This tab contains four columns describing the fluid name, its density (kg m-3), heat capacity (J kg-1 K-1) and thermal conductivity (W m-1 K-1).

This tab contains the data required for the model to build the present-day sedimentary column. The various columns detail the name of the sedimentary layer (character only) and various material properties such as density (kg m-3), heat capacity (J kg-1 K-1), porosity (fraction), thermal conductivity (W m-1 K-1), initial TOC content (wt %) and latent heats of organic maturation and dehydration (kJ kg-1). Information regarding the kind of carbonate contained in the sedimentary layer can be given in the last column if decarbonation reactions are considered. The mineral constitution of the carbonate can be chosen as marl (1), dolomite (2) or dolomite/evaporite mix (3). A zero (0) is entered in this column if decarbonation reactions are not required. The lithology tab also contains columns where the present-day top depth (m) and age (Ma) of each layer is given, which determine the depositional sequence and sedimentation rate for the layer (see Sect. 3.1). Note that the ages of the sedimentary layers must be unique. A hypothetical basement is added 10 m below the deepest sedimentary layer top depth.

This tab is similar to the lithology tab and contains information on eroded layers. Additional columns in this tab contain information regarding the erosion timing (Ma) and the thickness of the eroded layer (m). Note that the top depth of the eroded layer must coincide with the top of a sedimentary layer in the lithology tab. If part of sedimentary layer is indeed eroded before deposition continues (i.e., the eroded layer lay inside a deposited layer), the layer needs to be considered as unique layers separated by the eroded layer. Multiple eroded layers can have the same top depths provided that younger layers with the same top depth are eroded first if erosion of the older layer occurs after the deposition of the younger layer. Similarly, eroded layers have to be eroded prior to deposition of younger layers. The ages of the eroded layers cannot coincide with other layers.

This tab contains information necessary for the emplacement of sill intrusions. The top depth (m) and thickness (m) of the sill constrain the geometry of the intrusion. Additional information includes the time of emplacement (Ma), emplacement temperature (∘C), melt and solid densities (kg m-3), melt and solid heat capacities (J kg-1 K-1), thermal conductivity (W m-1 K-1), solidus and liquidus temperatures of the magma (∘C) and the latent heat of crystallization (kJ kg-1). The emplacement of the intrusion is assumed to be instantaneous. Note that the top depth of the sill cannot be the same as the top depth of a sedimentary layer. On the same note, the top depth of a sedimentary layer cannot be inside a sill intrusion. Emplacement ages cannot exactly coincide with layer ages.

This tab contains temperature data (∘C) vs. depth (m) for the sedimentary column. The data in this tab are used to construct a geothermal gradient by using the best linear fit and therefore need to contain at least two data points. Additionally, the first data point must coincide with the column top describing the surface temperature.

This tab contains present-day vitrinite reflectance data presented in depth (m) and VR values (%Ro). The standard deviation of the values when available can be included. These data are used for comparison of the modeled VR values to observations. This tab can be left blank if no measured information is available.

This tab contains present-day TOC content data (wt %) vs. depth (m) measured in the sedimentary column which are used to compare to the model results. This tab can be left blank if no measured information is available.

Each sedimentary layer, including the eroded layers, is deposited sequentially in time based on the depositional age. The rate of sedimentation for each layer is determined by the thickness of the layer and the difference in time between its top age and that of the layer deposited before it. Erosional layers in the sedimentary column are deposited in the same way as other layers. Erosion of the entire layer occurs in a single step at the specified erosion age. The temperature boundary conditions are accordingly adjusted for the height of the new sedimentary column. Note that the bottom boundary is extended to 5 times the thickness of the bottommost sill if that sill is close to or at the bottom boundary (hypothetical basement) in order to remove boundary effects and resolve aureole processes that are mostly limited to less than 4 times the sill thickness (Aarnes et al., 2010).

The thermal solver computes the temperature within the deposited sedimentary column by applying fixed temperatures at the top and bottom at every step which are calculated from the prescribed geotherm (see Sect. 2.5) and the energy diffusion equation: 1ϕρfcpf+1-ϕρrcpeff∂T∂t=∇⋅κeff∇T. κeff is the bulk thermal conductivity that includes the rock and fluid contributions as a geometric mean (Hantschel and Kauerauf, 2009): 2κeff=κr1-ϕκfϕ. Table 1 contains the definitions of all the notations used in the paper. The effective rock heat capacity accounts for the latent heat of fusion in the crystallizing parts of the sill between the solidus (TS) and liquidus (TL) temperature of the magma (e.g., Galushkin, 1997): 3cpeff=cpm1+LcTL-TScpmifTS<T<TLcpeff=cprifTS>T. Sills are emplaced instantaneously at the specified time and temperature within the sedimentary column. The emplacement of multiple sills in the same step is possible. The time steps used for thermal diffusion after sill emplacement are automatically calculated based on the sill thickness and the characteristic time required for thermal diffusion. The time step is initially small in order to accurately resolve the thermal evolution of the contact aureole around the sill and is gradually increased once the energy released by the cooling sill is dissipated.

Dehydration reactions in the host rock are implemented by modifying the thermal diffusion equation when temperatures of the sediments increase within a certain range (Galushkin, 1997; Wang, 2012): 4ϕρfcpf+1-ϕρrcpeff∂T∂t=∇⋅κ∇T-H5H=1-φρrLdTd1-Td2∂T∂t.

Vitrinite reflectance is a widely used indicator of thermal maturity and can be readily measured in the field. One of the most common methods used to calculate the thermal maturity of the source rock is the EASY%Ro method put forward by Sweeney and Burnham (1990). This model uses 20 parallel Arrhenius-type of first order reactions to describe the complex process of kerogen breakdown due to temperature increase. The reaction for the ith component is given by 6dwidt=-wiAexp⁡-EiRTt, where wi is the amount of material for component i, Ei is the activation energy for the given reaction and Tt is time-dependent temperature.

The total amount of material reacted is obtained by summing up the individual reactions: 7dwdt=∑idwidt. The fraction of reactant converted is 8F=1-ww0=1-∑ifiwiw0i, from which the vitrinite reflectance can be readily calculated by 9%Ro=exp⁡-1.6+3.7F. The amount of TOC that has reacted for any given time can be calculated by 10TOC(t)=TOCoF(t), and the rate of organic matter degradation by 11Rom=1-ϕρr∂TOC∂t. The maximum amount of TOC that can be reacted by this method is 85 % of the initial total. Note that, in the inner part of the contact aureole close to the sill, data show that all of the organic matter has been reacted or removed (e.g., LA1/68 in Sect. 5.2.2). We assume that all of the hydrocarbons released during thermal degradation are converted into carbon dioxide. The amount of organic carbon dioxide generated (RCO2) for a time step is given by 12RCO2=RommCO2, where mCO2 is a stoichiometric conversion factor (3.67) to transform carbon into carbon dioxide. Note that metamorphism of sedimentary rocks will generate CH4 (e.g., Aarnes et al., 2010; Iyer et al., 2017a), but in our model the reacted carbon is recalculated to CO2. If needed, the CO2 model output can be easily converted to either C or CH4.

The latent heat of organic maturation is accounted for in the energy equation: ϕρfcpf+1-ϕρrcpeff∂T∂t=∇⋅κ∇T-H-LomRom.

Carbonate minerals undergo decarbonation reactions as they are heated to high temperatures. This results in mineral transformations and the release of inorganic carbon dioxide which may significantly add to the CO2 budget associated with igneous intrusions. The amount of inorganic CO2 liberated during metamorphic transformation over a range of temperatures and fluid pressures for marl, dolomite and dolomite/evaporite mixture is pre-computed as a phase diagram using Perple_X (Connolly and Petrini, 2002) (Fig. 1). The model evaluates the total amount of inorganic CO2 liberated by carbonate layers based on the temperature and pressure evolution of the layer through time within the phase diagrams. Fluid pressure within the sedimentary column is calculated by integrating the fluid density over depth in addition to atmospheric pressure: 13PH2O=Patm+∫Zmin⁡Zmax⁡ρfg.

The entire sedimentary column including the eroded layers and igneous intrusions is reconstructed and the column nodes and elements for the FEM model are generated using the user-specified resolution. The nodes are initially collapsed onto each other in depth. Each sedimentary node is assigned a time during which it is expanded (or deposited) within the sedimentary column based on the layer age and its thickness. All of the elements and nodes associated with each igneous intrusion are expanded simultaneously during the corresponding emplacement time. Eroded layers are removed in a single time step specified by the erosion age and the corresponding nodes are collapsed. In order to correctly capture thermal diffusion across the large thermal gradient adjacent to a hot intrusion, the time step is initially very small and exponentially increases during the heating period after sill emplacement and before the next depositional event. The heating period of the sill, over which the exponential time sub-stepping is used, is analytically determined from the characteristic diffusion time for the sill thickness (Jaeger, 1959).

The model is one-dimensional and will therefore not resolve thermal effects that would require a full 3-D model.

This variable contains input information on the sedimentary layers in the column including the eroded layers. The information is saved as variables given in Table 2 and is sorted according to their top depths. Note that top depths are corrected for the eroded layers that are also included.

This variable contains input information on sill intrusions in the column. The information is saved as variables given in Table 3 and is sorted according to their top depths.

This variable contains input information on measured TOC, VR and temperature data for the sedimentary column. The information is saved as variables given in Table 4.

This variable contains the model results which are saved for every time step when applicable; i.e., variables that change over time have rows corresponding to the element or node number (depending on where they are defined) and columns corresponding to the time step number. The information is saved as variables given in Table 5.

This variable contains the amounts of CO2 released for every time step normalized to rock volume. The information is saved as variables given in Table 6.

The GUI presented during and after the model run contains three tabs containing graphical representations of the input data, time evolution of model results and CO2 release through time. An explanation of the tabs is given below using a hypothetical test case consisting of a sedimentary column with two sill intrusions and three eroded layers.

The Utgard sill complex is part of the North Atlantic Igneous Province (NAIP) in the Vøring and Møre Basins, off the shore of Norway. This region underwent massive volcanic activity at the Paleocene–Eocene boundary around ∼ 55 Ma (Aarnes et al., 2015). The Utgard High borehole 6607/5-2 was drilled through two sills emplaced in the Upper Cretaceous sedimentary layers. The drilled lithological column consists of nine layers with the oldest being deposited at 100 Ma (NPD Factpages, http://factpages.npd.no/factpages/) (Fig. 5). For simplicity, the material properties of the entire sedimentary column are set to constant values with the exception of TOC content. TOC content of the Paleocene and Upper Cretaceous sedimentary layers is set to initial values of 0.6 and 1.5 wt %, respectively. Carbonate and erosional layers are not considered. The modeled sedimentary layers are sequentially deposited at the sedimentation rate calculated from the layer top ages. The two sills are emplaced simultaneously within the Nise and Kvitnos formations at 55 Ma at a temperature of 1150 ∘C. Sedimentary rocks around the emplaced sills are progressively heated as the sills cool. The vitrinite reflectance values increase and the TOC content is reduced by thermally degrading organic matter to form CO2 (Fig. 6). Sedimentation after sill emplacement results in further burial and extension to produce the present-day sedimentary column. Vitrinite reflectance and TOC data from the Norwegian Petroleum Directorate (NPD) and a previous study (Aarnes et al., 2015) are used to benchmark the model and match very well with the modeled results (Fig. 7). Further information about the geological and model setting can be found in Aarnes et al. (2015) and the input file “1d_sill_input_utgard.xlsx”.

The Karoo Large Igneous Province was emplaced through the Karoo Basin in South Africa in the Early Jurassic. The basin contains sills and dykes of varying thickness (Chevallier and Woodford, 1999; du Toit, 1920; Svensen et al., 2015; Walker and Poldervaart, 1949), emplaced at about 182.6 Ma (Svensen et al., 2012). The basin stratigraphy consists of the Upper Carboniferous to the Triassic Karoo Supergroup and is divided into five groups (the Dwyka, Ecca, Beaufort, Stormberg and Drakensberg groups) with a postulated maximum cumulative thickness of 12 km and a preserved maximum thickness of 5.5 km (Tankard et al., 2009). The depositional environments of the sediments range from marine and glacial (the Dwyka Group), marine to deltaic (the Ecca Group), to fluvial (the Beaufort Group) and finally eolian (the Stormberg Group) (Catuneanu et al., 1998). The Karoo Basin is overlain by 1.65 km of preserved volcanic rocks of the Drakensberg Group, consisting mainly of stacked basalt flows erupted in a continental and dry environment (e.g., Duncan et al., 1984). Several recent studies have been devoted to contact metamorphism of the organic-rich Ecca Group (Aarnes et al., 2011b; Moorcroft and Tonnelier, 2016) and the possible consequences of thermogenic methane venting on the Early Jurassic climate (Svensen et al., 2007, 2015). Here, we present two borehole cases from the central (borehole KL1/78) and eastern (borehole LA1/68) parts of the basin previously studied and modeled by Aarnes et al. (2011b) and Svensen et al. (2015), respectively. The details regarding the relative timing of sill emplacement are poorly constrained, and we thus use the same age for all sills. If the sills are closely spaced, this will result in a higher maximum temperature in the sedimentary rocks between the sills (see Aarnes et al., 2011b). For the erosion history of the Karoo Basin, we refer to Braun et al. (2014) and a rapid Late Cretaceous erosion event.

This example has been added to provide an instance where the user may be interested in modeling the thermal aureole of an emplaced sill or dyke but without the effects associated with deposition of sedimentary layers and the thermal evolution of a basin, e.g., emplacement within an igneous or metamorphic rock. Here, we consider an emplacement of a 100 m thick sill into a 1.2 km thick igneous body that has cooled to a uniform temperature of 30 ∘C (Fig. 12). The host rock is constructed by defining top and bottom layers with the same material properties and ages that are very close to each other (the code does not allow for two layers with the exact same age). In this example, the top and bottom layers have ages of 10 and 10.0001 Ma, respectively, and the intrusion is emplaced at 1 Ma. A constant temperature for the host rock is defined by assigning the same temperature, 30 ∘C, to both intervals in the temperature tab of the Excel input file. Thus, the thermal evolution of the intrusion can be investigated independent of burial effects of a sedimentary basin if so desired (Fig. 13). Further information about the model setting can be found in the input file “1d_sill_input_dyke.xlsx”.