8 results on '"Mooney, Walter D."'
Search Results
2. Compositional Attributes of the Deep Continental Crust Inferred From Geochemical and Geophysical Data.
- Author
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Sammon, Laura G., McDonough, William F., and Mooney, Walter D.
- Subjects
SEISMIC wave velocity ,CONTINENTAL crust ,HEAT flux ,ANALYTICAL geochemistry ,SPEED measurements ,GEOCHEMISTRY - Abstract
This study provides a global assessment of the abundance of the major oxides in the deep continental crust. The combination of geochemistry and seismology better constrains the composition of the middle and lower continental crust better than either discipline can achieve alone. The inaccessible nature of the deep crust (typically >15 km) forces reliance on analog samples and modeling results to interpret its bulk composition, evolution, and physical properties. A common practice relates major oxide compositions of small‐ to medium‐scale samples (e.g., medium to high metamorphic grade terrains and xenoliths) to large scale measurements of seismic velocities (Vp, Vs, Vp/Vs) to determine the composition of the deep crust. We provide a framework for building crustal models with multidisciplinary constraints on composition. We present a global deep crustal model that documents compositional changes with depth and accounts for uncertainties in Moho depth, temperature, and physical and chemical properties. Our 3D compositional model of the deep crust uses the USGS Global Seismic Structure Catalog (Mooney, 2015) and a compilation of geochemical analyses on amphibolite and granulite facies lithologies (Sammon & McDonough, 2021, https://doi.org/10.1029/2021JB022791). We find a SiO2 gradient from 61.2 ± 7.3 to 53.3 ± 4.8 wt.% from the middle to the base of the crust, with the equivalent lithological gradient ranging from quartz monzonite to gabbronorite. In addition, we calculate trace element abundances as a function of depth from their correlations with major oxides. From here, other lithospheric properties, such as Moho heat flux (21.6−5.6+16.0 ${21.6}_{-5.6}^{+16.0}$ mW/m2), are derived. Plain Language Summary: Using many different geophysical and geochemical techniques together helps us understand the composition of the bottom two‐thirds of the continental crust. We cannot sample much of the continental crust directly because of how deep it is. Instead, we rely on rocks that have been brought to the surface and measurements of the speed of seismic waves traveling through the crust in order to determine what the deepest parts of the crust are made of. Accounting for various factors, such as crust temperature and tectonic setting, allows us to create a large‐scale model for the composition of the deep crust. Key Points: We present a global model for the composition of the deep continental crust constrained by geochemical and geophysical dataCrustal SiO2 content decreases with increasing depth, and compositions correlate to relative depth rather than absolute depthMoho heat flux is predicted at 21.6−5.6+16.0 ${21.6}_{-5.6}^{+16.0}$ mW/m2 [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. The character of the Moho and lower crust within Archean cratons and the tectonic implications.
- Author
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Abbott, Dallas H., Mooney, Walter D., and VanTongeren, Jill A.
- Subjects
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MOHOROVICIC discontinuity , *ARCHAEAN stratigraphic geology , *CRATONS , *PLATE tectonics , *SEISMOLOGY , *PETROLOGY ,KAAPVAAL Craton (South Africa) - Abstract
Abstract: Undisturbed mid Archean crust (stabilized by 3.0–2.9Ga) has several characteristics that distinguish it from post Archean crust. Undisturbed mid-Archean crust has a low proportion of internal seismic boundaries (as evidenced by converted phases in seismic receiver functions), lacks high seismic velocities in the lower crust and has a sharp, flat Moho. Most of the seismic data on mid-Archean crust comes from the undisturbed portions of the Kaapvaal and Zimbabwe (Tokwe segment) cratons. Around 67–74% of younger Archean crust (stabilized by 2.8–2.5Ga) has a sharp, flat Moho. Much of the crust with a sharp, flat Moho also lacks strong internal seismic boundaries, but there is not a one to one correspondence. In cases where its age is known, basaltic lower crust in Archean terranes is often but not always the result of post Archean underplating. Undisturbed mid-Archean cratons are also characterized by lower crustal thicknesses (Archean median range=32–39km vs. post-Archean average=41km) and lower crustal seismic velocities. These observations are shown to be distinct from those observed in any modern-day tectonic environment. The data presented here are most consistent with a model in which Archean crust undergoes delamination of dense lithologies at the garnet-in isograd resulting in a flat, sharp Moho reflector and a thinner and more felsic-intermediate crust. We discuss the implications of this model for several outstanding paradoxes of Archean geology. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
4. Crustal structure of the northeastern margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin
- Author
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Liu, Mingjun, Mooney, Walter D., Li, Songlin, Okaya, Nihal, and Detweiler, Shane
- Subjects
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SEISMOLOGICAL stations , *SEISMOLOGY - Abstract
Abstract: The 1000-km-long Darlag–Lanzhou–Jingbian seismic refraction profile is located in the NE margin of the Tibetan plateau. This profile crosses the northern Songpan-Ganzi terrane, the Qinling-Qilian fold system, the Haiyuan arcuate tectonic region, and the stable Ordos basin. The P-wave and S-wave velocity structure and Poisson''s ratios reveal many significant characteristics in the profile. The crustal thickness increases from northeast to southwest. The average crustal thickness observed increases from 42 km in the Ordos basin to 63 km in the Songpan-Ganzi terrane. The crust becomes obviously thicker south of the Haiyuan fault and beneath the West-Qinlin Shan. The crustal velocities have significant variations along the profile. The average P-wave velocities for the crystalline crust vary between 6.3 and 6.4 km/s. Beneath the Songpan-Ganzi terrane, West-Qinling Shan, and Haiyuan arcuate tectonic region P-wave velocities of 6.3 km/s are 0.15 km/s lower than the worldwide average of 6.45 km/s. North of the Kunlun fault, with exclusion of the Haiyuan arcuate tectonic region, the average P-wave velocity is 6.4 km/s and only 0.5 km/s lower than the worldwide average. A combination of the P-wave velocity and Poisson''s ratio suggests that the crust is dominantly felsic in composition with an intermediate composition at the base. A mafic lower crust is absent in the NE margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin. There are low velocity zones in the West-Qinling Shan and the Haiyuan arcuate tectonic region. The low velocity zones have low S-wave velocities and high Poisson''s ratios, so it is possible these zones are due to partial melting. The crust is divided into two layers, the upper and the lower crust, with crustal thickening mainly in the lower crust as the NE Tibetan plateau is approached. The results in the study show that the thickness of the lower crust increases from 22 to 38 km as the crustal thickness increases from 42 km in the Ordos basin to 63 km in the Songpan-Ganzi terrane south of the Kunlun fault. Both the Conrad discontinuity and Moho in the West-Qinling Shan and in the Haiyuan arcuate tectonic region are laminated interfaces, implying intense tectonic activity. The arcuate faults and large earthquakes in the Haiyuan arcuate tectonic region are the result of interaction between the Tibetan plateau and the Sino–Korean and Gobi Ala Shan platforms. [Copyright &y& Elsevier]
- Published
- 2006
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5. Crustal structure of mainland China from deep seismic sounding data
- Author
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Li, Songlin, Mooney, Walter D., and Fan, Jichang
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SEISMOLOGY , *METAMORPHIC rocks , *SEISMOLOGICAL stations - Abstract
Abstract: Since 1958, about ninety seismic refraction/wide angle reflection profiles, with a cumulative length of more than sixty thousand kilometers, have been completed in mainland China. We summarize the results in the form of (1) a new contour map of crustal thickness, (2) fourteen representative crustal seismic velocity–depth columns for various tectonic units, and, (3) a Pn velocity map. We found a north–south-trending belt with a strong lateral gradient in crustal thickness in central China. This belt divides China into an eastern region, with a crustal thickness of 30–45 km, and a western region, with a thickness of 45–75 km. The crust in these two regions has experienced different evolutionary processes, and currently lies within distinct tectonic stress fields. Our compilation finds that there is a high-velocity (7.1–7.4 km/s) layer in the lower crust of the stable Tarim basin and Ordos plateau. However, in young orogenic belts, including parts of eastern China, the Tianshan and the Tibetan plateau, this layer is often absent. One exception is southern Tibet, where the presence of a high-velocity layer is related to the northward injection of the cold Indian plate. This high-velocity layer is absent in northern Tibet. In orogenic belts, there usually is a low-velocity layer (LVL) in the crust, but in stable regions this layer seldom exists. The Pn velocities in eastern China generally range from 7.9 to 8.1 km/s and tend to be isotropic. Pn velocities in western China are more variable, ranging from 7.7 to 8.2 km/s, and may display azimuthal anisotropy. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
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6. An updated global earthquake catalogue for stable continental regions: reassessing the correlation with ancient rifts.
- Author
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Schulte, Saskia M. and Mooney, Walter D.
- Subjects
- *
EARTHQUAKES , *EARTH movements , *RIFTS (Geology) , *STRUCTURAL geology , *SEISMOLOGY , *GEOPHYSICS - Abstract
We present an updated global earthquake catalogue for stable continental regions (SCRs; i.e. intraplate earthquakes) that is available on the Internet. Our database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300M(moment magnitude)≥ 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in combination with a recently published global catalogue of rifts, we assess the correlation of intraplate seismicity with ancient rifts on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior rifts/taphrogens, (ii) rifted continental margins, (iii) non-rifted crust, (iv) possible interior rifts and (v) possible rifted margins. We find that approximately 27 per cent of all events are classified as interior rifts (i), 25 per cent are rifted continental margins (ii), 36 per cent are within non-rifted crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with rifted crust, although within the continental interiors (i.e. away from continental margins), non-rifted crust has experienced more earthquakes than interior rifts. No major change in distribution is found if only largeearthquakes are considered. The largest eventshowever, have occurred predominantly within rifts (50 per cent) and continental margins (43 per cent). Intraplate seismicity is not distributed evenly. Instead several zones of concentrated seismicity seem to exist. This is especially true for interior rifts/taphrogens, where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category. Of the four rifts/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch rift, India, and the East China rift system, may be controlled by diffuse plate boundary deformation more than by the presence of the ancient rifts themselves. The St. Lawrence depression, Canada, besides being an ancient rift, is also the site of a major collisional suture. Thus only at the Reelfoot rift (New Madrid seismic zone, NMSZ, USA), is the presence of features associated with rifting itself the sole candidate for causing seismicity. Our results suggest that on a global scale, the correlation of seismicity within SCRs and ancient rifts has been overestimated in the past. Because the majority of models used to explain intraplate seismicity have focused on seismicity within rifts, we conclude that a shift in attention more towards non-rifted as well as rifted crust is in order. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
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7. NACr14: A 3D model for the crustal structure of the North American Continent
- Author
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Tesauro, Magdala, Kaban, Mikhail, Mooney, Walter, Cloetingh, Sierd, Tectonics, Tesauro, Magdala, Kaban, Mikhail K., Mooney, Walter D., Cloetingh, Sierd, and Tectonics
- Subjects
3D crustal model ,Crustal recycling ,P-wave crustal velocity ,Crust ,Geophysics ,Tectonics ,Sequence (geology) ,Ocean surface topography ,Intracrustal boundaries ,Seismic tomography ,Pn velocity ,P-wave ,North American continent ,Geology ,Seismology ,Earth-Surface Processes ,Interpolation - Abstract
Based on the large number of crustal seismic experiments carried out in the last decades we create NACr14, a 3D crustal model of the North American continent at a resolution of 1 degrees x 1 degrees. We present maps of thickness and average velocities of the main layers that comprise the North American crystalline crust, obtained from the most recent seismic crustal models within the USGS crustal structure database. However, the crustal data are unevenly distributed and in some cases discrepancies exist between published models. In order to construct a consistent 3D crustal model with three layers in the crystalline crust, we refrained from a direct interpolation of the crustal seismic parameters in the database. Instead, we implemented the following sequence of steps: 1. Definition of the geometry of the main tectonic provinces of North America; 2. Selection and evaluation of the reliability of seismic crustal models in the database; 3. Estimation of the P-wave seismic velocity and thickness of the upper, middle and lower crust for each tectonic province; 4. Estimation of the interpolated Pn velocity distribution. The resulting average velocity of the crystalline crust is mostly consistent with that of the seismic points. The main variations of the structure of the crystalline crust of North America displayed in the model can be related to its tectonic evolution. The model, available in a digital form, can be used in various geophysical applications, such as the correction for the crustal effects in gravity and seismic tomography and models of dynamic topography, in order to detect heterogeneities characterizing the underlying upper mantle.
- Published
- 2014
8. High resolution regional crustal models from irregularly distributed data: Application to Asia and adjacent areas
- Author
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Ward Stolk, Fred Beekman, Mikhail K. Kaban, Magdala Tesauro, Sierd Cloetingh, Walter D. Mooney, Stolk, Ward, Kaban, Mikhail, Beekman, Fred, Tesauro, Magdala, Mooney, Walter D., and Cloetingh, Sierd
- Subjects
Interpolation method ,Asia ,Remove–compute–restore ,Aardwetenschappen ,550 - Earth sciences ,Crust ,Residual ,Geodesy ,Physics::Geophysics ,Discontinuity (linguistics) ,Geophysics ,Lithosphere ,Seismic tomography ,Isostasy ,Crustal model ,Remove-compute-restore ,Earth-Surface Processes ,Geothermal gradient ,Geophysic ,Geology ,Seismology ,Interpolation - Abstract
We propose a new methodology to obtain crustal models in areas where data is sparse and data spreading is heterogeneous. This new method involves both interpolating the depth to the Moho discontinuity between observations and estimating a velocity–depth curve for the crust at each interpolation location. The Moho observations are interpolated using a remove–compute–restore technique, used in for instance geodesy. Observations are corrected first for Airy type isostasy. The residual observations show less variation than the original observations, making interpolation more reliable. After interpolation, the applied correction is restored to the solution, leading to the final estimate of Moho depth. The crustal velocities have been estimated by fitting a velocity– depth curve through available data at each interpolation location. Uncertainty of the model is assessed, both for the Moho and the velocity model. The method has been applied successfully to Asia. The resulting crustal model is provided in digital form and can be used in various geophysical applications, for instance in assessing rheological properties and strength profiles of the lithosphere, the correcting gravity for the crustal effects, seismic tomography and geothermal modelling.
- Published
- 2013
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