scholarly journals Mechanical models to estimate the paleostress state from igneous intrusions

2018 ◽  
Author(s):  
Tara L. Stephens ◽  
Richard J. Walker ◽  
David Healy ◽  
Alodie Bubeck ◽  
Richard W. England
Keyword(s):  
Stress State ◽  
Tectonic Stress ◽  
Fracture Plane ◽  
Brittle Deformation ◽  
Deformation History ◽  
Deformation Structures ◽  
Igneous Intrusions ◽  
Vertical Opening ◽  
Mechanical Models ◽  
San Rafael

Abstract. Dikes and sills represent an important component of the deformation history in volcanic systems, but unlike dikes, sills are typically omitted from traditional paleostress analyses in tectonic studies. The emplacement of sheet intrusions is commonly associated with mode I fracturing in a low deviatoric stress state, where dilation is perpendicular to the fracture plane. Many natural examples of sills and dikes, however, are observed to accommodate minor shear offsets, in addition to a component of dilation. Here we present mechanical models for sills in the San Rafael Subvolcanic Field, Utah, which use field-derived measurements of intrusion attitude and opening angles to constrain the tectonic stress axes during emplacement, and the relative magma pressure for that stress state. The sills display bimodal dips to the NE and SW and consistent vertical opening directions, despite variable sill dips. Based on sill attitude and opening angles, we find that the sills were emplaced during a phase of NE-SW horizontal shortening. Calculated principal stress axes are consistent (within ~ 4°) with paleostress results for penecontemporaneous thrust faults in the area. The models presented here can be applied to any set of dilational structures, including dikes, sills, or hydrous veins, and represent a robust method for characterising the paleostress state in areas where other brittle deformation structures (e.g. faults), are not present.

scholarly journals Mechanical models to estimate the paleostress state from igneous intrusions

Solid Earth ◽  
2018 ◽  
Vol 9 (4) ◽  
pp. 847-858 ◽  
Author(s):  
Tara L. Stephens ◽  
Richard J. Walker ◽  
David Healy ◽  
Alodie Bubeck ◽  
Richard W. England
Keyword(s):  
Stress State ◽  
Tectonic Stress ◽  
Fracture Plane ◽  
Brittle Deformation ◽  
Deformation History ◽  
Deformation Structures ◽  
Igneous Intrusions ◽  
Vertical Opening ◽  
Mechanical Models ◽  
San Rafael

Abstract. Dikes and sills represent an important component of the deformation history in volcanic systems, but unlike dikes, sills are typically omitted from traditional paleostress analyses in tectonic studies. The emplacement of sheet intrusions is commonly associated with Mode I fracturing in a low deviatoric stress state, in which dilation is perpendicular to the fracture plane. Many natural examples of sills and dikes, however, are observed to accommodate minor shear offsets, in addition to a component of dilation. Here we present mechanical models for sills in the San Rafael subvolcanic field, Utah, which use field-based measurements of intrusion attitude and opening angles to constrain the tectonic stress axes during emplacement and the relative magma pressure for that stress state. The sills display bimodal dips to the NE and SW and consistent vertical opening directions, despite variable sill dips. Based on sill attitude and opening angles, we find that the sills were emplaced during a phase of NE–SW horizontal shortening. Calculated principal stress axes are consistent (within ∼ 4°) with paleostress results for penecontemporaneous thrust faults in the area. The models presented here can be applied to any set of dilational structures, including dikes, sills, or hydrous veins, and represent a robust method for characterising the paleostress state in areas where other brittle deformation structures (e.g. faults) are not present.

scholarly journals Delineating shallow Neogene deformation structures in northeastern Pará State using Ground Penetrating Radar

2003 ◽  
Vol 75 (2) ◽  
pp. 235-248 ◽  
Author(s):  
Dilce F. Rossetti
Keyword(s):  
Ground Penetrating Radar ◽  
Structural Models ◽  
Field Studies ◽  
Strike Slip ◽  
Brittle Deformation ◽  
Shallow Subsurface ◽  
Deformation Structures ◽  
Ground Penetrating ◽  
Slip Motion

The geological characterization of shallow subsurface Neogene deposits in northeastern Pará State using Ground Penetrating Radar (GPR) revealed normal and reverse faults, as well as folds, not yet well documented by field studies. The faults are identified mostly by steeply-dipping reflections that sharply cut the nearby reflections causing bed offsets, drags and rollovers. The folds are recognized by reflections that are highly undulating, configuring broad concave and convex-up features that are up to 50 m wide and 80 to 90 ns deep. These deformation structures are mostly developed within deposits of Miocene age, though some of the faults might continue into younger deposits as well. Although the studied GPR sections show several diffractions caused by trees, differential degrees of moisture, and underground artifacts, the structures recorded here can not be explained by any of these ''noises''. The detailed analysis of the GPR sections reveals that they are attributed to bed distortion caused by brittle deformation and folding. The record of faults and folds are not widespread in the Neogene deposits of the Bragantina area. These GPR data are in agreement with structural models, which have proposed a complex evolution including strike-slip motion for this area from the Miocene to present.

Study on the Influence of Seepage Behavior of Dam Foundation during Wenchuan Earthquake

2011 ◽  
Vol 255-260 ◽  
pp. 3642-3645
Author(s):  
Kai Hua Zeng ◽  
Hai Yan Ju ◽  
Han Xing Peng
Keyword(s):  
Stress State ◽  
Wenchuan Earthquake ◽  
Groundwater Level ◽  
Tectonic Stress ◽  
Seepage Water ◽  
Dam Foundation ◽  
Strong Earthquakes ◽  
Main Effect ◽  
Small Decline ◽  
Shrinkage Property

Earthquake occurred on May 12, 2008 in Wenchuan, Sichuan Province, China, with magnitude of 8.0 and epicenter intensity of VI. Chencun hydropower station in southern Anhui Province has been shocked strongly during Wenchuan Earthquake, which stations 1,500 km away from Wenchuan. Tectonic stress caused by strong earthquakes inevitably led to the changes of stress state, groundwater level and pore pressure in the dam foundation. Seepage water level observation of the dam foundation had been encrypted immediately. According to the experimental data, it was conformed that significant effects were displayed on the dam foundation seepage because of Wenchuan earthquake, shunhe fault near dam sites was the main effect zone of earthquake tectonic stress, the downrange of groundwater depth was self-evident. As the existence of acrylamide curtain, swelling-shrinkage property of the acrylamide gel restricted the change of groundwater level and rock stress state in the dam foundation caused by seismic tectonic stress; the groundwater level behind the acrylamide curtain had a small decline, and recovering quickly.

Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW Anatolia

2020 ◽  
Author(s):  
Salim Birkan Bayrak ◽  
Işıl Nur Güraslan ◽  
Alp Ünal ◽  
Ömer Kamacı ◽  
Şafak Altunkaynak ◽  
...  
Keyword(s):  
Shear Zone ◽  
Boundary Migration ◽  
Microstructural Analysis ◽  
Structural Data ◽  
Ductile Deformation ◽  
Brittle Deformation ◽  
Deformation History ◽  
Shear Sense ◽  
History Of ◽  
Dextral Shear

<p>Marmara granitoid (47 Ma) is a representative example of the Eocene post-collisional magmatism which produced several granitic plutons in NW Anatolia, Turkey. It is a W-E trending sill-like magmatic body which was concordantly emplaced into the metamorphic basement rocks of Erdek Complex and Saraylar Marble. The granitoid is represented by deformed granodiorite which displays well-developed lineation and foliation in meso-scale defined by the elongation of mica and feldspar crystals and recrystallization of quartz however, in some places, magmatic textures are preserved. Deformed granodiorite is broadly cut by aplitic and pegmatitic dikes and contains mafic enclaves which display the same deformation indicators with the main granitoid.</p><p>Microstructural analysis shows that the solid-state deformation of the Marmara granitoid is classified as ductile deformation with high temperatures and ductile-to-brittle deformation with relatively lower temperatures. Evidence for the ductile deformation of the granitoid is represented by chessboard extinction of quartz, grain boundary migration (GBM) and subgrain rotation recrystallisation (SGR) which exhibits that the deformation temperature changed from 600 <sup>o</sup>C to 400<sup>o</sup>C. Bulging recrystallization (BLG), grain size reduction of amphibole, biotite and plagioclases and microcracks on plagioclases were considered as overlying ductile-to-brittle deformation signatures which develop between 300-<250 <sup>o</sup>C temperatures.</p><p>All of these field and micro-structural data collectively suggest that the shear sense indicators such as micafish structures and δ type mantled porphyroclasts displayed stair-steppings pointing out to a right lateral movement, indicating that the structural evolution and deformation history of Marmara granitoid was controlled by a dextral shear zone.</p>

scholarly journals TESTING THE EFFECT OF UNDERMINING ON POSITIONAL ACCURACY OF THE DIGITAL TECHNICAL MAP OF OSTRAVA IN THE PŘÍVOZ CADASTRAL DISTRICT / PŘÍVOZ KADASTRINIO RAJONO ĮTAKOS OSTRAVOS SKAITMENINIO TECHNINIO ŽEMĖLAPIO POZICINIAM TIKSLUMUI PADARINIŲ TYRIMAS / АНАЛИЗ ВЛИЯНИЯ РАЗРУШАЮЩИХ СИЛ НА ПОЗИЦИОННУЮ ТОЧНОСТЬ ЦИФРОВОЙ ТЕХНИЧЕСКОЙ КАРТЫ Г. ОСТРАВА В КАДАСТРОВОМ РАЙОНЕ ПРИВОЗ

2011 ◽  
Vol 37 (3) ◽  
pp. 111-118
Author(s):  
Milan Mikoláš ◽  
Jiří Žváček ◽  
Michal Vaněk ◽  
Roman Donocik ◽  
Petra Zápalková ◽  
...  
Keyword(s):  
Rock Mass ◽  
Stress State ◽  
Coal Mining ◽  
Tectonic Stress ◽  
Surrounding Rock ◽  
Recent Past ◽  
Positional Accuracy ◽  
Landscape Morphology ◽  
The Town ◽  
Town Area

Intensive underground exploitation took place in the area of the Ostrava corporate town in recent past. After the coal mining was shut down in 1994 gradual subsidence in the town area has slowed down, however, establishing of the Digital Technical Map of Ostrava (DTMMO) dates back to 1992. When working a seam the original geostatic and tectonic stress state in the surrounding rock mass changes, which is accompanied by rock transformation and displacement from the roof towards the stope. Undermining is manifested in landscape morphology in many different ways that we can divide to continuous and discontinuous deformations. Residual mining effects could therefore have impacted positional accuracy of DTMMO in the last 18 years. The Bohumín 8-9/43 topographic sheet was selected for testing purposes in the Přívoz cadastral district. Santrauka Netolimoje praeityje Ostravos, miesto Čekijos rytuose, savivaldybėje buvo intensyviai eksploatuojama žemė. Nustojus užsiiminėti angliakasyba, nuo 1994-ųjų, palaipsnis žemės smukimas miesto vietovėse sulėtėjo. Skaitmeninis techninis Ostravos žemėlapis (DTMMO) sukurtas dar 1992 metais. Vykstant darbams žemės tarpsluoksnyje pirminis geostatinis ir tektoninis slėgis aplinkinėje uolienų masėje keitėsi, ir tai lėmė uolienų transformaciją ir slinktį. Kraštovaizdžio morfologijoje žala pasireiškia įvairiais būdais. Skiriama nenutrūkstamoji ir nutrūkstamoji deformacijos. Liekamasis kasybos poveikis per pstaruosius 18 metų galėjo paveikti pozicinį DTMMO tikslumą. Tiriant Přívoz kadastrinį rajoną, pasirinkta Bohumín 8-9/43 topografinio žemėlapio lapas. Резюме В недавнем прошлом в районе корпоративного г. Острава интенсивно эксплуатировались нижние слои грунта. После прекращения добычи угля в 1994 г. постепенное оседание поверхности города замедлилось. Созданная цифровая техническая карта г. Остравы (DTMMO) восходит к 1992 г. При работе с пластом возникающее исходное геостатическое и тектоническое возбуждение приводит к изменениям в окружающих пласт горных массивах, которые сопровождаются преобразованием пород и перемещениями в направлении забоя. Разрушение проявляется в морфологии ландшафта в самых разных формах, которые можно подразделить на непрерывные и разрывные деформации. Поэтому остаточные явления горных разработок могут оказывать влияние на позиционную точность DTMMO за последние 18 лет. Для анализа была выбрана топографическая плита Богумин 8-9/43 в кадастровом районе Привоз.

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