Crustal deformation induced by mantle dynamics: insights from models of gravitational lithosphere removal

Mantle-based stresses have been proposed to explain the occurrence of deformation in the interior regions of continental plates, far from the effects of plate boundary processes. We examine how the gravitational removal of a dense mantle lithosphere root may induce deformation of the overlying crust. Simplified numerical models and a theoretical analysis are used to investigate the physical mechanisms for deformation and assess the surface expression of removal. Three behaviours are identified: (1) where the entire crust is strong, stresses from the downwelling mantle are efficiently transferred through the crust. There is little crustal deformation and removal is accompanied by surface subsidence and a negative free-air gravity anomaly. Surface uplift and increased free-air gravity occur after the dense root detaches. (2) If the mid-crust is weak, the dense root creates a lateral pressure gradient in the crust that drives Poiseuille flow in the weak layer. This induces crustal thickening, surface uplift and a minor free-air gravity anomaly above the root. (3) If the lower crust is weak, deformation occurs through pressure-driven Poiseuille flow and Couette flow due to basal shear. This can overthicken the crust, producing a topographic high and a negative free-air gravity anomaly above the root. In the latter two cases, surface uplift occurs prior to the removal of the mantle stress. The modeling results predict that syn-removal uplift will occur if the crustal viscosity is less than ∼10^(21) Pa s, corresponding to temperatures greater than ∼400–500 °C for a dry and felsic or wet and mafic composition, and ∼900 °C for a dry and mafic composition. If crustal temperatures are lower than this, lithosphere removal is marked by the formation of a basin. These results can explain the variety of surface expressions observed above areas of downwelling mantle. In addition, observations of the surface deflection may provide a way to constrain the vertical rheological structure of the crust

Magmatic expressions of continental lithosphere removal

Gravitational lithosphere removal in continental interior has been inferred from various observations, including anomalous surface deflections and magmatism. We use numerical models and a simplified theoretical analysis to investigate how lithosphere removal can be recognized in the magmatic record. One style of removal is a Rayleigh-Taylor-type instability, where removal occurs through dripping. The associated magmatism depends on the lithosphere thermal structure. Four types of magmatism are predicted: (1) For relatively hot lithosphere (e.g., back arcs), the lithosphere can be conductively heated and melted during removal, while the asthenosphere upwells and undergoes decompression melting. If removal causes significant lithospheric thinning, the deep crust may be heated and melted. (2) For moderately warm lithosphere (e.g., average Phanerozoic lithosphere) in which the lithosphere root has a low density, only the lithosphere may melt. (3) If the lithosphere root has a high density in moderately warm lithosphere, only asthenosphere melt is predicted. (4) For cold lithosphere (e.g., cratons), no magmatism is induced. An alternate style of removal is delamination, where dense lithosphere peels along Moho. In most cases, the lithosphere sinks too rapidly to melt. However, asthenosphere can upwell to the base of the crust, resulting in asthenospheric and crustal melts. In delamination, magmatism migrates laterally with the detachment point; in contrast, magmatism in Rayleigh-Taylor-type instability has a symmetric shape and converges toward the drip center. The models may explain the diversity of magmatism observed in areas with inferred lithosphere removal, including the Puna Plateau and the southern Sierra Nevada

Calcium/calmodulin-dependent protein kinase II - does ageing mirror disease?

Calcium/calmodulin–dependent protein kinase II delta (CaMKIId) plays a fundamental role in cardiac dysfunction and is known to be overexpressed and hyper-activated in the diseased heart. A role for CaMKIId in compromised cardiovascular function associated with ageing has yet to be established. Here we compare CaMKIId expression and oxidation (a novel route of enzyme activation) in the diseased and in the aged heart and vasculature. Using a minimally invasive transverse aortic banding (MTAB) mouse model of cardiac hypertrophy as our disease model, we investigated whether alterations in CaMKIId and oxidised CaMKII (ox-CaMKII) observed during cardiac disease are also a key feature of ageing, where oxidative stress is apparent. Myocardial function was assessed in vivo by echocardiography and compared with that of sham-operated animals. A significant increase in systolic blood pressure (110±6.3 vs 78±2.6, MTAB vs sham, n=4), mean arterial pressure (75±3.3 vs 60±2.6 (mmHg), MTAB vs sham) and reduction in fractional shortening (39.4±4.4 vs 53.6±3.8 (%FS) MTAB vs sham, n=7, p<0.05) was observed in the hearts from hypertrophied animals demonstrating successful surgical intervention. Post-mortem analysis revealed increased heart weight:body weight in MTAB animals (5.48±0.17 vs 4.32±0.01, MTAB vs sham, n=6, p<0.05). Quantitative immunoblotting of CaMKIId and ox-CaMKII expression in whole heart homogenates from MTAB animals showed significant up-regulation of both when compared to sham controls (0.68±0.02 vs 0.47±0.01 MTAB v’s sham, n=7, p<0.01). Interestingly, similar results were obtained in hearts from aged animals. A significant increase in CaMKIId expression was evident in aged hearts (0.81±0.08 vs. 0.46±0.08 aged vs young, p=0.04, n=3) and preliminary data suggests ox-CaMKII levels also show an increase in comparison to young (1.5-fold increase, n=1). Similar experiments were also conducted in young and aged rat aortae to assess CaMKIId involvement in vascular function. Vessels from aged subjects showed a significant increase in wall thickness (16.4±0.9 vs. 28±1.5 (um), young vs. aged, p=0.002, n=3) which may suggest an altered phenotype comparable to that observed during disease. Further quantitative immunoblotting indicated that CaMKIId is highly expressed in the vasculature and initial results suggest some alterations in ox-CaMKII protein levels with ageing, parallel to that observed in the heart. Overall, this work highlights for the first time that ageing alone, produces similar physiological and biochemical alterations in the heart as observed during cardiac disease. In addition to this, preliminary data from the vasculature has revealed a similar trend, suggesting CaMKIId may play an important role in overall deterioration of cardiovascular function with progressive ageing

Compromised cardiovascular function in aged rats corresponds with increased expression and activity of calcium/calmodulin dependent protein kinase IIδ in aortic endothelium

Ageing is the greatest risk factor for cardiovascular disease. Calcium/calmodulin dependent protein kinase IIδ (CaMKIIδ) plays a fundamental role in the pathology of heart disease yet a potential role for CaMKIIδ in cardiovascular pathology associated with ageing remains unclear. Taking a combined in vivo and in vitro approach, we have for the first time investigated whether CaMKIIδ expression and CaMKII activity may be altered following age-related cardiovascular deterioration. Both cardiac contractility and aortic blood flow are compromised in aged rats and we have shown that this occurs in parallel with increased inflammation and crucially, autonomous activation of CaMKII. Endothelial cells isolated from young and aged aortae exhibit differences in cell phenotype and physiology. In line with observations in aortic tissue, aged aortic endothelial cells also show increased basal levels of pro-inflammatory markers and oxidative stress with concurrent increased basal activation of CaMKII. These results are the first to demonstrate that elevated CaMKIIδ expression and CaMKII activation occur in parallel with the pathological progression associated with ageing of the heart and vasculature. Specifically, CaMKIIδ expression is significantly increased and activated in the endothelium of aged aorta. As such, CaMKIIδ could serve as an important marker of endothelial dysfunction that accompanies the ageing process and may be an appropriate candidate for investigating targeted therapeutic intervention

The Deep Roots of the Rocky Mountains: Geophysical Studies of Western Canada

The Rocky Mountains in western Canada have some of the most spectacular scenery in the world, with rugged terrain and snow-covered peaks. The Rockies are part of the North American Cordillera, a ~4000 km mountain belt that runs along the western side of North America (Figure 1). This mountain belt formed over the last 200 million years, as rocks were added to the western side of North America during the convergence of tectonic plates.

Alcohol-specific activity in hospitals in England

Alcohol-related harm is placing increasing demands on the NHS. At a time when unprecedented efficiencies need to be made by the NHS and local authorities, preventative action must be taken seriously. This analysis explores trends in alcohol-specific activity in hospitals due to alcohol poisoning and alcohol-related inpatient admissions by looking at six years of hospital activity data in England. The analysis also explores the use of hospital services before and after a diagnosis of alcohol-related liver disease and highlights opportunities for preventative action to reduce future alcohol-related harm in England

Crustal deformation induced by mantle dynamics: insights from models of gravitational lithosphere removal

Mantle-based stresses have been proposed to explain the occurrence of deformation in the interior regions of continental plates, far from the effects of plate boundary processes. We examine how the gravitational removal of a dense mantle lithosphere root may induce deformation of the overlying crust. Simplified numerical models and a theoretical analysis are used to investigate the physical mechanisms for deformation and assess the surface expression of removal. Three behaviours are identified: (1) where the entire crust is strong, stresses from the downwelling mantle are efficiently transferred through the crust. There is little crustal deformation and removal is accompanied by surface subsidence and a negative free-air gravity anomaly. Surface uplift and increased free-air gravity occur after the dense root detaches. (2) If the mid-crust is weak, the dense root creates a lateral pressure gradient in the crust that drives Poiseuille flow in the weak layer. This induces crustal thickening, surface uplift and a minor free-air gravity anomaly above the root. (3) If the lower crust is weak, deformation occurs through pressure-driven Poiseuille flow and Couette flow due to basal shear. This can overthicken the crust, producing a topographic high and a negative free-air gravity anomaly above the root. In the latter two cases, surface uplift occurs prior to the removal of the mantle stress. The modeling results predict that syn-removal uplift will occur if the crustal viscosity is less than ∼10^(21) Pa s, corresponding to temperatures greater than ∼400–500 °C for a dry and felsic or wet and mafic composition, and ∼900 °C for a dry and mafic composition. If crustal temperatures are lower than this, lithosphere removal is marked by the formation of a basin. These results can explain the variety of surface expressions observed above areas of downwelling mantle. In addition, observations of the surface deflection may provide a way to constrain the vertical rheological structure of the crust