Towards a global lithospheric thermal model

2020 ◽  
Author(s):  
Sheona Masterton ◽  
Samuel Cheyney ◽  
Chris Green ◽  
Peter Webb
Keyword(s):  
Heat Flow ◽  
Curie Temperature ◽  
Thermal Structure ◽  
Magnetic Layer ◽  
Surface Heat ◽  
Local Context ◽  
Magnetic Data ◽  
Flow Data ◽  
Surface Heat Flow ◽  
Temperature Depth

<p>Temperature and heat flow are key parameters for understanding the potential for source rock maturation in sedimentary basins. Knowledge of the thermal structure of the lithosphere in both a regional and local context can provide important constraints for modelling basin evolution through time.</p><p>In recent years, global coverage of heat flow data constraints have enhanced scientific understanding of the thermal state of the lithosphere. However, sample bias and variability in sampling methods continues to be a major obstacle to heat flow-derived isotherm prediction, particularly in frontier areas where data are often sparse or poorly constrained. Consideration and integration of alternative approaches to predict temperature at depth may allow interpolation of surface heat flow in such data poor areas.   </p><p>We have attempted to integrate three independent approaches to modelling temperature with depth. The first approach is based on heat flow observations, in which a 1D steady-state model of the lithosphere is constructed from quality-assessed surface heat flow data, crustal thickness estimates and associated lithospheric thermal properties. The second approach is based on terrestrial (airborne, ground and shipborne) magnetic data, in which the maximum depth of magnetisation within the lithosphere is estimated using a de-fractal method and used as a proxy for Curie temperature depth. The third approach is based on satellite magnetic data and estimates the thickness of the magnetic layer within the lithosphere based on the varying amplitudes of satellite magnetic data, accounting for global variations in crustal magnetisation. Curie temperature depth results from each of these approaches have been integrated into a single global grid, then used to calculate temperature-depth variations through the crust.</p><p>We have evaluated our isotherm predictions by comparing them with temperature-depth control points and undertook qualitative and quantitative analyses of discrepancies that exist between different modelling approaches; this has provided insights into the origin of such discrepancies that can be integrated into our models to generate a better controlled global temperature-depth result.  </p><p>We present details of our methodology and the results of our integrated studies. We demonstrate areas where the independent results are in good agreement, providing vital information for high-level basin screening. We also highlight areas of disagreement and suggest possible causes for these discrepancies and potential resolutions.</p>

scholarly journals Adjoint inversion of the thermal structure of Southeastern Australia

2019 ◽  
Vol 219 (3) ◽  
pp. 1648-1659 ◽  
Author(s):  
B Mather ◽  
L Moresi ◽  
P Rayner
Keyword(s):  
Thermal Properties ◽  
Heat Flow ◽  
Heat Production ◽  
Thermal Structure ◽  
Surface Heat ◽  
Flow Data ◽  
Data Set ◽  
Surface Heat Flow ◽  
Southeastern Australia ◽  
Curie Depth

SUMMARY The variation of temperature in the crust is difficult to quantify due to the sparsity of surface heat flow observations and lack of measurements on the thermal properties of rocks at depth. We examine the degree to which the thermal structure of the crust can be constrained from the Curie depth and surface heat flow data in Southeastern Australia. We cast the inverse problem of heat conduction within a Bayesian framework and derive its adjoint so that we can efficiently find the optimal model that best reproduces the data and prior information on the thermal properties of the crust. Efficiency gains obtained from the adjoint method facilitate a detailed exploration of thermal structure in SE Australia, where we predict high temperatures within Precambrian rocks of 650 °C due to relatively high rates of heat production (0.9–1.4 μW m−3). In contrast, temperatures within dominantly Phanerozoic crust reach only 520 °C at the Moho due to the low rates of heat production in Cambrian mafic volcanics. A combination of the Curie depth and heat flow data is required to constrain the uncertainty of lower crustal temperatures to ±73 °C. We also show that parts of the crust are unconstrained if either data set is omitted from the inversion.

scholarly journals Surface heat flow and lithosphere thermal structure of the Rhenohercynian Zone in the greater Luxembourg region

Geothermics ◽  
2015 ◽  
Vol 56 ◽  
pp. 93-109 ◽  
Author(s):  
Tom Schintgen ◽  
Andrea Förster ◽  
Hans-Jürgen Förster ◽  
Ben Norden
Keyword(s):  
Heat Flow ◽  
Thermal Structure ◽  
Surface Heat ◽  
Surface Heat Flow ◽  
Rhenohercynian Zone

scholarly journals Cooling of the continental plate during flat-slab subduction

Geosphere ◽  
2021 ◽  
Author(s):  
Xiaowen Liu ◽  
Claire A. Currie ◽  
Lara S. Wagner
Keyword(s):  
Heat Flow ◽  
Numerical Models ◽  
Thermal Structure ◽  
Surface Heat ◽  
Surface Cooling ◽  
Flat Slab ◽  
Surface Heat Flow ◽  
Flat Slabs ◽  
Flat Slab Subduction ◽  
Subducting Plate

Most flat-slab subduction regions are marked by an absence of arc volcanism, which is consistent with closure of the hot mantle wedge as the subducting plate flattens below the continent. Farther inland, low surface heat flow is observed, which is generally attributed to cooling of the continent by the underlying flat slab. However, modern flat slabs have only been in place for <20 Ma, and it is unclear whether there has been sufficient time for cooling to occur. We use numerical models to assess temporal variations in continental thermal structure during flat-slab subduction. Our models show that the flat slab leads to continental cooling on timescales of tens of millions of years. Cool slab temperatures must diffuse through the continental lithosphere, resulting in a delay between slab emplacement and surface cooling. Therefore, the timescales primarily depend on the flat-slab depth with shallower slabs resulting in shorter timescales. The magnitude of cooling increases for a shallow or long-lived flat slab, old subducting plate, and fast convergence rates. For regions with flat slabs at 45–70 km depth (e.g., Mexico and Peru), shallow continental cooling initiates 5–10 Ma after slab emplacement, and low surface heat flow in these regions is largely explained by the presence of the flat slab. However, for the Pampean region in Chile, with an ~100-km-deep slab, our models predict that conductive cooling has not yet affected the surface heat flow. The low heat flow observed requires additional processes such as advective cooling from the infiltration of fluids released through dehydration of the flat slab.

Temperature structure of the Andean subduction zone as derived from the 3D geometry of crustal and upper mantle discontinuities

2020 ◽  
Author(s):  
Andres Tassara ◽  
Joaquín Julve ◽  
Iñigo Echeverría ◽  
Ingo Stotz
Keyword(s):  
Heat Flow ◽  
Heat Production ◽  
Thermal Structure ◽  
Surface Heat ◽  
Thermal Parameters ◽  
Continental Lithosphere ◽  
Flow Measurements ◽  
Study Region ◽  
Surface Heat Flow ◽  
Input Model

<p>The distribution of temperature inside active continental margins plays a fundamental role on regulating first order geodynamic processes as the isostatic balance, rheologic behavior of crust and mantle, magmagenesis, volcanism and seismogenesis. In spite of these major implications, well-constrained 3D thermal models are known for few regions of the world (Europe, Western USA, China) where large geophysical databases have been integrated into compositional and structural models of crust and lithospheric mantle from which a thermal model is derived. Here we present a three-dimensional representation of the distribution of temperature underneath the Andean active margin of South America (10°-45°S) that is based on a geophysically-constrained model for the geometry of the subducted slab, continental lithosphere-asthenosphere boundary (LAB), Moho discontinuity and an intracrustal discontinuity (ICD). This input model was constructed by forward modelling the satellite gravity anomaly under the constraint of most of the seismic information published for this region. We use analytical expressions of 1D conductive continental geotherms with adequate boundary conditions that consider the compositional stratification of crust and mantle included in the input model, and the advective thermal effect of slab subduction. The 1D geotherms are assembled into a 3D volume defining the thermal structure of the study region. We test the influence of several thermal parameters and structural configurations of the Andean lithosphere by comparing the resulting surface heat flow distribution of these different models against a database containing heat flow measurements that we compile from the literature. Our results show that the thermal structure and derived surface heat flow is dominantly controlled by the geometry of the thermal boundary layer at the base of the lithosphere, i.e. the slab upper surface below the forearc and LAB inland. Variations on the modeled configuration of the continental lithosphere (i.e. the way on which the geometry of the continental Moho and ICD are considered into the definition of a space-variable thermal conductivity or the length scale for radiogenic heat production) have an effect on surface heat flow that is lower than the average uncertainty of the measurements and therefore can be considered as second-order. The simplicity of our analytical approach allows us to compute hundreds of different models in order to test the sensitivity of results to changes on thermal parameters (conductivity, heat production, mantle potential temperature, etc), which provides a tool for discussing their possible range of values in the context of a subduction margin. We will also show how variations of these models impact on the Moho temperature and therefore in the expected mechanical behavior of crust and mantle in this geotectonic context</p>

The Tibet lithosphere is not all hot

2020 ◽  
Author(s):  
Bing Xia ◽  
Irina Artemieva ◽  
Hans Thybo
Keyword(s):  
Heat Flow ◽  
Large Scale ◽  
North China ◽  
Receiver Function ◽  
Thermal Structure ◽  
Surface Heat ◽  
Moho Depth ◽  
Good Match ◽  
Isostatic Compensation ◽  
Surface Heat Flow

<p>We calculated the thermal lithosphere structure of Tibet and adjacent regions based on the new thermal isostasy method. Moho depth is constrained by the published receiver function results. The calculated surface heat flow in the surrounded Tarim, North China, and Yangtze cratons have a good match with the real measurements of surface heat flow. We recognize the northern Tibet anomaly where has a relatively thin lithosphere with a thermal thickness of <80 km and surface heat flow of >80 - 100 mW/m 2 may cause by the removal of lithospheric mantle and upwelling of asthenosphere. In Lhasa Block, the cold and thick lithosphere (>200 km) with a surface heat flow of 40 - 50 mW/m 2. In the east Tibet, the heterogeneous thermal lithosphere does not follow the widely spread large scale strike-slip faults and suggested that the faults do not cut down to the lithosphere. The surrounding cratons have different thermal lithosphere features. The Tarim and Yangtze cratons show typical cold and thick lithosphere with a lithosphere of >200km and surface heat flow of <50 mW/m2. The western North China Craton has an intermated lithosphere with a thickness of 120-200km and surface heat flow of 45-60 mW/m2. Our result suggested that high and flat Tibet has different isostatic compensation in different blocks. The heterogeneous lithosphere thermal structure of the Tibet suggested that the uplife force drive are difference in Tibet.</p><div> <div> </div> </div>

A review of surface heat-flow data of the northern Middle Atlas (Morocco)

2017 ◽  
Vol 112 ◽  
pp. 58-71 ◽  
Author(s):  
Paolo Chiozzi ◽  
Alae-Eddine Barkaoui ◽  
Abdelkrim Rimi ◽  
Massimo Verdoya ◽  
Yassine Zarhloule
Keyword(s):  
Heat Flow ◽  
Surface Heat ◽  
Flow Data ◽  
Surface Heat Flow ◽  
Middle Atlas

Heat production and thermal conductivity of rocks from the Pikwitonei–Sachigo continental cross section, central Manitoba: implications for the thermal structure of Archean crust

1987 ◽  
Vol 24 (8) ◽  
pp. 1583-1594 ◽  
Author(s):  
David M. Fountain ◽  
Matthew H. Salisbury ◽  
Kevin P. Furlong
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Cross Section ◽  
Heat Production ◽  
Thermal Structure ◽  
Granulite Facies ◽  
Surface Heat ◽  
Gamma Ray Spectrometry ◽  
Surface Heat Flow ◽  
Greenstone Belts

The Pikwitonei and Sachigo subprovinces of central Manitoba provide a cross-sectional view of the Superior Province crust. In cross section, the upper to mid-level crust is composed of synformal greenstone belts surrounded by tonalitic gneisses, both of which are intruded by granitoid plutons. This crustal structure persists downward into the granulite facies, where keels of the greenstone belts can be found. To constrain thermal models of the crust, we measured heat production and thermal conductivity in 60 rocks from this terrain using standard gamma-ray spectrometry and divided bar techniques. Large vertical and lateral heterogeneities in heat production in the upper crust are evident; heat production is high in granites and metasedimentary rocks, intermediate in tonalite gneisses, and low in the portions of greenstone belts dominated by mafic meta-igneous rocks. In the deeper granulite facies rocks, heat production decreases by a factor of two in the tonalitic gneisses and remains low in the high-grade mafic rocks. When applied to the Pikwitonei–Sachigo crust cross section, the laboratory data here do not support step function or exponential models of the variation of heat production with depth. However, estimates of surface heat flow and surface heat production for various sites in the crustal model yield the well-known linear relationship between surface heat production and surface heat flow observed for heat-flow provinces for both one- and two-dimensional models. This demonstrates that determinations of heat production with depth based on inversion of the linear heat-production–heat-flow relationship are nonunique.

A lightweight thermal modelling tool for physics-based continental heat flow interpolation

2020 ◽  
Author(s):  
Alberto Pastorutti ◽  
Carla Braitenberg
Keyword(s):  
Temperature Field ◽  
Heat Flow ◽  
Central Europe ◽  
Heat Production ◽  
Surface Heat ◽  
Gravity Models ◽  
Forward Modelling ◽  
Flow Data ◽  
Satellite Gravity ◽  
Surface Heat Flow

<p><em>Both energy applications, such as assessing one of the controlling factors of conductive geothermal plays, and geodynamics modelling, are influenced by the large uncertainties arising from uneven sampling of the direct observable of the Earth's thermal state, surface heat flow. Heterogeneity in structure and composition of the continental lithosphere complicate the temperature field even in stable provinces in thermal equilibrium. The measurements deviate from what simple relationships with geological and geophysical data predict, requiring more sophisticated schemes such as those based on multivariate inversion (e.g. Mather et al. 2018) and geostatistics (e.g. the similarity method employed by Lucazeau, 2019).</em></p><p><em>Recently, we aimed at assessing the performance of satellite-gravity-constrained modelling of surface heat flow [1], with the aim of employing the unparalleled spatial uniformity of global gravity models in the fill-in of sparsely sampled surface heat flow data. The model we obtained, in a test area in Central Europe, provided additional information on the lithospheric structure and revealed a satisfactory coherence with the geological features in the area and their controlling effect on the conductive heat transport. That test was based on a fit of radioactive heat production to available heat flow data, based on a misfit linearization and substitution strategy, which we have shown to be independently consistent with available heat production relationships (e.g. Hasterok and Webb, 2017). Furthermore, model validation techniques provide additional metrics on the predictability in areas devoid of heat flow measurements.</em></p><p><em>T</em><em>o reach those objectives, we developed a finite-difference based solver for the heat equation in conductive, stable lithosphere, relying on the assumption of steady state, 3-D heat conduction from the thermal base of the lithosphere to surface. It allows for non-homogeneous heat production and thermal conductivity, and non-flat upper and bottom boundaries. Concurrent joint forward modelling of the gravity field is also possible.<br>Through compromise between complexity and approximation, it was designed favouring easy and fast forward modelling, such as in assessing parameter sensitivity and performing grid searches or parameter fitting. Geological models and parameters can be defined using an user-friendly plain text layer-wise definition, which is then turned into a volume, on a rectangular mesh.<br>Computational requirements are lean: a 75 × 75 × 104 node model such as the one employed in [1] can be forward-modelled on an ordinary workstation in 135 seconds. A direct solver is employed to solve the FD system of linear equations: the Matlab built-in Cholesky decomposition for sparse arrays (Davis, 2006).</em></p><p><em>Albeit initially developed as an ad-hoc tool for a proof of concept, its ease of use and versatility suggest its potential in other applications. We therefore present the solver and the accompanying tool set, both openly available, along with a set of promising examples.<br><br>[1] Pastorutti, A., Braitenberg, C. (2019) "A geothermal application for GOCE satellite gravity data: modelling the crustal heat production and lithospheric temperature field in Central Europe." Geophysical Journal International, doi:10.1093/gji/ggz344</em></p>

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