A whole crust resistivity cross-section across the AE forest Southern Uplands

Beamish, David. 1991 A whole crust resistivity cross-section across the AE forest Southern Uplands. Nottingham, UK, British Geological Survey, 26pp. (WN/91/025) (Unpublished)

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This report describes geoelectric modelling using data obtained from a reconnaissance MagnetoTe1luric (MT) survey carried out as part of the Southern Upland mapping programme. The 8 site survey, along a l4 km NW-SE profile, was centred on the Ae forest area to the east of Thornhill and to the SW of Moffatt. The measurements were undertaken across one of the fault-bounded tract sequences of greywackes in the Central Belt. The purpose of the limited survey was to investigate the possibility of ‘locally’ detecting concealed tectonostratigraphic structure by virtue of its (possible) resistivity expression. The MT method attempts to provide a resistivity cross-section, often through the whole crust. The sensors currently available restrict information to depths greater than several hundred metres. The present survey was carried out using a new 7-channel field instrument developed in-house by the BGS. The present report provides information on the modelling of the survey data and presents both one-dimensional (1-D) vertical profiles and a final 2-D whole crustal geoelectric section. l-D inversion of data from two sites within the Palaeozoic Lochmaben basin provide estimates of basin depth comparable with estimates obtained from gravity modelling. 2-D inversion of the profile data is undertaken using a new algorithm (OCCAM 2D) to provide a resistivity cross-section through the whole crust. Resistivities greater than 1000 ohm.m, tentatively associated with Silurian greywackes, extend to a depth of about 12 km. A relatively conducting (resistivities < 100 ohm.m) lower crust occurs at depths greater than l5 km in keeping with previous, low frequency MT observations across the Southern Uplands. A major set of lateral resistivity gradients are found, centred on a depth of about 2.5 km, to the NW of the northern end of the profile. Underlying this anomaly a modification in lower crustal resistivity is apparent at depths greater than l5 km. The resistivity cross-section suggests that a form of whole crustal modification occurs to the NW of the survey profile. The location of the main anomaly remains speculative since the reconnaissance survey was of limited length.

Item Type: Publication - Report
Programmes: Other/Admin
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
Additional Keywords: Magnetotelluric, resistivity, Southern Uplands
NORA Subject Terms: Earth Sciences
Date made live: 25 Jul 2017 08:16 +0 (UTC)

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