Using satellite data to decipher geodynamics of the northeast Atlantic

2021 ◽  
Author(s):  
Alexander Minakov ◽  
Carmen Gaina
Keyword(s):  
Upper Mantle ◽  
Seismic Velocity ◽  
Reference Model ◽  
Pure Shear ◽  
Bulk Composition ◽  
Regional Scale ◽  
Gravity Gradient ◽  
Atlantic Region ◽  
Study Region ◽  
Northeast Atlantic

<p>We explore the mantle density structure of the northeast Atlantic region by performing constrained linear inversion of the satellite gravity gradient tensor data using statistical prior information. The residual gravity gradient signal and the prior covariance matrix are obtained using a crustal model constrained by updated database of seismic reflection and refraction profiles. We construct a 3D reference density distribution in the upper mantle assuming a pure shear model for lithospheric rifting. The mantle reference density model is consistent with mineral phase equilibria assuming a pyrolitic bulk composition. The forward modeling of the gravity gradients in the 3D reference model is performed on a global scale using a spherical harmonics approach. The northeast Atlantic model is represented using a spherical shell covering the study region down the depth of 410 km. We use tesseroids as mass elements for solving the forward and inverse gravity problem at the regional scale. The relationship between the seismic velocity and density anomalies in the Iceland-Jan Mayen region and the low-density corridor across central Greenland are discussed for understanding the origin of heterogeneities in the upper mantle of the northeast Atlantic region and their possible connections with the Cenozoic Iceland plume activity.</p>

Are complex rift patterns the result of interacting crustal and mantle weaknesses, or of multiphase rifting? An analogue modelling study

2021 ◽  
Author(s):  
Frank Zwaan ◽  
Pauline Chenin ◽  
Duncan Erratt ◽  
Gianreto Manatschal ◽  
Guido Schreurs
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Reference Model ◽  
Pure Shear ◽  
Base Plate ◽  
Rigid Base ◽  
Extension Rate ◽  
Viscous Layer ◽  
Localize Deformation ◽  
Axis Parallel

<p>During extension of the continental lithosphere, deformation often localizes along pre-existing weaknesses originating from previous tectonic phases. When simulating such structures with analogue or numerical methods, modellers often focus on either crustal or mantle heterogeneities. By contrast, here we present results from 3D analogue models to test the combined effect and relative impact of (differently oriented) mantle and crustal weaknesses on rift systems.</p><p>Our model set-up involves a rigid base plate fixed to a mobile sidewall. When this sidewall moves outward, the edge of the base plate induces a “velocity discontinuity” (VD) that acts as an upper mantle fault/shear zone in a strong upper mantle. The VD is either parallel to the model axis, or 30˚ oblique. On top of this base plate, we apply a viscous layer representing the ductile lower crust, followed by a sand cover that simulates the brittle upper crust. Crustal weaknesses were either imposed by implementing “seeds” (i.e. ridges of viscous material at the base of the sand layer), or by pre-cutting the sand. Similar to the basal plate edge, we apply different crustal weakness orientations as well.</p><p>Without weaknesses in the model crust, an axis-parallel VD forms an axis-parallel rift basin above along the VD. When adding oblique seeds, they strongly localize deformation, creating a series of obliquely oriented graben. Yet the VD still induces faulting along the model axis, leading to the development of offset axial graben as well. Pre-cut faults also localize deformation but are less dominant than the seeds. As a result, the VD has more control and the axial rift structures are much more pronounced. In the oblique VD case, the reference model develops a series of en echelon graben along the VD. Axis-parallel seeds strongly localize faulting, to such a degree that the effect of the VD is very much overruled. Pre-cut faults allow more influence from the VD, but still dominate the system. Doubling the extension rate increases the strength of the viscous layer, enhancing coupling between the VD and sand cover, so that a series of en echelon graben crosscutting the seed-induced structures develop.</p><p>We find that the orientation and relative weakness of inherited weaknesses in the mantle and crust, as well as extension rates control subsequent rift structures. These structures and their relative evolution can be complex due to the interplay of the above factors, and importantly, all develop under the same pure shear extensional boundary condition. Our results show that very differently oriented rift structures can form during one phase of extension without the need to invoke multiple rift phases. Furthermore, coupling can change over time due to changes in extension velocity or gradual thinning of the lower crust, thus affecting rift evolution. These findings provide a strong incentive to reassess the tectonic history of various natural examples.</p>

SEISMIC PROPAGATION PATHS, REGIONAL TRAVELTIMES, AND CRUSTAL STRUCTURE IN THE WESTERN UNITED STATES

Geophysics ◽  
1964 ◽  
Vol 29 (2) ◽  
pp. 178-187 ◽  
Author(s):  
David J. Stuart ◽  
John C. Roller ◽  
Wayne H. Jackson ◽  
George B. Mangan
Keyword(s):  
United States ◽  
Upper Mantle ◽  
Seismic Velocity ◽  
Regional Scale ◽  
Close Relation ◽  
Western United States ◽  
Compressional Waves ◽  
Rock Density ◽  
Long Offset ◽  
Continental Interior

The U. S. Geological Survey, with VELA UNIFORM support, has recorded a network of about two thousand long‐offset refraction seismograms to provide information on the detection, location, and identification of seismic events. The measured velocities of compressional waves in upper‐mantle rocks, [Formula: see text], varies from at least 7.75 to 8.25 km/sec in the western United States. There seems to be a systematic variation of the velocity of [Formula: see text] with geologic environment and also with crustal thickness. Where the crust is thick (>35 km), measured values of the velocity of [Formula: see text] tend to be high (>8km/sec), and, where the crust is thin (<35 km), measured values of the velocity of [Formula: see text] tend to be low (<8 km/sec). The velocity of [Formula: see text] is generally low in the high mountains of the far west and generally high in the stable continental interior. The close relation between rock density and seismic velocity implies that, on a regional scale, a large part of isostatic compensation is achieved by density variations in upper‐mantle rocks.

Estimating compositions of the deep continental crust

2021 ◽  
Author(s):  
Laura Sammon ◽  
William McDonough ◽  
Walter Mooney
Keyword(s):  
Continental Crust ◽  
Seismic Velocity ◽  
Bulk Composition ◽  
Regional Scale ◽  
Geophysical Data ◽  
Seismic Velocities ◽  
Geochemical Model ◽  
Crustal Composition ◽  
Deep Crust ◽  
Multidisciplinary Model

&lt;p&gt;The deep continental crust's chemical makeup is central to the debate of crustal formation, evolution, strength, and bulk composition. The impenetrable depths and pressures of the deep (roughly &gt; 10 km) crust force geoscientists to rely on indirect sampling methods, studying medium- to high-grade metamorphic terrains and xenoliths to ascertain the composition of the middle and lower continental crust. Analyzing the deep crust in situ requires geophysical data, such as seismic velocities: Vp, Vs, and the Vp/Vs ratio. Each method provides a different perspective on deep crustal composition, but alone, neither is definitive.&amp;#160;&lt;/p&gt;&lt;p&gt;To address the nonuniqueness in crust composition modeling, we use thermodynamic modeling software (i.e. Perple_X) to relate observed seismic velocities to bulk compositions and mineralogies. We present a multidisciplinary model for the composition of Earth's deep crust, using geochemical and geophysical data. Through a Monte Carlo modeling approach, we determine the best-fit geochemical model for bulk middle and lower crustal compositions. For 12 different tectonic regimes, we quantify uncertainties in crustal composition, temperature, and seismic velocity while recognizing our own scientific biases. We present a global model of deep crustal composition conclude that regional scale geological variations benefit from a higher resolution model. Overall, our model forecasts 77% of the deepest continental crust has 45 to 55 wt.% SiO&lt;sub&gt;2&lt;/sub&gt;; 15% 55 to 65 wt.% SiO&lt;sub&gt;2&lt;/sub&gt;; 8% may have &gt; 65 wt.% SiO&lt;sub&gt;2&lt;/sub&gt;. Of perhaps equal or greater importance, however, we present a scalable, modular program that can be altered to incorporate additional petrological and geophysical constraints, allowing geoscientists to more easily compare different scenarios for the deep crust.&lt;/p&gt;

scholarly journals Evapotranspiration Estimation Using Remote Sensing Technology Based on a SEBAL Model in the Upper Reaches of the Huaihe River Basin

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1599
Author(s):  
Linshan Tan ◽  
Kaiyuan Zheng ◽  
Qiangqiang Zhao ◽  
Yanjuan Wu
Keyword(s):  
Remote Sensing ◽  
Meteorological Data ◽  
Regional Scale ◽  
Landsat 8 ◽  
Surface Reflectance ◽  
Huaihe River ◽  
Infiltration Capacity ◽  
Mountain Area ◽  
Study Region ◽  
Sebal Model

Understanding the spatial and temporal variations of evapotranspiration (ET) is vital for water resources planning and management and drought monitoring. The development of a satellite remote sensing technique is described to provide insight into the estimation of ET at a regional scale. In this study, the Surface Energy Balance Algorithm for Land (SEBAL) was used to calculate the actual ET on a daily scale from Landsat-8 data and daily ground-based meteorological data in the upper reaches of Huaihe River on 20 November 2013, 16 April 2015 and 23 March 2018. In order to evaluate the performance of the SEBAL model, the daily SEBAL ET (ETSEBAL) was compared against the daily reference ET (ET0) from four theoretical methods: the Penman-Monteith (P-M), Irmak-Allen (I-A), the Turc, and Jensen-Haise (J-H) method, the ETMOD16 product from the MODerate Resolution Imaging Spectrometer (MOD16) and the ETVIC from Variable Infiltration Capacity Model (VIC). A linear regression equation and statistical indices were used to model performance evaluation. The results showed that the daily ETSEBAL correlated very well with the ET0, ETMOD16, and ETVIC, and bias between the ETSEBAL with them was less than 1.5%. In general, the SEBAL model could provide good estimations in daily ET over the study region. In addition, the spatial-temporal distribution of ETSEBAL was explored. The variation of ETSEBAL was significant in seasons with high values during the growth period of vegetation in March and April and low values in November. Spatially, the daily ETSEBAL values in the mountain area were much higher than those in the plain areas over the study region. The variability of ETSEBAL in this study area was positively correlated with elevation and negatively correlated with surface reflectance, which implies that elevation and surface reflectance are the important factors for predicting ET in this study area.

scholarly journals Antarctic Upper Mantle Rheology

2021 ◽  
pp. M56-2020-19
Author(s):  
E. R. Ivins ◽  
W. van der Wal ◽  
D. A. Wiens ◽  
A. J. Lloyd ◽  
L. Caron
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Effective Viscosity ◽  
Seismic Velocity ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Velocity Model ◽  
Mantle Flow ◽  
S Wave ◽  
Velocity Changes

AbstractThe Antarctic mantle and lithosphere are known to have large lateral contrasts in seismic velocity and tectonic history. These contrasts suggest differences in the response time scale of mantle flow across the continent, similar to those documented between the northeastern and southwestern upper mantle of North America. Glacial isostatic adjustment and geodynamical modeling rely on independent estimates of lateral variability in effective viscosity. Recent improvements in imaging techniques and the distribution of seismic stations now allow resolution of both lateral and vertical variability of seismic velocity, making detailed inferences about lateral viscosity variations possible. Geodetic and paleo sea-level investigations of Antarctica provide quantitative ways of independently assessing the three-dimensional mantle viscosity structure. While observational and causal connections between inferred lateral viscosity variability and seismic velocity changes are qualitatively reconciled, significant improvements in the quantitative relations between effective viscosity anomalies and those imaged by P- and S-wave tomography have remained elusive. Here we describe several methods for estimating effective viscosity from S-wave velocity. We then present and compare maps of the viscosity variability beneath Antarctica based on the recent S-wave velocity model ANT-20 using three different approaches.

Quaternary sodic and potassic intraplate volcanism in northeast China controlled by the underlying heterogeneous lithospheric structures

Geology ◽  
2021 ◽  
Author(s):  
Xingli Fan ◽  
Qi-Fu Chen ◽  
Yinshuang Ai ◽  
Ling Chen ◽  
Mingming Jiang ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Northeast China ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Subcontinental Lithospheric Mantle ◽  
Seismic Velocities ◽  
S Wave ◽  
Crust And Upper Mantle ◽  
Potassic Volcanism

The origin and mantle dynamics of the Quaternary intraplate sodic and potassic volcanism in northeast China have long been intensely debated. We present a high-resolution, three-dimensional (3-D) crust and upper-mantle S-wave velocity (Vs) model of northeast China by combining ambient noise and earthquake two-plane wave tomography based on unprecedented regional dense seismic arrays. Our seismic images highlight a strong correlation between the basalt geochemistry and upper-mantle seismic velocity structure: Sodic volcanoes are all characterized by prominent low seismic velocities in the uppermost mantle, while potassic volcanoes still possess a normal but thin upper-mantle “lid” depicted by high seismic velocities. Combined with previous petrological and geochemical research findings, we propose that the rarely erupted Quaternary potassic volcanism in northeast China results from the interaction between asthenospheric low-degree melts and the overlying subcontinental lithospheric mantle. In contrast, the more widespread Quaternary sodic volcanism in this region is predominantly sourced from the upwelling asthenosphere without significant overprinting from the subcontinental lithospheric mantle.

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