Dependence of the Stress Field on Plate-Mantle Coupling and Lithospheric Structure.

Deformation in the Earth’s mobile tectonic plates (lithosphere) is governed by the forces acting on and within the lithosphere and the lithosphere’s response to the resulting state of stress (rheology). Determining the origins of variations in the lithospheric stress field is a fundamental aspect of understanding processes at multiple scales, including global tectonic patterns, intra-plate deformation, regional faulting behavior and grain-scale seismic anisotropy. The forces acting on and within the lithosphere that give rise to variations in stress can be broadly broken down into plate boundary interactions, mantle flow acting on the base of the lithosphere and changes in lithostatic pressure resulting from gradients in density and surface topography. To date, numerous studies have explored the role these different forces play in generating observed lithospheric stress patterns, although calculations of global stress patterns in a mechanically homogenous lithosphere still fail to match observed stress patterns in many regions. The discrepancy between calculated and observed stress patterns reflects either uncertainty in the forces applied to the lithosphere or the assumption of a mechanically homogenous lithosphere. While maintaining the assumption of a mechanically homogenous elastic lithosphere, this thesis re-examines the forces acting on and within the lithosphere in the light of recent advances in our knowledge of lithospheric structure, mantle rheology and mantle flow modeling. The modeling results from Chapters I and II reveal that lithospheric stress patterns are highly sensitive to the assumed isostatic state, density structure and thickness of the lithosphere, which vary significantly across tectonic provinces that exhibit large changes in lithospheric rheology. In contrast, taking into account enhanced mantle flow-induced basal shear beneath thick continental roots does not generate an equivalent increase in local stress magnitudes within the overlying lithosphere, which reflects the integration of basal shear over plate-scale wavelengths and effective transmission of stresses within the homogenous elastic lithosphere. The dominant theme that emerges from these results is the critical importance of moving from mechanically homogenous models to models with both vertical and lateral variations in lithospheric rheology. This transition is necessary to calibrate the contribution of different sources of stress to the total lithospheric stress field.Ph.D.GeologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75903/1/johnbn_1.pd

The effects of lithospheric thickness and density structure on Earth's stress field

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/89572/1/j.1365-246X.2011.05248.x.pd

A longitudinal analysis of urological chronic pelvic pain syndrome flares in the Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151272/1/bju14783.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151272/2/bju14783_am.pd

Protocol for a randomized controlled study of Iyengar yoga for youth with irritable bowel syndrome

<p>Abstract</p> <p>Introduction</p> <p>Irritable bowel syndrome affects as many as 14% of high school-aged students. Symptoms include discomfort in the abdomen, along with diarrhea and/or constipation and other gastroenterological symptoms that can significantly impact quality of life and daily functioning. Emotional stress appears to exacerbate irritable bowel syndrome symptoms suggesting that mind-body interventions reducing arousal may prove beneficial. For many sufferers, symptoms can be traced to childhood and adolescence, making the early manifestation of irritable bowel syndrome important to understand. The current study will focus on young people aged 14-26 years with irritable bowel syndrome. The study will test the potential benefits of Iyengar yoga on clinical symptoms, psychospiritual functioning and visceral sensitivity. Yoga is thought to bring physical, psychological and spiritual benefits to practitioners and has been associated with reduced stress and pain. Through its focus on restoration and use of props, Iyengar yoga is especially designed to decrease arousal and promote psychospiritual resources in physically compromised individuals. An extensive and standardized teacher-training program support Iyengar yoga's reliability and safety. It is hypothesized that yoga will be feasible with less than 20% attrition; and the yoga group will demonstrate significantly improved outcomes compared to controls, with physiological and psychospiritual mechanisms contributing to improvements.</p> <p>Methods/Design</p> <p>Sixty irritable bowel syndrome patients aged 14-26 will be randomly assigned to a standardized 6-week twice weekly Iyengar yoga group-based program or a wait-list usual care control group. The groups will be compared on the primary clinical outcomes of irritable bowel syndrome symptoms, quality of life and global improvement at post-treatment and 2-month follow-up. Secondary outcomes will include visceral pain sensitivity assessed with a standardized laboratory task (water load task), functional disability and psychospiritual variables including catastrophizing, self-efficacy, mood, acceptance and mindfulness. Mechanisms of action involved in the proposed beneficial effects of yoga upon clinical outcomes will be explored, and include the mediating effects of visceral sensitivity, increased psychospiritual resources, regulated autonomic nervous system responses and regulated hormonal stress response assessed via salivary cortisol.</p> <p>Trial registration</p> <p>ClinicalTrials.gov <a href="http://www.clinicaltrials.gov/ct2/show/NCT01107977">NCT01107977</a>.</p

3D Thermo-mechanical Model of Lithospheric Buoyancy-Driven Extension of the East African Rift

This contribution is provided to complement the manuscript published in 2021 in Geophysical Research Letters by these authors. The paper is entitled Role of Lithospheric Buoyancy Forces in Driving Deformation in East Africa from 3D Geodynamic Modeling. Here we provide our 3D thermo-mechanical model of lithospheric buoyancy-driven extension of the East African Rift and surroundings. The 3D thermo-mechanical model was simulated using the open source code ASPECT. The aim of this work is to investigate what forces drive continental rifting in East Africa and surroundings. We investigate rifting along the East African Rift (EAR), which is the largest continental rift on Earth. Some studies suggest relatively shallow forces, known as lithospheric buoyancy forces, dominate the rifting. However, others suggest that deeper forces arising from interactions with mantle flow are driving the extension in the EAR. Here, we use the code ASPECT to perform realistic 3D simulations to estimate the contribution of lithospheric buoyancy forces in driving the EAR. We find that lithospheric buoyancy forces are the primary driver of ~E-W rigid block motion across the EAR, whereas the deeper forces may be driving rift-parallel motions along the boundaries of rigid blocks. This result provides new insight into our understanding of how continents break-up. Lithospheric buoyancy forces are implemented using the ETOPO1 topography dataset, CRUST1.0 for crustal thicknesses and densities, and the model is isostatically compensated at 100 km. The model provided is contained in the directory (East_African_Rift_Lithospheric_Buoyancy_Driven_Extension_3D_Model), which includes files that allow for visualization in 3D using the software VISIT or PARAVIEW. Visualization parameters include: temperature field, viscosity, density, topography, pressure, compositional fields, mesh, velocities, and strain rate. We also provide the data file of our modeling outputs and inputs that are described as follow: The model outputs are in the following files: 1. East_African_Rift_Lithospheric_Buoyancy_Driven_Extension_3D_Model.csv Contains the same model as in the directory "East_African_Rift_Lithospheric_Buoyancy_Driven_Extension_3D_Model" but in .csv format, which can be used to extract information from the model and plot in another software such as Generic Mapping Tools (GMT). 2. model1_GPE.csv Gravitational Potential Energy (GPE) calculated by vertically integrating lithostatic pressure, derived form CRUST1.0 and ETOPO1, from the surface to 100 km depth formatted as: longitude [o], latitude [o], and GPE [TN/m] . 3. model2_dynamic_strain_rate.csv Calculated dynamic strain rate at the deforming zones formatted as: longitude [o], latitude [o], strain rate [1e-8/yr]. 4. model3_rigid_block_dynamic_velocity.csv Calculated dynamic velocities of the Somalian Plate, and for Victoria and Rovuma Blocks formatted as: longitude [o], latitude [o], East velocity [mm/yr], North velocity [mm/yr]. 5. model4_GPS_dynamic_velocity.csv Calculated dynamic velocities at GPS locations within the deforming zones of the East African Rift formatted as: longitude [o], latitude [o], East velocity [mm/yr], North velocity [mm/yr]. 6. model5_inputs_topography_layers_thickness_density.csv Model inputs for the 3D model lithospheric deformation model including formatted as: longitude [o], latitude [o], topography [m], base of upper crust [m], base of middle crust [m], base of lower crust [m], synthetic lithosphere thickness [m], upper crust density [kg/m3], middle crust density [kg/m3], lower crust density [kg/m3], compensated mantle lithosphere density [kg/m3]

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Rift jump and microcontinent formation in back-arc settings

European Geosciences Union (EGU) General Assembly, 19-30 Apr 2021.-- 1 pageBack-arc basins often present multiple spreading centres that form one after the other (e.g. Mariana subduction zone), propagate and rotate (e.g., Lau Basin) following trench retreat. In some cases, rift jumps can create continental fragments or microcontinents (e.g., Coral Sea, Central Mediterranean, Scotia Sea). The processes controlling rift jumps and possible formation of continental fragments are still not fully understood, but they are certainly related to the dynamics of subduction. In this work, we show how episodic trench retreat shapes the morphology of back-arc basins and can produce rift jumps. We use the finite element code ASPECT to model the rifting of continental lithosphere in 2D with boundary conditions that simulate the asymmetric type of extension caused by the trench retreat. We perform a parametric study in which we systematically vary the duration of different extensional phases, simulating episodes of trench retreat. Our results show that when extension is continuous, continental break-up occurs and a spreading centre develops. On the other hand, rift jump occurs in models with multiple extensional phases resulting in more complex morphologies that go from a hyperextend margin, to microcontinent formation, to spreading centre jumps within the newly formed oceanic lithosphere. In the first two cases (i.e., hyperextended margin and microcontinent), the length of the rift jump ranges from about 40 to 100 km and the timing varies from about 2 to 6 Myr. In the latter case (i.e., spreading centre jump within oceanic lithosphere) the length of the jump is significantly lower, 10-15 km, and the time needed for the ridge jump to occur is <2 Myr. These values depend on the rheological properties of the lithosphere, but, importantly, we show that the resulting scenario is controlled by the duration of the first extension stage and of the break before the next onePeer reviewe

Ridge Jumps and Mantle Exhumation in Back-Arc Basins

Back-arc basins in continental settings can develop into oceanic basins, when extension lasts long enough to break up the continental lithosphere and allow mantle melting that generates new oceanic crust. Often, the basement of these basins is not only composed of oceanic crust, but also of exhumed mantle, fragments of continental crust, intrusive magmatic bodies, and a complex mid-ocean ridge system characterised by distinct relocations of the spreading centre. To better understand the dynamics that lead to these characteristic structures in back-arc basins, we performed 2D numerical models of continental extension with asymmetric and time-dependent boundary conditions that simulate episodic trench retreat. We find that, in all models, episodic extension leads to rift and/or ridge jumps. In our parameter space, the length of the jump ranges between 1 and 65 km and the timing necessary to produce a new spreading ridge varies between 0.4 and 7 Myr. With the shortest duration of the first extensional phase, we observe a strong asymmetry in the margins of the basin, with the margin further from trench being characterised by outcropping lithospheric mantle and a long section of thinned continental crust. In other cases, ridge jump creates two consecutive oceanic basins, leaving a continental fragment and exhumed mantle in between the two basins. Finally, when the first extensional phase is long enough to form a well-developed oceanic basin (>35 km long), we observe a very short intra-oceanic ridge jump. Our models are able to reproduce many of the structures observed in back-arc basins today, showing that the transient nature of trench retreat that leads to episodes of fast and slow extension is the cause of ridge jumps, mantle exhumation, and continental fragments formation