al 1998). Above this thrust, within the outcrop of the Morar Pelite Formation (= Ladhar Bheinn Pelite in east Knoydart, Figs.…”

Section: Previous Structural Interpretationsmentioning

confidence: 99%

“…The Moine Nappe in the hangingwall of the Moine Thrust comprises a large (>50 x 200 km) outcrop of metasedimentary Morar Group rocks, together with a number of basement inliers, including the Glenelg-Attadale Inlier, all deformed under amphibolite-facies conditions (e.g. Barr et al 1986;Strachan et al 2010). The Moine Nappe contains a number of large-scale fold structures that broadly trend north-south in Knoydart and Morar (Fig.…”

Section: Geological Setting Of Knoydart Peninsulamentioning

confidence: 99%

“…Specifically these are: (i) the structural age of major folds such as the Loch Hourn Anticline and the Morar Antiform (Fig. 2), (ii) the presence or absence of an eastfacing 'Knoydart fold' and (iii) the presence or absence of the so-called 'Knoydart Slide' or thrust, separating a 'Knoydart Nappe' from the Moine Nappe (Poole & Spring 1974;Powell 1974;Barr et al 1986). The new evidence and analysis presented here clarify the internal structure of the southern part of the Moine Nappe, and also provide constraints as to the relative contribution of the different orogenic episodes that affected the Moine Nappe.…”

Section: Introductionmentioning

confidence: 99%

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Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

Krabbendam

Leslie

Goodenough

2014

SJG

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The Caledonian Orogen in Northern Scotland comprises two major thrust nappes: the Moine and the Sgurr Beag Nappe. The Moine Nappe contains early Neoproterozoic Morar Group rocks (Moine Supergroup) and basement inliers. This paper describes the structure and stratigraphy of the Knoydart peninsula, a key area within the southern Moine Nappe. The geology of Knoydart is dominated by a thick internally coherent sequence of Morar Group rocks. This sequence is shown to be deformed by large-scale, west-vergent and west-facing Caledonian (early Palaeozoic) folds that represent D2 within the southern Moine Nappe. Subsequent D3 deformation led to refolding or tightening of F2 folds, so that the major Morar Antiform is in essence a composite F2/F3 fold. F2 and F3 folds are broadly co-axial, but F3 folds have steeper axial planes.The F2/F3 folds refold a regional-scale, originally recumbent, isoclinal F1 fold nappe of probable Knoydartian (mid-Neoproterozoic) age. The F1 fold nappe is cored by a thin sliver of basement gneiss; the lower limb comprises migmatitic Morar Group rocks, exposed in the Morar Window. The upper limb of the F1 fold nappe occupies most of Knoydart and is stratigraphically coherent and right-way-up. Within this sequence, the upper unit of the Lower Morar Psammite is barely deformed, preserving trough-cross-bedding and largescale channels in thick beds. This suggests braided river deposition, similar to the Torridon Group west of the Moine Thrust and the Morar Group in the northern part of the Moine Nappe. On the basis of lithological similarity and stratigraphic disposition, it is suggested that the lowermost part of the Morar Group in Knoydart correlates with the Neoproterozoic Sleat Group on Skye.

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Section: Discussionmentioning

confidence: 99%

Section: Previous Structural Interpretationsmentioning

confidence: 99%

Section: Geological Setting Of Knoydart Peninsulamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

Krabbendam

Leslie

Goodenough

2014

SJG

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“…While there is some evidence of Grenville-age events (Holdsworth et al, 1994, p. 24), the structure of the region is dominated by Caledonian deformation that has been described in terms of an earlier phase of regional ductile detachment such as the Sgfirr Beag thrust (Tanner, 1971;Barr et al, 1986), and later large-scale open-to-tight upright folds (Harris and Johnson, 1991, p. 93). Deformation was accompanied by regional metamorphism up to sillimanite grade (Kennedy, 1949;Fettes et al, 1985).…”

Section: Regional Settingmentioning

confidence: 99%

Chromian Illite-Ankerite-Quartz Parageneses from the Kintail District of Southern Ross-Shire, Scotland

Clifford¹

1999

Mineralogical Magazine

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The Coire Dhuinnid fault zone contains emerald green chromian illite-ankerite-quartz rocks that are similar in appearance to the fuchsite(or mariposite)-carbonate-quartz parageneses that are commonplace in Archaean greenstone belts but which are rather rare in Phanerozoic rocks. The chromian illite contains 2.3 wt.% Cr20> low K20 (7.1 7.6 wt.%) and high H20+ (5.7 wt.%), and it is a 1M polytype with ~<10% of an illite/smectite interstratification indicative of a formation temperature of c. 175-200~ The host rocks contain high concentrations of Ni and Cr, and show low concentrations of Ti, Nb, Y and Zr, suggesting a tbrmer primitive mafic protolith (boninitic magma?); they are considered to be retrograde remnants of Lewisian rocks. The latter, and the associated rocks of the Moine Series, have been affected by CO2 metasomatism that was accompanied by the addition of Ca(+Sr), Fe and Mg, and by the removal of Na from, and the addition of H20 to the Moine metasediments. Radiogenic isotope studies of mineral separates and whole rock from sample no. 43 yielded ages of 483_+2 Ma (Ar-Ar dating on Cr illite), 413_+ 12 Ma (K-Ar dating on Cr illite), and 322 + 9 Ma (Rb-Sr dating on minerals and whole rock); the significance of this discrepant pattern is discussed.

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The stratigraphy, structure and regional significance of the Moine Rocks of Mull, Argyllshire, W. Scotland

1987

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Two right-way-up Moine lithostratigraphic units-the Shiaba (older) and Assapol (younger) Groupsare distinguished in the Ross of Mull. These were intruded in the west by the post-tectonic, Ross-ofMull granite complex at 414 k 3 Ma. Apparently undisturbed inclusions of Moine metasediments within the granite permit the boundary between the lithostratigraphic units to be followed westward almost to the supposed trace of the Moine thrust in the Sound of Iona. The Shiaba and Assapol Groups which have a transitional, albeit attenuated, stratigraphic contact are correlated with the Morar and Glenfinnan Divisions of Inverness-shire, the Sgurr Beag ductile thrust (slide) normally found at the MoradGlenfinnan Division boundary being absent. This implies that the stratigraphic relationship between these two divisions, which is elsewhere obscured by the thrust, is uniquely preserved on Mull.Within a local, Dl-D4 sequence, D2 and D3 structures are dominant. Originally subhorizontal D2 folds are intensely curvilinear on all scales about an originally flat-lying, NNW-SSE trending stretching lineation (L2). In sections parallel to L2, D2 minor folds display a constant sense of vergence throughout the Ross-of-Mull Moine Rocks, overturning generally NW-NNW. The present day structure is dominated by the almost upright, SSW-plunging D3 Assapol synform which overprints all earlier structures. Tentative correlation of the deformation sequence with that of Inverness-shire, suggests that the Dl-D2 structures of Mull, with accompanying moderate-to-high-grade rnetamorphism, may be Precambrian, while the D3 Assapol synform may be Caledonian.The presence of migmatites of kyanite grade means that metamorphic grade, established during MSI-MP2, is anomalously high for Moine rocks lying close to the supposed Caldonian front. This suggests that they may lie within one of the higher Caledonian thrust nappes of the North Highland Moine-possibly the Knoydart nappe, where metamorphic grade is comparable. The greenschist facies metamorphism and single phase of deformation affecting the 'Torridonian' rocks of Iona presents a significant contrast to the Moine rocks of the Ross of Mull. A major fault in the Sound of Iona is implied, but the Moine thrust itself probably does not outcrop.

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Caledonian ductile thrusting in a Precambrian metamorphic complex: The Moine of northwestern Scotland

Cited by 106 publications

References 0 publications

Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

Chromian Illite-Ankerite-Quartz Parageneses from the Kintail District of Southern Ross-Shire, Scotland

The stratigraphy, structure and regional significance of the Moine Rocks of Mull, Argyllshire, W. Scotland

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