Geophysical Studies of the Cheviot Hills

The Institute of Geological Sciences carried out Aeromagnetic Anomaly and Gravity Anomaly surveys in the Cheviots to enable the publication of the Aeromagnetic Anomaly map for the area in 1980 and the Bouguer Anomaly map in 1981. Robson and Green added to the gravity anomaly data following their ground level surveys conducted in 1981.

All this information was collected and synthesised by M.K. Lee for publication as ‘Regional Geophysics of the Cheviot Area’ for the Environmental Protection Unit in 1982 enabling a comprehensive understanding of the three dimensional structures of the Cheviot pluton, lavas and surrounding sedimentary rocks.

The maps that follow are based on those published in the latter publication.
Click on a map to open it in higher resolution.

Aeromagnetic Anomaly Map

Aeromagnetic Anomaly Map

This map results from survey flights carried out between 1959 and 1963. It is based on the 1:250,000 series Aeromagnetic Anomaly maps, Boarders and Farne sheets.

Main features:

A. Large positive anomaly over the granite with lower values over the less magnetic Standrop/Granophyric types and higher values corresponding to the highly magnetic Marginal type and the hornfels. The surrounding un-metamorphosed lavas create minor magnetic anomalies. 
The extension of the main anomaly to the south may relate to the metamorphic effects of the underlying Biddlestone laccolith.

B & C. Magnetic anomalies probably corresponding to the presence of lava below the surface sediments

Bouguer Gravity Anomaly Map

Bouguer Gravity Anomaly Map

This is a modification on the 1:250,000 Borders and Farne Sheets published by the Institute of Geological Sciences in 1981. Here, a density of -2.73g cm-3 has been used for the Bouguer corrections instead of the original value of 2.70 g cm-3 to represent the density of the Lower Palaeozic rocks that are assumed to underlie the entire Cheviot region.

Main features:

A. The clear negative anomaly with a minimum of 19 mgals centred on Cheviot granite. This suggests a low-density granite pluton with a density that corresponds to the Standrop/Granophyric varieties.

B. The subsidiary minimum over the rhyolitic lavas and Lower Carboniferous conglomerate in the Windy Gyle area.

C. A ‘low’ extension that corresponds to a thickening of Carboniferous sediments rather than subsurface extensions of the granite.

Second Derivative Gravity Anomaly Map

Second Derivative Gravity Anomaly Map

This map helps to separate anomalies due to different geological structures, emphasising near surface density contrasts at the expense of deep structures and regional trends.

Main features:

A. The negative anomaly that suggests a low-density granite with outward sloping contacts. It is centred to the north of the main granite outcrop indicating that granite lies close to the surface here.

B. The subsidiary minimum over the rhyolitic lavas and Lower Carboniferous conglomerate in the Windy Gyle area here extending WSW beyond the lava covered area. This suggests a thicker sequence of lavas together with the possibility of underlying Devonian sediments north of the Gyle fault.

C. Second derivative ‘high’ occurring where the Lower Palaeozic basement rock is exposed at the surface.

D & E. Second derivative ‘lows’ over thickening Carboniferous sediments at D extends to E along the Hetton fault.

F. A second derivative ‘high’ corresponding to the exposed Lower Paleozoic basement rock.

No vestige of a beginning, – no prospect of an end

error: