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Articles 1 - 9 of 9
Full-Text Articles in Tectonics and Structure
Kinematic Vorticity And Porphyroclast Rotation In Mylonites Of The Norumbega Fault System: Implications For Paleoviscometry, Hendrik Lenferink
Kinematic Vorticity And Porphyroclast Rotation In Mylonites Of The Norumbega Fault System: Implications For Paleoviscometry, Hendrik Lenferink
Honors College
Crystallographic and shape preferred orientation (SPO) fabrics that develop in mylonitic shear zones can preserve the mean kinematic vorticity number (Wm) of bulk flow. Microstructural methods exploiting dynamically recrystallized quartz and porphyroclast SPO fabrics typically yield conflicting values of Wm. The Sandhill Corner Mylonite Zone of the Norumbega Fault System, Maine, USA, serves as a case study for investigating this discrepancy; Wm estimates range from 0.90 to 1.00 employing the former method (Method 1) and from 0.3 to 0.6 employing the latter method (Method 2). Using a numerical model, I show how a low-viscosity layer (LVL) surrounding clasts affects their …
Integrated Analytical-Computational Analysis Of Microstructural Influences On Seismic Anisotropy, Scott E. Johnson, Christopher Gerbi, Andrew J. Goupee, Senthil Vel
Integrated Analytical-Computational Analysis Of Microstructural Influences On Seismic Anisotropy, Scott E. Johnson, Christopher Gerbi, Andrew J. Goupee, Senthil Vel
University of Maine Office of Research Administration: Grant Reports
The magnitudes, orientations and spatial distributions of elastic anisotropy in Earth's crust and mantle carry valuable information about gradients in thermal, mechanical and kinematic parameters arising from mantle convection, mantle-crust coupling and tectonic plate interactions. Relating seismic signals to deformation regimes requires knowledge of the elastic signatures (bulk stiffnesses) of different microstructures that characterize specific deformation environments, but the influence of microstructural heterogeneity on bulk stiffness has not been comprehensively evaluated. The objectives of this project are to: (1) scale up a preliminary method to determine the bulk stiffness of rocks using integrated analytical (electron backscatter diffraction) and computational (asymptotic …
Quantifying Syntectonic Weakening In Deep Orogenic Crust, Christopher Gerbi
Quantifying Syntectonic Weakening In Deep Orogenic Crust, Christopher Gerbi
University of Maine Office of Research Administration: Grant Reports
The primary intellectual impact of this project will be in improving our understanding of the mechanics that shape the Earth's crust. In recent years, earth scientists have used the increasing body of geodetic data towards that end, but the mechanical properties of the middle and lower crust remain only loosely constrained. This project focuses on the magnitude of strain weakening in shear zone networks. In detail, the research will explore the grain-scale and outcrop-scale deformation mechanisms in minerals that lead to this weakening, followed by modeling of the results to understand the weakening process on the larger scale. These conceptual …
Kinematic Vorticity Gauges And The Rheology Of Mylonitic Shear Zones, Scott E. Johnson
Kinematic Vorticity Gauges And The Rheology Of Mylonitic Shear Zones, Scott E. Johnson
University of Maine Office of Research Administration: Grant Reports
Many hazards encountered by humans, including earthquakes, volcanic eruptions and tsunamis, result from plate tectonics. How tectonic plates move and interact with one another, and how deformation that occurs at their interacting boundaries is localized into structures like the San Andreas fault in California, are first-order questions in the Earth Sciences. At active tectonic plate boundaries, GPS data have allowed a much clearer understanding of plate interactions, localization of deformation, and relations to seismic and volcanic hazards. However, such data provide little information about plate interaction and deformation at great depth. The most direct way to study these deeper processes …
Collaborative Research: St. Elias Erosion/Tectonics Project (Steep), Peter O. Koons
Collaborative Research: St. Elias Erosion/Tectonics Project (Steep), Peter O. Koons
University of Maine Office of Research Administration: Grant Reports
This is a multi-disciplinary study to address the evolution of the highest coastal mountain range on Earth - the St. Elias Mountains of southern Alaska and northwestern Canada. This orogen has developed over the past few million years as the Yakutat block, a continental-oceanic terrane, has attempted subduction beneath the eastern end of the Aleutian arc-trench system. The ~500 km-long, 150 km-wide St. Elias mountain range is the product of the dynamic balance between rapid uplift induced by crustal convergence and rapid exhumation by a regional system of large, fast-moving temperate glaciers. Most sediments are deposited either on a broad …
Coupled Deformation And Metamorphism, Fabric Development, Rheological Evolution And Strain Localization, Scott E. Johnson
Coupled Deformation And Metamorphism, Fabric Development, Rheological Evolution And Strain Localization, Scott E. Johnson
University of Maine Office of Research Administration: Grant Reports
When Earth's tectonic plates interact with one another the rocks that comprise them are deformed, commonly forming great mountain chains. During this deformation, the minerals that make up the rocks can become spatially or crystallographically aligned to form a fabric. The development of rock fabric is a primary factor affecting the strength, or rheological evolution of deforming rocks. Fabric development commonly involves coupling of both physical and chemical processes. For example, crenulation cleavage is the most common type of fabric in multiply deformed rocks, and its formation leads to extreme mineral segregation and rheological anisotropy. It is also commonly associated …
Collaborative Research: Erosional Forcing Of Late Quaternary Compressive Strain, West Central Taiwan, Phaedra Upton
Collaborative Research: Erosional Forcing Of Late Quaternary Compressive Strain, West Central Taiwan, Phaedra Upton
University of Maine Office of Research Administration: Grant Reports
The concept of steady-state growth of compressive orogens is one of the most accepted ideas in continental tectonics developed in the last two decades, yet surprisingly few direct data exist to test the models that have been advanced. Testing and refining the concept of steady-state mountain building requires identification of cases of transient response and dynamic feedback in compressive orogens, and documentation of the spatial and temporal scales at which crustal deformation responds to erosion. This project takes advantage of a unique natural experiment in the active fold-thrust belt of west-central Taiwan where enough modern seismologic, geodetic, structural and geochronologic …
Three-Dimensional Modeling Of Continental Subduction And The Evolution Of Ultra High Pressure Metamorphism, Peter O. Koons
Three-Dimensional Modeling Of Continental Subduction And The Evolution Of Ultra High Pressure Metamorphism, Peter O. Koons
University of Maine Office of Research Administration: Grant Reports
This project investigates driving forces and material behavior associated with continental subduction and ultra high-pressure metamorphism through an integration of numerical modeling of continental subduction and structural/petrological evolution of the material caught in the collision. The natural ultra high-pressure and high-pressure assemblages of the Western Gneiss of Norway provide rheological, geometric and geochronological information for the modeling, while the active obliquely convergent plate boundary of central New Zealand serves as a modern analog of a collision-subduction transition. Continental subduction zones represent regions where the crust-mantle interaction changes from nearly horizontal to dominantly vertical, accentuating the competing influences of body and …
Collaborative Research: The Tectonothermal Evolution Of A Convergent Orogen, Scott E. Johnson
Collaborative Research: The Tectonothermal Evolution Of A Convergent Orogen, Scott E. Johnson
University of Maine Office of Research Administration: Grant Reports
Understanding of orogenesis and its relations to mantle convection and plate tectonics relies on integrated studies of the interrelations among processes of deformation, metamorphism and magmatism. A well preserved portion of the northern Appalachian orogen is providing an outstanding laboratory for a truly integrative study of the evolution of mid-crustal processes that strongly influence orogenesis. This project is employing structural, microstructural, petrologic and thermobarometric analyses, and chemical and isotopic dating, to temporally and spatially link deformation, metamorphism and magmatism during the progressive growth of this orogenic belt. This information is being used to set constraints and boundary conditions on coupled, …