Structural histories in the SW Southern Uplands, Scotland

Abstract

The detailed structural histories in the SW part of the Southern Uplands are reviewed. The evolutionary sequences described from the southern part of the Central Belt are characteristic of a fold/thrust fault system which has been affected by strike-slip deformation. The present structure is characterized by tectonic domains usually less than 2 km across strike which show different internal deformation patterns and histories. The generalized deformation history of the area involves downslope movement, thrusting and folding followed by strike-slip deformation. The domain character of the area is considered to have developed by the juxtaposition of blocks throughout this deformation history. The concentration of anastomosing stratal disruption zones (developed by mixing of partially lithified sediment during deformation), and the geometry of folds and faults indicate the presence of an important shear zone towards the base of the Central Belt. A complex relationship between faulting, folding and cleavage development exists within this shear zone. Although cleavage development appears to post-date movement in some disruption zones, there is evidence that the disruption zone displacement was synchronous with or continued after cleavage development. These features indicate that the shear zone had a complex movement history spanning the lithification of the sediments. The structural histories described are compatible with an accretionary wedge model for the area although the nature of the basement which underlay the Southern Uplands during its evolution cannot be assessed from the outcrop-scale structures.

Geodynamic evolution of the Antarctic Peninsula during Mesozoic times and its bearing on Weddell Sea history

“…The tectonic setting of the Latady Formation is not known, but it does not appear to represent trench-fill sediment. In particular, the style of deformation associated with the Palmer Land event is inconsistent with accretionary-wedge type thrusting, with its associ- ated syn-sedimentary deformation, bedding disruption and bedding-parallel extension (Knipe et al 1988). (4) There is little one can deduce about the polarity of subduction beneath the peninsula from the magmatic record as roughly half of the proposed period of subduction (155-130) corresponded, from our present knowledge of the magmatic history, to a break in the record (160-141 Ma, Pankhurst 1982).…”

Geodynamic evolution of the Antarctic Peninsula during Mesozoic times and its bearing on Weddell Sea history

“…Folding deforms the youngest sedimentary infill, which is latest Tithonian in age . The onset of folding could be earlier, and penecontemporaneous with sedimentation, although syn-sedimentary deformation features with bedding disruption would be expected in this case, particularly in thrust zones (Knipe et al 1988). Without exception, structures described are ductile, or brittle-ductile (Williams 1970;Williams & Rowley 1971, 1972Rowley 1973Rowley , 1978Plummer 1974;Rowley & Williams 1974), and sedimentary sequences are described as repetitive and monotonous in sections up to 830m thick (Thomson et al 1978).…”

“…AP, Antarctic Peninsula; EWH, combined Ellsworth-Whitmore mountains-Haag Nunataks block; FP, Falkland Plateau; GFS, Gastre fault system; MBL, Marie Byrd Land; NZ, New Zealand; TI, Thurston Island; WSE, Weddell Sea Embayment. ated syn-sedimentary deformation, bedding disruption and bedding-parallel extension (Knipe et al 1988). (4) There is little one can deduce about the polarity of subduction beneath the peninsula from the magmatic record as roughly half of the proposed period of subduction (155-130) corresponded, from our present knowledge of the magmatic history, to a break in the record (160-141 Ma, Pankhurst 1982).…”

The nature and regional significance of structures in the Gala Group of the Southern Uplands terrane, Berwickshire coast, southeastern Scotland

“…Complex systems of mainly SE-verging folds and associated top-to-the-SE thrusts are recognized throughout much the Southern Uplands (e.g. Knipe & Needham, 1986;Knipe et al 1988) and are thought to have formed at relatively shallow crustal depths (< 10 km) based on the relatively low metamorphic grade (diagenetic to prehnitepumpellyite facies) (Oliver & Leggett, 1980;Kemp, Oliver & Baldwin, 1985).…”