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Sample records for natural lithospheric radioxenon

  1. Categorization of Radioxenon

    SciTech Connect

    Keller, Paul E.

    2012-04-26

    This report summarizes a study into some false positive issues in the use of radioxenon as a method to verify a clandestine nuclear weapons explosion. False positives arise due to similarities between the radioxenon signature generated in medical isotope production and that generated in a nuclear weapon explosion. This report also discusses how to categorize the radioxenon by levels of urgency for manual analysis and interpretation and recommends applying machine learning and time series analysis techniques in the automation of radioxenon characterization. The literature indicates that medical isotope production is a major contributor to atmospheric radioxenon and is the main source of confusion in determining the source of radioxenon. While radioxenon emissions from nuclear power plants can be distinguished from that from nuclear weapon explosions, emissions from medical isotope production generate signatures similar to certain nuclide ratios found in nuclear weapons explosions. Different techniques for analyzing nuclide concentrations and ratios as well as including other sensing modalities via sensor fusion are discussed.

  2. Generation of Radioxenon Isotopes

    DTIC Science & Technology

    2008-09-01

    container. Quartz Wool Aluminum Bottle Filter Paper U3O8 Powder Figure 1-A. Schematic of the RXG. The overall length...the detector calibration and was considered the superior approach. Radioxenon from Fissioning of U-235 The RXG is composed of 10.1 grams of U3O8 ...uranium oxide) powder , with the uranium being 95% U-235. A diagram of the RXG is shown in Figure 1-A. The uranium-oxide powder is double sealed in 3

  3. Triple Coincidence Radioxenon Detector

    SciTech Connect

    McIntyre, Justin I.; Aalseth, Craig E.; Bowyer, Ted W.; Hayes, James C.; Heimbigner, Tom R.; Morris, Scott J.; Reeder, Paul L.

    2004-09-22

    The Automated Radioxenon Sampler/Analyzer (ARSA) built by Pacific Northwest National Laboratory (PNNL) is on e of the world’s most sensitive systems for monitoring the four radioxenon isotopes 133Xe, 133mXE, 131mXe and 135Xe. However, due to size, weight and power specifications appropriate to meet treaty-monitoring requirements; the ARSA is unsuitable for rapid deployment using modest transportation means. To transition this technology to a portable unit can be easily and rapidly deployed can be achieved by significant reductions in size, weight and power consumption if concentration were not required. As part of an exploratory effort to reduce both the size of the air sample and the gas processing requirement PNNL has developed an experimental nuclear detector to test and qualify the use of triple coincidence signatures (beta, conversion electron, x-ray) from two of the radioxenon isotopes (135Xe and 133Xe) as well as the more traditional beta-gamma coincidence signatures used by the ARSA system. The additional coincidence requirement allows for reduced passive shielding, and makes it possible for unambiguous detection of 133Xe and 153Xe in the presence of high 222Rn backgrounds. This paper will discuss the experimental setup and the results obtained for a 133Xe sample with and without 222Rn as an interference signature.

  4. Using natural laboratories and modeling to decipher lithospheric rheology

    NASA Astrophysics Data System (ADS)

    Sobolev, Stephan

    2013-04-01

    Rheology is obviously important for geodynamic modeling but at the same time rheological parameters appear to be least constrained. Laboratory experiments give rather large ranges of rheological parameters and their scaling to nature is not entirely clear. Therefore finding rheological proxies in nature is very important. One way to do that is finding appropriate values of rheological parameter by fitting models to the lithospheric structure in the highly deformed regions where lithospheric structure and geologic evolution is well constrained. Here I will present two examples of such studies at plate boundaries. One case is the Dead Sea Transform (DST) that comprises a boundary between African and Arabian plates. During the last 15- 20 Myr more than 100 km of left lateral transform displacement has been accumulated on the DST and about 10 km thick Dead Sea Basin (DSB) was formed in the central part of the DST. Lithospheric structure and geological evolution of DST and DSB is rather well constrained by a number of interdisciplinary projects including DESERT and DESIRE projects leaded by the GFZ Potsdam. Detailed observations reveal apparently contradictory picture. From one hand widespread igneous activity, especially in the last 5 Myr, thin (60-80 km) lithosphere constrained from seismic data and absence of seismicity below the Moho, seem to be quite natural for this tectonically active plate boundary. However, surface heat flow of less than 50-60mW/m2 and deep seismicity in the lower crust ( deeper than 20 km) reported for this region are apparently inconsistent with the tectonic settings specific for an active continental plate boundary and with the crustal structure of the DSB. To address these inconsistencies which comprise what I call the "DST heat-flow paradox", a 3D numerical thermo-mechanical model was developed operating with non-linear elasto-visco-plastic rheology of the lithosphere. Results of the numerical experiments show that the entire set of

  5. Environmental Applications of Stable Xenon and Radioxenon Monitoring

    SciTech Connect

    Dresel, P. Evan; Olsen, Khris B.; Hayes, James C.; McIntyre, Justin I.; Waichler, Scott R.; Kennedy, B. M.

    2008-06-01

    Improved detection capabilities are needed at several Department of Energy sites to make remedial decisions about facilities and landfill cleanup. For facility monitoring air samples can be collected from within a facility and analyzed for short lived radioxenons to estimate inventories of residual plutonium holdup within the facility. For landfill cleanup activities soil gas sampling for xenon isotopes can be used to define the locations of spent fuel and transuranic wastes. Short-lived radioxenon isotopes are continuously produced by spontaneous fission of plutonium-240 in transuranic wastes. Large volume soil-gas samples provide extremely sensitive measurement of radioxenon in the subsurface; a characteristic of transuranic waste. The analysis employs a modified Automated Radioxenon Sampling and Analysis (ARSA) system. Proof of principle measurements at a Hanford Site liquid waste disposal site showed xenon-133 at levels in soil gas are approximately 16,000 times the detection limit and lower levels of xenon-135 from the spontaneous fission of plutonium-240 were also measured. Stable xenon isotopes are also produced by spontaneous fission but are subject to background concentrations in ambient air samples (facilities) but less so in soil gas where free exchange with ambient air is restricted. Rare gas mass spectrometry is used for highly precise stable xenon isotopic measurements. Stable xenon isotopic ratios from fission are distinct from natural xenon background ratios. Neutron capture on xenon-135 produces an excess of xenon-136 above fission ratios and thus provides a means of distinguishing reactor sources (e.g. spent fuel) from separated transuranic materials (plutonium).

  6. Progress in Advanced Spectral Analysis of Radioxenon

    SciTech Connect

    Haas, Derek A.; Schrom, Brian T.; Cooper, Matthew W.; Ely, James H.; Flory, Adam E.; Hayes, James C.; Heimbigner, Tom R.; McIntyre, Justin I.; Saunders, Danielle L.; Suckow, Thomas J.

    2010-09-21

    Improvements to a Java based software package developed at Pacific Northwest National Laboratory (PNNL) for display and analysis of radioxenon spectra acquired by the International Monitoring System (IMS) are described here. The current version of the Radioxenon JavaViewer implements the region of interest (ROI) method for analysis of beta-gamma coincidence data. Upgrades to the Radioxenon JavaViewer will include routines to analyze high-purity germanium detector (HPGe) data, Standard Spectrum Method to analyze beta-gamma coincidence data and calibration routines to characterize beta-gamma coincidence detectors. These upgrades are currently under development; the status and initial results will be presented. Implementation of these routines into the JavaViewer and subsequent release is planned for FY 2011-2012.

  7. The lithosphere

    SciTech Connect

    Not Available

    1983-01-01

    This document is the report of a week-long workshop on problems relating to the interpretations of the composition and dynamics of the lithosphere. A wide range of topics was discussed, dealing not only with the lithosphere itself, but also with possible interactions between the lithosphere and underlying mantle, down to and including the core-mantle boundary zone. Emphasis, very broadly, was on the physical and chemical properties of the lower crust and the subcrustal lithosphere: the physical and chemical characteristics of the prominent seismic discontinuities down to the core-mantle boundary; the nature and patterns of possible convection within the mantle and its relation to the generation, subduction, and intermixing of lithospheric and mantle material; the location and nature and evolution of reservoirs supplying magmas to the crust; and the various models that have been proposed to account for the location, nature, and geological history of these magma reservoirs. The general applicability of the plate tectonics model was assumed, but virtually every widely accepted explanation for the dynamics of that model and of possible unrelated phenomena such as deep-mantle plumes and hot spots was brought into question. 83 refs., 19 figs.

  8. Global radioxenon emission inventory based on nuclear power reactor reports.

    PubMed

    Kalinowski, Martin B; Tuma, Matthias P

    2009-01-01

    Atmospheric radioactivity is monitored for the verification of the Comprehensive Nuclear-Test-Ban Treaty, with xenon isotopes 131mXe, 133Xe, 133mXe and 135Xe serving as important indicators of nuclear explosions. The treaty-relevant interpretation of atmospheric concentrations of radioxenon is enhanced by quantifying radioxenon emissions released from civilian facilities. This paper presents the first global radioxenon emission inventory for nuclear power plants, based on North American and European emission reports for the years 1995-2005. Estimations were made for all power plant sites for which emission data were unavailable. According to this inventory, a total of 1.3PBq of radioxenon isotopes are released by nuclear power plants as continuous or pulsed emissions in a generic year.

  9. Automatic radioxenon analyzer for CTBT monitoring

    SciTech Connect

    Bowyer, T.W.; Abel, K.H.; Hensley, W.K.

    1996-12-01

    Over the past 3 years, with support from US DOE`s NN-20 Comprehensive Test Ban Treaty (CTBT) R&D program, PNNL has developed and demonstrated a fully automatic analyzer for collecting and measuring the four Xe radionuclides, {sup 131m}Xe(11.9 d), {sup 133m}Xe(2.19 d), {sup 133}Xe (5.24 d), and {sup 135}Xe(9.10 h), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a CTBT. Activity ratios permit discriminating radioxenon from nuclear detonation and that from nuclear reactor operations, nuclear fuel reprocessing, or medical isotope production and usage. In the analyzer, Xe is continuously and automatically separated from the atmosphere at flow rates of about 7 m{sup 3}/h on sorption bed. Aliquots collected for 6-12 h are automatically analyzed by electron-photon coincidence spectrometry to produce sensitivities in the range of 20-100 {mu}Bq/m{sup 3} of air, about 100-fold better than with reported laboratory-based procedures for short time collection intervals. Spectral data are automatically analyzed and the calculated radioxenon concentrations and raw gamma- ray spectra automatically transmitted to data centers.

  10. Measurements of Worldwide Radioxenon Backgrounds - The "EU" Project

    SciTech Connect

    Bowyer, Ted W.; Cooper, Matthew W.; Hayes, James C.; Forrester, Joel B.; Haas, Derek A.; Hansen, Randy R.; Keller, Paul E.; Kirkham, Randy R.; Lidey, Lance S.; McIntyre, Justin I.; Miley, Harry S.; Payne, Rosara F.; Saey, Paul R.; Thompson, Robert C.; Woods, Vincent T.; Williams, Richard M.

    2009-09-24

    Under the Comprehensive Nuclear-Test-Ban Treaty (CTBT), radioactive xenon (radioxenon) measurements are one of the principle techniques used to detect nuclear underground nuclear explosions, and specifically, the presence of one or more radioxenon isotopes allows one to determine whether a suspected event was a nuclear explosion or originated from an innocent source. During the design of the International Monitoring System (IMS), which was designed as the verification mechanism for the Treaty, it was determined that radioxenon measurements should be performed at 40 or more stations worldwide. At the time of the design of the IMS, however, very few details about the background of the xenon isotopes was known and it is now recognized that the backgrounds were probably evolving anyhow. This paper lays out the beginning of a study of the worldwide concentrations of xenon isotopes that can be used to detect nuclear explosions and several sources that also release radioxenons, and will have to be accounted for during analysis of atmospheric levels. Although the global concentrations of the xenon isotopes are the scope of a much larger activity that could span over several years, this study measures radioxenon concentrations in locations where there was either very little information or there was a unique opportunity to learn more about emissions from known sources. The locations where radioxenon levels were measured and reported are included.

  11. On the nature and origin of highly-refractory Archean lithosphere: Petrological and geophysical constraints from the Tanzanian craton

    NASA Astrophysics Data System (ADS)

    Gibson, S. A.; McMahon, S. C.; Day, J. A.; Dawson, J. B.

    2012-12-01

    The nature and timescales of garnet formation are important to understanding how subcontinental lithospheric mantle (SCLM) has evolved since the Archean, and also to mantle dynamics, because the presence of garnet greatly influences the density of the lower lithosphere and hence the long-term stability of thick (150 to 220 km) subcratonic lithosphere. Nevertheless, the widespread occurrence of garnet in the SCLM remains one of the 'holy grails' of mantle petrology. Garnets found in mantle xenoliths from the eastern margin of the Tanzanian Craton (Lashaine) have diverse compositions and provide major constraints on how the underlying deep (120 to 160 km) mantle evolved during the last 3 billion years. Certain harzburgite members of the xenolith suite contain the first reported occurrence of pyrope garnets with rare-earth element patterns similar to hypothetical garnets proposed to have formed in the Earth's SCLM during the Archean, prior to metasomatism [Stachel et al., 2004]. These rare ultradepleted low-Cr garnets occur in low temperature (~1050 oC) xenoliths derived from depths of ~120 km and coexist in chemical and textural equilibrium with highly-refractory olivine (Fo95.4) and orthopyroxene (Mg#=96.4). These phases are all more magnesian than generally encountered in global mantle harzburgites and diamond inclusions. The ultradepleted garnets form interconnecting networks around grains of orthopyroxene which give the rocks a banded appearance: we propose that the increase in pressure associated with cratonization may have caused isochemical exsolution of ultradepleted garnet from orthopyroxene. These unique garnets have not previously been identified in global suites of mantle xenoliths or diamond inclusions. We believe they are rare because their low concentrations of trace elements make them readily susceptible to geochemical overprinting. This highly-refractory low-density peridotite may be common in the 'shallow' SCLM but not normally brought to the

  12. Radioxenon detector calibration spike production and delivery systems

    SciTech Connect

    Foxe, Michael P.; Cameron, Ian M.; Cooper, Matthew W.; Haas, Derek A.; Hayes, James C.; Kriss, Aaron A.; Lidey, Lance S.; Mendez, Jennifer M.; Prinke, Amanda M.; Riedmann, Robin A.

    2016-03-01

    Abstract Beta-Gamma coincidence radioxenon detectors must be calibrated for each of the four-radioxenon isotopes (135Xe, 133Xe, 133mXe, and 131mXe). Without a proper calibration, there is potential for the misidentification of the amount of each isotope detected. It is important to accurately determine the amount of each radioxenon isotope, as the ratios can be used to distinguish between an anthropogenic source and a nuclear explosion. We have developed a xenon calibration system (XeCalS) that produces calibration spikes of known activity and pressure for field calibration of detectors. The activity concentrations of these calibration spikes are measured using a beta-gamma coincidence detector and a high purity germanium (HPGe) detector. We will present the results from the development and commissioning of XeCalS, along with the future plans for a portable spike implementation system.

  13. Radioxenons: Their role in monitoring a Comprehensive Test Ban Treaty

    SciTech Connect

    Perkins, R. W.; Casey, L. A.

    1996-06-01

    Monitoring for xenon radionuclides which are produced in a nuclear detonation can provide a strong deterrent to the violation of a Comprehensive nuclear Test Ban Treaty (CTBT). There are 18 known radioactive xenon isotopes produced in nuclear fission with half-lives ranging from less than one second to 11.9 days. However, only four of these remain in significant amounts more than a day after a detonation. In order for radioxenon monitoring to be practical, it was necessary to develop an automated measurement system which could operate unattended for periods of months, measure the entire spectrum of radioxenons, and provide hundreds of times better sensitivities than current laboratory procedures. This capability was developed at the US Department of Energy`s Pacific Northwest National Laboratory based on rapid separation of atmospheric xenon coupled with a unique high sensitivity measurement device for the radioxenons. A fieldable prototype analyzer is scheduled for testing in August 1996 with commercial availability planned by 1998.

  14. On the nature and origin of garnet in highly-refractory Archean lithosphere: implications for continent stabilisation

    NASA Astrophysics Data System (ADS)

    Gibson, Sally

    2014-05-01

    The nature and timescales of garnet formation in the Earth's subcontinental lithospheric mantle (SCLM) are important to our understanding of how this rigid outer shell has evolved and stabilised since the Archean. Nevertheless, the widespread occurrence of pyrope garnet in the sub-cratonic mantle remains one of the 'holy grails' of mantle petrology. The paradox is that garnet often occurs in mantle lithologies (dunites and harzburgites) which represent residues of major melting events (up to 40 %) whereas experimental studies on fertile peridotite suggest this phase should be exhausted by <20 % melting. Furthermore, garnets commonly found in mantle peridotite suites have diverse compositions that are typically in equilibrium with high-pressure, small-fraction, mantle melts suggesting they formed as a result of enrichment of the lithospheric mantle following cratonisation. This refertilisation -- which typically involves addition of Fe, incompatible trace elements and volatiles -- affects the lower 30 km of the lithosphere and potentially leads to negative buoyancy and destabilisation. Pyrope garnets found in mantle xenoliths from the eastern margin of the Tanzanian Craton (Lashaine) have diverse compositions and provide major constraints on how the underlying deep (120 to 160 km) mantle stabilised and evolved during the last 3 billion years. The garnets display systematic trends from ultra-depleted to enriched compositions that have not been recognised in peridotite suites from elsewhere (Gibson et al., 2013). Certain harzburgite members of the xenolith suite contain the first reported occurrence of pyrope garnets with rare-earth element (REE) patterns similar to hypothetical garnets proposed by Stachel et al. (2004) to have formed in the Earth's SCLM during the Archean, prior to metasomatism. These rare ultra-depleted low-Cr garnets occur in low temperature (~1050 oC) xenoliths derived from depths of ~120 km and coexist in chemical and textural equilibrium with

  15. Nature and melting processes of the lithosphere beneath the North-East Qiangqtang terrane, Central Tibet, during Eocene times.

    NASA Astrophysics Data System (ADS)

    Goussin, Fanny; Guillot, Stéphane; Schulmann, Karel; Cordier, Carole; Oliot, Emilien; Replumaz, Anne; Roperch, Pierrick; Dupont-Nivet, Guillaume

    2016-04-01

    pyroxene xenocrysts, suggest that enrichment occurred at the source by metasomatism of the lithospheric mantle. Further work will precise which mechanisms could have accounted for such a metasomatism of the mantle beneath the Northern Qiangtang terrane during Eocene, and whether the lower crust had an autochtonous or allochtonous nature.

  16. Observational Strategy of ACROSS towards the Time-evolving Natures in the Lithosphere

    NASA Astrophysics Data System (ADS)

    Kumazawa, M.; Fujii, N.; Kasahara, J.

    2005-12-01

    ACROSS (Accurately Controlled, Routinely Operated Signal System) is aiming at the detection of very small changes in physical states in the lithosphere, particularly for the focal region of the anticipated huge earthquakes as demanded socially. Our technical challenge is to device an ideal methodology to enable us to acquire the ideal observation data towards the real understanding of the EarthOs interiors even under the inherent noise and physical limitations. We need light to illuminate the dark EarthOs interiors, eyes to observe them and a brain to interpret the result: The light should be designed well to be really coherent, the eyes with high fidelity should be accurately synchronized to the light transmission and the brain should be smart enough to evolve by itself. In order for the whole system to be robust against noise, we have to devise all that can be done. In addition, a significant demand is imposed onto us; non-destructiveness against our environment. The recent progress of technology makes it possible what was impossible several years, so that we try to find out the ideal way to go. We have spent about 10 years for developmental works, which started a moment before the disastrous Kobe earthquake of 1995. Now we believe that the background theory has been known in addition to some of the basic technology elements, whereas the user-friendly hardware and other auxiliary tools including practical theory and software have not been acquired yet. The examples of the field observation have started to accumulate for demonstration as reported by companion papers. The data acquired by ACROSS in seismology is not seismogram but tensor transfer function (Green function) in frequency domain. The data carry substantially new information with high quality and rigorous estimate of reliability. The availability of ACROSS would change the strategy for underground study in the coming years. We would like to call for your attention and discussion to the next way to go

  17. Lithospheric processes

    SciTech Connect

    Baldridge, W.S.; Wohletz, K.; Fehler, M.C.

    1997-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The main objective was to improve understanding of the origin and evolution of the Earth`s lithosphere by studying selected processes, such as deformation and magmatic intrusion during crustal extension, formation and extraction of mantle melts, fluid transport of heat and mass, and surface processes that respond to deep-seated events. Additional objectives were to promote and develop innovative techniques and to support relevant educational endeavors. Seismic studies suggest that underplating of crust by mantle melts is an important crustal-growth mechanism, that low-angle faults can be seismogenic, and that shear deformation creates mantle anisotropy near plate boundaries. Results of geochemical work determined that magmas from oceanic intraplate islands are derived from a uniform depth in the upper mantle, whereas melts erupted at mid-ocean ridges are mixed from a range of depths. The authors have determined the extent and style of fluid infiltration and trace-element distribution in natural magmatic systems, and, finally, investigated {sup 21}Ne as a tool for dating of surficial materials.

  18. Lithospheric processes

    SciTech Connect

    Baldridge, W.

    2000-12-01

    The authors used geophysical, geochemical, and numerical modeling to study selected problems related to Earth's lithosphere. We interpreted seismic waves to better characterize the thickness and properties of the crust and lithosphere. In the southwestern US and Tien Shari, crust of high elevation is dynamically supported above buoyant mantle. In California, mineral fabric in the mantle correlate with regional strain history. Although plumes of buoyant mantle may explain surface deformation and magmatism, our geochemical work does not support this mechanism for Iberia. Generation and ascent of magmas remains puzzling. Our work in Hawaii constrains the residence of magma beneath Hualalai to be a few hundred to about 1000 years. In the crust, heat drives fluid and mass transport. Numerical modeling yielded robust and accurate predictions of these processes. This work is important fundamental science, and applies to mitigation of volcanic and earthquake hazards, Test Ban Treaties, nuclear waste storage, environmental remediation, and hydrothermal energy.

  19. (135)Xe measurements with a two-element CZT-based radioxenon detector for nuclear explosion monitoring.

    PubMed

    Ranjbar, Lily; Farsoni, Abi T; Becker, Eric M

    2017-04-01

    Measurement of elevated concentrations of xenon radioisotopes ((131m)Xe, (133m)Xe, (133)Xe and (135)Xe) in the atmosphere has been shown to be a very powerful method for verifying whether or not a detected explosion is nuclear in nature. These isotopes are among the few with enough mobility and with half-lives long enough to make their detection at long distances realistic. Existing radioxenon detection systems used by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) suffer from problems such as complexity, need for high maintenance and memory effect. To study the response of CdZnTe (CZT) detectors to xenon radioisotopes and investigate whether it is capable of mitigating the aforementioned issues with the current radioxenon detection systems, a prototype detector utilizing two coplanar CZT detectors was built and tested at Oregon State University. The detection system measures xenon radioisotopes through beta-gamma coincidence technique by detecting coincidence events between the two detectors. In this paper, we introduce the detector design and report our measurement results with radioactive lab sources and (135)Xe produced in the OSU TRIGA reactor. Minimum Detectable Concentration (MDC) for (135)Xe was calculated to be 1.47 ± 0.05 mBq/m(3).

  20. Impact of Monthly Radioxenon Source Time-Resolution on Atmospheric Concentration Predictions

    NASA Astrophysics Data System (ADS)

    Schöppner, Michael; Kalinowski, Martin; Plastino, Wolfango; Budano, Antonio; de Vincenzi, Mario; Ringbom, Anders; Ruggieri, Federico; Schlosser, Clemens

    2014-03-01

    The general characterisation of the global radioxenon background is of interest for the verification of the Comprehensive Nuclear-Test-Ban Treaty. Since the major background sources are only a few isotope production facilities, their source term has an emphasized influence on the worldwide monitoring process of radioxenon. In this work, two different datasets of source terms are applied through atmospheric transport modelling, to estimate the concentration at two radioxenon detection stations in Germany and Sweden. One dataset relies on estimated average annual emissions; the other includes monthly resolved measurements from an isotope production facility in Fleurus, Belgium. The quality of the estimations is then validated by comparing them to the radioxenon concentrations that have been sampled at two monitoring stations over the course of 1 year.

  1. Testing of the KRI-developed Silicon PIN Radioxenon Detector

    SciTech Connect

    Foxe, Michael P.; McIntyre, Justin I.

    2015-01-23

    Radioxenon detectors are used for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in a network of detectors throughout the world called the International Monitoring System (IMS). The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) Provisional Technical Secretariat (PTS) has tasked Pacific Northwest National Laboratory (PNNL) with testing a V.G. Khlopin Radium Institute (KRI) and Lares Ltd-developed Silicon PIN detector for radioxenon detection. PNNL measured radioxenon with the silicon PIN detector and determined its potential compared to current plastic scintillator beta cells. While the PNNL tested Si detector experienced noise issues, a second detector was tested in Russia at Lares Ltd, which did not exhibit the noise issues. Without the noise issues, the Si detector produces much better energy resolution and isomer peak separation than a conventional plastic scintillator cell used in the SAUNA systems in the IMS. Under the assumption of 1 cm3 of Xe in laboratory-like conditions, 24-hr count time (12-hr count time for the SAUNA), with the respective shielding the minimum detectable concentrations for the Si detector tested by Lares Ltd (and a conventional SAUNA system) were calculated to be: 131mXe – 0.12 mBq/m3 (0.12 mBq/m3); 133Xe – 0.18 mBq/m3 (0.21 mBq/m3); 133mXe – 0.07 mBq/m3 (0.15 mBq/m3); 135Xe – 0.45 mBq/m3 (0.67 mBq/m3). Detection limits, which are one of the important factors in choosing the best detection technique for radioxenon in field conditions, are significantly better than for SAUNA-like detection systems for 131mXe and 133mXe, but similar for 133Xe and 135Xe. Another important factor is the amount of “memory effect” or carry over signal from one radioxenon measurement to the subsequent sample. The memory effect is

  2. Improved β-γ Coincidence Detector For Radioxenon Detection

    SciTech Connect

    Cooper, Matthew W; Carman, April J; Hayes, James C; Heimbigner, Tom R; Hubbard, Charles W; Litke, Kevin E; McIntyre, Justin I; Morris, Scott J; Ripplinger, Michael D; Suarez, Reynold

    2005-08-31

    The Automated Radio-xenon Analyzer/Sampler (ARSA), built by Pacific Northwest National Laboratory (PNNL), can collect and detect several radioxenon isotopes. ARSA is very sensitive to 133Xe, 131mXe, 133mXe and 135Xe due to the compact high efficiency coincidence detector it uses. For this reason it is an excellent treaty monitoring and environmental sampling device. Although the system is shown to be both robust and reliable, based on several field tests, it is also complex due to a detailed photomultiplier tube gain matching regime. This complexity is a problem from a maintenance and quality assurance/quality control (QA/QC) standpoint. To reduce these issues a simplified coincident detector has been developed. A comparison of three different well detectors has been completed. In addition, a new plastic scintillator gas cell was constructed. The new simplified detector system has been demonstrated to equal or better performance compared with the original ARSA design in spectral resolution and efficiency and significantly easier to setup and calibrate.

  3. Environmental characterisation of a major radioxenon source in Europe

    NASA Astrophysics Data System (ADS)

    Saey, P. R. J.; Ringbom, A.; Becker, A.; Camps, J.; Paquet, N.; Sonck, M.; Taffary, T.; van der Meer, K.; Verboomen, B.; Zähringer, M.

    2009-04-01

    In the framework of the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) the atmospheric background of environmental radioxenon has been studied. It was recently shown that radiopharmaceutical facilities (RPF) have a major contribution to the general background of 133Xe and other xenon isotopes both in the northern and southern hemisphere. The daily International Monitoring System (IMS) noble gas measurements around the globe are influenced from such anthropogenic sources that could hide relevant radioxenon signals. To distinguish a nuclear explosion from releases from civil nuclear facilities, not only the activity concentration but also the ratio of different radioxenon isotopes (131mXe, 133mXe, 133Xe and 135Xe) plays a crucial role, since the ratios can be used to discriminate source types. Theoretical release and ratio studies were recently published, but no high-sensitive measurements in and close to radiopharmaceutical facilities have ever been performed. During the summer of 2008, a three week field campaign was carried out in the region around the Belgian radiopharmaceutical facility IRE in Fleurus, the world third largest one. The scope was to obtain the activity concentration of the releases and the isotopic composition. Two 6-hour noble gas measurements, using mobile SAUNA sampling equipment were collected each day at different distances from the facility (1 - 100 km). The sampling locations were guided by atmospheric dispersion model results. Three samples from the stack itself were also collected. All 38 samples were shipped after collection to and measured with a SAUNA at the laboratory in Stockholm, Sweden. The environmental concentrations of 133Xe were measured and found to be in the range between 0.7 - 4 105 mBq/m3. Nine samples contained all four CTBT relevant radioxenon isotopes. The concentrations of the stack spike samples were in the range 2 109 - 4 1010 mBq/m3. This corresponds to a daily release of around 1 TBq. This is

  4. Examining Changes in Radioxenon Isotope Activity Ratios during Subsurface Transport

    NASA Astrophysics Data System (ADS)

    Annewandter, R.

    2013-12-01

    The Non-Proliferation Experiment (NPE) has demonstrated and modelled the usefulness of barometric pumping induced soil gas sampling during On-Site inspections. Gas transport has been widely studied with different numerical codes. However, gas transport of all radioxenons in the post-detonation regime and their possible fractionation is still neglected in the open literature. Atmospheric concentrations of the radioxenons Xe-135, Xe-133m, Xe-133 and Xe-131m can be used to discriminate between civilian releases (nuclear power plants or medical isotope facilities), and nuclear explosion sources. It is based on the isotopic activity ratio method. Yet it is not clear whether subsurface migration of the radioxenons, with eventual release into the atmosphere, can affect the activity ratios due to fractionation. Fractionation can be caused by different diffusivities due to mass differences between the radioxenons. A previous study showed surface arrival time of a chemically inert gaseous tracer is affected by its diffusivity. They observed detectable amount for SF6 50 days after detonation and 375 days for He-3. They predict 50 and 80 days for Xe-133 and Ar-37 respectively. Cyclical changes in atmospheric pressure can drive subsurface gas transport. This barometric pumping phenomenon causes an oscillatoric flow in upward trending fractures which, combined with diffusion into the porous matrix, leads to a net transport of gaseous components - a ratcheting effect. We use a general purpose reservoir simulator (Complex System Modelling Platform, CSMP++) which has been applied in a range of fields such as deep geothermal systems, three-phase black oil simulations , fracture propagation in fractured, porous media, Navier-Stokes pore-scale modelling among others. It is specifically designed to account for structurally complex geologic situation of fractured, porous media. Parabolic differential equations are solved by a continuous Galerkin finite-element method, hyperbolic

  5. Constraints on the Thermal and Compositional Nature of the Oceanic Lithosphere-Asthenosphere Boundary from Seismic Anisotropy

    NASA Astrophysics Data System (ADS)

    Beghein, C.; Yuan, K.; Schmerr, N. C.; Xing, Z.

    2014-12-01

    In this study we modeled S-wave velocities, radial and azimuthal anisotropy beneath the Pacific ocean, and compared our model with detections of the Gutenberg (G) discontinuity at 40-100 km depth to evaluate its context and relation to the lithosphere-asthenosphere boundary (LAB). The G is often associated with the LAB, but its sharpness and the low correlation between its depth and oceanic plate age suggest a compositional origin, in contradiction with tomographic models of isotropic wave velocities. Here, we inverted fundamental and higher mode anisotropic Rayleigh wave phase velocity maps to which we applied non-linear crustal corrections. Our model defines three layers within the upper 250km of the mantle. The bottom layer is characterized by relatively low velocities, strong (3%) azimuthal anisotropy, fast seismic directions that follow the absolute plate motion (APM), and strong (5%) radial anisotropy with VSH>VSV. This suggests alignment of olivine fast axes with mantle flow direction in the asthenosphere. The middle layer has fast axes aligned with the paleospreading directions, and the boundary between the bottom and middle layers follows a half-space cooling model. This suggests a thermal origin of the LAB if we use the change in alignment of the fast axes with the APM as a proxy for the LAB. Remarkably, a change in azimuthal anisotropy is found between the two top layers at a roughly constant depth that coincides with the location of the G. The G is therefore located within the thermal lithosphere and is primarily associated with a vertical gradient in azimuthal anisotropy, which may result from compositional changes. Dehydration of the mantle underlying mid-ocean ridges offers a possible explanation for our results. It could generate a chemically depleted, viscous layer that becomes overprinted by lowered temperatures as the plate cools and migrates away from the ridge. The olivine fast axes would align with the spreading direction at the ridge in the

  6. Monitoring of reported sudden emission rate changes of major radioxenon emitters in the northern and southern hemispheres in 2008 to assess their contribution to the respective radioxenon backgrounds

    NASA Astrophysics Data System (ADS)

    Saey, P. R. J.; Auer, M.; Becker, A.; Colmanet, S.; Hoffmann, E.; Nikkinen, M.; Schlosser, C.; Sonck, M.

    2009-04-01

    Atmospheric radioxenon monitoring is a key component of the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Radiopharmaceutical production facilities (RPF) have recently been identified of emitting the major part of the environmental radioxenon measured at globally distributed monitoring sites deployed to strengthen the radionuclide part of the CTBT verification regime. Efforts to raise a global radioxenon emission inventory revealed that the global total emission from RPF's is 2-3 orders of magnitude higher than the respective emissions related to maintenance of all nuclear power plants (NPP). Given that situation we have seen in 2008 two peculiar hemisphere-specific situations: 1) In the northern hemisphere, a joint shutdown of the global largest four radiopharmaceutical facilities revealed the contribution of the normally 'masked' NPP related emissions. Due to an incident, the Molybdenum production at the "Institut des Radioéléments" (IRE) in Fleurus, Belgium, was shut down between Monday 25 August and 2 December 2008. IRE is the third largest global producer of medical isotopes. In the same period, but for different reasons, the other three worldwide largest producers (CRL in Canada, HFR in The Netherlands and NTP in South Africa) also had scheduled and unscheduled shutdowns. The activity concentrations of 133Xe measured at the Schauinsland Mountain station near Freiburg in Germany (situated 380 km SW of Fleurus) which have a mean of 4.8 mBq/m3 for the period February 2004 - August 2008, went down to 0.87 mBq/m3 for the period September - November 2008. 2) In the southern hemisphere, after a long break, the only radiopharmaceutical facility in Australia started up test production in late November 2008. In the period before the start-up, the background of radioxenon in Australia (Melbourne and Darwin) was below measurable quantities. During six test runs of the renewed RPF at ANSTO in Lucas Heights, up to 6 mBq/m3 of 133Xe were measured in

  7. Understanding radioxenon isotopical ratios originating from radiopharmaceutical facilities

    NASA Astrophysics Data System (ADS)

    Saey, P. R. J.; Ringbom, A.; Bowyer, T. W.; Becker, A.; de Geer, L.-E.; Nikkinen, M.; Payne, R. F.

    2009-04-01

    It was recently shown that radiopharmaceutical facilities (RPF) are major contributors to the general background of 133Xe and other xenon isotopes both in the northern and southern hemisphere. To distinguish a nuclear explosion signal from releases from civil nuclear facilities, not only the activity concentrations but also the ratios of the four different CTBT relevant radioxenon isotopes (131mXe, 133mXe, 133Xe and 135Xe) have to be well understood. First measurements taken recently in and around two of the world's largest RPF's: NTP at Pelindaba, South Africa and IRE at Fleurus, Belgium have been presented. At both sites, also stack samples were taken in close cooperation with the facility operators. The radioxenon in Belgium could be classified in four classes: the normal European background (133Xe activity between 0 - 5 mBq/m3) on one hand and then the samples where all four isotopes were detected with 133mXe/131mXe > 1. In northern South Africa the Pelindaba RPF is in practice the sole source of radioxenon. It generated a background of 133Xe at the measurement site some 230 km to the west of the RPF of 0 - 5 mBq/m3. In the cases where the air from the Pelindaba facility reached the measurement site directly and in a short time period, the 133Xe was higher, also 135Xe was present and in some samples 133mXe as well. The ratios of the activity concentrations of 135Xe/133Xe vs. 133mXe/131mXe (Multiple Isotope Ratio Plot - MIRC) have been analysed. For both facilities, the possible theoretical ratio's for different scenarios were calculated with the information available and compared with the measurements. It was found that there is an excess of 131mXe present in the European samples compared to theoretical calculations. A similar excess has also been seen in samples measured in northern America. In South Africa, neither the environmental samples nor the stack ones contained 131mXe at measurable levels. This can probably be explained by different processes and

  8. Field test of the PNNL Automated Radioxenon Sampler/Analyzer (ARSA)

    SciTech Connect

    Lagomarsino, R.J.; Ku, E.; Latner, N.; Sanderson, C.G.

    1998-07-01

    As part of the requirements of the Comprehensive Test Ban Treaty (CTBT), the Automated Radioxenon/Sampler Analyzer (ARSA) was designed and engineered by the Pacific Northwest National Laboratory (PNNL). The instrument is to provide near real-time detection and measurement of the radioxenons released into the atmosphere after a nuclear test. Forty-six field tests, designed to determine the performance of the ARSA prototype under simulated field conditions, were conducted at EML from March to December 1997. This final report contains detailed results of the tests with recommendations for improvements in instrument performance.

  9. Examining Changes in Radioxenon Isotope Activity Ratios during Subsurface Transport

    NASA Astrophysics Data System (ADS)

    Annewandter, Robert

    2014-05-01

    The Non-Proliferation Experiment (NPE) has demonstrated and modelled the usefulness of barometric pumping induced gas transport and subsequent soil gas sampling during On-Site inspections. Generally, gas transport has been widely studied with different numerical codes. However, gas transport of radioxenons and radioiodines in the post-detonation regime and their possible fractionation is still neglected in the open peer-reviewed literature. Atmospheric concentrations of the radioxenons Xe-135, Xe-133m, Xe-133 and Xe-131m can be used to discriminate between civilian releases (nuclear power plants or medical isotope facilities), and nuclear explosion sources. It is based on the multiple isotopic activity ratio method. Yet it is not clear whether subsurface migration of the radionuclides, with eventual release into the atmosphere, can affect the activity ratios due to fractionation. Fractionation can be caused by different mass diffusivities due to mass differences between the radionuclides. Cyclical changes in atmospheric pressure can drive subsurface gas transport. This barometric pumping phenomenon causes an oscillatoric flow in upward trending fractures or highly conductive faults which, combined with diffusion into the porous matrix, leads to a net transport of gaseous components - a so-called ratcheting effect. We use a general purpose reservoir simulator (Complex System Modelling Platform, CSMP++) which is recognized by the oil industry as leading in Discrete Fracture-Matrix (DFM) simulations. It has been applied in a range of fields such as deep geothermal systems, three-phase black oil simulations, fracture propagation in fractured, porous media, and Navier-Stokes pore-scale modelling among others. It is specifically designed to account for structurally complex geologic situation of fractured, porous media. Parabolic differential equations are solved by a continuous Galerkin finite-element method, hyperbolic differential equations by a complementary finite

  10. Operations of the Automated Radioxenon Sampler/Analyzer - ARSA

    SciTech Connect

    Hayes, James C.; Abel, Keith H.; Bowyer, Ted W.; Heimbigner, Tom R.; Panisko, Mark E.; Reeder, Paul L.; McIntyre, Justin I.; Thompson, Robert C.; Todd, Lindsay C.; Warner, Ray A.

    1999-09-01

    The Automated Radioxenon Sampler/ Analyzer (ARSA), designed and built by Pacific Northwest National Laboratory (PNNL), for the Department of Energy, has exceeded measurement requirements for noble gas measurement systems established by the Comprehensive Nuclear-Test-Ban Treaty. Two units, one at PNNL and a second, sent to DME Corp. of Florida, were built and extensively tested. Both systems have successfully demonstrated stable xenon yields greater than 1.5 cm3 for an eight-hour collection period, corresponding to minimum detectable concentrations for 133Xe on the order of 0.1 mBq/m3 three times per day. High stable xenon yields are critical in obtaining these low minimum detectable concentrations. A history of testing and results that led to the high xenon yields of the ARSA system is presented. A compilation of field tests, laboratory tests and baseline tests that led to cost reduction, power savings and size reduction of the ARSA are also discussed. Lastly, the type of data generated from the ARSA of interest to data center personnel are discussed.

  11. Nature and evolution of lithospheric mantle beneath the southern Ethiopian rift zone: evidence from petrology and geochemistry of mantle xenoliths

    NASA Astrophysics Data System (ADS)

    Alemayehu, Melesse; Zhang, Hong-Fu; Sakyi, Patrick Asamoah

    2016-06-01

    Mantle xenoliths hosted in Quaternary basaltic lavas from the Dillo and Megado areas of the southern Ethiopian rift are investigated to understand the geochemical composition and associated processes occurring in the lithospheric mantle beneath the region. The xenoliths are comprised of predominantly spinel lherzolite with subordinate harzburgite and clinopyroxenite. Fo content of olivine and Cr# of spinel for peridotites from both localities positively correlate and suggest the occurrence of variable degrees of partial melting and melt extraction. The clinopyroxene from lherzolites is both LREE depleted (La/Sm(N) = 0.11-0.37 × Cl) and LREE enriched (La/Sm(N) = 1.88-15.72 × Cl) with flat HREEs (Dy/Lu(N) = 0.96-1.31 × Cl). All clinopyroxene from the harzburgites and clinopyroxenites exhibits LREE-enriched (La/Sm(N) = 2.92-27.63.1 × Cl and, 0.45 and 1.38 × Cl, respectively) patterns with slight fractionation of HREE. The 143Nd/144Nd and 176Hf/177Hf ratios of clinopyroxene from lherzolite range from 0.51291 to 0.51370 and 0.28289 to 0.28385, respectively. Most of the samples define ages of 900 and 500 Ma on Sm-Nd and Lu-Hf reference isochrons, within the age range of Pan-African crustal formation. The initial Nd and Hf isotopic ratios were calculated at 1, 1.5, 2 and 2.5 Ga plot away from the trends defined by MORB, DMM and E-DMM which were determined from southern Ethiopian peridotites, thus indicating that the Dillo and Megado xenoliths could have been produced by melt extraction from the asthenosphere during the Pan-African orogenic event. There is no significant difference in 87Sr/86Sr ratios between the depleted and enriched clinopyroxene. This suggests that the melts that caused the enrichment of the clinopyroxene are mainly derived from the depleted asthenospheric mantle from which the xenoliths are extracted. Largely, the mineralogical and isotopic compositions of the xenoliths show heterogeneity of the CLM that could have been produced from various

  12. Rifting of the Tyrrhenian Basin: A Natural Laboratory to Study Extension of Continental Lithosphere and Conjugate Rifted Margin Formation

    NASA Astrophysics Data System (ADS)

    Ranero, C. R.; Sallares, V.; Grevemeyer, I.; Zitellini, N.; Vendrell, M. G.; Prada, M.; Moeller, S.; Party, M. C.; Medoc Cruise Party

    2011-12-01

    The Tyrrhenian basin has been created by extension of continental lithosphere above a retreating slab during the Neogene. The basin is not currently extending, but its structure preserves information of the time evolution of the rifting process. The basin opened from north to south with different amounts of extension. The northern region stopped opening after relatively low extension. The amount of extension increases southwards to a region where full crustal separation produced mantle exhumation. The final structure displays two conjugate margins with an asymmetric structure. We present results from a two-vessel seismic experiment that took place in spring 2010. The cruise was carried out with the Spanish R/V Sarmiento de Gamboa (SdG) and the Italian R/V Urania in a first leg. The ships collected 5 E-W trending wide-angle seismic (WAS) profiles across the entire basin using 17 Ocean Bottom Seismometers and 25 Ocean Bottom Hydrophones and a 4800 c.i. G-II gun array. During the second leg the R/V SdG collected 16 Multichannel Seismic Reflection (MCS) profiles using a 3.75 km-long streamer and a 3000 c.i. G-II gun array. MCS profiles were acquired coincident with the WAS profiles, and a number of additional lines concentrated in the central region of the basin where mantle exhumation took place. The seismic data covers the region of the basin that experienced different amount of extension from north to south. In this presentation we compare observations from different transects to study the evolution of the processes of continental margin formation by trading space (different areas with different extension factors) for time (evolution of extension). Each transect provides the tectonic structure, the geometry of sedimentary deposits, and seismic velocity distribution. This information allows to interpret the mechanisms of deformation and to study the symmetry-asymmetry structure of the conjugated margins, and thus of the processes involved in their formation. The

  13. Metastable Radioxenon Verification Laboratory (MRVL) Year-End Report

    SciTech Connect

    Cooper, Matthew W.; Hayes, James C.; Lidey, Lance S.

    2014-11-07

    This is the year end report that is due to the client. The MRVL system is designed to measure multiple radioxenon isotopes (135Xe, 133Xe, 133mXe and 133mXe) simultaneously. The system has 12 channels to load samples and make nuclear measurements. Although the MRVL system has demonstrated excellent stability in measurements of Xe-133 and Xe-135 over the year of evaluation prior to delivery, there has been concern about system stability over measurements performed on samples with orders of magnitude different radioactivity, and samples containing multiple isotopes. To address these concerns, a series of evaluation test have been performed at the end-user laboratory. The evaluation was performed in two separate phases. Phase 1 made measurements on isotopically pure Xe-133 from high radioactivity down to the system background levels of activity, addressing the potential count rate dependencies when activities change from extreme high to very low. The second phase performed measurements on samples containing multiple isotopes (Xe-135, Xe-133 and Xe-133m), and addressed concerns about the dependence of isotopic concentrations on the presence of additional isotopes. The MRVL showed a concentration dependence on the Xe-133 due to the amount of Xe-133m that was in the sample. The dependency is due to the decay of Xe-133m into Xe-133. This document focuses on the second phase and will address the analysis used to account for ingrowth of Xe-133 from Xe-133m.

  14. Calculation of Minimum-Detectable-Concentration Levels of Radioxenon Isotopes Using the PNNL ARSA System

    SciTech Connect

    McIntyre, Justin I.; Bowyer, Ted W.; Reeder, Paul L.

    2006-03-11

    Measurement of xenon fission product isotopes is a key element in the global network being established to monitor the Comprehensive Nuclear-Test-Ban Treaty. The automated Radio-xenon Analyzer/Sampler (ARSA), built by Pacific Northwest National Laboratory, can detect 131mXe, 133mXe, 133Xe, and 135Xe via a beta-gamma counting system. Due to the variable background and sources of these four radio-xenon isotopes, it is important to have as sensitive a detection system as possible and to quantify the Minimum-Detectable-Concentrations (MDC) that such a system will be able to detect to preclude false negative and false positive results. From data obtained from IAR in Germany MDC values for 133Xe were well below the 1 mBq/SCMA as required by the PTS for the Comprehensive Test BAn Treaty [WGB TL-11,1999].

  15. Categorisation of nuclear explosions from legitimate radioxenon sources with atmospheric transport modelling

    NASA Astrophysics Data System (ADS)

    Schoeppner, M.; Postelt, F.; Kalinowski, M.; Plastino, W.

    2012-04-01

    Radioxenon is produced during nuclear explosions and due to its high fission ratio during the reaction and its noble gas character the isotopes can be detected remote from the location of the explosion. Therefore it is used by the Comprehensive Nuclear-Test-Ban Organization (CTBTO) as an indicator for the nuclear character of an explosion and is monitored with the International Monitoring System (IMS). The concentration of radioxenon in the air is continuously measured by multiple stations worldwide and is in need of an automatic categorization scheme in order to highlight signals of interest and to sort out signals that can be explained by legitimate sources. The dispersion and transport of radioxenon emissions through the atmosphere can be simulated with atmospheric transport modelling. Many legitimate sources of radioxenon exist: Nuclear power plants and isotope production facilities are mainly responsible for the worldwide background. The characterisation of this background is an important prerequisite to discriminate nuclear explosion signals against the background. It has been discovered that the few existing isotope production facilities are the major contributors to the background, each with emission strengths in the order of magnitude or more than all nuclear power plants together. Therefore, especially the characterization of these few, but strong, emitters can improve the quality of the signal prediction. Since the location of such an emitter is usually known the source-receptor sensitivity matrices can be utilized together with measured radioxenon concentrations from IMS stations in order to deduct information about the time dependent emissions from the strong emitter. An automatic method to determine an approximated, time dependent source term of an emitter with known location has been developed and is presented. This is a potentially valid tool for the categorization of radioxenon samples, because it can be used to assess whether the measured

  16. Comparison of Phoswich and ARSA-type detectors for Radioxenon Measurements

    SciTech Connect

    Ward, Rebecca; Biegalski, Steven R.; Haas, Derek A.; Hennig, Wolfgang

    2009-12-01

    The monitoring of atmospheric radioxenon to ensure compliance with the Comprehensive Nuclear Test Ban Treaty has driven the development of improved detectors for measuring xenon, including the development of a phoswich detector. This detector uses only one PMT to detect beta-gamma coincidence, thus greatly reducing the bulk and electronics of the detector in comparison to the ARSA-type detector. In this experiment, 135Xe was produced through neutron activation and a phoswich detector was used to attain spectra from the gas. These results were compared to similar results from an ARSA-type beta-gamma coincidence spectrum. The spectral characteristics and resolution were compared for the coincidence and beta spectra. Using these metrics, the overall performance of the phoswich detector for beta-gamma coincidence of radioxenon was evaluated.

  17. Evaluation of radioxenon releases in Australia using atmospheric dispersion modelling tools.

    PubMed

    Tinker, Rick; Orr, Blake; Grzechnik, Marcus; Hoffmann, Emmy; Saey, Paul; Solomon, Stephen

    2010-05-01

    The origin of a series of atmospheric radioxenon events detected at the Comprehensive Test Ban Treaty Organisation (CTBTO) International Monitoring System site in Melbourne, Australia, between November 2008 and February 2009 was investigated. Backward tracking analyses indicated that the events were consistent with releases associated with hot commission testing of the Australian Nuclear Science Technology Organisation (ANSTO) radiopharmaceutical production facility in Sydney, Australia. Forward dispersion analyses were used to estimate release magnitudes and transport times. The estimated (133)Xe release magnitude of the largest event (between 0.2 and 34 TBq over a 2 d window), was in close agreement with the stack emission releases estimated by the facility for this time period (between 0.5 and 2 TBq). Modelling of irradiation conditions and theoretical radioxenon emission rates were undertaken and provided further evidence that the Melbourne detections originated from this radiopharmaceutical production facility. These findings do not have public health implications. This is the first comprehensive study of atmospheric radioxenon measurements and releases in Australia.

  18. Lithospheric dynamics near plate boundaries

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1992-01-01

    The progress report on research conducted between 15 Mar. - 14 Sep. 1992 is presented. The focus of the research during the first grant year has been on several problems broadly related to the nature and dynamics of time-dependent deformation and stress along major seismic zones, with an emphasis on western North America but with additional work on seismic zones in oceanic lithosphere as well. The principal findings of our research to date are described in the accompanying papers and abstract. Topics covered include: (1) Global Positioning System measurements of deformations associated with the 1987 Superstition Hills earthquake: evidence for conjugate faulting; (2) Global Positioning System measurements of strain accumulation across the Imperial Valley, California: 1986-1989; (3) present-day crustal deformation in the Salton Trough, southern California; (4) oceanic transform earthquakes with unusual mechanisms or locations: relation to fault geometry and state of stress in the lithosphere; and (5) crustal strain and the 1992 Mojave Desert earthquakes.

  19. Existing Data Format for Two-Parameter Beta-Gamma Histograms for Radioxenon

    SciTech Connect

    TW Bowyer; TR Heimbigner; JI McIntyre; AD McKinnon; PL Reeder; E Wittinger

    1999-03-23

    There is a need to establish a commonly acceptable format for storing beta-gated coincidence data for stations in the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The current aerosol RMS type data format is not applicable for radioxenon in that the current format contains implicit assumptions specific to conventional gamma-ray spectrometry. Some assumptions in the current RMS format are not acceptable for the beta-gated spectra expected from the U.S. Department of Energy PNNL Automated Radioxenon Sampler-Analyzer (ARSA) and other similar systems under use or development from various countries. The RMS data format is not generally applicable for radioxenon measurements in the CTBT for one or more of the following main reasons: 1) The RMS format does not currently support 2-dimensional data. That is, the RMS data format is setup for a simple l-dimensional gamma-ray energy histogram. Current data available from the ARSA system and planned for other radioxenon monitors includes spectral information from gamma-rays and betas/conversion electrons. It is worth noting that the beta/conversion electron energy information will be used to separate the contributions from the different radioxenons. 2) The RMS data format assumes that the conversion between counts and activity can be calculated based (in part) on a simple calibration curve (detector efficiency curve) that depends only on energy of the gamma-ray. In the case of beta-gated gamma-ray spectra and for 2-dimensional spectra, there are generally two detector calibration curves that must be convoluted, the lower energy cutoff for the betas must be considered, and the energy acceptance window must be taken into account to convert counts into activity. . 3) The RMS format has header information that contains aerosol-specific information that allows the activity (Bq) calculated to be converted into a concentration (Bq/SCM). This calculation is performed by dividing the

  20. Evaluation of environmental radioxenon isotopical signals from a singular large source emitter

    NASA Astrophysics Data System (ADS)

    Saey, P. R. J.; Bowyer, T. W.; Aldener, M.; Becker, A.; Cooper, M. W.; Elmgren, K.; Faanhof, A.; Hayes, J. C.; Hosticka, B.; Lidey, L. S.

    2009-04-01

    In the framework of the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) the atmospheric background of environmental radioxenon is been studied near areas that could be affected by man-made sources. It was recently shown that radiopharmaceutical facilities (RPF) make a major contribution to the general background of 133Xe and other xenon isotopes both in the northern and southern hemisphere. The daily IMS noble gas measurements around the globe are influenced from such anthropogenic sources that could mask radioxenon signals from a nuclear explosion. To distinguish a nuclear explosion signal from releases from civil nuclear facilities, not only the activity concentration but also the ratio of different radioxenon isotopes (131mXe, 133mXe, 133Xe and 135Xe) plays a crucial role, since the ratios can be used to discriminate source types. Theoretical release and ratio studies were recently published, but no measurements close to radiopharmaceutical facilities have ever been performed. The world's fourth largest radiopharmaceutical facility, NTP Radioisotopes Ltd, is located in Pelindaba, South Africa. Other than a small nuclear power plant, located 1300 km southwest, near Cape Town and a small research reactor in the DR of Congo, located 2700 km northwest, this is the only facility that is known to emit any radioxenon on the African continent south of the Equator. This source is likely very dominant with respect to xenon emission. This makes it a point source, which is a unique situation, as all other worldwide large radiopharmaceutical facilities are situated in regions surrounded by many other nuclear facilities. Between 10 November and 22 December 2008, radioxenon was measured continuously with a radioactive xenon measurement system, at the North-West University, Mafikeng, South Africa, which is situated 250 km northwest of Pelindaba. Fifty-six 12-hour samples were measured with a beta-gamma coincidence detector, of which 55 contained 133Xe with

  1. Nature of the lithospheric mantle beneath the Arabian Shield and genesis of Al-spinel micropods: Evidence from the mantle xenoliths of Harrat Kishb, Western Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Ahmed, Ahmed H.; Moghazi, Abdel Kader M.; Moufti, Mohamed R.; Dawood, Yehia H.; Ali, Kamal A.

    2016-01-01

    The Harrat Kishb area of western Saudi Arabia is part of the Cenozoic volcanic fields in the western margin of the Arabian Shield. Numerous fresh ultramafic xenoliths are entrained in the basanite lava of Harrat Kishb, providing an opportunity to study the nature and petrogenetic processes involved in the evolution of the lithospheric mantle beneath the Arabian Shield. Based on the petrological characteristics and mineralogical compositions, the majority of the mantle xenoliths ( 92%) are peridotites (lherzolites and pyroxene-bearing harzburgites); the remaining xenoliths ( 8%) are unusual spinel-rich wehrlites containing black Al-spinel micropods. The two types of mantle xenoliths display magmatic protogranular texture. The peridotite xenoliths have high bulk-rock Mg#, high forsterite (Fo90-Fo92) and NiO (0.24-0.46 wt.%) contents of olivine, high clinopyroxene Mg# (0.91-0.93), variable spinel Cr# (0.10-0.49, atomic ratio), and approximately flat chondrite-normalized REE patterns. These features indicate that the peridotite xenoliths represent residues after variable degrees of melt extraction from fertile mantle. The estimated P (9-16 kbar) and T (877-1227 °C) as well as the oxidation state (∆logfO2 = - 3.38 to - 0.22) under which these peridotite xenoliths originated are consistent with formation conditions similar to most sub-arc abyssal-type peridotites worldwide. The spinel-rich wehrlite xenoliths have an unusual amount ( 30 vol.%) of Al-spinel as peculiar micropods with very minor Cr2O3 content (< 1 wt.%). Olivines of the spinel-rich wehrlites have low-average Fo (Fo81) and NiO (0.18 wt.%) contents, low-average cpx Mg# (0.79), high average cpx Al2O3 content (8.46 wt.%), and very low-average spinel Cr# (0.01). These features characterize early mantle cumulates from a picritic melt fraction produced by low degrees of partial melting of a garnet-bearing mantle source. The relatively high Na2O and Al2O3 contents of cpx suggest that the spinel-rich wehrlites

  2. Neural Network Based State of Health Diagnostics for an Automated Radioxenon Sampler/Analyzer

    SciTech Connect

    Keller, Paul E.; Kangas, Lars J.; Hayes, James C.; Schrom, Brian T.; Suarez, Reynold; Hubbard, Charles W.; Heimbigner, Tom R.; McIntyre, Justin I.

    2009-05-13

    Artificial neural networks (ANNs) are used to determine the state-of-health (SOH) of the Automated Radioxenon Analyzer/Sampler (ARSA). ARSA is a gas collection and analysis system used for non-proliferation monitoring in detecting radioxenon released during nuclear tests. SOH diagnostics are important for automated, unmanned sensing systems so that remote detection and identification of problems can be made without onsite staff. Both recurrent and feed-forward ANNs are presented. The recurrent ANN is trained to predict sensor values based on current valve states, which control air flow, so that with only valve states the normal SOH sensor values can be predicted. Deviation between modeled value and actual is an indication of a potential problem. The feed-forward ANN acts as a nonlinear version of principal components analysis (PCA) and is trained to replicate the normal SOH sensor values. Because of ARSA’s complexity, this nonlinear PCA is better able to capture the relationships among the sensors than standard linear PCA and is applicable to both sensor validation and recognizing off-normal operating conditions. Both models provide valuable information to detect impending malfunctions before they occur to avoid unscheduled shutdown. Finally, the ability of ANN methods to predict the system state is presented.

  3. Lithospheric and crustal thinning

    NASA Technical Reports Server (NTRS)

    Moretti, I.

    1985-01-01

    In rift zones, both the crust and the lithosphere get thinner. The amplitude and the mechanism of these two thinning situations are different. The lithospheric thinning is a thermal phenomenon produced by an asthenospherical uprising under the rift zone. In some regions its amplitude can exceed 200%. This is observed under the Baikal rift where the crust is directly underlaid by the mantellic asthenosphere. The presence of hot material under rift zones induces a large negative gravity anomaly. A low seismic velocity zone linked to this thermal anomaly is also observed. During the rifting, the magmatic chambers get progressively closer from the ground surface. Simultaneously, the Moho reflector is found at shallow depth under rift zones. This crustal thinning does not exceed 50%. Tectonic stresses and vertical movements result from the two competing effects of the lithospheric and crustal thinning. On the one hand, the deep thermal anomaly induces a large doming and is associated with extensive deviatoric stresses. On the other hand, the crustal thinning involves the formation of a central valley. This subsidence is increased by the sediment loading. The purpose here is to quantify these two phenomena in order to explain the morphological and thermal evolution of rift zones.

  4. Comparison of new and existing algorithms for the analysis of 2D radioxenon beta gamma spectra

    DOE PAGES

    Deshmukh, Nikhil; Prinke, Amanda; Miller, Brian; ...

    2017-01-13

    The aim of this study is to compare radioxenon beta–gamma analysis algorithms using simulated spectra with experimentally measured background, where the ground truth of the signal is known. We believe that this is among the largest efforts to date in terms of the number of synthetic spectra generated and number of algorithms compared using identical spectra. We generate an estimate for the minimum detectable counts for each isotope using each algorithm. The paper also points out a conceptual model to put the various algorithms into a continuum. Finally, our results show that existing algorithms can be improved and some newermore » algorithms can be better than the ones currently used.« less

  5. State-of-Health Software for the Automated Radioxenon Sampler/Analyzer

    SciTech Connect

    Heimbigner, Tom R.; Bowyer, Ted W.; Hayes, James C.; Hubbard, Charles W.; McIntyre, Justin I.; Panisko, Mark E.; Ripplinger, Mike D.; Suarez, Reynold

    2004-09-22

    The Automated Radioxenon Analyzer/Sampler (ARSA) is a complex gas-collection and analysis system that requires constant online monitoring of system operations and overall system health. The software-control system records and monitors and over 100 different system sensors (temperature, pressures, voltages, etc.) A real-time record of the system state allows the system to monitor for unsafe conditions and maintain the system in a safe state regardless of external or internal failures (vacuum pump, valve or power failures, and runaway temperatures are a few examples). Another function of real-time monitoring allows the user to troubleshoot the system when a problem arises, should a minor sensor or a major system failure occur. This paper will outline the general scheme used by the state-of-health program to monitor and assess the system, the graphical user interface program and the alert message system, and give specific examples of proper system performance and some system failures.

  6. A program to generate simulated radioxenon beta–gamma data for concentration verification and validation and training exercises

    SciTech Connect

    McIntyre, Justin I.; Schrom, Brian T.; Cooper, Matthew W.; Prinke, Amanda M.; Suckow, Thomas J.; Ringbom, Anders; Warren, Glen A.

    2016-03-08

    Abstract Several hundred simulated radioxenon beta-gamma data files were developed to assist in evaluating the performance and results from radioxenon concentration calculation analysis at the International Data Center (IDC) and other National Data Centers (NDC). PNNL developed a Beta-Gamma Simulator (BGSim) that incorporated GEANT-modeled data sets from radioxenon decay chains, as well as functionality to use nuclear detector-acquired data sets to create new beta-gamma spectra with varying amounts of background, 133Xe, 131mXe, 133mXe, 135Xe, and 222Rn and its decay products. The program has been implemented on a web-based applications platform and allows the user to create very specific data sets that incorporate most of the operational parameters for the current beta-gamma systems deployed in the International Monitoring System (IMS) and the On-site Inspection (OSI) equipment. After an initial beta-gamma simulations program was developed, additional uses began to be identified for the program output: training sets of two-dimensional spectra for data analysts at the IDC and other NDC, spectra for exercises such as the Integrated Field Exercise 2014 (IFE14) held in Jordan at the Dead Sea, and testing new analysis methods and algorithms

  7. True Polar Wander of Bodies with Elastic Lithospheres: the Role of Elastic Energy in the Lithosphere

    NASA Astrophysics Data System (ADS)

    Matsuyama, Isamu M.; Nimmo, F.; Mitrovica, J. X.

    2006-09-01

    True polar wander (TPW) refers to the reorientation of the rotation axis of a body in response to changes in the inertia tensor due to mass redistribution. Since the state of the lowest kinetic energy for a rigid body corresponds to rotation about the principal axis associated with the largest moment of inertia, it is generally assumed that any internal energy dissipation will tend to drive the body to that state. The equatorial location of the Tharsis province on Mars, and the polar location of Enceladus' hot spot may be explained by reorientation of these bodies due to TPW (Matsuyama et al. 2006, JGR, 111, E02003; Nimmo and Pappalardo 2006, Nature, 441). Ojakangas and Stevenson (1986, BAAS, 18) indicate that the minimum total energy state may not correspond to principal axis rotation for planets with elastic lithospheres because reorientation generates elastic strains within the lithosphere, which reduces the energy available to drive further reorientation. We generalize the approach of Matsuyama et al. (2006, JGR, 111, E02003) to obtain TPW solutions by finding the minimum total energy state that includes a self-consistent elastic energy stored in the lithosphere. We expect the addition of the lithospheric strain term to reduce the total amount of reorientation compared to analyses that neglect this effect. This stabilizing effect is likely to be less important on bodies which have broken plates (Earth) compared with those that have continuous plates (Venus, Mars).

  8. How thick is the lithosphere?

    PubMed

    Kanamori, H; Press, F

    1970-04-25

    A rapid decrease in shear velocity in the suboceanic mantle is used to infer the thickness of the lithosphere. It is proposed that new and highly precise group velocity data constrain the solutions and imply a thickness near 70 km.

  9. Lithospheric Architecture Beneath Hudson Bay

    NASA Astrophysics Data System (ADS)

    Porritt, R. W.; Miller, M. S.; Darbyshire, F. A.

    2015-12-01

    Hudson Bay overlies some of the thickest Precambrian lithosphere on Earth, whose internal structures contain important clues to the earliest workings of plate formation. The terminal collision, the Trans-Hudson Orogen, brought together the Western Churchill craton to the northwest and the Superior craton to the southeast. These two Archean cratons along with the Paleo-Proterozoic Trans-Hudson internides, form the core of the North American craton. We use S to P converted wave imaging and absolute shear velocity information from a joint inversion of P to S receiver functions, new ambient noise derived phase velocities, and teleseismic phase velocities to investigate this region and determine both the thickness of the lithosphere and the presence of internal discontinuities. The lithosphere under central Hudson Bay approaches 􏰂350 km thick but is thinner (􏰂200-250 km) around the periphery of the Bay. Furthermore, the amplitude of the lithosphere-asthenosphere boundary (LAB) conversion from the S receiver functions is unusually large for a craton, suggesting a large thermal contrast across the LAB, which we interpret as direct evidence of the thermal insulation effect of continents on the asthenosphere. Within the lithosphere, midlithospheric discontinuities, significantly shallower than the base of the lithosphere, are often imaged, suggesting the mechanisms that form these layers are common. Lacking time-history information, we infer that these discontinuities reflect reactivation of formation structures during deformation of the craton.

  10. Maximum reasonable radioxenon releases from medical isotope production facilities and their effect on monitoring nuclear explosions.

    PubMed

    Bowyer, Theodore W; Kephart, Rosara; Eslinger, Paul W; Friese, Judah I; Miley, Harry S; Saey, Paul R J

    2013-01-01

    Fission gases such as (133)Xe are used extensively for monitoring the world for signs of nuclear testing in systems such as the International Monitoring System (IMS). These gases are also produced by nuclear reactors and by fission production of (99)Mo for medical use. Recently, medical isotope production facilities have been identified as the major contributor to the background of radioactive xenon isotopes (radioxenon) in the atmosphere (Stocki et al., 2005; Saey, 2009). These releases pose a potential future problem for monitoring nuclear explosions if not addressed. As a starting point, a maximum acceptable daily xenon emission rate was calculated, that is both scientifically defendable as not adversely affecting the IMS, but also consistent with what is possible to achieve in an operational environment. This study concludes that an emission of 5 × 10(9) Bq/day from a medical isotope production facility would be both an acceptable upper limit from the perspective of minimal impact to monitoring stations, but also appears to be an achievable limit for large isotope producers.

  11. Mechanical heterogeneities and lithospheric extension

    NASA Astrophysics Data System (ADS)

    Duretz, Thibault; Petri, Benoit; Mohn, Geoffroy; Schenker, Filippo L.; Schmalholz, Stefan

    2016-04-01

    Detailed geological and geophysical studies of passive margins have highlighted the multi-stage and depth-dependent aspect of lithospheric thinning. Lithospheric thinning involves a variety of structures (normal faults, low angle detachments, extensional shear zones, extraction faults) and leads to a complex architecture of passive margins (with e.g. necking zone, mantle exhumation, continental allochthons). The processes controlling the generation and evolution of these structures as well as the impact of pre-rift inheritance are so far incompletely understood. In this study, we investigate the impact of pre-rift inheritance on the development of rifted margins using two-dimensional thermo-mechanical models of lithospheric thinning. To first order, we represent the pre-rift mechanical heterogeneities with lithological layering. The rheologies are kept simple (visco-plastic) and do not involve any strain softening mechanism. Our models show that mechanical layering causes multi-stage and depth-dependent extension. In the initial rifting phase, lithospheric extension is decoupled: as the crust undergoes thinning by brittle (frictional-plastic) faults, the lithospheric mantle accommodates extension by symmetric ductile necking. In a second rifting phase, deformation in the crust and lithospheric mantle is coupled and marks the beginning of an asymmetric extension stage. Low angle extensional shear zones develop across the lithosphere and exhume subcontinental mantle. Furthemore, crustal allochthons and adjacent basins develop coevally. We describe as well the thermal evolution predicted by the numerical models and discuss the first-order implications of our results in the context of the Alpine geological history.

  12. Lithospheric architecture beneath Hudson Bay

    NASA Astrophysics Data System (ADS)

    Porritt, Robert W.; Miller, Meghan S.; Darbyshire, Fiona A.

    2015-07-01

    Hudson Bay overlies some of the thickest Precambrian lithosphere on Earth, whose internal structures contain important clues to the earliest workings of plate formation. The terminal collision, the Trans-Hudson Orogen, brought together the Western Churchill craton to the northwest and the Superior craton to the southeast. These two Archean cratons along with the Paleo-Proterozoic Trans-Hudson internides, form the core of the North American craton. We use S to P converted wave imaging and absolute shear velocity information from a joint inversion of P to S receiver functions, new ambient noise derived phase velocities, and teleseismic phase velocities to investigate this region and determine both the thickness of the lithosphere and the presence of internal discontinuities. The lithosphere under central Hudson Bay approaches ˜350 km thick but is thinner (˜200-250 km) around the periphery of the Bay. Furthermore, the amplitude of the LAB conversion from the S receiver functions is unusually large for a craton, suggesting a large thermal contrast across the LAB, which we interpret as direct evidence of the thermal insulation effect of continents on the asthenosphere. Within the lithosphere, midlithospheric discontinuities, significantly shallower than the base of the lithosphere, are often imaged, suggesting the mechanisms that form these layers are common. Lacking time-history information, we infer that these discontinuities reflect reactivation of formation structures during deformation of the craton.

  13. Analog Modeling of Continental Lithosphere Subduction

    NASA Astrophysics Data System (ADS)

    Willingshofer, E.; Sokoutis, D.; Luth, S.; Beekman, F.; Cloetingh, S.

    2012-12-01

    Lithospheric-scale analog modeling sheds light on the consequences of decoupling within the continental lithosphere and along plate interfaces during continental collision. The model results provide valuable information in terms of strain localization, deformation of the subducting slab and the evolution and architecture of the overlying mountain belt and its topography. A weak layer has been implemented in three-layer models to simulate decoupling along the plate interface and at different levels of the lithosphere (brittle-ductile transition, entire lower crust, crust-mantle boundary). Additionally, varying the strength of the mantle lithosphere of both the upper as well as the lower plate regulated the degree of plate coupling. Plate boundaries were orthogonal to the convergence direction. All models emphasize that strong decoupling at the plate interface is a pre-requisite for the subduction of continental lithosphere. In addition, deformation of the subducting slab was found to be sensitive to the strength contrast between the subduction zone and the mantle lithosphere of the downgoing as well as the upper plate. As such, a low strength contrast between the plate interface and the lower plate leads to deformation of the subducting slab by thickening and the development of a shallow slab. Conversely, when the strength contrast is high, deep slabs evolve which undergo relatively less deformation. Furthermore, the level of decoupling in the downgoing plate governs how much continental crust is subducted together with the mantle lithosphere. Shallow decoupling, at the brittle-ductile transition, results in subduction of the lower crust whereas small amounts of lower crust are subducted when decoupling occurs at the level of the Moho. Weak plate coupling and a weak lower crust of the lower plate steer the evolution of mountain belts such that deformation propagates outward, in the direction of the incoming plate, by successive imbrication of upper crustal thrust

  14. Constraints on Lithosphere Rheology from Observations of Volcano-induced Deformation

    NASA Astrophysics Data System (ADS)

    Zhong, S.; Watts, A. B.

    2011-12-01

    experimental results at lithospheric temperatures. Seamounts and oceanic islands are therefore a 'natural laboratory', we believe, to study lithospheric rheology on both short and long time scales.

  15. Is the Venusian lithosphere subducting?

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.; Schubert, Gerald

    1992-01-01

    Using data collected by the Magellan spacecraft, we are exploring the hypothesis that the cooler and more rigid outer layer of Venus (i.e., the lithosphere) is sinking (subducting) into the interior of Venus. If this process is occurring, it provides a mechanism for cooling the interior of Venus and also for recycling the lighter crustal rocks back into the interior. In addition, since subduction zones drive the plate tectonic motion on the Earth, evidence for lithospheric subduction on Venus raises the possibility of limited plate tectonic-like activity on Venus.

  16. Failure strength of icy lithospheres

    NASA Technical Reports Server (NTRS)

    Golombek, M. P.; Banerdt, W. B.

    1987-01-01

    Lithospheric strengths derived from friction on pre-existing fractures and ductile flow laws show that the tensile strength of intact ice under applicable conditions is actually an order of magnitude stronger than widely assumed. It is demonstrated that this strength is everywhere greater than that required to initiate frictional sliding on pre-existing fractures and faults. Because the tensile strength of intact ice increases markedly with confining pressure, it actually exceeds the frictional strength at all depths. Thus, icy lithospheres will fail by frictional slip along pre-existing fractures at yeild stresses greater than previously assumed rather than opening tensile cracks in intact ice.

  17. International challenge to predict the impact of radioxenon releases from medical isotope production on a comprehensive nuclear test ban treaty sampling station.

    PubMed

    Eslinger, Paul W; Bowyer, Ted W; Achim, Pascal; Chai, Tianfeng; Deconninck, Benoit; Freeman, Katie; Generoso, Sylvia; Hayes, Philip; Heidmann, Verena; Hoffman, Ian; Kijima, Yuichi; Krysta, Monika; Malo, Alain; Maurer, Christian; Ngan, Fantine; Robins, Peter; Ross, J Ole; Saunier, Olivier; Schlosser, Clemens; Schöppner, Michael; Schrom, Brian T; Seibert, Petra; Stein, Ariel F; Ungar, Kurt; Yi, Jing

    2016-06-01

    The International Monitoring System (IMS) is part of the verification regime for the Comprehensive Nuclear-Test-Ban-Treaty Organization (CTBTO). At entry-into-force, half of the 80 radionuclide stations will be able to measure concentrations of several radioactive xenon isotopes produced in nuclear explosions, and then the full network may be populated with xenon monitoring afterward. An understanding of natural and man-made radionuclide backgrounds can be used in accordance with the provisions of the treaty (such as event screening criteria in Annex 2 to the Protocol of the Treaty) for the effective implementation of the verification regime. Fission-based production of (99)Mo for medical purposes also generates nuisance radioxenon isotopes that are usually vented to the atmosphere. One of the ways to account for the effect emissions from medical isotope production has on radionuclide samples from the IMS is to use stack monitoring data, if they are available, and atmospheric transport modeling. Recently, individuals from seven nations participated in a challenge exercise that used atmospheric transport modeling to predict the time-history of (133)Xe concentration measurements at the IMS radionuclide station in Germany using stack monitoring data from a medical isotope production facility in Belgium. Participants received only stack monitoring data and used the atmospheric transport model and meteorological data of their choice. Some of the models predicted the highest measured concentrations quite well. A model comparison rank and ensemble analysis suggests that combining multiple models may provide more accurate predicted concentrations than any single model. None of the submissions based only on the stack monitoring data predicted the small measured concentrations very well. Modeling of sources by other nuclear facilities with smaller releases than medical isotope production facilities may be important in understanding how to discriminate those releases from

  18. Constraints on Composition, Structure and Evolution of the Lithosphere

    NASA Astrophysics Data System (ADS)

    Bianchini, Gianluca; Bonadiman, Costanza; Aulbach, Sonja; Schutt, Derek

    2015-05-01

    The idea for this special issue was triggered at the Goldschmidt Conference held in Florence (August 25-30, 2013), where we convened a session titled "Integrated Geophysical-Geochemical Constraints on Composition and Structure of the Lithosphere". The invitation to contribute was extended not only to the session participants but also to a wider spectrum of colleagues working on related topics. Consequently, a diverse group of Earth scientists encompassing geophysicists, geodynamicists, geochemists and petrologists contributed to this Volume, providing a comprehensive overview on the nature and evolution of lithospheric mantle by combining studies that exploit different types of data and interpretative approaches. The integration of geochemical and geodynamic datasets and their interpretation represents the state of the art in our knowledge of the lithosphere and beyond, and could serve as a blueprint for future strategies in concept and methodology to advance our knowledge of this and other terrestrial reservoirs.

  19. The structural evolution of the deep continental lithosphere

    NASA Astrophysics Data System (ADS)

    Cooper, C. M.; Miller, Meghan S.; Moresi, Louis

    2017-01-01

    Continental lithosphere houses the oldest and thickest regions of the Earth's surface. Locked within this deep and ancient rock record lies invaluable information about the dynamics that has shaped and continue to shape the planet. Much of that history has been dominated by the forces of plate tectonics which has repeatedly assembled super continents together and torn them apart - the Wilson Cycle. While the younger regions of continental lithosphere have been subject to deformation driven by plate tectonics, it is less clear whether the ancient, stable cores formed and evolved from similar processes. New insight into continental formation and evolution has come from remarkable views of deeper lithospheric structure using enhanced seismic imaging techniques and the increase in large volumes of broadband data. Some of the most compelling observations are that the continental lithosphere has a broad range in thicknesses (< 100 to > 300 km), has complex internal structure, and that the thickest portion appears to be riddled with seismic discontinuities at depths between 80 and 130 km. These internal structural features have been interpreted as remnants of lithospheric formation during Earth's early history. If they are remnants, then we can attempt to investigate the structure present in the deep lithosphere to piece together information about early Earth dynamics much as is done closer to the surface. This would help delineate between the differing models describing the dynamics of craton formation, particularly whether they formed in the era of modern plate tectonics, a transitional mobile-lid tectonic regime, or are the last fragments of an early, stagnant-lid planet. Our review paper (re)introduces readers to the conceptual definitions of the lithosphere and the complex nature of the upper boundary layer, then moves on to discuss techniques and recent seismological observations of the continental lithosphere. We then review geodynamic models and hypotheses for the

  20. Fossilized Dipping Fabrics in Continental Mantle Lithosphere as Possible Remnants of Stacked Oceanic Paleosubductions

    NASA Astrophysics Data System (ADS)

    Babuska, V.; Plomerova, J.; Vecsey, L.; Munzarova, H.

    2015-12-01

    We have examined seismic anisotropy within the mantle lithosphere of Archean, Proterozoic and Phanerozoic provinces of Europe by means of shear-wave splitting and P-wave travel-time deviations of teleseismic waves observed at dense arrays of seismic stations (e.g., Vecsey et al., Tectonophys. 2007). Lateral variations of seismic-wave anisotropy delimit domains of the mantle lithosphere, each of them having a consistent fabric. The domains, modeled in 3D by olivine aggregates with dipping lineation a, or foliation (a,c), represent microplates or their fragments that preserved their pre-assembly fossil fabrics in the mantle lithosphere. Evaluating seismic anisotropy in 3D, as well as mapping boundaries of the domains helps to decipher processes of the lithosphere formation. Systematically dipping mantle fabrics and other seismological findings seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or by stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- or D-type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered a half century ago (Hess, Nature 1964). Field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved in the subducting lithosphere to a depth of at least 200-300 km. We thus interpret the dipping anisotropic fabrics in domains of the European mantle lithosphere as systems of "frozen" paleosubductions (Babuska and Plomerova, PEPI 2006), and the lithosphere base as a boundary between a fossil anisotropy in the lithospheric mantle and an underlying seismic anisotropy related to present-day flow in the asthenosphere (Plomerova and Babuska, Lithos 2010).

  1. Understanding lithospheric stresses in Arctic: constraints and models

    NASA Astrophysics Data System (ADS)

    Medvedev, Sergei; Minakov, Alexander; Lebedeva-Ivanova, Nina; Gaina, Carmen

    2016-04-01

    This pilot project aims to model stress patterns and analyze factors controlling lithospheric stresses in Arctic. The project aims to understand the modern stresses in Arctic as well as to define the ways to test recent hypotheses about Cenozoic evolution of the region. The regions around Lomonosov Ridge and Barents Sea are of particular interest driven by recent acquisition of high-resolution potential field and seismic data. Naturally, the major contributor to the lithospheric stress distribution is the gravitational potential energy (GPE). The study tries to incorporate available geological and geophysical data to build reliable GPE. In particular, we use the recently developed integrated gravity inversion for crustal thickness which incorporates up-to-date compilations of gravity anomalies, bathymetry, and sedimentary thickness. The modelled lithosphere thermal structure assumes a pure shear extension and the ocean age model constrained by global plate kinematics for the last ca. 120 Ma. The results of this approach are juxtaposed with estimates of the density variation inferred from the upper mantle S-wave velocity models based on previous surface wave tomography studies. Although new data and interpretations of the Arctic lithosphere structure become available now, there are areas of low accuracy or even lack of data. To compensate for this, we compare two approaches to constrain GPE: (1) one that directly integrates density of modelled lithosphere and (2) one that uses geoid anomalies which are filtered to account for density variations down to the base of the lithosphere only. The two versions of GPE compared to each other and the stresses calculated numerically are compared with observations. That allows us to optimize GPE and understand density structure, stress pattern, and factors controlling the stresses in Arctic.

  2. The strength of Miranda's lithosphere

    NASA Technical Reports Server (NTRS)

    Pappalardo, Robert; Greeley, Ronald

    1991-01-01

    In attempting to understand the endogenic processes which have shaped the surface of an icy satellite, it is desirable to quantify the failure strength of the satellite's lithosphere. In a crust that is fractured on a large scale, frictional sliding along pre-existing fractures occurs in response to lower differential stresses than required to initiate fracture of pristine rock, thus governing failure of a brittle lithosphere. Failure is predicted along favorably oriented fracture planes; if fractures of all orientations are assumed to be present in the crust (as is expected of a heavily cratered lithosphere), frictional failure relations are directly applicable. The Coulomb criterion predicts that the shear stress (sigma sub t) and normal stress (sigma sub n) components on a fracture plane at failure are related as sigma sub t = mu-sigma sub n + S sub o, where S sub o is the cohesion and mu is the coefficient of friction. At moderate to high pressures, the frictional sliding strength of most materials is found to be sigma sub t = 0.85 sigma sub n.

  3. Revisiting the Ridge-Push Force Using the Lithospheric Geoid

    NASA Astrophysics Data System (ADS)

    Richardson, R. M.; Coblentz, D. D.

    2014-12-01

    energy required through filtering of the geoid. We evaluate the role of revised ridge push forces with plate-scale stress models. Our revised estimate of the ridge push force based on the lithospheric geoid, and corresponding stress models, further emphasizes the "active" rather than "passive" nature of the plates themselves in plate tectonics.

  4. The Role of the Mantle Lithosphere in Continent Stability

    NASA Astrophysics Data System (ADS)

    Carlson, R. W.; Ancuta, L. D.; Fouch, M. J.; Idleman, B. D.; Ionov, D. A.; James, D. E.; Meltzer, A.; Pearson, G.; Shirey, S. B.; Zeitler, P. K.

    2012-12-01

    compositions (Barry et al., Lithos, 2007) not obviously consistent with a plume contribution to this activity. We suggest instead that the basaltic activity relates to the fertile nature of the Mongolian lithospheric mantle and that this area will remain geologically unsettled until and unless the mantle lithosphere can be replaced with infertile mantle similar to that underlying cratons.

  5. Some Problems of the Lithosphere (Augustus Love Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Houseman, Gregory A.

    2015-04-01

    relationship between faulting and earthquake activity and the continuous deformation field below the seismogenic layer continues to be poorly understood. Prominent surface faults may be a natural consequence of the localization of strain caused by processes within the ductile layer such as shear heating, grain-size reduction, or simply the interaction of non-Newtonian constitutive law and irregular geometry. Where intra-plate convergence occurs the lithosphere must thicken, and the question naturally arises as to whether the thickened lithosphere will remain stable or somehow be removed by convective overturn with underlying asthenophere. Such overturn is expected of a viscous lithospheric layer that is denser than the asthenosphere; it will be denser because it is colder, unless there is some compositional contrast which makes it intrinsically buoyant. A relatively low viscosity is required, however, in order that the instability can grow at a sufficiently fast rate to overcome diffusive stabilisation of the temperature field. The high stresses created by plate convergence may provide the mechanism that activates the viscosity (and explains why the lithosphere elsewhere is generally stable). High-resolution tomographic investigations find convincing evidence of small-scale mantle drips occurring beneath recently active orogenic zones such as the western USA and the SE Carpathians. However, seismic observations of thickened lithosphere remaining beneath Tibet apparently contradict the interpretation of mantle overturn suggested by recent volcanism and uplift. Although the Tibetan mantle lithosphere may be relatively buoyant, the possibility that this layer has overturned internally may allow these conflicting interpretations to be reconciled.

  6. Limiting depth of magnetization in cratonic lithosphere

    NASA Technical Reports Server (NTRS)

    Toft, Paul B.; Haggerty, Stephen E.

    1988-01-01

    Values of magnetic susceptibility and natural remanent magnetization (NRM) of clino-pyroxene-garnet-plagioclase granulite facies lower crustal xenoliths from a kimberlite in west Africa are correlated to bulk geochemistry and specific gravity. Thermomagnetic and alternating-field demagnetization analyses identify magnetite (Mt) and native iron as the dominant magnetic phases (totaling not more than 0.1 vol pct of the rocks) along with subsidiary sulfides. Oxidation states of the granulites are not greater than MW, observed Mt occurs as rims on coarse (about 1 micron) Fe particles, and inferred single domain-pseudosingle domain Mt may be a result of oxidation of fine-grained Fe. The deepest limit of lithospheric ferromagnetism is 95 km, but a limit of 70 km is most reasonable for the West African Craton and for modeling Magsat anomalies over exposed Precambrian shields.

  7. Dipping fossil fabrics of continental mantle lithosphere as tectonic heritage of oceanic paleosubductions

    NASA Astrophysics Data System (ADS)

    Babuska, Vladislav; Plomerova, Jaroslava; Vecsey, Ludek; Munzarova, Helena

    2016-04-01

    Subduction and orogenesis require a strong mantle layer (Burov, Tectonophys. 2010) and our findings confirm the leading role of the mantle lithosphere. We have examined seismic anisotropy of Archean, Proterozoic and Phanerozoic provinces of Europe by means of shear-wave splitting and P-wave travel-time deviations of teleseismic waves observed at dense arrays of seismic stations (e.g., Vecsey et al., Tectonophys. 2007). Lateral variations of seismic-velocity anisotropy delimit domains of the mantle lithosphere, each of them having its own consistent fabric. The domains, modeled in 3D by olivine aggregates with dipping lineation a, or foliation (a,c), represent microplates or their fragments that preserved their pre-assembly fossil fabrics. Evaluating seismic anisotropy in 3D, as well as mapping boundaries of the domains helps to decipher processes of the lithosphere formation. Systematically dipping mantle fabrics and other seismological findings seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or from stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- or D-type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered a half century ago (Hess, Nature 1964). Field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved in the subducting lithosphere to a depth of at least 200-300 km. We thus interpret the dipping anisotropic fabrics in domains of the European mantle lithosphere as systems of "frozen" paleosubductions (Babuska and Plomerova, PEPI 2006) and the lithosphere base as a boundary between the fossil anisotropy in the lithospheric mantle and an underlying seismic anisotropy related to present-day flow in the asthenosphere (Plomerova and Babuska, Lithos 2010).

  8. Dynamic lithosphere within the Great Basin

    NASA Astrophysics Data System (ADS)

    Porter, Ryan C.; Fouch, Matthew J.; Schmerr, Nicholas C.

    2014-04-01

    place new constraints on the short-term, broad-scale lithospheric evolution of plate interiors, we utilize broadband seismic data from the Great Basin region of the Western United States to produce high-resolution images of the crust and upper mantle. Our results suggest that parts of the Great Basin lithosphere has been removed, likely via inflow of hot asthenosphere as subduction of the Farallon spreading center occurred and the region extended. In our proposed model, fragments of thermal lithosphere removed by this process were gravitationally unstable and subsequently sank into the underlying mantle, leaving behind less dense, stronger, chemically depleted lithosphere. This destabilization process promotes volcanism, deformation, and the reworking of continental lithosphere inboard from plate margins. Our results provide evidence for a new mechanism of lithospheric evolution that is likely common and significant in postsubduction tectonic settings.

  9. Remarkable isotopic and trace element trends in potassic through sodic Cretaceous plutons of the Yukon-Koyukuk Basin, Alaska, and the nature of the lithosphere beneath the Koyukuk terrane

    NASA Astrophysics Data System (ADS)

    Arth, Joseph G.; Criss, Robert E.; Zmuda, Clara C.; Foley, Nora K.; Patton, W. W., Jr.; Miller, T. P.

    1989-11-01

    During the period from 110 to 80 m.y. ago, a 450-km-long magmatic belt was active along the northern margin of Yukon-Koyukuk basin and on eastern Seward Peninsula. The plutons intruded Upper Jurassic(?) and Lower Cretaceous volcanic arc rocks and Cretaceous sedimentary rocks in Yukon-Koyukuk basin and Proterozoic and lower Paleozoic continental rocks in Seward Peninsula. Within Yukon-Koyukuk basin, the plutons vary in composition from calc-alkalic plutons on the east to potassic and ultrapotassic alkalic plutons on the west. Plutons within Yukon-Koyukuk basin were analyzed for trace element and isotopic compositions in order to discern their origin and the nature of the underling lithosphere. Farthest to the east, the calc-alkalic rocks of Indian Mountain pluton are largely tonalite and sodic granodiorite, and have low Rb (average 82 ppm), high Sr (>600 ppm), high chondrite-normalized (cn) Ce/Yb (16-37), low δ18O (+6.5 to +7.1), low initial 87Sr/86Sr (SIR) (0.704), and high initial 143Nd/144Nd (NIR) (0.5126). These rocks resemble those modelled elsewhere as partial melts and subsequent fractionates of basaltic or gabbroic metaigneous rocks, and may be products of melting in the deeper parts of the Late Jurassic(?) and Early Cretaceous volcanic arc. Farthest to the west, the two ultrapotassic bodies of Selawik and Inland Lake are high in Cs (up to 93 ppm), Rb (up to 997 ppm), Sr, Ba, Th, and light rare earth elements, have high (Ce/Yb)cn (30, 27), moderate to low δ18O (+8.4, +6.9), high SIR (0.712, 0.710), and moderate NIR (0.5121-0.5122). These rocks resemble rocks of Australia and elsewhere that were modelled as melts of continental mantle that had been previously enriched in large cations. This mantle may be Paleozoic or older. The farthest west alkalic pluton of Selawik Hills is largely monzonite, quartz monzonite, and granite; has moderate Rb (average 284 ppm), high Sr (>600 ppm), high (Ce/Yb)cn (15-25), moderate δ18O (+8.3 to +8.6), high SIR (0

  10. Remarkable isotopic and trace element trends in potassic through sodic Cretaceous plutons of the Yukon-Koyukuk Basin, Alaska, and the nature of the lithosphere beneath the Koyukuk terrane

    USGS Publications Warehouse

    Arth, Joseph G.; Criss, Robert E.; Zmuda, Clara C.; Foley, Nora K.; Patton, W.W.; Miller, T.P.

    1989-01-01

    During the period from 110 to 80 m.y. ago, a 450-km-long magmatic belt was active along the northern margin of Yukon-Koyukuk basin and on eastern Seward Peninsula. The plutons intruded Upper Jurassic(?) and Lower Cretaceous volcanic arc rocks and Cretaceous sedimentary rocks in Yukon-Koyukuk basin and Proterozoic and lower Paleozoic continental rocks in Seward Peninsula. Within Yukon-Koyukuk basin, the plutons vary in composition from calc-alkalic plutons on the east to potassic and ultrapotassic alkalic plutons on the west. Plutons within Yukon-Koyukuk basin were analyzed for trace element and isotopic compositions in order to discern their origin and the nature of the underling lithosphere. Farthest to the east, the calc-alkalic rocks of Indian Mountain pluton are largely tonalite and sodic granodiorite, and have low Rb (average 82 ppm), high Sr (>600 ppm), high chondrite-normalized (cn) Ce/Yb (16–37), low δ18O (+6.5 to +7.1), low initial 87Sr/86Sr (SIR) (0.704), and high initial 143Nd/144Nd (NIR) (0.5126). These rocks resemble those modelled elsewhere as partial melts and subsequent fractionates of basaltic or gabbroic metaigneous rocks, and may be products of melting in the deeper parts of the Late Jurassic(?) and Early Cretaceous volcanic arc. Farthest to the west, the two ultrapotassic bodies of Selawik and Inland Lake are high in Cs (up to 93 ppm), Rb (up to 997 ppm), Sr, Ba, Th, and light rare earth elements, have high (Ce/Yb)cn (30, 27), moderate to low δ18O (+8.4, +6.9), high SIR (0.712, 0.710), and moderate NIR (0.5121–0.5122). These rocks resemble rocks of Australia and elsewhere that were modelled as melts of continental mantle that had been previously enriched in large cations. This mantle may be Paleozoic or older. The farthest west alkalic pluton of Selawik Hills is largely monzonite, quartz monzonite, and granite; has moderate Rb (average 284 ppm), high Sr (>600 ppm), high (Ce/Yb)cn (15–25), moderate δ18O (+8.3 to +8.6), high SIR (0.708

  11. A numerical study of forced lithospheric thinning

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Anderson, A.; Fishbein, E.

    1985-01-01

    Subsolidus lithospheric thinning by mantle plumes may be involved in the creation of swells, hotspots, and rifts. Among the major questions concerning this process are the timescale on which it occurs and the structure of the plumes. The lithosphere is known to have been substantially thinned in 10 Ma or less. Current studies are focused on the lithospheric thinning by time-dependent plumes hypothesized to have large temperature differences across them.

  12. Venus Chasmata: A Lithospheric Stretching Model

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.; Head, J. W.

    1985-01-01

    An outstanding problem for Venus is the characterization of its style of global tectonics, an issue intimately related to the dominant mechanism of lithospheric heat loss. Among the most spectacular and extensive of the major tectonic features on Venus are the chasmata, deep linear valleys generally interpreted to be the products of lithospheric extension and rifting. Systems of chasmata and related features can be traced along several tectonic zones up to 20,000 km in linear extent. A lithospheric stretching model was developed to explain the topographic characteristics of Venus chasmata and to constrain the physical properties of the Venus crust and lithosphere.

  13. DANUBE 2004 Lithosphere Research Program

    NASA Astrophysics Data System (ADS)

    Hegedus, E.; Brueckl, E.; Csabafi, R.; Fancsik, T.; Grad, M.; Guterch, A.; Hajnal, Z.; Keller, R.; Kovacs, A. C.; Komminaho, K.; Kozlovskaya, E.; Tiira, T.; Torok, I.; Yliniemi, J.

    2005-12-01

    The DANUBE 2004 (Deep imAgiNg of hUngarian BasEment) lithosphere research program following significant seismic lithospheric experiments in Central Europe (e.g., CELEBRATION 2000), was coordinated by the ELGI, on the commission of the Public Agency for Radioactive Waste Management (PURAM), in international cooperation. The goal of the research program was to allocate and characterize the potential geological site for high-level radioactive waste disposal in SW Hungary (Central Europe) using seismic methods. The research program comprised of two main fields: 1) 2D, 3D active seismic measurements 2) passive seismotectonic monitoring 1) Detailed 2D seismic reflection measurements were carried out along four profiles in the study area using 20 m geophone spacing with >100 folds in order to image the deep geological structure of the potential waste disposal site. Tomographic imaging of the reflection data along the four profiles was also carried out, whereas a 40 km long wide angle tomographic profile and a 50 square kilometers 3D tomography were performed in the prospective location. 2) Passive seismotectonic monitoring of the waste disposal site is also part of the program. 30 SP stations with continuous data recording (100 sps) are used to gather the seismic signals emerging from local tectonic activity in the 2000 square kilometers area so as to locate tectonically active zones in the region. The passive monitoring focuses on low (M< or =1) magnitude seismic signals that are expected from the study area.

  14. Metasomatized lithosphere and the origin of alkaline lavas.

    PubMed

    Pilet, Sébastien; Baker, Michael B; Stolper, Edward M

    2008-05-16

    Recycled oceanic crust, with or without sediment, is often invoked as a source component of continental and oceanic alkaline magmas to account for their trace-element and isotopic characteristics. Alternatively, these features have been attributed to sources containing veined, metasomatized lithosphere. In melting experiments on natural amphibole-rich veins at 1.5 gigapascals, we found that partial melts of metasomatic veins can reproduce key major- and trace-element features of oceanic and continental alkaline magmas. Moreover, experiments with hornblendite plus lherzolite showed that reaction of melts of amphibole-rich veins with surrounding lherzolite can explain observed compositional trends from nephelinites to alkali olivine basalts. We conclude that melting of metasomatized lithosphere is a viable alternative to models of alkaline basalt formation by melting of recycled oceanic crust with or without sediment.

  15. Lithosphere dynamics and continental deformation

    NASA Astrophysics Data System (ADS)

    Bird, Peter

    1995-07-01

    The unifying theme in this section is the remarkable weakness of major faults. I will consider the diverse new evidence for weakness, and the evidence for high pore pressure localized in faults as a fundamental cause. With this background one can better understand why faults remain active even after large rotations with respect to stress: I will look at large Neogene (≤23.7 million year old) rotations about horizontal axes in the Basin and Range province, and about vertical axes along the Pacific margin. Recent developments will be summarized from studies of Neogene tectonics (neotectonics) in California, Alaska, and the Mississippi embayment, in the context of a weak North American stress field that results mainly from topographic forces. To close, I will present new geophysical studies relevant to the continuing controversy over whether the basic structure of the North American mantle lithosphere was altered by an early Tertiary episode of flat subduction.

  16. Lithospheric flexure at fracture zones

    NASA Technical Reports Server (NTRS)

    Sandwell, D.; Schubert, G.

    1982-01-01

    Studies attempting to demonstrate that lithospheric flexure occurs across the Pioneer and Mendocino fracture zones, and that the flexural topography is a topographic expression at these fracture zones, are presented. The flexure is modelled and compared with predicted depths with five bathymetric profiles which cross the two fracture zones at different ages. The model uses a thin elastic plate overlying an incompressible fluid half-space, and incorporates a temperature-dependent effective elastic thickness. Several conclusions were derived from this study. First, it is found that no significant slip on the fossil fault planes of the Mendocino and Pioneer fracture zones exists. In addition, the flexural amplitude is determined to increase with age. Finally, it is concluded that there is elastic coupling between the Mendocino and Pioneer fracture zones since the separation is less than a flexural wavelength.

  17. Deformation in the continental lithosphere

    NASA Astrophysics Data System (ADS)

    The Physical Properties of Earth Materials Committee, a technical committee of AGU's Tectonophysics Section, is organizing a dinner/colloquium as part of the Fall Meeting in San Francisco, Calif. This event will be held Monday, December 3rd, in the Gold Rush Room of the Holiday Inn Golden Gateway Hotel at 1500 Van Ness St. There will be a no-host bar from 6:30 to 7:30 P.M., followed by dinner from 7:30 to 8:30 P.M. Paul Tapponnier will deliver the after-dinner talk, “Large-Scale Deformation Mechanisms in the Continental Lithosphere: Where Do We Stand?” It will start at 8:30 P.M. and a business meeting will follow at 9:30 P.M.

  18. Dynamic topography as constraints on stress and viscosity in the mantle and lithosphere

    NASA Astrophysics Data System (ADS)

    Zhong, S.

    2015-12-01

    Pas, and convection-induced lithospheric stress is unlikely to exceed 200 MPa (i.e., the yield stress for plate interiors). I will discuss the general implications of the results for mantle dynamics including dynamic generation of plate tectonics and the nature of mantle structures (i.e., slabs and plumes) as imaged seismically.

  19. Rheology of the lithosphere: selected topics.

    USGS Publications Warehouse

    Kirby, S.H.; Kronenberg, A.K.

    1987-01-01

    Reviews recent results concerning the rheology of the lithosphere with special attention to the following topics: 1) the flexure of the oceanic lithosphere, 2) deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins, 3) the rheological stratification of the continents, 4) strain localization and shear zone development, and 5) strain-induced crystallographic preferred orientations and anisotropies in body-wave velocities. We conclude with a section citing the 1983-1986 rock mechanics literature by category.-Authors

  20. Rifting Thick Lithosphere - Canning Basin, Western Australia

    NASA Astrophysics Data System (ADS)

    Czarnota, Karol; White, Nicky

    2016-04-01

    The subsidence histories and architecture of most, but not all, rift basins are elegantly explained by extension of ~120 km thick lithosphere followed by thermal re-thickening of the lithospheric mantle to its pre-rift thickness. Although this well-established model underpins most basin analysis, it is unclear whether the model explains the subsidence of rift basins developed over substantially thick lithosphere (as imaged by seismic tomography beneath substantial portions of the continents). The Canning Basin of Western Australia is an example where a rift basin putatively overlies lithosphere ≥180 km thick, imaged using shear wave tomography. Subsidence modelling in this study shows that the entire subsidence history of the <300 km wide and <6 km thick western Canning Basin is adequately explained by mild Ordovician extension (β≈1.2) of ~120 km thick lithosphere followed by post-rift thermal subsidence. This is consistent with the established model, described above, albeit with perturbations due to transient dynamic topography support which are expressed as basin-wide unconformities. In contrast the <150 km wide and ~15 km thick Fitzroy Trough of the eastern Canning Basin reveals an almost continuous period of normal faulting between the Ordovician and Carboniferous (β<2.0) followed by negligible post-rift thermal subsidence. These features cannot be readily explained by the established model of rift basin development. We attribute the difference in basin architecture between the western and eastern Canning Basin to rifting of thick lithosphere beneath the eastern part, verified by the presence of ~20 Ma diamond-bearing lamproites intruded into the basin depocentre. In order to account for the observed subsidence, at standard crustal densities, the lithospheric mantle is required to be depleted in density by 50-70 kg m-3, which is in line with estimates derived from modelling rare-earth element concentrations of the ~20 Ma lamproites and global isostatic

  1. Yellowstone hotspot-continental lithosphere interaction

    NASA Astrophysics Data System (ADS)

    Jean, Marlon M.; Hanan, Barry B.; Shervais, John W.

    2014-03-01

    The Snake River Plain represents 17 m.y. of volcanic activity that took place as the North American continent migrated over a relatively fixed magma source, or hotspot. We present new Pb, Sr, and Nd data for a suite of 25 basalts collected from Western and Central Snake River Plain (SRP). The new isotope data, combined with previously published data from the SRP, provide a traverse of the Wyoming craton margin, from the 87Sr/86Sr = 0.706 line boundary of western SRP with Phanerozoic accreted terranes, east through the central and eastern SRP, to the Yellowstone Plateau. Low-K basalts from the western SRP, overlain by high-K basalts, provide a temporal record of regional source variation from ∼16.8 to 0.2 Ma. Principal Component Analysis (PCA) of the new and previously published SRP basalt Pb isotopes reveals that >97% of the total variability is accounted for by mixing between three end-members and is consistent with a sublithospheric Yellowstone hotspot mantle source with a radiogenic isotope composition similar to the mantle source of the early Columbia River Basalt Group (CRBG) and two continental lithosphere end-members, heterogeneous in age and composition. We use the SRP Pb, Sr, and Nd isotope data to model the Yellowstone Hotspot-continental lithosphere interaction by three component mixing between two continental lithospheric components, Archean lithosphere (CL1) that represents older lithosphere underlying the Yellowstone Plateau in the east, and Paleoproterozoic lithosphere (CL2) representing the younger lithosphere underlying the SRP in the west near the craton margin, and a sublithospheric end-member, representing the Yellowstone hotspot (PL). The results suggest a continuous flow of PL material westward as the NA continental lithosphere migrated over the upwelling hotspot along a shoaling gradient in the sub-continental mantle lithosphere. The model shows a decrease in Total Lithosphere end-members (CL1 + CL2) and the Lithosphere Ratio (CL1/CL2

  2. Estimates of radioxenon released from Southern Hemisphere medical isotope production facilities using measured air concentrations and atmospheric transport modeling.

    PubMed

    Eslinger, Paul W; Friese, Judah I; Lowrey, Justin D; McIntyre, Justin I; Miley, Harry S; Schrom, Brian T

    2014-09-01

    The International Monitoring System (IMS) of the Comprehensive-Nuclear-Test-Ban-Treaty monitors the atmosphere for radioactive xenon leaking from underground nuclear explosions. Emissions from medical isotope production represent a challenging background signal when determining whether measured radioxenon in the atmosphere is associated with a nuclear explosion prohibited by the treaty. The Australian Nuclear Science and Technology Organisation (ANSTO) operates a reactor and medical isotope production facility in Lucas Heights, Australia. This study uses two years of release data from the ANSTO medical isotope production facility and (133)Xe data from three IMS sampling locations to estimate the annual releases of (133)Xe from medical isotope production facilities in Argentina, South Africa, and Indonesia. Atmospheric dilution factors derived from a global atmospheric transport model were used in an optimization scheme to estimate annual release values by facility. The annual releases of about 6.8 × 10(14) Bq from the ANSTO medical isotope production facility are in good agreement with the sampled concentrations at these three IMS sampling locations. Annual release estimates for the facility in South Africa vary from 2.2 × 10(16) to 2.4 × 10(16) Bq, estimates for the facility in Indonesia vary from 9.2 × 10(13) to 3.7 × 10(14) Bq and estimates for the facility in Argentina range from 4.5 × 10(12) to 9.5 × 10(12) Bq.

  3. Estimates of Radioxenon Released from Southern Hemisphere Medical isotope Production Facilities Using Measured Air Concentrations and Atmospheric Transport Modeling

    SciTech Connect

    Eslinger, Paul W.; Friese, Judah I.; Lowrey, Justin D.; McIntyre, Justin I.; Miley, Harry S.; Schrom, Brian T.

    2014-09-01

    Abstract The International Monitoring System (IMS) of the Comprehensive-Nuclear-Test-Ban-Treaty monitors the atmosphere for radioactive xenon leaking from underground nuclear explosions. Emissions from medical isotope production represent a challenging background signal when determining whether measured radioxenon in the atmosphere is associated with a nuclear explosion prohibited by the treaty. The Australian Nuclear Science and Technology Organisation (ANSTO) operates a reactor and medical isotope production facility in Lucas Heights, Australia. This study uses two years of release data from the ANSTO medical isotope production facility and Xe-133 data from three IMS sampling locations to estimate the annual releases of Xe-133 from medical isotope production facilities in Argentina, South Africa, and Indonesia. Atmospheric dilution factors derived from a global atmospheric transport model were used in an optimization scheme to estimate annual release values by facility. The annual releases of about 6.8×1014 Bq from the ANSTO medical isotope production facility are in good agreement with the sampled concentrations at these three IMS sampling locations. Annual release estimates for the facility in South Africa vary from 1.2×1016 to 2.5×1016 Bq and estimates for the facility in Indonesia vary from 6.1×1013 to 3.6×1014 Bq. Although some releases from the facility in Argentina may reach these IMS sampling locations, the solution to the objective function is insensitive to the magnitude of those releases.

  4. Horizontal stresses induced by vertical processes in planetary lithospheres

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.

    1993-01-01

    Understanding the state of stress in the elastic lithosphere is of fundamental importance for planetary geophysics, as it is the link between the observed geologic structures on the surface and the processes which form and modify these structures. As such, it can provide valuable constraints for the difficult problem of determining interior structure and processes. On the Earth, most large scale, organized deformation can be related to lateral tectonics associated with plate dynamics; however, the tectonics on many extraterrestrial bodies (such as the Moon, Mars, and most of the outer-planet satellites) appears to be primarily vertical in nature, and the horizontal stresses induced by vertical motions and loads are expected to dominate the deformation of their lithospheres. The largest stress contributions from vertical loading come from the flexure of the lithosphere, which induces both bending moments and membrane stresses. We are concerned here only with nonflexural changes in the state of stress induced by processes such as sedimentary and volcanic deposition, erosional denudation, and changes in the thermal gradient that induce uplift or subsidence. This analysis is important both for evaluating stresses for specific regions in which the vertical stress history can be estimated, as well as for applying the proper loading conditions to global stress models. It is also of interest for providing a reference state of stress for interpreting stress measurements in the crust of the Earth.

  5. Lithosphere structure underneath the North China Craton inferred from elevation, gravity and geoid anomalies

    NASA Astrophysics Data System (ADS)

    Wang, K.

    2015-12-01

    The North China Craton (NCC) is a classical example of ancient destroyed cratons. The NCC experienced widespread thermotectonic reactivations in the Phanerozoic. Recent work suggested that the old craton has been significantly modified or destroyed during this process. However, most of the studies were confined to the Eastern NCC, the nature and evolution of the lithosphere beneath the Central and Western NCC was less constrained due to the lack of data. While, recent geodetic data, with the advantages of high resolution and coverage, offers an opportunity to study the deep structure underneath the whole NCC. Here we construct a lithospheric-scale 3D model based on the integration of regional elevation, gravity, geoid and thermal data together with available seismic data. The combined interpretation of these data provides information on the density and temperature distribution at different depth ranges. In the Eastern NCC, a rapid thickness decrease of both crust and lithosphere is reflected, concordant with abrupt changes in surface topography and Bouguer gravity anomaly. Our results together with the widespread magmatic rocks suggest that the Eastern NCC has experienced significant destruction of the lithospheric mantle with substantial modifications and thinning of the crust. In the Central and Western NCC, the generally thick and 'cold' lithosphere suggests that the cratonic mantle root is preserved in the central and western NCC, in agreement with the relatively low heat flow, rare magmatic activity and long-term tectonic stability observed at the surface, with some areas mildly modified as indicated by thin lithosphere.

  6. Seismic Migration Imaging of the Lithosphere beneath the Afar Rift System, East Africa

    NASA Astrophysics Data System (ADS)

    Lee, T. T. Y.; Chen, C. W.; Rychert, C.; Harmon, N.

    2015-12-01

    The Afar Rift system in east Africa is an ideal natural laboratory for investigating the incipient continental rifting, an essential component of plate tectonics. The Afar Rift is situated at the triple junction of three rifts, namely the southern Red Sea Rift, Gulf of Aden Rift and Main Ethiopian Rift (MER). The ongoing continental rifting at Afar transitions to seafloor spreading toward the southern Red Sea. The tectonic evolution of Afar is thought to be influenced by a mantle plume, but how the plume affects and interacts with the Afar lithosphere remains elusive. In this study, we use array seismic data to produce high-resolution migration images of the Afar lithosphere from scattered teleseismic wavefields to shed light on the lithospheric structure and associated tectonic processes. Our preliminary results indicate the presence of lithospheric seismic discontinuities with depth variation across the Afar region. Beneath the MER axis, we detect a pronounced discontinuity at 55 km depth, characterized by downward fast-to-slow velocity contrast, which appears to abruptly deepen to 75 km depth to the northern flank of MER. This discontinuity may be interpreted as the lithosphere-asthenosphere boundary. Beneath the Ethiopian Plateau, on the other hand, a dipping structure with velocity increase is identified at 70-90 km depth. Further synthesis of observations from seismic tomography, receiver functions, and seismic anisotropy in the Afar region will offer better understanding of tectonic significance of the lithospheric discontinuities.

  7. A sharp lithosphere-asthenosphere boundary imaged beneath eastern North America.

    PubMed

    Rychert, Catherine A; Fischer, Karen M; Rondenay, Stéphane

    2005-07-28

    Plate tectonic theory hinges on the concept of a relatively rigid lithosphere moving over a weaker asthenosphere, yet the nature of the lithosphere-asthenosphere boundary remains poorly understood. The gradient in seismic velocity that occurs at this boundary is central to constraining the physical and chemical properties that create differences in mechanical strength between the two layers. For example, if the lithosphere is simply a thermal boundary layer that is more rigid owing to colder temperatures, mantle flow models indicate that the velocity gradient at its base would occur over tens of kilometres. In contrast, if the asthenosphere is weak owing to volatile enrichment or the presence of partial melt, the lithosphere-asthenosphere boundary could occur over a much smaller depth range. Here we use converted seismic phases in eastern North America to image a very sharp seismic velocity gradient at the base of the lithosphere-a 3-11 per cent drop in shear-wave velocity over a depth range of 11 km or less at 90-110 km depth. Such a strong, sharp boundary cannot be reconciled with a purely thermal gradient, but could be explained by an asthenosphere that contains a few per cent partial melt or that is enriched in volatiles relative to the lithosphere.

  8. The Arctic lithosphere: an overview

    NASA Astrophysics Data System (ADS)

    Drachev, S.; Pease, V.; Stephenson, R.

    2012-04-01

    The Arctic is comprised of three deepwater oceanic basins, the Norwegian-Greenland, Eurasia, and Amerasia basins, surrounded by continental masses of the Achaean to Early Proterozoic North American, Baltica and Siberian cratons and intervening Neoproterozoic and Phanerozoic fold belts. Though the tectonic history of the Arctic continental realm spans almost three billions of years, the formation of the Arctic began with the creation of Pangaea-II supercontinent at end of Permian epoch. Between 250 and 150 Ma the Proto-Arctic was represented by the Anyui Ocean, or Angayuchum Sea - a Paleo-Pacific embayment into Pangaea II. During the Mesozoic Pangaea II was destroyed and the Anyi Ocean was isolated from the Paleo-Pacific, finally leading to the separation of Arctic Alaska-Chukchi Microcontinent from the North American side of Laurasia; the collision of this microplate with the Siberian margin occurred at ca. 125 Ma in association with the opening of the Canada Basin. The final stage of the Arctic formation took place in the Cenozoic, and was related to the propagation of the divergent Atlantic lithospheric plate boundary between North America and Baltica with the separation of the Lomonosov continental sliver from the Eurasian margin and opening of the Eurasia oceanic basin between 56 and 0 Ma. The present-day Arctic, especially its shelves and oceanic basins, is one of the least studied places on the Earth. Though we know the geology of the surrounding continental masses, there are still many questions remaining about major lithospheric divides beneath the Arctic seas, such as: • Where are the plate boundaries associated with the Amerasia Basin? • How and when did the Canada Basin open? • What was the pre-drift setting of the Chukchi Borderland? • Which tectonic processes formed the East Siberian shelves? • How and when did the major ridges in the Amerasia Basin form? • Where are the Early Tertiary plate boundaries in the Arctic? • What is the

  9. Intraplate Seismicity and Lithospheric Strength as Inferred from 3D Seismic Models

    NASA Astrophysics Data System (ADS)

    Mooney, W. D.; Pollitz, F. F.; Ritsema, J.

    2014-12-01

    Focal mechanism studies and other stress indicators indicate that intraplate earthquakes in central and eastern North America are consistent with an ENE-WSW compressive stress field that acts on existing faults. Here we argue that either locally thinned lithosphere (as beneath the Reelfoot Rift, central US) or regional lithospheric thinning (as beneath the edge of the North American craton or the rifted continental margin) constitutes zones of relatively low lithospheric strength where crustal strain accumulates. We use seismic surface waves to determine the 3D shear-wave seismic velocity structure of the lithosphere, and find that the Reelfoot Rift is underlain by a zone with low mantle seismic velocities that extends to at least 200 km depth. Thus, the Reelfoot Rift, which hosts the New Madrid Seismic Zone, is unique among North American paleo-rifts in term of the properties in the mantle. We hypothesize that this low-velocity mantle volume is weaker than its surroundings and that the Reelfoot Rift consequently has relatively lower elastic plate thickness that would tend to concentrate tectonic stress within this zone. On a continental scale, the 3D velocity model clearly identifies an approximately 220-km-thick, high seismic velocity lithospheric root beneath the North America craton which has a low rate of crustal seismicity and very few events with Mw≥6. We attribute the relatively aseismic nature of the craton to dry, cold conditions within the cratonic lower crust and mantle lithosphere. Conversely, we find that a high proportion of intraplate events are concentrated around the pronounced lateral gradient in lithospheric thickness that surrounds the craton. We attribute this observation to a lateral decrease in lithospheric strength at the edge of the North American craton. This relationship between intraplate seismicity and lithospheric properties is apparent in maps that compare regional and continental lithospheric thickness with crustal seismicity. We

  10. Lithospheric layering in the North American craton.

    PubMed

    Yuan, Huaiyu; Romanowicz, Barbara

    2010-08-26

    How cratons-extremely stable continental areas of the Earth's crust-formed and remained largely unchanged for more than 2,500 million years is much debated. Recent studies of seismic-wave receiver function data have detected a structural boundary under continental cratons at depths too shallow to be consistent with the lithosphere-asthenosphere boundary, as inferred from seismic tomography and other geophysical studies. Here we show that changes in the direction of azimuthal anisotropy with depth reveal the presence of two distinct lithospheric layers throughout the stable part of the North American continent. The top layer is thick ( approximately 150 km) under the Archaean core and tapers out on the surrounding Palaeozoic borders. Its thickness variations follow those of a highly depleted layer inferred from thermo-barometric analysis of xenoliths. The lithosphere-asthenosphere boundary is relatively flat (ranging from 180 to 240 km in depth), in agreement with the presence of a thermal conductive root that subsequently formed around the depleted chemical layer. Our findings tie together seismological, geochemical and geodynamical studies of the cratonic lithosphere in North America. They also suggest that the horizon detected in receiver function studies probably corresponds to the sharp mid-lithospheric boundary rather than to the more gradual lithosphere-asthenosphere boundary.

  11. Unstable extension of Enceladus' lithosphere

    NASA Astrophysics Data System (ADS)

    Bland, Michael T.; Beyer, Ross A.; Showman, Adam P.

    2007-12-01

    Regions near Enceladus' equator, Sarandib and Diyar Planitia, contain extensive sets of parallel ridges and troughs that may be diagnostic of the region's formation conditions. We present photoclinometry profiles across these ridges and troughs, which indicate that they are periodic, low-slope features with dominant wavelengths of 3 to 4 km and amplitudes between 100 and 400 m. The morphology of these terrains is consistent with formation via unstable extension of the lithosphere. Our numerical modeling demonstrates that unstable extension can generate large-scale topography under Enceladus-like conditions. Comparison of our photoclinometry profiles with the dominant wavelengths produced by our numerical model permits estimation of the background heat flow at the time the Sarandib-Diyar province formed. We estimate heat flows of 110 to 220mWm, suggesting that resurfacing of the planitiae was accompanied by strong, localized heating. The extension necessary to produce the ridges and troughs may have been caused by now-inactive diapirs, internal phase changes, or other mechanisms. Our heat flux estimates imply elastic thickness at the time of resurfacing of 0.4 to 1.4 km, which are sufficient to have allowed satellite reorientation if the province was underlain by a low-density region. It is therefore plausible that Enceladus has experienced multiple heating events, each leading to localized resurfacing and global reorientation.

  12. Seismic evidence for the layered mantle lithosphere: a comparsion between Zagros and South Africa

    NASA Astrophysics Data System (ADS)

    Sodoudi, Forough; Kind, Rainer

    2014-05-01

    Recent S receiver function studies present evidence for the existence of the layered mantle lithosphere beneath ancient cratons. However, the nature of these layers is still unclear. They can be attributed to the presence of accumulated melts, remnants of subduction interfaces, changes in anisotropic properties or fluids. Further characterization of these layers is needed to provide more insights into the assembly and evolution of cratons. Here we compare the mantle lithosphere of the ancient Kalahari craton with the relatively young mantle lithosphere of Zagros, which is assumed as the location of the future craton. We applied the S receiver function method to map the internal layering of the lithosphere and to image its lower limit. For this aim, we used teleseismic events recorded at 97 seismic stations within the Kalahari craton and those recorded at 61 permanent seismic stations in Iran. Our results reveal a thick and stratified mantle lithosphere beneath the Kalahari craton containing three significant negative velocity contrasts at 85, 150-200, and 260-280 km depth. Moreover, they imply that frozen-in anisotropy as well as notable compositional variations can lead to sharp Mid-Lithospheric Discontinuities (MLD) that can be clearly observed in the SRF data. We show that a 50 km thick anisotropic layer just below the Moho boundary with 3% S wave anisotropy may be responsible for producing a MLD at 85 km depth. The horizontal anisotropy in the upper lithosphere may be attributed to processes during the formation of the Kalahari Craton. Furthermore, significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second layer led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The largest velocity contrast (3.6-4.7%) is observed at a boundary located at

  13. Electromagnetic Studies Of The Lithosphere And Asthenosphere

    NASA Astrophysics Data System (ADS)

    Heinson, Graham

    In geodynamic models of the Earth's interior, the lithosphere and asthenosphere are defined in terms of their rheology. Lithosphere has high viscosity, and can be divided into an elastic region at temperatures below 350 °C and an anelastic region above 650 °C. Beneath the lithosphere lies the ductile asthenosphere, with one- to two-orders of magnitude lower viscosity. Asthenosphere represents the location in the mantle where the melting point (solidus) is most closely approached, and sometimes intersected. Seismic, gravity and isostatic observations provide constraints on lithosphere-asthenosphere structure in terms of shear-rigidity, density and viscosity, which are all rheological properties. In particular, seismic shear- and surface-wave analyses produce estimates of a low-velocity zone (LVZ) asthenosphere at depths comparable to the predicted rheological transitions. Heat flow measurements on the ocean floor also provide a measure of the thermal structure of the lithosphere.Electromagnetic (EM) observations provide complementary information on lithosphere-asthenosphere structure in terms of electrical conductivity. Laboratory studies of mantle minerals show that EM observations are very sensitive to the presence of melt or volatiles. A high conductivity zone (HCZ) in the upper mantle therefore represents an electrical asthenosphere (containing melt and/or volatile) that may be distinct from a rheological asthenosphere and the LVZ. Additionally, the vector propagation of EM fields in the Earth provides information on anisotropic conduction in the lithosphere and asthenosphere. In the last decade, numerous EM studies have focussed on the delineation of an HCZ in the upper mantle, and the determination of melt/volatile fractions and the dynamics of the lithosphere-asthenosphere. Such HCZs have been imaged under a variety of tectonic zones, including mid-ocean ridges and continental rifts, but Archaean shields show little evidence of an HCZ, implying that the

  14. Permeability Barrier Generation in the Martian Lithosphere

    NASA Astrophysics Data System (ADS)

    Schools, Joe; Montési, Laurent

    2015-11-01

    Permeability barriers develop when a magma produced in the interior of a planet rises into the cooler lithosphere and crystallizes more rapidly than the lithosphere can deform (Sparks and Parmentier, 1991). Crystallization products may then clog the porous network in which melt is propagating, reducing the permeability to almost zero, i.e., forming a permeability barrier. Subsequent melts cannot cross the barrier. Permeability barriers have been useful to explain variations in crustal thickness at mid-ocean ridges on Earth (Magde et al., 1997; Hebert and Montési, 2011; Montési et al., 2011). We explore here under what conditions permeability barriers may form on Mars.We use the MELTS thermodynamic calculator (Ghiorso and Sack, 1995; Ghiorso et al., 2002; Asimow et al., 2004) in conjunction with estimated Martian mantle compositions (Morgan and Anders, 1979; Wänke and Dreibus, 1994; Lodders and Fegley, 1997; Sanloup et al., 1999; Taylor 2013) to model the formation of permeability barriers in the lithosphere of Mars. In order to represent potential past and present conditions of Mars, we vary the lithospheric thickness, mantle potential temperature (heat flux), oxygen fugacity, and water content.Our results show that permeability layers can develop in the thermal boundary layer of the simulated Martian lithosphere if the mantle potential temperature is higher than ~1500°C. The various Martian mantle compositions yield barriers in the same locations, under matching variable conditions. There is no significant difference in barrier location over the range of accepted Martian oxygen fugacity values. Water content is the most significant influence on barrier development as it reduces the temperature of crystallization, allowing melt to rise further into the lithosphere. Our lower temperature and thicker lithosphere model runs, which are likely the most similar to modern Mars, show no permeability barrier generation. Losing the possibility of having a permeability

  15. Tracing lithosphere amalgamation through time: chemical geodynamics of sub-continental lithospheric mantle

    NASA Astrophysics Data System (ADS)

    Wittig, Nadine

    2014-05-01

    of Re-Os isotope dating of cratonic peridotites. Empiric mineralogical and geochemical data of continental and oceanic lithospheric mantle has been examined extensively and metasomatism has been studied in great detail. I will present a numerical modelling approach generating a comprehensive catalogue of variously depleted plagioclase-, spinel- and garnet-peridotite major and trace element compositions. In addition primary Pb, Sr, Nd, Hf and Os isotope data will approximate refractory mantle generated during Earth's major episodes of depletion and continental crust formation (1.2, 1.8, 2.9, 3.8 Ga). These hypothetical compositions will be compared to natural peridotites from on- and off-cratonic xenoliths, abyssal and orogenic peridotites to identify those rare samples least altered by interaction with silicate, hydrous and carbonatitic melts. Extremely depleted mantle has the potential to harbour Pb, Sr, Nd, Hf and Os isotope compositions that would be easily recognized if silicate melts were generated from this type of pristine mantle and the record of volcanic rocks will be examined to identify potential lithospheric melts.

  16. A Multi-Layer Phoswich Radioxenon Detection System, Reporting Period 07/01/07 - 09/30/07

    SciTech Connect

    David M. Hamby

    2007-10-25

    previous simulations, to confirm convergence of the solutions provided by our software methods. We have initiated our investigation into the radon signature expected in our XEPHWICH system. We intend to utilize this signature to confirm earth movement, in the event of an underground nuclear explosion, by continuously monitoring radon levels and noting increases in radon concentration in conjunction with increased levels of radioxenons. The research group is also designing and constructing a fission chamber to be used for the collection of radioxenon gases following neutron bombardment of HEU in the Oregon State University TRIGA reactor. To this point, we have completed milling the aluminum housing and have modeled fission product nuclide production associated with the fissioning of HEU. Additionally, the students have been busy compiling the appropriate information in preparation for irradiation approvals. Using beta spectra of three initial nuclides collected on the prototype phoswich detector, spectral identification by a preliminary neural network was compared to that of solvers of a linear system of equations. Pre-processing in areas such as smoothing and endpoint identification is also being investigated as a means of improving spectral identification.

  17. New Seismic Observables Constrain Structure within the Continental Lithosphere

    NASA Astrophysics Data System (ADS)

    Cunningham, E. E.; Lekic, V.

    2014-12-01

    The origin and stability of the continental lithosphere play a fundamental role in plate tectonics and enable the survival of Archean crust over billions of years. Recent advances in seismic data and imaging have revealed a velocity drop with depth within continental cratons too shallow to be interpreted as the lithosphere asthenosphere boundary (Rychert and Shearer 2009). The significance of this "mid lithospheric discontinuity" (MLD) - or multiple MLDs as suggested recently (Lekic & Fischer, 2013) - is not fully understood, and its implications for continental formation and stability are only beginning to be explored. Discrepancies call for both improving the constraints on the nature of the MLD, and relating these observations to tectonic setting and deformation history. The extensive coverage of the EarthScope USArray presents an unprecedented opportunity to systematically map the structure of the continental lithosphere. We use receiver functions (RFs) to isolate converted phases (Ps or Sp) produced across velocity discontinuities beneath a seismometer, and thereby constrain vertical density and seismic velocity variations. We show that at some stations, the apparent velocity contrast across the MLD demonstrates a dependence on seismic wave frequency, being greater at low frequencies than at high frequencies. This suggests that the MLD - at least in certain locations - is distributed across tens of kilometers in depth. The gradient of the MLD fingerprints physical process at play; a weak gradient indicates thermal origin, while an abrupt discontinuity implicates change in composition or partial melting. Furthermore, we map the strength, depth, and ratio of amplitudes of waves converted across the MLD and the Moho throughout the US. Because these receiver function based measurements only reveal relative velocity variations with depth, we combine them with frequency-dependent measurements of apparent incidence angles of P and S waves. Doing so allows us to

  18. Observational Constraints on Lithospheric Rheology and Their Implications for Lithospheric Dynamics and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Zhong, S.; Watts, A. B.

    2014-12-01

    Lithospheric rheology and strength are important for understanding crust and lithosphere dynamics, and the conditions for plate tectonics. Laboratory studies suggest that lithospheric rheology is controlled by frictional sliding, semi-brittle, low-temperature plasticity, and high-temperature creep deformation mechanisms as pressure and temperature increase from shallow to large depths. Although rheological equations for these deformation mechanisms have been determined in laboratory settings, it is necessary to validate them using field observations. Here we present an overview of lithospheric rheology constrained by observations of seismic structure and load-induced flexure. Together with mantle dynamic modeling, rheological equations for high-temperature creep derived from laboratory studies (Hirth and Kohlstedt, 2003; Karato and Jung, 2003) satisfactorily explain the seismic structure of the Pacific upper mantle (Hunen et al., 2005) and Hawaiian swell topography (Asaadi et al., 2011). In a recent study that compared modeled surface flexure and stress induced by volcano loads in the Hawaiian Islands region with the observed flexure and seismicity, Zhong and Watts (2013) showed that the coefficient of friction is between 0.25 and 0.7, and is consistent with laboratory studies and also in-situ borehole measurements. However, this study indicated that the rheological equation for the low-temperature plasticity from laboratory studies (e.g., Mei et al., 2010) significantly over-predicts lithospheric strength and viscosity. Zhong and Watts (2013) also showed that the maximum lithospheric stress beneath Hawaiian volcano loads is about 100-200 MPa, which may be viewed as the largest lithospheric stress in the Earth's lithosphere. We show that the relatively weak lithospheric strength in the low-temperature plasticity regime is consistent with seismic observation of reactivated mantle lithosphere in the western US and the eastern North China. We discuss here the causes

  19. Continental growth by successive accretion of oceanic lithosphere: Evidence from tilted seismic anisotropy

    NASA Astrophysics Data System (ADS)

    Babuska, V.; Plomerova, J.; Karato, S. I.

    2012-04-01

    Although many studies indicate that subduction-related accretion, subduction-driven magmatism and tectonic stacking are major crustal-growth mechanisms, how the mantle lithosphere forms remains enigmatic. Cook (AGU Geod. Series 1986) published a model of continental 'shingling' based on seismic reflection data indicating dipping structures in the deep crust of accreted terranes. Helmstaedt and Gurney (J. Geoch. Explor. 1995) and Hart et al. (Geology 1997) suggest that the Archean continental lithosphere consists of alternating layers of basalt and peridotite derived from subducted and obducted Archean oceanic lithosphere. Peridotite xenoliths from the Mojavian mantle lithosphere (Luffi et al., JGR 2009), as well as xenoliths of eclogites underlying the Sierra Nevada batholith in California (Horodynskij et al., EPSL 2007), are representative for oceanic slab fragments successively attached to the continent. Recent seismological findings also seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or by stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Aust. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- (or D-) type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered almost a half century ago (Hess, Nature 1964). Though it is difficult to determine seismic anisotropy within an active subducting slab (e.g., Healy et al., EPSL 2009; Eberhart-Phillips and Reyners, JGR 2009), field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved there to a depth of at least 200-300 km. Dipping anisotropic fabrics in domains of the European mantle lithosphere were interpreted as systems of 'frozen' paleosubductions (Babuska and Plomerova, PEPI 2006), and the lithosphere base as a boundary between a fossil anisotropy in the

  20. Lithospheric buoyancy and continental intraplate stresses

    USGS Publications Warehouse

    Zoback, M.L.; Mooney, W.D.

    2003-01-01

    Lithospheric buoyancy, the product of lithospheric density and thickness, is an important physical property that influences both the long-term stability of continents and their state of stress. We have determined lithospheric buoyancy by applying the simple isostatic model of Lachenbruch and Morgan (1990). We determine the crustal portion of lithospheric buoyancy using the USGS global database of more than 1700 crustal structure determinations (Mooney et al., 2002), which demonstrates that a simple relationship between crustal thickness and surface elevation does not exist. In fact, major regions of the crust at or near sea level (0-200 m elevation) have crustal thicknesses that vary between 25 and 55 km. Predicted elevations due to the crustal component of buoyancy in the model exceed observed elevations in nearly all cases (97% of the data), consistent with the existence of a cool lithospheric mantle lid that is denser than the asthenosphere on which it floats. The difference between the observed and predicted crustal elevation is assumed to be equal to the decrease in elevation produced by the negative buoyancy of the mantle lid. Mantle lid thickness was first estimated from the mantle buoyancy and a mean lid density computed using a basal crust temperature determined from extrapolation of surface heat flow, assuming a linear thermal gradient in the mantle lid. The resulting values of total lithosphere thickness are in good agreement with thicknesses estimated from seismic data, except beneath cratonic regions where they are only 40-60% of the typical estimates (200-350 km) derived from seismic data. This inconsistency is compatible with petrologic data and tomography and geoid analyses that have suggested that cratonic mantle lids are ??? 1% less dense than mantle lids elsewhere. By lowering the thermally determined mean mantle lid density in cratons by 1%, our model reproduces the observed 200-350+ km cratonic lithospheric thickness. We then computed

  1. Insolation driven variations of Mercury's lithospheric strength

    NASA Astrophysics Data System (ADS)

    Williams, Jean-Pierre; Ruiz, Javier; Rosenburg, Margaret A.; Aharonson, Oded; Phillips, Roger J.

    2011-01-01

    Mercury's coupled 3:2 spin-orbit resonance in conjunction with its relatively high eccentricity of ˜0.2 and near-zero obliquity results in both a latitudinal and longitudinal variation in annual average solar insolation and thus equatorial hot and cold regions. This results in an asymmetric temperature distribution in the lithosphere and a long wavelength lateral variation in lithosphere structure and strength that mirrors the insolation pattern. We employ a thermal evolution model for Mercury generating strength envelopes of the lithosphere to demonstrate and quantify the possible effects the insolation pattern has on Mercury's lithosphere. We find the heterogeneity in lithosphere strength is substantial and increases with time. We also find that a crust thicker than that of the Moon or Mars and dry rheologies for the crust and mantle are favorable when compared with estimates of brittle-ductile transition depths derived from lobate scarps. Regions of stronger and weaker compressive strength imply that the accommodation of radial contraction of Mercury as its interior cooled, manifest as lobate scarps, may not be isotropic, imparting a preferential orientation and distribution to the lobate scarps.

  2. Magnetic mineralogy of the Mercurian lithosphere

    NASA Astrophysics Data System (ADS)

    Strauss, B. E.; Feinberg, J. M.; Johnson, C. L.

    2016-11-01

    Mercury and Earth are the only inner solar system planets with active, internally generated dynamo magnetic fields. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission recently detected magnetic fields on Mercury that are consistent with lithospheric magnetization. We investigate the physical and chemical environment of Mercury's lithosphere, past and present, to establish the conditions under which magnetization may have been acquired and modified. Three factors are particularly crucial to the determination of crustal composition and iron mineralogy: redox conditions in the planet's crust and mantle, the iron content of the lithosphere, and, for any remanent magnetization, the temperature profile of the lithosphere and its evolution over time. We explore potential mechanisms for remanence acquisition and alteration on Mercury, whose surface environment is both hot and highly reducing. The long-term thermal history of Mercury's crust plays an important role in the longevity of any remanent crustal magnetization, which may be subject to remagnetization through thermal, viscous, and shock mechanisms. This thermal and compositional framework is used both to constrain plausible candidate minerals that could carry magnetic remanence on Mercury and to evaluate their capacity to acquire and retain sufficient magnetization to be detectable from satellite orbit. We propose that iron metal and its alloys are likely to be the dominant contributors to induced and remanent magnetization in Mercury's lithosphere, with additional contributions from iron silicides, sulfides, and carbides.

  3. Inelastic models of lithospheric stress - I. Theory and application to outer-rise plate deformation

    USGS Publications Warehouse

    Mueller, S.; Choy, G.L.; Spence, W.

    1996-01-01

    Outer-rise stress distributions determined in the manner that mechanical engineers evaluate inelastic stress distributions within conventional materials are contrasted with those predicted using simple elastic-plate models that are frequently encountered in studies of outer-rise seismicity. This comparison indicates that the latter are inherently inappropriate for studies of intraplate earthquakes, which are a direct manifestation of lithospheric inelasticity. We demonstrate that the common practice of truncating elastically superimposed stress profiles so that they are not permitted to exceed laboratory-based estimates of lithospheric yield strength will result in an accurate characterization of lithospheric stress only under relatively restrictive circumstances. In contrast to elastic-plate models, which predict that lithospheric stress distributions depend exclusively upon the current load, inelastic plate models predict that stress distributions are also significantly influenced by the plate-loading history, and, in many cases, this influence is the dominant factor in determining the style of potential seismicity (e.g. thrust versus normal faulting). Numerous 'intuitive' interpretations of outer-rise earthquakes have been founded upon the implicit assumption that a unique relationship exists between a specified combination of plate curvature and in-plane force, and the resulting lithospheric stress distribution. We demonstrate that the profound influence of deformation history often invalidates such interpretations. Finally, we examine the reliability of 'yield envelope' representations of lithospheric strength that are constructed on the basis of empirically determined frictional sliding relationships and silicate plastic-flow laws. Although representations of this nature underestimate the strength of some major interplate faults, such as the San Andreas, they appear to represent a reliable characterization of the strength of intraplate oceanic lithosphere.

  4. Lithospheric structure in the Pacific geoid

    NASA Technical Reports Server (NTRS)

    Marsh, B. D.; Hinojosa, J. H.

    1985-01-01

    The high degree and order SEASAT geoid in the central Pacific correlates closely with the structure of the cooling lithosphere. Relative changes in plate age across major fracture zones in relatively young seafloor frame the east-west trending pattern formed by the geoid anomalies. The field removal in bathymetry corresponds to removal of some of the low degree and order geoidal components, the step like structure across fracture zones is also removed. The regional thermal subsidence was removed from the bathymetry by subtracting a mean subsidence surface from the observed bathymetry. This produces a residual bathymetry map analogous to the usual residual depth anomaly maps. The residual bathymetry obtained in this way contains shallow depths for young seafloor, and larger depths for older seafloor, thus retaining the structure of the lithosphere while removing the subsidence of the lithosphere.

  5. Evidence for retrograde lithospheric subduction on Venus

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.; Schubert, Gerald

    1992-01-01

    Annular moats and outer rises around large Venus coronas such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the trenches and outer rises of terrestrial subduction zones. On earth, trenches and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the subducted slab; this lithospheric flexure model also accounts for the trenches and outer rises outboard of the major coronas on Venus. Accordingly, it is proposed that retrograde lithospheric subduction may be occurring on the margins of the large Venus coronas while compensating back-arc extension is occurring in the expanding coronas interiors. Similar processes may be taking place at other deep arcuate trenches or chasmata on Venus such as those in the Dali-Diana chasmata area of aestern Aphrodite Terra.

  6. Uppermantle anisotropy and the oceanic lithosphere

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.; Regan, J.

    1983-01-01

    Published Rayleigh and Love wave phase and group velocity data have been inverted taking into account sphericity, anelastic dispersion, and transverse isotropy. For a PREM-type modular parameterization, the thickness of the high velocity mantle seismic lithosphere (LID) varies in thickness from about 30 km for young ocean to about 50 km for old ocean, much less than previous estimates based on isotropic inversion of similar data. This LID thickness is comparable to the elastic or flexural thickness found from studies of seamount loading and flexure at trenches, suggesting that the thickness of the lithosphere may be controlled by mineralogy, composition, or crystal orientation rather than by temperature alone.

  7. Water in the Cratonic Mantle Lithosphere

    NASA Technical Reports Server (NTRS)

    Peslier, A. H.

    2016-01-01

    The fact that Archean and Proterozoic cratons are underlain by the thickest (>200 km) lithosphere on Earth has always puzzled scientists because the dynamic convection of the surrounding asthenosphere would be expected to delaminate and erode these mantle lithospheric "keels" over time. Although density and temperature of the cratonic lithosphere certainly play a role in its strength and longevity, the role of water has only been recently addressed with data on actual mantle samples. Water in mantle lithologies (primarily peridotites and pyroxenites) is mainly stored in nominally anhydrous minerals (olivine, pyroxene, garnet) where it is incorporated as hydrogen bonded to structural oxygen in lattice defects. The property of hydrolytic weakening of olivine [4] has generated the hypothesis that olivine, the main mineral of the upper mantle, may be dehydrated in cratonic mantle lithospheres, contributing to its strength. This presentation will review the distribution of water concentrations in four cratonic lithospheres. The distribution of water contents in olivine from peridotite xenoliths found in kimberlites is different in each craton (Figure 1). The range of water contents of olivine, pyroxene and garnet at each xenolith location appears linked to local metasomatic events, some of which occurred later then the Archean and Proterozoic when these peridotites initially formed via melting. Although the low olivine water contents (<10 ppm wt H2O) at > 6 GPa at the base of the Kaapvaal cratonic lithosphere may contribute to its strength, and prevent its delamination, the wide range of those from Siberian xenoliths is not compatible with providing a high enough viscosity contrast with the asthenophere. The water content in olivine inclusions from Siberian diamonds, on the other hand, have systematically low water contents (<20 ppm wt H2O). The xenoliths may represent a biased sample of the cratonic lithosphere with an over-­abundance of metasomatized peridotites with

  8. Lithospheric thinning beneath rifted regions of Southern California.

    PubMed

    Lekic, Vedran; French, Scott W; Fischer, Karen M

    2011-11-11

    The stretching and break-up of tectonic plates by rifting control the evolution of continents and oceans, but the processes by which lithosphere deforms and accommodates strain during rifting remain enigmatic. Using scattering of teleseismic shear waves beneath rifted zones and adjacent areas in Southern California, we resolve the lithosphere-asthenosphere boundary and lithospheric thickness variations to directly constrain this deformation. Substantial and laterally abrupt lithospheric thinning beneath rifted regions suggests efficient strain localization. In the Salton Trough, either the mantle lithosphere has experienced more thinning than the crust, or large volumes of new lithosphere have been created. Lack of a systematic offset between surface and deep lithospheric deformation rules out simple shear along throughgoing unidirectional shallow-dipping shear zones, but is consistent with symmetric extension of the lithosphere.

  9. Multidisciplinary approach to assess thermo-mechanical properties of the Asian lithosphere

    NASA Astrophysics Data System (ADS)

    Stolk, Ward; Kaban, Mikhail; Tesauro, Magdala; Beekman, Fred; Cloetingh, Sierd

    2013-04-01

    Assessing the thermo-mechanical properties of the lithospheric mantle is a complex business and still poses many problems. Seismic studies indicate large heterogeneities within the mantle lithosphere, but cannot discern between e.g. thermal and compositional effects. Similarly, gravity field analysis can constrain density heterogeneities, but is by its nature unable to distinguish between e.g. stacked density anomalies or lateral density anomalies. A joint analysis of both data types potentially leads to an improved insight in the mantle lithosphere, though the solution to the problem at hand remains non-unique and additional constraints are required. We have combined a high resolution tomography model with a recent global gravity field model to improve our knowledge of both the compositional and thermal aspects of the mantle lithosphere in the Asian continent. The preliminary results presented here will focus on the four major cratonic areas in Asia: the East European Platform, Siberia, Northeast China and India. These regions represent two distinct types of cratonic lithosphere (deep root and shallow root). Xenolith studies help us to further constrain the trade off between temperature and compositional effects.

  10. Assessing thermo-mechanical properties of the lithospheric mantle in Asia

    NASA Astrophysics Data System (ADS)

    Stolk, W.; Kaban, M. K.; Beekman, F.; Tesauro, M.; Cloetingh, S.

    2012-12-01

    Asia is a key natural laboratory for the study of active intra-continental deformation in response to the ongoing far-field collision of India and Eurasia. The resulting tectonic processes strongly depend on the thermo-mechanical structure of the lithosphere. However, the problem of the thermo-mechanical properties of the lithospheric mantle is complex and still not well resolved. While seismic studies give an indication of the heterogeneity of the mantle lithosphere it alone is insufficient to attribute these anomalies to thermal differences, since compositional difference may have a significant effect on observed wave velocities. Using solely gravity field analysis one cannot distinguish between e.g. stacked density anomalies or lateral density anomalies. Combining both datasets allows for a better insight into the mantle lithosphere, though the solution to the problem at hand remains non-unique. This study, of which the preliminary results will be presented here, attempts to gain insight into both compositional and thermal aspects of the mantle lithosphere in Asia. By combining a recent high resolution tomographic inversion with gravity field data, but without the assumption of a steady state mantle, a trade off between compositional and thermal effects can be made. Furthermore, susceptibility of the resulting model to small changes in parameter space can be obtained thus creating a 'playing field' for possible solutions to the thermo-mechanical problem. This 'playing field' can be further constrained by additional data from other sources, such as xenolith studies.

  11. Lithospheric thickness and mantle/lithosphere density contrast beneath Beta Rigio, Venus

    NASA Technical Reports Server (NTRS)

    Moore, William B.; Schubert, Gerald

    1995-01-01

    The spatial variation of the geoid/topography ratio over the large Venusian volcanic highland Beta Regio is suggestive of thermal compensation, i.e., support of the highland's topography by lithospheric thinning. Both the thickness of the lithosphere and the density contrast at its base can be inferred from a quadratic regression of suitably filtered (600 km less than wavelength less than 4000 km) geoid vs. topography data. The regression yields a mean lithospheric thickness of 270 km and a density contrast of magnitude 2.5% to 3.0%. Simple isostatic balance of the long-wavelength topography at Beta Regio requires thinning of the lithosphere by 50-60% beneath the rise.

  12. Variations in lithospheric thickness on Venus

    NASA Technical Reports Server (NTRS)

    Johnson, C. L.; Sandwell, David T.

    1992-01-01

    Recent analyses of Magellan data have indicated many regions exhibiting topograhic flexure. On Venus, flexure is associated predominantly with coronae and the chasmata with Aphrodite Terra. Modeling of these flexural signatures allows the elastic and mechanical thickness of the lithosphere to be estimated. In areas where the lithosphere is flexed beyond its elastic limit the saturation moment provides information on the strength of the lithosphere. Modeling of 12 flexural features on Venus has indicated lithospheric thicknesses comparable with terrestrial values. This has important implications for the venusian heat budget. Flexure of a thin elastic plate due simultaneously to a line load on a continuous plate and a bending moment applied to the end of a broken plate is considered. The mean radius and regional topographic gradient are also included in the model. Features with a large radius of curvature were selected so that a two-dimensional approximation could be used. Comparisons with an axisymmetric model were made for some features to check the validity of the two-dimensional assumption. The best-fit elastic thickness was found for each profile crossing a given flexural feature. In addition, the surface stress and bending moment at the first zero crossing of each profile were also calculated. Flexural amplitudes and elastic thicknesses obtained for 12 features vary significantly. Three examples of the model fitting procedures are discussed.

  13. Imaging Lithospheric Structure beneath the Indian continent

    NASA Astrophysics Data System (ADS)

    Maurya, S.; Montagner, J. P.; Mangalampally, R. K.; Stutzmann, E.; Burgos, G.; Kumar, P.; Davuluri, S.

    2015-12-01

    The lithospheric structure and thickness to the LAB are the most debated issues, especially beneath continents. In this context, the structure and thickness of the Indian lithosphere has been controversial. Paleomagnetic data reveals that the Indian continent moved northwards at exceptionally high speeds (18-20 cm/year) and subsequently slowed down to 4-5 cm/year after its collision with Asia ≈40 Myr ago. This super mobility has been explained by an unusually thin Indian lithosphere (≈100 km; Kumar et al., 2007) in contradiction with the thick lithosphere that commonly underlies old cratonic nuclei. It is pertinent to note that the thermobarometric estimates on the ultramafic xenoliths from 65 Myr kimberlites of the Central India (Babu et al. 2009) suggest an approximately 175 km thick lithosphere. Also, recent results of P and S wave travel time tomography of India suggest that the lithospheric roots are not uniformly thick on a regional scale. Although high velocity roots typical of Precambrian shields are preserved beneath a few cratons of the Indian shield, they seem to have suffered attrition, in the plume ravaged regions like the NDVP and the Southern SGT (Singh et al., 2014). We assembled a new massive surface wave database towards obtaining 3D isotropic and anisotropic models for the Indian sub-continent, using surface waves. This necessitated processing of data from more than 500 seismic broadband stations across India and surrounding regions. Surface waves group and phase dispersion measurements are performed in a broad frequency range (16-250s). Our phase velocity anomaly maps recover most of the known geological structures. The cratons are associated with high velocity (4-6%) anomalies till 200 sec, with the WDC being faster than the EDC. Slow velocities in NW India and very high velocity anomalies (6-8%) beneath the central part of the Indo-Gangetic plains are possibly associated with the subducting Indian lithosphere. The LAB depths inferred from

  14. Magnetic mineralogy of the Mercurian lithosphere

    NASA Astrophysics Data System (ADS)

    Strauss, Becky; Feinberg, Joshua; Johnson, Catherine

    2016-04-01

    Mercury and Earth are the only inner solar system planets with present-day core-dynamo magnetic fields, in contrast to the past fields of Mars and the Moon and the absence of evidence for a past or present field at Venus. Recently, the MESSENGER mission also measured magnetic fields from lithospheric magnetization on Mercury for the first time. These fields are consistent with remanent magnetization held by rocks exposed to an ancient, internally generated planetary magnetic field. However, the conditions for magnetization in the lithosphere of Mercury are unique among terrestrial planets, and the mechanisms for the acquisition (induced versus remanent) and alteration of magnetization are still unknown. We investigate the physical and chemical environment of Mercury's crust, past and present, to establish the conditions in which magnetization may have been acquired and subsequently modified. Three factors are particularly crucial to the determination of crustal composition and iron mineralogy: the temperature profile of the lithosphere and its evolution over time, redox conditions in the planet's crust and mantle, and the iron content of the lithosphere. We explore potential mechanisms for remanence acquisition and alteration on Mercury, whose surface environment is distinct from that of other inner solar system planets in that it is both very hot and highly reducing. The long-term thermal history of Mercury's crust plays an important role in the longevity of any crustal magnetization, which may be subject to remagnetization through thermal, viscous, and shock mechanisms. This thermal and compositional framework isused to constrain plausible candidate magnetic mineralogies, which can then be analyzed in terms of their capacity to acquire and retain magnetic remanence that is detectable from satellite orbit. We propose a suite of minerals and materials that could be carriers of remanence in the lithosphere of Mercury, including iron alloys, silicides, and sulfides.

  15. Lithospheric gravitational instability beneath the Southeast Carpathians

    NASA Astrophysics Data System (ADS)

    Lorinczi, P.; Houseman, G. A.

    2009-09-01

    The Southeast corner of the Carpathians, known as the Vrancea region, is characterised by a cluster of strong seismicity to depths of about 200 km. The peculiar features of this seismicity make it a region of high geophysical interest. In this study we calculate the seismic strain-rate tensors for the period 1967-2007, and describe the variation of strain-rate with depth. The observed results are compared with strain-rates predicted by numerical experiments. We explore a new dynamical model for this region based on the idea of viscous flow of the lithospheric mantle permitting the development of local continental mantle downwelling beneath Vrancea, due to a Rayleigh-Taylor instability that has developed since the cessation of subduction at 11 Ma. The model simulations use a Lagrangean frame 3D finite-element algorithm solving the equations of conservation of mass and momentum for a spatially varying viscous creeping flow. The finite deformation calculations of the gravitational instability of the continental lithosphere demonstrate that the Rayleigh-Taylor mechanism can explain the present distribution of deformation within the downwelling lithosphere, both in terms of stress localisation and amplitude of strain-rates. The spatial extent of the high stress zone that corresponds to the seismically active zone is realistically represented when we assume that viscosity decreases by at least an order of magnitude across the lithosphere. The mantle downwelling is balanced by lithospheric thinning in an adjacent area which would correspond to the Transylvanian Basin. Crustal thickening is predicted above the downwelling structure and thinning beneath the basin.

  16. Erosion of the continental lithosphere at the cusps of the Calabrian arc: Evidence from S receiver functions analysis

    NASA Astrophysics Data System (ADS)

    Miller, Meghan S.; Piana Agostinetti, Nicola

    2011-12-01

    Mediterranean tectonics has been characterized by an irregular, complex temporal evolution with episodic rollback and retreat of the subducted plate followed by period of slow trench-migration. To provide insight into the geodynamics of the Calabrian arc, we image the characteristics and lithospheric structure of the convergent, Apulian and Hyblean forelands at the cusps of the arc. Specifically we investigate the crustal and lithospheric thicknesses using teleseismic S-to-p converted phases, applied to the Adria-Africa plate margin for the first time. We find that the Moho in the Apulian foreland is nearly flat at ˜30 km depth, consistent with previous P receiver functions results, and that the Hyblean crustal thickness is more complex, which can be understood in terms of the nature of the individual pieces of carbonate platform and pelagic sediments that make up the Hyblean platform. The lithospheric thicknesses range between 70-120 km beneath Apulia and 70-90 km beneath Sicily. The lithosphere of the forelands at each end of the Calabrian arc are continental in nature, buoyant compared to the subducting oceanic lithosphere and have previously been interpreted as mostly undeformed carbonate platforms. Our receiver function images also show evidence of lithospheric erosion and thinning close to Mt. Etna and Mt. Vulture, two volcanoes which have been associated with asthenospheric upwelling and mantle flow around of the sides the slab. We suggest that as the continental lithosphere resists being subducted it is being thermo-mechanically modified by toroidal flow around the edges of the subducting oceanic lithosphere of the Calabrian arc.

  17. Geodynamic inversion to constrain the non-linear rheology of the lithosphere

    NASA Astrophysics Data System (ADS)

    Baumann, T. S.; Kaus, Boris J. P.

    2015-08-01

    One of the main methods to determine the strength of the lithosphere is by estimating it's effective elastic thickness. This method assumes that the lithosphere is a thin elastic plate that floats on the mantle and uses both topography and gravity anomalies to estimate the plate thickness. Whereas this seems to work well for oceanic plates, it has given controversial results in continental collision zones. For most of these locations, additional geophysical data sets such as receiver functions and seismic tomography exist that constrain the geometry of the lithosphere and often show that it is rather complex. Yet, lithospheric geometry by itself is insufficient to understand the dynamics of the lithosphere as this also requires knowledge of the rheology of the lithosphere. Laboratory experiments suggest that rocks deform in a viscous manner if temperatures are high and stresses low, or in a plastic/brittle manner if the yield stress is exceeded. Yet, the experimental results show significant variability between various rock types and there are large uncertainties in extrapolating laboratory values to nature, which leaves room for speculation. An independent method is thus required to better understand the rheology and dynamics of the lithosphere in collision zones. The goal of this paper is to discuss such an approach. Our method relies on performing numerical thermomechanical forward models of the present-day lithosphere with an initial geometry that is constructed from geophysical data sets. We employ experimentally determined creep-laws for the various parts of the lithosphere, but assume that the parameters of these creep-laws as well as the temperature structure of the lithosphere are uncertain. This is used as a priori information to formulate a Bayesian inverse problem that employs topography, gravity, horizontal and vertical surface velocities to invert for the unknown material parameters and temperature structure. In order to test the general methodology

  18. Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction

    NASA Astrophysics Data System (ADS)

    Pilet, Sebastien; Guex, Jean; Muntener, Othmar; Bartolini, Annachiara; Spangenberg, Jorge; Schoene, Blair; Schaltegger, Urs

    2016-04-01

    studies of the composition of the Kaapvaal craton have shown that sulfide minerals are enclosed in the basal part of the cratonic lithosphere. The formation of these sulfide minerals are linked to multiple refertilization/metasomatic events, which affected the base of the subcontinental lithospheric mantle from the Archean to the Proterozoic. We suggest that the transitions from an initial cool period to greenhouse conditions recorded by T-J and Pl-To sedimentary sections result of changing gas species emitted during the progressive thermal erosion of cratonic lithosphere by plume activity or thermal internal heating of the lithosphere. Our petrological model for LIP magmatism argues that initial gas emission was dominated by sulfur liberated from sulfide-bearing cratonic lithosphere causing global cooling and eustatic regression, which was followed by warming/transgression associated with the progressive increase of CO2 in the atmosphere associated to LIPs emission and metamorphic reactions in sedimentary basins. We suggest that the nature of the underlying lithosphere during large LIP eruption potentially exerts an important control on the consequences at the Earth's surface. This model offers an explanation for why LIPs erupted through oceanic lithosphere are not associated with climatic and biotic crises comparable to LIPs emitted through cratonic lithosphere.

  19. Electrical conductivity in the precambrian lithosphere of western canada

    PubMed

    Boerner; Kurtz; Craven; Ross; Jones; Davis

    1999-01-29

    The subcrustal lithosphere underlying the southern Archean Churchill Province (ACP) in western Canada is at least one order of magnitude more electrically conductive than the lithosphere beneath adjacent Paleoproterozoic crust. The measured electrical properties of the lithosphere underlying most of the Paleoproterozoic crust can be explained by the conductivity of olivine. Mantle xenolith and geological mapping evidence indicate that the lithosphere beneath the southern ACP was substantially modified as a result of being trapped between two nearly synchronous Paleoproterozoic subduction zones. Tectonically induced metasomatism thus may have enhanced the subcrustal lithosphere conductivity of the southern ACP.

  20. Radioxenon detections in the CTBT International Monitoring System likely related to the announced nuclear test in North Korea conducted on February 12, 2013

    SciTech Connect

    Ringbom, Anders; Axelssson, A.; Aldener, M.; Auer, M.; Bowyer, Ted W.; Fritioff, T.; Hoffman, Ian; Khrustalev, Kirill; Nikkinen, Mika; Popov, Vladimir Y.; Popov, Y.; Ungar, R. Kurt; Wotawa, G.

    2014-02-01

    Abstract: Observations of the radioxenon isotopes 133Xe and 131mXe collected at the IMS stations RN38 and RN58 on April 7-8, and April 12-13 2013, respectively, are unique with respect to the measurement history of these stations. Comparison of measured data with calculated isotopic ratios as well as analysis using atmospheric transport modeling indicate that it is likely that the xenon measured was created in the underground nuclear test conducted by North Korea on February 12, 2013, and released 7 weeks later. More than one release is required to explain all observations. The 131mXe source terms for each release were calculated to 7x1011 Bq, corresponding to about 1-10% of the total xenon inventory for a 10-kt explosion, depending on fractionation and release scenario. The observed ratios could not be used to obtain any information regarding the fissile material that was used in the test.

  1. Lithospheric structure in the Pacific geoid

    NASA Technical Reports Server (NTRS)

    Marsh, B. D.

    1984-01-01

    In order that sub-lithospheric density variations be revealed with the geoid, the regional geoid anomalies associated with bathymetric variations must first be removed. Spectral techniques were used to generate a synthetic geoid by filtering the residual bathymetry assuming an Airy-type isostatic compensation model. An unbiased estimated of the admittances show that for region under study, no single compensation mechanism will explain all of the power in the geoid. Nevertheless, because topographic features are mainly coherent with the geoid, to first order an isostationally compensated lithosphere cut by major E-W fracture zones accounts for most of the power in the high degree and other SEASAT geoid in the Pacific.

  2. Flexural deformation of the continental lithosphere

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Prior work focused primarily on the Adriatic and northern Ionian regions. The results of these studies have been summarized previously, and so are only briefly discussed. More recent work focuses on two different topics: (1) analysis of foredeep basin geometry, sedimentary style, and thrust belt structure in light of the kinematics at the associated plate boundary and subduction zone dynamics; and (2) the evolution and plate strength of early Proterozoic lithosphere.

  3. Flexure and rheology of Pacific oceanic lithosphere

    NASA Astrophysics Data System (ADS)

    Hunter, Johnny; Watts, Tony

    2016-04-01

    The idea of a rigid lithosphere that supports loads through flexural isostasy was first postulated in the late 19th century. Since then, there has been much effort to investigate the spatial and temporal variation of the lithosphere's flexural rigidity, and to understand how these variations are linked to its rheology. We have used flexural modelling to first re-assess the variation in the rigidity of oceanic lithosphere with its age at the time of loading, and then to constrain mantle rheology by testing the predictions of laboratory-derived flow laws. A broken elastic plate model was used to model trench-normal, ensemble-averaged profiles of satellite-derived gravity at the trench-outer rise system of circum-Pacific subduction zones, where an inverse procedure was used to find the best-fit Te and loading conditions. The results show a first-order increase in Te with plate age, which is best fit by the depth to the 400 ± 35°C plate-cooling isotherm. Fits to the observed gravity are significantly improved by an elastic plate that weakens landward of the outer rise, which suggests that bending-induced plate weakening is a ubiquitous feature of circum-Pacific subduction zones. Two methods were used to constrain mantle rheology. In the first, the Te derived by modelling flexural observations was compared to the Te predicted by laboratory-derived yield strength envelopes. In the second, flexural observations were modelled using elastic-plastic plates with laboratory-derived, depth-dependent yield strength. The results show that flow laws for low-temperature plasticity of dry olivine provide a good fit to the observations at circum-Pacific subduction zones, but are much too strong to fit observations of flexure in the Hawaiian Islands region. We suggest that this discrepancy can be explained by differences in the timescale of loading combined with moderate thermal rejuvenation of the Hawaiian lithosphere.

  4. Extremely depleted lithospheric mantle and diamonds beneath the southern Zimbabwe Craton

    NASA Astrophysics Data System (ADS)

    Smith, Chris B.; Pearson, D. Graham; Bulanova, Galina P.; Beard, Andrew D.; Carlson, Richard W.; Wittig, Nadine; Sims, Keith; Chimuka, Lovemore; Muchemwa, Ellah

    2009-11-01

    Inclusion-bearing diamonds, mantle xenoliths, and kimberlite concentrates from the Cambrian-aged Murowa and Sese kimberlites have been studied to characterise the nature of the lithospheric mantle beneath the southern Zimbabwe Craton. The diamonds are mostly octahedral, moderately rich in nitrogen with moderate to high aggregation, and contain mainly dunite-harzburgite mineral inclusions. Similarly, dunite xenoliths predominate over harzburgite and lherzolite and carry olivines with Mg/Mg + Fe (Mg#) values of 0.92-0.95, spanning the average signatures for Kaapvaal Craton peridotites. Eclogitic xenoliths are extremely rare, in contrast to the Kaapvaal mantle lithosphere. The Zimbabwe mantle assemblage has been only slightly affected by later silicic metasomatism and re-fertilisation with re-introduction of pyroxenes in contrast to the Kaapvaal and many cratonic lithospheric blocks elsewhere where strong metasomatism and re-fertilisation is widespread. Pyroxene, garnet and spinel thermobarometry suggests an ambient 40 mW m - 2 geotherm, with the lithosphere extending down to 210 km at the time of kimberlite eruption. Whole rock peridotite Re-Os isotope analyses yield T RD model ages of 2.7 to 2.9 Ga, providing minimum estimates of the time of melt depletion, are slightly younger in age than the basement greenstone formation. These model ages coincide with the mean T RD age of > 200 analyses of Kaapvaal Craton peridotites, whereas the average Re-Os model age for the Zimbabwe peridotites is 3.2 Ga. The Os data and low Yb n/Lu n ratios suggest a model whereby thick lithospheric mantle was stabilised during the early stages of crustal development by shallow peridotite melting required for formation of residues with sufficiently high Cr/Al to stabilise chromite which then transforms to low Ca, high Cr garnet. Sulphide inclusions in diamond produce minimum T RD model ages of 3.4 Ga indicating that parts of the lithosphere were present at the earliest stages of crust

  5. Metasomatic Enrichment of Oceanic Lithospheric Mantle Documented by Petit-Spot Xenoliths

    NASA Astrophysics Data System (ADS)

    Pilet, S.; Abe, N.; Rochat, L.; Hirano, N.; Machida, S.; Kaczmarek, M. A.; Muntener, O.

    2015-12-01

    Oceanic lithosphere is generally interpreted as mantle residue after MORB extraction. It has been proposed, however, that metasomatism could take place at the interface between the low-velocity zone and the cooling and thickening oceanic lithosphere or by the percolation of low-degree melts produced in periphery of Mid Ocean Ridges. This later process is observed in slow spreading ridges and ophiolites where shallow oceanic lithospheric mantle could be metasomatized/refertilized during incomplete MORB melt extraction. Nevertheless, direct evidence for metasomatic refertilization of the deep part of the oceanic lithospheric mantle is still missing. Xenoliths and xenocrysts sampled by petit-spot volcanoes interpreted as low-degree melts extracted from the base of the lithosphere in response to plate flexure, provide important new information about the nature and the processes associated with the evolution of oceanic lithospheric mantle. Here, we report, first, the presence of a garnet xenocryst in petit-spot lavas from Japan characterized by low-Cr, low-Ti content and mostly flat MREE-HREE pattern. This garnet is interpreted as formed during subsolidus cooling of pyroxenitic or gabbroic cumulates formed at ~1 GPa during the incomplete melt extraction at the periphery of the Pacific mid-ocean ridge. It is the first time that such processes are documented in fast spreading context. Second, we report petit-spot mantle xenoliths with cpx trace element "signatures" characterized by high U, Th, relative depletion in Nb, Pb, Ti and high but variable LREE/HREE ratio suggesting equilibration depth closed to the Gt/Sp transition zone. Such "signatures" are unknown from oceanic settings and show unexpected similarity to melt-metasomatized gt-peridotites sampled by kimberlites. This similarity suggests that metasomatic processes are not restricted to continental setting, but could correspond to a global mechanism at the lithosphere-asthenosphere boundary. As plate flexure

  6. Paleoproterozoic Collisional Structures in the Hudson Bay Lithosphere Constrained by Multi-Observable Probabilistic Inversion

    NASA Astrophysics Data System (ADS)

    Darbyshire, F. A.; Afonso, J. C.; Porritt, R. W.

    2015-12-01

    The Paleozoic Hudson Bay intracratonic basin conceals a Paleoproterozoic Himalayan-scale continental collision, the Trans-Hudson Orogen (THO), which marks an important milestone in the assembly of the Canadian Shield. The geometry of the THO is complex due to the double-indentor geometry of the collision between the Archean Superior and Western Churchill cratons. Seismic observations at regional scale show a thick, seismically fast lithospheric keel beneath the entire region; an intriguing feature of recent models is a 'curtain' of slightly lower wavespeeds trending NE-SW beneath the Bay, which may represent the remnants of more juvenile material trapped between the two Archean continental cores. The seismic models alone, however, cannot constrain the nature of this anomaly. We investigate the thermal and compositional structure of the Hudson Bay lithosphere using a multi-observable probabilistic inversion technique. This joint inversion uses Rayleigh wave phase velocity data from teleseismic earthquakes and ambient noise, geoid anomalies, surface elevation and heat flow to construct a pseudo-3D model of the crust and upper mantle. Initially a wide range of possible mantle compositions is permitted, and tests are carried out to ascertain whether the lithosphere is stratified with depth. Across the entire Hudson Bay region, low temperatures and a high degree of chemical depletion characterise the mantle lithosphere. Temperature anomalies within the lithosphere are modest, as may be expected from a tectonically-stable region. The base of the thermal lithosphere lies at depths of >250 km, reaching to ~300 km depth in the centre of the Bay. Lithospheric stratification, with a more-depleted upper layer, is best able to explain the geophysical data sets and surface observables. Some regions, where intermediate-period phase velocities are high, require stronger mid-lithospheric depletion. In addition, a narrow region of less-depleted material extends NE-SW across the Bay

  7. Lithospheric Thickness Modeled from Long Period Surface Wave Dispersion

    SciTech Connect

    Pasyanos, M E

    2008-05-15

    The behavior of surface waves at long periods is indicative of subcrustal velocity structure. Using recently published dispersion models, we invert surface wave group velocities for lithospheric structure, including lithospheric thickness, over much of the Eastern Hemisphere, encompassing Eurasia, Africa, and the Indian Ocean. Thicker lithosphere under Precambrian shields and platforms are clearly observed, not only under the large cratons (West Africa, Congo, Baltic, Russia, Siberia, India), but also under smaller blocks like the Tarim Basin and Yangtze craton. In contrast, it is found that remobilized Precambrian structures like the Saharan Shield and Sino-Korean Paraplatform do not have well-established lithospheric keels. The thinnest lithospheric thickness is found under oceanic and continental rifts, as well as along convergence zones. We compare our results to thermal models of continental lithosphere, lithospheric cooling models of oceanic lithosphere, lithosphere-asthenosphere boundary (LAB) estimates from S-wave receiver functions, and velocity variations of global tomography models. In addition to comparing results for the broad region, we examine in detail the regions of Central Africa, Siberia, and Tibet. While there are clear differences in the various estimates, overall the results are generally consistent. Inconsistencies between the estimates may be due to a variety of reasons including lateral and depth resolution differences and the comparison of what may be different lithospheric features.

  8. Identifying mantle lithosphere inheritance in controlling intraplate orogenesis

    NASA Astrophysics Data System (ADS)

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

    2016-09-01

    Crustal inheritance is often considered important in the tectonic evolution of the Wilson Cycle. However, the role of the mantle lithosphere is usually overlooked due to its difficulty to image and uncertainty in rheological makeup. Recently, increased resolution in lithosphere imaging has shown potential scarring in continental mantle lithosphere to be ubiquitous. In our study, we analyze intraplate deformation driven by mantle lithosphere heterogeneities from ancient Wilson Cycle processes and compare this to crustal inheritance deformation. We present 2-D numerical experiments of continental convergence to generate intraplate deformation, exploring the limits of continental rheology to understand the dominant lithosphere layer across a broad range of geological settings. By implementing a "jelly sandwich" rheology, common in stable continental lithosphere, we find that during compression the strength of the mantle lithosphere is integral in generating deformation from a structural anomaly. We posit that if the continental mantle is the strongest layer within the lithosphere, then such inheritance may have important implications for the Wilson Cycle. Furthermore, our models show that deformation driven by mantle lithosphere scarring can produce tectonic patterns related to intraplate orogenesis originating from crustal sources, highlighting the need for a more formal discussion of the role of the mantle lithosphere in plate tectonics.

  9. Flexure of lithosphere beneath the Alberta Foreland Basin: Evidence of an eastward stiffening continental lithosphere

    SciTech Connect

    Wu, P. )

    1991-03-01

    The flexure of the Mississippian Unconformity (MU) is used to constrain the stiffness of the lithosphere beneath the Alberta Foreland Basin (AFB). This flexure supports the sedimentological evidence for the absence of a forebulge in the AFB and implies that the peak of the forebulge lies further east of the Alberta Saskatchewan border. It is demonstrated that an eastwards stiffening lithosphere is required in order to fit the flexure of the MU. When flexural stiffness is expressed in terms of effective thickness, it varies from about 38km west of the Rocky Mountains to more than 200km underneath the North American craton. This variation of stiffness indicates that there is a strong lateral temperature and chemical variation underneath. Eastwards stiffening also implies an eastwards thickening of the elastic lithosphere. Such a model is in good agreement with recent petrological and geophysical evidences in the west and underneath the craton.

  10. Rheology, tectonics, and the structure of the Venus lithosphere

    NASA Technical Reports Server (NTRS)

    Zuber, M. T.

    1994-01-01

    Given the absence of ground truth information on seismic structure, heat flow, and rock strength, or short wavelength gravity or magnetic data for Venus, information on the thermal, mechanical and compositional nature of the shallow interior must be obtained by indirect methods. Using pre-Magellan data, theoretical models constrained by the depths of impact craters and the length scales of tectonic features yielded estimates on the thickness of Venus' brittle-elastic lithosphere and the allowable range of crustal thickness and surface thermal gradient. The purpose of this study is to revisit the question of the shallow structure of Venus based on Magellan observations of the surface and recent experiments that address Venus' crustal rheology.

  11. Role of orthopyroxene in rheological weakening of the lithosphere via dynamic recrystallization

    PubMed Central

    Farla, Robert J. M.; Karato, Shun-ichiro; Cai, Zhengyu

    2013-01-01

    For plate tectonics to operate on a terrestrial planet, the surface layer (the lithosphere) must have a modest strength (Earth, ≤200 MPa), but a standard strength profile based on olivine far exceeds this threshold value. Consequently, it is essential to identify mechanisms that reduce the strength of the lithosphere on Earth. Here we report results of high-strain laboratory deformation experiments on a representative olivine–orthopyroxene composition that show the addition of orthopyroxene substantially reduces the strength in the ductile regime within a certain temperature window. The reduction in strength is associated with the formation of small orthopyroxene and olivine grains. Our samples show heterogeneous microstructures similar to those observed in natural peridotites in shear zones: fine-grained regions containing both orthopyroxene and olivine that form interconnected bands where a large fraction of strain is accommodated. A model is developed to apply these results to geological conditions. Such a model, combined with our experimental observations, suggests that orthopyroxene may play a key role in the plastic deformation of the lithosphere in a critical temperature range, leading to long-term weakening associated with strain localization in the lithosphere. PMID:24067645

  12. Role of orthopyroxene in rheological weakening of the lithosphere via dynamic recrystallization.

    PubMed

    Farla, Robert J M; Karato, Shun-Ichiro; Cai, Zhengyu

    2013-10-08

    For plate tectonics to operate on a terrestrial planet, the surface layer (the lithosphere) must have a modest strength (Earth, ≤ 200 MPa), but a standard strength profile based on olivine far exceeds this threshold value. Consequently, it is essential to identify mechanisms that reduce the strength of the lithosphere on Earth. Here we report results of high-strain laboratory deformation experiments on a representative olivine-orthopyroxene composition that show the addition of orthopyroxene substantially reduces the strength in the ductile regime within a certain temperature window. The reduction in strength is associated with the formation of small orthopyroxene and olivine grains. Our samples show heterogeneous microstructures similar to those observed in natural peridotites in shear zones: fine-grained regions containing both orthopyroxene and olivine that form interconnected bands where a large fraction of strain is accommodated. A model is developed to apply these results to geological conditions. Such a model, combined with our experimental observations, suggests that orthopyroxene may play a key role in the plastic deformation of the lithosphere in a critical temperature range, leading to long-term weakening associated with strain localization in the lithosphere.

  13. Foundering lithosphere imaged beneath the southern Sierra Nevada, California, USA.

    PubMed

    Boyd, Oliver S; Jones, Craig H; Sheehan, Anne F

    2004-07-30

    Seismic tomography reveals garnet-rich crust and mantle lithosphere descending into the upper mantle beneath the southeastern Sierra Nevada. The descending lithosphere consists of two layers: an iron-rich eclogite above a magnesium-rich garnet peridotite. These results place descending eclogite above and east of high P wave speed material previously imaged beneath the southern Great Valley, suggesting a previously unsuspected coherence in the lithospheric removal process.

  14. Preface to "Insights into the Earth's Deep Lithosphere"

    SciTech Connect

    Pasyanos, M E

    2009-11-19

    Dear Readers: I am pleased to present a special issue of Tectonophysics entitled 'Insights into the Earth's Deep Lithosphere.' This compilation sought to capture the flavor of the increasing number of studies that are emerging to investigate the complex lithospheric structure of the earth. This issue evolved out of a Fall 2007 AGU special session entitled 'Understanding the Earth's Deep Lithosphere' that I organized with Irina Artemieva from the University of Copenhagen. For that session, we solicited talks that discussed the increasing number of methods that have surfaced to study various aspects of the earth's deep lithosphere. These methods include seismic, gravity, thermal, geochemical, and various combinations of these methods. The quality of the presentations (2 oral sessions with 16 talks and 23 associated poster presentations) was such that we felt that the emerging topic deserved a dedicated forum to address these questions in greater detail. The availability of new data sets has also improved the number and quality of lithospheric studies. With many new studies and methodologies, a better understanding of both continental and oceanic lithospheres is starting to emerge. Questions remain about the thickness and evolution of the lithosphere, the presence of lithospheric keels, the density and anisotropy of lithospheric roots, mechanisms of lithospheric thinning, and differences between mechanical, thermal and chemical boundary layers. While we did not get contributions on the full gamut of methods and regions, a lot of ground was covered in this issue's manuscripts. Like any collection of papers on the deep lithosphere, the topics are quite varied in methodology, geographic location, and what aspect of the lithosphere being studied. Still, the results highlight the rewarding aspects of earth structure, history, and evolution that can be gleaned. A brief synopsis of the papers contained in this issue is given.

  15. Theory and detection scheme of seismic EM signals transferred into the atmosphere from the oceanic and continental lithosphere

    NASA Astrophysics Data System (ADS)

    Novik, Oleg; Ershov, Sergey; Ruzhin, Yuri; Smirnov, Fedor; Volgin, Maxim

    2014-07-01

    Due to the compound structure of the medium and large portions of energy transferred, a seismic excitation in the oceanic or continental lithosphere disturbs all types of geophysical fields. To investigate the problem of electromagnetic (EM) disturbances in the atmosphere from the seismically activated lithosphere, we have formulated two mathematical models of interaction of fields of different physical nature resulting in arising of the low-frequency (from 0.1 to 10 Hz by amplitude of a few hundreds of pT) EM signals in the atmosphere. First we have considered the EM field generation in the moving oceanic lithosphere and then in the moving continental one. For both cases, the main physical principles and geological data were applied for formulation of the model and characteristics of the computed signals of different nature agree with measurements of other authors. On the basis of the 2D model of the seismo-hydro-EM-temperature interaction in the lithosphere-Ocean-atmosphere domain, a block-scheme of a multisensory vertically distributed (from a seafloor up to the ionosphere) tsunami precursors' detection system is described. On the basis of the 3D model of the seismo-EM interaction in a lithosphere-atmosphere domain, we explain why Prof. Kopytenko (Inst. IZMIRAN of Russian Acad. Sci.) and co-authors were able to estimate location of the future seismic epicenter area from their magnetic field measurements in the atmosphere near the earth's surface.

  16. Transient creep and convective instability of the lithosphere

    NASA Astrophysics Data System (ADS)

    Birger, Boris I.

    2012-12-01

    Laboratory experiments with rock samples show that transient creep, at which strain grows with time and strain rate decrease at constant stress, occurs while creep strains are sufficiently small. The transient creep at high temperatures is described by the Andrade rheological model. Since plate tectonics allows only small deformations in lithospheric plates, creep of the lithosphere plates is transient whereas steady-state creep, described by non-Newtonian power-law rheological model, takes place in the underlying mantle. At the transient creep, the effective viscosity, found in the study of postglacial flows, differs significantly from the effective viscosity, which characterizes convective flow, since timescales of these flows are very different. Besides, the transient creep changes the elastic crust thickness estimated within the power-law rheology of the lithosphere. Two problems of convective stability for the lithosphere with the Andrade rheology are solved. The solution of the first problem shows that the state, in which large-scale convective flow in the mantle occurs under lithospheric plates, is unstable and must bifurcate into another more stable state at which the lithospheric plates become mobile and plunge into the mantle at subduction zones. If the lithosphere had the power-law fluid rheology, the effective viscosity of the stagnant lithospheric plates would be extremely high and the state, in which large-scale convection occurs under the stagnant plates, would be stable that contradicts plate tectonics. The mantle convection forms mobile lithospheric plates if the effective viscosity of the plate is not too much higher than the effective viscosity of the underlying mantle. The Andrade rheology lowers the plate effective viscosity corresponding to the power-law fluid rheology and, thus, leads to instability of the state in which the plates are stagnant. The solution of the second stability problem shows that the state, in which the lithospheric plate

  17. Study of the time evolution of the lithosphere

    NASA Technical Reports Server (NTRS)

    Roufosse, M. C.

    1983-01-01

    The behavior and mechanical properties of the lithosphere were studied. This is a prerequisite to an understanding of the mechanisms and processes that occur in the Earth's mantle, which are masked by the lithospere. Geoid heights derived from the GEOS-3 and SEASAT radar altimeters were used. The correlation between bathymetry and geoid heights gives information on the mechanical properties of the lithosphere, such as its thickness, which is related to the age of the lithospheric plate. By probing in several locations spanning various temporal situations, the time evolution of the lithospheric plates were retraced.

  18. Lithospheric models of the North American continent

    NASA Astrophysics Data System (ADS)

    Tesauro, Magdala; Kaban, Mikhail; Mooney, Walter; Cloetingh, Sierd

    2015-04-01

    We constructed NACr14, a 3D model of the North American (NA) crust, based on the most recent seismic data from the USGS database. In comparison with the global crustal model CRUST 1.0, NACr14 is more heterogeneous, showing a larger spatial variability of the thickness and average velocities of the crustal layers. Velocities of the lower crust vary in a larger range than those of the other layers, while the thickness of all the three layers is on average between 11 and 13 km. The largest velocities of the crystalline crust (>6.6 km/s) reflect the presence of a 7.x layer (>7.0 km/s) in the lowermost part of the crust. Using NACr2014, a regional (NA07) and a global (SL201sv) tomography model, and gravity data, we apply an iterative technique, which jointly interprets seismic tomography and gravity data, to estimate temperature and compositional variations in the NA upper mantle. The results obtained demonstrate that temperature of the cratonic mantle is up to 150°C higher than when using a uniform compositional model. The differences between the two tomography models influence the results more strongly than possible changes of the depth distribution of compositional variations. Strong negative compositional density anomalies, corresponding to Mg # >92, characterize the upper mantle of the northwestern part of the Superior craton and the central part of the Slave and Churchill craton. The Proterozoic upper mantle of the western and more deformed part of the NA cratons, appears weakly depleted (Mg# ~91) when NA07 is used, in agreement with the results based on the interpretation of xenolith data. When we use SL2013sv, the same areas are locally characterized by high density bodies, which might be interpreted as the effect due to fragments of subducted slabs, as those close to the suture of the Appalachians and Grenville province. We used the two thermal models to estimate the integrated strength and the effective elastic thickness (Te) of the lithosphere. In the

  19. Ductile crustal flow in Europe's lithosphere

    NASA Astrophysics Data System (ADS)

    Tesauro, Magdala; Burov, Evgene B.; Kaban, Mikhail K.; Cloetingh, Sierd A. P. L.

    2011-12-01

    Potential gravity theory (PGT) predicts the presence of significant gravity-induced horizontal stresses in the lithosphere associated with lateral variations in plate thickness and composition. New high resolution crustal thickness and density data provided by the EuCRUST-07 model are used to compute the associated lateral pressure gradients (LPG), which can drive horizontal ductile flow in the crust. Incorporation of these data in channel flow models allows us to use potential gravity theory to assess horizontal mass transfer and stress transmission within the European crust. We explore implications of the channel flow concept for a possible range of crustal strength, using end-member 'hard' and 'soft' crustal rheologies to estimate strain rates at the bottom of the ductile crustal layers. The models show that the effects of channel flow superimposed on the direct effects of plate tectonic forces might result in additional significant horizontal and vertical movements associated with zones of compression or extension. To investigate relationships between crustal and mantle lithospheric movements, we compare these results with the observed directions of mantle lithospheric anisotropy and GPS velocity vectors. We identify areas whose evolution could have been significantly affected by gravity-driven ductile crustal flow. Large values of the LPG are predicted perpendicular to the axes of European mountain belts, such as the Alps, Pyrenees-Cantabrian Mountains, Dinarides-Hellenic arc and Carpathians. In general, the crustal flow is directed away from orogens towards adjacent weaker areas. Gravitational forces directed from areas of high gravitational potential energy to subsiding basin areas can strongly reduce lithospheric extension in the latter, leading to a gradual late stage inversion of the entire system. Predicted pressure and strain rate gradients suggest that gravity driven flow may play an essential role in European intraplate tectonics. In particular, in a

  20. Lithospheric delamination underneath Far East Russia

    NASA Astrophysics Data System (ADS)

    Ntaflos, Theodoros; Koutsovitis, Petros; Aschchepkov, Igor; Hauzenberger, Christoph; Prikhodko, Vladimir; Asseva, Anna

    2013-04-01

    In the back-arc environment of Far East Russia, mantle xenoliths from Sikhoti-Alin( Komku area, KO) and Primorie (Sviyaginsky area, SV), Far East Russia are fertile spinel lherzolites with traces of amphibole, phlogopite and hyalophane in some of the studied samples. Though samples from both localities are fertile there is a systematic difference in their fertility. The KO samples have mg# varying from 0.891 to 0.899 and are slightly more fertile than the SV samples that have mg# ranging from 0.898 to 0.904. LA-ICP-MS analyses on clinopyroxenes confirm this trend as the (La/Yb)N in KO samples range from 0.1to 1.0 and in SV samples from 0.15 to 1.73. The estimated equilibration temperatures for the KO suite range from 940 °C to 1035 °C and for the SV suite from 770 to 945. The differences in the estimated equilibrium temperatures between the KO and SV suites suggest that the less fertile SV suite originated in shallower depths than the more fertile KO suite. Pargasitic amphibole, kaersutite, and extremely Ti-rich phlogopite, up to 14 wt% TiO2, are associated with intergranular glass indicating clearly metasomatism of undersaturated hydrous alkaline melts. Incompatible element abundances, besides Ba, Sr and Ti that are slightly enriched in the amphibole, are similar in both phases suggesting minor metasomatism due to percolation of small amounts of water-rich fluids. The Sr and Nd cpx isotopic ratios range from 0.702599 to 0.703567 and 0.512915 to 513153, repectively and the model Nd isotope age range from 1.5 to 2.2 Ga indicating an old (Proterozoic?) partial melt event. The lithospheric mantle beneath the studied area represents the residue after partial melting of up to 2 % of a primitive mantle and is comparable to that of Mongolia. Despite the fact that the studied area experienced several subducting episodes, the lithospheric mantle appears to be unaffected from the upwelling fluids/melts of the subducted slab(s). Since there is no indication for plume

  1. Deformation of Indian Ocean Lithosphere Implies Highly Non-linear Rheological Law for Oceanic Lithosphere

    NASA Astrophysics Data System (ADS)

    Gordon, Richard; Houseman, Gregory

    2015-04-01

    The width of diffuse oceanic plate boundaries is determined by the rheology of oceanic lithosphere. Here we apply thin viscous sheet models, which have been successfully applied to deformation in several continental deforming zones, to investigate the deformation of oceanic lithosphere in the diffuse oceanic plate boundaries between the India, Capricorn, and Australia plates. We apply kinematic boundary conditions based on the current motion between these plates. We neglect buoyancy forces due to plate thinning or thickening and assume that the thin viscous sheet has the same depth-integrated non-linear viscosity coefficient everywhere. Our initial models have only one adjustable parameter, n, the power-law exponent, with n=1, 3, 10, 30, 100. The predicted width of the deforming zone decreases with increasing n, with n ≥ 30 explaining the observations. This n-value is higher than has been estimated for continental lithosphere, and suggests that more of the strength of oceanic lithosphere lies in layers deforming by faulting or by dislocation glide than for continental lithosphere. To obtain a stress field that better fits the distribution and type of earthquake focal mechanisms in the diffuse oceanic plate boundary, we add a second adjustable parameter, representing the effect of slab-pull stretching the oceanic plate near the Sumatra trench. We show that an average velocity increment on this boundary segment of 5 mm/a (relative to the average velocity of the India and Australia plates) fits the observed distribution of fault types better than velocities of 3.3 mm/a or 10 mm/a.

  2. Lithospheric architecture of the Levant Basin (Eastern Mediterranean region): A 2D modeling approach

    NASA Astrophysics Data System (ADS)

    Inati, Lama; Zeyen, Hermann; Nader, Fadi Henri; Adelinet, Mathilde; Sursock, Alexandre; Rahhal, Muhsin Elie; Roure, François

    2016-12-01

    This paper discusses the deep structure of the lithosphere underlying the easternmost Mediterranean region, in particular the Levant Basin and its margins, where the nature of the crust, continental versus oceanic, remains debated. Crustal thickness and the depth of the lithosphere-asthenosphere boundary (LAB) as well as the crustal density distribution were calculated by integrating surface heat flow data, free-air gravity anomaly, geoid and topography. Accordingly, two-dimensional, lithospheric models of the study area are discussed, demonstrating the presence of a progressively attenuated crystalline crust from E to W (average thickness from 35 to 8 km). The crystalline crust is best interpreted as a strongly thinned continental crust under the Levant Basin, represented by two distinct components, an upper and a lower crust. Further to the west, the Herodotus Basin is believed to be underlain by an oceanic crust, with a thickness between 6 and 10 km. The Moho under the Arabian Plate is 35-40 km deep and becomes shallower towards the Mediterranean coast. It appears to be situated at depths ranging between 20 and 23 km below the Levant Basin and 26 km beneath the Herodotus Basin, based on our proposed models. At the Levantine margin, the thinning of the crust in the transitional domain between the onshore and the offshore is gradual, indicating successive extensional regimes that did not reach the beak up stage. In addition, the depth to LAB is around 120 km under the Arabian and the Eurasian Plates, 150 km under the Levant Basin, and it plunges to 180 km under the Herodotus Basin. This study shows that detailed 2D lithosphere modeling using integrated geophysical data can help understand the mechanisms responsible for the modelled lithospheric architecture when constrained with geological findings.

  3. Imaging the Subduction of Continental Lithosphere in the Banda Sea Region

    NASA Astrophysics Data System (ADS)

    Fichtner, A.; De Wit, M.; van Bergen, M.

    2014-12-01

    We present a 3D tomographic model of Australasia obtained by full seismic waveform inversion. Our model features a sharp lateral velocity contrast extending to >200 km depth, coincident with the abrupt transition from low to high Helium ratios in arc volcanics near 123°E (see figure). The joint analysis of the tomographic model and isotope data (for He, Pb, Nd, Sr) suggests that the North Australian craton subducted beneath the Banda Sea to around 100 km depth. The continuous increase of computing power combined with advances in numerical seismology allow us to develop full waveform inversion techniques that translate complete seismograms into 3D Earth models. The natural incorporation of any type of body and surface waves in full waveform inversion improves tomographic resolution in terms of both resolution length and amplitude recovery. We applied full waveform inversion to Australasia, including the Sunda and Banda arcs. The correlation of the tomographic model with isotope signatures of arc volcanics supports the shallow-angle subduction of North Australian lithosphere. The integrated data suggest that the late Jurassic ocean lithosphere north of the North Australian craton was capable of entraining large volumes of continental lithosphere. A plausible explanation involves delamination within the continental crust, separating upper from lower crustal units. This interpretation is consistent with the existence of a massive accretionary complex on Timor island, with evidence from Pb isotope analysis for lower-crust involvement in arc volcanism; and with the approximate gravitational stability of the subducted lithosphere as inferred from the tomographic images. The Banda arc example demonstrates that continental lithosphere in arc-continent collisions may not generally be preserved, thus increasing the complexity of tectonic reconstructions and models of recycling continental crust.

  4. Low surface gravitational acceleration of Mars results in a thick and weak lithosphere: Implications for topography, volcanism, and hydrology

    NASA Astrophysics Data System (ADS)

    Heap, Michael J.; Byrne, Paul K.; Mikhail, Sami

    2017-01-01

    Surface gravitational acceleration (surface gravity) on Mars, the second-smallest planet in the Solar System, is much lower than that on Earth. A direct consequence of this low surface gravity is that lithostatic pressure is lower on Mars than on Earth at any given depth. Collated published data from deformation experiments on basalts suggest that, throughout its geological history (and thus thermal evolution), the Martian brittle lithosphere was much thicker but weaker than that of present-day Earth as a function solely of surface gravity. We also demonstrate, again as a consequence of its lower surface gravity, that the Martian lithosphere is more porous, that fractures on Mars remain open to greater depths and are wider at a given depth, and that the maximum penetration depth for opening-mode fractures (i.e., joints) is much deeper on Mars than on Earth. The result of a weak Martian lithosphere is that dykes-the primary mechanism for magma transport on both planets-can propagate more easily and can be much wider on Mars than on Earth. We suggest that this increased the efficiency of magma delivery to and towards the Martian surface during its volcanically active past, and therefore assisted the exogeneous and endogenous growth of the planet's enormous volcanoes (the heights of which are supported by the thick Martian lithosphere) as well as extensive flood-mode volcanism. The porous and pervasively fractured (and permeable) nature of the Martian lithosphere will have also greatly assisted the subsurface storage of and transport of fluids through the lithosphere throughout its geologically history. And so it is that surface gravity, influenced by the mass of a planetary body, can greatly modify the mechanical and hydraulic behaviour of its lithosphere with manifest differences in surface topography and geomorphology, volcanic character, and hydrology.

  5. A Multi-Layer Phoswich Radioxenon Detection System (7th Qtr Report), Reporting Period 10/01/07 - 12/31/07

    SciTech Connect

    David M. Hamby

    2008-01-29

    Description of activities conducted this report period: (1) Electronics Development--To improve the overall performance of the two-channel digital pulse processor (DPP2), the PCB has been redesigned and the new printed board is now under assembly. The system is enhanced with two new fast ADCs from Analog Devices (AD9230-250), each with a sampling rate of 250 MHz and a resolution of 12 bits. The data bus uses a high performance Low Voltage Differential Signaling (LVDS) standard. The offset and gain of each channel are separately controlled digitally by the GUI software. (2) GUI Software Development--A GUI is being developed using the Python programming language. All functions from the preceding MATLAB code have been re-implemented including basic waveform readout, pulse shape discrimination, and plotting of energy spectra. In addition, the GUI can be used to control sampling runs based on the number of pulses captured, either in real or live time. Calibration coefficients and pulse shape discrimination boundaries can be changed on the fly so that the detector may be characterized experimentally. Plots generated by the GUI can be exported as graphic data. At present, the software has only been tested using one channel, pending availability of the new DPP board (DPP2). However, the functions have been written to allow easy expansion to two channels. (3) Light Collection Modeling--The XEPHWICH design has been modeled to determine its light capture efficiency. Research in the 7th quarter includes additional simulations representing significant increase in data resolution, well over an order of magnitude greater than previous simulations. The final data set represents approximately 11 billion visible photons divided equally among 110 thousand data points. A laboratory experiment is being designed and executed to experimentally determine light capture efficiency as a function of position within the scintillators. (4) Radioxenon Fission Source--We have designed and

  6. Seismic imaging of the lithosphere beneath Hudson Bay: Episodic growth of the Laurentian mantle keel

    NASA Astrophysics Data System (ADS)

    Darbyshire, Fiona A.; Eaton, David W.; Bastow, Ian D.

    2013-07-01

    The Hudson Bay basin in northern Canada conceals one of the major collisional zones of the Canadian Shield, the Trans-Hudson Orogen (THO), which marks the Paleoproterozoic collision between the Archean Superior and Western Churchill cratons at ˜1.9-1.8Ga. Improved knowledge of upper mantle structure beneath the region is essential to establish the nature of the THO, specifically whether Himalayan-style plate tectonics operated in Paleoproterozoic times. Detailed seismological constraints on lithospheric architecture are also required to advance our understanding of the mechanism and timing of keel formation. We use surface wave tomography to illuminate new details of the lithospheric architecture of the Hudson Bay region, resolving both seismic wavespeed and azimuthal anisotropy. Phase velocity maps are calculated from fundamental-mode Rayleigh wave dispersion curves, then used to construct a 3D model exploring upper mantle structure to depths of ˜300km. Fast shear wavespeeds suggest a lithospheric thickness varying from ˜180km to almost 280 km beneath the Hudson Bay region. The new study confirms previous inferences that there is no correlation between crustal ages and lithospheric thickness. Patterns of shear wavespeed and azimuthal anisotropy indicate a layered lithosphere. In the uppermost mantle, both the highest velocities and the anisotropic fast directions wrap around the Bay. This structure is likely related to the formation processes of the Paleozoic intracratonic basin. At greater depth (˜70-150km) we resolve two high-wavespeed cores separated by a relatively narrow near-vertical lower-velocity curtain. This internal architecture is suggested to result from the terminal phase of a modern-style plate-tectonic collision between the Archean Superior and Churchill cratons during the Trans-Hudson orogeny, entrapping juvenile Proterozoic material. The lower lithosphere (≥160km depth) has a relatively homogeneous wavespeed structure across the region

  7. Interference of lithospheric folding in Central Asia by simultaneous Indian and Arabian plate indentation

    NASA Astrophysics Data System (ADS)

    Smit, J. H. W.; Cloetingh, S. A. P. L.; Burov, E.; Sokoutis, D.; Kaban, M.; Tesauro, M.; Burg, J.-P.

    2012-04-01

    Although large-scale folding of the crust and the lithosphere in Central Asia as a result of the indentation of India has been extensively documented, the impact of continental collision between Arabia and Eurasia has been largely overlooked. The resulting Neogene shortening and uplift of the Zagros, Albors, Kopet Dagh and Kaukasus mountain belts in Iran and surrounding areas is characterised by a simultaneous onset of major topography growth at ca. 5 Ma. At the same time, the adjacent Caspian, Turan and Amu Darya basins underwent an acceleration in subsidence. It is common knowledge that waves with different orientations will interfere with each other. Folding, by its nature similar to a standing wave, is not likely to be an exception. We demonstrate that collision of the Eurasian plate with the Arabian and Indian plates generates folding of the Eurasian lithosphere in two different directions and that interaction between both generates characteristic interference patterns that can be recognised from the regional gravity signal. We present evidence for interference of lithospheric folding patterns induced by Arabian and Indian collision with Eurasia. Wavelengths (from 50 to 250 km) and spatial patterns are inferred from satellite-derived topography and gravity models and attest for rheologically stratified lithosphere with relatively strong mantle rheology (thickness of strong mechanical core on the order of 40-50 km) and less competent crust (thickness of the mechanical core on the order of 10-15 km). The observations are compared with inferences from numerical and analogue tectonic experiments for a quantitative assessment of factors such as lithosphere rheology and stratification, lateral variations in lithosphere strength, thermo-mechanical age and distance to the plate boundary on the activity of folding as a mechanism of intra-plate deformation in this area. The observed interference of the patterns of folding appears to be primarily the result of spatial

  8. Radioxenon spiked air

    DOE PAGES

    Watrous, Matthew G.; Delmore, James E.; Hague, Robert K.; ...

    2015-08-27

    Four of the radioactive xenon isotopes (131mXe, 133mXe, 133Xe and 135Xe) with half-lives ranging from 9 h to 12 days are produced from nuclear fission and can be detected from days to weeks following their production and release. Being inert gases, they are readily transported through the atmosphere. Sources for release of radioactive xenon isotopes include operating nuclear reactors via leaks in fuel rods, medical isotope production facilities, and nuclear weapons' detonations. They are not normally released from fuel reprocessing due to the short half-lives. The Comprehensive Nuclear-Test-Ban Treaty has led to creation of the International Monitoring System. The Internationalmore » Monitoring System, when fully implemented, will consist of one component with 40 stations monitoring radioactive xenon around the globe. Monitoring these radioactive xenon isotopes is important to the Comprehensive Nuclear-Test-Ban Treaty in determining whether a seismically detected event is or is not a nuclear detonation. A variety of radioactive xenon quality control check standards, quantitatively spiked into various gas matrices, could be used to demonstrate that these stations are operating on the same basis in order to bolster defensibility of data across the International Monitoring System. This study focuses on Idaho National Laboratory's capability to produce three of the xenon isotopes in pure form and the use of the four xenon isotopes in various combinations to produce radioactive xenon spiked air samples that could be subsequently distributed to participating facilities.« less

  9. Radioxenon spiked air

    SciTech Connect

    Watrous, Matthew G.; Delmore, James E.; Hague, Robert K.; Houghton, Tracy P.; Jenson, Douglas D.; Mann, Nick R.

    2015-08-27

    Four of the radioactive xenon isotopes (131mXe, 133mXe, 133Xe and 135Xe) with half-lives ranging from 9 h to 12 days are produced from nuclear fission and can be detected from days to weeks following their production and release. Being inert gases, they are readily transported through the atmosphere. Sources for release of radioactive xenon isotopes include operating nuclear reactors via leaks in fuel rods, medical isotope production facilities, and nuclear weapons' detonations. They are not normally released from fuel reprocessing due to the short half-lives. The Comprehensive Nuclear-Test-Ban Treaty has led to creation of the International Monitoring System. The International Monitoring System, when fully implemented, will consist of one component with 40 stations monitoring radioactive xenon around the globe. Monitoring these radioactive xenon isotopes is important to the Comprehensive Nuclear-Test-Ban Treaty in determining whether a seismically detected event is or is not a nuclear detonation. A variety of radioactive xenon quality control check standards, quantitatively spiked into various gas matrices, could be used to demonstrate that these stations are operating on the same basis in order to bolster defensibility of data across the International Monitoring System. This study focuses on Idaho National Laboratory's capability to produce three of the xenon isotopes in pure form and the use of the four xenon isotopes in various combinations to produce radioactive xenon spiked air samples that could be subsequently distributed to participating facilities.

  10. Spectral Analysis of Radioxenon

    DTIC Science & Technology

    2008-09-01

    reasons for spectral fitting being a supplement to the standard energy spectrum ROI method. Fermi- Kurie plot Given the difficulty in fitting a beta...continuum, it is important to find an alternative method. A Fermi- Kurie plot (Krane 1988) is one method, which allows a beta spectrum to be plotted ...corrective function takes into account the initial and final spin and polarity states. A rb itr ar y un its Figure 6. Fermi- Kurie plot . T (MeV

  11. Understanding lithospheric stresses: systematic analysis of controlling mechanisms with applications to the African Plate

    NASA Astrophysics Data System (ADS)

    Medvedev, Sergei

    2016-10-01

    gives us confidence that our methodology appropriately models the stress pattern of Africa, and that it may be further applied to other plates on Earth. Our modelling approach allows us to quantify several important features controlling the lithospheric stress pattern. Even though the initial oversimplified model does not fit the observations satisfactorily, it shows how ridge push may create significant compressive stresses in the lithosphere. More complex models show the importance of the density structure of the lithosphere, specifically in the subcrustal lithosphere. The stress regime within the TAP mainly results from a global balance of masses and mass moments between continental and oceanic parts of the plate. The orientation of stresses, in turn, is influenced more by local features expressed by topographic and crustal density variations, whereas existent subcrustal density variations appear to be smoothed by the crust above. The models show that accounting separately for either basal tractions or rheological heterogeneities brings moderate improvement, but the combination of these two mechanisms results in a substantially better match between model and observations. The bending stresses caused by isostatical re-adjustment improve the model match, but they have to be analysed with caution because of their depth-dependent nature.

  12. Three-dimensional density structure of the lunar upper lithosphere

    NASA Astrophysics Data System (ADS)

    Liang, Q.; Du, J.; Chen, C.; Li, Y.

    2011-12-01

    The lithosphere of the Moon has a thickness over 1200 km according to the seismology studies. It records the giant impact events during the processes of solidification. The upper lithosphere including the crust and the upper mantle was thought to be a nonuniform layer in thickness and seismic velocity, yet the lateral density structure remains poorly understood. The global gravity data thus provides a significant constraint on the three-dimensional (3-D) density structure of the Moon. Previous studies assumed that the crust and the mantle have constant density the gravity anomalies are only produced by the variations of interface between the crust and the mantle. Therefore, the constant density may give overestimation or underestimation of the Moho depth. In contrast, we apply a 3-D inverse method in spherical coordinate to the lunar gravity anomaly. It is a direct way in recovering the density structures beneath mascon basins or the lateral density heterogeneities in the upper lithosphere. The gravity anomaly we use in this study is the Bouguer gravity anomaly calculated at 1750 km radius relative to the reference radius, 1737.153 km[1], from the newly gravity field model SGM100i[2] and the topography model LRO_LTM02[1]. In order to understand the global feature of density variation, we truncate the long wavelength anomaly up to the order of 30 to reconstruct the density distribution above the depth of 100 km in the Moon. With the inverse technique, we obtain a global 3-D density structure of the lunar lithosphere down to 100 km depth. The major features are dominated by the mascons with dense materials and the broad region of the farside highland with relative low density mass. From this structure, the huge mass concentrations are found beneath the South Pole-Aitken (SPA) basin, meaning that the oblique impact not only excavated the SPA basin into deep but also made the mantle uplifted close to a depth of 30 km (relative to a 1738 km radius). We suggest here that

  13. Evolution of the oceanic lithosphere inferred from Po/So waves traveling in the Philippine Sea Plate

    NASA Astrophysics Data System (ADS)

    Shito, Azusa; Suetsugu, Daisuke; Furumura, Takashi

    2015-07-01

    Po/So waves are characterized by their high-frequency content and long-duration travel over great distances (up to 3000km) through the oceanic lithosphere. Po/So waves are developed by the multiple forward scattering of P and S waves due to small-scale stochastic random heterogeneities. To study the nature of these heterogeneities, Po/So waves are analyzed in the Philippine Sea Plate, which consists of three regions with different lithospheric ages. In the Philippine Sea Plate, Po/So waves propagate in the youngest region (15 Ma) and propagate more effectively in older regions. We investigate the mechanism of this propagation efficiency using numerical finite difference method simulations of 2-D seismic wave propagation. The results of this study demonstrate that the increase in propagation efficiency of Po/So waves depends on the age of the oceanic lithosphere, and this relationship can be qualitatively explained by thickening of the oceanic lithosphere including small-scale heterogeneities and a reduction in the intrinsic attenuation. These small-scale heterogeneities may form continuously in oceanic lithosphere from the time of its formation at a spreading ridge, via the solidification of melts distributed in the asthenosphere.

  14. Temperature-dependent transient creep and dynamics of cratonic lithosphere

    NASA Astrophysics Data System (ADS)

    Birger, Boris I.

    2013-11-01

    Large-scale mantle convection forms the upper boundary layer (lithosphere) where the vertical temperature drop is about 1300 K. Theoretical rheology and laboratory experiments with rock samples show that transient creep occurs while creep strains are sufficiently small. The transient creep is described by the temperature-dependent Andrade rheological model. Since plate tectonics allows only small deformations in lithospheric plates, creep of the lithosphere plates is transient whereas steady-state creep, described by non-Newtonian power-law rheological model, takes place in the underlying mantle. The solution of stability problem shows that the lithosphere is stable but small-scale convective oscillations are attenuated very weakly in regions of thickened lithosphere beneath continental cratons (subcratonic roots) where the thickness of the lithosphere is about 200 km. These oscillations create small-scale convective cells (the horizontal dimensions of the cells are of the order of the subcratonic lithosphere thickness). Direction of motion within the cells periodically changes (the period of convective oscillations is of the order of 3 × 108 yr). In this study, the oscillations of cratonic lithosphere caused by initial relief perturbation are considered. This relief perturbation is assumed to be created by overthrusting in orogenic belts surrounding cratons. The perturbation of the Earth's surface relief leads to a fast isothermal process of isostatic recovery. In the presence of vertical temperature gradient, vertical displacements, associated with the recovery process in the lithosphere interior, instantly produce the initial temperature perturbations exciting thermoconvective oscillations in the cratonic lithosphere. These small-amplitude convective oscillations cause oscillatory crustal movements which form sedimentary basins on cratons.

  15. Subduction-driven recycling of continental margin lithosphere.

    PubMed

    Levander, A; Bezada, M J; Niu, F; Humphreys, E D; Palomeras, I; Thurner, S M; Masy, J; Schmitz, M; Gallart, J; Carbonell, R; Miller, M S

    2014-11-13

    Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones.

  16. The model of lithospheric thickness beneath China from gravity data

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Ravat, D.

    2015-12-01

    We compare estimates of lithospheric thickness from several studies in China and examine whether the available gravity field anomalies can constrain these estimates. Ma (1987) suggested based on integrated geophysics that the lithospheric thickness varies from ~130 km in Qinling Dabie orogenic belt to ~60 km in Beijing, and ~50 km in Bohai bay. Lebedev and Nolet (2003) determined the lithospheric thickness in Bohai bay to be ~140 km from S wave tomography. Sodoudi et al.'s (2006) estimate of the lithospheric thickness is 72 km in Qinling Dabie orogenic belt and ~60 km in north China block. Since physical character differences exist between lithosphere and asthenosphere, it is possible to determine the thickness of lithospheric though gravity data. In this study, we use the crustal thickness obtained from teleseismic receiver functions (Li et al., 2014) to model the Moho gravity field variation and then remove this variation from the observed gravity field. Based on the residual field, the lithospheric thickness is obtained by the Parker inversion. Results show that the lithospheric thickness beneath China varies from ~80 km in the north of XinJiang to ~140 km in Tibet, and it changes to ~100 km in Eastern China. The residual field used for inversion is smooth which results in a smooth lithosphere-asthenosphere boundary (LAB). The LAB is generally in agreement with the previous seismic inversion result along profiles in eastern China (e.g. Li et al., 2011) and suggests that our method could be used to estimate the regional lithospheric variation in other areas in China, and somewhere else.

  17. Lithospheric cooling as a basin forming mechanism within accretionary crust.

    NASA Astrophysics Data System (ADS)

    Holt, P. J.; Allen, M.; van Hunen, J.; Björnseth, H. M.

    2009-04-01

    Widely accepted basin forming mechanisms are limited to flexure of the lithosphere, lithospheric stretching, lithospheric cooling following rifting and, possibly, dynamic topography. In this work forward models have been used to investigate lithospheric growth due to cooling beneath accretionary crust, as a new basin forming mechanism. Accretionary crust is formed from collision of island arcs, accretionary complexes and fragments of reworked older crust at subduction zones, and therefore has thin lithosphere due to melting and increased convection. This is modeled using a 1D infinite half space cooling model similar to lithospheric cooling models for the oceans. The crustal composition and structure used in the models has been varied around average values of accretionary crust to represent the heterogeneity of accretionary crust. The initial mantle lithosphere thickness used in the model was 20 km. The model then allows the lithosphere to thicken as it cools and calculates the subsidence isostatically. The model produces sediment loaded basins of 2-7 km for the various crustal structures over 250 Myrs. Water-loaded tectonic subsidence curves from the forward models were compared to tectonic subsidence curves produced from backstripping wells from the Kufrah and Ghadames basins, located on the accretionary crust of North Africa. A good match between the subsidence curves for the forward model and backstripping is produced when the best estimates for the crustal structure, composition and the present day thickness of the lithosphere for North Africa are used as inputs for the forward model. This shows that lithospheric cooling provides a good method for producing large basins with prolonged subsidence in accretionary crust without the need for initial extension.

  18. Sedimentary loading, lithospheric flexure and subduction initiation at passive margins

    SciTech Connect

    Erickson, S.G. . Dept. of Earth Sciences)

    1992-01-01

    Recent theoretical models have demonstrated the difficulty of subduction initiation at passive margins, whether subduction is assumed to initiate by overcoming the shear resistance on a thrust fault through the lithosphere or by failure of the entire lithosphere in bending due to sedimentary loading. A mechanism for subduction initiation at passive margins that overcomes these difficulties incorporates the increased subsidence of a marginal basin during decoupling of a previously locked margin. A passive margin may decouple by reactivation of rift-related faults in a local extensional or strike-slip setting. Flexure of marginal basins by sedimentary loading is modeled here by the bending of infinite and semi-infinite elastic plates under a triangular load. The geometry of a mature marginal basin fits the deflection produced by loading of an infinite plate in which the flexural rigidity of continental lithosphere is larger than that of oceanic lithosphere. Decoupling of such a locked passive margin by fault reactivation may cause the lithospheric bending behavior of the margin to change from that of an infinite plate to that of a semi-infinite plate, with a resultant increase in deflection of the marginal basin. The increase in deflection depends on the flexural rigidities of continental and oceanic lithosphere. For flexural rigidities of 10[sup 30]-10[sup 31] dyn-cm (elastic lithosphere thicknesses 24--51 km), the difference in deflections between infinite and semi-infinite plates is 15--17 km, so that decoupling sinks the top of the oceanic lithosphere to depths of ca 35 km. Additional sedimentation within the basin and phase changes within the oceanic crust may further increase this deflection. Subduction may initiate if the top of the oceanic lithosphere sinks to the base of the adjacent elastic lithosphere.

  19. Perennial plate tectonics with lasting mantle lithosphere scars

    NASA Astrophysics Data System (ADS)

    Heron, P.; Pysklywec, R. N.; Stephenson, R.

    2015-12-01

    Although the conventional theory of plate tectonics can explain non-rigid behaviour at plate boundaries, it cannot adequately explain the processes involved in deformation and seismicity within plate interiors. Here, we consider that the pre-existing deformation or "scarring" within the mantle lithosphere may have a very long lived presence that could incorporate deformation of the plate interior and plate boundary. Mantle lithosphere scars from continent-continent collisions could generate virtual plate boundaries that remain over long timescales, producing "perennial" plate tectonics. Local geophysical studies can map the crustal environment well, and global whole mantle tomography models are rapidly improving, yet high-resolution images of the mantle lithosphere are often not available in regions where scarring may be present. Where mantle lithosphere heterogeneities have been observed (usually interpreted simply as subduction scars), the same attention has not been afforded to them as, for example, re-activation of faults within the Earth's crust. In idealized numerical simulations, we compare how relic scarring at varying depths in the lithosphere affects patterns of deformation. High-resolution thermal-mechanical numerical experiments explore continental lithospheric deformation featuring a weakened crust and mantle lithosphere scars. Our models show that deep lithospheric scars can control the tectonic evolution of a region over shallow geological features, indicating the importance of mantle lithosphere heterogeneities. The Altyn Tagh Fault (ATF) in central China is an example of an ancient continental collision zone that undergoes periodic deformation during times of regional compression. We suggest that the ATF may be a locale where a long-lasting mantle lithosphere scar can control the subsequent crustal evolution and deformation, with ancient plate boundaries having a "perennial" plate tectonic presence.

  20. Folded Lithospheric Basins in Central Asia: Altai-Sayan and Tien Shan basins in a folding lithosphere

    NASA Astrophysics Data System (ADS)

    Delvaux, Damien; Cloetingh, Sierd; Beekman, Fred; Sokoutis, Dimitrios; Burov, Evguenii; Buslov, Misha; Abdrakhmatov, Kanatbeck

    2014-05-01

    Central Asia is a classic example for continental lithospheric folding. In particular, the Altay-Sayan belt in South-Siberia and the Kyrgyz Tien Shan display a special mode of lithospheric deformation, involving decoupled lithospheric mantle folding and upper crustal folding and faulting. A review of the paleostress data and tectono-stratigraphic evolution of the Kurai-Chuya basin in Siberian Altai, Zaisan basin in Kazakh South Altai and Issyk-Kul basin in Kyrgyz Tien Shan suggests that these basins were initiated in an extensional context and later inverted by a combination of fault-controlled deformation and flexural folding. They deformed by a combination of lithospheric buckling inducing surface tilting, uplift and subsidence, together with upper crustal fault-controlled deformation. They are good examples of Folded Lithospheric Basins (FLB) which typically form in a buckling lithosphere. Their characteristic basin fill and symmetry, inner structure, folding wavelength and amplitude, thermal regime and time frame are examined in relation to basement structure, stress field, strain rate, timing of deformation, and compared to existing modelling results. Both regions of active lithospheric folding have a heterogeneous crust with a long history of accretion-collision, subsequently reactivated as a far-field effect of the Indian-Eurasian collision. Thanks to the youthfulness of the tectonic deformation in this region (peak deformation in late Pliocene - early Pleistocene), the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures.

  1. Radioxenon detections in the CTBT international monitoring system likely related to the announced nuclear test in North Korea on February 12, 2013.

    PubMed

    Ringbom, A; Axelsson, A; Aldener, M; Auer, M; Bowyer, T W; Fritioff, T; Hoffman, I; Khrustalev, K; Nikkinen, M; Popov, V; Popov, Y; Ungar, K; Wotawa, G

    2014-02-01

    Observations made in April 2013 of the radioxenon isotopes (133)Xe and (131m)Xe at measurement stations in Japan and Russia, belonging to the International Monitoring System for verification of the Comprehensive Nuclear-Test-Ban Treaty, are unique with respect to the measurement history of these stations. Comparison of measured data with calculated isotopic ratios as well as analysis using atmospheric transport modeling indicate that it is likely that the xenon measured was created in the underground nuclear test conducted by North Korea on February 12, 2013, and released 7-8 weeks later. More than one release is required to explain all observations. The (131m)Xe source terms for each release were calculated to 0.7 TBq, corresponding to about 1-10% of the total xenon inventory for a 10 kt explosion, depending on fractionation and release scenario. The observed ratios could not be used to obtain any information regarding the fissile material that was used in the test.

  2. Cratonic lithosphere: an electrifying view (Invited)

    NASA Astrophysics Data System (ADS)

    Jones, A. G.

    2013-12-01

    Deep-probing electromagnetic studies reveal the vertical and lateral electrical conductivity structure of cratonic lithosphere. At lithospheric temperatures and for silicate mantle minerals, semi-conduction is from small polaron hopping and, in the presence of water, proton conduction, both of which is thermally-driven and can be described by an Arrhenius equation. There is little compositional sensitivity, save for the far higher water contents prevalent in pyroxenes (typically 200-400 wt ppm) compared to olivine (typically 10-100 wt ppm), with the latter exhibiting a depth dependence and the former none. Seismological methods are sensitive to temperature and composition, and virtually insensitive to low amounts of water. Taken together, the two are highly complementary. Seismological and magnetotelluric studies across Southern Africa can be employed together to constraint temperature and water content, where there is a significant difference at 100 km depth between the Kaapvaal Craton compared to the Angola (Congo) Craton compared to the Zimbabwe Craton. The Congo Craton is driest but hottest, the Kaapvaal Craton exhibits laterally-varying water content and is coldest, and the Zimbabwe Craton is the wettest and intermediate in temperature. Such thermal and water content variation results in lateral rheological variation, with the wettest and warmest being more deformable. For the Canadian Shield, there is again significant lateral variation at 100 km, with the Superior Province being mostly dry, and the Slave Craton and Rae/Hearne Provinces being far wetter. By 200 km however, all of the Canadian Shield is dry, consistent with the xenolith-based observations from the Kaapvaal Craton of far higher water contents in olivine at 100 km (50-100 wt ppm) decreasing with depth to around 10 wt ppm at 200 km. The lithosphere beneath the Kimberley area of the Kaapvaal Craton has been forward modeled in a manner that is self-consistent not only with the seismological and

  3. Evidence for a large-scale remnant of subducted lithosphere beneath Fiji.

    PubMed

    Chen, W P; Brudzinski, M R

    2001-06-29

    We combine spatial variations of P- and S-wave speeds, 1000 fault plane solutions, and 6600 well-determined hypocenters to investigate the nature of subducted lithosphere and deep earthquakes beneath the Tonga back-arc. We show that perplexing patterns in seismicity and fault plane solutions can be accounted for by the juxtaposition of a steep-dipping Wadati-Benioff zone and a subhorizontal remnant of slab that is no longer attached to the actively subducting lithosphere. The detached slab may be from a previous episode of subduction along the fossil Vitiaz trench about 5 to 8 million years ago. The juxtaposition of slabs retains a large amount of subducted material in the transition zone of the mantle. Such a configuration, if common in the past, would allow the preservation of a primordial component in the lower mantle.

  4. Long-wave tangential stresses in the lithosphere and mantle of Venus

    SciTech Connect

    Zharkov, V.N.; Marchenkov, K.I.; Lyubimov, V.M.

    1987-01-01

    The loading coefficients are calculated for real models of Venus taking into account the asthenosphere for anomalous density waves positioned at different characteristic levels. An associated analysis of the topography and the non-equilibrium part of the gravitational field allows one to determine long-wave primary tangential stresses in the lithosphere and mantle for zonal harmonics with n = 2-8. The stresses in the lithosphere of Venus are approximately equal to 30 bar, while those in the lower mantle can be up to 45 bar, but they are only on the order of a few bars in the weakened upper mantle. The low level of tangential stresses in the core and mantle of Venus is an important indication that the interior of the planet is intensely heated. A conclusion is drawn on aseismic nature of Venus.

  5. Stratigraphic modeling of foreland basins: Interpreting thrust deformation and lithosphere rheology

    SciTech Connect

    Flemings, P.B.; Jordan, T.E. )

    1990-05-01

    The authors incorporate the processes of erosion and deposition in a numerical model to predict the stratal geometries and facies patterns produced during episodic thrusting in a nonmarine foreland basin. The resultant stratigraphic record is characterized by a stairstepped facies package in which each retrogradation of facies (toward the thrust) marks the onset of a thrusting event. The retrogradation of facies coincides with the migration of the forebulge toward the thrust and the generation of an erosional unconformity. In the past, changes in basin wavelength during basin evolution have been interpreted to record viscoelastic relaxation of the lithosphere. This model suggests that changes in basin wavelength are a natural consequence of the interplay between thrust and sediment loading on an elastic lithosphere.

  6. Thermomechanical model of the North American lithosphere

    NASA Astrophysics Data System (ADS)

    Tesauro, Magdala; Kaban, Mikhail; Cloetingh, Sierd; Mooney, Walter

    2014-05-01

    An integrated thermomechanical model of the lithosphere has been constructed based on various data sets and method. A consistent 3D model of the North American crust is based on the most recent seismic data from the USGS database. To this aim, we (1) defined the geometry of the main geological provinces of North America, (2) selected and evaluated the reliability of seismic crustal models in the database, (3) estimated the P-wave seismic velocity and thickness of the upper, middle and lower crust for each geological province. Temperature variations in the upper mantle have been estimated, taking into account compositional changes in cratonic regions, by applying a new inversion technique, which jointly interpret seismic velocities and gravity data. First, we inverted two tomography models into temperatures, using a uniform composition representative of a 'Primitive' mantle, which was affected by a small amount of melt extraction. In the next step, the thermal component of the density was estimated according to these initial thermal fields and was subtracted from the total density, to obtain the compositional component. These preliminary results might be affected by compositional changes of the cratonic upper mantle, usually depleted in heavy constituents. Then, the gravity effect of temperature variations is estimated and removed from the mantle gravity anomalies. The residual (temperature free) mantle anomalies are used to evaluate compositional changes in the cratonic mantle. We re-estimated the temperatures, using this new composition, and repeat calculations of the thermal and compositional density variations. These steps are reiterated until the convergence is reached. The results show that the upper mantle of the Archean North American cratons is characterized by temperatures higher than ~150°C compared to the initial thermal model, and by strong negative compositional density anomalies (-0.03 g/cm3), corresponding to Mg # (100xMg/(Mg+Fe)) >92. In turn, in

  7. Evidence for retrograde lithospheric subduction on Venus

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.; Schubert, Gerald

    1992-01-01

    Though there is no plate tectonics per se on Venus, recent Magellan radar images and topographic profiles of the planet suggest the occurrence of the plate tectonic processes of lithospheric subduction and back-arc spreading. The perimeters of several large coronae (e.g., Latona, Artemis, and Eithinoha) resemble Earth subduction zones in both their planform and topographic profile. The planform of arcuate structures in Eastern Aphrodite were compared with subduction zones of the East Indies. The venusian structures have radii of curvature that are similar to those of terrestrial subduction zones. Moreover, the topography of the venusian ridge/trench structures is highly asymmetric with a ridge on the concave side and a trough on the convex side; Earth subduction zones generally display the same asymmetry.

  8. Seasat observations of lithospheric flexure seaward of trenches

    NASA Technical Reports Server (NTRS)

    Mcadoo, D. C.; Martin, C. F.

    1984-01-01

    Lithospheric flexure seaward of deep ocean trenches is evident in Seasat altimeter observations of the marine geoid. In fact, mechanical models of lithospheric flexure can be tested directly on the Seasat altimeter data. A simple elastic model has been used for the oceanic lithosphere and, after least squares adjustments, estimates have been recovered of model parameters including outer rise (OR) amplitude, OR wavelength, and effective lithospheric thickness. Effective lithospheric thicknesses have been recovered for six regions: the Mariana, the Kuril, the Philippine, the Aleutian, the Izu-Bonin, and the Middle America OR's. These results support the proposition that effective thickness Te increases with age of lithosphere in approximate accord with the relation Te approximately C x square root of age where C approximately 4 km/square root of (m.y.). In fact, altimetric results agree more closely with this relation than do published results based on bathymetric data. The close agreement with the thickness-age relation suggests that there is no longer any need to assume that significant horizontal compression acts across the Kuril, Marianas, and Izu-Bonin trenches. This thickness-age relation implies that flexural strength of the oceanic lithosphere is temperature controlled.

  9. SEASAT observations of lithospheric flexure seaward of trenches

    NASA Technical Reports Server (NTRS)

    Mcadoo, D. C.; Martin, C. F.

    1983-01-01

    Lithospheric flexure seaward of deep ocean trenches in SEASAT altimeter observations of the marine geoid. In fact, mechanical models of lithospheric flexure can be tested directly on the SEASAT altimeter data. A simple elastic model was used for the oceanic lithosphere and, after least squares adjustments, estimates of model parameters were recovered including Outer Rise (OR) amplitude, OR wavelength, and effective lithospheric thickness. Effective lithospheric thickness was recovered for five regions: the Mariana, the Kuril, the Philippine, the Aleutian and the Middle America OR. These results support the suggestion of Bodine et al. (1981) that effective thickness, T, increased with age of lithosphere in approximate accord with the relation T approximately equals x age to the 1/2 power where C approximately equals 4 km x my to the -1/2 power. Altimetric results agree more closely with this relation than do published results based on bathymetric data. The close agreement with the thickness-age relation suggests that there is no longer any need to assume that significant horizontal compression acts across the Kuril, Marianas and Izo-Bonin trenches. This thickness-age relation implies that flexural strength of the oceanic lithosphere is temperature controlled.

  10. The Lithospheric Structure of Southern Africa from Magnetotelluric Sounding

    NASA Astrophysics Data System (ADS)

    Evans, R. L.; Jones, A. G.; Atekwana, E. A.

    2014-12-01

    Measurements of mantle electrical conductivity, made through the magnetotelluric method, offer considerable insight into the structure of cratonic lithosphere. A particularly expansive data set has been collected in Southern Africa, started through the Southern Africa Magnetotelluric Experiment (SAMTEX) experiment, now continuing north through Zambia as part of the Project for Rift Initiation Development and Evolution (PRIDE) experiment. The combined data set highlights large variability in lithospheric structure that broadly correlates with surface geology: cratonic lithosphere is generally thick and electrically resistive, while much thinner lithosphere is seen beneath mobile belts. In areas of relatively uniform resistivity structure, we have constructed resistivity-depth profiles and use new laboratory data to place constraints on the water content of lithospheric mantle. Uncertainty in our estimates arises from differences between different laboratory results, but our data are generally consistent with a slightly damp upper lithospheric mantle above a dry and strong cratonic root. Other areas show complexity of structure that is difficult to understand using current knowledge of conductivity -the Bushveld complex, where the mantle is highly conductive, is one such example. In southwestern Zambia, the lithosphere is seen to be very thin (around 50km) beneath mobile belt terrain, as was inferred nearly 40 years ago on the basis of high heatflow. The mantle is highly conductive, most likely due to a combination of elevated temperatures, water content and perhaps a trace amount of melting. This anomalous structure may be linked to the southwest propagation of the East African Rift system.

  11. Lithospheric structure of Venus from gravity and topography

    NASA Astrophysics Data System (ADS)

    Jiménez-Díaz, Alberto; Ruiz, Javier; Kirby, Jon F.; Romeo, Ignacio; Tejero, Rosa; Capote, Ramón

    2015-11-01

    There are many fundamental and unanswered questions on the structure and evolution of the venusian lithosphere, which are key issues for understanding Venus in the context of the origin and evolution of the terrestrial planets. Here we investigate the lithospheric structure of Venus by calculating its crustal and effective elastic thicknesses (Tc and Te, respectively) from an analysis of gravity and topography, in order to improve our knowledge of the large scale and long-term mechanical behaviour of its lithosphere. We find that the venusian crust is usually 20-25 km thick with thicker crust under the highlands. Our effective elastic thickness values range between 14 km (corresponding to the minimum resolvable Te value) and 94 km, but are dominated by low to moderate values. Te variations deduced from our model could represent regional variations in the cooling history of the lithosphere and/or mantle processes with limited surface manifestation. The crustal plateaus are near-isostatically compensated, consistent with a thin elastic lithosphere, showing a thickened crust beneath them, whereas the lowlands exhibit higher Te values, maybe indicating a cooler lithosphere than that when the venusian highlands were emplaced. The large volcanic rises show a complex signature, with a broad range of Te and internal load fraction (F) values. Finally, our results also reveal a significant contribution of the upper mantle to the strength of the lithosphere in many regions.

  12. Rejuvenation of the lithosphere by the Hawaiian plume.

    PubMed

    Li, Xueqing; Kind, Rainer; Yuan, Xiaohui; Wölbern, Ingo; Hanka, Winfried

    2004-02-26

    The volcanism responsible for creating the chain of the Hawaiian islands and seamounts is believed to mark the passage of the oceanic lithosphere over a mantle plume. In this picture hot material rises from great depth within a fixed narrow conduit to the surface, penetrating the moving lithosphere. Although a number of models describe possible plume-lithosphere interactions, seismic imaging techniques have not had sufficient resolution to distinguish between them. Here we apply the S-wave 'receiver function' technique to data of three permanent seismic broadband stations on the Hawaiian islands, to map the thickness of the underlying lithosphere. We find that under Big Island the lithosphere is 100-110 km thick, as expected for an oceanic plate 90-100 million years old that is not modified by a plume. But the lithosphere thins gradually along the island chain to about 50-60 km below Kauai. The width of the thinning is about 300 km. In this zone, well within the larger-scale topographic swell, we infer that the rejuvenation model (where the plume thins the lithosphere) is operative; however, the larger-scale topographic swell is probably supported dynamically.

  13. Lithospheric cooling and thickening as a basin forming mechanism

    NASA Astrophysics Data System (ADS)

    Holt, Peter J.; Allen, Mark B.; van Hunen, Jeroen; Bjørnseth, Hans Morten

    2010-12-01

    Widely accepted basin forming mechanisms are limited to flexure of the lithosphere, and lithospheric stretching followed by cooling and thermal subsidence. Neither of these mechanisms works for a group of large basins, sometimes known as "intracontinental sags". In this paper we investigate cooling and thickening of initially thin lithosphere as a basin forming mechanism, by a combination of forward modelling and a backstripping study of two Palaeozoic North African basins: Ghadames and Al Kufrah. These are two of a family of basins, once unified, which lie over the largely accretionary crust of North Africa and Arabia. Such accretionary crust tends to be juvenile, consisting of amalgamated island arcs, accretionary prisms and melanges, and typically has near-normal crustal thicknesses but initially thin mantle lithosphere. Post-accretion subsidence is modelled using a plate cooling model similar to cooling models for oceanic lithosphere. The crustal composition and thickness used in the models are varied around average values of accretionary crust to represent likely heterogeneity. The model allows the lithosphere to thicken as it cools and calculates the resulting isostatic subsidence. Water-loaded tectonic subsidence curves from these forward models are compared to tectonic subsidence curves produced from backstripped wells from Al Kufrah and Ghadames Basins. A good match between the subsidence curves for the forward model and backstripping is produced when the best estimates for the crustal structure, composition and the present day thickness of the lithosphere for North Africa are used as inputs for the forward model. The model produces sediment loaded basins of 2-7 km thickness for the various crustal assemblies over ~ 250 Myr. This shows that lithospheric cooling provides a viable method for producing large basins with prolonged subsidence, without the need for initial extension, provided the condition of initially thin mantle lithosphere is met.

  14. Lithospheric thinning in the Eastern Indian Craton: Evidence for lithospheric delamination below the Archean Singhbhum Craton?

    NASA Astrophysics Data System (ADS)

    Mandal, Prantik

    2017-02-01

    We herein present shear velocity structure extending down to 300 km depth below the Archean Singhbhum-Odisha Craton (SOC) and Proterozoic Chotanagpur granitic-gneissic terrain (CGGT), which has been obtained through the inversion modeling of P-receiver functions. We use three-component broadband recordings of 200 teleseismic earthquakes (30° ≤ ∆ ≤ 90°) from a 15 station seismic network that has been operational in the Eastern Indian shield since February 2013. We obtain the thinnest crust of 35 km overlying a thin lithosphere of 78 km, below the region near south Singhbhum shear zone, which could be attributed to the 1.6 Ga plume activity associated with Dalma volcanic. However, the thickest crust of 47 km overlying a thin lithosphere of 81 km is noticed below the region near the Singhbhum granite of 3.6 Ga. This thinning of lithosphere could be attributed to the delamination of lithospheric root due to the Himalayan orogeny with a shortening rate of 2 cm/year. This delamination model in SOC gets further support from the densification of the lower crust, which could result from repeated episodes of basaltic underplating associated with episodes related to Dalma ( 1.6 Ga) and Rajmahal ( 117 Ma) volcanisms. This led to relatively more mafic, heterogeneous and deformed crustal structure in SOC as well as EGMB (with an average crustal Vs of 4.0 km/s) in comparison to that in CGGT (with an average crustal Vs of 3.9 km/s), as seen through our modeling results. The thickest lithosphere of 100 km is observed in the southwestern SOC as well as northeastern CGGT. We also notice that a sharp and flat Moho in CGGT, which could be attributed to thermal reactivation and large volume melting of the mafic cratonic crust during the late Archean subduction process and associated volcanism episodes. This model gets further support from the estimated 169 km thick lower Vs zone in the upper mantle below CGGT. Our modeling results also support a northward subduction of Archean

  15. Constraints of the Style of Tibetan Lithospheric Deformation and their Consequences for Resolving the Orogeny Paradox.

    NASA Astrophysics Data System (ADS)

    Silver, P. G.; Flesch, L.

    2005-12-01

    The process of continent-continent collision is central to our understanding of continental dynamics. The Tibetan plateau, the most spectacular manifestation of this phenomenon, has long been used as a natural laboratory for studying the collisional process. While the most obvious properties of Tibet, namely its high topography and thickened crust, are easily explained by the shortening and thickening of continental lithosphere, idealized by the deformation of a thin viscous sheet, there remain basic thermomechanical properties that do not fit this simple picture. In particular, the expected advective thickening of continental geotherms predicts a strong, cool, upper mantle. In contrast, the basic morphology of the plateau, the observation of low mantle seismic velocities, the presence of N-S-oriented normal faulting, and significant volcanic activity, all argue instead for weak, high temperature lithosphere beneath the plateau. This discrepancy, which we have referred to as the "Orogeny Paradox", has led researchers to propose models that invoke more complex styles of deformation, such as mantle delamination, lower crustal flow, and continental subduction. The simple thin-viscous-sheet model, as well as these more complex models, make predictions about the relationship between crust and mantle deformation, that form the basis for a test. We have recently completed a study of the mechanical properties of Tibet (Flesch et al., 2005) and surrounding regions that places important constraints on the actual style of Tibetan lithospheric deformation. This study jointly modeled the surface deformation field estimated from geodesy and Quaternary fault slip, and the mantle deformation field inferred from shear-wave splitting observations. The results strongly support a lithosphere in which its crust and mantle components are mechanically coupled, deform coherently, and are roughly similar in strength. It is thus difficult to reconcile these observations with the more

  16. Influence of heterogeneities within the lithosphere on the deformation pattern of continental rift systems.

    NASA Astrophysics Data System (ADS)

    Philippon, Melody; Thieulot, Cedric; van Wijk, Jolante; Sokoutis, Dimitrios; Willingshofer, Ernst; Cloetingh, Sierd

    2013-04-01

    Understanding how heterogeneities within the lithosphere influence the deformation pattern in continental rifts still remains a challenge and is of real importance to constrain continental break-up. We have selected the Main Ethiopian Rift in East Africa and the Rio Grande Rift in the south-western U.S. These two rifts are perfect natural laboratories to investigate the effect of inherited as they share similar structural characteristics but develop above different kinds of lithosphere-scale heterogeneities. From a structural point of view both rifts show similar length (1000km), width (50 to 70 km) and asymmetry. The Main Ethiopian rift is the NE-SW trending plate boundary between the Nubian and Somalian plates that has been developing for the past 11 Ma above a palaeo-Proterozoic lithospheric-scale weak zone re-heated by the Afar hotspot, whereas the Rio Grande Rift is the eastern "boundary" of the Basin & Range system which has been developing for the past 30 Ma in the frame of a westward-retreating Farallon subduction zone. However, the Rio Grande Rift shows evidence of low angle normal faulting whereas the Main Ethiopian Rift shows steeply dipping (with a mean close to 70°) normal faults. The Main Ethiopian Rift shows larger volume of erupted lavas than the Rio Grande Rift. Combined with a structural analyses of both rifts, we present here a series of 2D cross sections numerical models that allow better understanding of the influence of initial heterogeneities such as 1) the rheological state of the crust; 2) the presence of a crustal-scale to lithospheric-scale discrete weak or strong zone, 3) the effects of the presence of magma. We illustrate that rheological boundaries are not reactivated if the rheological contrast it too high, which is the case of the Rio Grande Rift that developed to the east of the North American Craton within thinned lithosphere. We also illustrate that the width of the weak zone do no have any influence on the exhumation of the

  17. Subduction-Driven Recycling of Continental Margin Lithosphere

    NASA Astrophysics Data System (ADS)

    Levander, Alan; Bezada, Maximiliano; Niu, Fenglin; Palomeras, Imma; Humphreys, Eugene; Carbonell, Ramon; Gallart, Josep; Schmitz, Michael; Miller, Meghan

    2016-04-01

    Subduction recycling of oceanic lithosphere, a central theme of plate tectonics, is relatively well understood. Recycling continental lithosphere is more difficult to recognize, can take a number of different forms, and appears to require an external trigger for initiation. Delamination and localized convective downwelling are two processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. We describe a related process that can lead to the loss of continental lithosphere adjacent to a subduction zone: Subducting oceanic plates can entrain and recycle lithospheric mantle from an adjacent continent and disrupt the continental lithosphere far inland from the subduction zone. Body wave tomograms from dense broadband seismograph arrays in northeastern South America (SA) and the western Mediterranean show larger than expected volumes of positive velocity anomalies which we identify as the subducted Atlantic slab under northeastern SA, and the Alboran slab beneath the Gibraltar arc (GA). The positive anomalies lie under and are aligned with the continental margins at sublithospheric depths. The continental margins along which the subduction zones have traversed, i.e. the northeastern SA plate boundary and east of GA, have significantly thinner lithosphere than expected. The thinner than expected lithosphere extends inland as far as the edges of nearby cratons as determined from receiver function images and surface wave tomography. These observations suggest that subducting oceanic plates viscously entrain and remove continental mantle lithosphere from beneath adjacent continental margins, modulating the surface tectonics and pre-conditioning the margins for further deformation. The latter can include delamination of the entire lithospheric mantle and include the lower crust, as around GA, inferred by results from active and passive seismic experiments. Viscous removal of continental margin lithosphere creates LAB topography leading

  18. Lithospheric structure on Venus from tectonic modelling of compressional features

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.; Golombek, M. P.

    1987-01-01

    In previous studies, extensional models were used that incorporated realistic rheologies in order to constrain lithospheric structure. Lithospheric modelling is considered herein from the standpoint of compressional deformation. Features of presumed compressional tectonic origin are reviewed and a model for compressional folding based on lithospheric strength envelopes are presented that include the effects of both brittle and ductile yielding as well as finite elastic strength. Model predictions are then compared with the widths and spacings of observed tectonic features and it is concluded that the results are consistent with a thin crust overlying a relatively stronger mantle, with thermal gradients probably in the range of 10 to 15 deg/km.

  19. Introduction of sub-lithospheric component into melted lithospheric base by propagating crack: Case study of migrated Quaternary volcanoes in Wudalianchi, China

    NASA Astrophysics Data System (ADS)

    Chuvashova, Irina; Sun, Yi-min

    2016-04-01

    mantle beneath the northern Songliao basin and that admixture of the common sub-lithospheric component was locally introduced into the melted region by mechanism of propagating crack. This study is based on analytical data obtained for volcanic rocks in the Chinese-Russian Wudalianchi-Baikal Research Center on recent volcanism and environment. Major oxides were determined by "wet chemistry" at the Institute of the Earth's Crust SB RAS, Irkutsk. Trace-elements were measured by ICP-MS technique using mass-spectrometer Agilent 7500ce of the Center for collective use "Microanalysis" (Limnological Institute of SB RAS, Irkutsk) and Nd, Pb, and Sr isotopes by TIMS technique using mass-spectrometer Finnigan MAT 262 of the Center for collective use "Geodynamics and geochronology" (Institute of the Earth's Crust SB RAS). The work was supported by the RFBR grant № 16-05-00774. References Chuvashova, I.S., Rasskazov, S.V., Liu, J., Meng, F., Yasnygina, T.A., Fefelov, N.N., Saranina, E.V., 2009. Isotopically-enriched components in evolution of Late Cenozoic potassic magmatism in Heilongjiang province, northeast China, Proceedings of the Irkutsk State University. Series of Earth Sciences, 2 (2), pp. 181-198. Guide book for field mission to Wudalianchi National Park, China, 2010. Prepared by Wudalianchi National Park and Nature Management Committee Heilongjiang province, 50 p. Foulger, G.R., 2010. Plates vs. plumes: a geological controversy. Wiley-Blackwell, 328 p. Rasskazov, S.V., Yasnygina, T.A., Chuvashova, I.S. Mantle sources of the Cenozoic volcanic rocks of East Asia: Derivatives of slabs, the sub-lithospheric convection, and the lithosphere. Russian Journal of Pacific Geology. 2014. V. 8 (5), 355-371. Wang, Y., Chen, H., 2005. Tectonic controls on the Pleistocene-Holocene Wudalianchi volcanic field (northeastern China), Journal of Asian Earth Sciences, 24, pp. 419-431.

  20. An Equivalent Source Method for Modelling the Lithospheric Magnetic Field Using Satellite and Airborne Magnetic Data

    NASA Astrophysics Data System (ADS)

    Kother, L. K.; Hammer, M. D.; Finlay, C. C.; Olsen, N.

    2014-12-01

    We present a technique for modelling the lithospheric magnetic field based on estimation of equivalent potential field sources. As a first demonstration we present an application to magnetic field measurements made by the CHAMP satellite during the period 2009-2010. Three component vector field data are utilized at all latitudes. Estimates of core and large-scale magnetospheric sources are removed from the satellite measurements using the CHAOS-4 model. Quiet-time and night-side data selection criteria are also employed to minimize the influence of the ionospheric field. The model for the remaining lithospheric magnetic field consists of magnetic point sources (monopoles) arranged in an icosahedron grid with an increasing grid resolution towards the airborne survey area. The corresponding source values are estimated using an iteratively reweighted least squares algorithm that includes model regularization (either quadratic or maximum entropy) and Huber weighting. Data error covariance matrices are implemented, accounting for the dependence of data error variances on quasi-dipole latitudes. Results show good consistency with the CM5 and MF7 models for spherical harmonic degrees up to n = 95. Advantages of the equivalent source method include its local nature and the ease of transforming to spherical harmonics when needed. The method can also be applied in local, high resolution, investigations of the lithospheric magnetic field, for example where suitable aeromagnetic data is available. To illustrate this possibility, we present preliminary results from a case study combining satellite measurements and local airborne scalar magnetic measurements of the Norwegian coastline.

  1. Evidence for recycled Archaean oceanic mantle lithosphere in the Azores plume.

    PubMed

    Schaefer, Bruce F; Turner, Simon; Parkinson, Ian; Rogers, Nick; Hawkesworth, Chris

    2002-11-21

    The compositional differences between mid-ocean-ridge and ocean-island basalts place important constraints on the form of mantle convection. Also, it is thought that the scale and nature of heterogeneities within plumes and the degree to which heterogeneous material endures within the mantle might be reflected in spatial variations of basalt composition observed at the Earth's surface. Here we report osmium isotope data on lavas from a transect across the Azores archipelago which vary in a symmetrical pattern across what is thought to be a mantle plume. Many of the lavas from the centre of the plume have lower 187Os/188Os ratios than most ocean-island basalts and some extend to subchondritic 187Os/188Os ratios-lower than any yet reported from ocean-island basalts. These low ratios require derivation from a depleted, harzburgitic mantle, consistent with the low-iron signature of the Azores plume. Rhenium-depletion model ages extend to 2.5 Gyr, and we infer that the osmium isotope signature is unlikely to be derived from Iberian subcontinental lithospheric mantle. Instead, we interpret the osmium isotope signature as having a deep origin and infer that it may be recycled, Archaean oceanic mantle lithosphere that has delaminated from its overlying oceanic crust. If correct, our data provide evidence for deep mantle subduction and storage of oceanic mantle lithosphere during the Archaean era.

  2. Investigating the Lithospheric Structure of Southern Madagascar

    NASA Astrophysics Data System (ADS)

    Tilmann, F. J.; Yuan, X.; Rumpker, G.; Heit, B.; Rambolamana, G.; Rindraharisaona, E.; Priestley, K. F.

    2013-12-01

    The island of Madagascar occupies a key region in both the assembly and the multi-stage breakup of Gondwanaland, itself part of the super-continent Pangaea. Madagascar consists of an amalgamation of continental material, with the oldest rocks being of Archaean age. Its ancient fabric is characterised by several shear zones, some of them running oblique to the N-S trend, in particular in the south of the island. More recently during the Neogene, moderate volcanism has occurred in the Central and Northern part of the island, and there are indications of uplift throughout Eastern Madagascar over the last 10 Ma. Although Madagascar is now located within the interior of the African plate and far away from major plate boundaries (> 1000 km from the East African rift system and even further from the Central and South-West Indian Ridges), its seismic activity indicates that some deformation is taking place, and present-day kinematic models based on geodetic data and earthquake moment tensors in the global catalogues identify a diffuse N-S-oriented minor boundary separating two microplates, which appears to pass through Madagascar. In spite of the presence of Archaean and Proterozoic rocks continent-wide scale studies indicate a thin lithosphere (<120 km) throughout Madagascar, but are based on sparse data and cannot resolve the difference between eastern and western Madagascar. We are operating a ENE-WSW oriented linear array of 25 broadband stations in southern Madagascar, extending from coast to coast and sampling the sedimentary basins in the west as well as the metamorphic rocks in the East, cutting geological boundaries seen at the surface at high angle. The array crosses the prominent Bongolava-Ranotsara shear zone which is thought to have been formed during Gondwanaland assembly. The array recorded the magnitude 5.3 earthquake of January 25, 2013 which occurred just off its western edge. In addition, in May 2013 we have deployed 25 short period sensors in the

  3. Determination of the Earth's lithospheric magnetic field with satellite data

    NASA Astrophysics Data System (ADS)

    Kotsiaros, Stavros; Olsen, Nils; Finlay, Christopher

    2016-07-01

    Satellites such as Magsat, Ørsted, CHAMP and Swarm provide the most effective means of determining on a global scale the Earth's lithospheric magnetic field. In particular, the Swarm three-satellite constellation mission aims at capturing the smallest-scale features of the lithospheric field that have ever been captured from space. To achieve that, explicit advantage of the constellation aspect of Swarm has to be taken by using gradient estimates. We derive lithospheric field models using more than one year of magnetic gradient data, which are approximated by first differences of field vector data between the two lower Swarm satellites and along each satellite orbit, respectively. We find that gradient data are less sensitive to large-scale external field fluctuations. Moreover, gradient data appear to be a very efficient way of increasing the resolution of lithospheric field models and thus providing an initial validation of the gradient concept underlying the Swarm mission.

  4. Global strength and elastic thickness of the lithosphere

    NASA Astrophysics Data System (ADS)

    Tesauro, Magdala; Kaban, Mikhail K.; Cloetingh, Sierd A. P. L.

    2012-06-01

    The strength and effective elastic thickness (Te) of the lithosphere control its response to tectonic and surface processes. Here, we present the first global strength and effective elastic thickness maps, which are determined using physical properties from recent crustal and lithospheric models. Pronounced strength contrasts exist between old cratons and areas affected by Tertiary volcanism, which mostly coincide with the boundaries of seimogenic zones. Lithospheric strength is primarily controlled by the crust in young (Phanerozoic) geological provinces characterized by low Te (~ 25 km), high topography (> 1000 m) and active seismicity. In contrast, the old (Achaean and Proterozoic) cratons of the continental plates show strength primarily in the lithospheric mantle, high Te (over 100 km), low topography (< 1000 m) and very low seismicity.

  5. Lithospheric Stress and Deformation (Paper 7R0323)

    NASA Astrophysics Data System (ADS)

    McNutt, Marcia

    1987-07-01

    The study of the mechanisms, magnitudes, and modes of lithospheric stress and deformation occupies a central position in the discipline of Tectonophysics. It is therefore difficult in assembling a comprehensive review to place limits on what should be included. For example, one cannot discuss stress and deformation apart from considerations of the rheological models of the lithosphere which link the two and ultimately control the behavior of plates at their margins and in their interiors. Once admitting to the importance of rheological considerations in discussing stress and deformation, one is then compelled to include information relating to the thermal state of the lithosphere, since temperature is one of the foremost environmental variables controlling rheology. Furthermore, lithospheric processes cannot be considered in isolation from those affecting the asthenosphere, since surely there exists some coupling between the motion of the lithosphere and convection in the Earth's interior. In fact, an understanding of lithospheric stress and deformation can be considered a prerequisite to solving problems in geodynamics because it is through the lithospheric filter that one detects the consequences of thermal and compositional anomalies at greater depth. The topic of this report cannot even be cleanly separated from reviews in other disciplines such as Seismology and Geodesy. The magnitude and orientation of lithospheric stress is often indicated by earthquakes, while lithospheric strain can be observed geodetically. The philosophy I have adopted here is that some overlap with other review papers in this series is unavoidable, and probably desirable from the standpoint of emphasizing how recent work n other areas of geophysics has contributed to the advancement in our understanding of the lithosphere's state-of-stress and mechanisms of deformation. I have, however, resisted the temptation to include extraterrestrial studies, presumably covered in the Planetary

  6. Tearing of the Indian lithospheric slab beneath southern Tibet revealed by SKS-wave splitting measurements

    NASA Astrophysics Data System (ADS)

    Chen, Yun; Li, Wei; Yuan, Xiaohui; Badal, José; Teng, Jiwen

    2015-03-01

    Shear wave birefringence is a direct diagnostic of seismic anisotropy. It is often used to infer the northern limit of the underthrusting Indian lithosphere, based on the seismic anisotropy contrast between the Indian and Eurasian plates. Most studies have been made through several near north-south trending passive-source seismic experiments in southern Tibet. To investigate the geometry and the nature of the underthrusting Indian lithosphere, an east-west trending seismic array consisting of 48 seismographs was operated in the central Lhasa block from September 2009 to November 2010. Splitting of SKS waves was measured and verified with different methods. Along the profile, the direction of fast wave polarization is about 60° in average with small fluctuations. The delay time generally increases from east to west between 0.2 s and 1.0 s, and its variation correlates spatially with north-south oriented rifts in southern Tibet. The SKS wave arrives 1.0-2.0 s later at stations in the eastern part of the profile than in the west. The source of the anisotropy, estimated by non-overlapped parts of the Fresnel zones at stations with different splitting parameters, is concentrated above ca. 195 km depth. All the first-order features suggest that the geometry of the underthrusting Indian lithospheric slab in the Himalayan-Tibetan collision zone beneath southern Tibet is characterized by systematic lateral variations. A slab tearing and/or breakoff model of Indian lithosphere with different subduction angles is likely a good candidate to explain the observations.

  7. The effects of strain heating in lithospheric stretching models

    NASA Technical Reports Server (NTRS)

    Stanton, M.; Hodge, D.; Cozzarelli, F.

    1985-01-01

    The deformation by stretching of a continental type lithosphere has been formulated so that the problem can be solved by a continuum mechanical approach. The deformation, stress state, and temperature distribution are constrained to satisfy the physical laws of conservation of mass, energy, momentum, and an experimentally defined rheological response. The conservation of energy equation including a term of strain energy dissipation is given. The continental lithosphere is assumed to have the rheology of an isotropic, incompressible, nonlinear viscous, two layered solid.

  8. Solar Insolation Driven Variations of Mercury's Lithospheric Strength

    NASA Astrophysics Data System (ADS)

    Williams, Jean-pierre; Ruiz, J.; Rosenburg, M. A.; Aharonson, O.; Phillips, R. J.

    2010-10-01

    Mercury's coupled 3:2 spin-orbit resonance in conjunction with its relatively high eccentricity of 0.2 results in a surface variation in annual average solar insolation and thus equatorial hot and cold regions. This results in an asymmetric temperature distribution in the lithosphere and a long wavelength lateral variation in lithosphere structure and strength that mirrors the insolation pattern. We employ a thermal evolution model for Mercury generating strength envelopes of the lithosphere to demonstrate and quantify the possible effects the insolation pattern has on Mercury's lithosphere. We find the heterogeneity in lithosphere strength is substantial, increases with time, and is accentuated by the differential timing of the mantle contribution to the lithosphere strength. For example, by the end of late heavy bombardment ( 4 Ga) we find a difference in brittle-ductile transition depth of 6 km between the hot and cold equatorial thermal poles and 24 km between the hot equatorial pole and the latitudes ±90°. We also find that a crust thicker than that of the Moon or Mars and dry rheologies for the crust and mantle are favorable when compared with estimates of brittle-ductile transition depths derived from lobate scarps. Regions of stronger and weaker compressive strength imply that the accommodation of radial contraction of Mercury as its interior cooled, manifest as lobate scarps, may not be isotropic, imparting a preferential orientation and distribution to the lobate scarps. Although many of the parameters of the model are poorly constrained for Mercury, the overall lithospheric heterogeneity remains regardless of the choice of parameters. The latitudinal surface temperature variation experienced by Mercury is not unlike that of the Earth's Moon presently and thus one should expect an analogous latitude dependence on lithospheric strength to have developed over time on the Moon as well. Funded by the NSF Astrophysics Research Grants program (AST-0709151).

  9. Fertile Lithospheric Mantle beneath Far East Russia; evidence for Lithospheric delamination

    NASA Astrophysics Data System (ADS)

    Ntaflos, T.; Koutsovitis, P.; Aschchepkov, I.; Hauzenberger, C. A.; Prikhodko, V.; Barkar, A.

    2012-12-01

    In the back-arc environment of Far East Russia, mantle xenoliths from Sikhoti-Alin( Komku area, KO) and Primorie (Sviyaginsky area, SV), Far East Russia are fertile spinel lherzolites with traces of amphibole, phlogopite and hyalophane in some of the studied samples. Though samples from both localities are fertile there is a systematic difference in their fertility. The KO samples have mg# varying from 0.891 to 0.899 and are slightly more fertile than the SV samples that have mg# ranging from 0.898 to 0.904. LA-ICP-MS analyses on clinopyroxenes confirm this trend as the (La/Yb)N in KO samples range from 1.49 to 5.4 and in SV samples from 0.15 to 1.73. The estimated equilibration temperatures for the KO suite range from 940 °C to 1035 °C and for the SV suite from 770 to 945. The differences in the estimated equilibrium temperatures between the KO and SV suites suggest that the less fertile SV suite originated in shallower depths than the more fertile KO suite. Kaersutite, and extremely Ti-rich phlogopite, up to 14 wt% TiO2, are associated with intergranular glass indicating clearly metasomatism of undersaturated alkaline melts. Pargasitic amphibole occurs as inclusion in clinopyroxene. Incompatible element abundances, besides Ba, Sr and Ti that are slightly enriched in the amphibole, are similar in both phases suggesting minor metasomatism due to percolation of small amounts of water-rich fluids. The lithospheric mantle beneath the studied area represents the residue after partial melting of up to 2 % of a primitive mantle and is comparable to that of Mongolia. Despite the fact that the studied area experienced several subducting episodes, the lithospheric mantle appears to be unaffected from the upwelling fluids/melts of the subducted slab(s). Since there is no indication for plume activity, and/or evidence for refertilization, it is likely that the lithospheric mantle has been delaminated as the result of tectonic events (lithospheric attenuation, inverse

  10. Lithospheric growth at margins of cratons

    NASA Astrophysics Data System (ADS)

    Snyder, D. B.

    2002-09-01

    Deep seismic reflection profiles collected across Proterozoic-Archean margins are now sufficiently numerous to formulate a consistent hypothesis of how continental nuclei grow laterally to form cratonic shields. This picture is made possible both because the length of these regional profiles spans all the tectonic elements of an orogen on a particular cratonic margin and because of their great depth range. Key transects studied include the LITHOPROBE SNORCLE 1 transect and the BABEL survey, crossing the Slave and Baltic craton margins, respectively. In most cases, the older (Archean) block appears to form a wedge of uppermost mantle rock embedded into the more juvenile (Proterozoic) block by as much as 100-200 km at uppermost mantle depths and Archean lithosphere is therefore more laterally extensive at depth than at the surface. Particularly bright reflections along the Moho are cited as evidence of shear strain within a weak, low-viscosity lower crustal channel that lies along the irregular top of the indenting wedge. The bottom of the wedge is an underthrust/subduction zone, and associated late reversal in subduction polarity beneath the craton margin emerges as a common characteristic of these margins although related arc magmatism may be minor.

  11. Lithospheric imaging via teleseismic scattering tomography

    NASA Astrophysics Data System (ADS)

    Frederiksen, A. W.; Revenaugh, J.

    2004-12-01

    The coda of the teleseismic P phase consists largely of energy scattered by small inhomogeneities in the receiver-side lithosphere. Given large collections of teleseismic data from dense permanent networks, previous workers have successfully back-propagated coda energy back to scattering source points using various kinematic migration schemes, as well as by inverting using an inverse scattering/radon transform approach. Under the Born approximation, seismic scattering is a linear process; therefore it is possible to approach coda scattering as a linear waveform inversion problem, mathematically similar to transmission-based tomography. Assuming ray-theoretical propagation and Rayleigh scattering, we pose the inverse scattering problem in tomographic form, and recover perturbations in density and P and S velocities from Pp and Ps scattered data. The method is applied to data from the Southern California Seismic Network (SCSN) covering the San Jacinto-Anza region. The results show a considerable correlation between seismicity and velocity perturbation structure, particularly in the region between the Mission Creek and Banning fault branches. Features connecting the Coyote Creek and Elsinore faults at right angles are correlated with seismicity lineations and may represent conjugate faulting with no surface expression.

  12. Lithosphere - asthenosphere boundary (LAB) around the Trans-European Suture Zone (TESZ)

    NASA Astrophysics Data System (ADS)

    Plomerova, J.; Babuska, V.; Vecsey, L.; Passeq Working Group

    2012-04-01

    platform in the west and the East European Craton in the east. Lateral variations of anisotropic parameters across the zone indicate differences in mantle lithosphere fabrics on both sides. Distinct deepening of the LAB towards the east across the TESZ is detected by different approaches of the LAB modelling, but on the other hand, it is the region where European LAB models differ substantially (Jones et al., Lithos 2010). This finding re-opens a question to which extent different methods identify the same discontinuity, though discrepancies may also reflect differences in resolution and accuracy of individual methods. On the other hand, if there are differences in a nature of the LAB, we should try to understand which physical parameters are relevant to the most important interface in the upper mantle from the plate-tectonic point of view.

  13. Thermal thickness and evolution of Precambrian lithosphere: A global study

    USGS Publications Warehouse

    Artemieva, I.M.; Mooney, W.D.

    2001-01-01

    The thermal thickness of Precambrian lithosphere is modeled and compared with estimates from seismic tomography and xenolith data. We use the steady state thermal conductivity equation with the same geothermal constraints for all of the Precambrian cratons (except Antarctica) to calculate the temperature distribution in the stable continental lithosphere. The modeling is based on the global compilation of heat flow data by Pollack et al. [1993] and more recent data. The depth distribution of heat-producing elements is estimated using regional models for ???300 blocks with sizes varying from 1?? ?? 1?? to about 5?? ?? 5?? in latitude and longitude and is constrained by laboratory, seismic and petrologic data and, where applicable, empirical heat flow/heat production relationships. Maps of the lateral temperature distribution at depths 50, 100, and 150 km are presented for all continents except Antarctica. The thermal thickness of the lithosphere is calculated assuming a conductive layer overlying the mantle with an adiabat of 1300??C. The Archean and early Proterozoic lithosphere is found to have two typical thicknesses, 200-220 km and 300-350 km. In general, thin (???220 km) roots are found for Archean and early Proterozoic cratons in the Southern Hemisphere (South Africa, Western Australia, South America, and India) and thicker (>300 km) roots are found in the Northern Hemisphere (Baltic Shield, Siberian Platform, West Africa, and possibly the Canadian Shield). We find that the thickness of continental lithosphere generally decreases with age from >200 km beneath Archean cratons to intermediate values of 200 ?? 50 km in early Proterozoic lithosphere, to about 140 ?? 50 km in middle and late Proterozoic cratons. Using known crustal thickness, our calculated geotherms, and assuming that isostatic balance is achieved at the base of the lithosphere, we find that Archean and early Proterozoic mantle lithosphere is 1.5% less dense (chemically depleted) than the

  14. Geodynamic Inversion to Constrain the Nonlinear Rheology of the Lithosphere

    NASA Astrophysics Data System (ADS)

    Kaus, B.; Baumann, T.

    2015-12-01

    The rheology of the lithosphere is of key importance for the physics of the lithosphere. Yet, it is probably the most uncertain parameter in geodynamics as experiments have to be extrapolated to geological conditions and as existing geophysical methods such as EET estimation make simplifying assumptions about the structure of the lithosphere. Here, we therefore discuss a new method that employs thermo-mechanical lithospheric-scale forward models of the lithosphere using a realistic initial geometry constructed from geophysical data sets. We employ experimentally determined creep-laws for the various parts of the lithosphere, but assume that the parameters of these creep-laws as well as the temperature structure of the lithosphere are uncertain. This is used as a priori information to formulate a Bayesian inverse problem that employs topography, gravity, horizontal and vertical surface velocities to invert for the unknown material parameters and temperature structure. In order to test the general methodology, we first perform a geodynamic inversion of a synthetic forward model of intraoceanic subduction with known parameters. This requires solving an inverse problem with 14-16 parameters, depending on whether temperature is assumed to be known or not. With the help of a massively parallel direct-search combined with a Markov Chain Monte Carlo method, solving the inverse problem becomes feasible. Results show that the rheological parameters and particularly the effective viscosity structure of the lithosphere can be reconstructed in a probabilistic sense. This also holds, with somewhat larger uncertainties, for the case where the temperature distribution is parametrized. Finally, we apply the method to a cross-section of the India-Asia collision system. In this case, the number of parameters is larger, which requires solving around 1.9 × 106 forward models. The resulting models fit the data within their respective uncertainty bounds, and show that the Indian mantle

  15. Growth of lithospheric-scale fault system in NE Tibet: numerical modeling constrained by high-resolution seismic reflection data

    NASA Astrophysics Data System (ADS)

    Fu, Zhen; Zhang, Haiming

    2016-04-01

    The growth of lithospheric-scale fault system is strongly coupled with the deformation of continental lithosphere in Tibetan Plateau. Therefore, prediction of fault growth is important to understand the tectonic history of continental deformation with fault system. Recently, high-resolution seismic reflection profiling across the Kunlun fault in northeasten Tibet reveals several fault systems at the scale of lithosphere. A 2D mid-crustal strain-transfer model, which emphasized on the lateral heterogeneity of crust, was proposed to explain the seismic reflection profiling under the condition of compression. In order to understand the dynamic process of lithospheric deformation, an elastic-plastic constitutive relationship in finite element modeling is used to investigate the mechanism of the fault growth in the section under the condition of compression by allowing permanent strains to develop in response to the applied loads. The vertical and lateral heterogeneity of material, effect of plastic parameters and geometry of models from nature structure are all discussed in this study. The results compared with high-resolution seismic image show that well-designed geomechanical modeling can produce overall process of fault growth for both continuum without preexisting fault and discontinuous deformation with a peexisting fault. But the model of the Kunlun fault cutting down the Moho is not supported by the results compared with the seismic data.

  16. Investigating the Lithospheric Structure of Southern Madagascar

    NASA Astrophysics Data System (ADS)

    Tilmann, Frederik; Yuan, Xiaohui; Rümpker, Georg; Gerard, Rambolamana; Elisa, Rindraharisaona; Priestley, Keith

    2014-05-01

    The island of Madagascar occupies a key region in both the assembly and the multi-stage breakup of Gondwanaland, itself part of the super-continent Pangaea. Madagascar consists of an amalgamation of continental material, with the oldest rocks being of Archaean age. Its ancient fabric is characterised by several shear zones, some of them running oblique to the N-S trend, in particular in the south of the island. More recently during the Neogene, moderate volcanism has occurred in the Central and Northern part of the island, and there are indications of uplift throughout Eastern Madagascar over the last 10 Ma. Although Madagascar is now located within the interior of the African plate and far away from major plate boundaries (> 1000 km from the East African rift system and even further from the Central and South-West Indian Ridges), its seismic activity indicates that some deformation is taking place, and present-day kinematic models based on geodetic data and earthquake moment tensors in the global catalogues identify a diffuse N-S-oriented minor boundary separating two microplates, which appears to pass through Madagascar. In spite of the presence of Archaean and Proterozoic rocks continent-wide scale studies indicate a thin lithosphere (<120 km) throughout Madagascar, but are based on sparse data. We are operating a ENE-WSW oriented linear array of 25 broadband stations in southern Madagascar, extending from coast to coast and sampling the sedimentary basins in the west as well as the metamorphic rocks in the East, cutting geological boundaries seen at the surface at high angle. The array crosses the prominent Bongolava-Ranotsara shear zone which is thought to have been formed during Gondwanaland assembly, although this interpretation has recently been questioned. The array recorded the magnitude 5.3 earthquake of January 25, 2013 which occurred just off its western edge. In addition, in May 2013 we have deployed 25 short period sensors in the eastern part of the

  17. Lithosphere-Atmosphere-Ionosphere coupling model

    NASA Astrophysics Data System (ADS)

    Kachakhidze, M. K., III

    2015-12-01

    The present work offers interpretation of a mechanism of formation of hypothetic ideal electromagnetic contour, creation of which is envisaged in incoming earthquake focal zone. Model of generation of EM emissions detected before earthquake is based on physical analogues of distributed and conservative systems and focal zones. According to the model the process of earthquake preparation from the moment of appearance of cracks in the system, including completion of series of foreshocks, earthquake and aftershocks, are entirely explained by oscillating systems.According to the authors of the work electromagnetic emissions in radio diapason is more universal and reliable than other anomalous variations of various geophysical phenomena in earthquake preparation period; Besides, VLF/LF electromagnetic emissions might be declared as the main precursor of earthquake because it might turn out very useful with the view of prediction of large (M5) inland earthquakes and to govern processes going on in lithosphere-atmosphere-ionosphere coupling (LAIC) system. Based on this model, in case of electromagnetic emissions spectrum monitoring in the period that precedes earthquake it is possible to determine, with certain accuracy, the time, location and magnitude of an incoming earthquake simultaneously.The present item considers possible physical mechanisms of the geophysical phenomena, which may accompany earthquake preparation process and expose themselves several months, weeks or days prior to earthquakes. Such as: Changing of intensity of electro-telluric current in focal area; Perturbations of geomagnetic field in forms of irregular pulsations or regular short-period pulsations; Perturbations of atmospheric electric field; Irregular changing of characteristic parameters of the lower ionosphere (plasma frequency, electron concentration, height of D layer, etc.); Irregular perturbations reaching the upper ionosphere, namely F2-layer, for 2-3 days before the earthquake

  18. Lithospheric thermal and strength model of the Arctic region

    NASA Astrophysics Data System (ADS)

    Struijk, Maartje; Tesauro, Magdala; Lebedeva-Ivanova, Nina; Beekman, Fred; Gaina, Carmen; Cloetingh, Sierd

    2016-04-01

    We estimate the lithospheric strength distribution in the Arctic region. With this aim, we use the most recently updated models of the Arctic's crust of Lebedeva-Ivanova et al. (in preparation), based on seismic and gravity data. These models include the thickness and density of the crust and sediments, the boundaries between the continental and oceanic crust, and the age of the oceanic lithosphere. We estimate the temperature variation in the continental lithosphere by using the one-dimensional steady-state heat conductive equation, assuming a ratio between the upper and lower crust of 0.5 and 0.7 and a constant surface heat flow of 50 and 65 mWm ^ 2, respectively. We take also into account the temperature dependence of the the thermal conductivity in the lithospheric mantle. We adopt the cooling plate model of McKenzie (1976) to estimate the temperature in the oceanic domain. At a depth of 50 km, the resulting thermal models show a stronger lateral variations in the oceanic (~550 °C) than in the continental lithosphere (~100°C). Within the continental domain, the increase of a surface heat flow from 50 to 65mWm ^ 2 raises the temperatures of ~300 °C. This is translated in a significant lithospheric strength reduction (from 3x10 ^ 13 Pa to ~ 0.5x10 ^ 13 Pa) and decoupling between the crust and mantle lithosphere. Other parameters, such as the crustal rheology and thickness cause second order strength variations. Continental strength variations reflect the different tectonic evolution of the Artic basins and ridges.

  19. Thermomechanical lithospheric structure of the central Fennoscandian Shield

    NASA Astrophysics Data System (ADS)

    Kaikkonen, P.; Moisio, K.; Heeremans, M.

    2000-05-01

    The deep seismic sounding (DSS) profiles BALTIC, including its southern continuation, the Sovetsk-Kohtla-Järve (SKJ) profile, SVEKA, the northern part of BABEL, POLAR, FENNIA and Pechenga-Kovdor-Kostomuksha, were used in studying the present-day thermomechanical structure of the central Fennoscandian Shield. These profiles are located in different tectonic units, which represent different stages in Precambrian crustal and lithospheric growth. First, present-day geotherms were constructed for several points along the DSS profiles. Successively, strength envelopes were calculated using the obtained geotherms and rheological flow laws. Variations in strain rate were also considered in the computations of the strength envelopes. The integrated crustal and lithospheric strengths, the thicknesses of the mechanically strong crust (MSC) and mechanically strong lithosphere (MSL), and the rheological thickness of the lithosphere were derived from these strength envelopes. The obtained mechanical structures for different regions were analysed and compared with other geophysical data; e.g., seismicity-depth and isotherm-depth distributions. The rheological results show lateral variations in the lithospheric strength reflecting the geometry of the lithosphere and following roughly the same trend as the geochronological development of the Fennoscandian Shield. The mechanical structure shows distinct decoupling of the weak lower crust and the strong upper mantle, particularly with a wet rheology. This decoupling interrupts the transmission of the differential stress from the brittle upper crust to the ductile lower crust and through it to the mantle lithosphere. The weak lower crustal layer is also detected with a dry rheology in the Svecofennian area, whereas in the Archaean side, it is not distinct. The assumed frictional transition temperature of 350°C varies between the depths of 25 and 44 km with an average value of 35 km. This is in good agreement with the observed focal

  20. Global model for the lithospheric strength and effective elastic thickness

    NASA Astrophysics Data System (ADS)

    Tesauro, Magdala; Kaban, Mikhail K.; Cloetingh, Sierd A. P. L.

    2013-08-01

    Global distribution of the strength and effective elastic thickness (Te) of the lithosphere are estimated using physical parameters from recent crustal and lithospheric models. For the Te estimation we apply a new approach, which provides a possibility to take into account variations of Young modulus (E) within the lithosphere. In view of the large uncertainties affecting strength estimates, we evaluate global strength and Te distributions for possible end-member 'hard' (HRM) and a 'soft' (SRM) rheology models of the continental crust. Temperature within the lithosphere has been estimated using a recent tomography model of Ritsema et al. (2011), which has much higher horizontal resolution than previous global models. Most of the strength is localized in the crust for the HRM and in the mantle for the SRM. These results contribute to the long debates on applicability of the "crème brulée" or "jelly-sandwich" model for the lithosphere structure. Changing from the SRM to HRM turns most of the continental areas from the totally decoupled mode to the fully coupled mode of the lithospheric layers. However, in the areas characterized by a high thermal regime and thick crust, the layers remain decoupled even for the HRM. At the same time, for the inner part of the cratons the lithospheric layers are coupled in both models. Therefore, rheological variations lead to large changes in the integrated strength and Te distribution in the regions characterized by intermediate thermal conditions. In these areas temperature uncertainties have a greater effect, since this parameter principally determines rheological behavior. Comparison of the Te estimates for both models with those determined from the flexural loading and spectral analysis shows that the 'hard' rheology is likely applicable for cratonic areas, whereas the 'soft' rheology is more representative for young orogens.

  1. Temporal evolution of continental lithospheric strength in actively deforming regions

    USGS Publications Warehouse

    Thatcher, W.; Pollitz, F.F.

    2008-01-01

    It has been agreed for nearly a century that a strong, load-bearing outer layer of earth is required to support mountain ranges, transmit stresses to deform active regions and store elastic strain to generate earthquakes. However the dept and extent of this strong layer remain controversial. Here we use a variety of observations to infer the distribution of lithospheric strength in the active western United States from seismic to steady-state time scales. We use evidence from post-seismic transient and earthquake cycle deformation reservoir loading glacio-isostatic adjustment, and lithosphere isostatic adjustment to large surface and subsurface loads. The nearly perfectly elastic behavior of Earth's crust and mantle at the time scale of seismic wave propagation evolves to that of a strong, elastic crust and weak, ductile upper mantle lithosphere at both earthquake cycle (EC, ???10?? to 103 yr) and glacio-isostatic adjustment (GIA, ???103 to 104 yr) time scales. Topography and gravity field correlations indicate that lithosphere isostatic adjustment (LIA) on ???106-107 yr time scales occurs with most lithospheric stress supported by an upper crust overlying a much weaker ductile subtrate. These comparisons suggest that the upper mantle lithosphere is weaker than the crust at all time scales longer than seismic. In contrast, the lower crust has a chameleon-like behavior, strong at EC and GIA time scales and weak for LIA and steady-state deformation processes. The lower crust might even take on a third identity in regions of rapid crustal extension or continental collision, where anomalously high temperatures may lead to large-scale ductile flow in a lower crustal layer that is locally weaker than the upper mantle. Modeling of lithospheric processes in active regions thus cannot use a one-size-fits-all prescription of rheological layering (relation between applied stress and deformation as a function of depth) but must be tailored to the time scale and tectonic

  2. Global Lithospheric Apparent Susceptibility Distribution Converted from Geomagnetic Models by CHAMP and Swarm Satellite Magnetic Measurements

    NASA Astrophysics Data System (ADS)

    Du, Jinsong; Chen, Chao; Xiong, Xiong; Li, Yongdong; Liang, Qing

    2016-04-01

    magnetic measurements and obtained global lithospheric apparent susceptibility distribution models. Finally, we compared these deduced models with previous results in the literature and some other geophysical, geodetic and geologic datum. Both tests and applications suggest, indeed, that the improved AS85 method can be adopted as a fast and effective interpretation tool of global induced large-scale magnetic anomaly field models in form of spherical harmonics. Arkani-Hamed, J. & Srangway, D.W., 1985. Lateral variations of apparent magnetic susceptibility of lithosphere deduced from Magsat data, J. Geophys. Res., 90(B3), 2655-2664. Gubbins, D., Ivers, D., Masterton, S.M. & Winch, D.E., 2011. Analysis of lithospheric magnetization in vector spherical harmonics, Geophys. J. Int., 187(1), 99-117. Hemant, K. & Maus, S., 2005. Geological modeling of the new CHAMP magnetic anomaly maps using a geographical information system technique, J. Geophys. Res., 110, B12103, doi: 10.1029/2005JB003837. Masterton, S.M., Gubbins, D., Müller, R.D. & Singh, K.H., 2013. Forward modeling of oceanic lithospheric magnetization, Geophys. J. Int., 192(3), 951-962. Nolte, H.J. & Siebert, M., 1987. An analytical approach to the magnetic field of the Earth's crust, J. Geophys., 61, 69-76. This study is supported by State Key Laboratory of Geodesy and Earth's Dynamics (Institute of Geodesy and Geophysics, Chinese Academy of Sciences) (SKLGED2015-5-5-EZ), Natural Science Fund of Hubei Province (2015CFB361), International Cooperation Project in Science and Technology of China (2010DFA24580), China Postdoctoral Science Foundation (2015M572217 and 2014T70753), Hubei Subsurface Multi-scale Imaging Key Laboratory (Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan) (SMIL-2015-06) and National Natural Science Foundation of China (41574070, 41104048 and 41504065).

  3. A Preliminary Study on the Lithosphere-Asthenosphere Boundary beneath the South China Sea

    NASA Astrophysics Data System (ADS)

    Lee, T. T. Y.; Chen, C. W.

    2014-12-01

    The lithosphere-asthenosphere boundary (LAB) is an important boundary at which the rigid lithosphere translates coherently upon the viscous asthenosphere. New observations have been made on LAB through detailed seismic analysis, especially that from receiver functions. Previous studies have found LAB depth varies significantly, systematically getting shallower from continental to oceanic lithosphere. In smaller scale, the depth and sharpness of LAB also differ from region to region, suggesting the effects of a combination of thermal and compositional origins. In this study, we investigate the LAB beneath the South China Sea, a region poorly instrumented that conventional seismological are less effective and impractical. The South China Sea is on the Sunda Plate, which is considered to be once the southeastern part of the Eurasia Plate before separating with a distinct moving direction from that of India-Eurasia continental collision. The South China Sea is Phanerozoic in age and continental in nature, but the striped magnetic anomalies observed from the sea floor have suggested multiple spreading events since early Miocene, indicating the presence of latter formed oceanic lithosphere. Previous seismic studies of this region focused mainly on shallow basin structure pertaining to petroleum exploration. The lithospheric structure, particularly the LAB, remains elusive, while it provides important insight into the complex tectonic history in this region. To image the LAB, we use the precursor of SS phase. The precursor bounces at the LAB discontinuity at depth would appear before the SS and presents a signal amenable to analysis for depth and properties. We collect seismic waveform data recorded mainly at Japan and Cocos Islands of corresponding teleseismic events from Southern Sumatera and Japan, with SS and potential precursors bouncing beneath the South China Sea. We employ an analysis technique, velocity spectral analysis (vespagrams), to identify precursory

  4. Wrinkle ridges, reverse faulting, and the depth penetration of lithospheric stress in lunae planum, Mars

    NASA Technical Reports Server (NTRS)

    Zuber, M. T.

    1993-01-01

    Tectonic features on a planetary surface are commonly used as constraints on models to determine the state of stress at the time the features formed. Quantitative global stress models applied to understand the formation of the Tharsis province on Mars constrained by observed tectonics have calculated stresses at the surface of a thin elastic shell and have neglected the role of vertical structure in influencing the predicted pattern of surface deformation. Wrinkle ridges in the Lunae Planum region of Mars form a conentric pattern of regularly spaced features in the eastern and southeastern part of Tharsis; they are formed due to compressional stresses related to the response of the Martian lithosphere to the Tharsis bulge. As observed in the exposures of valley walls in areas such as the Kasei Valles, the surface plains unit is underlain by an unconsolidated impact-generated megaregolith that grades with depth into structurally competent lithospheric basement. The ridges have alternatively been hypothesized to reflect deformation restricted to the surface plains unit ('thin skinned deformation') and deformation that includes the surface unit, megaregolith and basement lithosphere ('thick skinned deformation'). We have adopted a finite element approach to quantify the nature of deformation associated with the development of wrinkle ridges in a vertically stratified elastic lithosphere. We used the program TECTON, which contains a slippery node capability that allowed us to explicitly take into account the presence of reverse faults believed to be associated with the ridges. In this study we focused on the strain field in the vicinity of a single ridge when slip occurs along the fault. We considered two initial model geometries. In the first, the reverse fault was assumed to be in the surface plains unit, and in the second the initial fault was located in lithospheric basement, immediately beneath the weak megaregolith. We are interested in the conditions underwhich

  5. Formation of Oceanic Lithosphere by Basal Magma Accretion

    NASA Astrophysics Data System (ADS)

    Hamza, V. M.; Cardoso, R. R.; Alexandrino, C. H.

    2009-12-01

    The thermal models of the lithosphere proposed to date have failed to provide satisfactory accounts of some of the important features in large-scale variations of ocean floor bathymetry and heat flow. The systematic difference between model calculations and observational data have given rise to the so-called “oceanic heat flow paradox”, for which no satisfactory solution has been found for over the last forty years. In the present work, we point out that this paradox is a consequence of the assumption that lateral temperature variations are absent in the sub-lithospheric mantle. In the present work we propose a simple magma accretion model and examine its implications for understanding the thermal field of oceanic lithosphere. The new model (designated VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere, similar in character to those observed in magma solidification processes in the upper crust. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer (the Peclet number) is considered a space dependent variable. The solution to the problem of variable basal heat input has been obtained by the method of integral transform. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling and Plate models. Another noteworthy feature of the new model is its ability to account for the main observational features in the thermal behavior of both young and old oceanic lithosphere. Thus, heat flow and bathymetry variations calculated on the basis of the VBA model provide vastly improved fits to respective observational datasets. More importantly, the improved fits to bathymetry and heat flow have been achieved for the entire age range of oceanic lithosphere and without the need to invoke

  6. Electrical lithosphere beneath the Kaapvaal craton, southern Africa

    NASA Astrophysics Data System (ADS)

    Evans, Rob L.; Jones, Alan G.; Garcia, Xavier; Muller, Mark; Hamilton, Mark; Evans, Shane; Fourie, C. J. S.; Spratt, Jessica; Webb, Susan; Jelsma, Hielke; Hutchins, Dave

    2011-04-01

    A regional-scale magnetotelluric (MT) experiment across the southern African Kaapvaal craton and surrounding terranes, called the Southern African Magnetotelluric Experiment (SAMTEX), has revealed complex structure in the lithospheric mantle. Large variations in maximum resistivity at depths to 200-250 km relate directly to age and tectonic provenance of surface structures. Within the central portions of the Kaapvaal craton are regions of resistive lithosphere about 230 km thick, in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography, but thinner than inferred from seismic body wave tomography. The MT data are unable to discriminate between a completely dry or slightly "damp" (a few hundred parts per million of water) structure within the transitional region at the base of the lithosphere. However, the structure of the uppermost ˜150 km of lithosphere is consistent with enhanced, but still low, conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for Kaapvaal xenoliths. The electrical lithosphere around the Kimberley and Premier diamond mines is thinner than the maximum craton thickness found between Kimberley and Johannesburg/Pretoria. The mantle beneath the Bushveld Complex is highly conducting at depths around 60 km. Possible explanations for these high conductivities include graphite or sulphide and/or iron metals associated with the Bushveld magmatic event. We suggest that one of these conductive phases (most likely melt-related sulphides) could electrically connect iron-rich garnets in a garnet-rich eclogitic composition associated with a relict subduction slab.

  7. Comprehensive plate models for the thermal evolution of oceanic lithosphere

    NASA Astrophysics Data System (ADS)

    Grose, Christopher J.; Afonso, Juan Carlos

    2013-09-01

    Seafloor spreading and the cooling of oceanic lithosphere is a fundamental feature of plate tectonics in the Earth, the details of which are unveiled by modeling with constraints from mineral physics and geophysical observations. To work toward a more complete model of the thermal evolution of oceanic lithosphere, we investigate the contributions of axial hydrothermal circulation, oceanic crust, and temperature-pressure-dependent thermal properties. We find that models with only temperature-dependent properties disagree with geophysical observations unless properties are artificially modified. On the other hand, more comprehensive models are in better agreement with geophysical observations. Our preferred model requires a thermal expansivity reduction of 15% from a mineral physics estimate, and predicts a plate thickness of about 110-130 km. A principal result of our analysis is that the oceanic crust is a major contributor to the cooling of oceanic lithosphere. The oceanic crust acts as an insulating lid on the mantle, causing the rate of lithospheric cooling to increase from "crustal" values near the ridge to higher mantle values at old-age. Major consequences of this insulation effect are: (a) low seafloor subsidence rate in proximity to ridge axes (<5 Ma), (b) the thermal structure of oceanic lithosphere is significantly warmer than previous models, (c) seafloor heat flow is significantly lower over young (<35 Ma) seafloor compared to simple models, (d) a low net seafloor heat flux (˜27 TW), and (e) temperature at the base of the seismogenic zone extends to 700-800°C mantle.

  8. Descending lithosphere slab beneath the Northwest Dinarides from teleseismic tomography

    NASA Astrophysics Data System (ADS)

    Šumanovac, Franjo; Dudjak, Darko

    2016-12-01

    The area of study covers the marginal zone between the Adriatic microplate (African plate) and the Pannonian segment (Eurasian plate). We present a tomography model for this area, with special emphasis on the northwest Dinarides. A dense distribution of temporary seismic stations in the area of the Northern Dinarides along with permanent seismic stations located in the area, allowed us to construct this P-wave tomographic model. We assembled our travel-time dataset based on 26 seismic stations were used to collect the dataset. Teleseismic events were recorded for a period of 18 months and a set of 76 distant earthquakes were used to calculate the P-wave travel-time residuals. We calculated relative rather than absolute arrival-time residuals in the inversion to obtain depths of 0-400 km. We imaged a pronounced fast velocity anomaly below the NW Dinarides which directly indicates a lithosphere slab downgoing beneath the Dinarides. This fast anomaly extends towards the NW direction to at least 250 km depth, and we interpreted it as a descending lithosphere slab. The thrusting of the Adriatic microplate may be brought about by sub-lithosphere rising movement beneath the Pannonian region, along with a push from African plate. In our interpretation, the Adriatic lower lithosphere has been detached from the crust, and steeply sinks beneath the Dinarides. A lithosphere model of the contact between the Adriatic microplate and Pannonian tectonic segment was constructed based on the tomographic velocity model and results of previous crustal studies.

  9. Isotopic evidence for lithospheric thinning during extension: Southeastern Great Basin

    SciTech Connect

    Daley, E.E.; DePaolo, D.J. Lawrence Berkeley Lab., CA )

    1992-02-01

    Mafic rocks erupted during late Cenozoic extension near Las Vegas, Nevada, show temporal patterns of variation in Nd and Sr isotope ratios and in bulk chemistry. The patterns indicate that depths of magma generation were varying through time and that lithospheric mantle was partially replaced with asthenospheric mantle as extension proceeded. In alkalic rocks, {epsilon}{sub Nd} changed through time from {minus}9.1 (typical of lithospheric mantle in this area) before the onset of major (16 Ma) extension to +6.4 (typical of asthenospheric mantle) after extension (4.6 Ma). Near the end of the period of major extension (10-6 Ma), tholeiitic rocks erupted, the {epsilon}{sub Nd} of which ranged from {minus}10.1 to {minus}7.9; this indicates that the lithosphere had not thinned sufficiently by that time to bring asthenospheric mantle into the depth range of tholeiitic magma generation (33-50 km). The lithosphere in the Las Vegas area appears to have thinned by about 50%, less than would be predicted by the magnitude of upper crustal extension (a factor of 3 or 4), and indicative of a nonuniform lithospheric response to extension.

  10. Thermoelastic stress in oceanic lithosphere due to hotspot reheating

    NASA Technical Reports Server (NTRS)

    Zhu, Anning; Wiens, Douglas A.

    1991-01-01

    The effect of hotspot reheating on the intraplate stress field is investigated by modeling the three-dimensional thermal stress field produced by nonuniform temperature changes in an elastic plate. Temperature perturbations are calculated assuming that the lithosphere is heated by a source in the lower part of the thermal lithosphere. A thermal stress model for the elastic lithosphere is calculated by superposing the stress fields resulting from temperature changes in small individual elements. The stress in an elastic plate resulting from a temperature change in each small element is expressed as an infinite series, wherein each term is a source or an image modified from a closed-from half-space solution. The thermal stress solution is applied to midplate swells in oceanic lithosphere with various thermal structures and plate velocities. The results predict a stress field with a maximum deviatoric stress on the order of 100 MPa covering a broad area around the hotspot plume. The predicted principal stress orientations show a complicated geographical pattern, with horizontal extension perpendicular to the hotspot track at shallow depths and compression along the track near the bottom of the elastic lithosphere.

  11. Thermal stresses due to cooling of a viscoelastic oceanic lithosphere

    SciTech Connect

    Denlinger, R.P. ); Savage, W.Z. )

    1989-01-10

    Theories based upon thermal contraction of cooling oceanic lithosphere provide a successful basis for correlating seafloor bathymetry and heat flow. The horizontal components of the contraction of the lithosphere as it cools potentially give rise to large thermal stresses. Current methods to calculate these stresses assume that on the time scales of cooling, the lithosphere initially behaves as an inviscid fluid and instantly freezes into an elastic solid at some critical temperature. These instant-freezing methods inaccurately predict transient thermal stresses in rapidly cooling silicate glass plates because of the temperature dependent rheology of the material. The temperature dependent rheology of the lithosphere may affect the transient thermal stress distribution in a similar way, and for this reason the authors use a thermoviscoelastic model to estimate thermal stresses in young oceanic lithosphere. This theory is formulated here for linear creep processes that have an Arrhenius rate dependence on temperature. Results show that the stress differences between instant freezing and linear thermoviscoelastic theory are most pronounced at early times (0-20 m.y.) when the instant freezing stresses may be twice as large. The solutions for the two methods asymptotically approach the same solution with time. A comparison with intraplate seismicity shows that both methods underestimate the depth of compressional stresses inferred from the seismicity in a systematic way.

  12. Majorite Garnet and Lithosphere Evolution: Kaapvaal Craton

    NASA Astrophysics Data System (ADS)

    Griffin, W. L.; Tessalina, S.; O'Reilly, S. Y.

    2013-12-01

    The uppermost 50-70 km of the subcontinental lithospheric mantle (SCLM) beneath the Kaapvaal Craton (S. Africa) consists largely of highly-depleted chromite harzburgites. These rocks are understudied, mainly because of their uniformity and their lack of indicator minerals such as garnet and clinopyroxene (cpx). Kimberlite-borne xenoliths of these rocks contain rare volumes of cpx-spinel (modal 76/24) symplectite, with smooth grain boundaries; many studies have suggested that these might represent low-pressure breakdown products of garnet (majorite + olivine → cpx + spinel). Our reconstruction of a suite of these grains, using element mapping and EMP analysis of constituent minerals, gives a majoritic garnet with mean composition 21.8% CaO, 15.8% Cr2O3, 9.22% Al2O3, Si=3.118, mg#=0.93. The majorite contents suggest formation at depths of 250-280 km. Ni contents imply temperatures ≥1500 °C, but have large uncertainties related to the subtraction of olivine (ca 20%) during the reconstruction calculation. LAM-ICPMS analyses show strongly sinuous REE patterns with CN Dy/Lu <0.1 and Ce/Dy >100. Most analyses have negative Eu anomalies, consistent with chromite compositions that indicate strongly reducing conditions (ΔfO2(FMQ) = -4 to -5). Melt modeling suggests that the harzburgites are products of 30-40% melting of asthenospheric mantle at 250 km depth, leaving residues of ol+opx+chromite. The presence of the majorites and their overall LREE enrichment are ascribed to the introduction of carbonatitic metasomatic fluids, similar to those recorded by diamond-inclusions (subcalcic garnets), shortly after the depletion. We suggest that the melting, the metasomatism and the ultimate breakdown of the majorite track a process of mantle upwelling, with melt-extraction at depth providing the buoyancy that allowed the residual harzburgites to rise to shallow levels and stabilize the SCLM. Os-isotope analyses of sulfides associated with the majorites give TRD = 2.5-3.4 Ga

  13. Oceanic lithosphere and asthenosphere: The thermal and mechanical structure

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Froidevaux, C.; Yuen, D. A.

    1976-01-01

    A coupled thermal and mechanical solid state model of the oceanic lithosphere and asthenosphere is presented. The model includes vertical conduction of heat with a temperature dependent thermal conductivity, horizontal and vertical advection of heat, viscous dissipation or shear heating, and linear or nonlinear deformation mechanisms with temperature and pressure dependent constitutive relations between shear stress and strain rate. A constant horizontal velocity u sub 0 and temperature t sub 0 at the surface and zero horizontal velocity and constant temperature t sub infinity at great depth are required. In addition to numerical values of the thermal and mechanical properties of the medium, only the values of u sub 0, t sub 0 and t sub infinity are specified. The model determines the depth and age dependent temperature horizontal and vertical velocity, and viscosity structures of the lithosphere and asthenosphere. In particular, ocean floor topography, oceanic heat flow, and lithosphere thickness are deduced as functions of the age of the ocean floor.

  14. Statistical analysis of the lithospheric magnetic anomaly data

    NASA Astrophysics Data System (ADS)

    Pavon-Carrasco, Fco Javier; de Santis, Angelo; Ferraccioli, Fausto; Catalán, Manuel; Ishihara, Takemi

    2013-04-01

    Different analyses carried out on the lithospheric magnetic anomaly data from GEODAS DVD v5.0.10 database (World Digital Magnetic Anomaly Map, WDMAM) show that the data distribution is not Gaussian, but Laplacian. Although this behaviour has been formerly pointed out in other works (e.g., Walker and Jackson, Geophys. J. Int, 143, 799-808, 2000), they have not given any explanation about this statistical property of the magnetic anomalies. In this work, we perform different statistical tests to confirm that the lithospheric magnetic anomaly data follow indeed a Laplacian distribution and we also give a possible interpretation of this behavior providing a model of magnetization which depends on the variation of the geomagnetic field and both induced and remanent magnetizations in the terrestrial lithosphere.

  15. Lithospheric structure of the south-central United States

    SciTech Connect

    Mickus, K.L. ); Keller, G.R. )

    1992-04-01

    Recent seismic data in the Ouachita Mountains area and the Gulf of Mexico make it possible to construct a lithospheric-scale cross section (transect) from the midcontinent region to the gulf. The authors constructed a transect in the form of a gravity model, but it incorporates all available seismic, drill hole, and geologic data as constraints. The thrust sheets of the Ouachita orogenic belt appear as a thin veneer covering the southern part of the Arkoma basin and the preserved Paleozoic continental margin. Mesozoic rifting is evident in three areas: (1) southern Arkansas and northern Louisiana where extension was minor, (2) the vicinity of the Texas-Louisiana coastline where modification of the lithosphere and subsidence were considerable, and (3) the deep Gulf of Mexico where rifting was successful. A significant variation in the average density of the mantle, which could delineate the North American craton as a lithospheric feature, was detected near the Paleozoic continental margin.

  16. Properties of the lithosphere and asthenosphere deduced from geoid observations

    NASA Technical Reports Server (NTRS)

    Turcotte, D. L.

    1985-01-01

    Data from the GEOS-3 and SEASAT Satellites provided a very accurate geoid map over the oceans. Broad bathymetric features in the oceans such as oceanic swells and plateaus are fully compensated. It is shown that the geoid anomalies due to the density structures of the lithosphere are proportional to the first moment of the density distribution. The deepening of the ocean basins is attributed to thermal isostasy. The thickness of the oceanic lithosphere increases with age due to the loss of heat to the sea floor. Bathymetry and the geoid provide constraints on the extent of this heat loss. Offsets in the geoid across major fracture zones can also be used to constrain this problem. Geoid bathymetry correlations show that the Hawaiian and Bermuda swells and the Cape Verde Rise are probably due to lithospheric thinning.

  17. Lithospheric records of orogeny within the continental U.S.

    NASA Astrophysics Data System (ADS)

    Porter, Ryan; Liu, Yuanyuan; Holt, William E.

    2016-01-01

    In order to better understand the tectonic evolution of the North American continent, we utilize data from the EarthScope Transportable Array network to calculate a three-dimensional shear velocity model for the continental United States. This model was produced through the inversion of Rayleigh wave phase velocities calculated using ambient noise tomography and wave gradiometry, which allows for sensitivity to a broad depth range. Shear velocities within this model highlight the influence of orogenic and postorogenic events on the evolution of the lithosphere. Most notable is the contrast in crustal and upper mantle structure between the relatively slow western and relatively fast eastern North America. These differences are unlikely to stem solely from thermal variations within the lithosphere and highlight both the complexities in lithospheric structure across the continental U.S. and the varying impacts that orogeny can have on the crust and upper mantle.

  18. Oceanic earthquakes and the tectonic evolution of oceanic lithosphere

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1988-01-01

    The body waveform inversion method of Nabelek (1984) is used to study the centroid depths and source properties of oceanic earthquakes. The source parameters for 50 earthquakes which occurred along slowly spreading midocean ridges between 1962 and 1983 are used to examine the mechanical characteristics of the median valley, including the water depth in the epicentral region, the depth range of seismic faulting, the centroid depth and seismic moment versus spreading rate, and the seismic moment budget. The locations and source characteristics of oceanic intraplate earthquakes are discussed, including near-ridge earthquakes, lithospheric stress, and earthquakes in older oceanic lithosphere. The results suggest that the median valley form by the necking of a strong layer. The properties of near-ridge earthquakes support the hypothesis that thermal stress generated by diferential cooling of the plate can be stored and accumulated over millions of years. Earthquakes in older oceanic lithosphere are most likely to reflect stresses generated by plate driving forces.

  19. A global view of the lithosphere-asthenosphere boundary.

    PubMed

    Rychert, Catherine A; Shearer, Peter M

    2009-04-24

    The lithosphere-asthenosphere boundary divides the rigid lid from the weaker mantle and is fundamental in plate tectonics. However, its depth and defining mechanism are not well known. We analyzed 15 years of global seismic data using P-to-S (Ps) converted phases and imaged an interface that correlates with tectonic environment, varying from 95 +/- 4 kilometers beneath Precambrian shields and platforms to 81 +/- 2 kilometers beneath tectonically altered regions and 70 +/- 4 kilometers at oceanic island stations. High-frequency Ps observations require a sharp discontinuity; therefore, this interface likely represents a boundary in composition, melting, or anisotropy, not temperature alone. It likely represents the lithosphere-asthenosphere boundary under oceans and tectonically altered regions, but it may constitute another boundary in cratonic regions where the lithosphere-asthenosphere boundary is thought to be much deeper.

  20. Model geoid anomalies due to subduction of inextensible lithosphere

    SciTech Connect

    Willemann, R.J.; Anderson, C.A.

    1987-08-01

    We compute geoid slopes from models of subduction in which the subducted lithosphere is much stronger than the surrounding mantle. Geoid slope contributions from both the lithospheric slab and mantle boundary deformations are computed from finite element analysis of mantle flow. The finite element model includes a slab of finite length and a depth dependent Newtonian rheology for the surrounding mantle. We find that observed geoid anomalies at subduction zones, which are positive, cannot be matched by models with uniform mantle viscosity. However, even with a strong subducted lithosphere, the ratio of driving load to boundary deformation is significantly increased by a ten-fold increase of viscosity with depth, resulting in a geoid high. We find that the sign of the geoid slopes within 3000 km of the trench are independent of maximum depth of the slab for maximum depths from 700 km to 2800 km. copyright American Geophysical Union 1987

  1. Lithospheric strength and elastic thickness of the Barents Sea and Kara Sea region

    NASA Astrophysics Data System (ADS)

    Gac, Sébastien; Klitzke, Peter; Minakov, Alexander; Faleide, Jan Inge; Scheck-Wenderoth, Magdalena

    2016-11-01

    Interpretation of tomography data indicates that the Barents Sea region has an asymmetric lithospheric structure characterized by a thin and hot lithosphere in the west and a thick and cold lithosphere in the east. This suggests that the lithosphere is stronger in the east than in the west. This asymmetric lithosphere strength structure may have a strong control on the lithosphere response to tectonic and surface processes. In this paper, we present computed strength and effective elastic thickness maps of the lithosphere of the Barents Sea and Kara Sea region. Those are estimated using physical parameters from a 3D lithospheric model of the Barents Sea and Kara Sea region. The lithospheric strength is computed assuming a temperature-dependent ductile and brittle rheology for sediments, crust and mantle lithosphere. Results show that lithospheric strength and elastic thickness are mostly controlled by the lithosphere thickness. The model generally predicts much larger lithospheric strength and elastic thickness for the Proterozoic parts of the East Barents Sea and Kara Sea. Locally, the thickness and lithology of the continental crust disturb this general trend. At last, the gravitational potential energy (GPE) is computed. Our results show that the difference in GPE between the Barents Sea and the Mid-Atlantic Ridge provides a net horizontal force large enough to cause contraction in the western and central Barents Sea.

  2. International challenge to predict the impact of radioxenon releases from medical isotope production on a comprehensive nuclear test ban treaty sampling station

    SciTech Connect

    Eslinger, Paul W.; Bowyer, Ted W.; Achim, Pascal; Chai, Tianfeng; Deconninck, Benoit; Freeman, Katie; Generoso, Sylvia; Hayes, Philip; Heidmann, Verena; Hoffman, Ian; Kijima, Yuichi; Krysta, Monika; Malo, Alain; Maurer, Christian; Ngan, Fantine; Robins, Peter; Ross, J. Ole; Saunier, Olivier; Schlosser, Clemens; Schöppner, Michael; Schrom, Brian T.; Seibert, Petra; Stein, Ariel F.; Ungar, Kurt; Yi, Jing

    2016-06-01

    Abstract The International Monitoring System (IMS) is part of the verification regime for the Comprehensive Nuclear-Test-Ban-Treaty Organization (CTBTO). At entry-into-force, half of the 80 radionuclide stations will be able to measure concentrations of several radioactive xenon isotopes produced in nuclear explosions, and then the full network may be populated with xenon monitoring afterward (Bowyer et al., 2013). Fission-based production of 99Mo for medical purposes also releases radioxenon isotopes to the atmosphere (Saey, 2009). One of the ways to mitigate the effect of emissions from medical isotope production is the use of stack monitoring data, if it were available, so that the effect of radioactive xenon emissions could be subtracted from the effect from a presumed nuclear explosion, when detected at an IMS station location. To date, no studies have addressed the impacts the time resolution or data accuracy of stack monitoring data have on predicted concentrations at an IMS station location. Recently, participants from seven nations used atmospheric transport modeling to predict the time-history of 133Xe concentration measurements at an IMS station in Germany using stack monitoring data from a medical isotope production facility in Belgium. Participants received only stack monitoring data and used the atmospheric transport model and meteorological data of their choice. Some of the models predicted the highest measured concentrations quite well (a high composite statistical model comparison rank or a small mean square error with the measured values). The results suggest release data on a 15 min time spacing is best. The model comparison rank and ensemble analysis suggests that combining multiple models may provide more accurate predicted concentrations than any single model. Further research is needed to identify optimal methods for selecting ensemble members and those methods may depend on the specific transport problem. None of the submissions based only

  3. A Sharp Edge of the Cratonic Lithosphere of North America

    NASA Astrophysics Data System (ADS)

    Harper, T. B.; Skryzalin, P. A.; Menke, W. H.; Levin, V. L.; Darbyshire, F. A.

    2015-12-01

    Using teleseismic travel time delays, we develop a tomographic model of the lithosphere beneath northeastern North America, from the shore of James Bay in Quebec to the Atlantic coast of New England and to a depth of 300 km. Three major terranes lie within this cratonic margin: the 2.7 Ga Superior province, the 1 Ga Grenville orogenic belt and the 0.3-0.4 Ga Appalachian terranes, which are bounded by the Grenville Front (GF) and Appalachian Front (AF), respectively. Additionally, the 0.8 Ga Avalon terrain was accreted to coastal New England by strike-skip faulting during the Appalachian orogeny. Our tomographic model uses earthquake seismograms recorded by permanent US and Canadian stations, the Transportable Array and the temporary QMIII deployment. All data were corrected for instrument response and record sections were examined visually to identify gross errors in response and timing. Differential arrival times of P and PKP waves were determined by cross-correlation and have a maximum amplitude of about ±1 second. In our model, lithospheric boundaries do not correlate well with geological boundaries, nor do they strike parallel to them. The seismically-fast (by 5% relative to AK135) cratonic lithosphere of North America is much thicker than that of the younger terranes, extending to 200 km or more depth but with a sharp east-dipping eastern edge located (at Moho depths) 100-250 km northwest of the GF. The lithosphere beneath the Grenville and Appalachian terranes, which were affected by subduction during the Grenville and Appalachian orogenies, is slower (by 4%). A sliver of seismically-fast lithosphere, extending to ~150 km depth, occurs along the Atlantic coast and is interpreted as the Avalonian lithosphere.

  4. Thermal rejuvenation of continental lithosphere in the Michigan Basin Area

    SciTech Connect

    Ahern, J.L.; Dikeou, P.J.

    1985-01-01

    Using depths to formation tops from almost 500 wells, the authors have determined changes in shape of the Michigan Basin during the Phanerozoic. Flexural rigidity of the lithosphere was then estimated for several time intervals by assuming that changes in shape were caused by deflection of an elastic plate subjected to a disk load. It is found that the flexural rigidity generally increased over time, from less than 10/sup 29/ dyne-cm early in the basin's history, to more than 10/sup 30/ dyne-cm late in the basin's development. They attribute this increase in rigidity to cooling and thickening of the elastic portion of the lithosphere as the basin was subsiding. Low flexural rigidity early in the basin's history indicates that the lithosphere was probably rejuvenated prior to basin subsidence. The rejuvenation process is investigated using a finite-difference thermal model in which a 142-km plate is temporarily heated from below. Taking the depth to the 450/sup 0/C isotherm to be the effective elastic thickness of the lithosphere, rigidity predicted by the thermal model is consistent with the observed increase in rigidity over time. They conclude that the lithosphere in this area was rejuvenated approximately 500 million years ago. As the lithosphere cooled, it thickened; it also contracted and subsided. Observed rapid subsidence between about 500 and 450 million years ago cannot be explained by thermal contraction; in fact, it occurs when the thermal model predicts heating and uplift. This subsidence episode may have been the result of densification processes accompanying rejuvenation.

  5. Heterogeneity of Water Concentrations in the Mantle Lithosphere Beneath Hawaii

    NASA Technical Reports Server (NTRS)

    Bizimis, M.; Peslier, A. H.; Clague, D.

    2017-01-01

    The amount and distribution of water in the oceanic mantle lithosphere has implications on its strength and of the role of volatiles during plume/lithosphere interaction. The latter plays a role in the Earth's deep water cycle as water-rich plume lavas could re-enrich an oceanic lithosphere depleted in water at the ridge, and when this heterogeneous lithosphere gets recycled back into the deep mantle. The main host of water in mantle lithologies are nominally anhydrous minerals like olivine, pyroxene and garnet, where hydrogen (H) is incorporated in mineral defects by bonding to structural oxygen. Here, we report water concentrations by Fourier transform infrared spectrometry (FTIR) on olivine, clino- and orthopyroxenes (Cpx & Opx) from spinel peridotites from the Pali vent and garnet pyroxenite xenoliths from Aliamanu vent, both part of the rejuvenated volcanism at Oahu (Hawaii). Pyroxenes from the Aliamanu pyroxenites have high water concentrations, similar to the adjacent Salt Lake Crater (SLC) pyroxenites (Cpx 400-500 ppm H2O, Opx 200 ppm H2O). This confirms that pyroxenite cumulates form water-rich lithologies within the oceanic lithosphere. In contrast, the Pali peridotites have much lower water concentrations than the SLC ones (<25 ppm vs. 50-96 ppm H2O respectively) despite being relatively fertile with >10% modal Cpx and low spinel Cr# (0.09-0.10). The contrast between the two peridotite suites is also evident in their trace elements and radiogenic isotopes. The Pali Cpx are depleted in light REE, consistent with minimal metasomatism. Those of SLC have enriched light REE patterns and Nd and Hf isotopes consistent with metasomatism by alkaline melts. These observations are consistent with heterogeneous water distribution in the oceanic lithosphere that may be related to metasomatism, as well as relatively dry peridotites cross-cut by narrow (?) water-rich melt reaction zones.

  6. Project Skippy explores lithosphere and mantle beneath Australia

    NASA Astrophysics Data System (ADS)

    van der Hilst, Rob; Kennett, Brian; Christie, Doug; Grant, John

    A new project is probing the seismic structure of the lithosphere and mantle beneath Australia. The Skippy Project, named after the bush kangaroo, exploits Australia's regional seismicity and makes use of recent advances in digital recording technology to collect three-component broadband seismic data from over 60 sites across the continent (Figure 1).The main goal of the Skippy Project, which is run by Australian National University's Research School of Earth Sciences (RSES), is to delineate the three-dimensional seismic structure of the lithosphere and mantle beneath the continent.

  7. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    PubMed

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere.

  8. Seismic Tomography of the Arctic Lithosphere and Asthenosphere

    NASA Astrophysics Data System (ADS)

    Schaeffer, Andrew; Lebedev, Sergei

    2015-04-01

    Lateral variations in seismic velocities in the upper mantle, mapped by seismic tomography, primarily reflect variations in the temperature of the rocks at depth. Seismic tomography thus provides a proxy for lateral changes in the temperature and thickness of the lithosphere, in addition to delineating the deep boundaries between tectonic blocks with different properties and age of the lithosphere. Our new, 3D tomographic model of the upper mantle and the crust of the Arctic region is constrained by an unprecedentedly large global dataset of broadband waveform fits (over one million seismograms) and provides improved resolution of the lithosphere, compared to other available models. The most prominent high-velocity anomalies, seen down to 150-200 km depths, indicate the cold, thick, stable mantle lithosphere beneath Precambrian cratons. The northern boundaries of the Canadian Shield's and Greenland's cratonic lithosphere closely follow the coastlines, with the Greenland and North American cratons clearly separated from each other. Sharp velocity gradients in western Canada indicate that the craton boundary at depth closely follows the Rocky Mountain Front. High velocities between the Great Bear Arc and Beaufort Sea provide convincing evidence for the recently proposed 'MacKenzie Craton', unexposed at the surface. In Eurasia, cratonic continental lithosphere extends northwards beneath the Barents and eastern Kara Seas. The boundaries of the Archean cratons and intervening Proterozoic belts mapped by tomography indicate the likely offshore extensions of major Phanerozoic sutures and deformation fronts. The old oceanic lithosphere of the Canada Basin is much colder and thicker than the younger lithosphere beneath the adjacent Amundsen Basin, north of the Gakkel Ridge. Beneath the slow-spreading Gakkel Ridge, we detect the expected low-velocity anomaly associated with partial melting in the uppermost mantle; the anomaly is weaker, however, than beneath faster

  9. Lithospheric structural controls on magma composition: the Kenya Rift

    NASA Astrophysics Data System (ADS)

    Omenda, P. A.; Simiyu, S.; Anthony, E. Y.; Keller, G. R.; Dean, R. L.

    2001-12-01

    Lithospheric structure, as delineated by geophysics, plays a fundamental role in both felsic and mafic magmatic compositions in the Kenya Rift. With respect to the mafic rocks, there are, first, silica-undersaturated basanites of the Chyulu Hills. This location is off-axis to the rift, where the lithosphere is thick. The lavas have been modeled as high-pressure, small degree partial melts. This origin contrasts to that for the silica-saturated transitional basalts, basaltic trachy-andesites, and andesites in the axis of the rift. These magmas were generated by higher degrees of partial melt and are also much more evolved, with Mg numbers approximately 40 to 50. The lavas have seen substantial crystal fractionation prior to eruption. An important component of lithospheric structure within the rift axis is the Kenya Dome: it is an area of thick crust and high elevation and heat flow. The crust is made thicker by a 6.8 km/sec lower crustal layer. Immediately below this crust is a very slow upper mantle. Velocities become more lithospheric to the south of the Kenya Dome in the vicinity of Suswa. This lithosphere then thickens southward into Tanzania. The felsic central volcanoes of the rift, which are significant geothermal targets, reflect these lithospheric variations. Eburru and Olkaria are both centered on the Kenya Dome. Eburru is pantellerite and can be modeled as resulting from crystallization of silica-saturated basalt. Olkaria is comendite and resulted from fusion of lower crustal syenite. That we find such distinct petrogenesis for two closely spaced volcanoes indicates that this area of very warm mantle has the temperatures necessary to generate high degree partial melt magmas, which evolve into pantellerites, and also fuse the lower crust. Suswa, which is the southernmost volcano and in the area where lithosphere thickens, is composed on phonolites, which can be modeled as resulting from crystallization of silica-undersaturated mafic parents. Presumably

  10. Tibetan Apples and Oranges: Surficial Sutures and Overlapping Lithospheres

    NASA Astrophysics Data System (ADS)

    Chen, W. P.; Hung, S. H.; Wang, C. Y.; Tseng, T. L.

    2014-12-01

    Multi-scale, finite-frequency tomography across the Himalayas-Tibet shows a clear, subhorizontal anomaly of high VP and VSin the upper mantle that can be traced from under N. India all the way to beneath central Tibet. This configuration of the "Greater India" (GI), or the submerged, northern portion of the Indian shield, is combined with other constraints to reconstruct position of the Indian lithospheric mantle (ILM) relative to Asia back to about 15 Ma ago, or the onset of the latest magmatic activity in Tibet. By then, the leading edge of the ILM (Indian mantle front, IMF) has advanced subhorizontally past the entire Lhasa terrane and also probably have caused the lithospheric mantle beneath the Qiangtang terrane to thicken. The thickening is likely to have led to Rayleigh-Taylor instability, causing widespread but small volume of magmatic activity in northern Tibet. Meanwhile, the detached lithospheric mantle foundered through the upper mantle to rest at the bottom of the mantle transition zone (MTZ), just above the lower mantle. This detached lithospheric mantle manifests itself as a large-scale seismic anomaly of high compressional wave speed (VP) but curiously is undetectable through shear-waves. Based on laboratory data for nominally anhydrous olivine and its high-pressure polymorphs (NAO), the discordant results between P- and S-waves is explained by abundant hydroxyls in the foundered lithospheric mantle, a hypothesis supported by other evidences as well. Since NAO can hold ~1 wt% of water throughout the upper mantle and the MTZ, foundering of thickened lithospheric mantle caused by continental collision is an under-appreciated but effective pathway for water to enter the deep mantle. Currently, the Indus-Yarlung suture between northern India and the Lhasa terrane appears to be an inactive, crustal feature, as the GI continues to pass beneath it. On the other hand, even though the IMF has now advanced northward beyond the Bangong-Nujiang suture (BNS

  11. Seismic imaging of the downwelling Indian lithosphere beneath central Tibet.

    PubMed

    Tilmann, Frederik; Ni, James

    2003-05-30

    A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from approximately 100- to approximately 400-kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet.

  12. Extensional and compressional instabilities in icy satellite lithospheres

    NASA Technical Reports Server (NTRS)

    Herrick, David L.; Stevenson, David J.

    1990-01-01

    The plausibility of invoking a lithospheric instability mechanism to account for the grooved terrains on Ganymede, Encedalus, and Miranda is presently evaluated in light of the combination of a simple mechanical model of planetary lithospheres and asthenospheres with recent experimental data for the brittle and ductile deformation of ice. For Ganymede, high surface gravity and warm temperatures render the achievement of an instability sufficiently great for the observed topographic relief virtually impossible; an instability of sufficient strength, however, may be able to develop on such smaller, colder bodies as Encedalus and Miranda.

  13. Parameters driving strain localization in the lithosphere are highly scale-dependent

    NASA Astrophysics Data System (ADS)

    Jolivet, Laurent

    2016-04-01

    Modelling lithospheric deformation requires specifying mechanisms that promote strain localization. This can be done in different ways, such as the inclusion of weaker zones in the model setup (to initiate subduction or slab tearing, for instance) or using various sorts of weakening processes depending upon temperature, grain-size, fluid content or metamorphic reactions, among others. In most cases, this choice is ad hoc because the relevant parameters are largely unknown, especially at the scale of geodynamic models. Two lines of research have been developed, a traditional one which seeks to determine the rheological parameters of natural or synthetic rocks experimentally, and a more recent one, promoted by the development of fast computing, which aims at reproducing a natural tectonic or rheological evolution through time, not only geometries. The latter requires that the parameters allowing this reproduction are significant at the scale of the model, and which may be different from those obtained in the experimental lab, thus questioning the extrapolation through a wide range of scales of experimental parameters. This apparent discrepancy is due to the intrinsic complexity of the lithosphere, and even more so for the continental lithosphere with its highly heterogeneous crust and its long tectonic history, which implies the co-existence of many different parameters active in nature. In this presentation, we review the main localizing factors and look to the range of scales in which they are significant. Small-scale processes such as grain-size reduction, coexistence of several mineralogical phases with different strength and rheological behaviour, fluid-rock interactions and/or metamorphic reactions, often cannot initiate strain localization in nature but are all efficient to locally reduce the strength of rock material once localization has started. Some exceptions to this rule, however, exist, such as the mixing of ductile and brittle behaviour in the same

  14. 3-D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle: III. Thermochemical tomography in the Western-Central U.S.

    NASA Astrophysics Data System (ADS)

    Afonso, Juan Carlos; Rawlinson, Nicholas; Yang, Yingjie; Schutt, Derek L.; Jones, Alan G.; Fullea, Javier; Griffin, William L.

    2016-10-01

    We apply a novel 3-D multiobservable probabilistic tomography method that we have recently developed and benchmarked, to directly image the thermochemical structure of the Colorado Plateau and surrounding areas by jointly inverting P wave and S wave teleseismic arrival times, Rayleigh wave dispersion data, Bouguer anomalies, satellite-derived gravity gradients, geoid height, absolute (local and dynamic) elevation, and surface heat flow data. The temperature and compositional structures recovered by our inversion reveal a high level of correlation between recent basaltic magmatism and zones of high temperature and low Mg# (i.e., refertilized mantle) in the lithosphere, consistent with independent geochemical data. However, the lithospheric mantle is overall characterized by a highly heterogeneous thermochemical structure, with only some features correlating well with either Proterozoic and/or Cenozoic crustal structures. This suggests that most of the present-day deep lithospheric architecture reflects the superposition of numerous geodynamic events of different scale and nature to those that created major crustal structures. This is consistent with the complex lithosphere-asthenosphere system that we image, which exhibits a variety of multiscale feedback mechanisms (e.g., small-scale convection, magmatic intrusion, delamination, etc.) driving surface processes. Our results also suggest that most of the present-day elevation in the Colorado Plateau and surrounding regions is the result of thermochemical buoyancy sources within the lithosphere, with dynamic effects (from sublithospheric mantle flow) contributing only locally up to ˜15-35%.

  15. Deformation Processes In SE Tibet: How Coupled Are The Surface And The Deeper Lithosphere? (Invited)

    NASA Astrophysics Data System (ADS)

    Zeitler, P. K.; Meltzer, A.

    2010-12-01

    We all like to cite the Himalayan collision as a type example of continent-continent collision, and the region has been used as a natural laboratory by a considerable number of diverse investigations. Southeastern Tibet and the Lhasa Block provide an interesting case to consider in this context. Surrounding portions of the Himalayan-Tibet system have been and are being intensely deformed, whereas the Andean-arc lithosphere of the Lhasa Block has remained enigmatically unscathed. High elevations throughout much of the terrane are fairly uniform but the eastern and western portions of block have experienced very different degrees of exhumation. Regions that experienced more exhumation have thinner crustal thicknesses, with the results that that Moho is warped up with respect to the surface. Thicker, less-exhumed portions of the Lhasa Block currently are underlain by what is inferred to be eclogitized lower crust, but this eclogitization is not seen where exhumation is significant. Beneath SE Tibet, subduction of the Indian lithosphere has been complicated, with tomographic imaging showing variations in mantle structure that do not register with the strike of surface features. Adjacent to the Lhasa Block, the Namche Barwa-Gyala metamorphic massif demonstrates a strong coupling between shallower crustal flow and localized erosion that is significant for the evolution of the Lhasa Block in the way that this feature controls base level for the upper Tsangpo drainage and thus the erosional driver for the system. More broadly, a weak lower crust and lower-crustal flow have been invoked by many workers to explain aspects of the region’s deformation patterns and topography. Thus it would seem that in SE Tibet, mid-to-upper crustal, lower-crustal, and whole-lithosphere processes all have the potential to either impact Earth-surface dynamics or be impacted by them. This leads to a number of questions about the 4D nature and scale of compensation, controls on the evolution of

  16. Silicate melt metasomatism in the lithospheric mantle beneath SW Poland

    NASA Astrophysics Data System (ADS)

    Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Grégoire, Michel; Kukuła, Anna

    2014-05-01

    /(Mg+Fe) ratios of olivine and pyroxenes. Thus, the variation of relative volumes of olivine and orthopyroxene as well as the decrease of mg# of rock-forming silicates is well explained by reactive melt percolation in the peridotitic protolith consisting of high mg# olivine and pyroxenes (in the area studied by us that protolith was characterised by olivine containing 90.5 - 92.0 mole % forsterite). The rocks which were subjected to significant decrease of mg# of silicates (down to 84) may be difficult to distinguish from cumulates. However, since the alkaline basaltic melts do not precipitate orthopyroxene under lithospheric pressures, their mineral composition is different than that of mantle harzburgites. Kelemen PB, Dick HJB, Quick JE (1992) Formation of harzburgite by pervasive melt/rock reaction in the upper mantle. Nature 358: 635-641. Tursack E, Liang Y (2012) A comparative study of melt-rock reactions in the mantle: laboratory dissolution experiments and geological field observations. Contributions to Mineralogy and Petrology 163: 861-876

  17. An equivalent source method for modelling the global lithospheric magnetic field

    NASA Astrophysics Data System (ADS)

    Kother, Livia; Hammer, Magnus D.; Finlay, Christopher C.; Olsen, Nils

    2015-10-01

    We present a new technique for modelling the global lithospheric magnetic field at Earth's surface based on the estimation of equivalent potential field sources. As a demonstration we show an application to magnetic field measurements made by the CHAMP satellite during the period 2009-2010 when it was at its lowest altitude and solar activity was quiet. All three components of the vector field data are utilized at all available latitudes. Estimates of core and large-scale magnetospheric sources are removed from the measurements using the CHAOS-4 model. Quiet-time and night-side data selection criteria are also employed to minimize the influence of the ionospheric field. The model for the remaining lithospheric magnetic field consists of magnetic equivalent potential field sources (monopoles) arranged in an icosahedron grid at a depth of 100 km below the surface. The corresponding model parameters are estimated using an iteratively reweighted least-squares algorithm that includes model regularization (either quadratic or maximum entropy) and Huber weighting. Data error covariance matrices are implemented, accounting for the dependence of data variances on quasi-dipole latitude. The resulting equivalent source lithospheric field models show a degree correlation to MF7 greater than 0.7 out to spherical harmonic degree 100. Compared to the quadratic regularization approach, the entropy regularized model possesses notably lower power above degree 70 and a lower number of degrees of freedom despite fitting the observations to a very similar level. Advantages of our equivalent source method include its local nature, the possibility for regional grid refinement and the production of local power spectra, the ability to implement constraints and regularization depending on geographical position, and the ease of transforming the equivalent source values into spherical harmonics.

  18. Microstructural and geochemical constraints on the evolution of deep arc lithosphere

    NASA Astrophysics Data System (ADS)

    Chin, Emily J.; Soustelle, Vincent; Hirth, Greg; Saal, Alberto E.; Kruckenberg, Seth C.; Eiler, John M.

    2016-07-01

    Mantle xenoliths from the Sierra Nevada, California, USA, sampled a vertical column (60-120 km) of lithosphere that formed during Mesozoic continental arc magmatism. This lithosphere experienced an anticlockwise P-T-t path resulting in rapid cooling that effectively "quenched in" features inherited from earlier high-temperature conditions. Here we combine new mineral chemistry data (water, trace element, and major element concentrations) with mineral crystallographic preferred orientations (CPOs) to investigate the relationship between melt infiltration and deformation. The peridotites record a refertilization trend with increasing depth, starting from shallow, coarse-protogranular, less-melt-infiltrated spinel peridotite with strong, orthorhombic olivine CPO to deep, fine-porphyroclastic, highly melt-infiltrated garnet peridotite with weak, axial-[010] olivine CPO. In contrast to the observed axial-[010] CPOs, subgrain boundary orientations and misorientation axes suggest the dominant activation of the (001)[100] slip system, suggesting deformation under moderately hydrous conditions. After accounting for effects of subsolidus cooling, we see coherent trends between mineral trace element abundance and water content, indicating that melt infiltration led to an increase in water content of the peridotites. However, measured olivine and pyroxene water contents in all peridotites (5-10 and 30-500 wt ppm, respectively) are lower than that required to promote dominant (001)[100] slip system observed in both natural and experimental samples. These results suggest that deformation occurred earlier along the P-T path, probably during or shortly after hydrous melt infiltration. Subsequent rapid cooling at 90 Ma led to water loss from olivine (owing to decreased solubility at low temperature), leaving behind a deep arc lithosphere that remained viscously coupled to the Farallon slab until the opening of the slab window in the late Cenozoic.

  19. Seismic Reflection Imaging of the Lithosphere-asthenosphere Boundary Across the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Singh, S. C.; Marjanovic, M.; Audhkhasi, P.; Mehouachi, F.

    2015-12-01

    Until now, the nature of the lithosphere-asthenosphere boundary (LAB) has been constrained by teleseismic data, which has resolution of tens of kilometres and sample the LAB sparsely. Seismic reflection imaging technique, in contrast, can provide both lateral and vertical resolution of a few hundred meters, but has not been used for imaging deep structures, thus so far. In March-April 2015, we acquired over 2,750 km of ultra-deep seismic reflection data in the Atlantic Ocean. To image LAB variations as a function of age one of our profiles extends continuously starting from 75 Ma old oceanic lithosphere off the margin of Africa, crosses the Mid-Atlantic Ridge at zero age, to up to 25 Ma old South America lithosphere. To image large differences in the LAB depth we also cross three major fracture zones in the equatorial Atlantic. For imaging deep structures, we used a very large energy source, 10,170 cubic inches, rich in low frequencies and a 12 km long multi-component streamer allowing to record low frequency energy reflected from deep earth and remove reverberation in the water column. Initial results show reflected seismic energy from 50-60 km depth. The seismic reflection experiment will be complemented by seismic refraction study to determine the crustal and upper mantle P-wave velocity, magnetotelluric study to determine resistivity, and broadband ocean bottom seismometer experiment for teleseismic study, collocated with our seismic reflection profiles. In this paper, we will present the design of the seismic reflection experiment and preliminary results from the onboard processed data.

  20. The crust and lithosphere thicknesses in South America: trying to find the lithosphere- asthenosphere boundary

    NASA Astrophysics Data System (ADS)

    Heit, B.; Sodoudi, F.; Yuan, X.; Bianchi, M.; Kind, R.

    2007-05-01

    During the past years, a series of seismological investigations have been carried out to study the crustal and mantle structures all over the world. In South America, this investigation has not been an easy task as there are different regions where the geodynamics involves the subduction of an oceanic plate, the building of a mountain range as the Andes, the interaction with older lithosphere as the Brazilian Shield and the presence of active deformation fronts between the last two regions. In order to investigate the thickness of the lithosphere in such a complex context we have performed S-wave receiver function analysis (Vinnik and Farra, 2000; Li et al., 2004). The S receiver function technique looks for the S-to-P converted waves at seismic discontinuities beneath a station in the same way as the conventional P receiver function method that deals with P-to-S conversions. The S receiver function technique have proved to be useful to map the Moho and the LAB in many regions where other methods (i.e. surface waves) failed to provide reliable information (e.g. Li et al., 2004; Kumar et al., 2004a, 2004b; Sodoudi et al., 2006). We present here the results of S receiver function technique that has been applied to all the available temporary seismic experiments (e.g. BANJO, SEDA, REFUCA, BLSP) and the permanent stations from the IRIS network. We have been able to investigate the upper mantle discontinuities at all the depths beneath the stations and obtained coherent Moho depths along the entire Andes and in other South American continental regions. The LAB has been clearly detected below some stations, particularly those that are located far away from the subduction zone. By comparing our results with those from the P receiver functions, we have been able to further constrain the thicknesses of the crust and LAB in different regions including shields, mobile belts, basins and mountain ranges. At many stations we have also been able to map the upper mantle

  1. European Lithospheric Mantle; geochemical, petrological and geophysical processes

    NASA Astrophysics Data System (ADS)

    Ntaflos, Th.; Puziewicz, J.; Downes, H.; Matusiak-Małek, M.

    2017-04-01

    The second European Mantle Workshop occurred at the end of August 2015, in Wroclaw, Poland, attended by leading scientists in the study the lithospheric mantle from around the world. It built upon the results of the first European Mantle Workshop (held in 2007, in Ferrara, Italy) published in the Geological Society of London Special Publication 293 (Coltorti & Gregoire, 2008).

  2. Lithospheric strength variations in Mainland China: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Deng, Yangfan; Tesauro, Magdala

    2016-10-01

    We present a new thermal and strength model for the lithosphere of Mainland China. To this purpose, we integrate a thermal model for the crust, using a 3-D steady state heat conduction equation, with estimates for the upper mantle thermal structure, obtained by inverting a S wave tomography model. With this new thermal model and assigning to the lithospheric layers a "soft" and "hard" rheology, respectively, we estimate integrated strength of the lithosphere. In the Ordos and the Sichuan basins, characterized by intermediate temperatures, strength is primarily concentrated in the crust, when the rheology is soft, and in both the crust and upper mantle, when the rheology is hard. In turn, the Tibetan Plateau and the Tarim basin have a weak and strong lithosphere mainly on account of their high and low temperatures, respectively. A comparison of temperatures, strength, and effective viscosity variations with earthquakes distribution and their seismic energy released indicates that both the deep part of the crust and the upper mantle of the Tibetan Plateau are weak and prone to flow toward adjacent areas. The high strength of some of the tectonic domains surrounding Tibet (Tarim, Ordos, and Sichuan basins) favors the flow toward the weak western part of South China block.

  3. Lithospheric and atmospheric interaction on the planet Venus

    NASA Technical Reports Server (NTRS)

    Volkov, Vladislav P.

    1991-01-01

    Lithospheric and atmospheric interaction in the planet Venus are discussed. The following subject areas are covered: (1) manifestation of exogenic processes using photogeological data; (2) the chemical composition and a chemical model of the troposphere of Venus; (3) the mineral composition of surface rock on Venus; and (4) the cycles of volatile components.

  4. Imaging the lithospheric structure beneath the Indian continent

    NASA Astrophysics Data System (ADS)

    Maurya, S.; Montagner, J.-P.; Kumar, M. Ravi; Stutzmann, E.; Kiselev, S.; Burgos, G.; Rao, N. Purnachandra; Srinagesh, D.

    2016-10-01

    We present a high-resolution 3-D lithospheric model of the Indian plate region down to 300 km depth, obtained by inverting a new massive database of surface wave observations, using classical tomographic methods. Data are collected from more than 550 seismic broadband stations spanning the Indian subcontinent and surrounding regions. The Rayleigh wave dispersion measurements along 14,000 paths are made in a broad frequency range (16-250 s). Our regionalized surface wave (group and phase) dispersion data are inverted at depth in two steps: first an isotropic inversion and next an anisotropic inversion of the phase velocity including the SV wave velocity and azimuthal anisotropy, based on the perturbation theory. We are able to recover most of the known geological structures in the region, such as the slow velocities associated with the thick crust in the Himalaya and Tibetan plateau and the fast velocities associated with the Indian Precambrian shield. Our estimates of the depth to the Lithosphere-Asthenosphere boundary (LAB) derived from seismic velocity Vsv reductions at depth reveal large variations (120-250 km) beneath the different cratonic blocks. The lithospheric thickness is 120 km in the eastern Dharwar, 160 km in the western Dharwar, 140-200 km in Bastar, and 160-200 km in the Singhbhum Craton. The thickest (200-250 km) cratonic roots are present beneath central India. A low velocity layer associated with the midlithospheric discontinuity is present when the root of the lithosphere is deep.

  5. Seismicity in Romania--evidence for the sinking lithosphere.

    PubMed

    Roman, C

    1970-12-19

    The revision of Romanian earthquakes shows a distribution suggesting a sinking lithosphere under the Carpathian arc. Thermal and gravitational anomalies, as well as petrological and tectonic features, provide further evidence on the cause and character of intermediate earthquakes of Romania. This is consistent with the theory of plate tectonics in south-east Europe.

  6. Horizontal stress in planetary lithospheres from vertical processes

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.

    1991-01-01

    Understanding the stress states in a lithosphere is of fundamental importance for planetary geophysics. It is closely linked to the processes which form and modify tectonic features on the surface and reflects the behavior of the planet's interior, providing a constraint for the difficult problem of determining interior structure and processes. The tectonics on many extraterrestrial bodies (Moon, Mars, and most of the outer planet satellites) appears to be mostly vertical, and the horizontal stresses induced by vertical motions and loads are expected to dominate the deformation of their lithospheres. Herein, only changes are examined in the state of stress induced by processes such as sedimentary and volcanic deposition, erosional denudation, and changes in the thermal gradient that induce uplift or subsidence. This analysis is important both for evaluating stresses for specific regions in which the vertical stress history can be estimated, as well as for applying the proper loading conditions to global stress models. All references to lithosphere herein should be understood to refer to the elastic lithosphere, that layer which deforms elastically or brittlely when subjected to geologically scaled stresses.

  7. Convective instability within the Tibetan Lithospheric Mantle (Invited)

    NASA Astrophysics Data System (ADS)

    Houseman, G. A.; Molnar, P. H.; Evans, L.; England, P. C.

    2013-12-01

    Studies of seismic surface waves in Asia show that shear-wave speeds at depths of ~120-250km beneath the Tibetan Plateau are higher than is generally observed for continents, other than beneath Archaean cratons. The high-speed layer has been interpreted as continental lithosphere that was thickened during the convergence between India and Asia. This interpretation contradicts conceptual models in which gravitational instabilities remove a significant fraction of the mantle lithosphere beneath Tibet during that convergence. In contrast, the suggestion of relatively recent (post-early-Miocene) surface uplift of the Plateau, inferred from the onset of normal faulting across the plateau, synchronous increased rates of compressional deformation in the surroundings of the the plateau, and widespread volcanism in the northern part of the plateau, implies action of a mechanism that increased the gravitational potential energy of, and temperatures within, the Tibetan lithosphere in a way that would not occur if the mantle lithosphere had simply thickened continually throughout the India-Asia convergence. A resolution to this paradox is suggested by the observation that, while shear-wave speeds are indeed high at depths of 120-250 km beneath the Tibetan plateau, they are anomalously low at shallower depths, implying a temperature inversion that is hard to reconcile with uninterrupted lithospheric thickening. We suggest that the ensemble of observations may be explained by the convective overturn of a lithospheric root that is depleted in iron such that it remains buoyant with respect to normal upper mantle. The increased rate of strain within the Tibetan lithosphere once convergence began reduced its effective viscosity, and continuing convergence thickened the lithospheric root. These conditions led to convective overturn, similar to the original conceptual models, with the difference that the overturn was confined within the root, which remains buoyant with respect to the

  8. Seismic constraints on the lithosphere-asthenosphere boundary

    NASA Astrophysics Data System (ADS)

    Rychert, Catherine A.

    2014-05-01

    The basic tenet of plate tectonics is that a rigid plate, or lithosphere, moves over a weaker asthenospheric layer. However, the exact location and defining mechanism of the boundary at the base of the plate, the lithosphere-asthenosphere boundary (LAB) is debated. The oceans should represent a simple scenario since the lithosphere is predicted to thicken with seafloor age if it thermally defined, whereas a constant plate thickness might indicate a compositional definition. However, the oceans are remote and difficult to constrain, and studies with different sensitivities and resolutions have come to different conclusions. Hotspot regions lend additional insight, since they are relatively well instrumented with seismic stations, and also since the effect of a thermal plume on the LAB should depend on the defining mechanism of the plate. Here I present new results using S-to-P receiver functions to image upper mantle discontinuity structure beneath volcanically active regions including Hawaii, Iceland, Galapagos, and Afar. In particular I focus on the lithosphere-asthenosphere boundary and discontinuities related to the base of melting, which can be used to highlight plume locations. I image a lithosphere-asthenosphere boundary in the 50 - 95 km depth range beneath Hawaii, Galapagos, and Iceland. Although LAB depth variations exist within these regions, significant thinning is not observed in the locations of hypothesized plume impingement from receiver functions (see below). Since a purely thermally defined lithosphere is expected to thin significantly in the presence of a thermal plume anomaly, a compositional component in the definition of the LAB is implied. Beneath Afar, an LAB is imaged at 75 km depth on the flank of the rift, but no LAB is imaged beneath the rift itself. The transition from flank of rift is relatively abrupt, again suggesting something other than a purely thermally defined lithosphere. Melt may also exist in the asthenosphere in these regions

  9. Hyperextension of continental lithospheric mantle to oceanic-like lithosphere: the record of late gabbros in the Ronda subcontinental lithospheric mantle section (Betic Cordillera, S-Spain)

    NASA Astrophysics Data System (ADS)

    Hidas, Karoly; Garrido, Carlos; Targuisti, Kamal; Padron-Navarta, Jose Alberto; Tommasi, Andrea; Marchesi, Claudio; Konc, Zoltan; Varas-Reus, Maria Isabel; Acosta Vigil, Antonio

    2014-05-01

    Rupturing continents is a primary player in plate tectonic cycle thus longevity, stability, evolution and breakup of subcontinental lithosphere belongs for a long time to a class of basic geological problems among processes that shape the view of our Earth. An emerging body of evidences - based on mainly geophysical and structural studies - demonstrates that the western Mediterranean and its back-arc basins, such as the Alborán Domain, are hyperextended to an oceanic-like lithosphere. Formation of gabbroic melts in the late ductile history of the Ronda Peridotite (S-Spain) - the largest (ca. 300 km2) outcrop of subcontinental lithospheric mantle massifs on Earth - also attests for the extreme thinning of the continental lithosphere that started in early Miocene times. In the Ronda Peridotite, discordant gabbroic veins and their host plagioclase lherzolite, as well as gabbroic patches in dunite were collected in the youngest plagioclase tectonite domains of the Ojén and Ronda massifs, respectively. In Ojén, gabbro occurs as 1-3 centimeter wide discordant veins and dikes that crosscut the plagioclase tectonite foliation at high angle (60°). Within the veins cm-scale igneous plagioclase and clinopyroxene grains show a shape preferred orientation and grow oriented, subparallel to the trace of high temperature host peridotite foliation and oblique to the trend of the vein. In contrast to Ojén, mafic melts in the Ronda massif crystallized along subcentimeter wide anastomozing veins and they often form segregated interstitial melt accumulations in the host dunite composed of plagioclase, clinopyroxene and amphibole. Despite the differences in petrography and major element composition, the identical shape of calculated REE patterns of liquid in equilibrium with clinopyroxenes indicates that the percolating melt in Ronda and Ojén shares a common source. However, unlike gabbros from the oceanic lithosphere that shows clinopyroxene in equilibrium with LREE-depleted MORB

  10. Fabrics of Mantle Lithosphere of Fennoscandia Inferred from Seismic Anisotropy

    NASA Astrophysics Data System (ADS)

    Vecsey, L.; Plomerova, J.; Munzarova, H.; Babuska, V.

    2015-12-01

    Though crust in Archean cratons often displays a relatively simple architecture in comparison with younger orogens, where Moho topography and deep crustal structure are more complex, differences in structure of the mantle lithosphere are less prominent. The mantle lithosphere of Fennoscandia is built by domains with their own fossil inclined fabrics, which are similar to those we retrieved in younger continental provinces from investigations of seismic anisotropy. Passive seismic experiments SVEKALAPKO and LAPNET provided data for structural studies of the upper mantle beneath Fennoscandia. We evaluate the large-scale anisotropy in the upper mantle from (1) splitting of SKS waves (Vecsey et al., 2008), (2) directional terms of relative P-wave travel time residuals, (3) teleseismic tomography and (4) jointly interpreted body-wave anisotropic parameters (Plomerova et al., 2011). The domains of mantle lithosphere are sharply bounded both in the Proterozoic and Archean provinces and can be modelled in 3D by peridotite aggregates with dipping lineation a or foliation (a,c). The domains represent lithosphere fragments retaining fossil olivine preferred orientation created before the micro-plates assembled. Wedge-like penetration of the Archean domain into the Proterozoic province in the south-central Finland, supported by alternating ages of mantle xenoliths, seems to continue towards the north, where a westward shift of a boundary between regions with positive and negative velocity perturbations in teleseismic P-wave tomography can indicate an inclination of the Baltic-Bothnia Megashear Zone. We search for a mechanism which could create the observed inclined fabrics within continental assemblages. Such mechanism should differ from simple cooling processes which would lead to a horizontal stratification of the lithosphere without creating domains exhibiting different fabrics.

  11. Southwestward weakening of Wyoming lithosphere during the Laramide orogeny

    NASA Astrophysics Data System (ADS)

    Gao, Min; Fan, Majie; Moucha, Robert

    2016-08-01

    The mechanism of Laramide deformation in the central Rocky Mountains remains enigmatic. It is generally agreed that the deformation resulted from low-angle subduction of the Farallon plate beneath the North American plate during the latest Cretaceous-early Eocene; however, recent studies have suggested the importance of slab removal or slab rollback in causing this deformation. Here we infer Wyoming lithosphere structure and surface deformation pattern by conducting 2-D flexural subsidence modeling in order to provide constraints on the mechanism of Laramide deformation. We assume that Wyoming lithosphere behaved as an infinite elastic plate subject to tectonic loading of mountain ranges and conduct 2-D flexural subsidence modeling to major Laramide basins to document lithospheric stiffness and mountain load height. Our results show that the stiffness of Wyoming lithosphere varied slightly in each basin during the ~30 Myr duration of the Laramide deformation and decreased from northeastern Wyoming (Te = 32-46 km) to southwestern Wyoming (Te = 6-9 km). Our results also imply that the increase of equivalent load height of major Laramide ranges accelerated during the early Eocene. We propose that the bending stresses induced by the topographic load of the Sevier fold-and-thrust belt combined with crust-mantle decoupling initiated by the overthickened Sevier hinterland and the end loads due to the low-angle subduction at the western edge of the thick Wyoming craton have caused the southwestward decrease of lithospheric stiffness in Wyoming. Moreover, we attribute the accelerated load height gain during the early Eocene to both dynamic and isostatic effects associated with slab rollback.

  12. Preseismic Lithosphere-Atmosphere-Ionosphere Coupling

    NASA Astrophysics Data System (ADS)

    Kamogawa, Masashi

    hardly verified so far, a statistical approach has been unique way to promote the research. After the 2000s, several papers showing robust statistical results have arisen. In this paper, we focus on publications satisfying the following identification criteria: 1) A candidate of precursor, namely anomaly, is quantitatively defied. 2) Two time-series of anomalies and earthquake are constructed within the fixed thresholds such as a minimum magnitude, a region, and a lead-time. 3) To obtain a statistical correlation, a statistical process which includes four relations considering all combination among earthquake - no earthquake versus anomaly and no anomalies is applied, e. g., phi correlation. 4) For correlations under various thresholds the results keep consistency. 5) Large anomalies appear before large earthquakes. One of papers based on the identification criteria, which concerns preseismic geoelectrically anomalies, is introduced as an educative example. VAN method in Greece, i. e., Geo-electric potential difference measurement for precursor study in Greece, has been often discussed in the point of view of success and failure performance for practical prediction [Varotsos et al, Springer, 2011] to show a correlation and then less number of papers shows the statistical correlation with satisfying the identification criteria [Geller (ed.), GRL, 1996], so that the phenomena had been controversial. However, recent related study in Kozu-Island, Japan which satisfied the criteria showed the robust correlation [Orihara and Kamogawa et al., PNAS, 2012]. Therefore, the preseismic geoelectric anomalies are expected to be a precursor. Preseismic lithosphere-atmosphere-ionosphere coupling has been intensively discussed [Kamogawa, Eos, 2006]. According to review based on the identification criteria with considering recent publications, plausible precursors have been found, which are tropospheric anomaly [Fujiwara and Kamogawa, GRL, 2004], daytime electron depletion in F region

  13. Western United States lithosphere-asthenosphere interaction: Modern day small scale convection, plume and ancient lithospheric heterogeneity

    NASA Astrophysics Data System (ADS)

    Yuan, Huaiyu

    I present teleseismic imaging results from several temporary arrays in the southern and northern Rockies in the western U.S. This part continental lithosphere is a perfect lab in the world to study continent growth, stabilization and reactivation due to numerical mantle processes since the continental formation. A major hypothesis to test in this dissertation is the continent in the southern and northern Rockies retains its upper mantle structural heterogeneities formed during the early accretionary events, and remains as a kinematically stable lithosphere during subsequent tectonic events since the accretion. The main goals of this dissertation are to pursuit fine scale high resolution lithospheric seismic images of this region, focusing two primary key structures that record different stages of continent growth: the old Precambrian suture zones that mark the amalgamation of distinctly aged lithospheric provinces in 1.8--1.6 Ga, and the late Cenozoic Yellowstone hotspot track system that has been injecting magma into stable continental crust since 17 Ma. Methods such as body-wave tomography, receiver functions and a newly developed shear-wave splitting method are used in this thesis.

  14. Strike-slip earthquakes in the oceanic lithosphere: Observations of exceptionally high apparent stress

    USGS Publications Warehouse

    Choy, G.L.; McGarr, A.

    2002-01-01

    The radiated energies, Es, and seismic moments, Mo, for 942 globally distributed earthquakes that occurred between 1987 to 1998 are examined to find the earthquakes with the highest apparent stresses (??a = ?? Es/Mo, where ?? is the modulus of rigidity). The globally averaged ??a for shallow earthquakes in all tectonic environments and seismic regions is 0.3 MPa. However, the subset of 49 earthquakes with the highest apparent stresses (??a greater than about 5.0 MPa) is dominated almost exclusively by strike-slip earthquakes that occur in oceanic environments. These earthquakes are all located in the depth range 7-29 km in the upper mantle of the young oceanic lithosphere. Many of these events occur near plate-boundary triple junctions where there appear to be high rates of intraplate deformation. Indeed, the small rapidly deforming Gorda Plate accounts for 10 of the 49 high-??a events. The depth distribution of ??a, which shows peak values somewhat greater than 25 MPa in the depth range 20-25 km, suggests that upper bounds on this parameter are a result of the strength of the oceanic lithosphere. A recently proposed envelope for apparent stress, derived by taking 6 per cent of the strength inferred from laboratory experiments for young (less than 30 Ma) deforming oceanic lithosphere, agrees well with the upper-bound envelope of apparent stresses over the depth range 5-30 km. The corresponding depth-dependent shear strength for young oceanic lithosphere attains a peak value of about 575 MPa at a depth of 21 km and then diminishes rapidly as the depth increases. In addition to their high apparent stresses, which suggest that the strength of the young oceanic lithosphere is highest in the depth range 10-30 km, our set of high-??a earthquakes show other features that constrain the nature of the forces that cause interplate motion. First, our set of events is divided roughly equally between intraplate and transform faulting with similar depth distributions of ??a for

  15. Lithospheric deformation and mantle/crust coupling related to slab roll-back and tearing processes: the role of magma-related rheological weakening highlighted by 3D numerical modeling

    NASA Astrophysics Data System (ADS)

    Menant, Armel; Jolivet, Laurent; Guillou-Frottier, Laurent; Sternai, Pietro; Gerya, Taras

    2016-04-01

    Active convergent margins are the locus of various large-scale lithospheric processes including subduction, back-arc opening, lithospheric delamination, slab tearing and break-off. Coexistence of such processes results in a complex lithospheric deformation pattern through the rheological stratification of the overriding lithosphere. In this context, another major feature is the development of an intense arc- and back-arc-related magmatism whose effects on lithospheric deformation by rheological weakening are largely unknown. Quantifying this magma-related weakening effect and integrating the three-dimensional (3D) natural complexity of subduction system is however challenging because of the large number of physico-chemical processes involved (e.g. heat advection, dehydration of subducted material, partial melting of the mantle wedge). We present here a set of 3D high-resolution petrological and thermo-mechanical numerical experiments to assess the role of low-viscosity magmatic phases on lithospheric deformation associated with coeval oceanic and continental subduction, followed by slab retreat and tearing processes. Results in terms of crustal kinematics, patterns of lithospheric deformation and distribution and composition of magmatic phases are then compared to a natural example displaying a similar geodynamical evolution: the eastern Mediterranean subduction zone. Our modeling results suggest that the asthenospheric flow controls the ascending trajectories of mantle-derived magmatic sources developed in the mantle wedge in response to dehydration of oceanic slab. Once stored at the base of the overriding continental crust, low-viscosity mantle- and crustal-derived magmatic phases allow to decrease the lithospheric strength. This weakening then enhances the propagation of localized extensional and strike-slip deformation in response to slab roll-back and extrusion tectonics respectively. In addition, we show that storage of large amounts of low-viscosity magmas

  16. Lithospheric structure and deformation of the North American continent

    NASA Astrophysics Data System (ADS)

    Tesauro, Magdala; Kaban, Mikhail; Cloetingh, Sierd; Mooney, Walter

    2013-04-01

    We estimate the integrated strength and elastic thickness (Te) of the North American lithosphere based on thermal, density and structural (seismic) models of the crust and upper mantle. The temperature distribution in the lithosphere is estimated considering for the first time the effect of composition as a result of the integrative approach based on a joint analysis of seismic and gravity data. We do this via an iterative adjustment of the model. The upper mantle temperatures are initially estimated from the NA07 tomography model of Bedle and Van der Lee (2009) using mineral physics equations. This thermal model, obtained for a uniform composition, is used to estimate the gravity effect and to remove it from the total mantle gravity anomalies, which are controlled by both temperature and compositional variations. Therefore, we can predict compositional variations from the residual gravity anomalies and use them to correct the initial thermal model. The corrected thermal model is employed again in the gravity calculations. The loop is repeated until convergence is reached. The results demonstrate that the lithospheric mantle is characterized by strong compositional heterogeneity, which is consistent with xenolith data. Seismic data from the USGS database allow to define P-wave velocity and thickness of each crustal layer of the North American geological provinces. The use of these seismic data and of the new compositional and thermal models gives us the chance to estimate lateral variation of rheology of the main lithospheric layers and to evaluate coupling-decoupling conditions at the layers' boundaries. In the North American Cordillera the strength is mainly localized in the crust, which is decoupled from the mantle lithosphere. In the cratons the strength is chiefly controlled by the mantle lithosphere and all the layers are generally coupled. These results contribute to the long debates on applicability of the "crème brulée" or "jelly-sandwich" models for the

  17. Applying modern measurements of Pleistocene loads to model lithospheric rheology

    NASA Astrophysics Data System (ADS)

    Beard, E. P.; Hoggan, J. R.; Lowry, A. R.

    2011-12-01

    The remnant shorelines of Pleistocene Lake Bonneville provide a unique opportunity for building a dataset from which to infer rheological properties of the lower crust and upper mantle. Multiple lakeshores developed over a period of around 30 kyr which record the lithosphere's isostatic response to a well-constrained load history. Bills et al. (1994) utilized a shoreline elevation dataset compiled by Currey (1982) in an attempt to model linear (Maxwell) viscosity as a function of depth beneath the basin. They estimated an effective elastic thickness (Te) for the basin of 20-25 km which differs significantly from the 5-15 km estimates derived from models of loading on geologic timescales (e.g., Lowry and Pérez-Gussinyé, 2011). We propose that the discrepancy in Te modeled by these two approaches may be resolved with dynamical modeling of a common rheology, using a more complete shoreline elevation dataset applied to a spherical Earth model. Where Currey's (1982) dataset was compiled largely from observations of depositional shoreline features, we are developing an algorithm for estimating elevation variations in erosional shorelines based on cross-correlation and stacking techniques similar to those used to automate picking of seismic phase arrival times. Application of this method to digital elevation models (DEMs) will increase the size and accuracy of the shoreline elevation dataset, enabling more robust modeling of the rheological properties driving isostatic response to unloading of Lake Bonneville. Our plan is to model these data and invert for a relatively small number of parameters describing depth- and temperature-dependent power-law rheology of the lower crust and upper mantle. These same parameters also will be used to model topographic and Moho response to estimates of regional mass variation on the longer loading timescales to test for inconsistencies. Bills, B.G., D.R. Currey, and G.A. Marshall, 1994, Viscosity estimates for the crust and upper

  18. Garnet: a key to unraveling Earth's dynamic lithosphere

    NASA Astrophysics Data System (ADS)

    Smit, M. A.; Scherer, E. E.; Mezger, K.; Lee, J.; Ratschbacher, L.; Kooijman, E.; Stearns, M. A.

    2015-12-01

    Garnet enables constraints on all parameters relevant to lithosphere studies: pressure, temperature, strain, and time. This aspect, in combination with its widespread occurrence in metamorphic rocks and ability to resist retrogression, make the mineral a prime target in research into the dynamics of mountain belts. Garnet-based petrological and geochemical tools have diversified and improved as a result of recent advancements in spatial and analytical resolution. In particular, our ability to obtain precise age constraints using garnet Lu-Hf and Sm-Nd geochronology, and interpret these in a geological context has greatly improved. This contribution highlights a series of recent enhancements to the garnet toolkit and demonstrates its versatility in two case studies set in an archetypal collisional orogen: the Pamir-Himalaya-Tibet mountain chain. To enable a more effective use of garnet geochronology, we investigated the retentiveness of Lu-Hf and Sm-Nd isotope signatures in naturally metamorphosed garnet. Diffusive re-equilibration of these signatures is shown to occur to a minor, if not insignificant, extent during crustal metamorphism, thus firmly establishing these methods as reliable geochronometers. Diffusive major-element zoning analysis of the same garnet led to the development of a new thermometric tool, which was shown to provide reliable temperature estimates for a wide variety of rocks and terranes. We used Lu-Hf garnet geochronology to show that mid-crustal flow and 'Barrovian-type' metamorphism of rocks now exposed in the North Himalayan Gneiss Domes in Central Tibet commenced in the early Eocene. This result is the first to confirm that crustal thickening and contraction in the Tibetan Himalaya was broadly synchronous with the collision between Greater India and Eurasia. Garnet dating and thermometry, and rutile U-Pb thermochronology in the Pamir revealed a history of heating to 750-830 °C, commencing at 37 Ma in the South Pamir and occurring

  19. The Lithospheric Geoid as a Constraint on Plate Dynamics

    NASA Astrophysics Data System (ADS)

    Richardson, R. M.; Coblentz, D. D.

    2015-12-01

    100 years after Wegener's pioneering work there is still considerable debate about the dynamics of present-day plate motions. A better understanding of present-day dynamics is key to a better understanding of the supercontinent cycle. The Earth's gravity field is one of the primary data sets to help constrain horizontal density contrasts, and hence plate dynamic forces. Previous work has shown that the global average for the geoid step up from old oceanic lithosphere across passive continental margins to stable continental lithosphere is about 6-9m, and the global average for the geoid anomaly associated with cooling oceanic lithosphere (the so-called "ridge push") is 10-12m. The ridge geoid anomaly corresponds to a net force of ~3x1012N/m (averaged over the thickness of the lithosphere) due to 'ridge push.' However, for individual continental margins and mid-ocean ridge systems, there is considerable variation in the geoid step and geoid anomaly and consequently the associated forces contributing to the stress field. We explore the variation in geoid step across passive continental margins looking for correlations with age of continental breakup (and hence place within the supercontinent cycle), hot spot tracks, continental plate velocities, long-wavelength geoid energy (that may be masking signal), and small scale convection. For mid-ocean ridges, we explore variations in geoid anomaly looking for correlations with plate spreading rates, hot spot tracks, long-wavelength geoid energy (that may be masking signal), and small scale convection. We use a band-pass spherical harmonic filter on the full geoid (e.g., EGM2008-WGS84, complete to spherical harmonic degree and order 2159) between orders 6 and 80. The evaluation of the role of spatial variations in the geoid gradient for cooling oceanic lithosphere and across the continental margin in the dynamics of the intraplate stress field requires high spatial resolution modeling. We perform a high resolution finite

  20. Matching Lithosphere velocity changes to the GOCE gravity signal

    NASA Astrophysics Data System (ADS)

    Braitenberg, Carla

    2016-07-01

    Authors: Carla Braitenberg, Patrizia Mariani, Alberto Pastorutti Department of Mathematics and Geosciences, University of Trieste Via Weiss 1, 34100 Trieste Seismic tomography models result in 3D velocity models of lithosphere and sublithospheric mantle, which are due to mineralogic compositional changes and variations in the thermal gradient. The assignment of density is non-univocal and can lead to inverted density changes with respect to velocity changes, depending on composition and temperature. Velocity changes due to temperature result in a proportional density change, whereas changes due to compositional changes and age of the lithosphere can lead to density changes of inverted sign. The relation between velocity and density implies changes in the lithosphere rigidity. We analyze the GOCE gradient fields and the velocity models jointly, making simulations on thermal and compositional density changes, using the velocity models as constraint on lithosphere geometry. The correlations are enhanced by applying geodynamic plate reconstructions to the GOCE gravity field and the tomography models which places today's observed fields at the Gondwana pre-breakup position. We find that the lithosphere geometry is a controlling factor on the overlying geologic elements, defining the regions where rifting and collision alternate and repeat through time. The study is carried out globally, with focus on the conjugate margins of the African and South American continents. The background for the study can be found in the following publications where the techniques which have been used are described: Braitenberg, C., Mariani, P. and De Min, A. (2013). The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, 54(4), 321-334. doi:10.4430/bgta0105---- Braitenberg, C. and Mariani, P. (2015). Geological implications from complete Gondwana GOCE-products reconstructions and link to lithospheric roots. Proceedings of 5th

  1. Lithospheric Decoupling and Rotations: Hints from Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Muluneh, A. A.; Cuffaro, M.; Doglioni, C.; Kidane, T.

    2014-12-01

    Plates move relative to the mantle because some torques are acting on them. The shear in the low-velocity zone (LVZ) at the base of the lithosphere is the expression of these torques. The decoupling is allowed by the low viscosity in the LVZ, which is likely few orders of magnitudes lower than previously estimated. The viscosity value in the LVZ controls the degree of coupling/decoupling between the lithosphere and the underlying mantle. Lateral variations in viscosity within the LVZ may explain the velocity gradient among tectonic plates as the one determining the Ethiopian Rift (ER) separating Africa from Somalia. While it remains not fully understood the mechanisms of the torques acting on the lithosphere (thermally driven mantle convection or the combination of mantle convection with astronomical forces such as the Earth's rotation and tidal drag), the stresses are transmitted across the different mechanical layers (e.g., the brittle upper crust, down to the viscous-plastic ductile lower crust and upper mantle). Differential basal shear traction at the base of the lithosphere beneath the two sides of the East African Rift System (EARS) is assumed to drive and sustain rifting. In our analysis, the differential torques acting on the lithospheric/crustal blocks drive kinematics and block rotations. Since, ER involves the whole lithosphere, we do not expect large amount of rotation. Rotation can be the result of the whole plate motion on the sphere moving along the tectonic equator, or the second order sub-rotation of a single plate. Further rotation may occur along oblique plate boundaries (e.g., left lateral transtensional setting at the ER). Small amount of vertical axis rotation of blocks in northern ER could be related to the presence of local, shallower decollement layers. Shallow brittle-ductile transition (BDT) zone and differential tilting of crustal blocks in the northern ER could hint a possibility of detachment surface between the flow in the lower

  2. Viscoelastic Lithosphere Response and Stress Memory of Tectonic Force History (Invited)

    NASA Astrophysics Data System (ADS)

    Kusznir, N. J.

    2009-12-01

    While great attention is often paid to the details of creep deformation mechanisms, brittle failure and their compositional controls when predicting the response of lithosphere to tectonic forces, the lithosphere’s elastic properties are usually neglected; a viscous rheology alone is often used to predict the resulting distribution of stress with depth or to determine lithosphere strength. While this may simplify geodynamic modelling of lithosphere response to tectonic processes, the omission of the elastic properties can often give misleading or false predictions. The addition of the elastic properties of lithosphere material in the form of a visco-elastic rheology results is a fundamentally different lithosphere response. This difference can be illustrated by examining the application of horizontal tectonic force to a section of lithosphere incorporating the brittle-visco-elastic response of each infinitesimal lithosphere layer with temperature and stress dependent viscous rheology. The transient response of a visco-elastic lithosphere to a constant applied tectonic force and the resulting distribution of stress with depth are substantially different from that predicted by a viscous lithosphere model, with the same lithosphere composition and temperature structure, subjected to a constant lateral strain rate. For visco-elastic lithosphere subject to an applied horizontal tectonic force, viscous creep in the lower crust and mantle leads to stress decay in these regions and to stress amplification in the upper lithosphere through stress redistribution. Cooling of lithosphere with a visco-elastic rheology results in thermal stresses which, as a consequence of stress dissipation by creep and brittle failure, results in a complex and sometimes counter-intuitive distribution of stress with depth. This can be most clearly illustrated for the cooling of oceanic lithosphere, however similar or more complex behaviour can be expected to occur for continental lithosphere

  3. South China Sea crustal thickness and lithosphere thinning from satellite gravity inversion incorporating a lithospheric thermal gravity anomaly correction

    NASA Astrophysics Data System (ADS)

    Kusznir, Nick; Gozzard, Simon; Alvey, Andy

    2016-04-01

    The distribution of ocean crust and lithosphere within the South China Sea (SCS) are controversial. Sea-floor spreading re-orientation and ridge jumps during the Oligocene-Miocene formation of the South China Sea led to the present complex distribution of oceanic crust, thinned continental crust, micro-continents and volcanic ridges. We determine Moho depth, crustal thickness and continental lithosphere thinning (1- 1/beta) for the South China Sea using a gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir, 2008). The gravity inversion method provides a prediction of ocean-continent transition structure and continent-ocean boundary location which is independent of ocean isochron information. A correction is required for the lithosphere thermal gravity anomaly in order to determine Moho depth accurately from gravity inversion; the elevated lithosphere geotherm of the young oceanic and rifted continental margin lithosphere of the South China Sea produces a large lithosphere thermal gravity anomaly which in places exceeds -150 mGal. The gravity anomaly inversion is carried out in the 3D spectral domain (using Parker 1972) to determine 3D Moho geometry and invokes Smith's uniqueness theorem. The gravity anomaly contribution from sediments assumes a compaction controlled sediment density increase with depth. The gravity inversion includes a parameterization of the decompression melting model of White & McKenzie (1999) to predict volcanic addition generated during continental breakup lithosphere thinning and seafloor spreading. Public domain free air gravity anomaly, bathymetry and sediment thickness data are used in this gravity inversion. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we improve the determination of pre-breakup rifted margin conjugacy, rift orientation and sea-floor spreading trajectory. SCS conjugate margins

  4. HuBLE-UK: the Hudson Bay Lithospheric Experiment: Insights into the Formation of the Canadian Shield From Broadband Seismology

    NASA Astrophysics Data System (ADS)

    Bastow, I. D.; Thompson, D. A.; Kendall, J.-M.; Helffrich, G.; Wookey, J.; Snyder, D.; Eaton, D.; Darbyshire, F.

    2012-04-01

    The Canadian Shield is one of the largest exposures of Precambrian rocks on Earth. It is a mosaic of several Archean terranes that were brought together during a series of Paleoproterozoic orogens culminating in the so-called Trans-Hudson orogen, which is thought to have been similar to the Himalayan orogen in scale and nature. The tectonic evolution and lithospheric subdivisions of this region are poorly understood, but new seismic networks in northern Hudson Bay provide fresh opportunity to place constraints on the Preachbrian processes that formed and shaped it. Using a combination of seismic tomography, anisotropy and receiver function analysis we show that the lithosphere of the northern Hudson Bay region retains a strong signature of Archean-Paleoproterozoic tectonics. We map the boundary between the upper (Churchill) and lower (Superior) plates that collided ca. 1.8 Ga and identify backazimuth dependent shear-wave splitting parameters (phi, dt) on Baffin Island that indicate complex anisotropy (e.g., dipping fabric) beneath the region. Our results support the view that significant lithospheric deformation occurred during the Paleoproterozoic and that modern-day plate tectonic processes were thus in operation by at least ca. 1.8 Ga.

  5. Physico-chemical constraints on cratonic lithosphere discontinuities

    NASA Astrophysics Data System (ADS)

    Aulbach, Sonja; Rondenay, Stéphane; Huismans, Ritske

    2014-05-01

    The origins of the mid-lithospheric discontinuity (MLD) and lithosphere-asthenosphere boundary (LAB) have received much attention over the recent years. Peculiarities of cratonic lithosphere construction - compositional and rheological stratification due to thickening in collisional settings or by plume subcretion, multiple metasomatic overprints due to longevity - offer a variety of possibilities for the generation of discontinuities. Interconnected small degrees of conductive partial melt (carbonate-rich melts, such as carbonatites and kimberlites, or highly alkaline melts) at the cratonic LAB, which produce seismic discontinuities, may be generated in the presence of volatiles. These depress the peridotite solidus sufficiently to intersect the mantle adiabat at depths near the cratonic LAB at ~160-220 km, i.e. above the depth of metal saturation where carbonatite becomes unstable. The absence of agreement between the different seismic and magnetotelluric estimates for the depth of the LAB beneath Kaapvaal may be due to impingement of a plume, leading to a pervasively, but heterogeneously metasomatised ('asthenospherised') hot and deep root. Such a root and hot sublithosphere may yield conflicting seismic-thermal-geochemical depths for the LAB. The question arises whether the chemical boundary layer should be defined as above or below the asthenospherised part of the SCLM, which has preserved isotopic, compositional (non-primitive olivine forsterite content) and physical evidence (e.g. from teleseismic tomography and receiver functions) for a cratonic heritage and which therefore is still distinguishable from the asthenospheric mantle. If cratonic lithosphere overlies anomalously hot mantle for extended periods of time, the LAB may be significantly thinned, aided by penetration of relatively high-degree Fe-rich partial melts, as has occurred beneath the Tanzanian craton. Xenoliths from the deep Slave craton show little evidence for 'asthenospherisation'. Its root

  6. Satellite tidal magnetic signals constrain oceanic lithosphere-asthenosphere boundary

    PubMed Central

    Grayver, Alexander V.; Schnepf, Neesha R.; Kuvshinov, Alexey V.; Sabaka, Terence J.; Manoj, Chandrasekharan; Olsen, Nils

    2016-01-01

    The tidal flow of electrically conductive oceans through the geomagnetic field results in the generation of secondary magnetic signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain magnetic signals due to tidal flow; however, there are no reports that these signals have been used to infer subsurface structure. We use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere. PMID:27704045

  7. Thermal stresses due to cooling of a viscoelastic oceanic lithosphere

    USGS Publications Warehouse

    Denlinger, R.P.; Savage, W.Z.

    1989-01-01

    Instant-freezing methods inaccurately predict transient thermal stresses in rapidly cooling silicate glass plates because of the temperature dependent rheology of the material. The temperature dependent rheology of the lithosphere may affect the transient thermal stress distribution in a similar way, and for this reason we use a thermoviscoelastic model to estimate thermal stresses in young oceanic lithosphere. This theory is formulated here for linear creep processes that have an Arrhenius rate dependence on temperature. Our results show that the stress differences between instant freezing and linear thermoviscoelastic theory are most pronounced at early times (0-20 m.y. when the instant freezing stresses may be twice as large. The solutions for the two methods asymptotically approach the same solution with time. A comparison with intraplate seismicity shows that both methods underestimate the depth of compressional stresses inferred from the seismicity in a systematic way. -from Authors

  8. Thick plate flexure. [for lithospheric models of Mars and earth

    NASA Technical Reports Server (NTRS)

    Comer, R. P.

    1983-01-01

    Analytical expressions are derived for the displacements and stresses due to loading of a floating, uniform, elastic plate of arbitrary thickness by a plane or axisymmetric harmonic load. The solution is exact except for assumptions of small strains and linear boundary conditions, and gravitation within the plate is neglected. For typical earth parameters its predictions are comparable to those of the usual thin plate theory frequently assumed in studies of lithospheric flexure, gravity and regional isostasy. Even for a very thick lithosphere, which may exist in some regions of Mars, the thin plate theory is a better approximation to the thick plate solution than the elastic half-space limit, except for short-wavelength loads.

  9. On geoid heights and flexure of the lithosphere at seamounts

    NASA Astrophysics Data System (ADS)

    Watts, A. B.; Ribe, N. M.

    1984-12-01

    The sea surface height has now been mapped to an accuracy of better than ±1 m by using radar altimeters on board orbiting satellites. The major influence on the mean sea surface height is the marine geoid which is an equipotential surface. We have carried out preliminary studies of how oceanic volcanoes, which rise above the ocean floor as isolated seamounts and oceanic islands or linear ridges, contribute to the marine geoid. Simple one- and two-dimensional models have been constructed in which it is assumed that the oceanic lithosphere responds to volcanic loads as a thin elastic plate overlying a weak fluid substratum. Previous studies based on gravity and bathymetry data and uplift/subsidence patterns show that the effective flexural rigidity of oceanic lithosphere and the equivalent elastic thickness Te increase with the age of the lithosphere at the time of loading. The models predict that isolated seamounts emplaced on relatively young lithosphere on or near a mid-ocean ridge crest will be associated with relatively low amplitude geoid anomalies (about 0.4-0.5 m/km of height), while seamounts formed on relatively old lithosphere, on ridge flanks, will be associated with much higher amplitude anomalies (1.4-1.5 m/km). Studies of the Seasat altimetric geoid prepared by NASA's Jet Propulsion Laboratory support these model predictions; geoid amplitudes are relatively low over the Mid-Pacific Mountains and Line Islands, which formed on or near a mid-ocean ridge crest, and relatively high over the Magellan Seamounts and Wake Guyots, which formed off ridge. Direct modeling of the altimetric geoid over these features is complicated, however, by the wide spacing of the satellite tracks (which can exceed 100 km) and poor bathymetric control beneath individual satellite tracks. In regions where multibeam bathymetric surveys are available, models can be constructed that fit the altimetric geoid to better than ±1 m. Studies of geoid anomalies over the Emperor seamount

  10. Tidal tectonics and lateral variations of lithospheric thickness

    NASA Astrophysics Data System (ADS)

    Beuthe, M.

    2012-09-01

    Most icy satellites of the outer planets show prominent tectonic features on a global scale which can be due to periodic tides, polar wander, despinning, contraction (or expansion), orbital recession and convection [1]. Among these causes, periodic tides stand out because they can explain recent tectonic activity on Europa [2] and Enceladus [3, 4] whereas other mechanisms (apart from convection) most likely occurred in the far past. Periodic tides include diurnal tides associated with an eccentric orbit (obliquity tides are usually negligible) and nonsynchronous rotation. Until now, tidal stresses have been computed under the assumption of spherical symmetry [5]. However the thickness of the lithosphere (or ice crust) is affected (1) by solar insolation, making it thinner at the equator, and (2) by internal heating, making it thinner for example at the south pole of Enceladus (where active plumes have been detected by the probe Cassini). I compute here tidal stresses assuming that the lithospheric thickness varies with latitude.

  11. The Gutenberg discontinuity: melt at the lithosphere-asthenosphere boundary.

    PubMed

    Schmerr, Nicholas

    2012-03-23

    The lithosphere-asthenosphere boundary (LAB) beneath ocean basins separates the upper thermal boundary layer of rigid, conductively cooling plates from the underlying ductile, convecting mantle. The origin of a seismic discontinuity associated with this interface, known as the Gutenberg discontinuity (G), remains enigmatic. High-frequency SS precursors sampling below the Pacific plate intermittently detect the G as a sharp, negative velocity contrast at 40- to 75-kilometer depth. These observations lie near the depth of the LAB in regions associated with recent surface volcanism and mantle melt production and are consistent with an intermittent layer of asthenospheric partial melt residing at the lithospheric base. I propose that the G reflectivity is regionally enhanced by dynamical processes that produce melt, including hot mantle upwellings, small-scale convection, and fluid release during subduction.

  12. Satellite tidal magnetic signals constrain oceanic lithosphere-asthenosphere boundary.

    PubMed

    Grayver, Alexander V; Schnepf, Neesha R; Kuvshinov, Alexey V; Sabaka, Terence J; Manoj, Chandrasekharan; Olsen, Nils

    2016-09-01

    The tidal flow of electrically conductive oceans through the geomagnetic field results in the generation of secondary magnetic signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain magnetic signals due to tidal flow; however, there are no reports that these signals have been used to infer subsurface structure. We use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere.

  13. Structure of the deep oceanic lithosphere in the Northwestern Pacific ocean basin derived from active-source seismic data

    NASA Astrophysics Data System (ADS)

    Ohira, A.; Kodaira, S.; Nakamura, Y.; Fujie, G.; Arai, R.; Miura, S.

    2015-12-01

    Many seismological studies have detected the sharp seismic discontinuities in the upper mantle, some of which are interpreted the lithosphere-asthenosphere boundary (LAB). However there are few data at the old Pacific plate, in particular at ocean basin, which is critical information for understanding nature of the oceanic LAB. In 2014 we conducted an active-source refraction/reflection survey along a 1130-km-long line in southeast of the Shatsky Rise. Five ocean bottom seismometers (OBSs) were deployed and recovered by R/V Kairei of JAMSTEC. We used an airgun array with a total volume of 7,800 cubic inches with firing at intervals of 200 m. Multi-channel seismic reflection (MCS) data were also collected with a 444-channel, 6,000-m-long streamer cable. In OBS records the apparent velocity of the refraction waves from the uppermost mantle was high (< 8.6 km/sec), and considered to be caused by preferred orientation of olivine (e.g., Kodaira et al., 2014). Another remarkable feature is wide-angle reflection waves from the deep lithosphere at large (150-500 km) offsets. We applied the traveltime mapping method (Fujie et al., 2006), forward analysis (Zelt and Smith, 1992) and the amplitude modeling (Larsen and Grieger, 1998) to the OBS data. The results show that deep mantle reflectors exist at the depths from 35 to 60 km, and one possible explanation is that these reflectors correspond to patched low velocity zones around the base of the lithosphere. On MCS sections the clear and sharp Moho was imaged only at the southwestern end of the profile, but Moho was ambiguous or even not imaged in the most part of the profile. Since our seismic line covers the oceanic lithosphere with different ages that correspond to different stages of the Shatsky activity, the Moho appearance may reflect the variation of the Shatsky activity.

  14. The compositional and thermal structure of the lithosphere from thermodynamically-constrained multi-observable probabilistic inversion

    NASA Astrophysics Data System (ADS)

    Afonso, J. C.; Fullea, J.; Yang, Y.; Jones, A. G.; Griffin, W. L.; Connolly, J. A. D.; O'Reilly, S. Y.; Lebedev, S.

    2012-04-01

    Our capacity to image and characterize the thermal and compositional structure of the lithospheric and sublithospheric upper mantle is a fundamental prerequisite for understanding the formation and evolution of the lithosphere, the interaction between the crust-mantle and lithosphere-asthenosphere systems, and the nature of the lithosphere-asthenosphere boundary (LAB). In this context, the conversion of geophysical observables (e.g. travel-time data, gravity anomalies, etc) into robust estimates of the true physical and chemical state of the Earth's interior plays a major role. Unfortunately, available methods/software used to make such conversions are not well suited to deal with one or more of the following problems: 1) Strong non-linearity of the system. Traditional linearized inversions do not generally provide reliable estimates. 2) The temperature effect on geophysical observables is much greater than the compositional effect, therefore the latter is much harder to isolate. 3) Non-uniqueness of the compositional field. Different compositions can fit equally well seismic and potential field observations. 4) Strong correlations between physical parameters and geophysical observables complicate the inversion procedure and their effects are poorly understood. 5) Trade-off between temperature and composition in wave speeds. In this contribution we present a new full-3D multi-observable inversion method particularly designed to circumvent these problems. Some other key aspects of the method are: a) it combines multiple datasets (ambient noise tomography, receiver function analysis, body-wave tomography, magnetotelluric, geothermal, petrological, and gravity) in a single thermodynamic-geophysical framework, b) a general probabilistic (Bayesian) formulation is used to appraise the data, c) neither initial models nor well-defined a priori information is required, and d) it provides realistic uncertainty estimates. Both synthetic models and preliminary results for real

  15. The base of the seismogenic zone in the oceanic lithosphere

    NASA Astrophysics Data System (ADS)

    Greg, H.; Behn, M.; McGuire, J.

    2008-12-01

    Geophysical observations indicate that seismicity in the oceanic lithosphere is generally limited to depths above the 600°C isotherm. This relationship is in good agreement with extrapolation of experimental data on the frictional behavior of olivine (Boettcher et al., 2007). Under laboratory conditions, a transition from unstable to stable frictional sliding is observed at a temperature of approximately 1000°C. By accounting for the rate-dependence of crystal plasticity at asperities, the same transition is predicted to occur at a temperature of approximately 600°C in the Earth. While this agreement is encouraging, several issues remain poorly constrained - resolution of which may provide important insights into understanding the dynamics of earthquakes in general. A unique aspect of many oceanic earthquakes is that they likely occur in what was previously undamaged rock. Owing to upwelling and corner flow, the mantle rocks cool below the 600°C isotherm prior to any brittle deformation. Thus, rocks in the source regions for these earthquakes are likely intact at relatively high pressure with no pore fluids present. In other words, almost all the mechanisms hypothesized to produce weakening along faults in continental settings are unlikely to be active prior to an earthquake in the oceanic lithosphere. These rocks could thus be capable of supporting shear stresses in the range of 500 MPa at depths of 20 to 30 km. We will review these rheological constraints, discuss the evidence (or lack thereof) for high stresses based on earthquake seismology, and investigate alternate mechanisms that could be responsible for weakening the oceanic lithosphere - such as penetration of fluid from the surface to the greatest depths of lithospheric seismicity.

  16. Variations in effective elastic thickness of the North American lithosphere

    NASA Technical Reports Server (NTRS)

    Bechtel, Timothy D.; Forsyth, Donald W.; Sharpton, Virgil L.; Grieve, Richard A. F.

    1990-01-01

    A technique for estimating flexural rigidity that is not limited to sedimentary basins is used here to map variations in the effective elastic thickness of the North American lithosphere. The effective elastic thickness ranges from a minimum of about 4 km in the Basin and Range Province to more than 100 km in the Precambrian core of the continent. This finding supports the idea that flexural rigidity has increased with time since the last thermal event.

  17. A Top to Bottom Lithospheric Study of Africa and Arabia

    SciTech Connect

    Pasyanos, M

    2006-10-31

    We study the lithospheric structure of Africa, Arabia and adjacent oceanic regions with fundamental-mode surface waves over a wide period range. Including short period group velocities allows us to examine shallower features than previous studies of the whole continent. In the process, we have developed a crustal thickness map of Africa. Main features include crustal thickness increases under the West African, Congo, and Kalahari cratons. We find crustal thinning under Mesozoic and Cenozoic rifts, including the Benue Trough, Red Sea, and East, Central, and West African rift systems. Crustal shear wave velocities are generally faster in oceanic regions and cratons, and slower in more recent crust and in active and formerly active orogenic regions. Deeper structure, related to the thickness of cratons and modern rifting, is generally consistent with previous work. Under cratons we find thick lithosphere and fast upper mantle velocities, while under rifts we find thinned lithosphere and slower upper mantle velocities. There are no consistent effects in areas classified as hotspots, indicating that there seem to be numerous origins for these features. Finally, it appears that the African Superswell has had a significantly different impact in the north and the south, indicating specifics of the feature (temperature, time of influence, etc.) to be dissimilar between the two regions. Factoring in other information, it is likely that the southern portion has been active in the past, but that shallow activity is currently limited to the northern portion of the superswell.

  18. Oceanic lithosphere and asthenosphere - Thermal and mechanical structure

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Yuen, D. A.; Froidevaux, C.

    1976-01-01

    A coupled thermomechanical subsolidus model of the oceanic lithosphere and asthenosphere is developed which includes vertical heat conduction, a temperature-dependent thermal conductivity, heat advection by a horizontal and vertical mass flow that depends on depth and age, contributions of viscous dissipation or shear heating, a linear or nonlinear deformation law relating shear stress and strain rate, as well as a temperature- and pressure-dependent viscosity. The model requires a constant horizontal velocity and temperature at the surface, but zero horizontal velocity and constant temperature at great depths. The depth- and age-dependent temperature, horizontal and vertical velocities, and viscosity structure of the lithosphere and asthenosphere are determined along with the age-dependent shear stress in those two zones. The ocean-floor topography, oceanic heat flow, and lithosphere thickness are deduced as functions of ocean-floor age; seismic velocity profiles which exhibit a marked low-velocity zone are constructed from the age-dependent geotherms and assumed values of the elastic parameters. It is found that simple boundary-layer cooling determines the thermal structure at young ages, while effects of viscous dissipation become more important at older ages.

  19. The State of Lithospheric Stress in Greater Thailand

    NASA Astrophysics Data System (ADS)

    Meyers, B.; Furlong, K. P.; Pananont, P.; Pornsopin, P.

    2013-12-01

    Thailand and its surrounding regions occupy an important, but often overlooked, location in terms of plate tectonics and lithospheric deformation. The lateral extrusion of Tibet southeastward and eastward along deep strike slip faults to the north and the Sumatra-Andaman subduction zone to the south and west bound the region of greater Thailand. While it is adjacent to some of the most seismically active plate boundaries and intra-plate regions on Earth, this region has experienced only a low level of background seismicity. Thus, the long-term seismic potential of greater Thailand remains highly uncertain. Although historic seismicity is one indicator for future seismicity it is not the only tool we have for determining seismic hazard; we can assess the state of lithospheric stress. The stress conditions in this apparent aseismic region will be controlled by the forces acting on it boundaries. We can analyze those conditions through a study of fault structure, earthquake activity, and kinematics in the boundary area. Using Global Seismic Network (GSN) data augmented with Thai seismic network data to constrain the kinematics, and numerical finite element modeling of crustal and lithospheric deformation of the region, we are able to determine to overall stress conditions. This stress model can be compared to the known fault states in Thailand to assess the potential for earthquake activity.

  20. Improved determination of vector lithospheric magnetic anomalies from MAGSAT data

    NASA Technical Reports Server (NTRS)

    Ravat, Dhananjay

    1993-01-01

    Scientific contributions made in developing new methods to isolate and map vector magnetic anomalies from measurements made by Magsat are described. In addition to the objective of the proposal, the isolation and mapping of equatorial vector lithospheric Magsat anomalies, isolation of polar ionospheric fields during the period were also studied. Significant progress was also made in isolation of polar delta(Z) component and scalar anomalies as well as integration and synthesis of various techniques of removing equatorial and polar ionospheric effects. The significant contributions of this research are: (1) development of empirical/analytical techniques in modeling ionospheric fields in Magsat data and their removal from uncorrected anomalies to obtain better estimates of lithospheric anomalies (this task was accomplished for equatorial delta(X), delta(Z), and delta(B) component and polar delta(Z) and delta(B) component measurements; (2) integration of important processing techniques developed during the last decade with the newly developed technologies of ionospheric field modeling into an optimum processing scheme; and (3) implementation of the above processing scheme to map the most robust magnetic anomalies of the lithosphere (components as well as scalar).

  1. A global coupled model of the lithosphere and mantle dynamics

    NASA Astrophysics Data System (ADS)

    Iaffaldano, G.; Bunge, H.

    2004-12-01

    Understanding the dynamics of global lithospheric motion is one of the most important problems in geodynamics today. Mantle convection is commonly accepted as the driving force for plate motion but, while the kinematics of plate movement is well known from space geodetic and paleomagnetic observations, we lack a rigorous description of the coupled mantle convection-plate motion system. Here we present first results from a coupled mantle convection-global lithosphere motion model following a similar effort by Lithgow-Bertelloni and Guynn. Our plate motion code is SHELLS, a thinsheet FEM code developed by Bird which computes global plate motion and explicitly accounts for faults. The global mantle convection code is TERRA, a high-resolution 3-D FEM code developed and parallelized by Bunge and Baumgardner. We perform simple modeling experiments in which the shear tractions applied to the bottom of the lithosphere arise directly from the mantle circulation model. Our mantle circulation model includes a history of subduction and accounts, among others, for variations in mantle viscosity and strong bottom heating from the core. We find that our results are sensitive to the amount of core heating, an inference that has received renewed attention lately, and that models with stronger core heating overall are in better agreement with observations of intraplate stresses derived from the World Stress Map.

  2. Local recovery of lithospheric stress tensor from GOCE gravitational tensor

    NASA Astrophysics Data System (ADS)

    Eshagh, Mehdi

    2017-01-01

    SUMMARYThe sub-<span class="hlt">lithospheric</span> stress due to mantle convection can be computed from gravity data and propagated through the <span class="hlt">lithosphere</span> by solving the boundary-value problem of elasticity for the Earth's <span class="hlt">lithosphere</span>. In this case, a full tensor of stress can be computed at any point inside this elastic layer. Here, we present mathematical foundations for recovering such a tensor from gravitational tensor measured at satellite altitudes. The mathematical relations will be much simpler in this way than the case of using gravity data as no derivative of spherical harmonics or Legendre polynomials is involved in the expressions. Here, new relations between the spherical harmonic coefficients of the stress and gravitational tensor elements are presented. Thereafter integral equations are established from them to recover the elements of stress tensor from those of the gravitational tensor. The integrals have no closed-form kernels, but they are easy to invert and their spatial truncation errors are reducible. The integral equations are used to invert the real data of the gravity field and steady-state ocean circulation explorer (GOCE) mission, in November 2009, over the South American plate and its surroundings to recover the stress tensor at a depth of 35 km. The recovered stress fields are in good agreement with the tectonic and geological features of the area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6278843','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6278843"><span>Observations of flexure and the rheology of the oceanic <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bodine, J.H.; Steckler, M.S.; Bodine, J.H.; Watts, A.B.</p> <p>1981-05-10</p> <p>Observations of flexure indicate that the effective flexural rigidity of oceanic <span class="hlt">lithosphere</span> is a function of the age of the <span class="hlt">lithosphere</span> at the time of loading, and hence temperature. We have used a yield stress envelope model constrained by data from experimental rock mechanics to determine how the flexure parameters and rheologic properties of oceanic <span class="hlt">lithosphere</span> are related. The results of our model for seamounts and oceanic island loads in the interior of plates suggest that following loading, rapid stress relaxation occurs as the plate 'thins' from its short-term to its long-term (>10/sup 6/ years) mechanical thickness. The mechanical thickness, which determines the effective flexural rigidity of the plate, is strongly dependent on temperature and weakly dependent on load size and duration (>1-10 m.y.). The results of our model for convergent plate boundaries suggest that changes in the shape of the Outer Rise along an individual trench system may be due to variations in the horizontal load acting across the boundary (<1 kbar). The model predicts a narrow zone of high strain accumulation seaward of a trench which is in agreement with variations in crustal velocities and seismicity patterns observed along some trench systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050166884','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050166884"><span>Volcanism and Volatile Recycling on Venus from <span class="hlt">Lithospheric</span> Delamination</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Elkins-Tanton, L. T.; Hess, P. C.; Smrekar, S. E.; Parmentier, E. M.</p> <p>2005-01-01</p> <p>Venus has an unmoving <span class="hlt">lithosphere</span>, a young surface indicative of volcanic resurfacing, and a wide variety of volcanic and tectonic features. The planet s ubiquitous magmatic features include 100,000 small shield volcanoes as well as the descriptively named pancakes, ticks, and arachnoids [1]. Coronae, volcanic and tectonic features up to 2,600 km in diameter, have been attributed to <span class="hlt">lithospheric</span> interactions with upwelling plumes [e.g., 2], but more recently to delamination of the lower <span class="hlt">lithosphere</span> with [3] or without [4] a central upwelling. Lavas issuing from different volcanic features appear to have a range of compositions, as evidenced by their apparent viscosities and by data from Soviet landers. Steep-sided or "pancake" domes [e.g., 5] appear to consist of more viscous magma [6], perhaps silicic compositions created by remelting basaltic crust [7]. These steep-sided domes are associated with coronae and with shield volcanoes effusing basaltic magmas [7,8] with apparently low viscosities (low enough to allow fluid flow for hundreds of km, creating channels reminiscent of water rivers on Earth). Pancake domes, in contrast, can be up to 3 km in height and have volumes from 30 to approx.3,000 km3 [calculated from data in 8], and hundreds dot the planet [6-8].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/123343','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/123343"><span>Geoid data and thermal structure of the oceanic <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Richardson, W.P.; Stein, S.; Stein, C.A.</p> <p>1995-07-15</p> <p>A long-standing question is whether old oceanic <span class="hlt">lithosphere</span> continues cooling as the boundary layer of a halfspace or approaches thermal equilibrium as modeled by a finite thickness plate. Although the latter is the most direct inference from seafloor depths and heat flow, other explanations have been proposed. We investigate this issue using published results for the derivative of the oceanic geoid with age estimated from geoid offsets across fracture zones. Such data have not been used extensively in analyses of the thermal evolution of the <span class="hlt">lithosphere</span>, primarily because they are inconsistent with two commonly used thermal models; a halfspace or a 125-km-thick plate. Recent studies, however, find that depth and heat flow data are better fit by a thinner (95 km) plate model. We thus compile published geoid slope results, and find that these data, though scattered, can discriminate between the models. Geoid slope changes with age, rather than being constant as predicted for a cooling halfspace. This variation is greater than predicted for a thick plate and is better fit by a thin plate. Geoid data should thus be useful for improving thermal models of the <span class="hlt">lithosphere</span>. 30 refs., 4 figs., 1 tab.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Litho.189...28J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Litho.189...28J"><span>The <span class="hlt">lithosphere</span>-asthenosphere system beneath Ireland from integrated geophysical-petrological modeling - I: Observations, 1D and 2D hypothesis testing and modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jones, Alan G.; Afonso, Juan Carlos; Fullea, Javier; Salajegheh, Farshad</p> <p>2014-02-01</p> <p>Modeling the continental <span class="hlt">lithosphere</span>'s physical properties, especially its depth extent, must be done within a self-consistent petrological-geophysical framework; modeling using only one or two data types may easily lead to inconsistencies and erroneous interpretations. Using the LitMod approach for hypothesis testing and first-order modeling, we show how assumptions made about crustal information and the probable compositions of the <span class="hlt">lithospheric</span> and sub-<span class="hlt">lithospheric</span> mantle affect particular observables, particularly especially surface topographic elevation. The critical crustal parameter is density, leading to ca. 600 m error in topography for 50 kg m- 3 imprecision. The next key parameter is crustal thickness, and uncertainties in its definition lead to around ca. 4 km uncertainty in LAB for every 1 km of variation in Moho depth. Possible errors in the other assumed crustal parameters introduce a few kilometers of uncertainty in the depth to the LAB. We use Ireland as a <span class="hlt">natural</span> laboratory to demonstrate the approach. From first-order arguments and given reasonable assumptions, a topographic elevation in the range of 50-100 m, which is the average across Ireland, requires that the <span class="hlt">lithosphere</span>-asthenosphere boundary (LAB) beneath most of Ireland must lie in the range 90-115 km. A somewhat shallower (to 85 km) LAB is permitted, but the crust must be thinned (< 29 km) to compensate. The observations, especially topography, are inconsistent with suggestions, based on interpretation of S-to-P receiver functions, that the LAB thins from 85 km in southern Ireland to 55 km in central northern Ireland over a distance of < 150 km. Such a thin <span class="hlt">lithosphere</span> would result in over 1000 m of uplift, and such rapid thinning by 30 km over less than 150 km would yield significant north-south variations in topographic elevation, Bouguer anomaly, and geoid height, none of which are observed. Even juxtaposing the most extreme probable depleted composition for the <span class="hlt">lithospheric</span> mantle</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA....10849W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA....10849W"><span><span class="hlt">Lithospheric</span> structure and geodynamic evolution of the northern Molucca Sea area constrained by 3-D gravity field inversion of a combined sea-surface and satellite gravity dataset</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Widiwijayanti, C.; Tiberi, C.; Diament, M.; Deplus, C.; Mikhailov, V.; Louat, R.; Tikhotsky, S.; Gvishiani, A.</p> <p>2003-04-01</p> <p>The Molucca Sea extending from northeastern Indonesia to southern Philippines islands, is a zone of oceanic basin closure between two opposite-facing subduction zones. This convergence results in the collision of two subduction zones, which style evolves from the southern to the northern parts of the Molucca Sea. In order to provide new insights into the present-day <span class="hlt">lithospheric</span> structures in the Molucca Sea area, we inverted satellite and sea-surface gravity data into an iterative scheme including a priori seismological data. The seismological data were collected from two networks of Ocean Bottom Seismometer (OBS). These data allowed us to locate local seismic events and to build 3D tomographic images. We relate these results to the different stages of collision. The gravity data consists of combined sea-surface and satellite derived gravity. We used Kolmogorov-Wiener optimal (mean-square) filter to extract the gravity signal associated with <span class="hlt">lithospheric</span> structures, then analyzed it to determine main regional features of <span class="hlt">lithospheric</span> structure. For this purpose we employed a selection of Euler solutions based on a new clustering technique. To identify the geometry and <span class="hlt">nature</span> of <span class="hlt">lithospheric</span> structures, we also performed a 3-D gravity inversion for the northern Molucca Sea data, introducing our tomographic model as an independent constraint. The combination of both methods permits us to obtain a coherent image of the <span class="hlt">lithospheric</span> structure. The results of this study illustrate the heterogeneity of <span class="hlt">lithospheric</span> units in the northern Molucca Sea, which results from the collision between the Sangihe margin and <span class="hlt">lithospheric</span> fragments from the Phillipine plate such as the Snellius plateau or the Halmahera volcanic arc. Three phenomena can explain the observed <span class="hlt">lithospheric</span> structure: 1) the rupture of the Molucca Sea plate, accompanied by the appearance at the surface of slices of oceanic crust, favoring the development of suture zones as the collision evolves, 2) the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PApGe.173.2727W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PApGe.173.2727W"><span><span class="hlt">Lithospheric</span> Structure of the Northeastern North China Craton Imaged by S Receiver Functions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Xingchen; Ding, Zhifeng; Zhu, Lupei</p> <p>2016-08-01</p> <p><span class="hlt">Lithosphere</span> thickness variation is important for understanding the significant tectonic reactivation of the North China Craton (NCC) in the Mesozoic and Cenozoic time. Here, we determined the <span class="hlt">lithospheric</span> structure in the northeastern NCC using S receiver functions from 305 teleseismic events recorded by 223 seismic stations. The Moho and <span class="hlt">lithosphere</span>-asthenosphere boundary (LAB) are imaged clearly beneath the region. The Moho depth decreases from ~45 km beneath the western NCC to ~25 km beneath the eastern NCC. We found that the <span class="hlt">lithospheric</span> thickness varies from 60 to 80 km beneath the Trans-North China Orogen (TNCO) and eastern NCC with no significant change of the LAB depth. The <span class="hlt">lithosphere</span> thickness beneath the northwestern Ordos plateau is 100-130 km. In addition, there is a mid-<span class="hlt">lithosphere</span> discontinuity at a depth of 80 km beneath the plateau that is connected to the base of thinned <span class="hlt">lithosphere</span> in TNCO and eastern NCC. We suggest that the mid-<span class="hlt">lithosphere</span> discontinuity represents a mechanically weak zone in the original cratonic <span class="hlt">lithosphere</span> of the NCC. The material in the lower <span class="hlt">lithosphere</span> of the craton, when warmed and hydrated by water released from the subducting slab of Western Pacific, became weak due to decrease in viscosity and/or partial melting and was subsequently removed through small-scale mantle convections.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMNH41A1594L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMNH41A1594L"><span>Numerical Simulation of the Variation of Schumann Resonance Associated with Seismogenic Processe in the <span class="hlt">Lithosphere</span>-Atmosphere-Ionosphere system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, L.; Huang, Q.; Wang, Y.</p> <p>2012-12-01</p> <p>The variations in the strength and frequency shift of the Schumann resonance (SR) of the electromagnetic (EM) field prior to some significance earthquakes were reported by a number of researchers. As a robust physical phenomenon constantly exists in the resonant cavity formed by the <span class="hlt">lithosphere</span>-atmosphere-ionosphere system, irregular variations in SR parameters can be <span class="hlt">naturally</span> attributed to be the potential precursory observables for forecasting earthquake occurrences. Schumann resonance (SR) of the EM field between the <span class="hlt">lithosphere</span> and the ionosphere occurs because the space between the surface of the Earth and the conductive ionosphere acts as a closed waveguide. The cavity is <span class="hlt">naturally</span> excited by electric currents generated by lightning. SR is the principal background in the electromagnetic spectrum at extremely low frequencies (ELF) between 3-69 Hz. We simulated the EM field in the <span class="hlt">lithosphere</span>-ionosphere waveguide with a 2-dimensional (2D), cylindrical whole-earth model by the hybrid pseudo-spectral and finite difference time domain method. Considering the seismogensis as a fully coupled seismoelectric process, we simulate the seismic wave and EM wave in this 2D model. The excitation of SR in the background EM field are generated by the electric-current impulses due to lightning thunderstorms within the lowest 10 kilometers of the atmosphere . The diurnal variation and the latitude-dependence in ion concentration in the ionosphere are included in the model. After the SR has reached the steady state, the impulse generated by the seismogenic process (pre-, co- and post-seismic) in the crust is introduced to assess the possible precursory effects on SR strength and frequency. The modeling results explain the observed fact of why SR has a much more sensitive response to continental earthquakes, and much less response to oceanic events; the reason is simply due to the shielding effect of the conductive ocean that prevents effective radiation of the seismoelectric</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI43B..03D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI43B..03D"><span><span class="hlt">Lithosphere</span> and Asthenosphere Properties beneath Oceans and Continents and their Relationship with Domains of Partial Melt Stability in the Mantle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dasgupta, R.</p> <p>2014-12-01</p> <p>The depth of the <span class="hlt">lithosphere</span>-asthenosphere boundary (LAB) and the change in properties across the <span class="hlt">lithosphere</span>, asthenosphere, and LAB in various tectonic settings are captured in a variety of geophysical data, including seismic velocities and electrical conductivity. A sharp drop in shear wave velocity and increase in electrical conductivity can potentially be caused by the appearance of partial melt at or below the LAB but the chemical and dynamic stability of partial melt across <span class="hlt">lithosphere</span> and at LAB remain debated. Here I apply the recent models of mantle melting in the presence of water and carbon [1, 2] to evaluate the domains of stability of partial melt both beneath continents and oceans. The model allows prediction of the possible presence, the fraction, and composition of partial melt as a function of depth, bulk C and H2O content, and fO2 [3] in various geologic/tectonic settings. The results show that while a hydrous, carbonated melt is stable only beneath LAB and in the asthenospheric mantle beneath oceans, continental mantle can contain a carbonate-rich melt within the <span class="hlt">lithosphere</span>. For geotherms corresponding to surface heat flux (SHF) of 40-50 mW m-2, which also match P-T estimates beneath cratons based on thermo-barometry of peridotite xenoliths [4], the solidus of fertile peridotite with trace amount of CO2 and H2O is crossed at depths as shallow as 80-120 km [5]. If elevated geotherms of the Proterozoic and Phanerozoic terrains are applied, carbonatitic melt becomes stable somewhat shallower. These depths are similar to those argued for a mid-<span class="hlt">lithospheric</span> discontinuity (MLD) where a negative velocity gradient has been detected much shallower than the proposed depth of LAB in many places. With a drop in oxygen fugacity with depth, a freezing of carbonatitic melt may be expected at intermediate depths (~150-200 km). At 200-250 km a hydrous, carbonated silicate melt may reappear owing to the interplay of fO2 and freezing point depression effect of CO</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014safc.book...77K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014safc.book...77K"><span><span class="hlt">Lithosphere</span>-Atmosphere-Ionosphere Coupling System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kachakhidze, Manana; Kachakhidze, Nino; Kaladze, Tamaz</p> <p>2014-06-01</p> <p>Modern ground-based and satellite methods of viewing enables to reveal those multiple anomalous geophysical phenomena which become evident in the period preceding earthquake and are directly connected with the process of its preparation. Lately special attention is attributed to the electromagnetic emissions fixed during large earthquake, and has already been successfully detected in Japan, America and Europe. Unfortunately there is no electromagnetic emissions detection network in Georgia, but the offered work, based on experimental data of foreign researchers and electrodynamics, presents an important theory about the electromagnetic emissions generation fixed in the earthquake preparation period. The extremely interesting methodology of possible prediction of earthquake is created and all anomalous geophysical phenomena are interpreted which take place some months, days or hours before earthquake in the lithosphereatmosphere-ionosphere coupling system. Most interesting is the idea of the authors to consider the electromagnetic radiation as the main earthquake precursor for the purpose of earthquake prediction, because of its informative <span class="hlt">nature</span> and to consider all other anomalous geophysical phenomena which accompany the process of earthquake preparation as earthquake indicators. The offered work is the completely novel approach in earthquake problem searching with the view of earthquake prediction. It can form the base for creation of principally new trend in seismology, to be called conditionally "Earthquake Predictology".</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T43C4733B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T43C4733B"><span>Structure of the <span class="hlt">Lithosphere</span> in Central Europe: Integrated Density Modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bielik, M.; Grinč, M.; Zeyen, H. J.; Plašienka, D.; Pasteka, R.; Krajňák, M.; Bošanský, M.; Mikuška, J.</p> <p>2014-12-01</p> <p>Firstly, we present new results related to the <span class="hlt">lithospheric</span> structure and tectonics of the Central Europe and the Western Carpathians. For geophysical study of the <span class="hlt">lithosphere</span> in Central Europe we calculated four original 2D <span class="hlt">lithosphere</span>-scales transects crossing this area from the West European Platform in the North to the Aegean Sea in the South and from the Adriatic Sea in the West to the East European Platform in the East. Modelling is based on the joint interpretation of gravity, geoid, topography and surface heat flow data with temperature-dependent density. Wherever possible, crustal structure is constrained by seismic data. The thickness of the <span class="hlt">lithosphere</span> decreases from the older and colder platforms to the younger and hotter Pannonian Basin with a maximum thickness under the Eastern and Southern Carpathians. The thickness of the Carpathian arc <span class="hlt">lithosphere</span> varies between 150 km in the North (the Western Carpathians) and about 300 km in the Vrancea zone (the Eastern and Southern Carpathian junction). In the Platform areas it is between 120 and 150 km and in the Pannonian Basin it is about 70 km. The models show that the Moesian Platform is overthrust from the North by the Southern Carpathians and from the South by the Balkanides and characterized by bending of this platform. In all transects, the thickest crust is found underneath the Carpathian Mountains or, as in the case of the Vrancea area, under their immediate foreland. The thickest crust outside the orogens is modelled for the Moesian Platform with Moho depths of up to 45 km. The thinnest crust is located under the Pannonian Basin with about 26-27 km. Secondly, our presentation deals with construction of the stripped gravity map in the Turiec Basin, which represents typical intramontane Neogene depression of the Western Carpathians. Based on this new and original gravity map corrected by regional gravity effect we were able to interpret the geological structure and tectonics of this sedimentary basin</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T13G..02Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T13G..02Z"><span>Lateral variations in <span class="hlt">lithospheric</span> and landscape evolution at both ends of the Himalaya-Tibet orogen</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zeitler, P. K.; Schmidt, J. L.; Meltzer, A.</p> <p>2015-12-01</p> <p>At the broadest scale, like many orogens the Himalaya encompass a range of orogenic features that are remarkably similar along much of the length of the mountain belt and its neighboring terranes. At one scale of consideration, these similarities appear to be a signal that fundamental processes associated with <span class="hlt">lithospheric</span> collision have been active. However, the vast size of the Himalaya and Tibet, the different climate regimes experienced by the orogen across time and space, and the along-strike variations in the continental and arc margins that faced one another before collision, make it at once remarkable that any similarities exist, and important to more critically evaluate their <span class="hlt">nature</span>. The eastern and western Himalayan syntaxes confound any attempt to generalize too much about the Himalaya-Tibet orogen. By area these features occupy at least 25% of the orogenic belt, and compared to the "main" portions of the arc they show clear differences in their <span class="hlt">lithospheric</span> structures, landscapes, and evolution. The boundary and initial conditions that shaped the eastern and western indentor corners were and are different, as is the <span class="hlt">nature</span> and timing of erosional exhumation. Some of the most active geologic processes on Earth have recently been in play within the syntaxes, and the evolution of landscapes and fluvial systems, important in developing the sedimentary record of the Himalaya-Tibet system, has been complex and variable in space and time. Southeasternmost Tibet and the Lhasa Block in particular exemplify this complexity both in its complex topographic evolution linked to surface processes and climate, and in lateral variability in <span class="hlt">lithospheric</span> structure. Taking a system viewpoint, an important question to debate is the degree to which there are features in the Himalaya-Tibet system that are robustly emergent, given the broad boundary conditions of the continental collision plus the suite of local and regional geodynamical processes that have operated during</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.V51D..03G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.V51D..03G"><span>Geochemical and Geophysical Estimates of <span class="hlt">Lithospheric</span> Thickness Variation Beneath Galápagos</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gibson, S. A.; Geist, D.</p> <p>2010-12-01</p> <p> base of the Galápagos thermal <span class="hlt">lithosphere</span>. An excellent correlation exists between the results of this modelling and our estimates of the top of the melt column from geochemical modelling. The seismic data suggest that the base of the thermal <span class="hlt">lithosphere</span> is ~56 km beneath western Galapagos and ~50 km beneath the northeast of the archipelago. These estimates are also consistent with those derived from models of conductive geotherms for plate ages of 5 and 10 Ma and a mantle potential temperature of 1400oC. We propose that thinner <span class="hlt">lithosphere</span> away from the postulated site of the present-day Galápagos plume axis, combined with the lateral deflection of the plume head, is responsible for active volcanism over a relatively large area. Non-uniform variations in <span class="hlt">lithospheric</span> thickness relative to distance from the Galápagos Spreading Centre are consistent with the complex <span class="hlt">nature</span> of the oceanic <span class="hlt">lithosphere</span> beneath this part of the Pacific. [1] Villagomez, D.R. et al., 2007. Upper mantle structure beneath the Galápagos Archipelago from surface wave tomography. JGR 112.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.U21A0007P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.U21A0007P"><span>Formation of the Oceanic <span class="hlt">Lithosphere</span> from the Upper Asthenosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Presnall, D. C.; Gudfinnsson, G. H.</p> <p>2007-12-01</p> <p>In a global examination of the chemistry of MORBs, we find that Na8-Fe8-axial depth data do not support large variations in the temperature and pressure of MORB extraction from the mantle. Instead, the complete absence of high-pressure (> ~1.5 GPa) olivine-controlled crystallization of MORBs combined with solidus phase relations in the CaO-MgO-Al2O3-SiO2-Na2O-FeO system indicate that the inverse and positive Na8-Fe8 variations are produced from a heterogeneous source by melt extraction over a very narrow range of P and T (~1.2-1.5 GPa and 1250-1280°C) at the plagioclase-spinel lherzolite transition. This is inconsistent with the existence of hot mantle plumes (Easter, Galapagos, Iceland, Azores, St. Helena, Tristan, Afar) on or close to ridges. However, it is consistent with the very flat 410 km discontinuity beneath the East Pacific Rise, which does not permit the existence of even a single hot plume (Easter) beneath the ridge (Melbourne and Helmberger, 2002, JGR, 107, doi:10.1029/2001B000332). The global absence of MORBs with a high-pressure major-element signature implies that the isolation of the East Pacific Rise from the deeper mantle applies to all ridges. A new model is developed (Presnall and Gudfinnsson, in press, Origin of the Oceanic <span class="hlt">Lithosphere</span>, J. Petrol.) that explains the formation of new seismic <span class="hlt">lithosphere</span> (~70 km thickness) by lateral and upward migration of the slightly melted upper part (~70-140 km depth) of the low-velocity zone toward the ridge. Although decompression melting occurs over a large pressure range, melt extraction is constrained to the very narrow P-T range given above by the maximum T in the mantle at which CO2 vapor can be extracted. This condition occurs at a pressure just below that of the abrupt 280°C temperature decrease of the carbonated lherzolite solidus at the base of the seismic <span class="hlt">lithosphere</span>. The constant association of strombolian and effusive eruptions at ridges (Clague, 2007, Geophys. Res. Abstr., 9, EUG, 02096</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.203.1961A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.203.1961A"><span>Australia's <span class="hlt">lithospheric</span> density field, and its isostatic equilibration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aitken, A. R. A.; Altinay, C.; Gross, L.</p> <p>2015-12-01</p> <p>Density is a key driver of tectonic processes, but it is a difficult property to define well in the <span class="hlt">lithosphere</span> because the gravity method is non-unique, and because converting to density from seismic velocity models, themselves non-unique, is also highly uncertain. Here we use a new approach to define the <span class="hlt">lithospheric</span> density field of Australia, covering from 100°E to 165°E, from 5°N to 55°S and from the crust surface to 300 km depth. A reference model was derived primarily from the recently released Australian Seismological Reference Model, and refined further using additional models of sedimentary basin thickness and crustal thickness. A novel form of finite-element method based deterministic gravity inversion was applied in geodetic coordinates, implemented within the open-source escript modelling environment. Three spatial resolutions were modelled: half-, quarter- and eighth-degree in latitude and longitude, with vertical resolutions of 5, 2.5 and 1.25 km, respectively. Parameter sweeps for the key inversion regularization parameters show that parameter selection is not scale dependent. The sweep results also show that finer resolutions are more sensitive to the uppermost crust, but less sensitive to the mid- to lower-crust and uppermost mantle than lower resolutions. All resolutions show similar sensitivity below about 100 km depth. The final density model shows that Australia's <span class="hlt">lithospheric</span> density field is strongly layered but also has large lateral density contrasts at all depths. Within the continental crust, the structure of the middle and lower crust differs significantly from the crystalline upper crust, suggesting that the tectonic processes or events preserved in the deep crust differ from those preserved in the shallower crust. The <span class="hlt">lithospheric</span> mantle structure is not extensively modified from the reference model, but the results reinforce the systematic difference between the density of the oceanic and continental domains, and help identify</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.8867A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.8867A"><span>The Neotectonic crustal uplift and <span class="hlt">lithospheric</span> softening in plate interiors caused by infiltration of mantle fluids into the <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Artyushkov, Eugene</p> <p>2013-04-01</p> <p>Large-scale crustal uplifts on the continents are commonly attributed to plate collision. Within the continents convergent boundaries now exist only in some regions, e.g., between the Eurasian and Indian plates. A predominant part of continental <span class="hlt">lithosphere</span> refers to intraplate areas. Thus, the Precambrian crust where shortening terminated half a billion years ago or earlier covers about 70% of the continental areas. However, during the Pliocene and Pleistocene most of the Precambrian crust underwent the uplifts from 100-200 m to 1-2 km. They occurred over most of the African continent, in Greenland and East Siberia, and in many other regions. Neotectonic crustal uplift widely occurred on the Phanerozoic <span class="hlt">lithosphere</span>. In most regions, e.g., in the Central and Northeastern Asia, the uplift by 1-2 km or more took place long after strong shortening of the crust in the Mesozoic and Paleozoic. It was accompanied by extension or compression of only a few per cent. In the absence of strong crustal thickening, the Neotectonic uplift in intraplate areas required a density decrease in the <span class="hlt">lithosphere</span> which was caused by two main processes. The first one is expansion of previously metamorphosed dense mafic rocks within the crust due to a secondary metamorphism, diaphtoresis, under the temperature T = 350-400 °C. This mechanism is evidenced by a strong heterogeneity of the uplift in space. Thus in the Archean East Siberia in many places the uplift varies by 300-500 m in regions, only 20 km wide. Rock expansion from diaphtoresis required an inflow into the crust of large volumes of fluid from the mantle. The second process is a convective replacement by the asthenosphere of a denser mantle <span class="hlt">lithosphere</span> whose viscosity was reduced by several orders of magnitude due to infiltration of fluids from the mantle. In many areas, e.g. in Central Asia and western North America this gave rise to a rise of the top of the asthenospheric layer by ~100 km. Over most of the continental areas</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.262..153Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.262..153Z"><span>Variation of olivine composition in the volcanic rocks in the Songliao basin, NE China: <span class="hlt">lithosphere</span> control on the origin of the K-rich intraplate mafic lavas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, L.-Y.; Prelević, D.; Li, N.; Mertz-Kraus, R.; Buhre, S.</p> <p>2016-10-01</p> <p><span class="hlt">Lithospheric</span> thickness and the heterogeneity of the mantle <span class="hlt">lithosphere</span> are two major parameters that play a role in determining the final composition of the mafic melts and their minerals. The Songliao basin in northeast China represents an ideal <span class="hlt">natural</span> laboratory to study the effect of these two parameters on early Pliocene to Holocene K-rich mafic lavas (K2O > 4 wt.%; K2O/Na2O > 1). A series of Cenozoic volcanic edifices (Erkeshan, Wudalianchi, Keluo and Xiaogulihe) are tentatively divided into three groups (Group 1 - thin, Group 2 - middle, and Group 3 - thick) according to the <span class="hlt">lithosphere</span> thickness. They are located in the northern region of the Songliao basin extending in a near north-south direction along a broad zone where the <span class="hlt">lithosphere</span> thickness increases gradually. We present a detailed petrographical and geochemical study on olivine macrocrysts in combination with new geochemical data on their host lavas, including major and trace element abundances as well as Sr, Nd, and Pb isotopic signatures. Our ultimate aim is to quantitatively and qualitatively determine the role of <span class="hlt">lithospheric</span> mantle thickness (named as "lid effect") and composition in the variation of mafic lavas and olivine composition. When corrected to Mg# = 0.72, a number of major elements in the lavas correlate with increasing <span class="hlt">lithospheric</span> thickness (L): Si72 and Al72 decrease, whereas Mg72, Fe72, Ti72 and P72 increase. Sm/Yb ratios in the lavas increase, implying that <span class="hlt">lithospheric</span> thickness exerts an important control. Group 3 mafic lavas are ultrapotassic (showing lamproite affinity) with K2O/Na2O > 4: their La/Sm and Pb isotope ratios deviate from the above correlations, indicating that the lavas from the thickest part of the basin exhibit the highest extent of metasomatic enrichment of the mantle source. Several parameters (e.g. [Ni], Ni/Mg, Ni/(Mg/Fe), Mn/Fe and Ca/Fe) in melt-related olivine from Group 1 and Group 2 lavas are controlled by variable <span class="hlt">lithosphere</span> thickness. Olivine</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1612809J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1612809J"><span>Using subsidence and P-T-t history on the Alpine Tethys margin to constrain <span class="hlt">lithosphere</span> deformation modes during continental breakup</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeanniot, Ludovic; Kusznir, Nick; Manatschal, Gianreto; Mohn, Geoffroy; Beltrando, Marco</p> <p>2014-05-01</p> <p>Mantle exhumation and hyper-extended crust, as observed on the Iberia-Newfoundland conjugate margins, are key components of both present-day and fossil analogue magma-poor rifted margins. Conceptual models of the Alpine Tethys paleogeography evolution show a complex subsidence history, determined by the <span class="hlt">nature</span> and composition of sedimentary, crustal and mantle rocks in the Alpine domains (Mohn et al., 2010). The relative timing of crustal rupture and decompressional melt initiation and inherited mantle composition control whether mantle exhumation may occur; the presence or absence of exhumed mantle therefore provides useful information on the timing of these events and constraints on <span class="hlt">lithosphere</span> deformation modes and composition. A single mode of <span class="hlt">lithosphere</span> deformation leading to continental breakup and sea-floor spreading cannot explain observations. We have determined the sequence of <span class="hlt">lithosphere</span> deformation modes for the fossil Alpine Tethys margin using a numerical model of the temporal and spatial evolution of <span class="hlt">lithosphere</span> deformation; the model has been calibrated against observations of subsidence and P-T-t history for the Alpine Tethys margin. A 2D finite element viscous flow model (FeMargin) is used to generate flow fields for a sequence of <span class="hlt">lithosphere</span> deformation modes, which are used to advect <span class="hlt">lithosphere</span> and asthenosphere temperature and material. FeMargin is kinematically driven by divergent deformation in the topmost 15-20 km of the <span class="hlt">lithosphere</span> inducing passive upwelling beneath that layer; the upper <span class="hlt">lithosphere</span> is assumed to deform by extensional faulting and magmatic intrusions, consistent with observations of deformation processes occurring at slow spreading ocean ridges (Cannat, 1996). We also include buoyancy enhanced upwelling in the kinematic model as proposed by Braun et al. (2000). We generate melt by decompressional melting using the parameterization and methodology of Katz et al. (2003). In the modelling of the Alpine Tethys margin</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880020858&hterms=Evolution+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DEvolution%2Bevidence','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880020858&hterms=Evolution+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DEvolution%2Bevidence"><span><span class="hlt">Lithospheric</span> evolution of the Northern Arabian Shield: Chemical and isotopic evidence from basalts, xenoliths and granites</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stein, M.</p> <p>1988-01-01</p> <p>The evolution of the upper-mantle and the lower-crust (the conteinental <span class="hlt">lithosphere</span>), is the area of Israel and Sinai was studied, using the chemical composition and the Nd-Sr isotopic systematics from mantle and crustal nodules, their host basalts, and granites. The magmatism and the metasomatism making the <span class="hlt">lithosphere</span> are related to uprise of mantle diapirs in the uppermost mantle of the area. These diapirs heated the base of the <span class="hlt">lithosphere</span>, eroded, and replaced it with new hot material. It caused a domal uplift of the <span class="hlt">lithosphere</span> (and the crust). The doming resulted in tensional stresses that in turn might develop transport channels for the basalt.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V54B..05C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V54B..05C"><span>Pseudotachylites and Earthquakes: New Evidence for the "Jelly Sandwich" Rheology of Continental <span class="hlt">Lithosphere</span> (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, W.; Yang, Z.</p> <p>2009-12-01</p> <p>The occurrence of pseudotachylite, an often-used proxy for brittle, seismogenic deformation, in mafic granulite facies has been cited as key evidence for the lower continental crust being stronger than the underlying uppermost mantle (“crème brûlée” model). Such reasoning seems unsound in that spectacular examples of pseudotachylite, exceeding 100 meters in length, occur in outcrops of the upper mantle. So if pseudotachylites indicate high mechanical strength, then the mantle <span class="hlt">lithosphere</span> must be strong, supporting the “jelly sandwich” model of rheology. Moreover, pseudotachylites do occur in rocks of amphibolite facies where hydrous minerals are abundant, ruling out the notion that pseudotachylite implies dry conditions in the crust. Recent results from laboratory experiments also indicate that in general, mafic granulite is weaker than peridotite (Wang et al. [2008] and H. Green, personal communication). Perhaps the only stone left unturned is the pathological case where absolute-dry, mafic granulite were to juxtapose with hydrous peridotite - a hypothetical situation not observed in <span class="hlt">nature</span> and yet to be linked with any specific, known geological processes. Meanwhile, cases of well-established, large- to moderate-sized earthquakes in the sub-continental mantle <span class="hlt">lithosphere</span> (SCML) have been steadily accumulating, including events that generated clear underside reflections off the Moho above the hypocenters. Furthermore, a continent-wide analysis of precisely determined focal depths along and near the East African rift system (EARS) shows that different segments of the EARS exhibit three distinct patterns in focal depths, with a clear bimodal distribution beneath well-known but amagmatic rift valleys. The peaks of seismic moment release occur in the upper to mid-crust and near and below the Moho - a pattern established in several regions more than 25 years ago that implies a similar vertical distribution in limiting stress of the continental <span class="hlt">lithosphere</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1210431N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1210431N"><span><span class="hlt">Lithospheric</span> inhomogeneity - the main factor controlling the Permo/Triassic Siberian plume location</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nikishin, Anatoly; Sobornov, Konstantin; Pravikova, Natalia</p> <p>2010-05-01</p> <p>Northwestern part of the Siberian platform is one of the interesting places to study the relations between the intraplate tectonics and the short-term large scale magmatic events. We will focus on four events which affected nearly the same area: (1) Vendian(~Ediacaran) to Early Paleozoic rapid subsidence without rifting; (2) Late Carboniferous to Early Permiam syncompressional subsidence; (3) Permo/Triassic large-scale Siberian (Tunguska) plume-related basaltic magmatism; (4) large-scale intraplate inversional tectonic events, close to the Triassic/Jurassic boundary. During the Riphean, several large sedimentary rift-related and passive margin related basins occupied the marginal parts of the platform. The total thicknesses of sediments locally exceeds 10 km. Approximately at the Riphean-Vendian boundary (630-620 Ma), a major collision took place along the northern (Taymyr), western (the Enisey Ridge) and southeastern (Transbaikal area) parts of the platform. The compression was transmitted to the inner domains of the platform, causing the long-wavelength intraplate basement-involved folding and thrusting, followed by general uplift and erosion. This compression was followed by rapid regional Vendian to Silurian subsidence, with the vertical amplitude of up to 5-7 km. This subsidence is likely thermally controlled, and does not reveal any relation with rifting. We propose this subsidence was related with <span class="hlt">lithosphere</span> cooling which followed the postcollisional delamination (figure). Rapid subsidence occured at nearly the same place during the Late Carboniferous-Early Permian times, synchronously with the main Uralian-West Siberian orogeny. It could have a syncompressional <span class="hlt">nature</span>. The depocentre of Permo/Triassic Siberian traps (flood basalts) is located rather close to the depocentre of previous, Vendian to Permian, subsidence. So we can imagine that the location of mantle plume intrusion in the <span class="hlt">lithosphere</span> was not occasional. At the same time, the Permo</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S31D4472K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S31D4472K"><span>Imaging <span class="hlt">Lithospheric</span>-scale Structure Beneath Northern Altiplano in Southern Peru and Northern Bolivia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kumar, A.; Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.</p> <p>2014-12-01</p> <p>The northern Altiplano plateau of southern Peru and northern Bolivia is one of the highest topographic features on the Earth, flanked by Western and Eastern Cordillera along its margin. It has strongly influenced the local and far field <span class="hlt">lithospheric</span> deformation since the early Miocene (Masek et al., 1994). Previous studies have emphasized the importance of both the crust and upper mantle in the evolution of Altiplano plateau (McQuarrie et al., 2005). Early tomographic and receiver function studies, south of 16° S, show significant variations in the crust and upper mantle properties in both perpendicular and along strike direction of the Altiplano plateau (Dorbath et. al., 1993; Myers et al., 1998; Beck and Zandt, 2002). In order to investigate the <span class="hlt">nature</span> of subsurface <span class="hlt">lithospheric</span> structure below the northern Altiplano, between 15-18° S, we have determined three-dimensional seismic tomography models for Vp and Vs using P and S-wave travel time data from two recently deployed local seismic networks of CAUGHT and PULSE. We also used data from 8 stations from the PERUSE network (PERU Subduction Experiment). Our preliminary tomographic models show a complex variation in the upper mantle velocity structure with depth, northwest and southeast of lake Titicaca. We see the following trend, at ~85 km depth, northwest of lake Titicaca: low Vp and Vs beneath the Western Cordillera, high Vs beneath the Altiplano and low Vp and Vs beneath the Eastern Cordillera. This low velocity anomaly, beneath Eastern Cordillera, seems to coincide with Kimsachata, a Holocene volcano in southern Peru. At depth greater than ~85 km: we find high velocity anomaly beneath the Western Cordillera and low Vs beneath the Altiplano. This high velocity anomaly, beneath Western Cordillera, coincides with the well-located Wadati-Benioff zone seismicity and perhaps represents the subducting Nazca slab. On the southeast of lake Titicaca, in northern Bolivia, we see a consistently high velocity anomaly</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PEPI..238....8B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PEPI..238....8B"><span>Assimilating <span class="hlt">lithosphere</span> and slab history in 4-D Earth models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bower, Dan J.; Gurnis, Michael; Flament, Nicolas</p> <p>2015-01-01</p> <p>We develop methods to incorporate paleogeographical constraints into numerical models of mantle convection. Through the solution of the convection equations, the models honor geophysical and geological data near the surface while predicting mantle flow and structure at depth and associated surface deformation. The methods consist of four constraints determined a priori from a plate history model: (1) plate velocities, (2) thermal structure of the <span class="hlt">lithosphere</span>, (3) thermal structure of slabs in the upper mantle, and (4) velocity of slabs in the upper mantle. These constraints are implemented as temporally- and spatially-dependent conditions that are blended with the solution of the convection equations at each time step. We construct Earth-like regional models with oceanic and continental <span class="hlt">lithosphere</span>, trench migration, oblique subduction, and asymmetric subduction to test the robustness of the methods by computing the temperature, velocity, and buoyancy flux of the <span class="hlt">lithosphere</span> and slab. Full sphere convection models demonstrate how the methods can determine the flow associated with specific tectonic environments (e.g., back-arc basins, intraoceanic subduction zones) to address geological questions and compare with independent data, both at present-day and in the geological past (e.g., seismology, residual topography, stratigraphy). Using global models with paleogeographical constraints we demonstrate (1) subduction initiation at the Izu-Bonin-Mariana convergent margin and flat slab subduction beneath North America, (2) enhanced correlation of model slabs and fast anomalies in seismic tomography beneath North and South America, and (3) comparable amplitude of dynamic and residual topography in addition to improved spatial correlation of dynamic and residual topography lows.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T21A2796D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T21A2796D"><span><span class="hlt">Lithospheric</span> strength variations in Mainland China: tectonic implications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Deng, Y.; Tesauro, M.</p> <p>2015-12-01</p> <p>We present new thermal and strength models of Mainland China. We integrate thermal model for the crust, using a 3D steady-state heat conduction equation, with estimates for the upper mantle thermal structure obtained by inverting an S-wave tomography model. Using the new thermal model and attributing to the <span class="hlt">lithospheric</span> layers a 'soft' and 'hard' rheology, respectively, we estimate the integrated strength of the <span class="hlt">lithosphere</span>. In the Ordos and the Sichuan basins, characterized by intermediate temperatures, strength is primarily concentrated in the crust, when the rheology is 'soft', and in both the crust and upper mantle, when the rheology is 'hard'. In turn, the Tibetan Plateau and the Tarim basin have a weak/strong <span class="hlt">lithosphere</span> mainly on account of their high/low temperatures. Deep earthquakes releasing high seismic energy, occurring beneath Tien Shan orogen, may be related to the brittle failure of anhydrous granulite-faciesrocks composing its lower crust. In contrast, the fluids released by the Indian slab favor the triggering of earthquakes located in the deep crust of south Tibet. Comparison of temperatures, strength and effective viscosity variations with the earthquakes distribution and their seismic energy released indicates that both the deep part of the crust and the upper mantle of the Tibetan Plateau are weak and prone to flow towards the adjacent areas. On account of the high strength of some of the tectonic domains surrounding Tibet, the flow is directed northward beneath the Qaidam basin and turns south of the Sichuan basin, moving toward the weak South China block.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.G43C..04M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.G43C..04M"><span>Strain rate and strength of the continental <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mazzotti, S.; Gueydan, F.</p> <p>2013-12-01</p> <p>Under the Wilson Cycle and Plate Tectonics paradigms, continents are divided between stable continental regions (SCR), which tend to remain un-deformed, and plate boundary zones (PBZ) that repeatedly accommodate deformation associated with opening and closing of tectonic plates. This long-term (> 1 Ma) perspective is reflected in short-term (< 100 a) deformation markers such as seismicity and GPS measurements, which highlight the first-order contrast in strain rates between SCR and PBZ. However, poor data resolution at low strain rates provides only rough upper limits on actual long- and short-term strain and seismicity rates in SCR regions, including in intraplate weak zones (paleo-PBZ) where debate is ongoing regarding short- and long-term deformation rates (e.g., New Madrid seismic zone). We propose to constrain first-order continental strain (and seismicity) rates using <span class="hlt">lithosphere</span> rheological models, including new strain-weakening rheologies, driven by tectonic forces. We estimate average strain rates that satisfy near-failure equilibrium between net driving forces and <span class="hlt">lithosphere</span> strength for cases that typify PBZ, cratons, and intraplate weak zones. Our model yields a range of strain rates that vary by up to six orders of magnitude between PBZ and cratons. In intraplate weak zones, structural and tectonic heritage results in significant weakening and yields strain rates compatible with GPS, seismicity, and geological markers. These results provide first-order constraints on long-term <span class="hlt">lithosphere</span> strength and deformation rates. In particular, we explore upper and lower bounds of possible strain rates in intraplate weak zones of North America, using a range of geotherm, rheology, and local stress conditions. These can be used to derived limits on seismicity rates in these regions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5023538','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5023538"><span>Strength and survival of subducted <span class="hlt">lithosphere</span> during the Laramide orogeny</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Spencer, J.E. )</p> <p>1993-04-01</p> <p>The strength of subducted ocean <span class="hlt">lithosphere</span> is influenced primarily by two competing processes. During subduction brittle rock strength increases because of increasing compressive stress across fracture surfaces which increases frictional resistance to sliding. The strength of rocks hot enough to be in the plastic deformation regime decreases primarily because of heat conducted from the overriding plate and the asthenosphere. A one-dimensional finite-element heat-flow program was used to simulate subduction in two dimensions where conductive heat flow parallel to the slab and to the upper plate could be neglected. Temperatures determined with this method, and pressures based on depth, were then used to calculate the form of the brittle-plastic failure envelope for subducted <span class="hlt">lithosphere</span>. An olivine flow law and strain rate of 10[sup [minus]15] s[sup [minus]1] were used for the plastic part of the failure envelope. The failure envelope was then used to calculate slab-parallel compressive strength and maximum sustainable bending moment. Modeling of Maramide subduction beneath southwestern North America, using slab ages and subduction rates for the Farallon plate from Engebretson et al., suggests that the subducted slab will not retain much strength beyond 1,000 to 1,200 km inland unless the thickness of the North American <span class="hlt">lithosphere</span>, and depth to the top of the slab, are significantly less than 200 km. Slab survival for distances of 1000 km seems assured. Survival for much greater distances is possible. The slab is predicted to have been up to several times stronger beneath southwestern North America than at the trench because much rock remains in the brittle regime and is under high confining pressure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V31E3062P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V31E3062P"><span>Modeling Plume-Triggered, Melt-Enabled <span class="hlt">Lithospheric</span> Delamination</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Perry-Houts, J.; Humphreys, G.</p> <p>2015-12-01</p> <p>It has been suggested that arrival of the Yellowstone plume below North America triggered a <span class="hlt">lithospheric</span> foundering event which aided the eruption of the Columbia River flood basalts. This hypothesis potentially accounts for some of the biggest mysteries related to the CRB's including their location as "off-track" plume volcanism; and the anomalous chemical signatures of the most voluminous units. The foundered <span class="hlt">lithosphere</span> appears to be a remnant chunk of Farallon slab, which had been stranded beneath the Blue Mountains terrain since the accretion of Siletzia. If this is the case then the mechanisms by which this slab stayed metastable between Siletzia accretion and CRB time, and then so suddenly broke loose, is unclear. The addition of heat and mantle buoyancy supplied by the Yellowstone plume provides a clue, but the geodynamic process by which the slab was able to detach remains unclear.Efforts to model numerically the underlying processes behind delamination events have been gaining popularity. Typically, such models have relied on drastically weakened regions within the crust, or highly non-linear rheologies to enable initiation and propagation of <span class="hlt">lithosphere</span> removal. Rather than impose such a weak region a priori, we investigated the role of mantle and crustal melt, generated by the addition of plume heat, as the source of such a rheologic boundary.We track melt generation and migration though geodynamic models using the Eulerian finite element code, ASPECT. Melt moves relative to the permeable, compacting, and viscously-deforming mantle using the approach of (Keller, et al. 2013) with the notable exception that ASPECT currently cannot model elasticity. Dike and sill emplacement is therefore still a work in progress. This work is still in the preliminary stages and results are yet inconclusive.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRB..118.3080F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRB..118.3080F"><span>Generation of continental rifts, basins, and swells by <span class="hlt">lithosphere</span> instabilities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fourel, LoïC.; Milelli, Laura; Jaupart, Claude; Limare, Angela</p> <p>2013-06-01</p> <p>Continents may be affected simultaneously by rifting, uplift, volcanic activity, and basin formation in several different locations, suggesting a common driving mechanism that is intrinsic to continents. We describe a new type of convective instability at the base of the <span class="hlt">lithosphere</span> that leads to a remarkable spatial pattern at the scale of an entire continent. We carried out fluid mechanics laboratory experiments on buoyant blocks of finite size that became unstable due to cooling from above. Dynamical behavior depends on three dimensionless numbers, a Rayleigh number for the unstable block, a buoyancy number that scales the intrinsic density contrast to the thermal one, and the aspect ratio of the block. Within the block, instability develops in two different ways in an outer annulus and in an interior region. In the outer annulus, upwellings and downwellings take the form of periodically spaced radial spokes. The interior region hosts the more familiar convective pattern of polygonal cells. In geological conditions, such instabilities should manifest themselves as linear rifts striking at a right angle to the continent-ocean boundary and an array of domal uplifts, volcanic swells, and basins in the continental interior. Simple scaling laws for the dimensions and spacings of the convective structures are derived. For the subcontinental <span class="hlt">lithospheric</span> mantle, these dimensions take values in the 500-1000 km range, close to geological examples. The large intrinsic buoyancy of Archean <span class="hlt">lithospheric</span> roots prevents this type of instability, which explains why the widespread volcanic activity that currently affects Western Africa is confined to post-Archean domains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T13C2391T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T13C2391T"><span>New thermal and gravity models of the North American <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tesauro, M.; Kaban, M. K.; Cloetingh, S.; Mooney, W. D.</p> <p>2011-12-01</p> <p>We present a new thermal model for the North American <span class="hlt">lithosphere</span> obtained from inversion of NA07 tomography model, following the method described in Cammarano et al. (2003). The advantage of using this seismic model is that it was calculated using an a priori crustal model, which minimizes trade-offs between the velocity structure in the crust and the upper mantle. We first estimate the mantle temperature distribution using a uniform composition and anelasticity model for the entire North American continent. The new results are in contrast with those obtained by previous studies based on interpretation of mantle xenoliths, predicting higher temperature and stronger thermal variability beneath the North American cratons. The reason of this disagreement might be related to the composition assumed and in particular to the iron depletion, characterizing the shallow mantle <span class="hlt">lithosphere</span> of the cratons, which is neglected in this model. Furthermore, the comparison between the thermal model and the gravity mantle anomalies, which are obtained after removing the crustal effect from the observed gravity field, demonstrates that mantle density heterogeneity is controlled not only by temperature variations but also by compositional changes. We use the new thermal model to estimate the pure thermal component of the mantle gravity anomalies. In the next step we obtain the compositional component, subtracting the former field from the latter. The compositional gravity anomalies are used to estimate lateral and vertical compositional changes of the mantle <span class="hlt">lithosphere</span> (e.g., percentage of iron depletion beneath the cratons), which are considered in the implementation of more robust thermal models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMMR11A2464D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMMR11A2464D"><span>Deformation of olivine single crystals under <span class="hlt">lithospheric</span> conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Demouchy, S.; Tommasi, A.; Cordier, P.</p> <p>2012-12-01</p> <p>The rheology of mantle rocks at <span class="hlt">lithospheric</span> temperatures (<1000°C) remains poorly constrained, in contrast to the extensive experimental data on creep of olivine single crystals and polycrystalline aggregates at high temperature (T > 1200°C). Consequently, we have performed tri-axial compression experiments on oriented single crystals and polycrystalline aggregates of San Carlos olivine at temperatures ranging from 800° to 1090°C. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at constant strain rates ranging from 7 × 10-6 s-1 to 1 × 10-4 s-1 . Compression was applied along three different crystallographic directions: [101]c, [110]c and [011]c, to activate the several slip systems. Yield differential stresses range from 88 to 1076 MPa. To constrain hardening, stick-and-slip, or strain localization behaviors, all samples were deformed at constant displacement rate for finite strains between 4 to 23 %. Hardening was observed in all experiments and the maximum differential stress often overcame the confining pressure. EBSD mapping highlights macroscale bending of the crystalline network in three crystals. TEM observations on several samples show dislocations with [100] and [001] Burgers vectors in all samples, but dislocation arrangements vary. The results from the present study permit to refining the power-law expressing the strain rate dependence on stress and temperature for olivine, allowing its application to the <span class="hlt">lithospheric</span> mantle. Our experiments confirm that previous published high-temperature power flow laws overestimate the strength of <span class="hlt">lithospheric</span> mantle and that the transition to low-temperature creep occurs at higher temperatures than it has previously been established.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1616228R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1616228R"><span>Rethinking the problem of ionosphere-<span class="hlt">lithosphere</span> coupling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruzhin, Yuri; Novikov, Victor</p> <p>2014-05-01</p> <p>An overview of research of possible relations between variations of geomagnetic field and seismicity is presented, including Sq-variations and geomagnetic storms. There are many papers demonstrating positive correlations between geomagnetic field variations and subsequent earthquake occurrence that allows to authors to talk about earthquake triggering impact provided by ionospheric processes on <span class="hlt">lithosphere</span>. Nevertheless, there is another opinion on negligible impact of geomagnetic disturbances on the earthquake source supported by statistical analysis of correlation between variations of geomagnetic field and global and regional seismicity. Mainly, the both points of view on this problem are based on statistical research without detailed consideration of possible physical mechanisms which may be involved into the supposed earthquake triggering, or very rough estimations of possible increase of stresses in the faults under critical (near to failure) state were made. Recently it was shown that the fluids may play very important role in the electromagnetic earthquake triggering, and the secondary triggering mechanism should be considered when the fluid migrating into the fault under electromagnetic action may provide fault weakening up to earthquake triggering threshold. At the same time, depending on fault orientation, local hydrological structure of the crust around the fault, location of fluid reservoirs, etc. it may be possible that fluid migration from the fault may provide the fault strengthening, and in this case the impact of variation of geomagnetic field may provide an opposite effect. In so doing, it is useless to apply only statistical approach for the problem of ionosphere-<span class="hlt">lithosphere</span> coupling, and in each case the possible behavior of fluids should be considered under electromagnetic impact on <span class="hlt">lithosphere</span>. Experimental results supporting this idea and obtained at the spring-block model simulating the seismic cycle (slow accumulation and sharp drop of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.P51B0923R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.P51B0923R"><span>Crustal and <span class="hlt">Lithospheric</span> Structure at Isidis Planitia, Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ritzer, J. A.; Hauck, S. A.</p> <p>2005-12-01</p> <p>Isidis Planitia is the site of a large free air gravity anomaly consistent with modification and sedimentary or magmatic filling of an impact basin. Mars Global Surveyor gravity and topography data of the Isidis basin on Mars are analyzed to elucidate the crustal and <span class="hlt">lithospheric</span> structure near the dichotomy boundary in the Eastern hemisphere. Global gravity and topography datasets are inverted using an extension of Banerdt's [1986] model for deformation of a thin elastic shell and a nominal assumption that Isidis was isostatically compensated prior to modification by infilling. Using this model we attempt to constrain potential variations in (and trade-offs among) local crustal thickness, density and thickness of basin fill material, and <span class="hlt">lithospheric</span> deformation. The permissible parameter space is limited by assuming that the local crustal thickness of the basin cannot be less than zero at the time of infilling. Our results suggest that the density of the fill inside Isidis must be more than 2500 kg/m3 and higher densities are probable. Recent work of Wieczorek and Zuber [2004] indicates that the most likely average crustal thickness of Mars is between 38 and 62 km. On the basis of this range of values for crustal thickness, we infer that the average density of the fill is more than 2900 kg/m3. A high fill density suggests that the material inside the basin is predominantly of igneous rather than sedimentary origin. Under the assumption of an average crustal density of 2900 kg/m3 the inferred thickness of the fill layer is at least 5 km, and could be significantly larger depending upon the degree of compensation of the basin before it was loaded by fill material. A comparison of the faulting observed at Nili Fossae to the predicted zone of extensional strain northwest of Isidis may further constrain the thickness of the elastic <span class="hlt">lithosphere</span> beneath the basin at the time of loading.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUSM.T23B..08S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUSM.T23B..08S"><span><span class="hlt">Lithospheric</span> scale model of Merida Andes, Venezuela (GIAME Project)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmitz, M.; Orihuela, N. D.; Klarica, S.; Gil, E.; Levander, A.; Audemard, F. A.; Mazuera, F.; Avila, J.</p> <p>2013-05-01</p> <p>Merida Andes (MA) is one of the most important orogenic belt in Venezuela and represents the northern culmination of South America Andes. During the last 60 years, several models have been proposed to explain the shallow and deep structure, using different geological, geophysical, seismological, geochemical and petrologic concepts; nevertheless, most of them have applied local observation windows, and do not represent the major structure of MA. Therefore, a multidisciplinary research group, coordinated by FUNVISIS, in close cooperation with UCV, ULA and PDVSA, is proposed in order to get the outlined goals in the project entitled GIAME ("Geociencia Integral de los Andes de MErida") was established, which aims to generate a <span class="hlt">lithospheric</span> scale model and the development of a temporal dynamic model for the MA. As a base for <span class="hlt">lithospheric</span> investigations of the Merida Andes, we are proposing three wide angle seismic profiles across the orogen on three representative sites, in order to determine the inner structure and its relation with the orogen's gravimetric root. To the date, there are no seismic studies at <span class="hlt">lithospheric</span> scale which cross MA. The wide angle seismic will be complemented with the re-processing and re-interpretation of existing reflection seismic data, which will allow to establish a relationship between MA and its associated flexural basins (Maracaibo and Barinas-Apure basins). Depending on the results of the VENCORP Project (VENezuelan COntinental Reflection Profiling), which might show some reliable results about crustal features and Moho reflectors along three long seismic profiles at Caribbean Moutain system, a reflection seismic profile across the central portion of MA is proposed. Additional tasks, consisting in MA quaternary deformation studies, using research methods like neotectonics and paleoseismology, georadar, numerical modeling, cinematic GPS, SAR interferometry, thermocronology, detailed studies on regional geology, flexural modeling</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Tectp.691....1L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Tectp.691....1L"><span>Circum-Arctic <span class="hlt">lithosphere</span>-basin evolution: An overview</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lane, Larry S.; Stephenson, Randell A.</p> <p>2016-11-01</p> <p>A new collection of papers spanning the breadth of the Arctic provides new insight into the region's geodynamic evolution. New results pertain to <span class="hlt">lithospheric</span> structure, the link between magmatic and extension-related tectonic processes, variations in the composition and velocity structure of the lower crust in the Amerasia Basin, and provenance and paleogeography of Paleozoic to Triassic successions across the Arctic. Elucidation of geodynamic processes in the Eurasia Basin suggests new hypotheses for future research in the complex and poorly understood Amerasia Basin. New results from detrital zircon provenance studies as well as from stratigraphic facies compilations constrain the Late Paleozoic to Triassic paleogeography of the Arctic realm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.S22E..01T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.S22E..01T"><span>Rheological Stratification of the Continental <span class="hlt">Lithosphere</span>: Constraints from Space Geodesy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thatcher, W.</p> <p>2003-12-01</p> <p>Postseismic transient deformation, isostatic rebound from removal of pluvial lake loads, and <span class="hlt">lithospheric</span> deflection due to reservoir impoundment are each converging on consistent rheological models for the crust and upper mantle of actively deforming continental regions. These results imply a strong elastic crust 25-40 km thick overlain by a viscoelastic substrate with an effective viscosity of ~10**18 to 10**19 Pa-s. The most surprising result of these studies is that the upper mantle is weaker than the lower crust. However, the lower crust in these regions may deform by ductile flow on longer time scales, and the data provide a lower bound of ~10**20 Pa-s for its effective viscosity. This bound on lower crustal viscosity is consistent with spectral admittance studies of the gravity field and its relation to topography in the western U. S. (Lowry et al., 2000). These results indicate effective elastic <span class="hlt">lithospheric</span> thickness is 5-15 km in the same regions where the post-loading results indicate the entire crust is strong over about 10 to 10,000 years. Recent (and not so recent) relevant results include: (1) Deformation imaged by InSAR and GPS following the 1992 Landers and 1999 Hector Mine, California earthquakes; (2) Leveling surveys following the 1959 M=7.3 Hegben Lake, Montana earthquake; (3) Isostatic rebound of Lake Bonneville, Utah; (4) Leveling surveys following filling of Lake Mead, Arizona in 1935. Postseismic transient deformation observed following several other recent large earthquakes provides potential constraints on bulk rheology of the <span class="hlt">lithosphere</span>. However, deformation following events at major plate boundaries, including the 1993 Hokkaido-oki (M=7.8), 1999 Taiwan (M=7.6) and 1999 Izmet (M=7.5) earthquakes is dominated by the effects of buried aseismic afterslip, making it difficult to extract any signals that may be due to bulk relaxation of the lower crust and upper mantle. This suggests that large intraplate earthquakes on faults adjacent to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.T43C1658L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T43C1658L"><span>Insights into the deep continental <span class="hlt">lithosphere</span> from xenolith studies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, C. A.; Rudnick, R. L.</p> <p>2006-12-01</p> <p>Studies of xenoliths provide a depth dimension to surface geology studies, and, in favorable circumstances, also provide the fourth dimension of time. In particular, geochemical studies of xenoliths provide insights into the processes that formed and modified the deep <span class="hlt">lithosphere</span> (e.g., melting, metamorphism, fluid infiltration, basaltic underplating) and when they occurred. While xenoliths can provide a glimpse of the types of lithologies present at depth and how they formed, they cannot be assumed to be representative of the deep <span class="hlt">lithosphere</span>, and inferences regarding the dominant lithologies present in the lower crust or upper mantle must be tempered by geophysical constraints on bulk physical properties of these regions. Mantle. Xenoliths from the <span class="hlt">lithospheric</span> mantle are generally composed of peridotite, with lesser amounts of pyroxenite and/or eclogite. Equilibration T for these lithologies can generally be determined on the basis of two-pyroxene thermometery; precise depths of equilibration are much harder to estimate unless the samples contain garnet. The crystallization ages of mantle xenoliths are also usually difficult to constrain, as zircon is a rare phase in most upper mantle lithologies and most xenoliths have resided above the blocking temperature of other radiogenic isotope systems (Rb-Sr, Sm-Nd, Lu-Hf) for a significant fraction of their histories. The Re- Os isotope system provides arguably the best means of determining the crystallization age of mantle xenoliths, but, like most model age approaches, carries significant uncertainty. Crust. Xenoliths from the lower continental crust can be extremely heterogeneous in composition, but mafic compositions dominate in a number of regions. Equilibration T and P may determined from coexisting phases and, in some cases, thermal histories deduced from presence of frozen metamorphic reactions (e.g., coronas). The presence of zircon and other U-bearing accessory phases provides the opportunity to determine the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1811429K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1811429K"><span>On searching applicants for mechanism of solar-<span class="hlt">lithosphere</span> relations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kairatkyzy, Dina; Andreyev, Alexey; Zhumabayeva, Saltanat; Seraliyev, Alibek</p> <p>2016-04-01</p> <p>It is actively discussed at present a question on possible influence of solar activity (high-speed solar wind streams bearing the "frozen" magnetic field lines of the Sun) on the stress status of the <span class="hlt">lithosphere</span> and, consequently, on the Earth's seismic activity (e.g. Zhang, 1998, Acta Seismologica Sinica; Khachikyan et al., EGU2016-2754-1; IUGG2015-3132). There are at least two ideas on possible applicants for physical mechanism of solar-<span class="hlt">lithosphere</span> relations: (i) - the muons of cosmic rays, which can penetrate the Earth's crust to a depth of at least the first ten kilometers and in tense seismic environment generate nuclear-electromagnetic cascade which energy can be a trigger of earthquake (Tsarev and Chechin, 1988, Preprint № 179, Physical Institute after Lebedev, Moscow); (ii) - the geomagnetic storms (Sobolev et al., 1998, Physics of the Earth #7) when the high-frequency oscillations of the geomagnetic field during the main phase of the storm generate significant induction currents which electric energy entering into the crust can be converted into mechanical energy increasing the stress status of the <span class="hlt">lithosphere</span> (Sobolev and Demin, Mechano-electric phenomena into the Earth. M . Nauka. 1980). Besides this, among the possible cosmogenic factors changing the stress state of the <span class="hlt">lithosphere</span>, could be the variation of the angular velocity of rotation of the Earth (e.g. Bostrom, 2000. Tectonic consequence of the Earth's Rotation), if it depends on solar activity variations. More of 50 years ago, Munk and Donald (The Rotation of the Earth, Cambrige University Press, 1960) suggested that the interaction between solar wind and geomagnetic field would probably influence the short period variation of angular velocity of the Earth. In this work, we check up this suggestion on the base of very precise data on the length of day (LOD) from 1986 to the present, which are presented by the International Earth Rotation and Reference Systems Service (IERS). Using the methods</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.8095V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.8095V"><span>Characterising East Antarctic <span class="hlt">Lithosphere</span> and its Rift Systems using Gravity Inversion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vaughan, Alan P. M.; Kusznir, Nick J.; Ferraccioli, Fausto; Leat, Phil T.; Jordan, Tom A. R. M.; Purucker, Michael E.; Golynsky, A. V. Sasha; Rogozhina, Irina</p> <p>2013-04-01</p> <p>Since the International Geophysical Year (1957), a view has prevailed that East Antarctica has a relatively homogeneous <span class="hlt">lithospheric</span> structure, consisting of a craton-like mosaic of Precambrian terranes, stable since the Pan-African orogeny ~500 million years ago (e.g. Ferracioli et al. 2011). Recent recognition of a continental-scale rift system cutting the East Antarctic interior has crystallised an alternative view of much more recent geological activity with important implications. The newly defined East Antarctic Rift System (EARS) (Ferraccioli et al. 2011) appears to extend from at least the South Pole to the continental margin at the Lambert Rift, a distance of 2500 km. This is comparable in scale to the well-studied East African rift system. New analysis of RadarSat data by Golynsky & Golynsky (2009) indicates that further rift zones may form widely distributed extension zones within the continent. A pilot study (Vaughan et al. 2012), using a newly developed gravity inversion technique (Chappell & Kusznir 2008) with existing public domain satellite data, shows distinct crustal thickness provinces with overall high average thickness separated by thinner, possibly rifted, crust. Understanding the <span class="hlt">nature</span> of crustal thickness in East Antarctica is critical because: 1) this is poorly known along the ocean-continent transition, but is necessary to improve the plate reconstruction fit between Antarctica, Australia and India in Gondwana, which will also better define how and when these continents separated; 2) lateral variation in crustal thickness can be used to test supercontinent reconstructions and assess the effects of crystalline basement architecture and mechanical properties on rifting; 3) rift zone trajectories through East Antarctica will define the geometry of zones of crustal and <span class="hlt">lithospheric</span> thinning at plate-scale; 4) it is not clear why or when the crust of East Antarctica became so thick and elevated, but knowing this can be used to test models of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840017060','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840017060"><span>Application of MAGSAT to <span class="hlt">Lithospheric</span> Modeling in South America. Part 2: Synthesis of Geologic and Seismic Data for Development of Integrated Crustal Models</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Keller, G. R.; Lidiak, E. G.; Hinze, W. J.; Braile, L. W.; Vonfrese, R. R. B. (Principal Investigator)</p> <p>1984-01-01</p> <p>Research activities performed on MAGSAT scalar data over South America, Central America, and the adjacent marine areas are summarized. The geologic utility of magnetic anomalies detected by satellite is demonstrated by focusing on the spherical-Earth interpretation of scalar MAGSAT data in combination with ancillary geological and geophysical data to obtain <span class="hlt">lithospheric</span> models for these regions related to their contemporary crustal dynamics processes, geologic history, current volcanism seismicity and <span class="hlt">natural</span> resources.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T13B1860B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T13B1860B"><span>Comparison of North America <span class="hlt">Lithospheric</span> Thickness from Seismic Tomography & Thermo-Dynamic Models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Billen, M. I.; van der Lee, S.</p> <p>2009-12-01</p> <p>To better understand the longevity of continental <span class="hlt">lithosphere</span> and the origin of its strength, it is necessary to understand how seismic observations of <span class="hlt">lithosphere</span> structure are related to the thermal and mechanical structure of the <span class="hlt">lithosphere</span>. In addition, while the strength of tectonic plates is commonly compared in terms of the effective elastic thickness, it is not clear what portion of the <span class="hlt">lithosphere</span> contributes to the elastic thickness. We have compared predicted <span class="hlt">lithosphere</span> thickness for North America from the surface wave tomography model NA04 [1] with the thermal <span class="hlt">lithosphere</span> thickness predicted by converting the seismic velocity structure to a temperature structure using the predicted seismic velocities for a pyrolitic mantle composition [2] corrected for attenuation [3], and the mechanical <span class="hlt">lithosphere</span> thickness resulting from instantaneous dynamic flow models with either a composite (Newtonian, non-Newtonian & plastic yielding) or Newtonian-only viscosity structure [4]. We find that the predicted thermal <span class="hlt">lithosphere</span> thickness (depth to 900C), which is consistent with observed heat-flow, is 100-125 km in cratonic regions, but less than 75 km in the Basin & Range Province (BRP). The mechanical thickness (depth to the maximum strain-rate gradient) is consistently deeper in cratonic regions (175-200 km), but similar to the thermal thickness in the BPR. However, if the mechanical thickness is defined in terms of a strain-rate cut-off for deformation at time-scales longer than 1 billion years, then predicted <span class="hlt">lithosphere</span> thickness is only 25-50 km in the BPR. We find that these estimates of <span class="hlt">lithosphere</span> thickness are not strongly dependent on the assumed yield stress of cold <span class="hlt">lithosphere</span> because the base of the mechanical <span class="hlt">lithosphere</span> is deforming viscously. However, models with a composite viscosity structure predict 20% thicker <span class="hlt">lithosphere</span> in the cratonic regions compared to Newtonian viscosity models, consistent with the expectation that mantle flow is less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.455..176K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.455..176K"><span>Continental collision with a sandwiched accreted terrane: Insights into Himalayan-Tibetan <span class="hlt">lithospheric</span> mantle tectonics?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kelly, Sean; Butler, Jared P.; Beaumont, Christopher</p> <p>2016-12-01</p> <p>Many collisional orogens contain exotic terranes that were accreted to either the subducting or overriding plate prior to terminal continent-continent collision. The ways in which the physical properties of these terranes influence collision remain poorly understood. We use 2D thermomechanical finite element models to examine the effects of prior 'soft' terrane accretion to a continental upper plate (retro-<span class="hlt">lithosphere</span>) on the ensuing continent-continent collision. The experiments explore how the style of collision changes in response to variations in the density and viscosity of the accreted terrane <span class="hlt">lithospheric</span> mantle, as well as the density of the pro-<span class="hlt">lithospheric</span> mantle, which determines its propensity to subduct or compress the accreted terrane and retro-<span class="hlt">lithosphere</span>. The models evolve self-consistently through several emergent phases: breakoff of subducted oceanic <span class="hlt">lithosphere</span>; pro-continent subduction; shortening of the retro-<span class="hlt">lithosphere</span> accreted terrane, sometimes accompanied by <span class="hlt">lithospheric</span> delamination; and, terminal underthrusting of pro-<span class="hlt">lithospheric</span> mantle beneath the accreted terrane crust or mantle. The modeled variations in the properties of the accreted terrane <span class="hlt">lithospheric</span> mantle can be interpreted to reflect metasomatism during earlier oceanic subduction beneath the terrane. Strongly metasomatized (i.e., dense and weak) mantle is easily removed by delamination or entrainment by the subducting pro-<span class="hlt">lithosphere</span>, and facilitates later flat-slab underthrusting. The models are a prototype representation of the Himalayan-Tibetan orogeny in which there is only one accreted terrane, representing the Lhasa terrane, but they nonetheless exhibit processes like those inferred for the more complex Himalayan-Tibetan system. Present-day underthrusting of the Tibetan Plateau crust by Indian mantle <span class="hlt">lithosphere</span> requires that the Lhasa terrane <span class="hlt">lithospheric</span> mantle has been removed. Some of the model results support previous conceptual interpretations that Tibetan</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUSM.U44A..05A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUSM.U44A..05A"><span>Growth rate of the <span class="hlt">lithospheric</span> mantle: variations in time and space</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Artemieva, I. M.</p> <p>2007-05-01</p> <p>Two global databases for the continents, (a) for tectono-thermal ages and (b) for <span class="hlt">lithospheric</span> thermal thickness (Artemieva, Tectonophysics, 2006 and available for download at the web-site), are used to calculate (i) the volume of the preserved continental <span class="hlt">lithosphere</span> of different ages within the individual cratons, (ii) the <span class="hlt">lithospheric</span> growth rate for different continents over the past 3.6 Ga, (iii) a global model of <span class="hlt">lithosphere</span> growth rate since the Archean. The submerged areas with continental crust are excluded from the analysis. On the scale of a craton, significant differences in the rates of <span class="hlt">lithosphere</span> growth are observed between the individual cratons. These data are compared with independent estimates of growth rate of juvenile crust on different continents as constrained by sedimentary record, geological and isotope data. On the global scale, the results show a general agreement between the global cumulative growth rate of the continental <span class="hlt">lithosphere</span> and juvenile crust (Condie, 1998). The most pronounced peak in <span class="hlt">lithosphere</span> growth occurred at 2.1-1.7 Ga, when the volume of <span class="hlt">lithospheric</span> mantle was increasing with the rate of ca. 10-20 (km3 per year). Contrary to growth models of juvenile crust, the peaks in growth rate of the <span class="hlt">lithospheric</span> mantle at ca. 2.7- 2.6 Ga and 1.3-1.1 Ga are weak, ca. 5-8 (km3 per year). The differences between the growth rates of the <span class="hlt">lithosphere</span> and juvenile crust are interpreted as indicator of the preservation rate of the cratonic <span class="hlt">lithosphere</span> since the Archean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T23A2571H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T23A2571H"><span>Episodic, Multi-staged <span class="hlt">Lithospheric</span> Delamination Responsible for Destruction of the North China Craton</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huang, J.; Wang, Y.; Zhong, S.</p> <p>2013-12-01</p> <p>Archean cratons represent the oldest tectonic units on the Earth and most of them are tectonically stable for >3 Ga. The North China Craton (NCC), however, had undergone extensive destruction during the Mesozoic to Cenozoic as seen from surface volcanism, magmatism, and tectonic deformation and geochemical and seismic observations suggesting removal and replacement of thick, old, and fertile cratonic <span class="hlt">lithosphere</span> with thin, young, and depleted oceanic-type <span class="hlt">lithosphere</span> [Griffin et al., 1998; Xu, 2001; Menzies et al., 2007; Zhu et al., 2012; Zhang et al., 2012]. <span class="hlt">Lithospheric</span> delamination has been proposed to explain different episodes of volcanism in the Jurassic [Gao et al., 2004; 2008] and Cretaceous [Yang et al., 2003; Wu et al., 2003] on NCC and hence as a mechanism for destruction of NCC. However, the relatively long period (~100 Myr) of volcanism associated with the destruction of NCC was considered as a challenge to the delamination process [Menzies et al., 2007] which typically lasts for several Myr [Conrad and Molnar, 1999]. Here we show that delamination for cratonic <span class="hlt">lithosphere</span> with chemically buoyant root and non-Newtonian rheology, different from that for normal <span class="hlt">lithosphere</span> that was considered in most previous geodynamic studies, is episodic and multi-staged and may last for tens to 100 Myrs. For cratonic <span class="hlt">lithosphere</span> with non-Newtonian rheology with relatively large chemical buoyancy, the cold, shallow part of the <span class="hlt">lithosphere</span> goes unstable first, causing significant stirring and mixing of asthenospheric mantle and cratonic <span class="hlt">lithosphere</span>. This delamination process may explain the main geochemical signatures in the Jurassic and Cretaceous volcanic rocks found in the NCC including their eclogite component [Gao et al., 2004, 2008] and sourcing both cratonic <span class="hlt">lithosphere</span> and asthenosphere [Zheng et al., 2000]. Subduction process, by increasing tectonic stress and water content, helps reduce the <span class="hlt">lithospheric</span> viscosity sufficiently to delaminate the entire</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T43A4685J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T43A4685J"><span>Constraining <span class="hlt">Lithosphere</span> Deformation Modes during Continental Breakup for the Iberia-Newfoundland Conjugate Margins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeanniot, L.; Kusznir, N. J.; Mohn, G.; Manatschal, G.</p> <p>2014-12-01</p> <p>How the <span class="hlt">lithosphere</span> and asthenosphere deforms during continental rifting leading to breakup and sea-floor spreading initiation is poorly understood. Observations at present-day and fossil analogue rifted margins show a complex OCT architecture which cannot be explained by a single simplistic <span class="hlt">lithosphere</span> deformation modes. This OCT complexity includes hyper-extended continental crust and <span class="hlt">lithosphere</span>, detachments faults, exhumed mantle, continental slivers and scattered embryonic oceanic crust. We use a coupled kinematic-dynamic model of <span class="hlt">lithosphere</span> and asthenosphere deformation to determine the sequence of <span class="hlt">lithosphere</span> deformation modes leading to continental breakup for Iberia-Newfoundland conjugate margin profiles. We quantitatively calibrate the models using observed present-day water loaded subsidence and crustal thickness, together with subsidence history and the age of melt generation. Flow fields, representing a sequence of <span class="hlt">lithosphere</span> deformation modes, are generated by a 2D finite element viscous flow model (FE-Margin), and used to advect <span class="hlt">lithosphere</span> and asthenosphere temperature and material. FE-Margin is kinematically driven by divergent deformation in the upper 15-20 km of the <span class="hlt">lithosphere</span> inducing passive upwelling below. Buoyancy enhanced upwelling (Braun et al. 2000) is also kinematically included. Melt generation by decompressional melting is predicted using the methodology of Katz et al., 2003. The extension magnitudes used in the <span class="hlt">lithosphere</span> deformation models are taken from Sutra et al (2013). The best fit calibrated models of <span class="hlt">lithosphere</span> deformation evolution for the Iberia-Newfoundland conjugate margins require (i) an initial broad region of <span class="hlt">lithosphere</span> deformation and passive upwelling, (ii) lateral migration of deformation, (iii) an increase in extension rate with time, (iv) focussing of deformation and (v) buoyancy induced upwelling. The preferred calibrated models predict faster extension rates and earlier continental crustal rupture and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998DPS....30.3804T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998DPS....30.3804T"><span><span class="hlt">Lithospheric</span> Displacement Features on Europa: More Reasons Why There May Be Subsurface Liquid Water</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tufts, B. R.; Greenberg, R.; Hoppa, G.; Geissler, P. E.</p> <p>1998-09-01</p> <p><span class="hlt">Lithospheric</span> displacement features consistent with the presence of a subsurface liquid layer at the time of the displacements, continue to be imaged by Galileo. Lateral motion features on recent images include bands near Moytura Regio, Tyre, and in regional maps centered at 40N, 229W, and 15N, 76W. A band NE of Tyre exhibits more than 30 km of dilation and left-lateral shear, making it comparable to large south polar gray bands. Class 2 (dilational) ridges in the Greenberg et al [1] classification system appear in many locations. Bands and dilational ridges may be variations on the theme of tidal cracking and "working," with the differences due to availability of lateral room and changes in tidal stress. The distribution of bands and ridges suggests that lateral motion is global and long-lived, consistent with [2, 3]. Within bands, the corners of the medial cracks seem to be rounded off with successive infilling [4]. One interpretation is that these corners were melted by a relatively warm infill material. Blocks bordering bands in the C3 wedges region show little or no cracking parallel to and adjacent to the bands, unlike the Uruk Sulcus region of Ganymede [5], suggesting that the subsurface decoupling layer allowing their motion was a low-friction one, e.g. liquid water. Also, more examples of possible ridge-induced plate flexure have been found, evidenced by flanking cracks and shading indicative of collateral depressions. Examples include ridges near Tyre and ridges antipodal to the possible flexure near Conamara Chaos, where flexural parameters suggest a thin <span class="hlt">lithosphere</span> [2]. Flexural parameters are not yet known for these newly-seen ridges. [1] Greenberg et al., Icarus, 1997. Sub. [2] Tufts et al. LPSC 29 1998. [3] Pappalardo and Sullivan, Icarus, 1996. 123: p. 557-567. [4] Sullivan et al., <span class="hlt">Nature</span>, 1998. 391: p. 371-373. [5] Head et al., 1997, LPSC 28.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.433..125T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.433..125T"><span>Low water contents in diamond mineral inclusions: Proto-genetic origin in a dry cratonic <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Taylor, Lawrence A.; Logvinova, Alla M.; Howarth, Geoffrey H.; Liu, Yang; Peslier, Anne H.; Rossman, George R.; Guan, Yunbin; Chen, Yang; Sobolev, Nikolay V.</p> <p>2016-01-01</p> <p>The mantle is the major reservoir of Earth's water, hosted within Nominally Anhydrous Minerals (NAMs) (e.g., Bell and Rossman, 1992; Peslier et al., 2010; Peslier, 2010; Nestola and Smyth, 2015), in the form of hydrogen bonded to the silicate's structural oxygen. From whence cometh this water? Is the water in these minerals representative of the Earth's primitive upper mantle or did it come from melting events linked to crustal formation or to more recent metasomatic/re-fertilization events? During diamond formation, NAMs are encapsulated at hundreds of kilometers depth within the mantle, thereby possibly shielding and preserving their pristine water contents from re-equilibrating with fluids and melts percolating through the <span class="hlt">lithospheric</span> mantle. Here we show that the NAMs included in diamonds from six locales on the Siberian Craton contain measurable and variable H2O concentrations from 2 to 34 parts per million by weight (ppmw) in olivine, 7 to 276 ppmw in clinopyroxene, and 11-17 ppmw in garnets. Our results suggest that if the inclusions were in equilibrium with the diamond-forming fluid, the water fugacity would have been unrealistically low. Instead, we consider the H2O contents of the inclusions, shielded by diamonds, as pristine representatives of the residual mantle prior to encapsulation, and indicative of a protogenetic origin for the inclusions. Hydrogen diffusion in the diamond does not appear to have modified these values significantly. The H2O contents of NAMs in mantle xenoliths may represent some later metasomatic event(s), and are not always representative of most of the continental <span class="hlt">lithospheric</span> mantle. Results from the present study also support the conclusions of Peslier et al. (2010) and Novella et al. (2015) that the dry <span class="hlt">nature</span> of the SCLM of a craton may provide stabilization of its thickened continental roots.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T13A4631R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T13A4631R"><span>Flexural Rigidity of the <span class="hlt">Lithosphere</span> as a Powerful Tool for the Continental Correlation: A study on the Paleo-fit of India and Madagascar</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ratheesh Kumar, R. T.</p> <p>2014-12-01</p> <p>The temporal evolution and spatial configuration of continents can be analyzed through their response to long-term forces, as a function of the elastic property of the <span class="hlt">lithosphere</span>, which is parameterized as effective elastic thickness (Te). The Te method has been widely used as a key proxy to examine the long-term strength/rigidity structure of the <span class="hlt">lithosphere</span>. The present study employs the gravity inversion and flexure inversion techniques that operate in spatial domain in order to estimate the spatial variation of Te as well as the Moho configuration along the western continental margins of India (WCMI) and eastern continental margin of Madagascar (ECMM). The main objective of the present study is to understand the <span class="hlt">nature</span> of isostasy and structure of the <span class="hlt">lithosphere</span> along these conjugate passive margins. The results correlate well with the continental and oceanic regional-scale structures including ridges and basins in the WCMI and ECMM that reveal their mode of evolution. This study obtained comparable results from both the passive margins such as a linear zone of anomalously low-Te (1-5 km) along the WCMI (~1680 km long), which exactly correlates with the low-Te patterns obtained all along the ECMM. These low-Te zones along the passive margins are attributed as paleo-rift inception points of <span class="hlt">lithosphere</span> thermally and mechanically weakened by the combined effects of the Marion hotspot and <span class="hlt">lithospheric</span> extension due to rifting. When these conjugate passive margins were correlated by matching the mirrored low-Te linear zones, obtained a best fit position of Madagascar against India during the Gondwana Rifting time. The hence derived India-Madagascar paleo-fit model is well justified by the best close-fit of the crustal geometry and bathymetry of the continental shelf margins, and also by the matching of tectonic lineaments, lithology and geochronological belts along the margins of both the continents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70019809','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70019809"><span>Continents as lithological icebergs: The importance of buoyant <span class="hlt">lithospheric</span> roots</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Abbott, D.H.; Drury, R.; Mooney, W.D.</p> <p>1997-01-01</p> <p>An understanding of the formation of new continental crust provides an important guide to locating the oldest terrestrial rocks and minerals. We evaluated the crustal thicknesses of the thinnest stable continental crust and of an unsubductable oceanic plateau and used the resulting data to estimate the amount of mantle melting which produces permanent continental crust. The <span class="hlt">lithospheric</span> mantle is sufficiently depleted to produce permanent buoyancy (i.e., the crust is unsubductable) at crustal thicknesses greater than 25-27 km. These unsubductable oceanic plateaus and hotspot island chains are important sources of new continental crust. The newest continental crust (e.g., the Ontong Java plateau) has a basaltic composition, not a granitic one. The observed structure and geochemistry of continents are the result of convergent margin magmatism and metamorphism which modify the nascent basaltic crust into a lowermost basaltic layer overlain by a more silicic upper crust. The definition of a continent should imply only that the <span class="hlt">lithosphere</span> is unsubductable over ??? 0.25 Ga time periods. Therefore, the search for the oldest crustal rocks should include rocks from lower to mid-crustal levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860003393','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860003393"><span>Thermal cooling of the oceanic <span class="hlt">lithosphere</span> from geoid height data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cazenae, A.</p> <p>1985-01-01</p> <p>Another type of geophysical observation has proved to be very useful in the study of thermal cooling of the oceanic <span class="hlt">lithosphere</span>. It is the geoid height derivative with respect to plate age, a quantity computed from the short wavelength geoid step across fracture zones measured by altimeter satellites. Two categories of simples models are proposed to describe cooling and contraction of the oceanic <span class="hlt">lithosphere</span> with age. Both plate model and half space model, give almost similar results up to ages of 50 to 70 ma, but predict quite distinct behavior of seafloor depth, heat flow and other parameters in old basins. Tests of thermal models are based on heat flow and topography data. However, heat flow is not very sensitive to the form of the thermal model. Large areas of the ocean floor are particularly shallow, and as a result topography data may not be very appropriate to discriminate between plate and half space models, and no clear concensus on a preferred model yet exists.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021340','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021340"><span>The Cascadia Subduction Zone: two contrasting models of <span class="hlt">lithospheric</span> structure</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Romanyuk, T.V.; Blakely, R.; Mooney, W.D.</p> <p>1998-01-01</p> <p>The Pacific margin of North America is one of the most complicated regions in the world in terms of its structure and present day geodynamic regime. The aim of this work is to develop a better understanding of <span class="hlt">lithospheric</span> structure of the Pacific Northwest, in particular the Cascadia subduction zone of Southwest Canada and Northwest USA. The goal is to compare and contrast the <span class="hlt">lithospheric</span> density structure along two profiles across the subduction zone and to interpet the differences in terms of active processes. The subduction of the Juan de Fuca plate beneath North America changes markedly along the length of the subduction zone, notably in the angle of subduction, distribution of earthquakes and volcanism, goelogic and seismic structure of the upper plate, and regional horizontal stress. To investigate these characteristics, we conducted detailed density modeling of the crust and mantle along two transects across the Cascadia subduction zone. One crosses Vancouver Island and the Canadian margin, the other crosses the margin of central Oregon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014E%26PSL.399...14C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014E%26PSL.399...14C"><span><span class="hlt">Lithosphere</span>-asthenosphere interactions near the San Andreas fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chamberlain, C. J.; Houlié, N.; Bentham, H. L. M.; Stern, T. A.</p> <p>2014-08-01</p> <p>We decipher the strain history of the upper mantle in California through the comparison of the long-term finite strain field in the mantle and the surface strain-rate field, respectively inferred from fast polarization directions of seismic phases (SKS and SKKS), and Global Positioning System (GPS) surface velocity fields. We show that mantle strain and surface strain-rate fields are consistent in the vicinity of San Andreas Fault (SAF) in California. Such an agreement suggests that the <span class="hlt">lithosphere</span> and strong asthenosphere have been deformed coherently and steadily since >1 Ma. We find that the crustal stress field rotates (up to 40° of rotation across a 50 km distance from 50° relative to the strike of the SAF, in the near-field of SAF) from San Francisco to the Central Valley. Both observations suggest that the SAF extends to depth, likely through the entire <span class="hlt">lithosphere</span>. From Central Valley towards the Basin and Range, the orientations of GPS strain-rates, shear wave splitting measurements and seismic stress fields diverge indicating reduced coupling or/and shallow crustal extension and/or presence of frozen anisotropy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatGe...9..227K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatGe...9..227K"><span>Groundwater flow as a cooling agent of the continental <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kooi, Henk</p> <p>2016-03-01</p> <p>Groundwater that flows through the outer shell of the Earth as part of the hydrologic cycle influences the distribution of heat and, thereby, the temperature field in the Earth’s crust. Downward groundwater flow in recharge areas lowers crustal temperatures, whereas upward flow in discharge areas tends to raise temperatures relative to a purely conductive geothermal regime. Here I present numerical simulations of generalized topography-driven groundwater flow. The simulations suggest that groundwater-driven convective cooling exceeds groundwater-driven warming of the Earth’s crust, and hence that groundwater flow systems cause net temperature reductions of groundwater basins. Moreover, the simulations demonstrate that this cooling extends into the underlying crust and <span class="hlt">lithosphere</span>. I find that horizontal components of groundwater flow play a central role in this net subsurface cooling by conveying relatively cold water to zones of upward groundwater flow. The model calculations suggest that the crust and <span class="hlt">lithosphere</span> beneath groundwater basins can cool by several tens of degrees Celsius where groundwater flows over large distances in basins that consist of crustal rock. In contrast, groundwater-induced cooling is small in unconsolidated sedimentary settings, such as deltas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/81086','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/81086"><span>Renewal: Continential <span class="hlt">lithosphere</span> evolution as a function of tectonic environment</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>McMillan, N.J.; Baldridge, W.S.</p> <p>1995-06-01</p> <p>The Cenozoic tectonic environment and stress regime of the southwestern United States have changed dramatically from compression during shallow-angle subduction during the Laramide orogeny in the early Cenozoic to the current mode of Basin and Range extension. Questions remain unresolved concerning the causes of this transition, including the timing of the initiation of extension (estimates range from 36 to 25 Ma), and is the Basin and Range simply an mega-example of back-arc extension, or is extension related to the subduction of an oceanic spreading center about 30 Ma? We have examined the patterns of magmagenesis and geochemical composition through Cenozoic time in southern New Mexico. We have defined four magma sources that have contributed to Cenozoic magmas. Immediately following the Laramide, magmas contain substantial contributions from the lower crust. Mid-Tertiary extension is related to the eruption of rhyolitic ash-flow tuffs and basalts. The basalts were generated by melting of the <span class="hlt">lithospheric</span> mantle; intercalated rhyolites have a strong upper crustal signature. Eruption of basalts and andesites with sources in the <span class="hlt">lithospheric</span> mantle and lower crust continued for several million years after rhyolitic volcanism ceased. The region was nearly void of volcanic activity for 16 million years despite continued extension, but at 10 Ma, basalts derived from the asthenosphere began to erupt.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1712551J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1712551J"><span>Impact of elasticity on <span class="hlt">lithospheric</span> shortening and strain localization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jaquet, Yoann; Schmalholz, Stefan M.; Duretz, Thibault</p> <p>2015-04-01</p> <p>The initiation of subduction is not well understood and also the mechanisms of localization in a compressive domain are incompletely understood. In order to better understand what controls strain localization during compression, we perform two dimensional numerical simulations with a finite element code using the MILAMIN solver with the Triangle mesh generator. Our model configuration consists of a <span class="hlt">lithosphere</span> composed of an upper crust, a lower crust and a mantle with each layer having its own non-Newtonian rheology. We add a thermal perturbation (+100°C) to the right bottom side of the model. The model is then shortened with a fixed strain rate (5*10-15s-1) and we vary both the bottom temperature and the shear modulus. The latter allows variations between two extreme rheological models: visco-elasto-plastic and visco-plastic. The results show that (1) the <span class="hlt">lithosphere</span> is subjected to buckling, (2) localization caused by shear heating can occur in one of the folds during ongoing buckling, and (3) a lower basal temperature favors higher stresses so that localization is facilitated. The visco-elasto-plastic model shows faster and more intense localization than the visco-plastic model. Moreover, as soon as strain localization initiates, strain rates suddenly increase by several orders of magnitude (>2) during a short period of time (</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19536263','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19536263"><span>Colorado Plateau magmatism and uplift by warming of heterogeneous <span class="hlt">lithosphere</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Roy, Mousumi; Jordan, Thomas H; Pederson, Joel</p> <p>2009-06-18</p> <p>The forces that drove rock uplift of the low-relief, high-elevation, tectonically stable Colorado Plateau are the subject of long-standing debate. While the adjacent Basin and Range province and Rio Grande rift province underwent Cenozoic shortening followed by extension, the plateau experienced approximately 2 km of rock uplift without significant internal deformation. Here we propose that warming of the thicker, more iron-depleted Colorado Plateau <span class="hlt">lithosphere</span> over 35-40 Myr following mid-Cenozoic removal of the Farallon plate from beneath North America is the primary mechanism driving rock uplift. In our model, conductive re-equilibration not only explains the rock uplift of the plateau, but also provides a robust geodynamic interpretation of observed contrasts between the Colorado Plateau margins and the plateau interior. In particular, the model matches the encroachment of Cenozoic magmatism from the margins towards the plateau interior at rates of 3-6 km Myr(-1) and is consistent with lower seismic velocities and more negative Bouguer gravity at the margins than in the plateau interior. We suggest that warming of heterogeneous <span class="hlt">lithosphere</span> is a powerful mechanism for driving epeirogenic rock uplift of the Colorado Plateau and may be of general importance in plate-interior settings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34..478M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34..478M"><span>Gravitational instability of mantle <span class="hlt">lithosphere</span> and core complexes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Molnar, Peter</p> <p>2015-03-01</p> <p>For a wide range of viscosity structures, convergent and downward flow of the mantle <span class="hlt">lithosphere</span> during the growth of gravitational instability induces not only thickening of overlying crust but also concurrent horizontal extension in the upper crust. Such extension, if it occurred in the Earth, would include normal faulting of the upper crust above a region of horizontal shortening in the lower crust and uppermost mantle. Convergent flow in the lower crust would also create shear stress on horizontal planes and localized upward flow of the lower crust. These features—extension of upper crust and exhumation of strained lower crust—characterize metamorphic core complexes exposed in regions of normal to thick continental crust. Thus, convergent flow and downwelling mantle <span class="hlt">lithosphere</span> might contribute to the development of core complexes, at least in some settings. If horizontal shortening and crustal thickening at depth do occur simultaneously with normal faulting at the surface of the Earth today, evidence of this process does not seem obvious, but perhaps it has occurred concurrently with widespread regional crustal extension in places like the Basin and Range Province, Tibet, the Pamir, or the Aegean. If such mantle flow does participate in the development of core complexes, a weak lower crust might not be a prerequisite for their formation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1982PApGe.120..389C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1982PApGe.120..389C"><span>The <span class="hlt">lithosphere</span> in the central-eastern Mediterranean area</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Calcagnile, G.; D'Ingeo, F.; Farrugia, P.; Panza, G. F.</p> <p>1982-03-01</p> <p>The <span class="hlt">lithosphere</span> beneath the central-eastern Mediterranean area has been investigated by the inversion of the regional dispersion relations derived from analysis of surface waves. It is possible to distinguish several types of crust with average S-wave velocities in the range 3.0 3.8 km/sec, and thicknesses varying from a minimum of about 30 km, which corresponds to the Apennines, Crete and Otranto Channel regions, to a maximum of about 51 km beneath the Ionian Sea, which can be considered as a submerged continent. Associated with these crustal features, large lateral variations have been detected in the <span class="hlt">lithosphere</span> thickness, which varies from a minimum of about 30 km corresponding to the Tyrrhenian Sea and south of Crete to a maximum of about 130 km corresponding to south-eastern Alps and north-central Greece, while the sub-Moho S-wave velocity varies in the range 4.2 4.8 km/sec. The constraint furnished by our results to the geological-tectonic setting of the investigated area, characterized by the continent continent collision between Africa and Europe, is pointed out.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17738235','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17738235"><span>Thermal structure of the <span class="hlt">lithosphere</span>: a petrologic model.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Macgregor, I D; Basu, A R</p> <p>1974-09-20</p> <p>A preliminary evaluation of the thermal history of the upper mantle as determined by petrologic techniques indicates a general correspondence with theoretically derived models. The petrologic data supply direct information which may be used as an independent calibration of calculated models, serve as a base for evaluating the assumptions of the theoretical approach, and allow more careful selection of the variables describing mantle thermal properties and processes. Like the theoretical counterpart, the petrological approach indicates that the <span class="hlt">lithosphere</span> is dominated by two thermal regimes: first, there is a continental regime which cools at rates of the order of 10(9) years and represents the longterm cooling of the earth. Secondly, superimposed on the continental evolution is the thermal event associated with the formation of an oceanic basin, and which may be thought of as a 10(8) year convective perturbation on the continental cycle. Of special interest is petrologic evidence for a sudden steepening of the thermal gradients across the <span class="hlt">lithosphere</span>-asthenosphere boundary not seen in the theoretical models. The unexpected change of slope points to the need for a critical reevaluation of the thermal processes and properties extant in the asthenosphere. The potential of the petrologic contribution has yet to be fully realized. For a start, this article points to an important body of independent evidence critical to our understanding of the earth's thermal history.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950032368&hterms=lithosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dlithosphere','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950032368&hterms=lithosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dlithosphere"><span>Compositional vs. thermal buoyancy and the evolution of subducted <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gaherty, James B.; Hager, Bradford H.</p> <p>1994-01-01</p> <p>We formulate 2-D Cartesian finite element models that explore the fate of compositionally defined <span class="hlt">lithosphere</span> as it encounters a viscosity increase at the boundary between the upper and lower mantle. Subducted <span class="hlt">lithosphere</span> is represented as a cold, stiff, layered composite of denser eclogite underlain by more buoyant harzburgite. Slabs impinging on a lower mantle 30 and 100 times more viscous than the upper mantle thicken and fold strongly as they penetrate the lower mantle. Approximately a factor of two thickening occurs via pure shear just above the discontinuity, with additional enhancement due to folding by over a factor of two. No separation of the individual slab components occurs at the discontinuity, and direct comparison with models in which compositional buoyancy is explicitly ignored indicates that slab evolution is largely controlled by the thermal buoyancy. These results are at odds with hypotheses about slab evolution in which the compositional buoyancy contributions lead to component separation and the formation of slab megaliths or a compositionally layered upper mantle.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5319811','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5319811"><span>Shear velocity structure of the northern California <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Levander, A.R. ); Kovach, R.L. )</p> <p>1990-11-10</p> <p>The authors have determined the regional shear velocity structure of the <span class="hlt">lithosphere</span> beneath the Coast Ranges and the Great Valley in northern California from inversion of three fundamental mode Rayleigh wave phase velocity curves. The dispersion measurements were made along three different paths crossing the Coast Ranges and Great Valley roughly perpendicular to the North American-Pacific plate boundary. The three dispersion curves diverge at periods greater than about 20 s; phase velocities are systematically higher from the northwest to the southeast along the transform margin. Inverting the phase velocities for crustal and upper mantle structure shows that this divergence is indicative of a 3-5% increase in the upper mantle shear velocity from the Napa-Great Valley region to the Diablo Range-Great Valley region. Crustal shear velocities are consistent with the lithologies expected in the middle and lower crust. The increase in mantle shear velocity from northwest to southeast is anticipated by a tectonic model for the development of the California transform margin in which asthenospheric material is emplaced at the base of the North American crust in the slab gap south of the Mendocino triple junction. Adjacent to the plate boundary, this process creates a subcrustal corridor of cooling asthenosphere which is gradually incorporated in the <span class="hlt">lithosphere</span> lid. They suggest that this causes the observed increase in upper mantle shear velocity away from the triple junction. Finite difference simulations of Rayleigh wave propagation across asthenosphere corridor models produce synthetic phase velocity curves which are similar to the field observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRB..121.3742C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRB..121.3742C"><span>Why intracontinental basins subside longer: 3-D feedback effects of <span class="hlt">lithospheric</span> cooling and sedimentation on the flexural strength of the <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cacace, M.; Scheck-Wenderoth, M.</p> <p>2016-05-01</p> <p>The aim of this study is to reevaluate the character and evolution of the large-scale subsidence of intracontinental basins using 3-D thermomechanical numerical simulations accounting for the coupling between sedimentation, rheology-dependent <span class="hlt">lithospheric</span> flexure, and thermal contraction by <span class="hlt">lithospheric</span> cooling. The flexural rigidity of the <span class="hlt">lithospheric</span> plate is controlled by elastic-brittle-plastic rheology, enabling the computation of thermal and mechanical feedback processes occurring during basin subsidence. Numerical results show that depending on the sediment loading history, a rheological stratified <span class="hlt">lithosphere</span> can subside over geological time scales without imposition of ad hoc geometric and kinematic initial conditions. Three-dimensional feedback effects of sedimentation on the thermomechanical structure of the plate result in a weakened lower crust mechanically decoupled from the underlying mantle and therefore easily reactivated even under low background stresses. Our results explain the first-order characteristics of the subsidence in intracontinental basins and reconcile basic observations of their deformation history.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JESS..124.1677R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JESS..124.1677R"><span>Satellite-derived geoid for the estimation of <span class="hlt">lithospheric</span> cooling and basal heat flux anomalies over the northern Indian Ocean <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rajesh, S.; Majumdar, T. J.</p> <p>2015-12-01</p> <p>The northern Indian Ocean consists of older Bay of Bengal (BOB) oceanic <span class="hlt">lithosphere</span> with numerous intra-plate loads; whereas, contrasting elements like active Mid-Ocean ridge divergence and slow spreading ridges are present in the relatively younger (<60 Ma) Arabian Sea oceanic <span class="hlt">lithosphere</span>. The mechanism of <span class="hlt">lithospheric</span> cooling of young age oceanic <span class="hlt">lithosphere</span> from the moderately active and slow spreading Carlsberg Ridge is analysed by considering the hypothesis of near <span class="hlt">lithospheric</span> convective action or whole upper mantle convection. We addressed these issues by studying the marine geoid at different spatial wavelengths and retrieved and compared their <span class="hlt">lithospheric</span> cooling signatures, plate spreading and distribution of mass and heat anomalies along with seismicity, bathymetry, gravity and isochron age data. Results show that progressive cooling of young-aged oceanic <span class="hlt">lithosphere</span> from the Mid-Ocean Carlsberg Ridge is because of conductive cooling and those signals are retrieved in the shorter wavelength band (111 < λ< 1900 km) of constrained residual geoid with mass anomaly sources near to sublithospheric. This shows steadiness in the geoid anomaly decay rate (˜-0.1 m/Ma), consistency in the growth of thermal boundary layer and progressive fall of basal temperature and heat flux (900- 300 K and 100-18 mW m-2) with increase of <span class="hlt">lithospheric</span> age. The above observations are attributed to the fact that the advective-convective action beneath the Mid-Ocean Carlsberg Ridge is driven by the basal temperature gradient between the <span class="hlt">lithosphere</span> and the near <span class="hlt">lithospheric</span> low viscose thin layer. But, for the case of old-aged oceanic <span class="hlt">lithosphere</span> in the BOB, the residual geoid anomaly cooling signals are not prominently seen in the same band as that of the Arabian Sea because of the Ninetyeast Ridge magmatism. However, its cooling anomaly signatures are retrieved at relatively higher band (1335 ≤ λ≤ 3081 km) having erratic geoid decay rates (-0.3 to 0.2 m/Ma) owing to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27362231','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27362231"><span>Mid-ocean-ridge seismicity reveals extreme types of ocean <span class="hlt">lithosphere</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schlindwein, Vera; Schmid, Florian</p> <p>2016-07-14</p> <p>Along ultraslow-spreading ridges, where oceanic tectonic plates drift very slowly apart, conductive cooling is thought to limit mantle melting and melt production has been inferred to be highly discontinuous. Along such spreading centres, long ridge sections without any igneous crust alternate with magmatic sections that host massive volcanoes capable of strong earthquakes. Hence melt supply, <span class="hlt">lithospheric</span> composition and tectonic structure seem to vary considerably along the axis of the slowest-spreading ridges. However, owing to the lack of seismic data, the <span class="hlt">lithospheric</span> structure of ultraslow ridges is poorly constrained. Here we describe the structure and accretion modes of two end-member types of oceanic <span class="hlt">lithosphere</span> using a detailed seismicity survey along 390 kilometres of ultraslow-spreading ridge axis. We observe that amagmatic sections lack shallow seismicity in the upper 15 kilometres of the <span class="hlt">lithosphere</span>, but unusually contain earthquakes down to depths of 35 kilometres. This observation implies a cold, thick <span class="hlt">lithosphere</span>, with an upper aseismic zone that probably reflects substantial serpentinization. We find that regions of magmatic <span class="hlt">lithosphere</span> thin dramatically under volcanic centres, and infer that the resulting topography of the <span class="hlt">lithosphere</span>-asthenosphere boundary could allow along-axis melt flow, explaining the uneven crustal production at ultraslow-spreading ridges. The seismicity data indicate that alteration in ocean <span class="hlt">lithosphere</span> may reach far deeper than previously thought, with important implications towards seafloor deformation and fluid circulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010044509&hterms=high+gravity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dhigh%2Bgravity','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010044509&hterms=high+gravity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dhigh%2Bgravity"><span><span class="hlt">Lithospheric</span> Thickness Variations from Gravity and Topography in Areas of High Crustal Remanent Magnetization on Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smrekar, S. E.; Raymond, C. A.</p> <p>2001-01-01</p> <p>Large regions of intense crustal re- manent magnetization were fortuitously discovered on Mars by the Mars Global Surveyor (MGS) spacecraft. Gravity and topography admittance studies are used to examine <span class="hlt">lithospheric</span> structure in the areas of intense magnetization. Areas with positively magnetized crust appear to have thinner crust and elastic <span class="hlt">lithosphere</span> than negatively magnetized crust. Additional information is contained in the original extended abstract.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T14B..02L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T14B..02L"><span>Convective Removal of Continental Margin <span class="hlt">Lithosphere</span> at the Edges of Subducting Oceanic Plates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Levander, A.; Bezada, M. J.; Palomeras, I.; Masy, J.; Humphreys, E.; Niu, F.</p> <p>2013-12-01</p> <p>Although oceanic <span class="hlt">lithosphere</span> is continuously recycled to the deeper mantle by subduction, the rates and manner in which different types of continental <span class="hlt">lithospheric</span> mantle are recycled is unclear. Cratonic mantle can be chemically reworked and essentially decratonized, although the frequency of decratonization is unclear. <span class="hlt">Lithospheric</span> mantle under or adjacent to orogenic belts can be lost to the deeper mantle by convective downwellings and delamination phenomena. Here we describe how subduction related processes at the edges of oceanic plates adjacent to passive continental margins removes the mantle <span class="hlt">lithosphere</span> from beneath the margin and from the continental interior. This appears to be a widespread means of recycling non-cratonic continental mantle. <span class="hlt">Lithospheric</span> removal requires the edge of a subducting oceanic plate to be at a relatively high angle to an adjacent passive continental margin. From Rayleigh wave and body wave tomography, and receiver function images from the BOLIVAR and PICASSO experiments, we infer large-scale removal of continental margin <span class="hlt">lithospheric</span> mantle from beneath 1) the northern South American plate margin due to Atlantic subduction, and 2) the Iberian and North African margins due to Alboran plate subduction. In both cases <span class="hlt">lithospheric</span> mantle appears to have been removed several hundred kilometers inland from the subduction zones. This type of ';plate-edge' tectonics either accompanies or pre-conditions continental margins for orogenic activity by thinning and weakening the <span class="hlt">lithosphere</span>. These processes show the importance of relatively small convective structures, i.e. small subducting plates, in formation of orogenic belts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Natur.535..276S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Natur.535..276S"><span>Mid-ocean-ridge seismicity reveals extreme types of ocean <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schlindwein, Vera; Schmid, Florian</p> <p>2016-07-01</p> <p>Along ultraslow-spreading ridges, where oceanic tectonic plates drift very slowly apart, conductive cooling is thought to limit mantle melting and melt production has been inferred to be highly discontinuous. Along such spreading centres, long ridge sections without any igneous crust alternate with magmatic sections that host massive volcanoes capable of strong earthquakes. Hence melt supply, <span class="hlt">lithospheric</span> composition and tectonic structure seem to vary considerably along the axis of the slowest-spreading ridges. However, owing to the lack of seismic data, the <span class="hlt">lithospheric</span> structure of ultraslow ridges is poorly constrained. Here we describe the structure and accretion modes of two end-member types of oceanic <span class="hlt">lithosphere</span> using a detailed seismicity survey along 390 kilometres of ultraslow-spreading ridge axis. We observe that amagmatic sections lack shallow seismicity in the upper 15 kilometres of the <span class="hlt">lithosphere</span>, but unusually contain earthquakes down to depths of 35 kilometres. This observation implies a cold, thick <span class="hlt">lithosphere</span>, with an upper aseismic zone that probably reflects substantial serpentinization. We find that regions of magmatic <span class="hlt">lithosphere</span> thin dramatically under volcanic centres, and infer that the resulting topography of the <span class="hlt">lithosphere</span>-asthenosphere boundary could allow along-axis melt flow, explaining the uneven crustal production at ultraslow-spreading ridges. The seismicity data indicate that alteration in ocean <span class="hlt">lithosphere</span> may reach far deeper than previously thought, with important implications towards seafloor deformation and fluid circulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018429','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018429"><span>Uplift of the Colorado Plateau due to <span class="hlt">lithosphere</span> attenuation during Laramide low-angle subduction</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Spencer, J.E.</p> <p>1996-01-01</p> <p>The Colorado Plateau is blanketed by Phanerozoic marine and nonmarine strata as young as Cretaceous that are now exposed at elevations of about 2 km. Crustal thickening due to magmatism and horizontal crustal shortening was far less than necessary to cause this uplift, which is commonly attributed to the consequences of mantle <span class="hlt">lithosphere</span> thinning and heating. The Colorado Plateau and the midcontinent region around Iowa consist of Precambrian bedrock overlain by a similar amount of Paleozoic platformal strata, and thus both regions once had similar <span class="hlt">lithospheric</span> buoyancy. Mesozoic sedimentation increased the crustal thickness and <span class="hlt">lithospheric</span> buoyancy of the Colorado Plateau relative to the midcontinent region. Backstripping calculations yield elevation without these sediments and lead to a calculated elevation difference between the two areas of about 1200 m, which represents unexplained plateau uplift. Review of constraints on uplift timing finds little support for a late Cenozoic uplift age and allows early to middle Cenozoic uplift, which is consistent with uplift mechanisms related to low-angle subduction that ended in the middle Cenozoic. Finite element heat flow calculations of low-angle subduction and <span class="hlt">lithosphere</span> attenuation, using a range of initial <span class="hlt">lithosphere</span> thicknesses and degree of attenuation, indicate that required uplift can result from tectonic removal of about 120 km of mantle <span class="hlt">lithosphere</span> from an initially 200-km-thick <span class="hlt">lithosphere</span>. This allows for partial preservation of North American mantle <span class="hlt">lithosphere</span> with its distinctive isotopic signature in some late Cenozoic volcanic rocks and is consistent with normal Pn velocities in the uppermost mantle beneath the plateau.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/255114','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/255114"><span>SHELLS: A thin-shell program for modeling neotectonics of regional or global <span class="hlt">lithosphere</span> with faults</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kong, X.; Bird, P.</p> <p>1995-11-10</p> <p>This report discusses a geophysical computer program called SHELLS, which model neotectonics of regional or global <span class="hlt">lithosphere</span> with faults. This model is based on spherical shell elements which uses isostacy and vertical integration of <span class="hlt">lithospheric</span> strength to reduce this to a two-dimensional problem.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10159431','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10159431"><span>Trace element characteristics of <span class="hlt">lithospheric</span> and asthenospheric mantle in the Rio Grande rift region</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Perry, F.V.</p> <p>1994-06-01</p> <p>Trace element analyses of 10 mafic volcanic rocks from the Colorado Plateau transition zone, Colorado Plateau, Rio Grande rift, and Great Plains were obtained to characterize the trace element characteristics of asthenospheric and <span class="hlt">lithospheric</span> mantle beneath these regions. Characterization of these mantle reservoirs using the trace element contents of basalts allows one to track the response of the <span class="hlt">lithosphere</span> to continental rifting and extension.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T41D2934G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T41D2934G"><span>Melt-induced weakening of the <span class="hlt">lithosphere</span>: theory and geodynamic implications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gerya, T.</p> <p>2015-12-01</p> <p>Melt-induced weakening can play critical role for enabling <span class="hlt">lithospheric</span> deformation in the areas of intense mantle-derived magmatism, such as mid-ocean ridges, rift zones and hot spots. It implies significant reduction in the long-term brittle strength of the deforming <span class="hlt">lithosphere</span> subjected to frequent melt percolation episodes. Such weakening corresponds to conditions when shear stress reaches the tensile yield strength of rocks at nearly equal melt and lithostatic pressures. The dominant features of melt transport in this regime are planar, sharply localized zones (dykes) in which melt is transported though the <span class="hlt">lithosphere</span> from the source region. Mechanical energy dissipation balance shows that the long-term effective strength of the melt-weakened <span class="hlt">lithosphere</span> is a strain-averaged rather than a time-averaged quantity. Its magnitude is mainly defined by the ratio between melt pressure and lithostatic pressure along dykes during short dyke emplacement episodes, which control most of the <span class="hlt">lithospheric</span> deformation and mechanical energy dissipation. We quantified the range of expected values of the <span class="hlt">lithospheric</span> strength by performing 2D numerical hydro-mechanical experiments on melt-bearing rock deformation as well as seismo-mechanical experiments on long-term <span class="hlt">lithospheric</span> deformation assisted by frequent short-term dyke propagation episodes. These numerical experiments showed that the long-term <span class="hlt">lithospheric</span> strength in the areas of intense magmatism can be as low as few MPa and is critically dependent on the availability of melt for enabling frequent episodes of dyke propagation through the <span class="hlt">lithosphere</span>. Short-lived viscous-plastic deformation is localized along propagating weak dykes whereas bulk of the <span class="hlt">lithosphere</span> only deforms elastically and is subjected to large deviatoric stresses. The experiments suggest that it is not the high strength of the elastically deforming strong <span class="hlt">lithospheric</span> blocks but the low strength of visco-plastically deforming dykes that define the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.1517H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.1517H"><span>Deformation of the <span class="hlt">lithosphere</span> and what microstructures can tell us about it (Stephan Mueller Medal Lecture)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heilbronner, Renée</p> <p>2016-04-01</p> <p>The <span class="hlt">lithosphere</span> is a roughly stratified and heterogeneous rock body that constitutes the outer layer of our planet. It is subdivided into irregularly shaped stiff plates that move with respect to one another deforming each other along their margins. At the large scale the <span class="hlt">lithosphere</span> is usually modeled as a flat-lying multi-layer, its rheological profile being based on flow laws determined experimentally for key minerals of the crust and upper mantle. At the somewhat smaller scale of field observations, geometrical and physical complexities become apparent: rocks are folded, sheared and fractured, and - in general - quite heterogeneously deformed. And finally, at the even smaller scale of mechanical testing and microscopic investigations, rocks are seen as polycrystalline aggregates or granular composites whose bulk properties depends both on the composition and shape of the individual grains and the spatial arrangement of the crystals with respect to one another. In other words, the physical properties of the <span class="hlt">lithosphere</span> and the inferred style or type of deformation depend very much on the scale of observation. Microstructures and textures (crystallographic preferred orientations) of deformed rocks provide a wealth of information: when used as archives of the deformation history, they allow us to unravel the tectonic evolution of the <span class="hlt">lithosphere</span> at plate boundaries. At the same time, they enable us to assess past and/or present geophysical properties. By comparing the microstructures of experimentally and <span class="hlt">naturally</span> deformed rocks it is possible to infer the active deformation mechanisms and thus to extrapolate flow laws to geological time scales. With the advent of digital image processing, microstructure and texture analysis have taken a great leap forward. By amalgamating methods from neighbouring disciplines such as mathematical morphometry, stereology, geostatistics, material sciences, etc., microstructure and texture analysis have come a long way since the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860027482&hterms=earthquake+prediction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dearthquake%2Bprediction','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860027482&hterms=earthquake+prediction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dearthquake%2Bprediction"><span>Thermoelastic stress - How important as a cause of earthquakes in young oceanic <span class="hlt">lithosphere</span>?</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bratt, S. R.; Bergman, E. A.; Solomon, S. C.</p> <p>1985-01-01</p> <p>Thermoelastic or thermal stress is a potentially important contributor to the state of stress in the oceanic <span class="hlt">lithosphere</span>. The present paper provides several simple models for the state of thermoelastic stress in a young oceanic <span class="hlt">lithosphere</span>, taking into account a comparison of the predictions of these models with the characteristics of near-ridge earthquakes. Attention is given to the characteristics of near-ridge earthquakes, sources of stress in an oceanic <span class="hlt">lithosphere</span>, previous models of thermal stress, the calculation of thermal stress, and thermal stress models. A test is conducted of the hypothesis that thermoelastic stress is a significant component of the stress field in a young oceanic <span class="hlt">lithosphere</span>. The considered models support the hypothesis that thermoelastic stress is a significant component of the stress field in a young oceanic <span class="hlt">lithosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850015165&hterms=Peridotite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DPeridotite','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850015165&hterms=Peridotite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DPeridotite"><span>Io: Generation of Silicate Magma by Shear Melting at the Base of a Basaltic <span class="hlt">Lithosphere</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Carr, M. H.</p> <p>1985-01-01</p> <p>Tidal theory and observational evidence indicates that about 1 w/sq. m. of energy is released at the surface of Io. In order to place limits on how much tidal energy can be dissipated within a rigid <span class="hlt">lithosphere</span>, depth-temperature profiles were calculated for different <span class="hlt">lithosphere</span> thickness assuming that the tidal energy was dissipated uniformly throughout the <span class="hlt">lithosphere</span>. Thus a thick <span class="hlt">lithosphere</span> implies that a significant fraction of the tidal energy is dissipated below the depth where solidus temperatures are reached. One possibility is that Io has a crust consisting of a low melting temperature fraction such as basalt, overlying a mantle of a high melting temperature fraction such as peridotite. Thus, if the <span class="hlt">lithosphere</span> of Io is thicker than 30 km, as appears probable, then high rates of silicate volcanism are implied and a significant fraction of the tidal energy must be dissipated by viscous deformation rather than rigid flexure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27708097','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27708097"><span>High-resolution <span class="hlt">lithosphere</span> viscosity and dynamics revealed by magnetotelluric imaging.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Lijun; Hasterok, Derrick</p> <p>2016-09-30</p> <p>An accurate viscosity structure is critical to truthfully modeling <span class="hlt">lithosphere</span> dynamics. Here, we report an attempt to infer the effective <span class="hlt">lithospheric</span> viscosity from a high-resolution magnetotelluric (MT) survey across the western United States. The high sensitivity of MT fields to the presence of electrically conductive fluids makes it a promising proxy for determining mechanical strength variations throughout the <span class="hlt">lithosphere</span>. We demonstrate how a viscosity structure, approximated from electrical resistivity, results in a geodynamic model that successfully predicts short-wavelength surface topography, <span class="hlt">lithospheric</span> deformation, and mantle upwelling beneath recent volcanism. We further show that this viscosity is physically consistent with and better constrained than that derived from laboratory-based rheology. We conclude that MT imaging provides a practical observational constraint for quantifying the dynamic evolution of the continental <span class="hlt">lithosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5572824','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5572824"><span>Growth, stabilization, and reactivation of Proterozoic <span class="hlt">lithosphere</span> in the southwestern United States</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bowring, S.A. ); Karlstrom, K.E. )</p> <p>1990-12-01</p> <p>Growth of Proterozoic continental <span class="hlt">lithosphere</span> in the southwestern United States involved assembly of tectonostratigraphic terranes during several pulses of convergent tectonism ca. 1.74, 1.70, and 1.65-1.60 Ga. Prograde metamorphism accompanied orogenic assembly, and peak metamorphic conditions outlasted deformation. Regions now characterized by the highest metamorphic grades underwent slow isobaric cooling and were not uplifted until more than 200 m.y. after assembly. Regions of low metamorphic grade were not uplifted substantially after assembly. The authors suggest that (1) relatively thin <span class="hlt">lithospheric</span> fragments were assembled into isostatically stable, normal thickness continental <span class="hlt">lithosphere</span>; (2) assembly did not erase <span class="hlt">lithospheric</span>-scale heterogeneities; (3) the present juxtaposition of different crustal levels reflects differential uplift related to 1.4-1.1 Ga tectonomagmatic activity; and (4) the boundaries between different <span class="hlt">lithospheric</span> blocks were repeatedly reactivated from Precambrian through Tertiary time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.424...38C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.424...38C"><span>Asymmetric vs. symmetric deep <span class="hlt">lithospheric</span> architecture of intra-plate continental orogens</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Calignano, Elisa; Sokoutis, Dimitrios; Willingshofer, Ernst; Gueydan, Frédéric; Cloetingh, Sierd</p> <p>2015-08-01</p> <p>The initiation and subsequent evolution of intra-plate orogens, resulting from continental plate interior deformation due to transmission of stresses over large distances from the active plate boundaries, is controlled by lateral and vertical strength contrasts in the <span class="hlt">lithosphere</span>. We present <span class="hlt">lithospheric</span>-scale analogue models combining 1) lateral strength variations in the continental <span class="hlt">lithosphere</span>, and 2) different vertical rheological stratifications. The experimental continental <span class="hlt">lithosphere</span> has a four-layer brittle-ductile rheological stratification. Lateral heterogeneity is implemented in all models by increased crustal strength in a central narrow block. The main investigated parameters are strain rate and strength of the <span class="hlt">lithospheric</span> mantle, both playing an important role in crust-mantle coupling. The experiments show that the presence of a strong crustal domain is effective in localizing deformation along its boundaries. After deformation is localized, the evolution of the orogenic system is governed by the mechanical properties of the <span class="hlt">lithosphere</span> such that the final geometry of the intra-plate mountain depends on the interplay between crust-mantle coupling and folding versus fracturing of the <span class="hlt">lithospheric</span> mantle. Underthrusting is the main deformation mode in case of high convergence velocity and/or thick brittle mantle with a final asymmetric architecture of the deep <span class="hlt">lithosphere</span>. In contrast, <span class="hlt">lithospheric</span> folding is dominant in case of low convergence velocity and low strength brittle mantle, leading to the development of a symmetric <span class="hlt">lithospheric</span> root. The presented analogue modelling results provide novel insights for 1) strain localization and 2) the development of the asymmetric architecture of the Pyrenees.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18..125Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18..125Y"><span>Seismic structure of the <span class="hlt">lithosphere</span> beneath NW Namibia: Impact of the Tristan da Cunha mantle plume</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yuan, Xiaohui; Heit, Benjamin; Brune, Sascha; Steinberger, Bernhard; Geissler, Wolfram H.; Jokat, Wilfried; Weber, Michael</p> <p>2017-01-01</p> <p>Northwestern Namibia, at the landfall of the Walvis Ridge, was affected by the Tristan da Cunha mantle plume during continental rupture between Africa and South America, as evidenced by the presence of the Etendeka continental flood basalts. Here we use data from a passive-source seismological network to investigate the upper mantle structure and to elucidate the Cretaceous mantle plume-<span class="hlt">lithosphere</span> interaction. Receiver functions reveal an interface associated with a negative velocity contrast within the <span class="hlt">lithosphere</span> at an average depth of 80 km. We interpret this interface as the relic of the <span class="hlt">lithosphere</span>-asthenosphere boundary (LAB) formed during the Mesozoic by interaction of the Tristan da Cunha plume head with the pre-existing <span class="hlt">lithosphere</span>. The velocity contrast might be explained by stagnated and "frozen" melts beneath an intensively depleted and dehydrated peridotitic mantle. The present-day LAB is poorly visible with converted waves, indicating a gradual impedance contrast. Beneath much of the study area, converted phases of the 410 and 660 km mantle transition zone discontinuities arrive 1.5 s earlier than in the landward plume-unaffected continental interior, suggesting high velocities in the upper mantle caused by a thick <span class="hlt">lithosphere</span>. This indicates that after <span class="hlt">lithospheric</span> thinning during continental breakup, the <span class="hlt">lithosphere</span> has increased in thickness during the last 132 Myr. Thermal cooling of the continental <span class="hlt">lithosphere</span> alone cannot produce the <span class="hlt">lithospheric</span> thickness required here. We propose that the remnant plume material, which has a higher seismic velocity than the ambient mantle due to melt depletion and dehydration, significantly contributed to the thickening of the mantle <span class="hlt">lithosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Litho.149....4H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Litho.149....4H"><span>Formation of cratonic <span class="hlt">lithosphere</span>: An integrated thermal and petrological model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Herzberg, Claude; Rudnick, Roberta</p> <p>2012-09-01</p> <p>The formation of cratonic mantle peridotite of Archean age is examined within the time frame of Earth's thermal history, and how it was expressed by temporal variations in magma and residue petrology. Peridotite residues that occupy the <span class="hlt">lithospheric</span> mantle are rare owing to the effects of melt-rock reaction, metasomatism, and refertilization. Where they are identified, they are very similar to the predicted harzburgite residues of primary magmas of the dominant basalts in greenstone belts, which formed in a non-arc setting (referred to here as "non-arc basalts"). The compositions of these basalts indicate high temperatures of formation that are well-described by the thermal history model of Korenaga. In this model, peridotite residues of extensive ambient mantle melting had the highest Mg-numbers, lowest FeO contents, and lowest densities at ~ 2.5-3.5 Ga. These results are in good agreement with Re-Os ages of kimberlite-hosted cratonic mantle xenoliths and enclosed sulfides, and provide support for the hypothesis of Jordan that low densities of cratonic mantle are a measure of their high preservation potential. Cratonization of the Earth reached its zenith at ~ 2.5-3.5 Ga when ambient mantle was hot and extensive melting produced oceanic crust 30-45 km thick. However, there is a mass imbalance exhibited by the craton-wide distribution of harzburgite residues and the paucity of their complementary magmas that had compositions like the non-arc basalts. We suggest that the problem of the missing basaltic oceanic crust can be resolved by its hydration, cooling and partial transformation to eclogite, which caused foundering of the entire <span class="hlt">lithosphere</span>. Some of the oceanic crust partially melted during foundering to produce continental crust composed of tonalite-trondhjemite-granodiorite (TTG). The remaining <span class="hlt">lithosphere</span> gravitationally separated into 1) residual eclogite that continued its descent, and 2) buoyant harzburgite diapirs that rose to underplate cratonic nuclei</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T41E..05P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T41E..05P"><span>Imaging <span class="hlt">Lithospheric</span> Cascadia Structure with Ambient Noise Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Porritt, R. W.; Allen, R. M.; Brudzinski, M. R.; Boyarko, D. C.; O'Driscoll, L.; Zhai, Y.; Levander, A.; Humphreys, E.; Pollitz, F. F.</p> <p>2010-12-01</p> <p>Imaging Cascadia <span class="hlt">Lithospheric</span> Structure with Ambient Noise Tomography Along strike variation has been observed throughout the Cascadia Subduction Zone in multiple studies with complementary data sets. Body-wave tomography shows a broad zone in the center of the slab with a weak high velocity signal in an atypically quiescent seismic zone (Obrebski and Allen, 2009). Characteristics of primitive basalts found in the arc volcanoes change along strike defining four distinct magma sources or plumbing systems (Schmidt et al, 2007). However, the most striking variation is in the recurrence rate of episodic tremor and slip throughout the region (Brudzinski and Allen, 2007). Determining the detailed velocity structure of the <span class="hlt">lithosphere</span> will help to unravel what role it plays in controlling the along strike variation of these separate observations. This study improves on previous observations by analysis of a surface wave model from ambient seismic noise cross-correlations with two Flexible Array deployments in addition to regional networks and the Transportable Array. Longer period bands than typically observed in ANT are recovered via improved statistical analysis resulting in robust group and phase velocity maps from 7-92 seconds. Thus structure is well resolved from the surface to approximately 100km in depth allowing for simultaneous interpretation of crust and uppermost mantle structure. Significant variations are observed along strike in this model. The high velocity mafic Siletzia terrain is observed in the lower-mid crust along the Cascadia forearc. This mafic material coincides with the region of long term tremor recurrence interval (~20 months) from Brudzinski and Allen (2007). The southern border of the Siletzia terrain is marked by a clear velocity variation along the expected Gorda-Juan de Fuca plate boundary. In this southern region, the root of the Klamath mountain is clearly compressing the subducting Gorda plate leading to increased vertical stress where</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.T51B0547P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.T51B0547P"><span>Subduction Stability: <span class="hlt">Lithospheric</span> Strength and Roll-back</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Patel, P. I.; Lavier, L.; Grand, S.</p> <p>2007-12-01</p> <p>In exploring the issue of subduction zone stability, we ran a series of simulations representing subduction systems consisting of simple 2D representations of oceanic <span class="hlt">lithosphere</span> subducting beneath continental <span class="hlt">lithosphere</span>. Our modelling software utilizes temperature dependent visco-elasto-plastic rheologies as well as a few proxies for significant chemical processes such as ecologitization and hydration. With externally imposed convergence rates, these models evolve from a contrived subduction initiation state to "normal-looking" subduction within approximately 10 million years. The simulations are then allowed to continue to evolve for up to 30 million more years. From our early results, we note that while most systems start with similar subduction geometries, they may deviate from each other over time. Notably, subduction initiated at "cooler" (and therefore stronger) junctures tend to form very stable subduction zones which maintain normal-looking geometries throughout the life of the simulation. However, subduction initiated at warmer margins tend to result in slab rollback relatively quickly. Systems with junctures of intermediate temperature also tend to subduct stably for a substantial amount of time, yet they too eventually result in rollback as the subducting slab entrains and removes some of the cooler <span class="hlt">lithosphere</span> near the juncture, allowing hotter asthenospheric material into the contact region between the plates. The hot, low-viscosity material sharply reduces the fluid-dynamically derived suction force that partially supports the stable subduction geometry, facilitating the retreat of the subducting slab as well as the rifting of the over-riding slab. These simulations incorporate a variety of approximations and assumptions which may not reflect the actual conditions within the Earth. However, they do offer a chance to observe how a system that at least appears geometrically similar to observed Earth systems may behave when subjected to varying</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20865000','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20865000"><span>Water and its influence on the <span class="hlt">lithosphere</span>-asthenosphere boundary.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Green, David H; Hibberson, William O; Kovács, István; Rosenthal, Anja</p> <p>2010-09-23</p> <p>The Earth has distinctive convective behaviour, described by the plate tectonics model, in which lateral motion of the oceanic <span class="hlt">lithosphere</span> of basaltic crust and peridotitic uppermost mantle is decoupled from the underlying mechanically weaker upper mantle (asthenosphere). The reason for differentiation at the <span class="hlt">lithosphere</span>-asthenosphere boundary is currently being debated with relevant observations from geophysics (including seismology) and geochemistry (including experimental petrology). Water is thought to have an important effect on mantle rheology, either by weakening the crystal structure of olivine and pyroxenes by dilute solid solution, or by causing low-temperature partial melting. Here we present a novel experimental approach to clarify the role of water in the uppermost mantle at pressures up to 6 GPa, equivalent to a depth of 190 km. We found that for lherzolite in which a water-rich vapour is present, the temperature at which a silicate melt first appears (the vapour-saturated solidus) increases from a minimum of 970 °C at 1.5 GPa to 1,350 °C at 6 GPa. We have measured the water content in lherzolite to be approximately 180 parts per million, retained in nominally anhydrous minerals at 2.5 and 4 GPa at temperatures above and below the vapour-saturated solidus. The hydrous mineral pargasite is the main water-storage site in the uppermost mantle, and the instability of pargasite at pressures greater than 3 GPa (equivalent to more than about 90 km depth) causes a sharp drop in both the water-storage capacity and the solidus temperature of fertile upper-mantle lherzolite. The presence of interstitial melt in mantle with more than 180 parts per million of water at pressures greater than 3 GPa alters mantle rheology and defines the <span class="hlt">lithosphere</span>-asthenosphere boundary. Modern asthenospheric mantle acting as the source for mid-oceanic ridge basalts has a water content of 50-200 parts per million (refs 3-5). We show that this matches the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T21A2800J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T21A2800J"><span><span class="hlt">Lithosphere</span> Structure and Mantle Characterization of the Alpine-Himalayan Belt: Atlas, Zagros and Tibet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jiménez-Munt, I.; Tunini, L.; Fernandez, M.; Verges, J.; Garcia-Castellanos, D.</p> <p>2015-12-01</p> <p>By combining geophysical and petrological information, we investigate the crust and upper mantle of three orogens of the Alpine-Himalayan Belt (Atlas, Zagros and Tibet), characterizing the <span class="hlt">lithosphere</span> from the thermal, compositional and seismological viewpoint. The modeling is based on an integrated geophysical-petrological methodology combining elevation, gravity, geoid, surface heat flow, seismic and geochemical data.The results show prominent <span class="hlt">lithospheric</span> mantle thickening beneath the Moroccan margin followed by thinning beneath the Atlas Mountains. Different convergence accommodation between the crust and <span class="hlt">lithospheric</span> mantle suggests a decoupled crustal-mantle mechanical response. In the northern Zagros the <span class="hlt">lithosphere</span>-asthenosphere boundary rises sharply below the Sanandaj Sirjan Zone in a narrow region, whereas in the central Zagros the thinning is smoother and affects a wider region. The transition from the Arabian to the Eurasian <span class="hlt">lithospheric</span> domain is located beneath the Zagros range, and it is marked by a change in the mantle velocity anomaly and in the <span class="hlt">lithospheric</span> mantle composition. In the western Himalaya-Tibetan orogen, the <span class="hlt">lithosphere</span> thickening is gradual reaching the maximum below the northern edge of the Plateau. The Indian <span class="hlt">lithospheric</span> mantle underlies the whole Tibetan Plateau up to the boundary with the Tarim Basin. In the eastern sector, the thickening generates sharp steps beneath the Himalaya Range, and it thins abruptly beneath the Qiangtang and the Songpan Ganzi terrains. The Indian underthrusting is restricted to the southern Plateau. Different Eurasian domains have been also identified beneath the Tarim Basin, the Altaids region and NE Plateau by means of different <span class="hlt">lithospheric</span> mantle compositions. The <span class="hlt">lithospheric</span> models crossing Zagros and Tibetan Plateau show that the present-day <span class="hlt">lithosphere</span> mantle structure of the Arabia-Eurasia and India-Eurasia collision zones are laterally-varying along the strike of both orogens, not just in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.5427K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.5427K"><span>Constraining the rheology of the <span class="hlt">lithosphere</span> through joint geodynamic and gravity inversion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaus, Boris; Baumann, Tobias; Popov, Anton</p> <p>2014-05-01</p> <p>Understanding the physics of <span class="hlt">lithospheric</span> deformation requires good constraints on <span class="hlt">lithospheric</span> rheology and in particular on the effective viscosity. Typically, rheology is determined from laboratory experiments on small rock samples, which are extrapolated to geological conditions - an extrapolation over 10 orders of magnitude in deformation rates. Ideally, we thus need a new independent method that allows constraining the effective rheology of the <span class="hlt">lithosphere</span> directly from geophysical data, which is the aim of this work. Our method uses the fact that the geodynamically controlling parameters of <span class="hlt">lithospheric</span> deformation are its effective viscosity and density structure. By appropriately parametrising the rheological structure of the <span class="hlt">lithosphere</span> we perform instantaneous forward simulations of present-day <span class="hlt">lithospheric</span> deformation scenarios with a finite element method to compute the gravity field as well as surface velocities. The forward modelling results can be compared with observations such as Bouguer anomalies and GPS-derived surface velocities. More precisely, we automatise the forward modelling procedure with a Markov-Chain Monte Carlo method, and in fact solve a joint geodynamic and gravity inverse problem. The resulting misfit can be illustrated as a function of rheological model parameters and a more detailed analysis allows constraining probabilistic parameter ranges. Yet, the <span class="hlt">lithosphere</span> has non-linear rheologies that can be plastic or temperature-dependent powerlaw creep depending on stresses. As the thermal structure of the <span class="hlt">lithosphere</span> is in general poorly constrained, and only affects the dynamics of the <span class="hlt">lithosphere</span> in an indirect manner, we developed a parameterised rheology that excludes a direct temperature dependency. To test the accuracy of this approximation we perform <span class="hlt">lithospheric</span>-scale collision forward models that incorporate a temperature-dependent visco-plastic rheology to create synthetic surface observations. In a second step, we deploy</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024148','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024148"><span>On the relations between cratonic <span class="hlt">lithosphere</span> thickness, plate motions, and basal drag</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Artemieva, I.M.; Mooney, W.D.</p> <p>2002-01-01</p> <p>An overview of seismic, thermal, and petrological evidence on the structure of Precambrian <span class="hlt">lithosphere</span> suggests that its local maximum thickness is highly variable (140-350 km), with a bimodal distribution for Archean cratons (200-220 km and 300-350 km). We discuss the origin of such large differences in <span class="hlt">lithospheric</span> thickness, and propose that the <span class="hlt">lithospheric</span> base can have large depth variations over short distances. The topography of Bryce Canyon (western USA) is proposed as an inverted analog of the base of the <span class="hlt">lithosphere</span>. The horizontal and vertical dimensions of Archean cratons are strongly correlated: larger cratons have thicker <span class="hlt">lithosphere</span>. Analysis of the bimodal distribution of <span class="hlt">lithospheric</span> thickness in Archean cratons shows that the "critical" surface area for cratons to have thick (>300 km) keels is >6-8 ?? 106 km2 . Extrapolation of the linear trend between Archean <span class="hlt">lithospheric</span> thickness and cratonic area to zero area yields a thickness of 180 km. This implies that the reworking of Archean crust should be accompanied by thinning and reworking of the entire <span class="hlt">lithospheric</span> column to a thickness of 180 km in accord with thickness estimates for Proterozoic <span class="hlt">lithosphere</span>. Likewise, extrapolation of the same trend to the size equal to the total area of all Archean cratons implies that the <span class="hlt">lithospheric</span> thickness of a hypothesized early Archean supercontinent could have been 350-450 km decreasing to 280-400 km for Gondwanaland. We evaluate the basal drag model as a possible mechanism that may thin the cratonic <span class="hlt">lithosphere</span>. Inverse correlations are found between <span class="hlt">lithospheric</span> thickness and (a) fractional subduction length and (b) the effective ridge length. In agreement with theoretical predictions, <span class="hlt">lithospheric</span> thickness of Archean keels is proportional to the square root of the ratio of the craton length (along the direction of plate motion) to the plate velocity. Large cratons with thick keels and low plate velocities are less eroded by basal drag than small</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830057093&hterms=electromagnetic+induction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Delectromagnetic%2Binduction','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830057093&hterms=electromagnetic+induction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Delectromagnetic%2Binduction"><span>Electromagnetic induction studies. [of earth <span class="hlt">lithosphere</span> and asthenosphere</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hermance, J. F.</p> <p>1983-01-01</p> <p>Recent developments in electromagnetic induction studies of the <span class="hlt">lithosphere</span> and the asthenosphere are reviewed. Attention is given to geoelectrical studies of active tectonic areas in terms of the major zones of crustal extension, the basin and range province along western regions of North America, and the Rio Grande rift. Studies have also been performed of tectonic activity around Iceland, the Salton Trough and Cerro Prieto, and the subduction zones of the Cascade Mountains volcanic belt, where magnetotelluric and geomagnetic variation studies have been done. Geomagnetic variations experiments have been reported in the Central Appalachians, and submarine electromagnetic studies along the Juan de Fuca ridge. Controlled source electromagnetic and dc resistivity investigations have been carried out in Nevada, Hawaii, and in the Adirondacks Mountains. Laboratory examinations on the conductivity of representative materials over a broad range of temperature, pressure, and chemistry are described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatGe..10..222K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatGe..10..222K"><span>Seawater cycled throughout Earth's mantle in partially serpentinized <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kendrick, M. A.; Hémond, C.; Kamenetsky, V. S.; Danyushevsky, L.; Devey, C. W.; Rodemann, T.; Jackson, M. G.; Perfit, M. R.</p> <p>2017-02-01</p> <p>The extent to which water and halogens in Earth's mantle have primordial origins, or are dominated by seawater-derived components introduced by subduction is debated. About 90% of non-radiogenic xenon in the Earth's mantle has a subducted atmospheric origin, but the degree to which atmospheric gases and other seawater components are coupled during subduction is unclear. Here we present the concentrations of water and halogens in samples of magmatic glasses collected from mid-ocean ridges and ocean islands globally. We show that water and halogen enrichment is unexpectedly associated with trace element signatures characteristic of dehydrated oceanic crust, and that the most incompatible halogens have relatively uniform abundance ratios that are different from primitive mantle values. Taken together, these results imply that Earth's mantle is highly processed and that most of its water and halogens were introduced by the subduction of serpentinized <span class="hlt">lithospheric</span> mantle associated with dehydrated oceanic crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.T34B..03K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T34B..03K"><span>Pre-seismic <span class="hlt">Lithosphere</span>, Atmosphere and Ionosphere Coupling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kamogawa, M.</p> <p>2006-12-01</p> <p>Pre-seismic anomalous states in the atmosphere and ionosphere as well as those in the telluric currents and ultra-low frequency electromagnetic waves have been reported since the 1970s. These pre-seismic phenomena have not yet been universally accepted, partly because the low occurrence frequency of large earthquakes has hindered establishing their statistical significance. Recent achievements in this respect, however, seem to be highly encouraging for promoting further studies on the pre-seismic <span class="hlt">lithosphere</span>-atmosphere-ionosphere (LAI) coupling. Liu et al. (JGR, 2006) constructed a set of quantitative definitions for ionospheric anomalies (depression of foF2) and examined the statistical correlation between thus defined ionospheric anomalies and all the Taiwan M>=5 earthquakes (184 in number) during the period 1994-1999. The results indicated that anomalies appeared within 5 days before the earthquakes. Examining the validity of the pre-seismic anomalous transmission of VHF electromagnetic waves beyond the line-of-sight, Fujiwara and Kamogawa et al. (GRL, 2004) statistically demonstrated the existence of atmospheric anomalies lasting for a few minutes to several hours before earthquakes. They found that the anomalies were significantly enhanced within 5 days before M>=4.8 earthquakes. If the pre-seismic atmospheric - ionospheric anomalies are real, some phenomena causing them should be detectable on the ground. If such causal phenomena are identified, the concept of <span class="hlt">lithosphere</span> - atmosphere - ionosphere coupling (LAI coupling) will be greatly strengthened. Possible mechanisms for energy-transport channels from the <span class="hlt">lithosphere</span> to the atmosphere-ionosphere are summarized as follows: First, the atmospheric electric field generated on/near the ground surface during the pre-seismic period may cause the ionospheric anomalies. Such an atmospheric electric field may be caused by ions generated from radon emissions. Actually, a number of reports have been published for pre</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T31E..02S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T31E..02S"><span>Fault models and constitutive laws across the <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shimamoto, T.</p> <p>2011-12-01</p> <p>Establishment of fault model is important not only for modeling earthquake cycles (stress accumulation, earthquake generation and afterslip), but also for analyzing tectonics of <span class="hlt">lithosphere</span>. Since Sibson (1977, J. Geol. Soc. London) proposed a famous fault model, several fault models have been proposed (Scholz, 1988, Geol. Rundschau; Shimamoto, 1989, J. Struct. Geol.; Kawamoto and Shimamoto, 1998, Tectonophy). There has not been much progress in fault models since then, and even those fault models had limited applications in the modeling earthquakes and tectonics because no constitutive laws describing brittle to high-temperature ductile deformation across the <span class="hlt">lithosphere</span> have been proposed. Moreover there was no additional experimental data reported to cover the brittle-ductile transition under large shearing deformation. However, the situation has been changing since Shimamoto (2004, JpGU) and Shimamoto and Noda, 2010, AGU) proposed an empirical friction to flow law which describes the transition from friction to fully plastic flow under shear for halite. Only frictional constitutive parameters and parameters in flow law are used and properties in the transitional regime can be predicted once those parameters are known. Thus this law provides a working model for reanalyzing diverse fault properties such as clay-bearing faults, for planning experimental researches to produce friction to flow behavior for realistic rocks, and for modeling fault and plate-boundary behaviors including generation of large earthquakes. I will summarize the current status on fault models and friction to flow constitutive laws across the <span class="hlt">lithosphere</span> focusing the following aspects. (1) Friction to flow transition for important rocks. Existing friction and flows laws will be combined to propose constitutive property across the <span class="hlt">lithosphere</span> (e.g., rate and state friction law combined with flow law for diabase). I will show how such a law can be used in the modeling using 2D modeling of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T14B..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T14B..01M"><span>Generation of Continental Rifts, Basins and Swells by <span class="hlt">Lithosphere</span> Instabilities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Milelli, L.; Fourel, L.; Jaupart, C. P.</p> <p>2012-12-01</p> <p>Domal uplifts, volcanism, basin formation and rifting have often struck the same continent in different areas at the same time. Their characteristics and orientations are difficult to reconcile with mantle convection or tectonic forces and suggest a driving mechanism that is intrinsic to the continent. The rifts seem to develop preferentially at high angles to the edge of the continent whereas swells and basins seem confined to the interior. Another intriguing geometrical feature is that the rifts often branch out in complicated patterns at their landward end. In Western Africa, for example, magmatic activity currently occurs in a number of uplifted areas including the peculiar Cameroon Volcanic Line that stretches away from the continental margin over about 1000 km. Magmatic and volcanic activity has been sustained along this line for 70 My with no age progression. The mantle upwelling that feeds the volcanoes is not affected by absolute plate motions and hence is attached to the continent. The Cameroon Volcanic Line extends to the Biu swell to the North and the Jos plateau to the West defining a striking Y-shaped pattern. This structure segues into several volcanic domes including the Air, the Hoggar, the Darfur, the Tibesti and the Haruj domes towards the Mediterranean coast. Another example is provided by North America, where the late Proterozoic-early Ordovician saw the formation of four major basins, the Michigan, Illinois, Williston and Hudson Bay, as well as of major rifts in southern Oklahoma and the Mississipi Valley within a short time interval. At the same time, a series of uplifts developed, such as the Ozark and Nashville domes. Motivated by these observations, we have sought an explanation in the continental <span class="hlt">lithosphere</span> itself. We describe a new type of convective instability at the base of the <span class="hlt">lithosphere</span> that leads to a remarkable spatial pattern at the scale of an entire continent. We carried out fluid mechanics laboratory experiments on buoyant</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T11A2536S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T11A2536S"><span>Seismic structure of the oceanic <span class="hlt">lithosphere</span> inferred from guided wave</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shito, A.; Suetsugu, D.; Furumura, T.; Sugioka, H.; Ito, A.</p> <p>2012-12-01</p> <p>Characteristic seismic waves are observed by seismological experiment using Broad-Band Ocean Bottom Seismometers (BBOBSs) conducted in the northwestern Pacific from 2007 to 2008 and from 2010 to 2011. The seismic waves have low frequency onset (< 1 Hz) followed by high frequency later phases (2.5-10 Hz). The high frequency later phases have large amplitude and long duration for both P and S waves. The seismic waves are observed commonly at the BBOBS array from events in the subducting Pacific plate. To investigate generation and propagation mechanisms of the seismic wave will help us to understand the seismic structure and the origin of the oceanic <span class="hlt">lithosphere</span>. High frequency phases travelling efficiently through the oceanic <span class="hlt">lithosphere</span> more than 3000 km are well known phenomenon. These phases were previously called as Po/So waves. Po/So waves were observed as early as 1935, and were studied actively from the 1970s to 1990s. However, the mechanism of generation and propagation of the phases are still controversial. The guided waves propagating in subducting plate are also common phenomenon in the subduction zone. The waves are generally characterized by separation of low frequency and high frequency components. In order to explain the separation, Martin and Rietbrock [2003] considered the trapping of waves in the waveguide formed by thin low velocity former oceanic crust at the top of the plate. However, large amplitude and long duration of the high frequency component cannot be achieved by the model. From the analysis of waveform observed at the eastern seaboard of northern Japan and numerical simulation of seismic wave propagation, Furumura and Kennet [2005] demonstrate that the guided wave travelling in the subducting plate is produced by multiple forward scattering of high-frequency seismic waves due to small-scale random heterogeneity in the plate structure. We apply the method proposed by Furumura and Kennett [2005] to reproduce the seismograms recorded by</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.3942P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.3942P"><span><span class="hlt">Lithospheric</span> response to plume- and plate-tectonic interactions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Puchkov, V.</p> <p>2012-04-01</p> <p>Plate movements and deformations of <span class="hlt">lithosphere</span> are driven mostly by a thermochemical convection in asthenosphere. Contrariwise, plume-tectonic processes result from a larger-scale thermochemical convection in the whole mantle, starting at the core-mantle boundary (CMB) and depending on core-mantle interactions. The plate-tectonic processes affect <span class="hlt">lithosphere</span> as a whole, dividing it into moving and deforming plates, while the plume-tectonic ones are manifested locally or regionally as LIPs (Large Igneous Provinces) and hot spots. Meeting in the <span class="hlt">lithosphere</span>, these processes interact, resulting in a series of tectonic effects that deserve a special consideration. 1. It was noted (e.g. Sengor, 2001; Li et al., 2008) that destruction of supercontinents is accompanied by growth of a superplume (LIP) activity within continental territories. Meanwhile, there are cases when a superplume activity is not connected with continents and conversely, superplumes on continents do not necessarily lead to their splitting. According to V. Trubitsyn (2000), the break-up of a supercontinent is a result of a "blanketing effect" of heat accumulation under it, inducing a restructuring of a convection pattern. I suggested that superplumes simply add the heat to this effect, supplying the process with an additional energy and making the break-up of a supercontinent more easy. 2. One more example of a joint action of plate and plume processes is a formation of continental passive margins, that belong to two types: volcanic and avolcanic (Jeffroy,2005; Melankholina, 2008, 2011). Such characteristics of the volcanic type as a high volcanic activity, underplating, presence of specific seaward-dipping reflectors, are the result of an interference of a passive rifting with active plume processes after the break-up of a supercontinent. 3. Another example of a co-operation of plume- and plate tectonic mechanics is well known: it is a formation of time-progressive volcanic chains (Morgan,1971</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PEPI..253...97B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PEPI..253...97B"><span><span class="hlt">Lithospheric</span> structure beneath NW Iran using regional and teleseismic travel-time tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bavali, K.; Motaghi, K.; Sobouti, F.; Ghods, A.; Abbasi, M.; Priestley, K.; Mortezanejad, G.; Rezaeian, M.</p> <p>2016-04-01</p> <p>We compute a 2-D tomogram using the P wave arrival time readings from a temporary seismic experiment to study the seismic structure of the crust and upper mantle in NW Iran. The study area includes the western margins of the South Caspian Basin (SCB), and the Sahand and Sabalan post-collisional volcanoes in NW Iran. We invert 2780 regional and teleseismic relative P wave arrival times recorded by 23 stations along the seismic profile extending from the western shoreline of the Caspian Sea to Lake Urumieh. Our tomographic results show a higher-velocity region beneath the SCB. The observed higher velocities strongly correlate with the observed positive gravity anomalies over the southwestern margins of the Caspian Sea, suggesting an oceanic like <span class="hlt">nature</span> for the SCB <span class="hlt">lithosphere</span>. The tomographic results also show several lower-velocity anomalies in the crust. The Sabalan volcano is underlain by a low-velocity zone in the lower crust, which is most likely thermal in <span class="hlt">nature</span>. In the Sahand region, the lower velocities are considerably shallower in depth and might be controlled by shallow sedimentary structures, as well as an anomalously warm upper crust. The shallow low-velocity regions are connected with deeper low-velocity zones 60-100 km deep in the upper mantle. This pattern points to a possible mantle source of post-collisional volcanism in NW Iran, i.e. the melting of a subducted slab.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S31A2343R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S31A2343R"><span>Constraining <span class="hlt">Lithospheric</span> Structure across the California Borderland using Receiver Functions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reeves, Z. A.; Lekic, V.; Weeraratne, D. S.; Kohler, M. D.</p> <p>2013-12-01</p> <p>Due to its complex history of deformation that has included subduction, rifting, and translational motions, the California (Continental) Borderland provides a unique geological setting for studying how the structure of oceanic and continental plates respond to deformation. Three component ocean bottom data gathered as part of the ALBACORE experiment in 2010-2011 allows us to expand on previous receiver function studies that characterized the crustal (Zhu and Kanamori, 2000) and mantle <span class="hlt">lithosphere</span> structure (Lekic et al., 2011) from the inner borderland into the outer borderland; stations west of the Patten Escarpment allow us to extend the constraints into the abyssal plain of the Pacific Plate. However, compared to coastal and ocean island stations used in previous studies, the ocean bottom data is characterized by low signal-to-noise ratios making it difficult to obtain interpretable receiver functions; therefore, developing strategies for de-noising the seismograms and obtaining reliable receiver functions from ocean bottom data is one of our main objectives. We explore multiple strategies in order to improve the signal-to-noise ratio and yield more easily interpretable receiver functions. In order to better isolate the sought-after structural signal, we carry out wavefield simulations through synthetic structures with varying thicknesses of sediment. By examining each waveform record, we find that highest signal-to-noise ratios are obtained by bandpass filtering the data in the 0.03-0.12 Hz frequency range. We show that the use of elastic wave-field decomposition method proposed by Bostock and Trehu (2012) improves the estimation of the P and S wavefields in comparison to the free-surface transform matrix (Kennett 1991) used for stations on the land surface. We then calculate and map variations in absolute shear wavespeed needed for optimal wavefield separation. Finally, we present both Ps and Sp receiver functions across the California Borderland and interpret</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002Litho..65..273A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002Litho..65..273A"><span>Power law olivine crystal size distributions in <span class="hlt">lithospheric</span> mantle xenoliths</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Armienti, P.; Tarquini, S.</p> <p>2002-12-01</p> <p>Olivine crystal size distributions (CSDs) have been measured in three suites of spinel- and garnet-bearing harzburgites and lherzolites found as xenoliths in alkaline basalts from Canary Islands, Africa; Victoria Land, Antarctica; and Pali Aike, South America. The xenoliths derive from <span class="hlt">lithospheric</span> mantle, from depths ranging from 80 to 20 km. Their textures vary from coarse to porphyroclastic and mosaic-porphyroclastic up to cataclastic. Data have been collected by processing digital images acquired optically from standard petrographic thin sections. The acquisition method is based on a high-resolution colour scanner that allows image capturing of a whole thin section. Image processing was performed using the VISILOG 5.2 package, resolving crystals larger than about 150 μm and applying stereological corrections based on the Schwartz-Saltykov algorithm. Taking account of truncation effects due to resolution limits and thin section size, all samples show scale invariance of crystal size distributions over almost three orders of magnitude (0.2-25 mm). Power law relations show fractal dimensions varying between 2.4 and 3.8, a range of values observed for distributions of fragment sizes in a variety of other geological contexts. A fragmentation model can reproduce the fractal dimensions around 2.6, which correspond to well-equilibrated granoblastic textures. Fractal dimensions >3 are typical of porphyroclastic and cataclastic samples. Slight bends in some linear arrays suggest selective tectonic crushing of crystals with size larger than 1 mm. The scale invariance shown by <span class="hlt">lithospheric</span> mantle xenoliths in a variety of tectonic settings forms distant geographic regions, which indicate that this is a common characteristic of the upper mantle and should be taken into account in rheological models and evaluation of metasomatic models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016DPS....4821619O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DPS....4821619O"><span>Constraints on <span class="hlt">Lithospheric</span> Rheology from Observations of Coronae on Venus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Rourke, Joseph G.; Smrekar, Suzanne; Moresi, Louis N.</p> <p>2016-10-01</p> <p>Coronae are enigmatic, quasi-circular features found in myriad geological environments. They are primarily distinguished as rings of concentric fractures superimposed on various topographic profiles with at least small-scale volcanism. Mantle plumes may produce coronae with interior rises, whereas coronae with central depressions are often attributed to downwellings like Rayleigh-Taylor instabilities. For almost three decades, modelers have attempted to reproduce the topographic and gravity profiles measured at coronae. Until recently, few studies also considered tectonic deformation and melt production. In particular, "Type 2" coronae have complete topographic rims but arcs of fractures extending less than 180°, signifying both brittle and ductile deformation. Only a narrow range of rheological parameters like temperature and volatile content may be compatible with these observations. Ultimately, identifying how <span class="hlt">lithospheric</span> properties differ between Earth and Venus is critical to understanding what factors permit plate tectonics on rocky, Earth-sized planets.Here we present a hierarchical approach to study the formation of coronae. First, we discuss an observational survey enabled by a new digital elevation model derived from stereo topography for ~20% of the surface of Venus, which offers an order-of-magnitude improvement over the horizontal resolution (10 to 20 kilometers) of altimetry data from NASA's Magellan mission. Next, we search this new dataset for signs of <span class="hlt">lithospheric</span> flexure around small coronae. Simple, thin-elastic plate models were fit to topographic profiles of larger coronae in previous studies, but data resolution impeded efforts to apply this method to the entire coronae population. Finally, we show simulations of the formation of coronae using Underworld II, an open-source code adaptable to a variety of geodynamical problems. We benchmark our code using models of pure Rayleigh-Taylor instabilities and then investigate the influence of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T33A1862M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T33A1862M"><span>Experimental Constraints on the Rheology of the <span class="hlt">Lithospheric</span> Mantle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mei, S.; Suzuki, A. M.; Kohlstedt, D. L.; Dixon, N. A.; Durham, W. B.</p> <p>2009-12-01</p> <p>To provide a better understanding of rheological properties of mantle rocks under <span class="hlt">lithospheric</span> conditions, we carried out a series of experiments on the steady-state creep behavior of polycrystalline olivine, the most abundant mineral of the upper mantle, at high pressures (~4 to 9 GPa), relatively low temperatures (673 ≤ T ≤ 1273 K), and anhydrous conditions using a deformation-DIA. Differential stress and sample displacement were monitored in-situ using synchrotron x-ray diffraction and radiography, respectively. The low-temperature plasticity of olivine is well constrained by our data with a Peierls stress of 6.2 ± 0.3 GPa and an activation energy of 290 ± 60 kJ/mol. The flow stress in the low-temperature plasticity regime characterized in this study is less temperature sensitive than reported in earlier studies using micro-indentation and load relaxation techniques, in which samples were deformed in a transient rather than steady-state fashion. A transition from low-T plasticity to high-T creep occurs at ~1300 K for a laboratory strain rate of ~10-5 s-1. Low-T plasticity dominates deformation of olivine-rich rocks at depths in the <span class="hlt">lithospheric</span> mantle where pressure is high enough to suppress frictional sliding while temperature is low enough not to activate dislocation climb. Extrapolation of our low-temperature flow law to a strain rate of 10-14s-1 and a temperature of 873 K, the cut-off temperature for earthquakes in the mantle, yields a strength of ~500 MPa. This value is similar to that obtained from the flow law of Evans and Goetze [1979] and a factor of five large than that calculated from the flow law of Raterron et al. [2004].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRE..121..255M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRE..121..255M"><span><span class="hlt">Lithospheric</span> flexure and gravity spreading of Olympus Mons volcano, Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Musiol, S.; Holohan, E. P.; Cailleau, B.; Platz, T.; Dumke, A.; Walter, T. R.; Williams, D. A.; Gasselt, S.</p> <p>2016-03-01</p> <p>The structural architecture of large volcanoes is governed substantially by gravity-driven deformation that is manifest as distinct processes such as basement flexure or volcanic spreading. Temporal effects and the mutual interplay of these processes have been investigated only to a limited extent, and so we present novel numerical models of the time-dependent deformation associated with them. The models simulate the combined effects of <span class="hlt">lithospheric</span> flexure and volcanic spreading during growth increments of an elastoplastic volcanic cone. Different spreading scenarios are considered by a variable coupling decoupling behavior at the interface between volcano and basement. We apply our models to Olympus Mons on Mars, which is characterized by upper to middle flank terraces on the shield, is encircled by a basal scarp that has an average slope of 30° and is surrounded by distant deposits that resemble large-scale slumping features on Earth. Our results are consistent with the interpretation that terraces on Olympus Mons' flanks form by thrust faulting that results from <span class="hlt">lithospheric</span> flexure. The presence and expression of terraces depend on the coupling of volcano and basement, on the time of volcano growth relative to mantle relaxation, and on the cohesion of the edifice. The encircling scarp may be related to a very low friction detachment at the edifice base, which leads to a normal fault regime on the lowermost flanks. With time and volcano growth, predicted stress and faulting regimes migrate only slightly, indicating that the structural architecture of volcanoes is largely set in the very early stages of formation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1019792','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1019792"><span>Experimental Constraints on the Strength of the <span class="hlt">Lithospheric</span> Mantle</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mei, S.; Suzuki, A; Kohlstedt, D; Dixon, N; Durham, W</p> <p>2010-01-01</p> <p>To provide a better understanding of rheological properties of mantle rocks under <span class="hlt">lithospheric</span> conditions, we carried out a series of experiments on the creep behavior of polycrystalline olivine at high pressures ({approx}4-9 GPa), relatively low temperatures (673 {le} T {le} 1273 K), and anhydrous conditions, using a deformation-DIA. Differential stress and sample displacement were monitored in situ using synchrotron X-ray diffraction and radiography, respectively. Experimental results were fit to the low-temperature plasticity flow law. On the basis of this analysis, the low-temperature plasticity of olivine deformed under anhydrous conditions is well constrained by our data with a Peierls stress of {sigma}{sub P} = 5.9 {+-} 0.2 GPa, a zero-stress activation energy of E{sub k}(0) = 320 {+-} 50 kJ mol{sup -1}, and A{sub P} = 1.4 x 10{sup -7} s{sup -1} MPa{sup -2}. Compared with published results for high-temperature creep of olivine, a transition from low-temperature plasticity to high-temperature creep occurs at {approx}1300 K for a strain rate of {approx}10{sup -5} s{sup -1}. For a geological strain rate of 10{sup -14} s{sup -1}, extrapolation of our low-temperature flow law to 873 K, the cutoff temperature for earthquakes in the mantle, yields a strength of {approx}600 MPa. The low-temperature, high-stress flow law for olivine in this study provides a solid basis for modeling tectonic processes occurring within Earth's <span class="hlt">lithosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V32A..04P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V32A..04P"><span>Re-Os systematics of the Siberian <span class="hlt">lithosphere</span>: Evidence for melt percolation and <span class="hlt">lithospheric</span> re-fertilization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pernet-Fisher, J.; Pearson, D.; Barry, P. H.; Howarth, G. H.; Pokhilenko, N. P.; Taylor, L. A.</p> <p>2013-12-01</p> <p>The Siberian craton underwent multiple episodes of kimberlite magmatism spanning the Silurian to the Jurassic, during which numerous mantle xenoliths from the sub-continental <span class="hlt">lithospheric</span> mantle (SCLM) were brought to the surface. During this time, kimberlite magmatism was interrupted by the emplacement of the Siberian Flood Basalts (SFB) at ~250 Ma, relating to the main stage of activity of the Siberian Superplume. This makes the Siberian craton an ideal location to characterize metasomatism of the SCLM over the life-cycle of a plume. We report new Re-Os isotope analyses on whole-rock and olivine separates, in parallel with detailed petrographic descriptions of two suites of peridotite xenoliths recovered from the Silurian Udachnaya (360 Ma) and Jurassic Obnazhennaya (160 Ma) kimberlite pipes, bracketing the climax of Superplume activity with eruption of the SFB. The 187Os/188Os values for Udachnaya are within the range of previously reported values [1]. The most depleted harzburgite sample displays the most unradiogenic 187Os/188Os (0.1082) yielding a Neoarchean (3.0-2.5 Ga) calculated model depletion age, consistent with estimated formation age of the Siberian <span class="hlt">lithospheric</span> keel [1]. Udachnaya lherzolite samples yield younger Proterozoic model depletion ages ranging from ~1-2 Ga (average 1.5 Ga). This age range is consistent with the final stages of craton building [2] and is likely to reflect metasomatic events associated with the re-fertilization of the mantle from harzburgite to lherzolite, at this time. In contrast, the younger Obnazhennaya peridotites contain olivine with Fo >92 associated with radiogenic 187Os/188Os (average 0.1330), within the range of typical fertile mantle. Garnet melt reconstructions of these peridotites show evidence of re-equilibration with basaltic melts derived from the Siberian Superplume [3]. It is clear that extensive percolation of basaltic melts through the SCLM during the main phase of plume activity has had a profound impact</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993Litho..30..309D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993Litho..30..309D"><span>Earth's earliest continental <span class="hlt">lithosphere</span>, hydrothermal flux and crustal recycling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Wit, Maarten J.; Hart, Roger A.</p> <p>1993-09-01</p> <p>The Kaapvaal craton in southern Africa and the Pilbara craton of northwestern Australia are the largest regions on Earth to have retained relatively pristine mid-Archaean rocks (3.0-4.0 Ga). The Kaapvaal craton covers about 1.2×10 6 km 2, and varies in <span class="hlt">lithospheric</span> thickness between 170 and 350 km. At surface, the craton can be subdivided into a number of Archaean sub-domains; some of the subdomains are also well defined at depth, and local variations in tomography of the <span class="hlt">lithosphere</span> correspond closely with subdomain boundaries at surface. The Archaean history of the Kaapvaal craton spans about 1 Gyr and can be conveniently subdivided into two periods, each of about the same length as the Phanerozoic. The first period, from circa 3.7-3.1 Ga, records the initial separation of the cratonic <span class="hlt">lithosphere</span> from the asthenosphere, terminating with a major pulse of accretion tectonics between 3.2 and 3.1 Ga, which includes the formation of "paired metamorphic belts". This period of continental growth can be compared to plate tectonic processes occurring in modern-day oceanic basins. However, the difference is that in the mid-Archaean, these oceanic processes appear to have occurred in shallower water depths than the modern ocean basins. The second period, from circa 3.1-2.6 Ga, records intra-continental and continental-edge processes: continental growth during this period occurred predominantly through a combination of tectonic accretion of crustal fragments and subduction-related igneous processes, in much the same way as has been documented along the margins of the Pacific and Tethys oceans since the Mesozoic. The intra-oceanic processes resulted in small, but deep-rooted continental nucleii; the first separation of this early continental <span class="hlt">lithosphere</span> could only have occurred when the mean elevation of mid-oceanicridges sank below sea-level. Substantial recycling of continental <span class="hlt">lithosphere</span> into the mantle must have occurred during this period of Earth history. During the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.450..197H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.450..197H"><span>Utilizing thermal isostasy to estimate sub-<span class="hlt">lithospheric</span> heat flow and anomalous crustal radioactivity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hasterok, D.; Gard, M.</p> <p>2016-09-01</p> <p>While surface heat flow relates to the heat loss through the <span class="hlt">lithosphere</span>, it can be difficult to quantify and separate the heat produced internally through radiogenic decay from the heat transferred across the base of the <span class="hlt">lithosphere</span> by mantle convection. In this study, we apply a thermo-isostatic analysis to Australia and estimate the sub-<span class="hlt">lithospheric</span> and radiogenic heat flow components by employing a simple 1-D conservation of energy model. We estimate an anomalous radiogenic heat production across much of eastern Australia generally accounting for >50 mW m-2, while western Australia appears to have high crustal compositionally corrected elevation, possibly related to chemical buoyancy of the mantle <span class="hlt">lithosphere</span>. A moderately high sub-<span class="hlt">lithospheric</span> heat flow (∼40 mW m-2) along the eastern and southeastern coast, including Tasmania, is coincident with locations of Cenozoic volcanism and supports an edge-driven convection hypothesis. However, the pattern of sub-<span class="hlt">lithospheric</span> heat flow along the margin does not support the existence of hotspot tracks. Thermo-isostatic models such as these improve our ability to identify and quantify crustal from mantle sources of heat loss and add valuable constraints on tectonic and geodynamic models of the continental <span class="hlt">lithosphere</span>'s physical state and evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34..396C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34..396C"><span>Strain localization at the margins of strong <span class="hlt">lithospheric</span> domains: Insights from analog models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Calignano, Elisa; Sokoutis, Dimitrios; Willingshofer, Ernst; Gueydan, Frédéric; Cloetingh, Sierd</p> <p>2015-03-01</p> <p>The lateral variation of the mechanical properties of continental <span class="hlt">lithosphere</span> is an important factor controlling the localization of deformation and thus the deformation history and geometry of intraplate mountain belts. A series of three-layer <span class="hlt">lithospheric</span>-scale analog models, with a strong domain (SD) embedded at various depths, are presented to investigate the development of topography and deformation patterns by having lateral heterogeneities within a weak continental <span class="hlt">lithosphere</span>. The experiments, performed at a constant velocity and under normal gravity, indicate that the presence or absence of the SD controls whether deformation is localized or distributed at a <span class="hlt">lithospheric</span> scale. Deformation and topography localize above the edges of the SD, while the SD region itself is characterized by minor amounts of surficial deformation and topography. The depth of the SD (within the ductile crust, ductile mantle <span class="hlt">lithosphere</span>, or both) controls the pattern of deformation and thus the topography. The presence of a SD in the ductile crust or in the mantle results in limited surficial topographic effects but large variations in the Moho topography. Strong Moho deflection occurs when the SD is in the ductile crust, while the Moho remains almost flat when the SD is in the mantle. When the SD occupies the ductile <span class="hlt">lithosphere</span>, the SD is tilted. These analog experiments provide insights into intraplate strain localization and could in particular explain the topography around the Tarim Basin, a <span class="hlt">lithospheric</span>-scale heterogeneity north of the India-Asia collision zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T43F..01L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T43F..01L"><span>Seismic and Thermal Structure of the Arctic <span class="hlt">Lithosphere</span>, From Waveform Tomography and Thermodynamic Modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lebedev, S.; Schaeffer, A. J.; Fullea, J.; Pease, V.</p> <p>2015-12-01</p> <p>Thermal structure of the <span class="hlt">lithosphere</span> is reflected in the values of seismic velocities within it. Our new tomographic models of the crust and upper mantle of the Arctic are constrained by an unprecedentedly large global waveform dataset and provide substantially improved resolution, compared to previous models. The new tomography reveals lateral variations in the temperature and thickness of the <span class="hlt">lithosphere</span> and defines deep boundaries between tectonic blocks with different <span class="hlt">lithospheric</span> properties and age. The shape and evolution of the geotherm beneath a tectonic unit depends on both crustal and mantle-<span class="hlt">lithosphere</span> structure beneath it: the <span class="hlt">lithospheric</span> thickness and its changes with time (these determine the supply of heat from the deep Earth), the crustal thickness and heat production (the supply of heat from within the crust), and the thickness and thermal conductivity of the sedimentary cover (the insulation). Detailed thermal structure of the basins can be modelled by combining seismic velocities from tomography with data on the crustal structure and heat production, in the framework of computational petrological modelling. The most prominent lateral contrasts across the Arctic are between the cold, thick <span class="hlt">lithospheres</span> of the cratons (in North America, Greenland and Eurasia) and the warmer, non-cratonic blocks. The <span class="hlt">lithosphere</span> of the Canada Basin is cold and thick, similar to old oceanic <span class="hlt">lithosphere</span> elsewhere around the world; its thermal structure offers evidence on its <span class="hlt">lithospheric</span> age and formation mechanism. At 150-250 km depth, the central Arctic region shows a moderate low-velocity anomaly, cooler than that beneath Iceland and N Atlantic. An extension of N Atlantic low-velocity anomaly into the Arctic through the Fram Strait may indicate an influx of N Atlantic asthenosphere under the currently opening Eurasia Basin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.431..186M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.431..186M"><span>Imaging Canary Island hotspot material beneath the <span class="hlt">lithosphere</span> of Morocco and southern Spain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miller, Meghan S.; O'Driscoll, Leland J.; Butcher, Amber J.; Thomas, Christine</p> <p>2015-12-01</p> <p>The westernmost Mediterranean has developed into its present day tectonic configuration as a result of complex interactions between late stage subduction of the Neo-Tethys Ocean, continental collision of Africa and Eurasia, and the Canary Island mantle plume. This study utilizes S receiver functions (SRFs) from over 360 broadband seismic stations to seismically image the <span class="hlt">lithosphere</span> and uppermost mantle from southern Spain through Morocco and the Canary Islands. The <span class="hlt">lithospheric</span> thickness ranges from ∼65 km beneath the Atlas Mountains and the active volcanic islands to over ∼210 km beneath the cratonic <span class="hlt">lithosphere</span> in southern Morocco. The common conversion point (CCP) volume of the SRFs indicates that thinned <span class="hlt">lithosphere</span> extends from beneath the Canary Islands offshore southwestern Morocco, to beneath the continental <span class="hlt">lithosphere</span> of the Atlas Mountains, and then thickens abruptly at the West African craton. Beneath thin <span class="hlt">lithosphere</span> between the Canary hot spot and southern Spain, including below the Atlas Mountains and the Alboran Sea, there are distinct pockets of low velocity material, as inferred from high amplitude positive, sub-<span class="hlt">lithospheric</span> conversions in the SRFs. These regions of low seismic velocity at the base of the <span class="hlt">lithosphere</span> extend beneath the areas of Pliocene-Quaternary magmatism, which has been linked to a Canary hotspot source via geochemical signatures. However, we find that this volume of low velocity material is discontinuous along strike and occurs only in areas of recent volcanism and where asthenospheric mantle flow is identified with shear wave splitting analyses. We propose that the low velocity structure beneath the <span class="hlt">lithosphere</span> is material flowing sub-horizontally northeastwards beneath Morocco from the tilted Canary Island plume, and the small, localized volcanoes are the result of small-scale upwellings from this material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34..694O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34..694O"><span><span class="hlt">Lithospheric</span> discontinuity structure in Alaska, thickness variations determined by Sp receiver functions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Driscoll, Leland J.; Miller, Meghan S.</p> <p>2015-04-01</p> <p>We present the first broad-scale image of <span class="hlt">lithospheric</span> thickness across the major tectonic domains of Alaska based on S wave receiver functions and joint interpretation with the potential field, seismic velocity, and heat flow measurements. Thus, we provide context for the distribution of strain throughout the Alaskan orocline. In the north, below the Brooks Range, a 130 km thick <span class="hlt">lithosphere</span> is resolved, consistent with the presence of strong <span class="hlt">lithosphere</span> that deflects strain to the south into central and southern Alaska. In southern Alaska beneath the Chugach and St. Elias Mountains, multiple interfaces are present, and we interpret a thinner (80-90 km) North American <span class="hlt">lithosphere</span> above a deeper interface that represents the base of the Yakutat microplate, thereby extending it to the area below the Wrangell Volcanic Field and St. Elias Mountains. Immediately north of the E-W striking Denali Fault, shallow negative conversions (80 km) denote thin <span class="hlt">lithosphere</span> in the greater back-arc region where heat flow is observed to be high. Thin <span class="hlt">lithosphere</span> in eastern Alaska and adjacent Yukon Territory coincides with the occurrence of inboard crustal seismicity and may be indicative of transmitted compression caused by the collision of the Yakutat microplate. Relatively thin <span class="hlt">lithosphere</span> (<90 km) south of the Arctic Alaska domain that is deforming throughout the Alaskan orocline may result from <span class="hlt">lithospheric</span> thinning associated with guided deformation. Expansion of this model using the upcoming Transportable Array will be critical to establish lateral continuity (or lack thereof) of <span class="hlt">lithospheric</span> structure and directly discriminate between existing regional deformation models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T23B2389S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T23B2389S"><span>Constraining the dynamical behavior of the western US <span class="hlt">lithosphere</span> through computational modeling: Evidence that lower crustal flow plays a significant role in load accommodation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Seunarine, L.; Lowry, A. R.</p> <p>2011-12-01</p> <p>The rheology of the continental <span class="hlt">lithosphere</span> at depth remains an unresolved issue in geodynamics. Debate persists over whether <span class="hlt">lithospheric</span> deformation includes flow of the lower crust between strong upper crustal and upper mantle layers (behavior analogous to a "jelly sandwich") or if flow is predominantly in a weak uppermost mantle beneath a strong crust (analogous to a "crème brulee"). The degree of Moho deflection accompanying <span class="hlt">lithospheric</span> flexure provides an important clue as to which dynamical behavior dominates: If the lower crust does not flow significantly, then the Moho can be expected to conform, in part or in whole, to the <span class="hlt">lithosphere</span>'s flexural response to surface and internal mass loads. Here we examine where strength resides in the <span class="hlt">lithosphere</span> using new estimates of western US Moho, along with estimates of internal mass variation associated with crustal composition and <span class="hlt">lithospheric</span> temperature, derived from receiver function analysis of Earthscope Transportable Array seismic data (Lowry & Perez-Gussinye, 2011). We consider two end-member models of elevation response to the mass fields. One model assumes that the Moho will deflect identically to the surface elevation in response to each mass field (an expected feature of a crème brulee scenario) while the other treats the Moho as an independent mass field with no flexural stress coupling to the surface (the extreme end-member for a jelly-sandwich). The crème brulee model is significantly less successful at reproducing observed western US elevations than the jelly sandwich model. The modeling approach allows density parameters relating the seismic and thermal fields to mass to vary, and estimates of optimal density parameters associated with each mass field are also very different between the two models. The jelly sandwich model yields density parameters similar to those derived from laboratory and geophysical analyses, while the crème brulee model minimizes density parameters related to composition</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.264..210Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.264..210Z"><span>Complex metasomatism of <span class="hlt">lithospheric</span> mantle by asthenosphere-derived melts: Evidence from peridotite xenoliths in Weichang at the northern margin of the North China Craton</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zou, Dongya; Zhang, Hongfu; Hu, Zhaochu; Santosh, M.</p> <p>2016-11-01</p> <p>The petrology, in situ analyses of major and trace elements as well as Sr isotopic compositions of spinel-facies lherzolite and harzburgite xenoliths from Weichang within the northern margin of the North China Craton (NCC) are reported for the first time in this study to evaluate the <span class="hlt">nature</span> and evolution of the <span class="hlt">lithospheric</span> mantle. These peridotite xenoliths display porphyroclastic texture and can be subdivided into two groups. Group I peridotites have slightly higher forsterite contents (Fo) (90.6-91.2) and 87Sr/86Sr ratios (0.7025-0.7043) in the cores than those in the rims (89.8-90.8; 0.7025-0.7038) of olivines and clinopyroxenes, respectively. The clinopyroxenes in these rocks exhibit uniform LREE-depleted patterns. These geochemical features suggest that the Group I peridotites were weakly metasomatized by recent asthenospheric melts. In contrast, Group II peridotites show sieve-texture and clear compositional zoning in minerals. The olivines and clinopyroxenes from these rocks have higher Fo (86.9-91.3) and 87Sr/86Sr ratios (0.7035-0.7049) in the cores than those in the rims (76.9-90.6; 0.7021-0.7046). The clinopyroxenes show three types of REE patterns: LREE-enriched, convex-upward and spoon-shaped. The LREE-enriched clinopyroxenes have the highest (La/Yb)N and lowest Ti/Eu and those with spoon-shaped REE patterns show an increase in LREE, Ba, Th and U contents from the cores to the rims. These features indicate that the Group II peridotites witnessed a high degree of refertilization by recent asthenosphere-derived silicate and carbonatite melts or their mixture. Compared with the data of the Mesozoic NCC <span class="hlt">lithospheric</span> mantle, the heterogeneous and low 87Sr/86Sr ratios (0.7025-0.7049) in the LREE-depleted clinopyroxenes reveal that the ancient <span class="hlt">lithospheric</span> mantle could have been modified by asthenospheric melts before the recent metasomatism event. We conclude that the <span class="hlt">lithospheric</span> mantle beneath Weichang underwent multiple modifications through asthenosphere-<span class="hlt">lithosphere</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.7565A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.7565A"><span>Global map of <span class="hlt">lithosphere</span> thermal thickness on a 1 deg x 1 deg grid - digitally available</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Artemieva, Irina</p> <p>2014-05-01</p> <p>This presentation reports a 1 deg ×1 deg global thermal model for the continental <span class="hlt">lithosphere</span> (TC1). The model is digitally available from the author's web-site: www.<span class="hlt">lithosphere</span>.info. Geotherms for continental terranes of different ages (early Archean to present) are constrained by reliable data on borehole heat flow measurements (Artemieva and Mooney, 2001), checked with the original publications for data quality, and corrected for paleo-temperature effects where needed. These data are supplemented by cratonic geotherms based on xenolith data. Since heat flow measurements cover not more than half of the continents, the remaining areas (ca. 60% of the continents) are filled by the statistical numbers derived from the thermal model constrained by borehole data. Continental geotherms are statistically analyzed as a function of age and are used to estimate <span class="hlt">lithospheric</span> temperatures in continental regions with no or low quality heat flow data. This analysis requires knowledge of <span class="hlt">lithosphere</span> age globally. A compilation of tectono-thermal ages of <span class="hlt">lithospheric</span> terranes on a 1 deg × 1 deg grid forms the basis for the statistical analysis. It shows that, statistically, <span class="hlt">lithospheric</span> thermal thickness z (in km) depends on tectono-thermal age t (in Ma) as: z=0.04t+93.6. This relationship formed the basis for a global thermal model of the continental <span class="hlt">lithosphere</span> (TC1). Statistical analysis of continental geotherms also reveals that this relationship holds for the Archean cratons in general, but not in detail. Particularly, thick (more than 250 km) <span class="hlt">lithosphere</span> is restricted solely to young Archean terranes (3.0-2.6 Ga), while in old Archean cratons (3.6-3.0 Ga) <span class="hlt">lithospheric</span> roots do not extend deeper than 200-220 km. The TC1 model is presented by a set of maps, which show significant thermal heterogeneity within continental upper mantle. The strongest lateral temperature variations (as large as 800 deg C) are typical of the shallow mantle (depth less than 100 km). A map of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910012279','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910012279"><span>Report of the panel on <span class="hlt">lithospheric</span> structure and evolution, section 3</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chase, Clement G.; Lang, Harold; Mcnutt, Marcia K.; Paylor, Earnest D.; Sandwell, David T.; Stern, Robert J.</p> <p>1991-01-01</p> <p>The panel concluded that NASA can contribute to developing a refined understanding of the compositional, structural, and thermal differences between continental and oceanic <span class="hlt">lithosphere</span> through a vigorous program in solid Earth science with the following objectives: determine the most fundamental geophysical property of the planet; determine the global gravity field to an accuracy of a few milliGals at wavelengths of 100 km or less; determine the global <span class="hlt">lithospheric</span> magnetic field to a few nanoTeslas at a wavelength of 100 km; determine how the <span class="hlt">lithosphere</span> has evolved to its present state via acquiring geologic remote sensing data over all the continents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.9235J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.9235J"><span>Mantle exhumation and OCT architecture dependency on <span class="hlt">lithosphere</span> deformation modes during continental breakup: Numerical experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeanniot, Ludovic; Kusznir, Nick; Manatschal, Gianreto; Cowie, Leanne</p> <p>2013-04-01</p> <p>The initiation of sea-floor spreading, during the continental breakup process, requires both the rupture of the continental crust and the initiation of decompression melting. This process results in mantle upwelling and at some point decompressional melting which creates new oceanic crust. Using numerical experiments, we investigate how the deformation mode of continental <span class="hlt">lithosphere</span> thinning and stretching controls the rupture of continental crust and <span class="hlt">lithospheric</span> mantle, the onset of decompression melting, their relative timing, and the circumstances under which mantle exhumation may occur. We assume that the topmost continental and ocean <span class="hlt">lithosphere</span>, corresponding to the cooler brittle seismogenic layer, deforms by extensional faulting (pure-shear deformation) and magmatic intrusion, consistent with the observations of deformation processes occurring at slow spreading ocean ridges (Cannat, 1996). We assume that deformation beneath this topmost <span class="hlt">lithosphere</span> layer (approximately 15-20 km thick) occurs in response to passive upwelling and thermal and melt buoyancy driven small-scale convection. We use a 2D finite element viscous flow model (FeMargin) to describe <span class="hlt">lithosphere</span> and asthenosphere deformation. This flow field is used to advect <span class="hlt">lithosphere</span> and asthenosphere temperature and material. The finite element model is kinematically driven by Vx for the topmost upper crust inducing passive upwelling beneath that layer. A vertical velocity Vz is defined for buoyancy enhanced upwelling as predicted by Braun et al. (2000). Melt generation is predicted by decompression melting using the parameterization and methodology of Katz et al. (2003). Numerical experiments have been used to investigate the dependency of continental crust and <span class="hlt">lithosphere</span> rupture, decompression melt initiation, rifted margin ocean-continent transition architecture and subsidence history on the half-spreading rate Vx, buoyancy driven upwelling rate Vz, the relative contribution of these deformation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/9545216','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/9545216"><span>Osmium isotopic evidence for ancient subcontinental <span class="hlt">lithospheric</span> mantle beneath the kerguelen islands, southern indian ocean</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hassler; Shimizu</p> <p>1998-04-17</p> <p>Upper mantle xenoliths found in ocean island basalts are an important window through which the oceanic mantle <span class="hlt">lithosphere</span> may be viewed directly. Osmium isotopic data on peridotite xenoliths from the Kerguelen Islands, an archipelago that is located on the northern Kerguelen Plateau in the southern Indian Ocean, demonstrate that pieces of mantle of diverse provenance are present beneath the Islands. In particular, peridotites with unradiogenic osmium and ancient rhenium-depletion ages (to 1.36 x 10(9) years old) may be pieces of the Gondwanaland subcontinental <span class="hlt">lithosphere</span> that were incorporated into the Indian Ocean <span class="hlt">lithosphere</span> as a result of the rifting process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890035271&hterms=lithosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dlithosphere','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890035271&hterms=lithosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dlithosphere"><span>Plume formation and <span class="hlt">lithosphere</span> erosion - A comparison of laboratory and numerical experiments</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Olson, Peter; Schubert, Gerald; Anderson, Charles; Goldman, Peggy</p> <p>1988-01-01</p> <p>The mechanics of thermal plume formation and intrusion into the <span class="hlt">lithosphere</span> are investigated using a combination of laboratory and numerical simulations. The sequence of events leading to <span class="hlt">lithospheric</span> thinning and uplift by thermal plumes is established, and some numerical estimates of the time scales for each stage in this process are derived that are applicable to the mantle. It is demonstrated that the two-dimensional finite element computations successfully reproduce the qualitative features seen in the experiments, with a quantitative discrepancy of typically 30 percent or less. The results of some calculations on plume formation and intrusion into model <span class="hlt">lithospheres</span> with a variety of rheologies are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA566462','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA566462"><span>LITHO1.0: An Updated Crust and <span class="hlt">Lithosphere</span> Model of the Earth (Postprint)</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2012-03-22</p> <p>AFRL-RV-PS- AFRL-RV-PS- TP-2012-0048 TP-2012-0048 LITHO1.0: AN UPDATED CRUST AND <span class="hlt">LITHOSPHERE</span> MODEL OF THE EARTH (POSTPRINT...01 Sep 2010 to 21 Mar 2012 4. TITLE AND SUBTITLE LITHO1.0: AN UPDATED CRUST AND <span class="hlt">LITHOSPHERE</span> MODEL OF THE EARTH (POSTPRINT) An 5a...sets of longer period phase data that help to constrain deep <span class="hlt">lithosphere</span> properties. To model these data, a starting model for the crust at a nominal</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA530686','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA530686"><span>LITHO1.0: An Updated Crust and <span class="hlt">Lithosphere</span> Model of the Earth</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2010-09-01</p> <p>REPRINT 3. DATES COVERED (From • To) TITLE AND SUBTITLE -llTHOLO: AN UPDATED CRUST AND <span class="hlt">LITHOSPHERE</span> MODEL OF THE EARTH J 5a. CONTRACT NUMBER FA8718-09...developing LITHO1.0: an updated crust and <span class="hlt">lithosphere</span> model of the Earth. The overall plan is to take the popular CRUST2.0 model—a global model of crustal... <span class="hlt">lithospheric</span> structure. The new model. LITHO 1.0, will be constrained by many different datasets, including extremely large new datasets of relatively</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10521344','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10521344"><span>Continuous deformation versus faulting through the continental <span class="hlt">lithosphere</span> of new zealand</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Molnar; Anderson; Audoine; Eberhart-Phillips; Gledhill; Klosko; McEvilly; Okaya; Savage; Stern; Wu</p> <p>1999-10-15</p> <p>Seismic anisotropy and P-wave delays in New Zealand imply widespread deformation in the underlying mantle, not slip on a narrow fault zone, which is characteristic of plate boundaries in oceanic regions. Large magnitudes of shear-wave splitting and orientations of fast polarization parallel to the Alpine fault show that pervasive simple shear of the mantle <span class="hlt">lithosphere</span> has accommodated the cumulative strike-slip plate motion. Variations in P-wave residuals across the Southern Alps rule out underthrusting of one slab of mantle <span class="hlt">lithosphere</span> beneath another but permit continuous deformation of <span class="hlt">lithosphere</span> shortened by about 100 kilometers since 6 to 7 million years ago.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1814446B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1814446B"><span>Geodynamic inversion to constrain the rheology of the <span class="hlt">lithosphere</span>: What is the effect of elasticity?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baumann, Tobias; Kaus, Boris; Thielmann, Marcel</p> <p>2016-04-01</p> <p>The concept of elastic thickness (T_e) is one of the main methods to describe the integrated strength of oceanic <span class="hlt">lithosphere</span> (e.g. Watts, 2001). Observations of the Te are in general agreement with yield strength envelopes estimated from laboratory experiments (Burov, 2007, Goetze & Evans 1979). Yet, applying the same concept to the continental <span class="hlt">lithosphere</span> has proven to be more difficult (Burov & Diament, 1995), which resulted in an ongoing discussion on the rheological structure of the <span class="hlt">lithosphere</span> (e.g. Burov & Watts, 2006, Jackson, 2002; Maggi et al., 2000). Recently, we proposed a new approach, which constrains rheological properties of the <span class="hlt">lithosphere</span> directly from geophysical observations such as GPS-velocity, topography and gravity (Baumann & Kaus, 2015). This approach has the advantage that available data sets (such as Moho depth) can be directly taken into account without making the a-priori assumption that the <span class="hlt">lithosphere</span> is thin elastic plate floating on the mantle. Our results show that a Bayesian inversion method combined with numerical thermo-mechanical models can be used as independent tool to constrain non-linear viscous and plastic parameters of the <span class="hlt">lithosphere</span>. As the rheology of the <span class="hlt">lithosphere</span> is strongly temperature dependent, it is even possible to add a temperature parameterisation to the inversion method and constrain the thermal structure of the <span class="hlt">lithosphere</span> in this manner. Results for the India-Asia collision zone show that existing geophysical data require India to have a quite high effective viscosity. Yet, the rheological structure of Tibet less well constrained and a number of scenarios give a nearly equally good fit to the data. Yet, one of the assumptions that we make while doing this geodynamic inversion is that the rheology is viscoplastic, and that elastic effects do not significantly alter the large-scale dynamics of the <span class="hlt">lithosphere</span>. Here, we test the validity of this assumption by performing synthetic forward models and retrieving</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PhDT.......156D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PhDT.......156D"><span><span class="hlt">Lithospheric</span> structure beneath Eastern Africa from joint inversion of receiver functions and Rayleigh wave velocities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dugda, Mulugeta Tuji</p> <p></p> <p>Crust and upper mantle structure beneath eastern Africa has been investigated using receiver functions and surface wave dispersion measurements to understand the impact of the hotspot tectonism found there on the <span class="hlt">lithospheric</span> structure of the region. In the first part of this thesis, I applied H-kappa stacking of receiver functions, and a joint inversion of receiver functions and Rayleigh wave group velocities to determine the crustal parameters under Djibouti. The two methods give consistent results. The crust beneath the GEOSCOPE station ATD has a thickness of 23+/-1.5 km and a Poisson's ratio of 0.31+/-0.02. Previous studies give crustal thickness beneath Djibouti to be between 8 and 10 km. I found it necessary to reinterprete refraction profiles for Djibouti from a previous study. The crustal structure obtained for ATD is similar to adjacent crustal structure in many other parts of central and eastern Afar. The high Poisson's ratio and Vp throughout most of the crust indicate a mafic composition, suggesting that the crust in Afar consists predominantly of new igneous rock emplaced during the late synrift stage where extension is accommodated within magmatic segments by diking. In the second part of this thesis, the seismic velocity structure of the crust and upper mantle beneath Ethiopia and Djibouti has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities to obtain new constraints on the thermal structure of the <span class="hlt">lithosphere</span>. Crustal structure from the joint inversion for Ethiopia and Djibouti is similar to previously published models. Beneath the Main Ethiopian Rift (MER) and Afar, the <span class="hlt">lithospheric</span> mantle has a maximum shear wave velocity of 4.1-4.2 km/s and extends to a depth of at most 50 km. In comparison to the <span class="hlt">lithosphere</span> away from the East African Rift System in Tanzania, where the lid extends to depths of ˜100-125 km and has a maximum shear velocity of 4.6 km/s, the mantle <span class="hlt">lithosphere</span> under the Ethiopian Plateau</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S11C..05H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S11C..05H"><span>Dynamics of the Pacific Northwest <span class="hlt">Lithosphere</span> and Asthenosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Humphreys, E.</p> <p>2013-12-01</p> <p>Seismic imaging resolves a complex structure beneath the Pacific Northwest (PNW) that is interpreted as: an high-velocity piece of accreted (~50 Ma) Farallon <span class="hlt">lithosphere</span> that deepens from being exposed (at coast, where it is called Siletzia) to lower crust in SE Washington and then descending vertically to ~600 km as a 'curtain' beneath central Idaho; a stubby Juan de Fuca slab (to <250 km in most places, and with a gap beneath much of Oregon); and very slow 'fingers' above the slab with an especially anomalous volume beneath central Oregon. The evacuation of asthenosphere with the descending Juan de Fuca slab presents an interesting problem. Typical corner-flow supply is prevented because the mantle wind blows eastward. A stagnation line between mantle drawn west into the mantle wedge and that flowing east in the far field may exist near the Farallon curtain. Other sources of supply to the Cascadia mantle wedge include: mantle flowing north beneath California, entrained with the Pacific Plate; flow from below the Juan de Fuca slab, perhaps especially through the Oregon gap; toroidal flow around the southern edge of the slab; and possible up-flow beneath the backarc. Anisotropy studies suggest the importance of toroidal flow. PNW <span class="hlt">lithosphere</span> stress is dominated by N-S compression, a result of the Sierra Nevada driving the PNW into British Columbia; this push, and oblique subduction, are responsible for PNW clockwise rotation. Modeled (in 2D, map view) north-directed tractions on the Cascadia mega-thrust average ~4 TN per meter of along-strike fault length, or probably a shear stress of ~40 MPa over much of the locked mega-thrust (i.e., much more shear stress than the typical earthquake stress drop of 1-10 MPa). Normal to the coast, southern Cascadia is relatively tensional (where margin-normal compression is less than typical ridge push by ~4 TN/m of along-strike fault length) whereas northern Cascadia is compressional. This indicates that the southern Cascadia</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFM.T51C0901C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFM.T51C0901C"><span>Relict Oceanic <span class="hlt">Lithosphere</span> in Cuba: Types and Emplacement Ages</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>CobiellaReguera, J. L.</p> <p>2001-12-01</p> <p>According to their composition and tectonic position, three different types of relict oceanic <span class="hlt">lithosphere</span> are present in Cuba: (1) the northern ophiolitic belt, a complex melange that extents more than 1000 km along the island, (2) the basement of the Cretaceous volcanic arc terrane: high temperature/low pressure amphibolites with some serpentinites and, (3) tectonic slices of serpentinite melanges (with eclogites and blueschists) and high pressure amphibolites, in the metamorphic Escambray massif (tectonostratigraphic terrane, microcontinent?) of southcentral Cuba. Available age constrains (paleontological and geochronological) indicate that relicts of oceanic <span class="hlt">lithosphere</span> in Cuba are upper Mesozoic in age. Geochemical, petrological, and regional geology data suggest that such oceanic relicts probably originated in two different tectonic environments in the Proto-Caribbean basin; (1) a small oceanic basin of Upper Jurassic- Neocomian age, related to drift between North America and a southern continental mass and (2) a suprasubduction marginal basin, between the southeastern North American passive margin and an Aptian-Albian volcanic arc. Tectonic emplacement of the Cuban relict oceanic Proto-Caribbean <span class="hlt">lithosphere</span> was likely related to several tectonic events and processes. Serpentinite melange slices and the high pressure amphibolites in the Jurassic and Cretaceous passive margin sequences of Escambray massif, characterized by low to moderate temperature and high pressure metamorphism, probably were emplaced from subduction and closure of the small oceanic depression located to the south (present geographic coordinates) of the volcanic arc in the Albian. The basement amphibolites of the volcanic arc terrane were derived from the Upper Jurassic-Neocomian oceanic crust, metamorphosed by the high temperatures and hot solutions related to the development on this crust of an Aptian-Albian volcanic arc with a north dipping subduction zone. These amphibolites were</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ESRv..118...45T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ESRv..118...45T"><span>Widespread refertilization of cratonic and circum-cratonic <span class="hlt">lithospheric</span> mantle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tang, Yan-Jie; Zhang, Hong-Fu; Ying, Ji-Feng; Su, Ben-Xun</p> <p>2013-03-01</p> <p>Studies of mantle xenoliths have confirmed that Archean subcontinental <span class="hlt">lithospheric</span> mantle (SCLM) is highly depleted in basaltic components (such as Al, Ca and Na) due to high-degree extraction of mafic and ultramafic melts and thus is refractory and buoyant, which made it chronically stable as tectonically independent units. However, increasing studies show that ancient SCLM can be refertilized by episodic rejuvenation events like infiltration of upwelling fertile material. The North China Craton is one of the most typical cases for relatively complete destruction of its Archean keel since the eruption of Paleozoic kimberlites, as is evidenced by a dramatic change in the compositions of mantle xenoliths sampled by Paleozoic to Cenozoic magmas, reflecting significant <span class="hlt">lithospheric</span> thinning and the change in the character of the SCLM. The compositional change has been interpreted as the result of refertilization of Archean SCLM via multiple-stage peridotite-melt reactions, suggested by linear correlations between MgO and indices of fertility, covariations of Al2O3 with CaO, La/Yb, 87Sr/86Sr, 143Nd/144Nd, 187Os/188Os and Re-depletion ages (TRD), high Re abundances, scatter in Re-Os isotopic plot, variable in situ TRD ages of sulfides, and correlation between TRD ages and olivine Fo of peridotite xenoliths in Paleozoic kimberlites and Cenozoic basalts on the craton. By integrating major and trace element, Sr, Nd and Os isotopic compositions of peridotite xenoliths and orogenic massif peridotites from the continents of Europe, Asia, America, Africa and Australia, together with previous studies of petrology and geochemistry of global peridotites, we suggest that (1) refertilization of cratonic and circum-cratonic <span class="hlt">lithospheric</span> mantle is widespread; (2) Archean SCLM worldwide has experienced a multi-stage history of melt depletion and refertilization since segregation from the convecting mantle; (3) cratonic SCLM may be more susceptible to compositional change caused by</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMNH31B1608L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMNH31B1608L"><span>Numerical Simulation of Electromagnetic Field Variation in the <span class="hlt">Lithosphere</span>-Atmosphere-Ionosphere Associated with Seismogenic Process in a Curvature Coordinate System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, L.; Zhao, Z.; Wang, Y.; Huang, Q.</p> <p>2013-12-01</p> <p>The <span class="hlt">lithosphere</span>-atmosphere- ionosphere (LAI) system formed an electromagnetic (EM) cavity that hosts the EM field excited by electric currents generated by lightning and other <span class="hlt">natural</span> sources. There have also been numerous reports on variations of the EM field existing in LAI system prior to some significance earthquakes. We simulated the EM field in the <span class="hlt">lithosphere</span>-ionosphere waveguide with a whole-earth model using a curvature coordinate by the hybrid pseudo-spectral and finite difference time domain method. Considering the seismogensis as a fully coupled seismoelectric process, we simulate the seismic wave and the EM wave in this 2D model. In the model we have observed the excitation of the Schumann Resonance (SR) as the background EM field generated by randomly placed electric-current impulses within the lowest 10 kilometers of the atmosphere. The diurnal variation and the latitude-dependence in ion concentration in the ionosphere are included in the model. After the SR reaching a steady state, an electric impulse is introduced in the shallow <span class="hlt">lithosphere</span> to mimic the seismogenic process (pre-, co- and post-seismic) to assess the possible precursory effects on SR strength and frequency. The modeling results can explain the observed fact of why SR has a much more sensitive response to continental earthquakes, and much less response to oceanic events. The fundamental reason is simply due to the shielding effect of the conductive ocean that prevents effective radiation of the seismoelectric signals from oceanic earthquake events into the LAI waveguide.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014244','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014244"><span>Slab pull and the seismotectonics of subducting <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Spence, William</p> <p>1987-01-01</p> <p>This synthesis links many seismic and tectonic processes at subduction zones, including great subduction earthquakes, to the sinking of subducted plate. Earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force. Interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity, providing details on how subduction occurs. Compression is localized across a locked interface thrust zone, because both the ridge push and the slab pull forces are resisted there. The slab pull force increases with increasing plate age; thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone, the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate. The 1960 Chile earthquake (Mw 9.5), the largest earthquake to occur in historic times, began its rupture at an interface bounding oceanic plate <30 m.y. old. However, this rupture initiation was associated with the locally oldest subducting <span class="hlt">lithosphere</span> (weakest coupling); the rupture propagated southward along an interface bounding progressively younger oceanic <span class="hlt">lithosphere</span>, terminating near the subducting Chile Rise. Prior to a great subduction earthquake, the sinking subducted slab will cause increased tension at depths of 50–200 km, with greatest tension near the shallow zone resisting plate subduction. Plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260–350 km, provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle. This explains K. Mogi's observations of M ≥ 7 thrust earthquakes at depths of 260–350 km, immediately downdip and within 3 years prior to five great, shallow</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.5825P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.5825P"><span>Imprints of weak <span class="hlt">lithospheric</span> plate boundaries in the observed geoid.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petrunin, Alexey G.; Kaban, Mikhail K.; Schmeling, Harro; Shahraki, Meysam</p> <p>2014-05-01</p> <p>The observed geoid is highly sensitive to both: density-viscosity variations within the Earth and <span class="hlt">lithosphere</span> dynamics. While geoid undulations induced by the mantle dynamics is a subject of numerous studies, the effect of plate tectonics on the geoid and dynamic topography remains an open issue. In present study we investigate a joint effect of weak zones, dividing <span class="hlt">lithospheric</span> plates, and lateral viscosity variations (LVV) in the whole mantle on the observed geoid. A new numerical technique is based on the substantially revised method introduced by Zhang and Christensen (1993) for solving the Navier-Stokes-Poisson equations in the spectral domain with strong LVV. Weak plate boundaries (WPB) are introduced based on the integrated global model of plate boundary deformations GSRM (Kreemer et al., 2003). We show that the effect of WPB on the geoid is significant and reaches -40 m to 70 m with RMS ~20 m. Maximal WPB-related anomalies are observed over large subduction zones in South America and the Southwestern Pacific in agreement with previous studies. The positive geoid anomaly in South America could be explained largely by a dynamic effect of decoupling of the Nazca and South American plates. Mid-ocean ridges are mostly characterized by negative changes of the geoid compared to the model without WPB. The amplitude of the effect depends on the viscosity contrasts across WPB until its value reaches the limit of 2.5-3 orders of magnitude. This value might be considered as the level at which plates are completely decoupled. The effect of WPB alone, exceeds the effect of LVV in the whole mantle and generally does not correlate with it. However, inclusion of LVV reduces the geoid perturbations due to WPB by about 10 m. Therefore, it is important to consider all these factors together. The geoid changes mainly result from changes of the dynamic topography, which are about -300 to +500 m. The obtained results show that including WPB may significantly improve the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013SolED...5.1641H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013SolED...5.1641H"><span>Seismic structure of the <span class="hlt">lithosphere</span> beneath the ocean islands near the mid-oceanic ridges</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Haldar, C.; Kumar, P.; Kumar, M. Ravi</p> <p>2013-10-01</p> <p>Deciphering the seismic character of the young <span class="hlt">lithosphere</span> near the mid-oceanic ridges (MOR) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs, using the P-to-s conversions isolated from good quality data recorded at 5 broadband seismological stations situated on the ocean Islands in their vicinity. Estimates of the crustal and <span class="hlt">lithospheric</span> thickness values from waveform modeling of the P receiver function stacks reveal that the crustal thickness varies between 6 and 8 km with the corresponding depths to the <span class="hlt">lithosphere</span> asthenosphere boundary (LAB) varying between 43 and 68 km. However, the depth to the LAB at Macquire Island is intriguing in view of the observation of a thick (~ 87 km) <span class="hlt">lithosphere</span> beneath a relatively young crust. At three other stations i.e., Ascension Island, Sao Jorge and Easter Island, we find evidence for an additional deeper low velocity layer probably related to the presence of a hotspot.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGeo...97....1D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGeo...97....1D"><span><span class="hlt">Lithospheric</span> detachment of India and Tibet inferred from thickening of the mantle transition zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Duan, Yaohui; Tian, Xiaobo; Liu, Zhen; Zhu, Gaohua; Nie, Shitan</p> <p>2016-07-01</p> <p>To spatially and temporally interpret eruptive volcanic activity and plateau uplift, the dynamic model of the Himalayan-Tibetan orogen requires several scenarios in which the deep part of the <span class="hlt">lithosphere</span> is removed. The removed cold, dense material sank deeply and may rest in the mantle transition zone, which is considered as the graveyard for descending mantle <span class="hlt">lithosphere</span>. Beneath the Himalayas and southern Tibet, stacking teleseismic P-wave receiver functions reveal thickening of the mantle transition zone (MTZ), which is caused by decreasing temperatures. We interpret the MTZ thickening beneath southern Tibet as being a result of a remnant of detached thickened Tibet mantle <span class="hlt">lithosphere</span>, whereas the other thickening is most likely caused by a <span class="hlt">lithospheric</span> slab that detached from the Indian plate and is sinking into the MTZ beneath the Himalayas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP43C1263K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP43C1263K"><span>New insights from satellite magnetic gradient observations into the determination of Earth's <span class="hlt">lithospheric</span> field</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kotsiaros, S.; Olsen, N.; Finlay, C. C.</p> <p>2015-12-01</p> <p>Satellites provide a large stream of data with global coverage and are ideal for deriving global models of the Earth's magnetic field. However, the determination of smaller-scale <span class="hlt">lithospheric</span> magnetic field features is problematic because the <span class="hlt">lithospheric</span> signal is contaminated by much larger and highly time-dependent contributions from sources in the ionosphere and magnetosphere. New possibilities open with the three Swarm satellites which provide high quality, simultaneous, measurements from different locations. In addition, North-South and East-West magnetic field gradients can be approximated by employing along-track and across-track field differences which act as high-pass filters of the data and data kernel. We present improvements of conventional <span class="hlt">lithospheric</span> field modeling approaches to better determine the small-scale <span class="hlt">lithospheric</span> field by incorporating gradient information.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850058940&hterms=comer&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcomer','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850058940&hterms=comer&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcomer"><span>Mars - Thickness of the <span class="hlt">lithosphere</span> from the tectonic response to volcanic loads</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Comer, R. P.; Solomon, S. C.; Head, J. W.</p> <p>1985-01-01</p> <p>The response to loading of the elastic <span class="hlt">lithosphere</span> of Mars by seven large volcanic features is estimated based on the hypothesis of a flexural origin for a definable set of load-concentric graben. From the locations of such graben, or from their absence, the <span class="hlt">lithospheric</span> thickness and flexural rigidity are inferred. For the Tharsis montes, Alba Patera, and Elysium Mons, elastic <span class="hlt">lithospheric</span> thicknesses at the time of loading range from 20 to 50 km, assuming a Young's modulus of a trillion dyn/sq cm. The thickness exceeded 120 km beneath Olympus Mons and Isidis Planitia. The corresponding ranges in flexural rigidity are approximately 10 to the 30th to 31st dyn cm and greater than 10 to the 32nd dyn cm, respectively. These results indicate a local thinning of the <span class="hlt">lithosphere</span> beneath portions of the central regions of the Tharsis and Elysium volcanic provinces at the time of loading-induced fracturing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6024082','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6024082"><span><span class="hlt">Lithospheric</span> age dependence of off-ridge volcano production in the North Pacific</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Batiza, R.</p> <p>1981-08-01</p> <p>Data for numbers of seamounts on North Pacific Ocean crust of different age indicate that the production rate of new off-ridge seamounts (volcanoes) is proportional to the inverse of the square root of the age of the <span class="hlt">lithosphere</span>. This observation is consistent with several hypotheses which have been offered to explain the origin of off-ridge oceanic volcanism and, in combination with petrologic and paleomagnetic evidence for small oceanic volcanoes, leads to a new self-consistent model for off-ridge volcanism. In this model, the production rate of off-ridge volcanoes is controlled primarily by the availability of fracture-zone conduit systems in the thickening <span class="hlt">lithosphere</span>. In contrast, mantle plume or ''hotspot'' volcanoes may punch through the oceanic <span class="hlt">lithosphere</span>. Decreasing production rate of off-ridge volcanoes on old oceanic <span class="hlt">lithosphere</span> may be associated with decreasing extent of partial melting of chemically and isotopically heterogeneous mantle material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810048217&hterms=Evolution+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DEvolution%2Bevidence','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810048217&hterms=Evolution+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DEvolution%2Bevidence"><span>Evolution of planetary <span class="hlt">lithospheres</span> - Evidence from multiringed structures on Ganymede and Callisto</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mckinnon, W. B.; Melosh, H. J.</p> <p>1980-01-01</p> <p>The thickness and viscosity of a planetary <span class="hlt">lithosphere</span> increase with time as the mantle cools, with a thicker <span class="hlt">lithosphere</span> leading to the formation of one (or very few) irregular normal faults concentric to the crater. Since a gravity wave or tsunami induced by impact into a liquid mantle would result in both radial and concentric extension features, which are not observed in the case of the large impact structures on Ganymede and Callisto, an alternative mechanism is proposed in which the varying ice/silicate ratios, tectonic histories, and erosional mechanisms of the two bodies are considered to explain the subtle differences in thin <span class="hlt">lithosphere</span> ring morphology between Ganymede and Callisto. It is concluded that the present <span class="hlt">lithosphere</span> thickness of Ganymede is too great to permit the development of any rings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870055316&hterms=heat+density&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dheat%2Bdensity','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870055316&hterms=heat+density&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dheat%2Bdensity"><span>Limits on modes of <span class="hlt">lithospheric</span> heat transport on Venus from impact crater density</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grimm, Robert E.; Solomon, Sean C.</p> <p>1987-01-01</p> <p>Based on the observed density of impact craters on the Venus surface obtained from Venera 15-16 radar images, a formalism to estimate the upper bounds on the contributions made to <span class="hlt">lithospheric</span> heat transport by volcanism and <span class="hlt">lithospheric</span> recycling is presented. The Venera 15-16 data, if representative of the entire planet, limit the average rate of volcanic resurfacing on Venus to less than 2 cu km/yr (corresponding to less than 1 percent of the global heat loss), and limit the rate of <span class="hlt">lithospheric</span> recycling to less than 1.5 sq km/yr (and probably to less than 0.5 sq km/yr), corresponding to 25 percent (and to 9 percent) of the global heat loss. The present results indicate that heat loss at <span class="hlt">lithospheric</span> levels in Venus is dominated by conduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.1725K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.1725K"><span>Geodynamic constraints on stress and strength of the continental <span class="hlt">lithosphere</span> during India-Asia collision.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaus, B. J. P.; Schmalholz, S. M.; Lebedev, S.; Deschamps, F.</p> <p>2009-04-01</p> <p>There has been quite some debate in recent years on what the long-term strength of the continental <span class="hlt">lithosphere</span> is and how it is related to the occurrence of earthquakes. One of the best studied areas in this respect is the India-Asia collision zone, where -in some profiles- the Moho depth is known to within a few km's. A relocation of earthquake source locations revealed that in India earthquakes occur throughout the whole <span class="hlt">lithosphere</span> whereas in Tibet, earthquakes are restricted to the upper 10-15 km of the crust with few exceptions slightly above or below the Moho. The lack of substantial earthquake activity in the sub-Moho mantle <span class="hlt">lithosphere</span> seems puzzling since (1D) strength envelop models for the continental <span class="hlt">lithosphere</span> predict large differential stresses (and brittle failure) in these locations. A way out of this paradox is to assume that the rheology of the mantle <span class="hlt">lithosphere</span> (i.e. the effective viscosity) is significantly smaller than usually assumed, either because of the effects of hydration, or because of increased Moho temperatures. As a consequence, the strength of the <span class="hlt">lithosphere</span> resides in the crust and not in the upper mantle as previously assumed. This conclusion gets some support from spectral-based inverse models of the effective elastic thickness (using topography and gravity as input data), which is typically smaller than the seismogenic thickness. Even though this explanation might appear appealing at first, there are at least two major problems with it: (1) Estimations of the effective elastic thickness (EET) of the <span class="hlt">lithosphere</span> are non-unique and model-dependent. Others, using a direct (non-spectral) modelling approach, find significantly larger values of the EET in the same locations (again using gravity & topography as constraints). (2) Long term geodynamic models indicate that if the mantle <span class="hlt">lithosphere</span> would indeed be as weak as suggested, it would be very difficult to generate plate-tectonics like behavior: Subducting slabs behave more</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V41E..06J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V41E..06J"><span>Support for a Uniformitarian Model of Continental Mantle <span class="hlt">Lithosphere</span> Formation from the "Near-Cratonic" Composition of Proterozoic Southern African Mantle <span class="hlt">Lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Janney, P. E.</p> <p>2014-12-01</p> <p>The transition at the end of the Archean between the generation of cratonic and mobile belt continental <span class="hlt">lithosphere</span> is regarded as a first-order change in the mode of generation of continental <span class="hlt">lithosphere</span>. It is widely debated whether this transition represented a fundamental change in the process by which the <span class="hlt">lithospheric</span> mantle was generated (i.e., as melting residues of deep-seated mantle upwellings to residues of relatively shallow mantle melting at subduction zones), or whether it primarily reflected a more gradual change in the conditions (i.e., temperatures, depths and degrees of melting) of <span class="hlt">lithosphere</span> generation in a suprasubduction zone setting. The marked contrast, in many cases, between the major element compositions of peridotite xenoliths from Archean cratons and those from adjacent post-Archean mobile belts has accentuated the significance of this transition. Peridotite xenoliths from the post-Archean mobile belt terranes surrounding the Kaapvaal craton in southern Africa are clearly Proterozoic in age from Re-Os isotope constraints, but they are unusual in that they share several key similarities in composition and mineralogy with Archean Kaapvaal peridotites (e.g., low bulk-rock Al2O3, relatively low modal olivine and high modal orthopyroxene). Although they lack the low FeO and high olivine Mg# values of the most extreme Kaapvaal samples, they show a very large degree of overlap (extending to olivine Mg# values of greater than 93 for example). These similarities support a common mode of origin for cratonic and post-cratonic <span class="hlt">lithosphere</span> in southern Africa (although varying somewhat in the degrees and depths of melt extraction) and a similar history of post-formation modification. A comparison of the conditions of melt extraction for cratonic and post-cratonic <span class="hlt">lithosphere</span> inferred from compatible and mildly incompatible trace elements will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Tectp.691..263S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Tectp.691..263S"><span>Apparently-deep events in the Middle Atlas resolved to be shallow: Implications for <span class="hlt">lithospheric</span> deformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Singh, Shashwat K.; Bezada, Maximiliano J.; Elouai, Driss; Harnafi, Mimoun</p> <p>2016-11-01</p> <p>The occurrence of intermediate depth seismicity in intracontinental settings is rare, but it has been postulated with various degrees of certainty in several regions. One such region is the Middle Atlas of Morocco. Since 1960, 75 intermediate depth earthquakes have been reported in this region by Spain's National Geographic Institute (IGN). The apparent deep <span class="hlt">nature</span> of these events is hard to reconcile with well-established geophysical evidence of a thin <span class="hlt">lithosphere</span> under the Middle Atlas, but has been associated with mantle delamination processes. We relocate 4 events with IGN-reported depths > 80 km that were recorded by a relatively dense temporary deployment; using a recent regional 3D velocity model obtained through teleseismic body and surface wave tomography. The relocation procedure uses a grid-search approach to minimize the mean normalized misfit, where each travel-time misfit is normalized by the estimated pick uncertainty. We find that our observed arrivals are much better fit by shallow (< 5 km) depths than the reported depths of > 80 km. We propose that these shallow foci earthquakes are the result of regional crustal deformation of this region caused by the present convergence between Africa and Eurasian Plate. We infer that if there are any ongoing delamination processes in the area, they are aseismic. This study is an example of how local earthquake locations in tectonically complex areas can be significantly improved by using a dense local seismic array and a well-constrained 3-D velocity model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012IzPSE..48..486G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012IzPSE..48..486G"><span>The phenomenon of synchronism in the magnetosphere-technosphere-<span class="hlt">lithosphere</span> dynamical system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guglielmi, A. V.; Zotov, O. D.</p> <p>2012-06-01</p> <p>Synchronism in geophysical events became the focus of the research in the second half of the last century when the study of this subject was almost simultaneously launched in the former Soviet Union and the United States. Interest in this issue has recently risen after a 20-year hiatus. The impetus was provided by the successful application of the synchronous detection technique to analyzing vast volumes of digital data on the electromagnetic waves in the magnetosphere and on the earthquakes. These studies revealed signs of the strictly periodic synchronous influence of the technosphere on the regime of electromagnetic oscillations in cosmic plasma and on seismic activity. The phenomenon of synchronism between the electromagnetic and seismic events manifests itself in the form of the so-called hour-mark effect and the weekend effect. The hourmark effect shows itself in the 24th, 48th, and 96th harmonics, and the weekend effect, in the 7th subharmonic of the circadian rhythm. The both effects indicate that the technosphere has a nontrivial impact on the magnetosphere and <span class="hlt">lithosphere</span>. The present review aims to introduce the morphology of the phenomenon and to focus the attention of researchers on the physical interpretation of the effects of synchronism, which is a challenging problem. Both the fundamental and practical value of the problem is analyzed. In particular, it is hypothesized that the study of the anthropogenic modulation of the <span class="hlt">natural</span> wave processes will promote the development of energy saving technologies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T23A2574S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T23A2574S"><span>Seismic evidence for stratification in composition and anisotropic fabric within the thick <span class="hlt">lithosphere</span> of Kalahari Craton</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sodoudi, F.; Yuan, X.; Kind, R.; Lebedev, S.; Tilmann, F. J.</p> <p>2013-12-01</p> <p>S receiver functions obtained from the data of 97 seismic stations present evidence for the existence of a layered and thick <span class="hlt">lithosphere</span> beneath the Kalahari Craton. We identified three negative discontinuities within the <span class="hlt">lithosphere</span> of the Archean cratons and Proterozoic mobile belts of southern Africa. We also employed a novel combination of SRFs and surface-wave analysis to constrain the anisotropic properties of the <span class="hlt">lithosphere</span> and its internal layering. Our results show that frozen-in anisotropy and compositional changes can generate sharp Mid-<span class="hlt">Lithospheric</span> Discontinuities (MLD) at depths of 85 and 150-200 km, respectively. We found that a 50 km thick anisotropic layer containing 3% S wave anisotropy and with a fast-velocity axis different from that in the layer beneath can account for the first MLD at about 85 km depth. This depth is largely consistent with that of 8° discontinuity suggested as a global characteristic of cratonic <span class="hlt">lithosphere</span>. Significant correlation between the depths of an apparent boundary separating the depleted and metasomatic refertilized <span class="hlt">lithosphere</span>, as inferred from chemical tomography, and those of our second MLD (at 150-200 km depth) led us to characterize this negative discontinuity as a compositional boundary, most likely due to the modification of the cratonic mantle <span class="hlt">lithosphere</span> by magma infiltration. We detected this MLD at a depth of about 150 km beneath the Zimbabwe Craton and Limpopo belt with a steep deepening to about 200 km underneath the Kaapvaal Craton and its passive margin. The deepening of this boundary is spatially correlated with the surficial expression of the ancient Thabazimbi-Murchison Lineament (TML). This may imply that the translithospheric TML isolates the <span class="hlt">lithospheric</span> block of the relatively younger Limpopo terrane from that of the ancient Kaapvaal terrane. Finally, the largest velocity contrast (3.6-4.7%) is observed at a boundary located at depths of 260-280 km beneath the Archean domains and the older</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011Litho.125..729M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011Litho.125..729M"><span>Constraints on the depth and thermal history of cratonic <span class="hlt">lithosphere</span> from peridotite xenoliths, xenocrysts and seismology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mather, Kathy A.; Pearson, D. Graham; McKenzie, Dan; Kjarsgaard, Bruce A.; Priestley, Keith</p> <p>2011-07-01</p> <p>Despite the relatively long-standing availability of numerical approaches for estimating palaeogeotherms using peridotite xenolith Pressure-Temperature (P-T) data, the practise of fitting xenolith P-T arrays to simple models of <span class="hlt">lithospheric</span> heat generation, in a non-quantitative manner, remains widespread. The lack of quantification in both the magnitude and uncertainty of heat flow and <span class="hlt">lithosphere</span> thickness estimates leads to difficulty in evaluating proposed models for <span class="hlt">lithosphere</span> evolution on a local and regional scale. Here, we explore the advantages of using a numerical approach to palaeogeotherm fitting, in terms of the ability to make objective comparisons of the effect that differing thermobarometer combinations and varying states of mineral and textural equilibrium have on the shape of the palaeogeotherm, and the resulting estimates of <span class="hlt">lithospheric</span> thickness and heat flow. We also make quantitative comparisons between <span class="hlt">lithospheric</span> mantle properties estimated using peridotite xenoliths versus single mineral xenocrysts. Using two reference peridotite xenolith databases from Bultfontein (S. Africa) and Somerset Island (Canada) we show that the same <span class="hlt">lithospheric</span> mantle properties are predicted using harzburgite versus lherzolite thermobarometry methods. Filtering mineral data for the effects of inter-mineral disequilibrium does not produce significantly different palaeogeotherms but does increase the quality of fit of the palaeogeotherm to the P-T data, allowing more confidence to be placed in comparisons between locations. Palaeogeotherms calculated using xenocryst data, screened for peridotitic affinities, show misfits that are 2-3 times greater than those obtained using xenoliths. <span class="hlt">Lithospheric</span> properties calculated from the Somerset Island xenocryst-based geotherm yield results that are within error of the xenolith estimate. A mutually consistent and quantitative palaeogeotherm fitting approach is used to evaluate existing hypotheses for the evolution of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005IJEaS..94..594Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005IJEaS..94..594Z"><span>Evolution of the <span class="hlt">lithosphere</span> in the area of the Rhine Rift System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ziegler, P. A.; Dèzes, P.</p> <p>2005-09-01</p> <p>The Rhine Rift System (RRS) forms part of the European Cenozoic Rift System (ECRIS) and transects the Variscan Orogen, Permo-Carboniferous troughs and Late Permian to Mesozoic thermal sag basins. Crustal and <span class="hlt">lithospheric</span> thicknesses range in the RRS area between 24 36 km and 50 120 km, respectively. We discuss processes controlling the transformation of the orogenically destabilised Variscan <span class="hlt">lithosphere</span> into an end-Mesozoic stabilised cratonic <span class="hlt">lithosphere</span>, as well as its renewed destabilisation during the Cenozoic development of ECRIS. By end-Westphalian times, the major sutures of the Variscan Orogen were associated with 45 60 km deep crustal roots. During the Stephanian-Early Permian, regional exhumation of the Variscides was controlled by their wrench deformation, detachment of subducted <span class="hlt">lithospheric</span> slabs, asthenospheric upwelling and thermal thinning of the mantle-<span class="hlt">lithosphere</span>. By late Early Permian times, when asthenospheric temperatures returned to ambient levels, <span class="hlt">lithospheric</span> thicknesses ranged between 40 km and 80 km, whilst the thickness of the crust was reduced to 28 35 km in response to its regional erosional and local tectonic unroofing and the interaction of mantle-derived melts with its basal parts. Re-equilibration of the <span class="hlt">lithosphere</span>-asthenosphere system governed the subsidence of Late Permian-Mesozoic thermal sag basins that covered much of the RRS area. By end-Cretaceous times, <span class="hlt">lithospheric</span> thicknesses had increased to 100 120 km. Paleocene mantle plumes caused renewed thermal weakening of the <span class="hlt">lithosphere</span>. Starting in the late Eocene, ECRIS evolved in the Pyrenean and Alpine foreland by passive rifting under a collision-related north-directed compressional stress field. Following end-Oligocene consolidation of the Pyrenees, west- and northwest-directed stresses originating in the Alps controlled further development of ECRIS. The RRS remained active until the Present, whilst the southern branch of ECRIS aborted in the early Miocene. Extensional</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1814533L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1814533L"><span><span class="hlt">Lithosphere</span> erosion and breakup due to the interaction between extension and plume upwelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lavecchia, Alessio; Thieulot, Cedric; Beekman, Fred; Cloetingh, Sierd; Clark, Stuart</p> <p>2016-04-01</p> <p>We have built up 2D numerical models of coupled crust - <span class="hlt">lithospheric</span> mantle - upper mantle systems. The reconstructed sections are subjected to external velocity fields and mantle plume impingement beneath the <span class="hlt">lithosphere</span>, both acting simultaneously. The models are designed to simulate the interaction between plumes and <span class="hlt">lithosphere</span> in an extensional setting with the main purpose to contribute to address the following questions: 1) Are plumes capable of weakening certain <span class="hlt">lithospheric</span> regions? Where and when are the main effects observed? 2a) Can a plume really cause a plate break-off and drifting with no external contribution; 2b) if yes, are there any particularly favorable conditions required? In our models a novel aspect is melt generation due to plume, upper mantle and <span class="hlt">lithospheric</span> mantle partial melting. Produced melts are capable to ascend across the reconstructed sections due to buoyancy. Furthermore, heat transport related to melt movement is taken into account and leads to a significant heating of host rocks at the melt neutral buoyancy depth. In absence of external stress or velocity fields, the effects of plume impingement beneath the <span class="hlt">lithosphere</span> are negligible at surface. Here the main observed feature is the production of doming at various length scales, depending on the adopted rheology for the crust. At depth, the main effect is a thermo-mechanical erosion of the <span class="hlt">lithospheric</span> mantle with production of melts and subsequent underplating of the crust. The heat flux due to plume impingement and crust underplating determines a weakening of crust and <span class="hlt">lithosphere</span>. However, the strength drop is not followed by an appreciable deformation. When external stress or velocity fields are applied, the coupled effects with plume presence and melt production lead to great modifications of the <span class="hlt">lithospheric</span> structure. Topography profiles are characterized by the presence of a horst and graben structure, and extensive erosion of the <span class="hlt">lithosphere</span> always occurs. The presence</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JSG....33..537P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JSG....33..537P"><span>Grainsize evolution in ductile shear zones: Implications for strain localization and the strength of the <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Platt, J. P.; Behr, W. M.</p> <p>2011-04-01</p> <p>At high stresses and low temperatures, grainsize reduction by dynamic recrystallization profoundly modifies rock rheology. Strain energy driven grain-boundary migration (ρGBM) is involved both in the nucleation of new grains by the grain-boundary bulging mechanism (BLG), and in the subsequent evolution of the microstructure. Above the Dmin line, which is a line in stress/grainsize space that defines the minimum size of nucleus that can form by BLG, ρGBM dominates the microstructure, and grain growth by surface energy driven grain-boundary migration (γGBM) is inhibited. The recrystallized grainsize is therefore dominated by the nucleation process, possibly controlled by the size of subgrains or dislocation cells within the old grains. This provides a first-order explanation for the experimentally observed grainsize-stress relationship. ρGBM is an important agent of recovery in rocks deformed by dislocation creep, sweeping out dislocations and counteracting work-hardening. We have derived a new flow law (DRX-assisted dislocation creep) based on this process, which exhibits grainsize sensitivity as a result of the role of ρGBM. If grainsize obeys the empirically-determined grainsize-stress relationship, DRX creep has an effective stress exponent of a little over 4, consistent with experimental observations and inferences from <span class="hlt">naturally</span> deformed rocks. DRX creep may be an important agent in weakening quartz at low temperatures, whereas current flow law data suggest it may not be important in olivine. Rocks deformed and dynamically recrystallized above the Dmin line may switch from climb-assisted dislocation creep to grainsize-sensitive creep (Coble creep, DRX creep, or creep dominated by grain-boundary sliding), resulting in weakening. <span class="hlt">Lithospheric</span>-scale shear zones are likely to evolve at approximately constant stress; under these conditions weakening results in an increase in strain rate, not a stress drop. The rate of dislocation motion, the dislocation density</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T11B1810W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T11B1810W"><span><span class="hlt">Lithosphere</span> structure of the west Qinling orogenic belt revealed by deep seismic reflection profile</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, H.</p> <p>2009-12-01</p> <p>The west Qinling orogen located in the northeastern margin of the Qinghai-Tibet plateau, is transformation zone between the N-S-trending and E-W-trending tectonics in the Chinese continent. Further study of the fine crust structure of the west Qinling orogen and its relationships with surrounding basins have very important significance for understanding tectonic response of the northeastern margin of the plateau about collision convergence of the Indian block and Asian block and learning formation and evolution of the plateau. In 2009, we reprocessed the data of the Tangke-Hezuo deep seismic reflection profiles collected in 2004 across the west Qinling orogen and the northern Songpan block. The new results show the <span class="hlt">lithosphere</span> fine structure of the west Qinling orogen. Reflection features indicate that an interface at 6.0-7.0s (TWT) divided the crust into the upper and lower crust, whose structural style and deformation are totally different. Integrating geological data, we deduce that the interface at 6.0-7.0s (depth with 18-21 km) was the basement detachment, which made deformation decoupled of the upper and lower crust. The multi-layered reflections in the upper crust reveal the sedimentary covers of the west Qinling orogen, disclose the thickness of the various structure layer and deformation degree, and provide a basis for the prospective evaluation of a multi-metallic mineral and energy exploration. The north dipping strong reflection characteristics of the lower crust in the west Qinling orogen constituted imbricate structure, such imbricate structural features provide seismology evidence for researching the west Qinling thrusting toward the northern Songpan block, and have great significance for studying formation and evolution of the Songpan-Garze structure. Moho reflections are observed around 17.0-17.2s, characterized by nearly horizontal reflections, which implies the west Qinling orogen underwent an intense extension post orogeny caused the <span class="hlt">lithosphere</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMNH31C1620X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMNH31C1620X"><span>Geophysical Exploration Technologies for the Deep <span class="hlt">Lithosphere</span> Research: An Education Materials for High School Students</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, H.; Xu, C.; Luo, S.; Chen, H.; Qin, R.</p> <p>2012-12-01</p> <p>The science of Geophysics applies the principles of physics to study of the earth. Geophysical exploration technologies include the earthquake seismology, the seismic reflection and refraction methods, the gravity method, the magnetic method and the magnetotelluric method, which are used to measure the interior material distribution, their structure and the tectonics in the <span class="hlt">lithosphere</span> of the earth. Part of the research project in SinoProbe-02-06 is to develop suitable education materials for carton movies targeting the high school students and public. The carton movies include five parts. The first part includes the structures of the earth's interior and variation in their physical properties that include density, p-wave, s-wave and so on, which are the fundamentals of the geophysical exploration technologies. The second part includes the seismology that uses the propagation of elastic waves through the earth to study the structure and the material distribution of the earth interior. It can be divided into earthquake seismology and artifice seismics commonly using reflection and refraction. The third part includes the magnetic method. Earth's magnetic field (also known as the geomagnetic field)extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun. The aim of magnetic survey is to investigate subsurface geology on the basis of anomalies in the Earth's magnetic field resulting from the magnetic properties of the underlying rocks. The magnetic method in the <span class="hlt">lithosphere</span> attempts to use magnetic disturbance to analyse the regional geological structure and the magnetic boundaries of the crust. The fourth part includes the gravity method. A gravity anomaly results from the inhomogeneous distribution of density of the Earth. Usually gravity anomalies contain superposed anomalies from several sources. The long wave length anomalies due to deep density contrasts are called regional anomalies. They are</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.5761I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.5761I"><span><span class="hlt">Lithospheric</span> architecture of the Levant Basin (Eastern Mediterranean region): A 2D modeling approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Inati, Lama; Zeyen, Hermann; Nader, Fadi-Henri; Adelinet, Mathilde; Sursock, Alexandre; Rahhal, Muhsin Elie; Roure, Francois</p> <p>2016-04-01</p> <p>One of the major uncertainties regarding the Levant Basin, known to be the site of rifting in the Late Paleozoic and Early Mesozoic, concerns its deep crustal configuration despite numerous old and recent geophysical studies in this region. The aim of this study is to deduce the deep structure of the <span class="hlt">lithosphere</span> underlying the easternmost Mediterranean region, in particular the Levant Basin and its margins, where the <span class="hlt">nature</span> of the crust, continental versus oceanic, remains debated and has major implications on understanding the regional tectonic and thermal evolution, and on constraining potential petroleum systems. The algorithm used is a trial and error method that delivers the crustal thickness and the depth of the <span class="hlt">lithosphere</span>-asthenosphere boundary (LAB) as well as the crustal density distribution by integrating surface heat flow data, free-air gravity anomaly, Geoid and topography data. Moho depth and crustal thickness were locally constrained by refraction data where available. The models representing two EW sections show a progressively attenuated crystalline crust in an EW direction (35 to 8 km). The SN section represents a 12 km thick crust to the south, thins to 9-7 km towards the Lebanese coast and reaches 20 km in the north. The crystalline crust is best interpreted as a strongly thinned continental crust under the Levant Basin, represented by two distinct components, an upper and a lower crust. Nevertheless, the Herodotus Basin shows a thin crust, likely oceanic, with a thickness between 6 and 10 kms. West of the Eratosthenes Seamount, a local crustal anomaly is interpreted to be the result of an underlying continental crust with a thickness of 13 kms. The Moho under the Arabian plate is 35-40 km deep and becomes shallower towards the Mediterranean coast. Within the Levant Basin, the Moho appears to be situated between 20 and 23 km, reaching 26 km in the Herodotus Basin. While depth to LAB is around 110 km under the Arabian and the Eurasian plates, it</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFM.S61A1105G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFM.S61A1105G"><span>Gravity Field Analysis and 3D Density Modeling of the <span class="hlt">Lithosphere</span> Along the Dead Sea Transform</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goetze, H.; Ebbing, J.; Hese, F.; Kollersberger, T.; Schmidt, S.; Rybakov, M.; Hassouneh, M.; Hrahsha, M.; El Kelani, R.</p> <p>2002-12-01</p> <p>The gravity field of Dead Sea Rift / Dead Sea Transform was investigated with regard to the isostatic state, the crustal density structure of the orogeny and the rigidity of the <span class="hlt">lithosphere</span> in the Central Arava Valley. Our multi-national and interdisciplinary gravity group with participants from the Geophysical Institute of Israel, the <span class="hlt">Natural</span> Resources Authority (Jordan), and the An-Najah National University (Palestine), is aiming to study the crustal density structure, the isostatic state of the <span class="hlt">lithosphere</span> and mechanical properties of the Dead Sea Rift system under the framework of the international DESERT program which is coordinated by the GeoForschungsZentrum (GFZ, Potsdam, Germany). The study area is located about 100 km away from both the basin of the Dead Sea and the Gulf of Elat/Aqaba basin, respectively. Between March and May 2002 some 800 new gravity observations were recorded at a local (Arava valley) and regional scale (along the DESERT seismic line). Station spacing in the Arava valley was 100 - 300 m and in the nearest neighborhood of the fault 50 m only. The survey of detailed observations covered an area of 10 by 10 km and was completed by a likewise dense survey at the western side of the valley in Israel. All gravity data were tied to the IGSN -71 gravity datum and are terrain-corrected as well. The station complete Bouguer gravity field, Free air anomaly and residual isostatic anomalies (based on both Airy and Vening-Meinesz models) were merged with the existing regional gravity data bases of the region. Constraining information for the 3D density models at regional and local came from recent geophysical field data acquisition and consist of seismic, seismological, electromagnetic, and geologic studies which represent the integrated part of the interdisciplinary research program. Novel methods e.g. curvature techniques, and Euler deconvolution of the gravity fields shed new insight into the structure of upper and lower crust and the causing</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140013140','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140013140"><span>Constraining the Composition of the Subcontinental <span class="hlt">Lithospheric</span> Mantle Beneath the East African Rift: FTIR Analysis of Water in Spinel Peridotite Mantle Xenoliths</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Erickson, Stephanie Gwen; Nelson, Wendy R.; Peslier, Anne H.; Snow, Jonathan E.</p> <p>2014-01-01</p> <p>The East African Rift System was initiated by the impingement of the Afar mantle plume on the base of the non-cratonic continental <span class="hlt">lithosphere</span> (assembled during the Pan-African Orogeny), producing over 300,000 kmof continental flood basalts approx.30 Ma ago. The contribution of the subcontinental <span class="hlt">lithospheric</span> mantle (SCLM) to this voluminous period of volcanism is implied based on basaltic geochemical and isotopic data. However, the role of percolating melts on the SCLM composition is less clear. Metasomatism is capable of hybridizing or overprinting the geochemical signature of the SCLM. In addition, models suggest that adding fluids to <span class="hlt">lithospheric</span> mantle affects its stability. We investigated the <span class="hlt">nature</span> of the SCLM using Fourier transform infrared spectrometry (FTIR) to measure water content in mantle xenoliths entrained in young (1 Ma) basaltic lavas from the Ethiopian volcanic province. The mantle xenoliths consist dominantly of spinel lherzolites and are composed of nominally anhydrous minerals, which can contain trace water as H in mineral defects. Eleven mantle xenoliths come from the Injibara-Gojam region and two from the Mega-Sidamo region. Water abundances of olivines in six samples are 1-5ppm H2O while the rest are below the limit of detection (<0.5 ppm H2O); orthopyroxene and clinopyroxene contain 80-238 and 111-340 ppm wt H2O, respectively. Two xenoliths have higher water contents - a websterite (470 ppm) and dunite (229 ppm), consistent with involvement of ascending melts. The low water content of the upper SCLM beneath Ethiopia is as dry as the oceanic mantle except for small domains represented by percolating melts. Consequently, rifting of the East African <span class="hlt">lithosphere</span> may not have been facilitated by a hydrated upper mantle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V32B..02S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V32B..02S"><span>Tracing the thermal evolution of continental <span class="hlt">lithosphere</span> through depth-dependent extension</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smye, A.; Lavier, L. L.; Stockli, D. F.; Zack, T.</p> <p>2015-12-01</p> <p>Rifting of continental <span class="hlt">lithosphere</span> requires a mechanism to reduce <span class="hlt">lithospheric</span> thickness from 100-150 kilometers to close to zero kilometers at the point of rupture. At magma-poor continental margins, this has long-thought to be caused by uniform stretching and thinning of the <span class="hlt">lithosphere</span> accompanied by passive upwelling of the asthenosphere [1]. For the last thirty years depth-dependent thinning has been proposed as an alternative to this model to explain the anomalously shallow environment of deposition along many continental margins [2, 3]. A critical prediction of this modification is that the lower crust and sub-continental <span class="hlt">lithospheric</span> mantle undergo a phase of increased heat flow, potentially accompanied by heating, during thinning of the <span class="hlt">lithospheric</span> mantle. Here, we test this prediction by applying recently developed U-Pb age depth profiling techniques [4] to lower crustal accessory minerals from the exhumed Alpine Tethys and Pyrenean margins. Inversion of diffusion-controlled U-Pb age profiles in rutile affords the opportunity to trace the thermal evolution of the lower crust through the rifting process. Resultant thermal histories are used to calculate thinning factors of the crust and <span class="hlt">lithospheric</span> mantle by 2D thermo-kinematic models of extending <span class="hlt">lithosphere</span>. Combined, we use the measured and modeled thermal histories to propose a mechanism to explain the initiation and growth of <span class="hlt">lithospheric</span> instabilities that lead to depth-dependent thinning at magma-poor continental margins. [1] McKenzie, D. (1978) EPSL 40, 25-32; [2] Royden, L. & Keen, C. (1980) EPSL 51, 343-361; [3] Huismans, R. & Beaumont, C. (2014) EPSL, 407, 148-162; [4] Smye, A. and Stockli, D. (2014) EPSL, 408, 171-182.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRB..118.6025Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRB..118.6025Z"><span><span class="hlt">Lithospheric</span> deformation induced by loading of the Hawaiian Islands and its implications for mantle rheology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhong, Shijie; Watts, A. B.</p> <p>2013-11-01</p> <p>long-term rheological properties of the <span class="hlt">lithosphere</span> are fundamental for understanding both surface tectonics and mantle dynamics on Earth. In this study, we have developed 3-D finite element models for computing the load-induced surface deformation and stress for <span class="hlt">lithosphere</span> and mantle with realistic nonlinear viscoelastic rheology including the frictional sliding, low-temperature plasticity, and high-temperature creep. We have determined the <span class="hlt">lithospheric</span> deformation and stress due to volcano loading in the Hawaiian Islands region for the last few million years. By comparing model predictions with seismic observations of the depth to the top of oceanic crust and depth dependence of seismicity in the Hawaiian Islands region, we have sought to constrain <span class="hlt">lithospheric</span> rheology. Our calculations show that the load-induced surface deformation is controlled by low-temperature plasticity and frictional sliding but is insensitive to high-temperature creep. <span class="hlt">Lithospheric</span> strength predicted from laboratory-derived low-temperature plasticity needs to be reduced significantly, and a frictional coefficient μf ranging from 0.1 to 0.7 is required in order to account for the observations. However, μf = 0.1 weakens the shallow part of the <span class="hlt">lithosphere</span> so much that it causes the minima in strain rate and stress to occur at too large depths to be consistent with the observed depth distribution of seismicity. Our results therefore suggest a value for μf between 0.25 and 0.7. Finally, the maximum stress that accumulates in the deformed <span class="hlt">lithosphere</span> beneath the Hawaiian Islands is about 100-200 MPa for models that match the observations, and this stress may be viewed as the largest <span class="hlt">lithospheric</span> stress on Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890010707','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890010707"><span><span class="hlt">Lithospheric</span> buckling and intra-arc stresses: A mechanism for arc segmentation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nelson, Kerri L.</p> <p>1989-01-01</p> <p>Comparison of segment development of a number of arcs has shown that consistent relationships between segmentation, volcanism and variable stresses exists. Researchers successfully modeled these relationships using the conceptual model of <span class="hlt">lithospheric</span> buckling of Yamaoka et al. (1986; 1987). <span class="hlt">Lithosphere</span> buckling (deformation) provides the needed mechanism to explain segmentation phenomenon; offsets in volcanic fronts, distribution of calderas within segments, variable segment stresses and the chemical diversity seen between segment boundary and segment interior magmas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JGRB..114.3202L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JGRB..114.3202L"><span><span class="hlt">Lithospheric</span> mantle duplex beneath the central Mojave Desert revealed by xenoliths from Dish Hill, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Luffi, Peter; Saleeby, Jason B.; Lee, Cin-Ty A.; Ducea, Mihai N.</p> <p>2009-03-01</p> <p>Low-angle subduction of oceanic <span class="hlt">lithosphere</span> may be an important process in modifying continental <span class="hlt">lithosphere</span>. A classic example is the underthrusting of the Farallon plate beneath North America during the Laramide orogeny. To assess the relevance of this process to the evolution and composition of continental <span class="hlt">lithosphere</span>, the mantle stratigraphy beneath the Mojave Desert was constrained using ultramafic xenoliths hosted in Plio-Pleistocene cinder cones. Whole-rock chemistry, clinopyroxene trace element and Nd isotope data, in combination with geothermometry and surface heat flow, indicate kilometer-scale compositional layering. The shallow parts are depleted in radiogenic Nd (ɛNd = -13 to -6.4) and are interpreted to be ancient continental mantle that escaped tectonic erosion by low-angle subduction. The deeper samples are enriched in radiogenic Nd (ɛNd = +5.7 to +16.1) and reveal two superposed mantle slices of recent origin. Within each slice, compositions range from fertile lherzolites at the top to harzburgites at the bottom: the latter formed by 25-28% low-pressure melt depletion and the former formed by refertilization of harzburgites by mid-ocean-ridge-basalt-like liquids. The superposition and internal compositional zonation of the slices preclude recent fertilization by Cenozoic extension-related magmas. The above observations imply that the lower Mojavian <span class="hlt">lithosphere</span> represents tectonically subcreted and imbricated <span class="hlt">lithosphere</span> having an oceanic protolith. If so, the lherzolitic domains may be related to melting and refertilization beneath mid-ocean ridges. The present Mojavian <span class="hlt">lithosphere</span> is thus a composite of a shallow section of the original North American <span class="hlt">lithosphere</span> underlain by Farallon oceanic <span class="hlt">lithosphere</span> accreted during low-angle subduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940016281&hterms=lithosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dlithosphere','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940016281&hterms=lithosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dlithosphere"><span>Rifting at Devana Chasma, Venus: Structure and estimation of the effective thickness of the elastic <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Senske, D. A.</p> <p>1993-01-01</p> <p>To understand the relationship between extension and sites on Venus interpreted to be associated with mantle upwelling, the characteristics of the northern part of Devana Chasma in Beta Regio are examined. The structure of this rift is compared to that of terrestrial continental rifts. To ascertain the degree to which the <span class="hlt">lithosphere</span> at Beta might be thinned, estimates of <span class="hlt">lithospheric</span> thickness are calculated using a plate flexure model. These values are compared to those determined for other parts of the planet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940011948','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940011948"><span>Effective elastic thickness of the Venusian <span class="hlt">lithosphere</span> with lateral viscosity variations in the mantle</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moresi, Louis</p> <p>1993-01-01</p> <p>Both the Earth and Venus have a convecting mantle at the top of which is a relatively strong, mechanical boundary layer. The surface topography and gravity signals which result from the convection within the viscous mantle are modified by the elastic properties of this <span class="hlt">lithospheric</span> boundary layer. In particular the ability of the <span class="hlt">lithosphere</span> to support loads and transmit stresses from below is a function of the wavelength of the load--the <span class="hlt">lithosphere</span> is strong to loading at shorter wavelengths. As a consequence it is usual to expect that long wavelength topography cannot be supported by the mechanical strength of the <span class="hlt">lithosphere</span> and must be compensated--isostatically or dynamically--within the uppermost mantle or the crust. The flexural rigidity of the <span class="hlt">lithosphere</span> can therefore be determined by estimating the greatest wavelength at which uncompensated surface topography can be supported, usually by measuring the admittance as a function of wavelength. In fact this procedure for determining the elastic thickness relies upon being able to distinguish topography with underlying support from that supported by the brittle <span class="hlt">lithosphere</span> on the basis of their each having a characteristic value of the admittance. However, in the presence of lateral viscosity variations in the mantle, it is possible for topography to be generated which is NOT compensated by density anomalies in the underlying mantle at the same wavelength. Although this effect is not likely to be important for the Earth, on Venus, where the high surface temperatures would be expected to give a weaker <span class="hlt">lithosphere</span>, lateral viscosity variations in the mantle can give a misleadingly large apparent elastic thickness for the <span class="hlt">lithosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018535','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018535"><span>Metastable mantle phase transformations and deep earthquakes in subducting oceanic <span class="hlt">lithosphere</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Kirby, S.H.; Stein, S.; Okal, E.A.; Rubie, David C.</p> <p>1996-01-01</p> <p>Earth's deepest earthquakes occur as a population in subducting or previously subducted <span class="hlt">lithosphere</span> at depths ranging from about 325 to 690 km. This depth interval closely brackets the mantle transition zone, characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher-pressure phases. Deep earthquakes thus provide the primary direct evidence for subduction of the <span class="hlt">lithosphere</span> to these depths and allow us to investigate the deep thermal, thermodynamic, and mechanical ferment inside slabs. Numerical simulations of reaction rates show that the olivine ??? spinel transformation should be kinetically hindered in old, cold slabs descending into the transition zone. Thus wedge-shaped zones of metastable peridotite probably persist to depths of more than 600 km. Laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting. This instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser, finer-grained phase. Hence in cold slabs, such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite. It is thus <span class="hlt">natural</span> to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs. This consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features. It explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone, where minerals in downgoing slabs should transform to spinel and ilmenite structures. The onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab. Even if a slab penetrates into the lower mantle, earthquakes</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.9229B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.9229B"><span>Mantle xenoliths from Marosticano area (Northern Italy): a comparison with Veneto Volcanic Province <span class="hlt">lithospheric</span> mantle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brombin, Valentina; Bonadiman, Costanza; Coltorti, Massimo</p> <p>2016-04-01</p> <p> redox conditions (Δlog fO2: +1.2 to -0.7, Ballhaus, 1991) to Lessinean and Val d'Adige xenoliths which may indicate a local oxidation of the mantle below this portion of VVP. References • Beccaluva L., Bianchini G., Bonadiman C., Coltorti M., Milani L., Salvini L., Siena F., Tassinari R. (2007). Intraplate <span class="hlt">lithospheric</span> and sublithospheric components in the Adriatic domain: Nephelinite to tholeiite magma generation in the Paleogene Veneto Volcanic Province, Southern Alps. Geological Society of America, 131-152. • Beccaluva L., Bonadiman C., Coltorti M., Salvini L., Siena F. (2001). Depletion events, <span class="hlt">nature</span> of metasomatizing agent and timing of enrichment processes in <span class="hlt">lithospheric</span> mantle xenoliths from the Veneto Volcanic Province. Journal of Petrology, 42, 173-187. • Gasperini D., Bosch D., Braga R., Bondi M., Macera P., Morten L. (2006). Ultramafic xenoliths from the Veneto Volcanic Province (Italy): Petrological and geochemical evidence for multiple metasomatism of the SE Alps mantle lithospere. Geochemical Journal, 40, 377-404. • Siena F., Coltorti M. (1989). <span class="hlt">Lithospheric</span> mantle evolution: evidences from ultramafic xenoliths in the Lessinean volcanics (Northern Itlay). Chemical Geology, 77, 347-364.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatGe...9..898P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatGe...9..898P"><span>Pre-subduction metasomatic enrichment of the oceanic <span class="hlt">lithosphere</span> induced by plate flexure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pilet, S.; Abe, N.; Rochat, L.; Kaczmarek, M.-A.; Hirano, N.; Machida, S.; Buchs, D. M.; Baumgartner, P. O.; Müntener, O.</p> <p>2016-12-01</p> <p>Oceanic <span class="hlt">lithospheric</span> mantle is generally interpreted as depleted mantle residue after mid-ocean ridge basalt extraction. Several models have suggested that metasomatic processes can refertilize portions of the <span class="hlt">lithospheric</span> mantle before subduction. Here, we report mantle xenocrysts and xenoliths in petit-spot lavas that provide direct evidence that the lower oceanic <span class="hlt">lithosphere</span> is affected by metasomatic processes. We find a chemical similarity between clinopyroxene observed in petit-spot mantle xenoliths and clinopyroxene from melt-metasomatized garnet or spinel peridotites, which are sampled by kimberlites and intracontinental basalts respectively. We suggest that extensional stresses in oceanic <span class="hlt">lithosphere</span>, such as plate bending in front of subduction zones, allow low-degree melts from the seismic low-velocity zone to percolate, interact and weaken the oceanic <span class="hlt">lithospheric</span> mantle. Thus, metasomatism is not limited to mantle upwelling zones such as mid-ocean ridges or mantle plumes, but could be initiated by tectonic processes. Since plate flexure is a global mechanism in subduction zones, a significant portion of oceanic <span class="hlt">lithospheric</span> mantle is likely to be metasomatized. Recycling of metasomatic domains into the convecting mantle is fundamental to understanding the generation of small-scale mantle isotopic and volatile heterogeneities sampled by oceanic island and mid-ocean ridge basalts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMDI21A1942D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMDI21A1942D"><span>Numerical Modeling of Gravity, Geoid, and the Thermal Structure of Oceanic <span class="hlt">Lithosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davis, D.; Grose, C. J.</p> <p>2010-12-01</p> <p>In or