Thermal modeling in the Midland valley of Scotland using BasinMod and HotPot

Vincent, C.J.; Rowley, W.J.. 2004 Thermal modeling in the Midland valley of Scotland using BasinMod and HotPot. Nottingham, UK, British Geological Survey, 60pp. (IR/04/144) (Unpublished)

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The Midland Valley of Scotland (MVS) has a complex geological history. The overall structure of the basin is that of a fault bounded, late Palaeozoic sedimentary basin. Volcanic intrusions and lavas are also present. It is generally believed that Dinantian extension tectonics resulted in mantle thinning, high heat flow and basaltic magmas. This regime is thought to have continued until the late Namurian when active extension appeared to give way to post-extensional thermal subsidence (Stephenson et al 2003). Westphalian volcanism was more limited and strike-slip tectonics was probably dominant. The majority of rocks at the surface are of Devonian to Carboniferous age. A few younger deposits are found in the MVS terrane suggesting that Mesozoic rocks probably covered the MVS before the latest period of uplift and erosion that is believed to have begun in the Palaeogene. This report concentrates on the eastern Midland Valley around the Firth of Forth. Three boreholes with suitably detailed stratigraphy and maturity (vitrinite reflectance) data were chosen and modelled using BasinMod™ (Platte River Software). The palaeo-heat flow curve was based on the assumption that extension would have caused high heat flow through the Carboniferous and into the Namurian. Given the lack of thermal maturity data, it was assumed that the heat flow would then gradually decrease to its present day level. The boreholes selected for use with BasinMod were successfully modelled using 420-660m Variscan (end-Carboniferous) erosion and 1300-1900m Palaeogene-Quaternary erosion. From using BasinMod to model maturity, high heat flow (up to 83mW/m2) resulting from tectonic activity appeared to have caused the most rapid increase on the maturity of the coals as indicated by their vitrinite reflectance. Maximum depth of burial for the base of the Silesian Limestone Coal Formation was 2900m and maximum temperature reached was 115°C during the Tertiary. Igneous intrusions were seen to have a very localised heating effect on the surrounding rocks. The HotPot model concentrates across a larger area of the eastern Midland Valley. A number of boreholes and several Earthvision grids were used to perform backstripping calculations and to construct the basin depositional history. The thermal history of the basin was then developed using a generalised model, based on high heat flow during the Carboniferous extensional phase of tectonics, decreasing slowly to the present day levels. The HotPot modelling results are given in section 4 of this report, and are compared with the BasinMod results in section 5. Using these two modelling packages in the Midland Valley allows comparison of two contrasting modelling techniques; the BasinMod model is based on thermal maturity data (vitrinite reflectance) and the HotPot model is based on mechanical compaction. Some conclusions drawn from the authors’ experience of using these two packages are presented in section 6. Finally, section 7 outlines products from these modelling packages that may be added to the DGSM GLOS.

Item Type: Publication - Report
Programmes: BGS Programmes > Digital Geoscience Spatial Model
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externaly peer-reviewed
Date made live: 16 Jan 2015 15:45 +0 (UTC)

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