229:, extending into Sutherland, the Basal Pelite and the lower part of the Lower Psammite is interpreted to be missing but the sequence is otherwise similar. The Lower Psammite is divided into the lower Altnaharra Psammite Formation, with the Glen Achall Semipelite Member at the top, and the upper Glascarnoch Psammite Formation. The Vaich Pelite Formation is the equivalent of the Morar Schists and the Crom Psammite Formation is matched to the Upper Psammite. Above this is the Diebidale Pelite Formation. On the Ross of Mull, four formations are recognised: the Lower Shiaba Psammite Formation at the base (no older beds exposed), the Shiaba Pelite Formation, the Upper Shiaba Psammite Formation and the Laggan Mor Formation, which becomes increasingly highly deformed as it approaches its contact with the younger Glennfinnan Group.
34:
253:, with fluvial deposition being replaced by shoreline deposits that were tidally influenced, before a deeper marine environment developed during the deposition of the Vaich Pelite Formation. This is interpreted to be a single progradation-retrogradation cycle. A second cycle began with a return to shallow water deposition in the lower part of the Crom Psammite Formation, grading upwards to a distal braid plain setting, before returning to a tidal shoreline and eventually to shallow water marine deposition in the Diebidale Pelite Formation.
261:, with the Torridon Group being more proximal to the mountains of the Grenville Orogen and the Morar Group more distal. Previous models of a rift setting are not consistent with the scale of the sedimentary systems observed, nor are there the expected rapid vertical and lateral changes in sedimentary facies typical of rift basins.
256:
A very similar pattern of cycles have been deduced for the
Torridon Group with which they have been correlated within the Wester Ross Supergroup. Due to movement on the Moine Thrust, the depositional areas of the Torridon and Morar groups are likely to have been separated by more than 100 km. These
245:
for the Morar Group. The main challenge has been differentiating between shallow marine shelf and fluvial settings for the deposition of the sequence. For the Ross succession, the Basal Pelite is interpreted to represent deposition in paleovalleys, similar to the
Diabaig Formation of the Torridon
224:
The group has been subdivided in several parts of its outcrop. In the
Knoydart and Morar areas, a fourfold subdivision is recognised starting from the oldest: Basal Pelite Formation, Lower Morar Psammite Formation, Morar Schists Formation and Upper Morar Psammite Formation. Further north in
315:
that carry slices of the
Altnaharra Psammite, each with a piece of Lewisian-type basement just above the thrust. Between the Moine Thrust and the Swordly Thrust (which is interpreted to form the base to the Glenfinnan Group in this part of the outcrop), there are the Ben Hope Thrust, the
627:
Krabbendam, M.; Ramsay, J.G.; Leslie, A.G.; Tanner, P.W.G.; Dietrich, D.; Goodenough, K.M. (2017). "Caledonian and
Knoydartian overprinting of a Grenvillian inlier and the enclosing Morar Group rocks: structural evolution of the Precambrian Proto-Moine Nappe, Glenelg, NW Scotland".
569:
Bird, A.; Cutts, K.; Strachan, R.; Thirlwall, M.F.; Hand, M. (2018). "First evidence of
Renlandian (c. 950–940 Ma) orogeny in mainland Scotland: Implications for the status of the Moine Supergroup and circum-North Atlantic correlations".
496:
Glendinning, R.W.A. (1988). "Sedimentary structures and sequences within a late
Proterozoic tidal shelf deposit: the Upper Morar Psammite Formation of northwestern Scotland". In Winchester, J.A. (ed.).
340:. The effects of the Relandian Orogeny have only been recognised locally within the group in northern Sutherland. The age range calculated for garnets sampled in the Meadie Schist is 950–940 Ma at
533:
Strachan, R.A.; Holdsworth, R.E.; Krabbendam, M.; Alsop, G.I. (2010). "The Moine
Supergroup of NW Scotland: insights into the analysis of polyorogenic supracrustal sequences". In Law, R.D. (ed.).
464:"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"
305:
unravelled the complex history of multiple phases of deformation. The folding involves the Sgurr Beag Thrust, showing that it postdates the deposition of the Loch Ness
Supergroup.
273:
while the youngest age is constrained by the dating of the oldest metamorphic/tectonic event that has affected the group since deposition. The youngest detrital zircon and
356:
of
Grenvillian age, the first stage of deformation (D1) within the Morar Group is interpreted to be Knoydartian age south-southeast directed ductile thrusting and related
277:
ages found for samples from the Morar Group are 1070–1000 Ma (million years ago). The oldest metamorphic event known from the Morar Group is that associated with the
597:
Simpson, A.; Glorie, S.; Hand, M.; Spandler, C.; Gilbert, S. (2023). "Garnet Lu-Hf speed dating: A novel method to rapidly resolve polymetamorphic histories".
363:
The D1 structures in the Glenelg area are affected by two later phases of folding that have been assigned to late Grampian (D2 460–440 Ma) and Scandian (D3).
348:
and 600°C. There is much more evidence of Knoydartian orogenesis across the Morar Group outcrop and it seems to have produced major structures. Around the
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70:
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349:
157:
events since their deposition. Originally interpreted to be lowest (oldest) part of a "Moine Supergroup", this sequence now forms part of the
297:
The structure of the Morar Group varies from south to north. In the southern part of the outcrop, around areas such as Morar, Knoydart and
212:
rocks in southeast Sutherland, to the southeast. It reaches the north coast of Sutherland to the north and extends as far south as the
391:
Krabbendam, M.; Strachan, R.; Prave, T. (2022). "A new stratigraphic framework for the early Neoproterozoic successions of Scotland".
514:
208:
to the northwest to the contact with the Glennfinnan Group, marked by the Sgurr Beag Thrust or Swordly Thrust, or locally
550:
324:
At least four orogenic events have been interpreted to affect the Morar Group, in order of age, the Renlandian, the
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360:. The peak metamorphic conditions for the Knoydartian are estimated at about 7 kb and 650°C.
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areas there are sufficient sedimentary structures preserved to provide constraints on the
8:
432:
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methods. Together these give an age range of 1000–950 Ma for deposition of the group.
33:
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similarities are consistent with a model in which both sequences were deposited in a
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537:. Special Publications, Geological Society London. Vol. 335. pp. 233–254.
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301:, rocks of this group are often intensely deformed. Loch Monar was the area where
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Continental Tectonics and Mountain Building: The Legacy of Peach and Horne
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Group. The Altnaharra Psammite is interpreted to have been deposited as a
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Folded Morar Schist of the Morar Group, in Glen Meadail near Inverie in
482:
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Dherue/Achness Thrust, the Naver Thrust and the Torrisdale Thrust.
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The oldest age of the Morar Group is constrained by the results of
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Later Proterozoic Stratigraphy of the Northern Atlantic Regions
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In Sutherland the Morar Group are affected by a series of
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Krabbendam, M.; Leslie, A.G.; Goodenough, K.M. (2014).
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200:The Morar Group outcrops over a large part of the
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352:, which is formed of Lewisian type gneisses and
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188:is everywhere a tectonic one, formed by the
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281:, which gives ages of 950–940 Ma, using
149:that have been subjected to a series of
667:Geological groups of the United Kingdom
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91:up to 9,000 metres (29,530 ft)
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393:Journal of the Geological Society
180:. The contact with the overlying
584:10.1016/j.precamres.2017.12.019
437:BGS Lexicon of Named Rock Units
344:/temperature conditions of 6–7
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1:
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271:detrital zircon geochronology
104:Psammite, semi-pelite, pelite
501:. Springer. pp. 14–15.
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630:Scottish Journal of Geology
507:10.1007/978-1-4615-7344-9_2
471:Scottish Journal of Geology
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429:British Geological Survey
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611:10.1016/j.gr.2023.04.011
243:depositional environment
192:or related structures.
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159:Wester Ross Supergroup
61:Wester Ross Supergroup
112:Conglomerate, breccia
572:Precambrian Research
233:Depositional setting
186:Loch Ness Supergroup
662:Geology of Scotland
642:10.1144/sjg2017-006
405:10.1144/jgs2021-054
202:Northwest Highlands
25:Stratigraphic range
483:10.1144/sjg2014-00
338:Caledonian Orogeny
279:Renlandian Orogeny
73:(tectonic contact)
599:Gondwana Research
516:978-1-4615-7344-9
358:isoclinal folding
206:Moine Thrust Belt
190:Sgurr Beag Thrust
147:sedimentary rocks
137:is a sequence of
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182:Glenfinnan Group
178:Lewisian complex
171:Paleoproterozoic
82:Lewisian complex
71:Glenfinnan Group
51:Geological group
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350:Glenelg inlier
336:phases of the
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303:John G. Ramsay
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143:Neoproterozoic
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433:"Morar Group"
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27:: 1000–950 Ma
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440:. Retrieved
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220:Stratigraphy
214:Ross of Mull
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117:Type section
605:: 215–234.
578:: 283–294.
477:: 125–142.
414:10023/24155
326:Knoydartian
251:braid plain
161:. They lie
155:metamorphic
135:Morar Group
19:Morar Group
656:Categories
367:References
328:, and the
299:Loch Monar
248:prograding
227:Ross-shire
636:: 13–35.
354:eclogites
293:Structure
122:Named for
96:Lithology
88:Thickness
67:Underlies
342:pressure
334:Scandian
330:Grampian
210:Devonian
174:basement
151:tectonic
78:Overlies
40:Knoydart
442:12 June
310:ductile
184:of the
176:of the
167:Archean
141:(lower
101:Primary
57:Unit of
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275:rutile
239:strain
196:Extent
139:Tonian
467:(PDF)
287:Sm–Nd
283:Lu-Hf
126:Morar
109:Other
547:ISBN
511:ISBN
444:2024
332:and
285:and
153:and
133:The
47:Type
638:doi
607:doi
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580:doi
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265:Age
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
