Analysis of a mica subfabric

Keppie, J. Duncan

doi:10.1144/sjg05020171

Cited by 5 publications

(2 citation statements)

References 14 publications

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“…The sequence of events in the metasedimentarj schist regime (Table 3) shows the effects of polyphase deformation during the Laxfordian episode on sediments deposited c. 2.1 b.y. ago (Bhattacharjee 1963(Bhattacharjee , 1968Keppie 1969;Bikerman et al 1975). The dominant fold-forming phase (F3) corresponds with the dominant fold-forming phase in the gneisses with which c. 1740 m.y.…”

Section: Scotlandmentioning

confidence: 99%

Scotland–Finland Precambrian correlations

Bowes¹

1975

Bull Geol Soc Finland

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Isotopic age determinations indicate the generally co-eval nature of major episodes of earth history shown by the Precambrian rocks of Scotland and Finland, viz. (1) the c. 2 800-2 600 m.y. Scourian and Presvecokarelidic episodes, (2) the c. 2 200 m.y. Inverian episode and the c. 2 300 m.y. episode in Finland, (3) the c. 2.1 b.y. deposition of the Loch Maree Group in Scotland and the Jatulian quartzite, Karelian schists and related geosynclinal deposits in Finland, and (4) the c. 1 975-1 700 m.y. Laxfordian and Svecokarelian episodes. The existence of spatially connected belts in Precambrian times is suggested by the correspondence in both the sequence of development and the orientations of structural elements resulting from polyphase deformation in the successively formed Precambrian orogenic belts. This matching of complex structural frameworks implies that, before the initiation of the British-Scandinavian Caledonides, the Baltic Shield extended westward to include northwestern Britain and the continental shelf of the eastern North Atlantic Ocean. The Caledonian belt would then have developed on a plate of continental crust, or between the separated parts of a rifted continental crustal segment.

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Section: Scotlandmentioning

confidence: 99%

Scotland–Finland Precambrian correlations

Bowes¹

1975

Bull Geol Soc Finland

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“…. In the southern region the dominant mica growth in schists of the Loch Maree Series took place during the Laxfordian orogeny (Keppie 1967(Keppie , 1969. In the northern region Lambert and Holland (in press) and T. D. B. Lyon (personal communication) have determined ages indicative of the Laxfordian orogeny and the regional studies of Chowdhary and Bowes (in press), Dash (1969) and D. Findlay (personal communication) suggest that the effects of this orogeny are widespread.…”

mentioning

confidence: 99%

Lewisian Chronology

Bowes

Khoury

Park

1971

SJG

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Letters to die Editors LEWISIAN CHRONOLOGY SIRS, The discussion by Park(1970) of aspects of Lewisian chronology centres around an assessment of the general review and interpretative papers of Bowes (1968d, b, 1969) which dealt mainly with the Lewisian of the Northwest Highlands of Scotland. However, neither much of the original evidence on which these syntheses are based, nor other significant information relating to the Lewisian of the Northwest Highlands and the Outer Hebrides (e.g. Bennison and Wright 1969, pp. 41-6; Hopgood 1964) are taken into account. In addition, a considerable amount of information now published, or being published, was not available to Dr Park. This is particularly the case for the central region of the Lewisian of the Northwest Highlands (cf. Bowes 1969, figs. 1, 2; Park 1970, fig. 1) which includes the type areas for the Scourian and Inverian orogenies (' cycles' of Bennison and Wright 1969) and for the Scourie dyke. The evidence presented by Bowes and Khoury (1965) that basic minor intrusions were emplaced during both the Inverian and Laxfordian orogenies is rejected by Park (1970, p. 388) together with the relevant chronology of the central belt (Bowes 19686, table 1; 1969, table 1) as if this were the sole evidence available (cf. Park 1970, table 1, note 2). Without the detailed evidence of Khoury (1965, 1968a, b) and Barooah (1967), hypothetical correlations are made of events separated by Bowes (19686, 1969) and a * simplified' chronology is presented by Park (1970, table 2). But the field evidence for the district between Kylesku and Scourie (Bowes 1969, fig. 2), based on systematic mapping, is clear. One set of basic dykes was emplaced during the Inverian orogeny about 2190 m.y. ago (cf. Park 1970, p. 381). This dyke set is deformed by the pre-Torridonian fold belts which are generally accepted as representing Laxfordian deformation (F of Park 1970, table 1). Another set of basic dykes intrude the deformed dykes (cf Bowes and Khoury 1965) and cross-cut the fold belts. Their emplacement during the Laxfordian orogeny is shown by their deformation by late Laxfordian movements. * Correlation ' of these different suites on the assumption that there is only one suite of basic dykes in the central region (' the so-called Scourie dyke suite'-Park 1970, p. 387), the extension of this assumption to include basic intrusions in the southern region as members of the ' main Scourie dyke suite ' (Park 1970, p. 388), and the related assumption that a strong foliation formed immediately preceding basic dyke injection in a sequence is the dominant Inverian foliation (Park 1970, p. 388) explains much of the confusion and the differences in interpretation of Park (1970) and Bowes (19686, 1969). Evidence against these assumptions is not confined to the central belt of mainland Lewisian. Both Dash (1967; 1969, p. 349)

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Variation in Degree of Hornblende Grain Alignment within two Boudinage Structures

Schwerdtner¹,

Sheehan²,

Rucklidge³

1971

Can. J. Earth Sci.

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The degree of preferred orientation of hornblende in two boudinage structures is analyzed by means of an X-ray texture goniometer. Relative values of reflected intensity for {110} are plotted on the stereographic net, and contoured at convenient intervals. As in conventional fabric diagrams for hornblende, {110} define a great-circle girdle whose breadth reveals the density of unimodal grouping of [001].The density of grouping of [001] varies throughout both boudinage structures. It decreases with increasing extension in structure A, and seems to have a similar trend in structure B, where the determined variation in degree of grain alignment is of doubtful statistical significance.The inverse relationship between the degree of preferred orientation and the magnitude of extension may be attributed to rotation of the principal directions of finite strain during syntectonic crystallization. Alternatively, reorientation of strained grains by annealing recrystallization may have produced the inverse trend.

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Analysis of a mica subfabric

Cited by 5 publications

References 14 publications

Scotland–Finland Precambrian correlations

Scotland–Finland Precambrian correlations

Lewisian Chronology

Variation in Degree of Hornblende Grain Alignment within two Boudinage Structures

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