Geology of the Llanidloes area: Geological description - Geophysics
This page is part of a category of pages providing a summary of the geology of the Llanidloes district (British Geological Survey Sheet 164). Links to other pages in this category can be found at the foot of the page. Authors: Wilson, D, Burt, C E, Davies, J R, Hall, M, Jones, N S, Leslie, A B, Lusty, P A J, Wilby, P R, and Aspden, J A. |
The Bouguer gravity anomaly map (Figure P930914). reveals a more-or-less steady increase in gradient towards the north-west of the district. This pattern, which is apparent on a regional scale, reflects the main structural trend within the basin and is consistent with the presence of dense Lower Palaeozoic or basement rocks at a shallower crustal level in the coastal tract to the west. Euler deconvolution analyses of the regional gravity data (McDonald et al., 1992[1]) suggests that the juxtaposition of rocks of different densities took place across long-lived basement structures such as the Glandyfi Lineament (Cave and Hains, 1986[2]) and Bronnant Fault (Davies et al., 1997[3]; Wilson et al., 1992[4]).
The regional aeromagnetic anomaly map (Figure P930915) shows a weak magnetic high in the south-eastern part of the district. The reasons for this anomaly are unclear but reflect the presence of magnetic basement or a concealed igneous complex at a relatively shallow crustal depth. The feature is one of a series of weak anomalies that broadly lie along the Pontesford Lineament, one of the component structures of the Welsh Borderland Fault System (Woodcock and Gibbons, 1988[5]).
References
- ↑ McDonald, A J W, Fletcher, C J N, Carruthers, R M, Wilson, D, and Evans, R B. 1992. Interpretation of the regional gravity and magnetic surveys of Wales using shaded relief and Euler deconvolution techniques. Geological Magazine, Vol. 129, 523–531.
- ↑ Cave, R, and Hains, B A. 1986. Geology of the country between Aberystwyth and Machynlleth. Memoir of the British Geological Survey. Sheet 163 (England and Wales).
- ↑ Davies, J R, Fletcher, C J N, Waters, R A, Wilson, D, Woodhall, D G, and Zalasiewicz, J A. 1997. Geology of the country around Llanilar and Rhayader. Memoir of the British Geological Survey, Sheets 178 and 179 (England and Wales).
- ↑ Wilson, D, Davies, J R, Waters, R A, and Zalasiewicz, J A. 1992. A fault-controlled depositional model for the Aberystwyth Grits turbidite system. Geological Magazine, Vol. 129, 595–607.
- ↑ Woodcock, N H, and Gibbons, W. 1988. Is the Welsh Borderland Fault System a terrane boundary? Journal of the Geological Society of London, Vol. 145, 915–923.