The cause of widespread Carboniferous and Early Permian magmatism that occurred across Northern Europe and the UK remains enigmatic. New Ar-40-Ar-39 radiometric dating reveals that some of the earliest manifestations of alkaline to sub-alkaline magmatism, found near the southern limit of the province in the Peak District of Central England (Waterswallows Sill: 328.6 +/- 4.2 Ma; Calton Hill: 316.4 +/- 3.7 Ma), coincided with episodes of extensional and thermal subsidence. The variable geochemical compositions, changing tectonics, and geographic location of the Peak District rocks provide opportunity to understand regional magmatic processes. A combination of geodynamic and geochemical modelling is done using new whole-rock major- and trace-element data, and Sr-Nd-Pb isotope results. To aid comparison, new geochemical data are also provided for the magmatism in Scotland and for the younger Whin Complex in Northern England (ca. 297 Ma). Due to different amounts of partial melting, olivine assimilation, and post-magmatic alteration, a new type of data visualization-the compatible element plot-is devised to aid interpretation. Given the shape of REE patterns, together with the Sc and V contents, it indicates melting took place within the garnet stability field. Geodynamic modelling of the Derbyshire carbonate platform and Edale Basin calculated a low beta-value (similar to 1.1) for a uniform extensional regime. However, the Caledonian and Acadian orogenies may have made the deep lithosphere beneath Britain unstable, promoting later founding and asthenospheric upwelling. To help with discussion on this scenario, a non-uniform lithospheric extension model is presented with a beta-value of 2. On this basis, an alternative model is introduced, whereby warmer-than-ambient (not hot) fingers of mantle plume under-flow facilitates decompression melting of the asthenosphere during extensional processes. In locations such as Derbyshire, magma ascended to the surface utilizing the deep-seated faults present in asymmetric basins. With such a model, a plume trace or significant doming may not necessarily be obvious but an interplay between tectonics, lithospheric structure and mantle processes is key.

Heat exchangers are vital to any geothermal system looking to use direct heat supplied via a district heat network. Attention on geothermal schemes in the UK has been growing, with minimal attention on the performance of heat exchangers. In this study, different types of heat exchangers are analysed for the Cheshire Basin as a case study, specifically the Crewe area, to establish their effectiveness and optimal heat transfer area. The results indicate that counter-current flow heat exchangers have a higher effectiveness than co-current heat exchangers. Optimisation of the heat exchange area can produce total savings of £43.06 million and £71.5 million, over a 25-year lifetime, in comparison with a fossil-fuelled district heat network using geothermal fluid input temperatures of 67 °C and 86 °C, respectively.

The block and basin tectonostratigraphic framework for the northern Pennine (rift) Basin, within which buoyant granite intrusions core intra-basin fault-bounded blocks, has long held traction. However, many of the elements of this framework are rooted in primitive tectonic models and, perhaps unsurprisingly, corresponding depositional models often reflect this. Using sedimentological and sedimentary provenance approaches, the synrift (Mississippian) fluvio-deltaic Fell Sandstone Formation and age-equivalent strata within the northern Pennine Basin are examined. Highlighted divergences from classically depicted models relate to occurrences of pre-Carboniferous basement domes or monoclines, which are unbounded by major vertically displacing (>100 m) fault systems. Such structures in the northern Pennine Basin are all granite-cored and their origins are associated with their buoyancy and flexural isostatic processes. One such basement dome, the Cheviot Block, confined and deflected the Fell Sandstone fluvio-deltaic system from the west, causing locally elevated net sand content and variations in the dominant palaeodrainage direction. Central parts of the Alston Block, which forms a regional monocline along an east–west axis, were comparatively uplifted because of flexural isostatic responses to granite intrusions. The findings presented are at variance not only with classically depicted depositional models for the region, but also with more general depictions of dominantly normal fault-driven rift basin systems. Supplementary material: Tables of data locations with derivation, trace element data and major element (oxide) data are available at https://doi.org/10.6084/m9.figshare.c.5733257

Deep hot sedimentary aquifers (HSAs) are targeted for geothermal exploitation in the Cheshire Basin, UK. In this study, a single extraction well targeting the Collyhurst Sandstone Formation was modelled on MATLAB coupling heat and fluid flux. The Collyhurst Sandstone Formation in the Crewe area of the Cheshire Basin is expected to be found at a depth of 2.8–3.5 km, and was chosen as an area for geothermal exploration due to the high demand for energy. Model results suggest that low-enthalpy, deep geothermal systems with thick HSAs are affected by both geological and engineering parameters. The results of this study highlight that the thermal gradient, hydraulic conductivity, production rate, length and position of the well screen are the key parameters capable of affecting the success and viability of any single well scheme. Poor planning during exploration and development can hinder the productivity of any single-well scheme, and these parameters must be considered to fully understand the risk. Engineering parameters, such as the length of the well screen, can be used during well planning to mitigate geological risks in the aquifer, whilst the results presented can also be used as a guide for energy potential under varying conditions.

Local seismic and borehole-based mapping of the Carboniferous Pennine Coal Measures and Warwickshire Group successions in the Canonbie Coalfield (SW Scotland) provides evidence of repeated episodes of positive inversion, syn-depositional folding and unconformities. A Duckmantian (Westphalian B) episode of NE–SW transpression is recognized, based on onlapping seismic reflector geometries against NE-trending positive inversion structures and contemporaneous NNE-trending syn-depositional growth folding. The basin history thus revealed at Canonbie is at variance with generally accepted models in neighbouring northern England that imply subsidence was due to post-rift thermal subsidence during late Carboniferous times. A late Westphalian–Stephanian unconformity recognized within the Warwickshire Group succession signifies NW–SE, c . 10% local basin shortening during a time of major shortening in the late Carboniferous Variscan foreland, contradicting suggestions that maximum Variscan shortening had negligible impact on Carboniferous basins in northern Britain. Local inversion structures appear to have strongly influenced local late Westphalian–Stephanian depocentres. In this respect, the Variscan foreland at Canonbie may have resembled a ‘broken’ foreland system. Variations in crustal rheology, fault strength and orientation, and mid-crustal detachments are suggested to have played important roles in determining strain localization and the nature of Westphalian–Stephanian depocentres in the Canonbie Coalfield.

Many of the most widely used deep geothermal resource maps for the UK are produced by contouring around sparsely distributed and often unreliable data points. We thus present a MATLAB-based 3D finite difference temperature modelling methodology, which provides a means for producing more resolute and geologically realistic versions of these maps. Our case study area in northern England represents an area where both sedimentary basins and radiothermal granite bodies comprise potential geothermal resources. We divide our 3D model into geological units, which are then assigned separate thermal properties. Assuming conductive heat transfer and steady-state and fixed boundary conditions, we calculate 3D regional subsurface temperature. Due to our averaging technique for thermal properties, the resolution of our geological model is scarcely compromised with respect to similar finite element methods. One predicted ‘hot spot’ at 1 km depth in the central part of our case study area corresponds with the granitic North Pennine Batholith. Other shallow hot spots correspond with thermally insulating sedimentary rock units and geological structures that incorporate these units. Predictive heat flow density maps highlight areas with accelerated surface heat flow associated with shallow conductive basement rock and heat producing granite bodies. Our predicted subsurface temperatures show broad similarities with measured equilibrium borehole temperatures. Inaccuracies may relate to convective heat transfer involving fault systems, or input variables relating to the geological model. Our predictive subsurface temperature and heat flow density maps are more resolute and geologically realistic relative to pre-existing contoured maps. The method presented here represents a useful tool for understanding controls on subsurface temperature distribution and geothermal potential.

Few deep wells have been drilled in the Cheshire Basin, resulting in high geological and financial risk of geothermal developments. Although the geothermal gradient in the basin can be predicted, the transmissivity of aquifers at depth are unknown. This has led to an investigation of lower risk strategies such as deep coaxial borehole heat exchangers (BHEs) for spatial heating, rather than traditional doublet methods. A model of a deep coaxial BHE was designed within MATLAB using the finite-difference method. The model produces accurate results in comparison to an analytical solution with a fast computational time. Results indicate that under best case geological parameters sustainable heat loads in excess of 298.7 kW can be produced from deep coaxial borehole heat exchangers at a depth of 2.8 km over the duration of a 20 year operational cycle. The thermal gradient and conductivity for this scenario were set at 27 ?C/km and 3 W/m?C, respectively. The thermal gradient, depth of borehole, volumetric flow rate and thermal conductivity of the surrounding rock all impact the heat load and outlet temperature of a deep coaxial borehole heat exchanger. The coefficient of system performance decreases with increased volumetric flow rates due to an increase in power consumption within the borehole heat exchanger. For an optimal flow rate of 4 l/s (calculated as the flow rate to produce most net power at the end of a heating season), the coefficient of system performance was 5.29. The thermal performance and efficiency of the system provides confidence that the geothermal resource of the Cheshire Basin has significant potential to be developed via deep coaxial borehole heat exchangers. Additionally, regression analysis was undertaken in this study. These models can be used to predict heat loads and outlet temperatures at the end of a heating season without the need for complex numerical modelling.

The Carboniferous northern Pennine Basin remains the type locality for the ‘block and basin’ tectonic framework model. It has been widely believed that during periods of tectonic extension, large low‐density bodies within the basement permit buoyant blocks to resist isostatic subsidence. However, lithosphere‐scale structural and geodynamic modelling experiments dispute this; suggesting instead that the formation of intra‐basinal highs occurs prior to lithospheric extension. In northern UK, this tectonic framework is controlled by a combination of tectonic stress, isostasy and the buoyancy forces of low‐density granite, lithospheric flexure and, importantly, the inherited structural framework. It is hoped that further study can lead to a greater appreciation of the interplay of structural and geodynamic process that control the ‘block and basin’ framework.

As a consequence of 19th and 20th century coal mining, a vast quantity of subsurface data has been accumulated on Britain’s late Carboniferous Coal Measures and the basins in which they have accumulated. Here we discuss current understanding of the geological evolution of the British Isles during this period, as well as how these data can be repurposed as the UK seeks to reduce its greenhouse gas emissions. It is widely assumed that Britain’s Coal Measures accumulated during a period of tectonically quiescent, thermally induced post-rift subsidence and that the lateral extent of the Variscan foreland in southern England and Wales was restricted. Burial history curves constructed from stratigraphic successions across the UK suggest, however, that during the late Carboniferous the UK was characterised by accelerated subsidence rates as far north as northern England and Scotland, beyond any perceivable flexure-induced foredeep. On local scales, seismic and borehole-based mapping shows that many individual depocentres were strongly influenced by syn-depositional faulting, folding and positive inversion. This influence is illustrated by repeated local unconformities within the late Carboniferous succession across England and Scotland as well as variable isochore thickness trends. We propose that this succession was influenced by a combination of both local tectonic controls and regional controls such as supralithospheric orogenic loading and sublithospheric dynamic loading. In this sense, we believe that the British Variscan foreland system, as the British Isles should be referred to as during the late Carboniferous, resembled a ‘broken’ foreland system such as that of Patagonia, South America. Understanding the nature of Britain’s Coal Measures has gained renewed importance given the need to reduce carbon emissions and seek alternative sources of energy. Across the UK, there are a number of active projects aiming to harness latent heat from abandoned underground coalmines. In addition, coupled CO2 sequestration and enhanced coal bed methane recovery offers a further, if riskier, low carbon subsurface energy prospect. To aid deep geothermal exploration, subsurface data from northern England is being compiled in order to construct regional 3D geothermal models. Our models highlight hot areas within the subsurface more realistically than equivalent maps based on contouring around individual borehole temperature measurements that are skewed by sparsely distributed data points and, potentially, inaccurate measurements. Deep heat-producing granite bodies and the variable thickness of thermally resistive rock units, such as the Pennine Coal Measures Group, are highlighted as dominant controls on the distribution of deep geothermal energy in northern England.

Intra-basinal highs within classic ‘block and basin’ style tectonic frameworks, in areas such as northern England, are underpinned by large granite bodies. This is widely believed to relate to the relative ‘rigidity’ and ‘buoyancy’ of granite in relation to accommodating basement. It has been suggested that during periods of tectonic extension, normal faulting around the peripheral regions of granite batholiths permits granite-cored blocks to resist subsidence, thus forming stable areas during periods of widespread faulting-induced subsidence. However, one-dimensional modelling indicates that relatively less dense crust is incapable of resisting subsidence in this way. Instead, when local isostasy is assumed, the occurrence of granite-cored, intra-basinal highs relates to initial isostatic compensation following granite emplacement. Differential sediment loading during extensional tectonism exaggerates this profile. An integrated two-dimensional lithospheric numerical modelling approach highlights the role of flexural rigidity in limiting the amplitude whilst increasing the wavelength of isostatic deflection. In light of these models, it is suggested that such a response leaves residual second-order stresses associated with the under-compensated buoyancy of the granite body and flexural tension. The observed basin geometries of the Carboniferous North Pennine Basin can be replicated by incorporating a density deficiency within the crust, flexural rigidity, simple shear deformation within the shallower subsurface and pure shear deformation within the deeper subsurface. In adopting this technique, the regional flexural profile in response to underlying granite bodies and large extensional faults can be reproduced and thus, to an extent, validated. It is proposed that the interaction of three factors dictate the tectonic framework within a partially granitic, brittle-ductile lithosphere and the occurrence of inter-basinal highs: 1) non-tectonic, ‘second-order’ stresses such as the flexural response of the lithosphere and residual, under-compensated buoyancy forces in relation to granite bodies; 2) extensional tectonic stress and importantly; 3) inherited basement fabric.

The Mesopotamian Basin is a wide sedimentary basin and its evolution is poorly understood. In this study, subsidence analysis has been carried out to provide insights into the tectonic events that have influenced the basin’s evolution, considering the controversy in the chronostratigraphy of the basin that can help to increase more realistic petroleum system modeling. Data constraints for the subsidence analysis have been provided from stratigraphic and wireline log data from 14 wells that penetrate the Cenozoic and Mesozoic successions down to Middle Jurassic strata. Results from the subsidence analysis reveal distinct tectonic phases of extension in the early part of this basin’s history. A main extensional event occurred at approximately 160 Ma with a lithospheric stretching factor of 1.38. There is a doubt whether this event extended to 130 Ma or was followed by another extension. A second extensional phase occurred about 130 Ma and lasted for approximately 20 Myr with a stretching factor from 1.08 to 1.15 across the study area. In about 100 Ma, the southeast part of the basin was subject to a flexural subsidence phase that was followed by two strike-slip related subsidence phases which initiated about 75 Ma to 60 Ma. The second phase was restricted to the northeast part of the study area. Further to the northeast, there is evidence of another strike-slip related subsidence phase during Eocene. During the Miocene, a rapid increase in subsidence highlights the last tectonic event. Comparing these interpreted results to the geodynamic events shows that the first extensional phase may be caused by the late phase of Triassic-Jurassic rifting in the southern Neo-Tethys. Cretaceous extensional phase(s) should be attributed to the extensional phases during the subduction in the Neo-Tethys, while there is no evidence of a rift. The flexural event in the Late Cretaceous is consistent with the initiation of the ophiolite obduction, in more recent geodynamic studies, and it was followed by two transpressional phases of the ophiolite obduction, during the late part of the Late Cretaceous and Paleocene. Since the obduction did not span to Eocene, it should be related to the subduction in the Neo-Tethys. Eventually, the Arabia-Eurasia collision caused the rapid increasing in subsidence. These tectonic events should be considered in the petroleum system models and can be extended to cover the entire basin in the future.

Local low-density basement anomalies are an important part of a rift basin’s inherited structural framework that can influence basin stratigraphy. Large granitic intrusions can cause local alterations in the basement’s density and often spatially correlate with fault-bounded highs (blocks) or convex-shaped regional flexural highs due to their isostatic responses. We investigate the influence of local low-density basement anomalies on the deposition of the fluviodeltaic Fell Sandstone Formation in the northern Pennine rift basin, northern England. The integration of a variety of data sources has enabled regional correlation of the Fell Sandstone Formation with basinal, time-equivalent stratigraphy. Spatial variations in the preserved facies, palaeocurrent and sedimentological characteristics of the Fell Sandstone are documented and the most important controls upon these variations are considered. Along the eastern margin of the granite-cored, flexural Cheviot High, the Fell Sandstone fluvial system is locally confined by the High leading to preservation of ~98% well-sorted sandstone. In the Northumberland-Solway Basin, the Fell Sandstone fluvial system is less confined, leading to sediment dispersal and downstream reduction of net sand. Based on this study, proximity to the dominant clastic sediment source, regional subsidence variations and basin palaeotopography are considered important controls upon spatial variations across the Fell Sandstone Formation. Regional subsidence variations and basin palaeotopography in the northern Pennine Basin are influenced by the Cheviot High and the Maryport-Stublick-Ninety Fathom fault system, which bounds the Northumberland-Solway Basin and the Lake District and Alston Blocks. Both the Cheviot High and the Lake District and Alston Blocks are structures caused by the isostatic responses of local granite-induced low-density basement anomalies. This study shows that flexural highs can act as baffles to fluvial systems, locally confining them and leading to the deposition of high quality reservoir. Fault-bounded highs can act as barriers and their deep bordering half-graben troughs can act as confines for clastic sediment, leading to starvation further down system.

Abstract A combination of fieldwork, basin analysis and modelling techniques has been used to try and understand the role, as well as the timing, of the subsidence–uplift mechanisms that have affected the Azerbaijan region of the South Caspian Basin (SCB) from Mesozoic to Recent. Key outcrops have been studied in the eastern Greater Caucasus, and the region has been divided into several major tectonic zones that are diagnostic of different former sedimentary realms representing a complete traverse from a passive margin setting to slope and distal basin environments. Subsequent deformation has caused folds and thrusts that generally trend from NW–SE to WNW–ESE. Offshore data has been analysed to provide insights into the regional structural and stratigraphic evolution of the SCB to the east of Azerbaijan. Several structural trends and subsidence patterns have been identified within the study area. In addition, burial history modelling suggests that there are at least three main components of subsidence, including a relatively short-lived basin-wide event at 6 Ma that is characterized by a rapid increase in the rate of subsidence. Numerical modelling that includes structural, thermal, isostatic and surface processes has been applied to the SCB. Models that reconcile the observed amount of fault-controlled deformation with the magnitude of overall thinning of the crust generate a comparable amount of subsidence to that observed in the basin. In addition, model results support the tectonic scenario that SCB crust has a density that is compatible with an oceanic composition and is being under-thrust beneath the central Caspian region.

The Tucano and Sergipe-Alagoas basins of northeast Brazil form part of a regional extensional basin system that was operative during the Mesozoic breakup of South America and Africa with both basins developing on Precambrian crust. The synchronous development of the rift basins suggest that they are genetically linked in space and time. Whereas the offshore Sergipe-Alagoas basin is characterized by a substantial thickness of post-rift sediment, the Tucano basin either failed to develop or at least preserve a significant thickness of post-rift sediment. Observed primary porosities within both pre- and syn-rift Tucano basin sediment imply that significant post-rift sedimentation never occurred. Failure to develop significant post-rift subsidence has important thermal and mechanical implications for the reaction of the lithosphere to rifting and can be explained in terms of. (1) depth-dependent lithospheric extension in which intracrustal detachments allow the extension of the crust to be decoupled from the thinning of the lithospheric mantle, (2) small rates of extension that allow the lithosphere to cool during rifting, and/or (3) lithospheric rifting during which the flexural strength of the lithosphere remains high. With respect to points (2) and (3), forward modeling demonstrates that finite rifting rates over a 20-25 m.y. period are insufficient to cool the lithosphere to the point where post-rift subsidence fails to develop. An interesting complication arises when the flexural strength of the lithosphere remains large during rifting: it tends to suppress the vertical motions of the lithosphere, such as those engendered by the cooling of the lithosphere following rifting, thereby reducing significantly the amplitude of the post-rift subsidence. Thus, the lack of post-rift sedimentation within a basin does not necessarily imply that extension has been limited to the crust.From our kinematic modeling of the Tucano basin, the observed negative free-air and Bouguer gravity anomalies (- 120 mGals) suggest that the flexural strength of the lithosphere has remained sufficiently large to maintain the load of the sediment. We can model successfully the observed Tucano basin architecture and gravity anomaly irrespective of whether we assume depth-dependent or depth-independent lithospheric extension primarily because the flexural strength of the lithosphere tends to ''buffer'' or suppress the amplitude of the post-rift subsidence. In contrast, the adjacent Sergipe-Alagoas basin is associated with low-amplitude gravity anomalies which may reflect a resetting of flexural strength during rifting. Prior to rifting, however, there was no appreciable elevation difference between the Tucano and Sergipe-Alagoas regions (as might be induced by a hot-spot for example) implying that the flexural strength of the lithosphere was similar. The total thickness of the syn- and post-rift sediments within the Sergipe-Alagoas basin is about the same as the thickness of rift-phase sediments in the Tucano basin. Thus, the amount of crustal extension responsible for each basin was similar. However, since the Sergipe-Alagoas basin contains 4-5 km of post-rift sediments, lithospheric mantle thinning in this region must have been significantly greater than the crustal extension to overcome the effects of ''flexural bufferring''.The need for lithospheric mantle thinning to be greater that crustal extension in the Sergipe-Alagoas region was also a result obtained by modeling the development of the ocean/continent boundary between Brazil and Africa. From our coupled kinematic and rheological model of lithospheric extension, we predict that the ocean/continent boundary should form preferentially at the location of greatest crustal and lithospheric mantle thinning, that is, within the region of maximum depth-independent lithospheric extension. The ocean/continent boundary formed east of the Sergipe-Alagoas basin despite the fact that the Tucano basin represents the region of greatest crustal thinning. If extension had been uniform with depth beneath these basins, the ocean/continent boundary should have formed in the Tucano basin. As it did not, some form of intracrustal detachment appears to have been operative to reduce lithospheric mantle thinning beneath the Tucano basin while enhancing it beneath the offshore regions of the Sergipe-Alagoas basin.