ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉At the 2015 United Nations International Climate Change Conference in Paris (COP21), 197 national parties committed to limit global warming to well below 2°C. But current plans and pace of progress are still far from sufficient to achieve this objective. Here we review the role that geoscience and the subsurface could play in decarbonizing electricity production, industry, transport and heating to meet UK and international climate change targets, based on contributions to the 2019 Bryan Lovell meeting held at the Geological Society of London. Technologies discussed at the meeting involved decarbonization of electricity production via renewable sources of power generation, substitution of domestic heating using geothermal energy, use of carbon capture and storage (CCS), and more ambitious technologies such as bioenergy and carbon capture and storage (BECCS) that target negative emissions. It was noted also that growth in renewable energy supply will lead to increased demand for geological materials to sustain the electrification of the vehicle fleet and other low-carbon technologies. The overall conclusion reached at the 2019 Bryan Lovell meeting was that geoscience is critical to decarbonization, but that the geoscience community must influence decision-makers so that the value of the subsurface to decarbonization is understood.〈/span〉

Description: 〈span〉Mantle lithosphere heterogeneities are well documented, are ubiquitous, and have often been thought to control lithosphere-scale deformation. Here, we explore the influence of deep scarring in crustal deformation in three dimensions by considering the Ouachita orogeny in the southeastern United States, an example of a continental collision where mantle structure is present but not previously linked to the regional crustal tectonics. We present state-of-the-art continental compressional models in the presence of inherited three-dimensional lithospheric structure. Our models find that the surface expression of the Ouachita orogeny is localized by, and projected from, the controlling mantle scarring, in keeping with geological and geophysical observations. We are able to produce a large-scale arcuate orogeny with associated basin development appropriate to the Ouachita orogeny, alongside smaller-scale crustal faulting related to the region. This study offers a new and alternative hypothesis to the tectonic history of the Ouachita orogeny, with previous research having focused exclusively on crustal structures. The findings have broad implications, demonstrating the important potential role of the mantle lithosphere in controlling crustal dynamics and highlighting the requirement to consider deeper structure and processes when interpreting tectonic evolution of lithospheric-scale deformation.〈/span〉

Description: The Carboniferous Bowland Shale of northern England has drawn considerable attention because it has been estimated to have 1329 trillion cubic feet hydrocarbons in-place (gas and liquids) resource potential (Andrews 2013). Here we report on the oil and gas generation characteristics of three selected Bowland Shale whole-rock samples taken from cores and their respective kerogen concentrates. Compositional kinetics and phase properties of the primary and secondary fluids were calculated through the PhaseKinetics and GOR-Fit approaches and PVT modelling software. The three Bowland Shale samples contain immature, marine type II kerogen. Pyrolysate compositions imply primary generation of paraffinic–naphthenic–aromatic (PNA) oil with low contents of wax and sulphur. Bulk kinetic parameters have many similarities to those of productive American Palaeozoic marine shale plays. The secondary gas generation potential of Bowland Shale is greater than the primary gas potential although it requires a 10 kcal mol –1 higher activation energy to achieve peak production. Primary oil, primary gas and secondary gas reach their maximum generation at 137, 150 and 200°C respectively for a 3°C Ma –1 heating rate. Different driving forces of expulsion including the generation of hydrocarbon and overpressure caused by phase separation during sequential periods of subsidence and uplift could be inferred.

Description: Near-surface thrust fault splays and antithetic backthrusts at the tips of major thrust fault systems can distribute slip across multiple shallow fault strands, complicating earthquake hazard analyses based on studies of surface faulting. The shallow expression of the fault strands forming the Seattle fault zone of Washington State shows the structural relationships and interactions between such fault strands. Paleoseismic studies document an ~7000 yr history of earthquakes on multiple faults within the Seattle fault zone, with some backthrusts inferred to rupture in small (M ~5.5–6.0) earthquakes at times other than during earthquakes on the main thrust faults. We interpret seismic-reflection profiles to show three main thrust faults, one of which is a blind thrust fault directly beneath downtown Seattle, and four small backthrusts within the Seattle fault zone. We then model fault slip, constrained by shallow deformation, to show that the Seattle fault forms a fault propagation fold rather than the alternatively proposed roof thrust system. Fault slip modeling shows that back-thrust ruptures driven by moderate (M ~6.5–6.7) earthquakes on the main thrust faults are consistent with the paleoseismic data. The results indicate that paleoseismic data from the back-thrust ruptures reveal the times of moderate earthquakes on the main fault system, rather than indicating smaller (M ~5.5–6.0) earthquakes involving only the backthrusts. Estimates of cumulative shortening during known Seattle fault zone earthquakes support the inference that the Seattle fault has been the major seismic hazard in the northern Cascadia forearc in the late Holocene.

Description: The origin and age of topography along the west Greenland margin is a matter of continued debate. Evidence for tectonically driven Neogene uplift has been argued from interpretations of offshore seismic surveys, onshore fission-track data and inferred episodes of cooling. Here, analysis of seismic reflection profiles and 1D modelling of exploration wells along the Greenland margin of Davis Strait demonstrate that the data are consistent with a model of ancient continental topography affected by late Cretaceous–early Palaeocene rifting followed by thermal subsidence where offshore Neogene tectonic uplift is not required. This interpretation for the offshore evolution of the west Greenland margin has implications for the adjacent onshore evolution and for other continental margins developed throughout the Atlantic–Arctic rift system.

Description: 〈span〉〈div〉Abstract〈/div〉At the 2015 United Nations international climate change conference in Paris (COP21), 197 national parties committed to limit global warming to well below 2°C. But current plans and pace of progress are still far from sufficient to achieve this objective. Here we review the role that geoscience and the subsurface could play in decarbonising electricity production, industry, transport, and heating, to meet UK and international climate change targets, based on contributions to the 2019 Bryan Lovell meeting held at the Geological Society of London. Technologies discussed at the meeting involved decarbonisation of electricity production via renewable sources of power generation, substitution of domestic heating using geothermal energy, use of carbon capture and storage (CCS), and more ambitious technologies such as bioenergy and carbon capture and storage (BECCS) that target negative emissions. It was noted also that growth in renewable energy supply will lead to increased demand for geological materials to sustain the electrification of the vehicle fleet and other low-carbon technologies. The overall conclusion reached at the 2019 Bryan Lovell meeting was that geoscience is critical to decarbonisation, but that the geoscience community must influence decision makers so that the value of the subsurface to decarbonisation is understood.〈/span〉

Description: Neoproterozoic basaltic magmatism in the Dalradian Supergroup of Scotland and Ireland was associated with the break-up of the Rodinia supercontinent. Magmas were erupted in rift-related basins along a strike length of at least 700 km and during a time period of c. 80 Ma. New major and trace element analyses of metabasalts from several formations are presented to trace the variations in magma compositions in time and space. The primary magmas resulted from variable degrees of mixing of melts derived from mantle sources similar to those of normal and enriched mid-ocean ridge basalts; some younger lavas also show evidence of contamination with continental crust. In contrast to speculations about magmatism elsewhere in Rodinia, the evidence here suggests that there was no involvement of a mantle plume in basalt generation. For example, the Scottish promontory of Laurentia drifted rapidly southwards through c. 25{degrees} over the duration of the magmatism, with no evidence of significant elevation above sea level, as might be expected from involvement of a plume. Generation of the primary magmas might have taken place predominantly through decompression melting in depleted upper mantle containing enriched streaks and blobs. Both the Dalradian lithostratigraphy and the metabasaltic compositions are consistent with extreme lithospheric stretching and possibly rupture during the earliest phase of magmatism, whereas generation of later magmatism appears to have been associated with major fault systems, possibly on a foundering continental margin. Supplementary materialChemical analyses of Dalradian metavolcanic rocks (major elements recalculated to 100%, anhydrous) are available at www.geolsoc.org.uk/SUP18468.

Description: : Neoproterozoic basaltic magmatism in the Dalradian Supergroup of Scotland and Ireland was associated with the break-up of the Rodinia supercontinent. Magmas were erupted in rift-related basins along a strike length of at least 700 km and during a time period of c . 80 Ma. New major and trace element analyses of metabasalts from several formations are presented to trace the variations in magma compositions in time and space. The primary magmas resulted from variable degrees of mixing of melts derived from mantle sources similar to those of normal and enriched mid-ocean ridge basalts; some younger lavas also show evidence of contamination with continental crust. In contrast to speculations about magmatism elsewhere in Rodinia, the evidence here suggests that there was no involvement of a mantle plume in basalt generation. For example, the Scottish promontory of Laurentia drifted rapidly southwards through c . 25° over the duration of the magmatism, with no evidence of significant elevation above sea level, as might be expected from involvement of a plume. Generation of the primary magmas might have taken place predominantly through decompression melting in depleted upper mantle containing enriched streaks and blobs. Both the Dalradian lithostratigraphy and the metabasaltic compositions are consistent with extreme lithospheric stretching and possibly rupture during the earliest phase of magmatism, whereas generation of later magmatism appears to have been associated with major fault systems, possibly on a foundering continental margin. Supplementary material: Chemical analyses of Dalradian metavolcanic rocks (major elements recalculated to 100%, anhydrous) are available at www.geolsoc.org.uk/SUP18468 .

Description: The postorogenic collapse of the early Paleozoic Caledonian orogeny is well documented; however, several different plate tectonic models exist for the convergent phase involving closure of the Iapetus Ocean and the collision of Laurentia and Baltica. Receiver function analysis of 11 broadband seismometers along a 270 km transect in the East Greenland Caledonides reveals the existence of an east-dipping high velocity slab. Numerical modeling demonstrates that relict subducted and eclogitized crust is a plausible explanation. Thus, eastward subduction preceded subsequent west-dipping subduction during the formation of the East Greenland and Scandinavian Caledonides. This is a key constraint for understanding the Caledonian and continental margin evolution in the North Atlantic realm.

Description: 〈p〉This review of the role of the mantle lithosphere in plate tectonic processes collates a wide range of recent studies from seismology and numerical modelling. A continually growing catalogue of deep geophysical imaging has illuminated the mantle lithosphere and generated new interpretations of how the lithosphere evolves. We review current ideas about the role of continental mantle lithosphere in plate tectonic processes. Evidence seems to be growing that scarring in the continental mantle lithosphere is ubiquitous, which implies a reassessment of the widely held view that it is the inheritance of crustal structure only (rather than the lithosphere as a whole) that is most important in the conventional theory of plate tectonics (e.g. the Wilson cycle). Recent studies have interpreted mantle lithosphere heterogeneities to be pre-existing structures and, as such, linked to the Wilson cycle and inheritance. We consider the current fundamental questions in the role of the mantle lithosphere in causing tectonic deformation, reviewing recent results and highlighting the potential of the deep lithosphere in infiltrating every aspect of plate tectonics processes.〈/p〉