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dc.contributor.authorClark, G. C.en
dc.date.accessioned2018-05-14T10:11:47Z
dc.date.available2018-05-14T10:11:47Z
dc.date.issued1961
dc.identifier.urihttp://hdl.handle.net/1842/29688
dc.description.abstracten
dc.description.abstractThe metasedimentary rocks of the area have had a complex structural and metamorphic history. The structural analysis indicates that the rocks have suffered four periods of folding, and by study of the major and minor structures of each generation the age relationships of the fold movements can be established. The history of the fold episodes may be summarised:en
dc.description.abstract1. first period of isoclinal folding. No major isoclinal folds have been recognized, but first minor structures are widespread and indicate that the whole area has been isoclinally folded. This first period of folding is probably the structural equivalent to the first movement episode recognized in Morar by W.Q. Kennedy (1955) - the formation of the Morar nappe.en
dc.description.abstract2. period of tight, asymmetric folding during which all the rocks of the area were again folded. The second folds are Similar in style and their orientation has been considerably modified by the third fold movement. The evidence suggests that after the second period of folding had taken place the rocks were vertically oriented.en
dc.description.abstract3. period of open asymmetric folding about a N.N.E -S.S .W. 177. axial plane trend. The third folds are partly Similar and partly Concentric in style. The Diollaid Bheag Antiform, a fold some two miles wide, formed during this period of folding.en
dc.description.abstract4. period of open asymmetric folding about a N.W. -S.r. axial plane trend. The fourth folds are of local occurrence, and their affect upon the orientation of the rocks and structures of the earlier fold movements is only slight.en
dc.description.abstractIt has been found that the stratigraphical succession established by Richey and Kennedy (1939) in the Lioìne rocks of Morar, could not be extended into the whole of the area mapped. The structural evidence indicates that the rocks have been isoclinally folded, and it is concluded that the stratigraphical succession has been repeated. The few sedimentary structures that have been found indicate that the pelitic rocks of An Stac and Rois-Bheinn are stratigraphically younger than the psammitic rocks which have been correlated with the Upper Psammitic Group of Morar (Richey, 1938). It is suggested that the original stratigraphical succession may have consisted of four main lithological groups. In the area mapped all the psammitic and pelitic bands contain thin calc- silicate ribs. Richey and Kennedy (1939) stated that these calc- silicate ribs are absent in the Lower Psammitic Group and Lower Striped Schists of the Llorar succession. It may be suggested therefore that the lower part of the Ilorar stratigraphical succession is not represented in the area mapped.en
dc.description.abstractThe rocks of the central and eastern parts of the area have been strongly migmatised, the migmatisation taking place before and during the second period of folding. In the area of migmatisation the rocks are coarsely crystalline gneisses and the pelitic rocks have been transformed into oligoclase -biotite- gneiss and locally, granite gneiss. Thick discordant pegmatite veins are common.en
dc.description.abstractIt is concluded that during migmatisation the rocks were at sillimanite grade of metamorphism, and associated with this period of high grade metamorphism the anorthitehornblende and anorthite -pyroxene metamorphic zones of the calc-silicate rocks were developed. Recrystallisation again occurred during or after the third and fourth fold movements, but it is probable that regrowth of garnet did not take place. Throughout the area the biotites, and occasionally the garnets, show alteration to chlorite, and these features of retrogressive activity must have taken place during or after these late phases of recrystallisation.en
dc.description.abstractDuring the four periods of folding it is evident that the rocks responded to deformation in a very plastic manner, no cataclastic, or brittle structures found in the area can be definitely correlated with the four fold movements. The style of the fold periods is such that the intensity of deformation decreases, from isoclinal folding during the first fold movement, to very open asymmetric folding during the fourth movement episode. It is interesting to note that the metamorphic history shows a similar decrease in intensity. The evidence suggests that at approximately the same time as the first and second fold movements the grade of metamorphism of the rocks was extremely high, but during the later periods of open folding, the rocks only suffered low grade metamorphism. (fig. 27)en
dc.description.abstractThe suggested age relationship between metamorphism and movement is only tentative. Because the rocks have undergone recrystallisation several times during their movement history, and that recrystallisation appears to have taken place during or after the final fold movement, an accurate correlation between the metamorphic and structural histories is difficult to establish. The several phases of folding provide important 'marker horizons in the structural and metamorphic history, and only by comparison and correlation with the structure and meta-morphism of adjacent areas will the complete age relationship between metamorphism and movement be determined.en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2018 Block 18en
dc.relation.isreferencedbyen
dc.titleThe structural and metamorphic history of the Lochailort (Moidart) areaen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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