Sample records for piezometry
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NASA Astrophysics Data System (ADS)
Van der Werf, Thomas F.; Chatzaras, Vasileios; Tikoff, Basil; Drury, Martyn R.
2016-04-01
Baja California is an active transtensional rift zone, which links the San Andreas Fault with the East Pacific Rise. The erupted basalts of the Holocene San Quintin volcanic field contain xenoliths, which sample the lower crust and upper mantle beneath Baja California. The aim of this research is to gain insight in the rheology of the lower crust and the upper mantle by investigating the xenolith microstructure. Microstructural observations have been used to determine the dominant deformation mechanisms. Differential stresses were estimated from recrystallized grain size piezometry of plagioclase and clinopyroxene for the lower crust and olivine for the upper mantle. The degree of deformation can be inferred from macroscopic foliations and the deformation microstructures. Preliminary results show that both the lower crust and the upper mantle have been affected by multiple stages of deformation and recrystallization. In addition the dominant deformation mechanism in both the lower crust and the upper mantle is dislocation creep based on the existence of strong crystallographic preferred orientations. The differential stress estimates for the lower crust are 10-29 MPa using plagioclase piezometry and 12-35 MPa using clinopyroxene piezometry. For the upper mantle, differential stress estimates are 10-20 MPa. These results indicate that the strength of the lower crust and the upper mantle are very similar. Our data do not fit with the general models of lithospheric strength and may have important implications for the rheological structure of the lithosphere in transtensional plate margins and for geodynamic models of the region.
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NASA Astrophysics Data System (ADS)
Zammouri, Mounira; Ribeiro, Luis
2017-05-01
Groundwater flow model of the transboundary Saharan aquifer system is developed in 2003 and used for management and decision-making by Algeria, Tunisia and Libya. In decision-making processes, reliability plays a decisive role. This paper looks into the reliability assessment of the Saharan aquifers model. It aims to detect the shortcomings of the model considered properly calibrated. After presenting the calibration results of the effort modelling in 2003, the uncertainty in the model which arising from the lack of the groundwater level and the transmissivity data is analyzed using kriging technique and stochastic approach. The structural analysis of piezometry in steady state and logarithms of transmissivity were carried out for the Continental Intercalaire (CI) and the Complexe Terminal (CT) aquifers. The available data (piezometry and transmissivity) were compared to the calculated values, using geostatistics approach. Using a stochastic approach, 2500 realizations of a log-normal random transmissivity field of the CI aquifer has been performed to assess the errors of the model output, due to the uncertainty in transmissivity. Two types of bad calibration are shown. In some regions, calibration should be improved using the available data. In others areas, undertaking the model refinement requires gathering new data to enhance the aquifer system knowledge. Stochastic simulations' results showed that the calculated drawdowns in 2050 could be higher than the values predicted by the calibrated model.
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NASA Astrophysics Data System (ADS)
Brandstätter, Jennifer; Kurz, Walter; Rogowitz, Anna
2017-08-01
In this study we present microstructural data from hydrothermal veins in the sedimentary cover and the igneous basement recovered from Hole U1414A, Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project), to constrain deformation mechanism operating in the subducting Cocos Plate. Cathodoluminescence studies, mechanical e-twin piezometry and electron backscatter diffraction (EBSD) analyses of carbonate veins were used to give insights into the deformation conditions and to help to understand the tectonic deformation history of the Cocos Plate offshore Costa Rica. Analyses of microstructures in the sedimentary rocks and in the basalt of the igneous basement reveal brittle deformation, as well as crystal-plastic deformation of the host rock and the vein material. Cathodoluminescence images showed that in the basalt fluid flow and related precipitation occurred over several episodes. The differential stresses, obtained from two different piezometers using the same parameter (twin density), indicate various mean differential stresses of 49 ± 11 and 69 ± 30 MPa and EBSD mapping of calcite veins reveals low-angle subgrain boundaries. Deformation temperatures are restricted to the range from 170°C to 220°C, due to the characteristics of the existing twins and the lack of high-temperature intracrystalline deformation mechanisms (>220°C). The obtained results suggest that deformation occurred over a period associated with changes of ambient temperatures, occurrence of fluids and hydrofracturing, induced differential stresses due to the bending of the plate at the trench, and related seismic activity.
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Brandstätter, Jennifer; Kurz, Walter; Rogowitz, Anna
2017-08-01
In this study we present microstructural data from hydrothermal veins in the sedimentary cover and the igneous basement recovered from Hole U1414A, Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project), to constrain deformation mechanism operating in the subducting Cocos Plate. Cathodoluminescence studies, mechanical e-twin piezometry and electron backscatter diffraction (EBSD) analyses of carbonate veins were used to give insights into the deformation conditions and to help to understand the tectonic deformation history of the Cocos Plate offshore Costa Rica. Analyses of microstructures in the sedimentary rocks and in the basalt of the igneous basement reveal brittle deformation, as well as crystal-plastic deformation of the host rock and the vein material. Cathodoluminescence images showed that in the basalt fluid flow and related precipitation occurred over several episodes. The differential stresses, obtained from two different piezometers using the same parameter (twin density), indicate various mean differential stresses of 49 ± 11 and 69 ± 30 MPa and EBSD mapping of calcite veins reveals low-angle subgrain boundaries. Deformation temperatures are restricted to the range from 170°C to 220°C, due to the characteristics of the existing twins and the lack of high-temperature intracrystalline deformation mechanisms (>220°C). The obtained results suggest that deformation occurred over a period associated with changes of ambient temperatures, occurrence of fluids and hydrofracturing, induced differential stresses due to the bending of the plate at the trench, and related seismic activity.
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Kurz, Walter; Rogowitz, Anna
2017-01-01
Abstract In this study we present microstructural data from hydrothermal veins in the sedimentary cover and the igneous basement recovered from Hole U1414A, Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project), to constrain deformation mechanism operating in the subducting Cocos Plate. Cathodoluminescence studies, mechanical e‐twin piezometry and electron backscatter diffraction (EBSD) analyses of carbonate veins were used to give insights into the deformation conditions and to help to understand the tectonic deformation history of the Cocos Plate offshore Costa Rica. Analyses of microstructures in the sedimentary rocks and in the basalt of the igneous basement reveal brittle deformation, as well as crystal‐plastic deformation of the host rock and the vein material. Cathodoluminescence images showed that in the basalt fluid flow and related precipitation occurred over several episodes. The differential stresses, obtained from two different piezometers using the same parameter (twin density), indicate various mean differential stresses of 49 ± 11 and 69 ± 30 MPa and EBSD mapping of calcite veins reveals low‐angle subgrain boundaries. Deformation temperatures are restricted to the range from 170°C to 220°C, due to the characteristics of the existing twins and the lack of high‐temperature intracrystalline deformation mechanisms (>220°C). The obtained results suggest that deformation occurred over a period associated with changes of ambient temperatures, occurrence of fluids and hydrofracturing, induced differential stresses due to the bending of the plate at the trench, and related seismic activity. PMID:29081570
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NASA Astrophysics Data System (ADS)
Manteca, Ivan Alhama
The Agua Amarga coastal aquifer, located in the south of Alicante province, has been subjected to successive anthropogenic actions: salt works activity (1925-1975) and water withdrawal to supply the Alicante I and II desalination plants (since 2003). These interventions have influenced the salinity and the flow regime. Due to the existence of a salt marsh of ecological interest linked to the aquifer, the 'Mancomunidad de los Canales del Taibilla' (agency responsible for the desalination plants) designed a piezometric network for monitoring piezometry and electrical conductivity (in operation since May 2008). Soil humidity and piezometrics levels have been recovered by means of a seawater pouring programme over the salt marsh (since December 2009),which represents the third anthropic intervention. In this memoria, we investigate the Agua Amarga coastal aquifer to develop a physical conceptual model. Firstly, the study area is characterized in relation to climatology, geology, geomorphology and hydrogeology, using published information, describing, in addition, the desalination plants catchment system. Next, based on hydrogeological studies prior to the start up of the desalination plants, the aquifer is characterized: type, lithology, hydraulic parameters, thickness, surface extension, etc. Water quantity relating to rainfall, water withdrawal and pourings over the salt marsh, have been integrated in conjunction with data from monthly piezometric campaigns. In adittion, in order to gain insight into the groundwater mixing processes, chemical and isotope analyses were carried out on meteoric water and groundwater samples taken at different locations. The results were used to elaborate a conceptual physical model and a water budget. As an extension tool to understand processes and assess aquifer management, a 3-D fluid-flow and solute-transport model is designed with SEAWAT. Also, the 2-D physical characterization of scenarios with seawater intrusion and salt flats is presented. Finally, after describing ecological values of the salt marsh, the effect of the seawater pouring programme on aquifer piezometry and salinity is studied, assessing the possibility of applying this pilot scheme to other scenarios.
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NASA Astrophysics Data System (ADS)
Khomsi, Sami; Echihi, Oussema; Slimani, Naji
2012-03-01
A set of different data including high resolution seismic sections, petroleum wire-logging well data, borehole piezometry, structural cross-sections and outcrop analysis allowed us to characterise the tectonic framework, and its relationships with the deep aquifers seated in Cretaceous-Miocene deep reservoirs. The structural framework, based on major structures, controls the occurrence of deep aquifers and sub-basin aquifer distributions. Five structural domains can be defined, having different morphostructural characteristics. The northernmost domain lying on the north-south axis and Zaghouan thrust system is a domain of recharge by underflow of the different subsurface reservoirs and aquifers from outcrops of highly fractured reservoirs. On the other hand, the morphostructural configuration controls the piezometry of underground flows in the Plio-Quaternary unconfined aquifer. In the subsurface the Late Cretaceous-Miocene reservoirs are widespread with high thicknesses in many places and high porosities and connectivities especially along major fault corridors and on the crestal parts of major anticlines. Among all reservoirs, the Oligo-Miocene, detritic series are widespread and present high cumulative thicknesses. Subsurface and fieldwork outline the occurrence of 10 fractured sandy reservoirs for these series with packages having high hydrodynamic and petrophysical characteristics. These series show low salinities (maximum 5 g/l) in the northern part of the study area and will constitute an important source of drinkable water for the next generations. A regional structural cross-section is presented, compiled from all the different data sets, allowing us to define the major characteristics of the hydrogeological-hydrogeothermal sub-basins. Eight hydrogeological provinces are defined from north-west to south-east. A major thermal anomaly is clearly identified in the south-eastern part of the study area in Sfax-Sidi Il Itayem. This anomaly is possibly related to major faults pertaining to the Sirt basin and controlled by a deep thermal anomaly. Many exploration targets are identified especially along the Cherichira-Kondar thrust where the Oligocene subcropping reservoirs are well developed. They are highly fractured and show good hydrodynamic characteristics.
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Identifying and quantifying urban recharge: a review
NASA Astrophysics Data System (ADS)
Lerner, David N.
2002-02-01
The sources of and pathways for groundwater recharge in urban areas are more numerous and complex than in rural environments. Buildings, roads, and other surface infrastructure combine with man-made drainage networks to change the pathways for precipitation. Some direct recharge is lost, but additional recharge can occur from storm drainage systems. Large amounts of water are imported into most cities for supply, distributed through underground pipes, and collected again in sewers or septic tanks. The leaks from these pipe networks often provide substantial recharge. Sources of recharge in urban areas are identified through piezometry, chemical signatures, and water balances. All three approaches have problems. Recharge is quantified either by individual components (direct recharge, water-mains leakage, septic tanks, etc.) or holistically. Working with individual components requires large amounts of data, much of which is uncertain and is likely to lead to large uncertainties in the final result. Recommended holistic approaches include the use of groundwater modelling and solute balances, where various types of data are integrated. Urban recharge remains an under-researched topic, with few high-quality case studies reported in the literature.
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NASA Astrophysics Data System (ADS)
Neves, Maria C.; Costa, Luis; Monteiro, José P.
2016-06-01
Karst aquifers in semi-arid regions, like Querença-Silves (Portugal), are particularly vulnerable to climate variability. For the first time in this region, the temporal structure of a groundwater-level time series (1985-2010) was explored using the continuous wavelet transform. The investigation focused on a set of four piezometers, two at each side of the S. Marcos-Quarteira fault, to demonstrate how each of the two sectors of the aquifer respond to climate-induced patterns. Singular spectral analysis applied to an extended set of piezometers enabled identification of several quasi-periodic modes of variability, with periods of 6.5, 4.3, 3.2 and 2.6 years, which can be explained by low-frequency climate patterns. The geologic forcing accounts for ~15 % of the differential variability between the eastern and western sectors of the aquifer. The western sector displays spatially homogenous piezometric variations, large memory effects and low-pass filtering characteristics, which are consistent with relatively large and uniform values of water storage capacity and transmissivity properties. In this sector, the 6.5-year mode of variability accounts for ~70 % of the total variance of the groundwater levels. The eastern sector shows larger spatial and temporal heterogeneity, is more reactive to short-term variations, and is less influenced by the low-frequency components related to climate patterns.
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NASA Astrophysics Data System (ADS)
Wex, S.; Mancktelow, N. S.; Hawemann, F.; Pennacchioni, G.; Camacho, A.
2016-12-01
The over 600 km long mid-crustal Woodroffe Thrust developed during the intraplate Petermann Orogeny around 550 Ma. Ductile shearing was accommodated along a shallowly south-dipping plane with a top-to-north shear sense. Due to late-stage open folding of the thrust plane, a nearly continuous N-S profile of 60 km length in the direction of thrusting is now exposed. Metamorphic conditions of 500 °C - 600 °C at roughly 0.8 GPa and the rare availability of aqueous fluids are well constrained along the entire transect, providing an ideal framework for studying variation in microstructure and texture in the dominantly "dry" felsic middle continental crust. During the ductile thrusting quartz dynamically recrystallized by subgrain rotation and grain boundary migration, whereas plagioclase and K-feldspar underwent fracturing and neocrystallization. Quartz crystallographic preferred orientation (CPO) shows progressive variation from dominant prism to mixed rhomb/basal slip, while plagioclase and K-feldspar CPO is random. Flow stresses, estimated from quartz grain size piezometry, decrease towards higher metamorphic grade and deeper structural levels, yielding a strain rate that is up to two orders of magnitude faster than the geological average of 10-13 - 10-15 s-1. On this basis, a qualitative rheological model is developed explaining the observed cyclic interplay between ductile shearing (mylonitization) and brittle fracturing (pseudotachylyte formation) in the relatively "dry" middle continental crust, where the syn-deformational influx of water has not been pervasive.
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Hydrogeological functioning of the tablecloth of the Midelt Furrow (High Moulouya, MOROCCO)
NASA Astrophysics Data System (ADS)
Ikhmerdi, H.; Boukdir, A.; Kossir, A.; Alili, L.; Ben-Said, E.
2018-05-01
The superficial tablecloth of furrow of Midelt belongs to the bowl of High Moulouya which stretches out from the west eastward between the High Atlas in the South and the Medium Atlas west and in the Northeast. The methodology used includes the synthesis of geological data, piezometry, hydrodynamics, hydroclimatology and water quality. This study provides the following results: The flow mode of the water table is general SW to NE on the left bank of the Moulouya river and on the right bank, the flow is from the NW to the SE. The piezometric ratings vary from 1460 to 1780 m. The hydraulic gradient is the order of 2% on average. The transmissivity is usually about 10-3 m2/s. the punctual flows can reach 50 l / s (case of the drilling N ° IRE 879/38 realized in the alluviums of the Outat). The flow provided by the sources from conglomerates and lake limestones of the Plio-Villafranchien is 50 l / s. The unit of the Mio- Plio-Quaternary aquifer is fed from the infiltrations of rains, by the wadis which cross the banks of the conglomerates and by the landing of the tablecloths of Lias, Dogger and Cretaceous this feeding is however weak in because of the discontinuity of the formations and the poor permeability of the different levels. From a qualitative point of view the groundwater analysis of the aquifer shows that their overall quality is average to good.
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NASA Astrophysics Data System (ADS)
Stewart, Craig A.; Miranda, Elena A.
2017-12-01
We investigate how the rheological evolution of shear zone rocks from beneath the brittle-ductile transition (BDT) is affected by coeval ductile shear and pseudotachylyte development associated with seismicity during the earthquake cycle. We focus our study on footwall rocks of the South Mountains core complex, and we use electron backscatter diffraction (EBSD) analyses to examine how strain is localized in granodiorite mylonites both prior to and during pseudotachylyte development beneath the BDT. In mylonites that are host to pseudotachylytes, deformation is partitioned into quartz, where quartz exhibits crystallographic-preferred orientation patterns and microstructures indicative of dynamic recrystallization during dislocation creep. Grain size reduction during dynamic recrystallization led to the onset of grain boundary sliding (GBS) accommodated by fluid-assisted grain size-sensitive (GSS) creep, localizing strain in quartz-rich layers prior to pseudotachylyte development. The foliation-parallel zones of GBS in the host mylonites, and the presence of GBS traits in polycrystalline quartz survivor clasts indicate that GBS zones were the ductile precursors to in situ pseudotachylyte generation. During pseudotachylyte development, strain was partitioned into the melt phase, and GSS deformation in the survivor clasts continued until crystallization of melt impeded flow, inducing pseudotachylyte development in other GBS zones. We interpret the coeval pseudotachylytes with ductile precursors as evidence of seismic events near the BDT. Grain size piezometry yields high differential stresses in both host mylonites ( 160 MPa) and pseudotachylyte survivor clasts (> 200 MPa), consistent with high stresses during interseismic and coseismic phases of the earthquake cycle, respectively.
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NASA Astrophysics Data System (ADS)
Cawood, T. K.; Platt, J. P.
2017-12-01
A widely-accepted model for the rheology of crustal-scale shear zones states that they comprise distributed strain at depth, in wide, high-temperature shear zones, which narrow to more localized, high-strain zones at lower temperature and shallower crustal levels. We test and quantify this model by investigating how the width, stress, temperature and deformation mechanisms change with depth in the Simplon Shear Zone (SSZ). The SSZ marks a major tectonic boundary in the central Alps, where normal-sense motion and rapid exhumation of the footwall have preserved evidence of older, deeper deformation in rocks progressively further into the currently-exposed footwall. As such, microstructures further from the brittle fault (which represents the most localized, most recently-active part of the SSZ) represent earlier, higher- temperature deformation from deeper crustal levels, while rocks closer to the fault have been overprinted by successively later, cooler deformation at shallower depths. This study uses field mapping and microstructural studies to identify zones representing deformation at various crustal levels, and characterize each in terms of zone width (representing width of the shear zone at that time and depth) and dominant deformation mechanism. In addition, quartz- (by Electron Backscatter Diffraction, EBSD) and feldspar grain size (measured optically) piezometry are used to calculate the flow stress for each zone, while the Ti-in-quartz thermometer (TitaniQ) is used to calculate the corresponding temperature of deformation. We document the presence of a broad zone in which quartz is recrystallized by the Grain Boundary Migration (GBM) mechanism and feldspar by Subgrain Rotation (SGR), which represents the broad, deep zone of deformation occurring at relatively high temperatures and low stresses. In map view, this transitions to successively narrower zones, respectively characterized by quartz SGR and feldspar Bulge Nucleation (BLG); quartz BLG and brittle deformation of feldspar; and finally, a zone of generally brittle deformation. These zones represent deformation in progressively narrower regions at shallower depths, under lower temperatures and higher stresses.
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NASA Astrophysics Data System (ADS)
Lachaal, Fethi; Bédir, Mourad; Tarhouni, Jamila; Gacha, Ayadi Ben; Leduc, Christian
2011-06-01
The Zéramdine and Mahdia-Jébéniana blocks are located in the Sahel region in east-central Tunisia. Active tectonics have divided the region into numerous sub-units, as result of multiple phases of distension and compression. The Miocene fluvio-deltaic sediment sandy layers have aquiferous capacities but their hydraulic properties are still unknown, due to the lack of investigation wells. This study proposes a new description of the regional hydrogeology of Miocene deposits. Seismic-reflection and wireline logging of petroleum and water wells were used to understand the structure and the geometry of the Miocene reservoirs. The groundwater flow and its relationship to the sedimentary and tectonic context were then identified by studying piezometry and hydrochemistry. Two Miocene deep aquifer systems were identified: (1) Zéramdine-Béni Hassen to the north and (2) Jébéniana-Ksour Essef to the south. These aquifers are separated by the Mahdia graben. Other major tectonic structures, such as the Zéramdine fault corridor, the Moknine graben, and the El-Jem half-graben represent lateral boundaries for these aquifers. Other deeper sandy and clayey-sandy reservoirs were also identified in the area. Their repartition, thickness and depth vary from one block to other. Hydrodynamics of the deep aquifers seems to be controlled by geological structures. Two independent compartments were identified: in the northern block groundwater flows from West to East and from Northwest to Southeast, while in the southern block it flows from Northwest to Southeast. Geochemical facies are of two types: Na-Ca-Cl-SO 4 for the Zéramdine-Béni Hassen deep aquifer and Na-Cl for the Jébéniana-Ksour Essef deep aquifer. The hydrodynamic and geochemical results confirm the sharing of the Miocene sediments into two aquifers.
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A Transient Groundwater Flow Model for Evaluating River-Aquifer Exchange
NASA Astrophysics Data System (ADS)
Zanini, A.; Chelli, A.; Pecoraro, R.; Celico, F.
2014-12-01
The study area is an industrial site (in the North of Italy) contaminated through heavy metal and chlorinated hydrocarbons. The site presents an area of about 5 km2 and a complex geology. During 2013 and 2014 the hydrogeological conceptual model was reviewed and the result was a main unconfined aquifer that presents an impervious bottom at about 30 m below ground. A small portion of the aquifer is split by a non-continuous aquitard. Below the impervious bottom, there are confined aquifers that are not polluted. The boundary conditions of the aquifer are constant head upstream (obtained from a regional piezometry) and constant head downstream that represents a lake stage. Moreover a river inside the study area, that could feed or dry the aquifer depending on its stage, manages the groundwater head levels. The study area presents more than 100 pumping wells that have the objective of realizing a hydraulic barrier and to prevent the flow of pollutants downstream. The area is monitored with about 120 monitoring wells, which are used, through a periodic sampling and monitoring, to control the pollution and to estimate the flow direction. During the last year a numerical flow model has been developed by means of MODFLOW 2000 (Harbaugh, 2000) with the aim at becoming a management tool of the hydraulic barrier. The calibration procedure, initially, was performed in steady state condition using the PEST procedure (Doherty, 2007). The goal was to reproduce the monthly observations at the monitoring wells varying the hydraulic conductivity of the main aquifer and of the aquitard. The second step of the calibration was the extension of the calibration to transient data. The period from September 1st 2013 to June 31st 2014 was reproduced. In order to avoid problem with the starting conditions only the observations collected in 2014 were used to estimate the aquifer parameters. The period September 1st 2013 to December 31st was used as warm up in order to obtain reliable starting conditions for the 2014. The result of the work was a model that allows to reproduce with high reliability the collected observations and to understand the groundwater flow direction depending on the river stage.
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NASA Astrophysics Data System (ADS)
Chatzaras, Vasileios; Kruckenberg, Seth C.; Cohen, Shaina M.; Medaris, L. Gordon, Jr.; Withers, Anthony C.; Bagley, Brian
2016-04-01
The effect of finite strain ellipsoid geometry on crystallographic preferred orientation (CPO) is well known for crustal minerals (e.g., quartz, calcite, biotite, and hornblende). In the upper mantle, however, it remains poorly constrained how strain and fabric may affect olivine CPO. We present data from a suite of 40 spinel peridotite xenoliths from Marie Byrd Land (west Antarctica), which support an interpretation that fabric geometry rather than deformation conditions control the development of olivine CPO. We use X-ray computed tomography (XRCT) to quantitatively determine spinel fabric (orientation and geometry). Olivine CPOs, determined by Electron Backscattered Diffraction (EBSD), are plotted with respect to the XRCT-derived spinel foliation and lineation; this approach allows for the accurate, and unbiased, identification of CPO symmetries and types in mantle xenoliths. The combined XRCT and EBSD data show that the xenoliths are characterized by a range of fabric geometries (from oblate to prolate) and olivine CPO patterns; we recognize the A-type, axial-[010], axial-[100], and B-type patterns. The mantle xenoliths equilibrated at temperatures 779-1198 oC, as determined by 2-Px geothermometry. Using a geotherm consistent with the stability of spinel in all xenoliths, the range of equilibration temperatures occurs at depths between 39 and 72 km. Olivine recrystallized grain size piezometry reveals differential stresses ranging 2-60 MPa. Analysis of low-angle misorientation axes show a wide range in the distribution of rotation axes, with dominant {0kl}[100] slip. We use Fourier Transform Infrared (FTIR) spectroscopy to estimate the water content in the xenolith with the B-type CPO pattern. FTIR analysis shows that the equilibrium H concentration in olivine is low (4-13 ppm H2O). Combining these data, we observe that olivine CPO symmetry is controlled neither by the deformation conditions (stress, temperature, pressure, water content) for the range of conditions estimated in the Marie Byrd Land xenoliths, nor by the activation of the slip systems predicted by deformation experiments. Rather, our data show that olivine CPO is controlled by transitions in strain-induced fabric geometry. Microstructures and deformation mechanism maps suggest that deformation is dominated by dislocation-accommodated grain boundary sliding. We propose that slip of olivine glide planes and rotation of olivine grains occur so as to accommodate the imposed material flow, which is guided by the 3D strain-induced fabric geometry. As a result of this process, the axial-[010] and B-type patterns form in relation to oblate fabric ellipsoids, the A-type pattern forms in a range of fabric ellipsoids, and the axial-[100] pattern is associated with prolate fabric ellipsoids. We therefore suggest that the well-known process of strain geometry-induced development of CPO is also applicable to upper mantle rocks.
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Rheological structure of the lithosphere in plate boundary strike-slip fault zones
NASA Astrophysics Data System (ADS)
Chatzaras, Vasileios; Tikoff, Basil; Kruckenberg, Seth C.; Newman, Julie; Titus, Sarah J.; Withers, Anthony C.; Drury, Martyn R.
2016-04-01
How well constrained is the rheological structure of the lithosphere in plate boundary strike-slip fault systems? Further, how do lithospheric layers, with rheologically distinct behaviors, interact within the strike-slip fault zones? To address these questions, we present rheological observations from the mantle sections of two lithospheric-scale, strike-slip fault zones. Xenoliths from ˜40 km depth (970-1100 ° C) beneath the San Andreas fault system (SAF) provide critical constraints on the mechanical stratification of the lithosphere in this continental transform fault. Samples from the Bogota Peninsula shear zone (BPSZ, New Caledonia), which is an exhumed oceanic transform fault, provide insights on lateral variations in mantle strength and viscosity across the fault zone at a depth corresponding to deformation temperatures of ˜900 ° C. Olivine recrystallized grain size piezometry suggests that the shear stress in the SAF upper mantle is 5-9 MPa and in the BPSZ is 4-10 MPa. Thus, the mantle strength in both fault zones is comparable to the crustal strength (˜10 MPa) of seismogenic strike-slip faults in the SAF system. Across the BPSZ, shear stress increases from 4 MPa in the surrounding rocks to 10 MPa in the mylonites, which comprise the core of the shear zone. Further, the BPSZ is characterized by at least one order of magnitude difference in the viscosity between the mylonites (1018 Paṡs) and the surrounding rocks (1019 Paṡs). Mantle viscosity in both the BPSZ mylonites and the SAF (7.0ṡ1018-3.1ṡ1020 Paṡs) is relatively low. To explain our observations from these two strike-slip fault zones, we propose the "lithospheric feedback" model in which the upper crust and lithospheric mantle act together as an integrated system. Mantle flow controls displacement and the upper crust controls the stress magnitude in the system. Our stress data combined with data that are now available for the middle and lower crustal sections of other transcurrent fault systems support the prediction for constant shear strength (˜10 MPa) throughout the lithosphere; the stress magnitude is controlled by the shear strength of the upper crustal faults. Fault rupture in the upper crust induces displacement rate loading of the upper mantle, which in turn, causes strain localization in the mantle shear zone beneath the strike-slip fault. Such forced localization leads to higher stresses and strain rates in the shear zone compared to the surrounding rocks. Low mantle viscosity within the shear zone is critical for facilitating mantle flow, which induces widespread crustal deformation and displacement loading. The lithospheric feedback model suggests that strike-slip fault zones are not mechanically stratified in terms of shear stress, and that it is the time-dependent interaction of the different lithospheric layers - rather than their relative strengths - that governs the rheological behavior of the plate boundary, strike-slip fault zones.
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Selected topics of fluid mechanics
Kindsvater, Carl E.
1958-01-01
The fundamental equations of fluid mechanics are specific expressions of the principles of motion which are ascribed to Isaac Newton. Thus, the equations which form the framework of applied fluid mechanics or hydraulics are, in addition to the equation of continuity, the Newtonian equations of energy and momentum. These basic relationships are also the foundations of river hydraulics. The fundamental equations are developed in this report with sufficient rigor to support critical examinations of their applicability to most problems met by hydraulic engineers of the Water Resources Division of the United States Geological Survey. Physical concepts are emphasized, and mathematical procedures are the simplest consistent with the specific requirements of the derivations. In lieu of numerical examples, analogies, and alternative procedures, this treatment stresses a brief methodical exposition of the essential principles. An important objective of this report is to prepare the user to read the literature of the science. Thus, it begins With a basic vocabulary of technical symbols, terms, and concepts. Throughout, emphasis is placed on the language of modern fluid mechanics as it pertains to hydraulic engineering. The basic differential and integral equations of simple fluid motion are derived, and these equations are, in turn, used to describe the essential characteristics of hydrostatics and piezometry. The one-dimensional equations of continuity and motion are defined and are used to derive the general discharge equation. The flow net is described as a means of demonstrating significant characteristics of two-dimensional irrotational flow patterns. A typical flow net is examined in detail. The influence of fluid viscosity is described as an obstacle to the derivation of general, integral equations of motion. It is observed that the part played by viscosity is one which is usually dependent on experimental evaluation. It follows that the dimensionless ratios known as the Euler, Froude, Reynolds, Weber, and Cauchy numbers are defined as essential tools for interpreting and using experimental data. The derivations of the energy and momentum equations are treated in detail. One-dimensional equations for steady nonuniform flow are developed, and the restrictions applicable to the equations are emphasized. Conditions of uniform and gradually varied flow are discussed, and the origin of the Chezy equation is examined in relation to both the energy and the momentum equations. The inadequacy of all uniform-flow equations as a means of describing gradually varied flow is explained. Thus, one of the definitive problems of river hydraulics is analyzed in the light of present knowledge. This report is the outgrowth of a series of short schools conducted during the spring and summer of 1953 for engineers of the Surface Water Branch, Water Resources Division, U. S. Geological Survey. The topics considered are essentially the same as the topics selected for inclusion in the schools. However, in order that they might serve better as a guide and outline for informal study, the arrangement of the writer's original lecture notes has been considerably altered. The purpose of the report, like the purpose of the schools which inspired it, is to build a simple but strong framework of the fundamentals of fluid mechanics. It is believed that this framework is capable of supporting a detailed analysis of most of the practical problems met by the engineers of the Geological Survey. It is hoped that the least accomplishment of this work will be to inspire the reader with the confidence and desire to read more of the recent and current technical literature of modern fluid mechanics.
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NASA Astrophysics Data System (ADS)
Mertineit, M.; Zulauf, G.; Peinl, M.; Zanella, F.; Bornemann, O.
2009-04-01
Anhydrite layers from Gorleben salt dome, embedded in a halite matrix from Asse salt dome, both northern Germany, were deformed under bulk plain strain using a thermomechenical apparatus (Zulauf et al., 2007, 2009). The initial layer thickness Hi ranges from 0.85 to 2.5 mm. Further deformation conditions were as follows: T =345Ë C, max=4.59 MPa, ezmax=-40%, Ä-=2*10-7s-1. During the deformation process, load cells record the stress along Y and Z. The displaced material could escape in X. The deformed samples were scanned using a computer tomograph at the Universitätsklinikum Frankfurt/Main. The CT data allow the generation of 3D-modells using the software Smoooth. We deformed six samples with the layer (S) perpendicular to the X-axis and four samples with the layer perpendicular to the Z-axis. Depending on the orientation of the layer (Sâ¥X or Sâ¥Z), the expected structures should be folds or boudins, respectively, the geometry of which should strongly depend on Hi. In cases were the layer was orientated parallel to the shortening axis (Sâ¥X), the anhydrite layer shows Mohr-Coulomb fractures. The fracture walls were thrust on top of each other. The space between hanging and foot wall is filled with salt. The angle between the fractures and the YZ-plain ranges from 10Ë to 25Ë , rarely up to 70Ë , dependent on the finite strain. In thin layers (Hi=0.85 and 1 mm) rarely non-cylindrical folds developed. In both cases (Sâ¥X and Sâ¥Z) the layer thickness did not significantly change during deformation. In cases were the layer was orientated perpendicular to the shortening axis (Sâ¥Z) boudins developed by extensional fracture. The number of boudins and their size depend strongly on the initial layer thickness Hi. With increasing layer thickness Hi the width of boudins Wa increases linearly. Wa = -0.2 + 1.4 * Hi (1) This relation between Hi and Wa is further compatible with equation (16.4) of Price and Cosgrove (1990) which also considers rheological parameters. Moreover experiments carried out under bulk constrictional strain (Zulauf et al., 2007, 2009) show a similar dependency of the initial layer thickness and boudin width. For microstructual investigations of the halite matrix, thin sections (XZ- and YZ-sections) were prepared and etched following the method of Urai et al. (1987). First microfabric data show that halite behaves viscous whereas anhydrite deforms by fracturing or rare folding under the chosen deformation conditions. Halite deforms by climb-controlled dislocation creep with strain hardening (Carter et al., 1993). Anhydrite, on the other hand, was deformed in the brittle-plastic regime, characterized by twinning, kinking and fracturing. The subgrain size of halite has been used to estimate the differential stress (Schléder & Urai, 2005, 2007), that was compared with the stress recorded by the load cells. The subgrain size of deformed halite varies between 0.04 and 0.07mm, resulting in differential stresses between 3.3 +1.5/-0.8 MPa (Sâ¥X) and 4.2 +3.0/-1.2 MPa (Sâ¥Z), although the conditions for piezometry are not completely fulfilled (e.g. lack of steady state during deformation in some samples). These stress values in the matrix fit with the stress values recorded during deformation. Close to rigid anhydrite the subgrain size decreases to values of 0.02 - 0.03 mm, reflecting peak stress up to 6.7 +3.7/-0.7 MPa. We do not know the reasons why folding of the anhydrite layer is largely lacking, although the viscosity contrast between halite and anhydrite should be appropriate for folding. Possible reasons are the lack in confining pressure or mechanical anisotropies in the undeformed anhydrite. Further investigations will focus on the texture of halite and on microfabrics of the anhydrite. References Carter, N.L., Horseman, S.T., Russel, J.E. & Handin, J (1993): Rheology of rocksalt, J. Struct. Geol., Vol. 15, No. 9/10, p. 1257-1271 Price, N.J.; Cosgrove, J.W. (1990): Analysis of Geological Structures, by Neville J. Price and John W. Cosgrove, pp. 516., Cambridge, UK: Cambridge University Press, August 1990 Schléder, Z. & Urai, J. L. (2005): Microstructual evolution of deformation-modified primary halite from the Middle Triassic Röt Formation at Hengelo, The Netherlands, Int. J. Earth Sci., 94, p. 941-955 Schléder, Z. & Urai, J. L. (2007): Deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive Eocene-Oligocene rocksalt from Eyvanekey plateau and Garmsar hills (central Iran), J. Struct. Geol., 29, p. 241-255 Urai, J. L., Spiers, C. J., Peach, C. J., Franssen, R. C. M. W. & Liezenberg, J. L. (1987): Deformation mechanisms operating in naturally deformed halite rocks as deducted from microstructural investigations, Geol. Mijnbouw, 66, p. 165-176 Zulauf, G., Zulauf, J. & Bornemann, O. (2007): Deformation of a halite-anhydrite sequence under bulk constriction: Preliminary results from thermomechanical experiments, in: Wallner, M, Lux, K.-H., Minkley, W. & Reginal Hardy jr., H. (Eds.). The mechanical behavior of salt-Understanding of THMC processes in salt, Taylor & Francies, London: 63-68 Zulauf, G., Zulauf, J., Bornemann, O., Kihm, N., Peinl, M., Zanella, F. (2009): Experimental deformation of a single-layer anhydrite in halite matrix under bulk constriction: 1. Geometric and kinematic aspects, J. Struct. Geol. (submitted)
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NASA Astrophysics Data System (ADS)
Zulauf, G.; Zulauf, J.; Peinl, M.; Kihm, N.; Zanella, F.; Bornemann, O.
2009-04-01
The internal parts of salt diapirs are characterized by constrictional deformation supporting steeply plunging prolate fabrics and related linear (L>S) fabrics (Talbot and Jackson 1987). The youngest folds recognized in stems of salt diapirs are known from German Zechstein salt as curtain folds (Kulissen- or Vorhangfalten, Hartwig 1925) because the steeply inclined bedding planes define steeply plunging cylindrical folds. The grain-shape lineation tends to parallel the hinge lines of curtain folds. In cases of rheological stratification (e.g. stiff anhydrite or shale layers embedded in a weaker halite matrix), the curtain folds should be associated with boudins, the latter resulting from vertical extension parallel to the steep axes of the curtain folds. A new deformation apparatus has been used to model the internal kinematics of rheologically stratified salt diapirs. Composite natural samples consisting of a single layer of Gorleben anhydrite, embedded in matrix of Asse halite (both from Zechstein formation of northern Germany), were constrictionally deformed at temperature, T = 345Ë C, strain rate, Ä- = 10-7 s-1, maximum viscosity, η = 2 x 1013 Pa s, and maximum finite strain, eX = 122%. Viscous flow of Asse halite under the conditions listed above was accommodated by dislocation creep, which can be approximated by the equation obtained experimentally by Carter et al. (1993) for low stresses. Dislocation creep was related to formation of subgrains which are forming a striking chessboard pattern in sections cut parallel to the major stretching axis, X. The subgrain size, D, has been used to estimate the differential stress, , using the equation obtained by Schléder and Urai (2005) after combining the calibrations published by Carter et al. (1993) and Franssen (1993). The piezometrically derived stress values are between 2 and 6 MPa. Although the prerequisites for piezometry are not fully met in the present case of Asse halite (e.g. steady-state deformation is not given in each run), the derived stresses are quite similar to the actual stresses recorded by the load cells of the machine. At advanced state of constriction (eX > 90%) a strong increase in strain hardening of halite led to a transient tension fracture that healed up and was shortened by folding during the final phase of viscous deformation. Tiny prismatic anhydrite inclusions disseminated inside the halite matrix were reoriented during constriction resulting in a linear grain-shape fabric. 3D-images of the anhydrite layer, based on computer tomography, revealed rare kink folds with axes subparallel to X, and boudins which result from brittle tension fracture. With increasing layer thickness, Hi, the width of boudins, Wa, increases linearly and can be described by Wa = -0.3 + 1.3 * Hi (1). The normalized width of boudins (Wd = Wa/Hi) is almost constant at 1.5 ±1.0. These geometrical parameters can be used to reveal fracture boudinage under bulk constriction. The oblique orientation of most of the boudins, with respect to the principal strain axes, results from folding o the boudins by a second generation of folds, the latter with axes subperpendicular to the layer. Similar structures have been produced using plasticine as rock analogue (Zulauf and Zulauf, 2005). The necks between the anhydrite boudins are different in shape and composition. Some necks are entirely filled with viscous halite. Others show open space that is coated with black organic matter (as shown by fluorescence microscopy) and/or with halite, both resulting from precipitation from a fluid. Fluorescence microscopy has also revealed organic matter inside fluid inclusions which are resting on grain boundaries of initial (only naturally deformed) Asse halite. The shape of these fluid inclusions varies significantly from isolated bubbles to finger like tubes (see also Urai et al., 1987), all of which show a central part that is dark under the fluorescence microscope (probably NaCl brine) and an outer bright rim consisting of organic matter. In some cases the tubes are fusing into dark fluid films which are decorating the grain boundary. Grain boundary fluid inclusions are still present in experimentally deformed samples. However, these fluid inclusions are stretched and are more irregularly distributed along the grain boundaries compared to those of the initial samples. Organic matter is still present in the outer rims of the inclusions as is shown by fluorescence microscopy. Of particular interest are the interfaces of viscous halite and rigid anhydrite which were acting as rheological boundaries, along which halite was strongly sheared. In these high-strain domains the grain boundary fluid inclusions were also strongly stretched resulting in accumulation and trapping of fluid phases at these sites. This observation explains why the open space in the neck domains is coated with organic matter. After the latter was expelled from deformed and fused grain boundary fluid inclusions it migrated into the open neck space where it was precipitated. First investigations using RAMAN spectroscopy have confirmed that the composition of the organic matter of fluid inclusions and black coatings of open necks is the same. We argue that the release of fluids from grain boundaries has significantly controlled the strain hardening which is a characteristic feature at advanced states of finite strain. The new data presented above might have implications for selecting rock salt of the Asse type as host rock for a radioactive waste repository. Further investigations will focus on the texture (crystallographic preferred orientation) of deformed halite and on the composition of the fluid inclusions inside both undeformed and deformed samples. References: Carter, N.L. et al., 1993. J. Struct. Geol. 15, 1257-1271. Franssen, R.C.M.W., 1993. PhD thesis, Rijksuniversiteit Utrecht. Hartwig, G., 1925. Jahresberichte Niedersächsischer Geologischer Verein 17, 1-74. Schléder, Z. and Urai, J.L., 2005. Int. J. Earth Sciences, 94, 941-955. Talbot, C.J., Jackson, M.P.A., 1987. AAPG Bull. 71, 1086-1093. Urai, J.L. et al., 1987. Geologie en Mijnbouw, 66, 165-176. Zulauf, J., Zulauf, G., 2005. J. Struct. Geol. 27, 1061-1068.