Editing Fracturing and faulting - St. Kilda: an illustrated account of the geology

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Several structures are seen in exposures of the Conachair Granite in the cliffs and tidal rock shelves which extend south-eastwards from the jetty in Village Bay. On the rock shelves a conspicuous reddened fault plane trending at 300° and dipping 75° north-east can be followed for about 150 m up to the jetty, cutting an earlier fault trending at 330° and dipping 60° north-east. The younger fault extends into a zone of shattered Mullach Sgar Complex forming the course of the Abhainn Mhor between 60 m and 140 m. Similar 300°-trending faults coated with orthoclase and quartz are exposed in the cliffs surrounding the cave at the south-east end of the shelves, where they in turn are cut by vertical planes trending at 220° which are also mineralised with felsitic material. Post-mineralisation slickensides on the later set of fractures suggests that the most recent movement was mainly vertical with a small north-easterly horizontal component. Vertical slickensided planes with a similar orientation (220°) can be seen beside the slipway to the jetty, where again they cut the earlier faults dipping at 55° north-east and trending 305°.
 
Several structures are seen in exposures of the Conachair Granite in the cliffs and tidal rock shelves which extend south-eastwards from the jetty in Village Bay. On the rock shelves a conspicuous reddened fault plane trending at 300° and dipping 75° north-east can be followed for about 150 m up to the jetty, cutting an earlier fault trending at 330° and dipping 60° north-east. The younger fault extends into a zone of shattered Mullach Sgar Complex forming the course of the Abhainn Mhor between 60 m and 140 m. Similar 300°-trending faults coated with orthoclase and quartz are exposed in the cliffs surrounding the cave at the south-east end of the shelves, where they in turn are cut by vertical planes trending at 220° which are also mineralised with felsitic material. Post-mineralisation slickensides on the later set of fractures suggests that the most recent movement was mainly vertical with a small north-easterly horizontal component. Vertical slickensided planes with a similar orientation (220°) can be seen beside the slipway to the jetty, where again they cut the earlier faults dipping at 55° north-east and trending 305°.
  
In Glen Mor several drift covered NW-trending faults can be located from stream exposures of shattered rock; the kink in the Abhainn à Ghlinne Mhoir shown in [[:File:P991867.jpg|(Plate 37A)]] follows one of these faults. They appear to be terminated by NE–SW-trending faults along which such features as the Dun Passage, Cambir Neck and probably Soay Sound have been formed by erosion. The latest set of faults appears to have developed more or less contemporaneously with the intrusion of the suite of late dykes and cone sheets. For example, at Geo na Lashulaich [[:File:P991866.jpg|(Figure 36)]] several cone sheets converge on a pre-existing NE–SW fault, and while a similar fault cutting Conachair Granite at Geo nan Sgarbh displaces some basic sheets, another sheet appears to have been intruded along the fault plane for several metres.
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In Glen Mor several drift covered NW-trending faults can be located from stream exposures of shattered rock; the kink in the Abhainn a Ghlinne Mhoir shown in Plate 37A follows one of these faults. They appear to be terminated by NE–SW-trending faults along which such features as the Dun Passage, Cambir Neck and probably Soay Sound have been formed by erosion. The latest set of faults appears to have developed more or less contemporaneously with the intrusion of the suite of late dykes and cone sheets. For example, at Geo na Lashulaich [[:File:P991866.jpg|(Figure 36)]] several cone sheets converge on a pre-existing NE–SW fault, and while a similar fault cutting Conachair Granite at Geo nan Sgarbh displaces some basic sheets, another sheet appears to have been intruded along the fault plane for several metres.
  
 
Field relationships suggest that the following sequence of structural events can be distinguished on St Kilda:
 
Field relationships suggest that the following sequence of structural events can be distinguished on St Kilda:

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