Full paleostress tensor determination: case of the Panasqueira Mine, Portugal.

Mapping Intimacies ◽

10.5194/egusphere-egu2020-2192 ◽

2020 ◽

Author(s):

Christophe Pascal ◽

Luís Jaques ◽

Atsushi Yamaji

Keyword(s):

Plate Tectonics ◽

Three Dimensions ◽

Additional Stress ◽

Stress Regime ◽

Vein Formation ◽

Significant Step ◽

Central Portugal ◽

Panasqueira Mine ◽

Shape Ratio ◽

Tectonic Forces

<p>The quantification of tectonic forces or, alternatively, stresses represents a significant step towards the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we attempt to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as natural laboratory, and focused on the measurement of sub-horizontal quartz veins, which are favorably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulphide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of rupture laws, and obtained the six parameters of the paleostress tensor that prevailed during vein formation. Our results suggests a NW-SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressures of ~300 MPa and differential stress lower than ~20 MPa.</p>

Download Full-text

Chilling Out

10.1093/oso/9780198717867.003.0010 ◽

2018 ◽

Author(s):

Roy Livermore

Keyword(s):

Plate Tectonics ◽

Volcanic Eruptions ◽

Atmospheric Temperature ◽

Ocean Currents ◽

Mountain Ranges ◽

Continental Rifts ◽

Earth’S Climate ◽

The One ◽

Tectonic Forces

The Earth’s climate changes naturally on all timescales. At the short end of the spectrum—hours or days—it is affected by sudden events such as volcanic eruptions, which raise the atmospheric temperature directly, and also indirectly, by the addition of greenhouse gases such as water vapour and carbon dioxide. Over years, centuries, and millennia, climate is influenced by changes in ocean currents that, ultimately, are controlled by the geography of ocean basins. On scales of thousands to hundreds of thousands of years, the Earth’s orbit around the Sun is the crucial influence, producing glaciations and interglacials, such as the one in which we live. Longer still, tectonic forces operate over millions of years to produce mountain ranges like the Himalayas and continental rifts such as that in East Africa, which profoundly affect atmospheric circulation, creating deserts and monsoons. Over tens to hundreds of millions of years, plate movements gradually rearrange the continents, creating new oceans and destroying old ones, making and breaking land and sea connections, assembling and disassembling supercontinents, resulting in fundamental changes in heat transport by ocean currents. Finally, over the very long term—billions of years—climate reflects slow changes in solar luminosity as the planet heads towards a fiery Armageddon. All but two of these controls are direct or indirect consequences of plate tectonics.

Download Full-text

9. Volcanoes beyond Earth

Volcanoes: A Very Short Introduction ◽

10.1093/actrade/9780199582204.003.0009 ◽

2020 ◽

pp. 128-142

Author(s):

Michael J. Branney ◽

Jan Zalasiewicz

Keyword(s):

Solar System ◽

Plate Tectonics ◽

Planetary Systems ◽

The Moon ◽

Mountain Belts ◽

Tectonic Forces

‘Volcanoes beyond Earth’ highlights volcanoes on other planets. There are many more volcanoes on Venus than there are on Earth, and many remain active. In the absence of plate tectonics and the kind of tectonic forces that raise Earth-style mountain belts, and of streams, rivers, and shorelines, it is volcanism and volcanic products that dominate the surface of this planet. Fossil volcanism occurs in the Moon, Mercury, and Mars; Io, the hypervolcanic moon of Jupiter; and the ice volcanoes of the Solar System. There is potential for volcanism on exoplanets within distant planetary systems.

Download Full-text

Field evidence for fluid facilitated fracturing and Dissolution-Precipitaion creep explains observed off-fault tremor and continuous deformation: Field examples from the Alpine Fault, New Zealand

10.5194/egusphere-egu21-8214 ◽

2021 ◽

Author(s):

Jack McGrath ◽

Sandra Piazolo ◽

Rebecca Morgan ◽

John Elliott

Keyword(s):

New Zealand ◽

Host Rock ◽

Tectonic Stress ◽

High Signal ◽

Deformation Region ◽

Stress Regime ◽

Continuous Deformation ◽

Alpine Fault ◽

Vein Formation ◽

Field Evidence

<div> <p>Geophysical observations show that the Alpine Fault in New Zealand is characterised by mid-crustal off-fault recurring tremor events and off-fault regions of continuous deformation. While geodesy indicates that deformation is distributed across the South Island, evidence from the rock record shows deformation accommodated in a region within several km from the fault. This zone is characterized by a 100-300 m wide mylonitised central fault zone and an approximately 8--10km, wide deformation region marked by the presence of Alpine foliation. Magnetotelluric surveys of the Southern Alps indicate a mid-crustal, high signal area coinciding with the location of the recurring tremors.&#160;&#160;</p> </div><div> <p>While the mylonites and their associated mechanisms have been extensively studied in the field area, the wider off-fault deformation region has not had the same scrutiny. In the latter region, we observe frequent layer parallel, folded and crosscutting quartz veins. Quartz vein orientation and geometries are consistent with fracturing in the presence of fluid within an overall tectonic stress regime. The observed overprinting of older veins by younger vein generations, as well as their successive reorientations, indicate recurring fracturing within a continuously deforming region. Quantitative analysis of vein geometries including their width and displacement shows that vein formation may trigger the observed mid-crustal tremor signal. Microstructural signatures within the host rock are consistent with dissolution-precipitation creep as the main deformation mechanism in the host rock and pre-existing veins.&#160;&#160;</p> </div><div> <p>In summary, according to field evidence both geophysically observed transient and continuous deformation take place in the presence of fluid and occur contemporaneously. This implies that strain accommodation in the host rock facilitated by dissolution-precipitation creep is insufficient; consequently, stress is build-up over time triggering intermittent fracturing.&#160;&#160;</p> </div>

Download Full-text

Compiling and correlating paleostress fields across Central Europe - A paleostress chart for northern Bavaria and adjacent areas

10.5194/egusphere-egu21-10098 ◽

2021 ◽

Author(s):

Florian Duschl ◽

Tobias Stephan ◽

Saskia Köhler ◽

Daniel Köhn ◽

Harald Stollhofen ◽

...

Keyword(s):

Central Europe ◽

Plate Tectonics ◽

Structural Data ◽

Original Data ◽

Fault Reactivation ◽

Detailed Knowledge ◽

Temporal And Spatial Distribution ◽

Stress Regime ◽

Tectonic Events ◽

Temporal And Spatial

<p>Detailed knowledge on the temporal and spatial distribution of faults and fractures not only reveals the geodynamic and tectonic evolution of the lithosphere. It is also of increasing importance with regard to economic, social, and environmental challenges such as nuclear waste disposal, gas storage, geothermal energy, natural hazards, and mineral resource exploration. In this context reliable data on both timing and kinematics of deformation and their regional impact on faulting and fracture formation provide crucial information to evaluate exploration, storage, and production risks, which in turn stresses the need for comprehensive data on paleostress fields and their influence on deformation, fault reactivation, fluid activity, and hydrothermal mineralization.</p><p>In this study we present a first comprehensive approach to compile and visualize information on the crustal paleostress field of Central Europe with a focus on northern Bavaria and adjacent areas. The compilation includes published structural data from kinematic paleostress analyses (e.g. fault-slip analysis, tectonic stylolites) and geo- and thermochronological ages of fracture mineralization and fault activity, respectively. The present compilation comprises structural records from more than 40 studies and age information from more than 100 geo-thermochronological studies. All structural data are categorized according to its tectonic stress regime and quality-ranked for reliability and comparability. The consequent linkage of structural data with thermochronological data wherever possible allows to correlate local paleostress fields and deformation patterns with regional to global tectonic events. As one result, the &#8220;Paleostress Chart for Northern Bavaria and adjacent Areas&#8221; visualizes the temporal and spatial evolution of several regions in Central Europe together with known tectonic phases, sedimentary unconformities and the plate kinematic framework since the Carboniferous.</p><p>This compilation may therefore help to better understand the timing and the spatio-temporal evolution of crustal stress patterns for tectonic events across Central Europe in the context of plate tectonics.&#160;</p><p>We aim to supplement and improve existing paleostress models on both, regional, and temporal scale by compiling published and original data. In the long term the database is intended as a continuing compilation where data from all across Central Europe are supposed to be included and refined subsequently.</p>

Download Full-text

Earth System Science in Three Dimensions

STEM Education ◽

10.4018/978-1-4666-7363-2.ch062 ◽

2015 ◽

pp. 1159-1176

Author(s):

Meghan E. Marrero ◽

Glen Schuster ◽

Amanda Bickerstaff

Keyword(s):

Curriculum Design ◽

Plate Tectonics ◽

School Curriculum ◽

Three Dimensions ◽

Mixed Methods Case Study ◽

Interactive Tools ◽

Student Focus ◽

Understanding Of Science ◽

Virtual Interactive

NASA-Sponsored Project 3D-VIEW [Virtual Interactive Environmental Worlds] is a lower middle school curriculum aimed at using 3D stereo technologies to enhance students' understanding of science concepts. In Project 3D-VIEW, ten to twelve-year-old students use 3D stereo technologies, including stereophotographs, 3D-animations, 3D illustrations, and 3D interactive tools, to visualize concepts such as plate tectonics, the composition of the atmosphere, biological succession, and erosion. This mixed methods case study provides an overview of the project's successful use of 3D technologies, as evidenced by student test scores as well as a qualitative analysis of student focus groups and interviews with teachers and administrators. The findings indicate that using 3D technologies within a context of standards and research-based curriculum design can improve student engagement as well as performance on standardized tests.

Download Full-text