Pop-Up Structures and the Fracture Pattern in the Balsam Lake Area, Southern Ontario

An examination of topographic lineaments detectable in Landsat TM images and measurement of joints in outcrop in the Balsam Lake area reveals a systematic bedrock fracture pattern with three principal sets oriented 091°, 027°, and 152°. The 027° trend is parallel to a major aeromagnetic anomaly, the Niagara-Pickering Linear Zone (NPLZ), which underlies the Balsam Lake area and is thought to mark the sub-Paleozoic continuation of the Proterozoic Central Metasedimentary Belt Boundary Zone (CMBBZ). Possible origins of the main joint sets due to Acadian (091° set), Alleghanian (152° set) and St. Lawrence rift system tectonics (091° and 027° sets) are discussed. En-echelon pop-up structures have a mean principal trend of 118°. They displace Lake Algonquin paleobeaches, suggesting formation less than 12,500 years ago. The orientation of the pop-up structures is subnormal to the current in situ maximum horizontal stress direction, SHmax (020°), and is parallel to members of the 091° joint set, indicating possible nuclea-tion on favourably-oriented pre-existing joints. These pop-ups are the only features in the Balsam Lake area with strong evidence for a neotectonic age.L'examen des linéaments topographiques repérables sur les images Landsat (TM) et la mesure des diaclases dans un affleurement de la région de Balsam Lake révèle la présence d'un réseau de fractures dont l'orientation des trois principaux ensembles est 091°, 027° et 152°. La direction 027° est parallèle à une anomalie aéromagnétique majeure, la zone linéaire Niagara-Pickering, présente sous la région de Balsam Lake; on croit qu'elle identifie le prolongement sub-paléozoïque de l'aire limite de la zone méta-sédimentaire centrale protérozoïque. On traite des origines possibles des principaux ensembles de fractures attribuables aux systèmes acadien (091°), alléghanien (152°) et du rift du Saint-Laurent (091 °et 027°). La direction des structures de soulèvement en échelon est de 118°. Elles ont déplacé des paléo-plages du Lac Algonquin, indiquant ainsi une formation postérieure à 12 500 ans. L'orientation des structures de soulèvement est subnormale à la direction de la contrainte horizontale maximale actuelle, SHmax(020°), et est parallèle à des éléments de l'ensemble des fractures de direction 091°, montrant ainsi leur formation possible dans des fractures existantes bien orientées. Ces structures de soulèvement sont les seuls éléments de la région démontrant un âge néotectonique.Eine Untersuchung der topographischen Lineamente die in Landsat TM-Bildern nachweisbar sind und Messungen der Fugen in den Aufschlùssen des Balsam Lake-Gebiets lassen ein systematisches Bruchmuster des anstehenden Gesteins erkennen mit drei nach 091°, 027° und 152° ausgerichteten Haupteinheiten. Die Ausrichtung nach 027° ist parallel zu einer wichtigen aeromagnetischen Anomalie, der linearen Zone von Niagara-Pickering, die unter dem Balsam Lake-Gebiet liegt; man halt sie fur eine subpalàozoische Fortfùhrung des Grenz-bereichs der proterozoischen zentralen metasedimentàren Gùrtel-zone. Man diskutiert môgliche Ursprùnge der Hauptfugen-systeme, die auf die akadische (091° System), alleghanische (152° System) und Sankt-Lorenz-Spaltensystem Tektonik (091° und 027° System) zurùckgefùhrt werden. Die gestaffelten Hebungsstrukturen haben eine durchschnittliche Hauptrichtung von 118°. Sie haben Palào-Strànde vom Lake Algonquin versetzt, und weisen so auf eine Bildung vor weniger als 12,500 Jahren. Die Orientierung der Hebungsstrukturen ist subnormal zu der gegenwàrtigen maximalen horizontalen Stressrichtung, S"m" (020°) und parallel zu Elementen des 091° Fugen-systems, was auf ihre môgliche Bildung auf gùnstig orientierten schon vorhandenen Fugen weist. Dièse Hebungen sind die einzi-gen Strukturen im Balsm Lake-Gebiet, welche deutlich ein neotektonisches Alter belegen

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

Advances in interdisciplinary studies of work teams : theories of self-managing work teams

Subduction zones are complex 3-D features in which one tectonic plate sinks underneath another into the deep mantle. During subduction the overriding plate (OP) remains in physical contact with the subducting plate and stresses generated at the subduction zone interface and by mantle flowforce the OP to deform.We present results of 3-D dynamic laboratory models of subduction that include an OP.We introduce newinterplate materials comprising homogeneous mixtures of petrolatum and paraffin oil to achieve progressive subduction. The rheology of these mixtures is characterized by measurements using a strain rate controlled rheometer. The results show that the strength of the mixture increases with petrolatum content, which can be used as a proxy for the degree of mechanical coupling along the subduction interface. Results of subduction experiments are presented with different degrees of mechanical coupling and the influence this has on the dynamics and kinematics of subduction. The modelling results show that variations in the degree of mechanical coupling between the plates have a major impact on subduction velocities, slab geometry and the rate of OP deformation. In all experiments the OP is displaced following trench migration and experiences overall extension localized in the plate interior. This suggests that OP deformation is driven primarily by the toroidal component of subduction-related mantle return flow. The subduction rate is always very slow in experiments with medium mechanical coupling, and subduction stops prematurely in experiments with very high coupling. This implies that the shear forces along the plate interface in natural subduction zone systems must be relatively low and do not vary significantly. Otherwise a higher variability in natural subduction velocities should be observed for mature, nonperturbed subduction zones. The required low shear force is likely controlled by the rheology of highly hydrated sedimentary and basaltic rocks

Rheology of petrolatum-paraffin oil mixtures:Applications to analogue modelling of geological processes

Paraffins have been widely used in analogue modelling of geological processes. Petrolatum and paraffin oil are commonly used to lubricate model boundaries and to simulate weak layers. In this paper, we present rheological tests of petrolatum, paraffin oil and several homogeneous mixtures of the two. The results show that petrolatum and all petrolatum-paraffin oil mixtures are strain, strain rate and temperature dependent under typical experimental strain rates (10-3-10-1s-1). For the same conditions, pure paraffin oil is a slightly temperature-dependent, linear, Newtonian fluid. All mixtures have yield stress and flow stress (strain softening) values that decrease with decreasing shear rate, and with increasing relative amounts of paraffin oil. The degree of strain rate dependence (shear thinning) also decreases with increasing paraffin oil content. Because these materials have rheologies that can be characterized and controlled, they are suitable for use in a large number of analogue model settings, either as a lubricant or to simulate weak layers. When used as a lubricant, mixtures with higher paraffin oil content should perform better than pure petrolatum

Structural inheritance in amagmatic rift basins: Manifestations and mechanisms for how pre-existing structures influence rift-related faults

In the context of rift basin formation, structural inheritance describes the influence of pre-existing structures on new rift-related structures, including faults. Pre-existing structures in the crust or upper mantle can determine where rift basins form. As these basins evolve, pre-existing structures in the rocks underneath the newly formed basin can also interact with the far-field strain or stress field, leading to variations in the orientations and kinematics of individual rift-related faults. Given that continental rifts commonly form in pre-deformed lithosphere, structural inheritance is likely to be the norm, not the exception. As such, structural inheritance has implications for reconstructing the paleotectonic history of rifts, investigating seismic hazards, and understanding the fluid transport and storage capabilities of natural fracture systems in the context of geo-energy and ore deposits. The aim of this review is to provide a framework for recognising the various expressions of structural inheritance and their underlying mechanisms in amagmatic rift basins. We synthesise field and geophysical observations and the results of analogue and numerical models to: (1) demonstrate how different inheritance mechanisms (frictional reactivation vs. local re-orientation of the far-field strain and/or stress) can produce different geometric and kinematic relationships between pre-existing structures and rift-related faults; (2) classify these mechanisms in terms of hard-linked and soft-linked inheritance; and (3) show that different mechanisms can be activated at different depths by the same pre-existing structure. These insights can help us better interpret basement structures under the sedimentary cover of rift basins, which are not often well-imaged in geophysical data, and understand the multi-stage evolution of rift basins worldwide