GPUSPH is a fully three-dimensional model for the simulation of the thermal and rheological evolution of lava flows that relies on the Smoothed Particle Hydrodynamics (SPH) numerical method. Thanks to the Lagrangian, meshless nature of SPH, the model incorporates a more complete physical description of the emplacement process and rheology of lava that considers the free surface, the irregular boundaries represented by the topography, the solidification fronts and the non-Newtonian rheology with temperature-dependent parameters. GPUSPH follows the very general Herschel–Bulkley rheological model, which encompasses Newtonian, power-law and Bingham flow behaviours, with both constant and temperature-dependent parameters, and can thus be used to explore in detail the impact of rheology on the behaviour of lava flows and on their emplacement. To illustrate this possibility, we present some preliminary applications of the model for studying the rheology of lava flows with different constitutive relationships and thermal regimes using the real topography of the Mt Etna volcano.

The paper focuses on the Romanche transform margin on the African side of the Equatorial Atlantic, and draws from thermomechanical numerical modelling and subsequent GIS-based thermal history grid processing.Our modelling indicates that the early post-break-up thermal history of the transform margin is controlled by the cooling patterns of the adjacent pull-apart terrains, the pre-rift heat-flow regime, laterally passing seafloor spreading centres, and cooling of the newly accreted oceanic crust in two corridors located in front of and behind the spreading centres.The pre-rift thermal regime controls the background heat flow on top of which the thermal transients develop. If it is cold, the transient anomalies are very distinct on this background. If it is warm, the transient anomalies tend to blend in with background heat flow much better. The most prominent anomalies are related to thinning in the pull-apart terrains located between transforms. They are up to three times wider than anomalies related to the laterally passing spreading centre, the anomaly of which becomes no wider than 20–25 km. Together with oceanic crust accreted in corridors in front of and behind the passing centre, its heat transfer into the transform margin tends to slow down the cooling of the syn-break-up anomalies developed in the pull-apart terrains by rifting.

A three-dimensional (3D) thermal–kinematic modelling approach based on finite-element techniques is used to study lower-crustal viscosity at transform margins during the continent–ocean transform development stage and after the ridge has passed by. Nine modelling scenarios combining different equilibrium surface heat flows and lower-crustal rheologies are studied. Modelling results indicate that substantial parts of the lower crust at transform margins have the potential to flow at geologically appreciable strain rates, which can lead to uplift/subsidence, as well as lateral variations, in upper- and lower-crustal thicknesses and Moho depth. These low-viscosity zones (i.e. parts of the lower crust with effective viscosities of less than 1018 Pa s) make up distinct ductility distributions that vary in space and time during margin evolution. Three basic ductility patterns and related thermal processes can be identified: reduced lower-crustal viscosities originating at the continental rift and the continent–ocean boundary (COB), respectively; reduced lower-crustal viscosities along the transform caused by the migrating ridge; and the background distribution of lower-crustal ductility resulting from the equilibrium temperature field. Superposition of all three ductility patterns and the complex interaction of the underlying perturbations of the temperature field result in distinct differences in the potential of lower-crustal flow both in space (parallel and perpendicular to the transform) and with time. Thus, modelling results provide templates for understanding lower-crustal flow at transform margins in general and await further studies comparing model predictions with actual field observations.

This paper provides an overview of the existing knowledge of transform margins including their dynamic development, kinematic development, structural architecture and thermal regime, together with the factors controlling these. This systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock, seal rock and reservoir rock distribution, expulsion timing, trapping style and timing, and migration patterns. The paper then introduces individual contributions to this volume and their focus.

It is widely assumed that the boundary layer above the core is the source of intraplate volcanoes such as Hawaii, Samoa, and Yellowstone, and that the sub-plate boundary layer at the top of the mantle is thin and entirely subsolidus. In fact, this upper layer is thicker and has higher expansivity, buoyancy, and insulating power than the lower one, and may have higher potential temperatures. The observed seismic structure of the low-velocity zone (LVZ) including attenuation, anisotropy, sharp boundaries, and a reduction of both compressional and shear moduli can be taken as strong evidence for the ubiquitous presence of melt in the upper mantle. If the LVZ contains as little as 1%–2% melt, then it is the most plausible and accessible source for midplate magmas; deeply rooted active upwellings are unnecessary. The upper boundary layer is also the most plausible source of ancient isotopic signatures of these magmas and their inclusions.

Crustal xenoliths are key subvolcanic material for studying processes that operate in a magma dyke during intrusion into its surrounding country rock. The Biot number is the appropriate parameter to advance knowledge of the rock–magma thermal interaction. We present an interactive approach that combines the petrological study of natural subvolcanic samples, through crustal xenoliths, which represents an essential pilot to explore and constrain the input parameters and boundary conditions in numerical simulations of fluid dynamics under a volcano. Our results – as a function of different dyke depths, aspect ratios and temperature gradients at the host and dyke – allow an accurate interpretation of the thermal history of magma flow in the dyke, revealing significant differences in heat transfer and thermal resistance between the crust and ascending magma. Conclusively, melt flow within rigid-walled channels depends directly on the depth (pressure gradient) and width of the dyke according to a balance between the rate of magma input and heat loss that determines how fast the magma may ascend. In addition, and with implications for crustal assimilation, there is evidence of a strong relationship between the preconditioning temperature and the integrity of the host rock over the time that xenoliths are immersed in the magma dyke.

Based on present knowledge of mantle peridotites from the Ligurian Tethys ophiolites, this paper presents new ideas and a new model for passive rifting to ocean spreading in the slow–ultraslow rifting Europe–Adria realm. Relevant points include: (i) the positive feedback between deformation and melt percolation during passive magmatic rifting; (ii) the positive feedback between natural evidence and experimental data on the behaviour of the mantle lithosphere during passive rifting; (iii) the significance of hidden magmatism and the associated melt thermal advection; (iv) the role of the wedge-shaped weakened and softened axial zone; and (v) the evidence of a transition from passive to active rifting in the Ligurian Tethys.Passive rifting induced passive asthenospheric upwelling and the onset of partial melting. Fractional melts migrated through the mantle lithosphere and stagnated at shallow levels (the hidden magmatism). Melt thermal advection heated the mantle lithosphere to temperatures (T) of ≥1200°C and formed a wedge-shaped axial zone of rheological softened/weakened mantle peridotites that served as the future locus of continental break-up. The hotter/deeper asthenosphere ascended within this axial zone, underwent partial melting and formed aggregated mid-ocean ridge basalts (MORBs) that migrated within dunite channels to form olivine gabbro intrusions and basaltic lava flows. Rifting evolved from passive to active, and the actively upwelling asthenosphere established a ridge-type system and thermal regime.

The origin and evolution of Mars’s inventory of volatile elements is pivotal to a wide range of physical, chemical, geological, and biological issues and concerns. The identification of subglacially erupted volcanoes on Mars suggests that ice sheets existed at high and low latitudes repeatedly over geological time, but the importance of those volcanoes is not just as a simple Boolean climate signal. Like terrestrial subglacially erupted volcanoes, they can potentially yield a more holistic range of paleoenvironmental parameters, including ice thickness, thermal regime, and surface elevation. On Earth, at least nine different types of terrestrial subglacial volcanic successions can be identified using landform characteristics, lithofacies, and sequence architecture. The principal characteristics of each are reviewed in this paper, together with the first empirical comparative analysis of the morphometry of the landforms. All were probably erupted in association with wet-based ice and there are different implications for volcanic landforms erupted under different glacial thermal regimes (polar, subpolar). However, they represent our best sources of information with which to assess Mars analogs, some of which (as on Earth) may have been the source of megascale meltwater outburst floods. Applying the results of this paper to three different morphological types of candidate subglacial volcanoes on Mars indicates that it is difficult to suggest a plausible glaciovolcanic analogy for Mars’s tall cones; they more closely resemble pyroclastic mounds erupted subaerially or subaqueously, under ice-free conditions. Conversely, Mars’s low-domes may be very extensive, inflated, subglacial “interface sills” formed under comparatively thick ice of any thermal regime. Finally, the very large, flat-topped constructs on Mars resemble mafic tuyas emplaced in thick (up to 2 km) temperate ice. However, because of their very large size compared to terrestrial analogs, the possibility also exists that the latter are polygenetic stratovolcanoes, formed subglacially either within very thick ice, or as multiple superimposed lava-fed deltas emplaced in much thinner ice that repeatedly re-formed on the volcanoes after each eruptive episode. A plausible terrestrial analogy for the latter is the long-lived James Ross Island stratovolcano in Antarctica.

The lack of high heatflow values at hotspots has been interpreted as showing that the mechanism forming the associated swells is not reheating of the lower half of oceanic lithosphere. Alternatively, it has recently been proposed that the hotspot surface heatflow signature is obscured by fluid circulation. We re-examine closely spaced heatflow measurements near the Hawaii, Réunion, Crozet, Cape Verde, and Bermuda hotspots. We conclude that hydrothermal circulation may redistribute heat near the swell axes, but it does not mask a large and spatially broad heatflow anomaly. There may, however, be heatflow perturbations associated with the cooling of igneous intrusions emplaced during hotspot formation. Although such effects may raise heatflow at a few sites, the small heatflow anomalies indicate that the mechanisms producing hotspots do not significantly perturb the thermal state of the lithosphere.

Ice sheets play a fundamental role within Earth's climate system and in shaping landscapes. Despite extensive research, the maximum extent and basal dynamics of the Laurentide Ice Sheet (LIS) during the last glacial cycle remain elusive and debated in many areas. Recently, cosmogenic nuclides (e.g., 36Cl, 26Al, 10Be) have played an important role in improving our understanding of LIS extent and behavior. Applications of cosmogenic nuclides to LIS research include surface exposure dating of glacial features, constraining magnitudes of glacial erosion, addressing long-term subaerial exposure and ice sheet burial histories, and burial dating of glacial sediments. These techniques have contributed to the depiction of a more extensive LIS than previously reconstructed for the Last Glacial Maximum. In addition, cosmogenic nuclide research has definitively shown that the LIS covered intensely weathered terrain along its deeply dissected eastern margin, where there were steep gradients in the effectiveness of basal erosion related to basal thermal regime. Cosmogenic nuclide applications, those already employed as well as those yet to be discovered, will undoubtedly continue to contribute to our ever-improving understanding of ice sheet history and dynamics.

Western Anatolia, one of the world's best-known extensional terrains, is characterized by the presence of several moderate- to high-enthalpy geothermal fields. Geothermal fluids have helium isotope compositions reflecting mixing between mantle and crustal helium components, the former ranging between 0.58% and 45% of the total helium in a given sample. Regarding the distribution of heat and mantle He and their correlation with tectonic structure and volcanism in western Anatolia, the prominent features are as follows: (1) the association between highest heat and highest 3He lies along the eastern segment of the Büyük Menderes graben, (2) the high heat and high 3He occur in the vicinity of the Quaternary Kula volcanism, (3) high-enthalpy fields exist in close vicinity to the young alkaline volcanics, (4) relatively high mantle He contributions occur in areas of not only the young alkaline, but also the old calc-alkaline volcanics, and (5) there is a lack of volcanic exposures along the Büyük Menderes graben (except at its western and southeastern terminations), where the highest values are recorded for both heat and helium. The first three features collectively suggest that the transfer mechanism for both heat and helium is probably mantle melting accompanying the current extension in western Anatolia, yet the latter two further indicate that this may be accomplished via subsurface plutonic activities. The large range observed in the helium isotope compositions may be linked with differential (local) extension rates and associated melt generation in the respective areas. This suggestion can be substantiated by He isotope data from more of the region.

During 1973 and 1974, precision temperatures (±0.02°C absolute) were measured in four drill holes, ranging in depth from 42 to 122 m, in Clear Lake, Lake County, California. The departure of the measured temperatures from their predrilling values was found to vary considerably among the holes. It is a function of the length of time after drilling that the buoy system supporting the plastic casing survived the storms on the lake, as well as the duration of the drilling disturbance. With one exception, CL-73-7, most of the holes were lost within a month after drilling. Thermal-conductivity measurements on the sediment cores from the holes were measured using the needle-probe technique. These measurements indicate that the sapropelic muds that underlie most of the main body of the lake and the peat of the southeast, or Highlands Arm, of the lake have thermal conductivities only slightly greater than that of water. Conductivities of the coarse-grained sediments associated with the deltaic deposits of Kelsey Creek are two to three times that of water and are not grouped as tightly as the fine-grained muds and peats. Heat flows calculated from the above measurements are 1.5 to 1.6 heat-flow units (HFU) in the main basin of Clear Lake and about 2.4 HFU in the Highlands Arm of the lake. These values are considerably lower than expected, based on heat-flow measurements in The Geysers 25 km south of Clear Lake. A correction for an average sedimentation rate in the lake of 0.68 mm/yr would raise the observed heat flows about 13 percent. Although the exact thickness of sediment is unknown, a correction for the refraction effect caused by the thermal conductivity contrast between the low-conductivity lake sediments and the higher conductivity surrounding rock would tend to increase the heat flow at depth in the main basin only slightly for any reasonable thickness of sediment. In the Highlands Arm of the lake, the geometry is different, and the correction could raise the observed heat flux at depth as much as three times that observed, again for reasonable sediment thicknesses. However interesting these numbers are, it should be cautioned that sediment composition and thickness below about 200 m in the lake are unknown, and large differences in conductivity could drastically change these corrections. The possibility of such high heat flows, though, is encouraging enough that future measurements at greater depths should be contemplated. Aside from the refraction effects there are other possible causes of the low heat flows: (1) Clear Lake is bounded by faults and at least one fault is inferred to pass beneath the main body of the lake—downward cold water movement along such faults could absorb heat and decrease the heat flux; and (2) water may be moving down through the sediments, although generally the permeability of lake sediments is rather low. Depending on the velocity of the movement, a substantial reduction in heat flow could result. The downward movement of water over such a large area (114 km2) could be a source of recharge for The Geysers-Clear Lake geothermal system.

Extension zones within continents have complex patterns of tectonic evolution. The Basin and Range Province of western North America provides an ideal location to study the mode of extension in continental regions. We have utilized numerical models to test two distinct geological models of extension that have been proposed for the Basin and Range: (1) a model in which extension takes place by uniform (or pure shear) stretching; and (2) a model in which extension occurs along discrete low-angle shear zones by a simple shear mechanism. These numerical models indicate that both styles of extension produce results generally consistent with observed heat flow, gravity, and elevation data. Distinctive patterns in these data are maintained primarily during the period of extension, implying that present day observations are dominantly a consequence of an ongoing process. The results further imply that the effects of present day extension will obscure the evidence of previous extensional episodes at least as far as the parameters of heat flow, elevation, and gravity are concerned.