Elastic Thickness Research Articles

Gravity anomalies and crustal structure of the Lunar far side highlands

The far side of the lunar hemisphere is dominated by a large number of impact craters having a smaller diameter and few Mare basins compared to the near side of the Moon. This study presents a detailed analyses of gravity anomalies derived from Gravity Recovery and Interior Laboratory (GRAIL) mission and topography over the central equatorial region of Lunar far side covering the major impact basins such as Dirichlet-Jackson, Korolev, Hertzsprung and adjoining regions of the highlands, to understand sub-surface structure. Bouguer gravity anomaly map of the region is prepared using the density of 2.7 g/cc, which is estimated using fractals based approach. The spectral analyses using Maximum Entropy Method of calculated Bouguer anomaly and topography provided an estimated of Effective Elastic Thickness (Te) as 19 km and also a cut-off wavelength of 270 km for separating Regional and residual Bouguer gravity anomalies. Further a crustal thickness of this region of Moon is estimated by inversion of regional Bouguer gravity anomalies, which varies from 20 to 71 km.An estimated crustal thickness of Dirichlet Jackson and Hertzpsrung, Korolev basins varies between 39 and 65 km, 20–65 km and 39–64 km, respectively. The residual gravity anomaly map shows symmetric gravity highs and lows in Dirichlet-Jackson, Hertzsprung and Korolev basins. These gravity highs can be attributed to high-density mare basalts within inner rims of these basins. The observed nature of gravity anomalies and crustal thickness map can be attributed to the buried impact crater under this region.

Micromechanical analysis of the elastic response of glass-epoxy hybrid composites containing silica nanoparticles

ABSTRACTThe effects of adding silica nanoparticles on the elastic properties of glass-epoxy hybrid composites are investigated using a micromechanical method. Influences of silica nanoparticle volume fraction and diameter, the interphase elastic modulus and thickness, the glass fiber volume fraction and aspect ratio as well as off-axis angle on the elastic properties of unidirectional glass fiber-reinforced epoxy hybrid composites containing silica nanoparticles are studied. The results reveal that the addition of silica nanoparticles can improve the elastic modulus in the transverse direction, while the axial elastic modulus is not affected by silica nanoparticles.

Elastic thickness determination based on Vening Meinesz–Moritz and flexural theories of isostasy

Elastic thickness (Te) is one of mechanical properties of the Earth's lithosphere. The lithosphere is assumed to be a thin elastic shell, which is bended under the topographic, bathymetric and sedi ...

Structure, mechanical properties and evolution of the lithosphere below the northwest continental margin of India

The continental breakup history at the northwest continental margin of India remained conjectural due to lack of clearly discernable magnetic anomaly identifications and the presence of several enigmatic structural/basement features whose structure was partly obscured by the Late Cretaceous Deccan magmatic event. In this study, a detailed analysis of the existing seismic and seismological data covering both onshore and offshore areas of the northwest Indian margin along with 3-D/2-D constrained potential field (gravity, magnetic and geoid) modeling has been carried out. The crustal structure and lithosphere–asthenosphere boundary (LAB) delineated across the margin provided valuable insights on the mechanism of continental extension. An analysis of the residual geoid anomaly (degree-10) map and the modeled LAB below Deccan volcanic province (DVP) revealed significant variation in upper mantle characteristics between the northwest (NW) and south central (SC) parts of DVP having thinner lithosphere in the NW part. The depth to LAB ranges 80–130 km at the margin with gradual thinning towards the western offshore having sharp gradient in the south (SC part of DVP) and gentle gradient in the north (NW part of DVP). The Moho configuration obtained from seismically constrained 3-D gravity inversion reveals that Moho depths vary 34–42 km below DVP and gradually thins to 16–20 km in the western offshore. The effective elastic thickness (Te) map computed through 3-D flexural modeling indicates that the Te values are in general lower in the region and range 12–25 km. Such lower Te values could be ascribed to the combined effect of the lithosphere stretching during Gondwana fragmentation in the Mesozoic and subsequent thermal influence of the Reunion plume. Based on the crustal stretching factors (β), Te estimates and the modeled lithosphere geometry at the margin in this study, we propose that the lithosphere below Laxmi–Gop basin region (β > 3.0) had undergone continuous stretching since India–Madagascar rifting (~ 88 Ma) /much prior to this event. However, this continuous stretching did not lead to breakup. Due to syn-rift cooling, the developed necking zone (brittle–ductile deformation) got ceased and led to the development of a new necking zone between Seychelles and Laxmi Ridge. Subsequent stretching between Seychelles and the Laxmi Ridge contemporaneous with the Deccan flood basalts eruption led to the seafloor spreading in the Western Basin (anomaly C28n). Thus, the Laxmi Ridge became a continental sliver.

Lateral Variations in Foreland Flexure of a Rifted Continental Margin: The Aquitaine Basin (SW France)

AbstractRift inheritance can play a key role in foreland basin geometry and behavior. If the foreland basin initiates soon after rifting, thermal cooling can also contribute significantly to subsidence. We investigate the effects of crustal inheritance (Aptian‐Cenomanian rifting) on the evolution of the Campanian to middle Miocene flexural Aquitaine foreland basin, northern Pyrenees, France. Surface and subsurface data define rifted crustal geometry and postrift thermal subsidence. Analysis of Bouguer gravity anomalies coupled with flexural modeling constrains the lateral variations of elastic thickness, plate flexure, and controlling loads. The Aquitaine foreland is divided along‐strike into three sectors. The relative role of surface and subsurface (i.e., buried) loading varies along‐strike, and the elastic thickness values decrease from the northeast (25 km) to the southwest (7 km) where the plate is the most stretched. The eastern foreland crust was not rifted and underwent a simple flexural subsidence in response to orogenesis. The central sector was affected by crustal stretching. Here the basin is modeled by combining topographic and buried loads, with postrift thermal subsidence. In the western sector, the foreland basin was created mainly by postrift thermal subsidence. The eastern and central sectors are separated by the Eastern Crustal Lineament, which is one of a series of inherited transverse faults that segment the orogen.

Signatures of Lithospheric Flexure and Elevated Heat Flow in Stereo Topography at Coronae on Venus

AbstractSignatures of lithospheric flexure were previously identified at a dozen or more large coronae on Venus. Thin plate models fit to topographic profiles return elastic parameters, allowing derivation of mechanical thickness and surface heat flows given an assumed yield strength envelope. However, the low resolution of altimetry data from the NASA Magellan mission has hindered studying the vast majority of coronae, particularly those less than a few hundred kilometers in diameter. Here we search for flexural signatures around 99 coronae over ∼20% of the surface in Magellan altimetry data and stereo‐derived topography that was recently assembled from synthetic aperture radar images. We derive elastic thicknesses of ∼2 to 30 km (mostly ∼5 to 15 km) with Cartesian and axisymmetric models at 19 coronae. We discuss the implications of low values that were also noted in earlier gravity studies. Most mechanical thicknesses are estimated as <19 km, corresponding to thermal gradients >24 K km−1. Implied surface heat flows >95 mW m−2—twice the global average in many thermal evolution models—imply that coronae are major contributors to the total heat budget or Venus is cooling faster than expected. Binomial statistics show that “Type 2” coronae with incomplete fracture annuli are significantly less likely to host flexural signatures than “Type 1” coronae with largely complete annuli. Stress calculations predict extensional faulting where nearly all profiles intersect concentric fractures. We failed to identify systematic variations in flexural parameters based on type, geologic setting, or morphologic class. Obtaining quality, high‐resolution topography from a planetwide survey is vital to verifying our conclusions.

Influence of Rift Superposition on Lithospheric Response to East African Rift System Extension: Lapur Range, Turkana, Kenya

AbstractThe Turkana Depression of northern Kenya lies at the intersection of the NW‐SE trending late Mesozoic‐early Paleogene South Sudan and Anza rifts and the N‐S trending late Paleogene‐Recent East African Rift System (EARS). A low‐temperature thermochronology study in the Lapur Range reveals a complex tectonothermal evolution related to multiple periods of regional and local tectonism. Zircon (U‐Th)/He data from Precambrian basement record rapid Early Cretaceous denudational cooling. Coeval subsidence in the adjacent Anza and South Sudan rifts (Morley, Bosworth, et al., 1999; Schull, 1988) suggests that the northern Turkana region acted as a basement high separating the grabens, as well as an axial source of sediment. Between ~95 and 90 Ma, a period of reheating commenced with burial of Lapur basement beneath ~500 m of Late Cretaceous‐Eocene Lapur Sandstone and ~1.5–3.5 km of latest Eocene‐early Miocene Turkana volcanics. Apatite fission track (AFT) and apatite (U‐Th‐Sm)/He data record a transition to rapid denudational cooling in the mid‐Miocene (~14 Ma) in response to EARS‐related extension in the northern Turkana Basin. Thermal history models indicate that the Lapur Range experienced ~90–100°C of mid‐Miocene to Plio‐Pleistocene cooling, yielding the first Neogene AFT ages reported from Kenya related to EARS exhumation. We attribute the larger magnitude of cooling in the Lapur Range compared to other regions of the EARS to the attenuated crustal thickness and elevated heat flow of the Turkana Depression, crustal properties inherited from earlier Cretaceous‐Paleogene rifting. The resulting low effective elastic thickness of the Turkana lithosphere allowed for increased isostatic footwall uplift in response to EARS extension.

Moho depth and equivalent elastic thickness of the lithosphere over the Vema Channel: A new evidence of an aborted ridge

We investigate the Vema Channel in terms of spatial variations of the elastic thickness (Te) in the frame of the thin plate flexure model using the convolutive method. The modeling of the Moho in terms of the thin plate flexure model is done by a least squares approximation of the Moho obtained from gravity inversion. The flexure is calculated by the convolution of the crustal load with the point-load flexure response curves. The RMS difference between the gravity and flexure Moho surfaces is minimized by varying the Te by inverse modeling. The result is a solution of the flexed crust that is in best agreement with the long-wavelength component of the gravity field.The flexure Moho depths vary between 12 and 18 km and agree well with those obtained from gravity inversion. The spatial variations of Te range from 2 to 30 km and have a good correlation with the geological interpretation for an aborted ridge near Vema Channel, called in this paper as the Vema Aborted Ridge (VAR). The occurring of seamounts appears to be correlated to a weak and deformed region. Attempts of crustal breakup are marked by high Te values (30 km) while lower values (3–12 km) are found for the suggested aborted ridge. The VAR is on Isochron of 93 Ma and shows symmetrical older along both sides of its axis. Asymmetric magnetic anomalies are found over the ridge and may be related to upper-extended continental crust broken by the Vema.

Ancient selenophysical structure of the Grimaldi basin: Constraints from GRAIL gravity and LOLA topography

The Grimaldi impact basin is located near the western limb of the moon and lies to the southwest of the Oceanus Procellarum. A clearly visible positive gravity anomaly exists in its low-lying inner wall, implying a subsurface mass concentration beneath the crater. Exploration of this basin could extend our meaningful and fundamental understanding of giant impact processes as well as the structure of mare basins/craters. Limited by the low-resolution of previous gravity field models, it was once impossible to explore the structure beneath Grimaldi. The recent high-resolution gravity data from the Gravity Recovery and Interior Laboratory mission make it possible to break through this barrier. Prior to our investigation of the selenophysical structure around crater Grimaldi, we developed a flexure model that includes surface and subsurface loads. A localized admittance analysis was performed by combining high-resolution gravity data with the high-resolution topography data obtained from Lunar Orbiter Laser Altimeter. Within 2σSTD error constraints, we estimated the best-fit parameters over Grimaldi as well as two other places in its neighborhood. All the predicted admittances show a goodness of fit with their corresponding observations. The large load ratio (∼9.2) found at the Grimaldi is an indirect mirror of the dominant subsurface load, consistent with its large positive gravity anomaly in its low-lying floor. Not only the crustal thickness of 48 km but also the crustal density of 2500 kg m−3 found around Grimaldi shows a great accordance with the recent results of GRAIL. Given the best-fit parameters of f, bc and ρc, the elastic thickness Te is found to be around 28 km over Grimaldi. Taking into account the best-fit values in its neighborhood, a regional elastic thickness of 30 km could be roughly concluded around Grimaldi, which is completely in the previous ranges (20 < Te < 60 km) from Clementine. Our result of the elastic thickness is quite larger than those on the lunar nearside volcanic complexes of the recent GRAIL study. Considering fewer thermal activities occurred on the lunar limb or farside than its nearside, we can then deduce that the lithosphere could be possibly cold and therefore developed a corresponding dense elastic thickness.

Effective elastic thickness in the Central Andes. Correlation to orogenic deformation styles and lower crust high-gravity anomaly

Global studies have assessed the importance of elastic thickness (Te) on orogenic evolution, showing that the style and nature of upper crustal shortening are influenced by the inherited lithospheric strength. Thus, pioneer works have identified that the upper crustal deformation style in the easternmost sector of the Central Andes in South America are related to the elastic thickness (Te). There, the thick-skinned and pure-shear style of Santa Bárbara system was initially related to the existence of low Te values. In contrast, the thin-skinned and simple-shear style of deformation in the Subandean system involves high Te values. However, more recent Te studies in the Central Andes present conflicting results which lead to question this straightforward relation. Results from these studies show a strong dependence on the applied methodology hampering the general understanding of the lithospheric thermo-mechanical state of the Central Andes. To contribute to this issue, we perform a high-resolution Te map, using forward modeling by solving flexural equation of infinite plate model in two dimensions. To achieve this, the crust-mantle interface was calculated using a high-resolution gravity anomaly dataset which combines satellite and terrestrial data, and an average density contrast. Additionally, the gravity anomaly and the foreland basin depth in the Central Andes were best predicted by considering that lower crustal rocks fill the space deflected downward in the plate model. The obtained Te values show an inverse correlation with previous heat flow studies, and a strong spatial correlation with the styles and mechanisms of deformation in the easternmost sector of the Central Andes. In the Santa Bárbara system Te values less than 10 km predominate, whereas in the Subandean system high Te values were observed. Such high values correlate with the orogenic curvature and with an shallower gravity Moho zone, which breaks the regional trend of the Central Andes. This shallower gravity Moho is linked to a high-gravity anomaly located in the east part of the Eastern Cordillera and Subandean system. These results are also correlated with a high-velocity zone in the upper mantle previously found by receiver functions studies. This correlation could indicate changes in the properties of the lower crustal rocks that justify the shallower gravity Moho zone and explain in part the highest Te values.

3D Process-Oriented Gravity Modelling applied north of 49°S on the Argentine continental margin

The Process-Oriented Gravity Modelling (POGM) technique represents a useful way to distinguish the contribution that different geological processes make to the observed gravity in passive margins. The POGM is an innovative gravity modelling approach that can give us information about the role that processes such as sedimentation and magmatic underplating, together with their loading effects, may play in the evolution of a margin. In this work, the POGM methodology has been applied with in a 2D and 3D approach. 2D profiles spaced every one arc-minute in the area of the Argentine continental margin, between 38.5°S and 49°S latitude and 64°W and 50°W longitude, were used to generate the latter.The 3D POGM was also solved and the result was compared with that obtained from 2D profiles. The comparison with the observed anomaly, using the 3D approach from 2D profiles gave results with enhanced resolution.The best fit between the calculated and observed gravity anomaly is given by an effective elastic thickness of 15 km. A cortical thickness map obtained as a result of the POGM calculations shows basin areas characterized by a thinned crust and a structural variation where the continental-oceanic boundary (COB) could be indicated. Besides, results of POGM allow us to detect an alignment between the Valdés and Rawson basins and possibly a third basin as a probable aulacogen. A stretching factor analysis shows that in these basins a stretching period existed but it did not reach the stage of oceanic crust formation. A strong positive residue in the Colorado basin is shown by the flexural isostatic anomaly, suggesting that the basin may continue in subsidence.

Flexural modeling of the elastic lithosphere at an ocean trench: A parameter sensitivity analysis using analytical solutions

The outer rise is a topographic bulge seaward of the trench at a subduction zone that is caused by bending and flexure of the oceanic lithosphere as subduction commences. The classic model of the flexure of oceanic lithosphere w(x) is a hydrostatic restoring force acting upon an elastic plate at the trench axis. The governing parameters are elastic thickness Te, shear force V0, and bending moment M0. V0 and M0 are unknown variables that are typically replaced by other quantities such as the height of the fore-bulge, wb, and the half-width of the fore-bulge, (xb−xo). However, this method is difficult to implement with the presence of excessive topographic noise around the bulge of the outer rise. Here, we present an alternative method to the classic model, in which lithospheric flexure w(x) is a function of the flexure at the trench axis w0, the initial dip angle of subduction β0, and the elastic thickness Te. In this investigation, we apply a sensitivity analysis to both methods in order to determine the impact of the differing parameters on the solution, w(x). The parametric sensitivity analysis suggests that stable solutions for the alternative approach requires relatively low β0 values (<15°), which are consistent with the initial dip angles observed in seismic velocity-depth models across convergent margins worldwide. The predicted flexure for both methods are compared with observed bathymetric profiles across the Izu-Mariana trench, where the old and cold Pacific plate is characterized by a pronounced outer rise bulge. The alternative method is a more suitable approach, assuming that accurate geometric information at the trench axis (i.e., w0 and β0) is available.

Petrogenesis of alkalic seamounts on the Galápagos Platform

In the hotspot-fed Galápagos Archipelago there are transitions between volcano morphology and composition, effective elastic thickness of the crust, and lithospheric thickness in the direction of plate motion from west to east. Through sampling on the island scale it is unclear whether these transitions are gradational or sharp and whether they result in a gradational or a sharp boundary in terms of the composition of erupted lavas. Clusters of interisland seamounts are prevalent on the Galápagos Platform, and occur in the transition zone in morphology between western and eastern volcanoes providing an opportunity to evaluate sharpness of the compositional boundary resulting from these physical transitions. Two of these seamounts, located east of Isabela Island and southwest of the island of Santiago, were sampled by remotely operated vehicle in 2015 during a telepresence-supported E/V Nautilus cruise, operated by the Ocean Exploration Trust. We compare the chemistries of these seamount lavas with samples erupted subaerially on the islands of Isabela and Santiago, to test whether seamounts are formed from melt generation and storage similar to that of the western or eastern volcanoes, or transitional between the two systems. There are no systematic variations between the two seamounts and variability in all samples can be related through < 10% fractional crystallization at 500–900MPa. Both seamounts are interpreted to represent a single magmatic episode and eruptive event. Trace element compositions indicate they formed downstream of the hotspot center. The calculated extents of melting are consistent with generation of magmas sourcing the seamounts beneath lithosphere of intermediate thickness (~ 56km). The seamount lavas have compositions that are nearly identical to a subset of lavas erupted subaerially on Santiago Island, suggesting lateral magma transport on the order of 10km from their source region prior to eruption. The compositional characteristics and, in particular, depth of crystallization suggest that although seamount magmas have a transitional melting signature, they are discretized on the island scale, through homogenization in the lithospheric mantle and redistributed by vertical and horizontal diking in the shallow crust. Due to this homogenization, it remains unclear whether the variation in erupted lava chemistries from west to east are representative of sharp or gradual changes in mantle composition and structure across the archipelago.

Cenozoic intraplate tectonics in Central Patagonia: Record of main Andean phases in a weak upper plate

Contraction in intraplate areas is still poorly understood relative to similar deformation at plate margins. In order to contribute to its comprehension, we study the Patagonian broken foreland (PBF) in South America whose evolution remains controversial. Time constraints of tectonic events and structural characterization of this belt are limited. Also, major causes of strain location in this orogen far from the plate margin are enigmatic. To unravel tectonic events, we studied the Cenozoic sedimentary record of the central sector of the Patagonian broken foreland (San Bernardo fold and thrust belt, 44°30′S-46°S) and the Andes (Meseta de Chalia, 46°S) following an approach involving growth-strata detection, U-Pb geochronology and structural modeling. Additionally, we elaborate a high resolution analysis of the effective elastic thickness (Te) to examine the relation between intraplate contraction location and variations in lithospheric strength. The occurrence of Eocene growth-strata (~44–40Ma) suggests that contraction in the Andes and the Patagonian broken foreland was linked to the Incaic phase. Detection of synextensional deposits suggests that the broken foreland collapsed partially during Oligocene to early Miocene. During middle Miocene times, the Quechua contractional phase produced folding of Neogene volcanic rocks and olistostrome deposition at ~17Ma. Finally, the presented Te map shows that intraplate contraction related to Andean phases localized preferentially along weak lithospheric zones (Te<15km). Hence, the observed strain distribution in the PBF appears to be controlled by lateral variations in the lithospheric strength. Variations in this parameter could be related to thermo-mechanical weakening produced by intraplate rifting in Paleozoic-Mesozoic times.

Thermo-mechanical analysis of the Andean lithosphere over the Chilean-Pampean flat-slab region

Flat subduction segments are generally related to cold lithospheric zones, which suggest low Heat flow values and therefore a deeper Curie isotherm. In this study we perform a geophysical analysis by using high - resolution magnetic data, obtaining shallower Curie point depths through the Chilean-Pampean flat-slab zone. Then using temperatures from borehole data and Curie Point Depths, we performed a Heat Flow map which indicates the existence of mean to high thermal anomalies across the Chilean - Pampean flat-slab. These results were contrasted with Elastic Thickness map (Te) obtained from the Eigen-6C4 gravity model. Low Te values acquired indicate zones with weak mechanical behavior in correspondence to thermal anomalous zones. This spatial correlation suggests that the local high thermal anomalies are conditioning the mechanical behavior of the lithosphere in the study area and the locations of geothermal sources. Overall, our results indicate that the thermal structure of the flat-slab segment is more heterogeneous than previously thought. This has implications for evolution, maturity and fluid circulation in foreland basins of the Main and Frontal cordilleras and the Precordillera thrust belts. Finally, further studies will allow improving our database as well as extending our understanding of the thermal structure of the Chilean-Pampean flat-slab.

Flexural Isostasy: Constraints From Gravity and Topography Power Spectra

AbstractWe have used spherical harmonic coefficients that describe Earth's gravity anomaly and topography fields to quantify the role of isostasy in contributing to crustal and upper mantle structure. Power spectra reveal that the gravity effect of topography and its flexural compensation contribute significantly to the observed free‐air gravity anomaly spectra for spherical harmonic degree 33 &lt; n &lt; 400, which corresponds to wavelength 100 &lt; λ &lt; 1200 km. The best fit is for an elastic plate (flexure) model with an elastic thickness, Te, of 34.0 ± 4.0 km. Smaller values underpredict the observed gravity spectra while higher values overpredict. The best fit Te is a global average and so there will be regions where Te is lower and higher. This is confirmed in studies of selected regions such as the Hawaiian‐Emperor seamount chain and the Himalaya fold and thrust belt where we show that flexural isostatic anomalies are near zero in regions where Te~34.0 km and of large amplitude in regions of lower and higher Te. Plate flexure may also contribute at higher (n &gt; 400) and lower (n &lt; 33) degrees, but topography appears either uncompensated or fully compensated at these degrees, irrespective of the actual Te. All isostatic models underpredict the spectra at 2 &lt; n &lt; 12 and so we interpret the low‐order Earth's gravity field as caused, at least in part, by nonisostatic processes due to dynamic motions such as those associated with convective upwellings and downwellings in Earth's mantle.

Lithospheric flexural strength and effective elastic thicknesses of the Eastern Anatolia (Turkey) and surrounding region

The Lithospheric structure of Eastern Anatolia and the surrounding region, including the northern part of the Arabian platform is investigated via the analysis and modeling of Bouguer anomalies from the Earth Gravitational Model EGM08. The effective elastic thickness of the lithosphere (EET) that corresponds to the mechanical cores of the crust and lithospheric mantle is determined from the spectral coherence between Bouguer anomalies and surface elevation data. Its average value is 18.7km. From the logarithmic amplitude spectra of Bouguer anomalies, average depths of the lithosphere-asthenosphere boundary (LAB), Moho, Conrad and basement in the study area are constrained at 84km, 39km, 16km and 7km, respectively. The geometries of the LAB and Moho are then estimated using the Parker-Oldenburg inversion algorithm. We also present a lithospheric strength map obtained from the spatial variations of EET determined by Yield Stress Envelopes (YSE). The EET varies in the range of 12–23km, which is in good agreement with the average value obtained from spectral analysis. Low EET values are interpreted as resulting from thermal and flexural lithospheric weakening. According to the lithospheric strength of the Eastern Anatolian region, the rheology model consists of a strong but brittle upper crust, a weak and ductile lower crust, and a weak lower part of the lithosphere. On the other hand, lithosphere strength corresponds to weak and ductile lower crust, a strong upper crust and a strong uppermost lithospheric mantle for the northern part of the Arabian platform.

Origin of the Dongsha Event in the South China Sea

Post-rift tectonic activities have been widely observed in the northern continental margin of the South China Sea, especially during the late Miocene. Large numbers of faults became active. Unconformities, uplift of faulted blocks, sequence tilting, erosion along the Dongsha massif and canyon incision were also discriminated at this stage in the Pearl River Mouth basin (PRMB) and the area to the east. This tectonism has been named Dongsha Event. A number of hypotheses have been put forward to explain the mechanism of the Dongsha Event, such as high-velocity lower crustal flow, magmatic underplating, and arc–continent collision. To investigate the tectonic dynamics, sequence contact relationships, fault activities, and magmatism were analyzed along large numbers of seismic profiles that cover the eastern PRMB and Southwest Taiwan Basin. The timing, affected regions, and differences in the intensity of tectonic deformation were assessed, upon which the plate bending model was favored. In order to check the reasonableness of plate bending model, effective elastic thickness and other geodynamic parameters were calculated constrained by uplift area width and regarding the trench as sediment filling. A maximum Te value of ~27 km and a minimum value of ~4 km were obtained. Integrating with the former stress field calculation, we conclude that the Dongsha Event was mainly affected by subduction and collision of the South China Sea toward the Philippine Sea plate. This event commenced at about 10 Ma and peaked at around 3.6 Ma. Although the high effective elastic thickness required is a problem to be addressed, this research provides by far the most comprehensive evidences to the mechanism of the Dongsha Event.

1945Remote ischemic conditioning by single cuff inflation improves aortic elastic properties and endothelial glycocalyx thickness in acute myocardial infarction patients

1945Remote ischemic conditioning by single cuff inflation improves aortic elastic properties and endothelial glycocalyx thickness in acute myocardial infarction patients

Variations of the effective elastic thickness over the Ross Sea and Transantarctic Mountains and implications for their structure and tectonics

The effective elastic thickness (Te) is a proxy for lithospheric strength, and it depends primarily on the thermal gradient and composition of the lithosphere. Accordingly, spatial variations in Te reflect changes in lithospheric properties and can be used to better understand the structure and tectonics of particular regions. In this paper, we investigate the Ross Sea and Transantarctic Mountains in terms of Te using gravity and topographic data and the fan wavelet transform technique. The results reveal that relatively high Te values dominate in the extensional basins of the Ross Sea and the hinterland of Transantarctic Mountains, whereas very low Te values occur along the Transantarctic Mountain Front and in the deep ocean basin, with the lowest Te values are found the vicinity of Ross Island and onshore in northern Victoria Land. In addition, the spatial variations in Te correlate well with lithospheric structure at the regional scale. By combining these findings with published seismic and heat flow data, we conclude that the presence of a zone of anomalously lowTe values parallel to the coast indicates that the lithosphere beneath the Transantarctic Mountain Front is extremely weak due to Cenozoic volcanism and extension. The Te values increase from the Transantarctic Mountain Front (7km) toward the center of the continent (~80km), which indicates that the continental lithosphere underlying East Antarctica belongs to the classic Gondwanan craton. The increase in Te indicates that the Transantarctic Mountain Front marks the continent-continent boundary between East Antarctica and West Antarctica. The Te values in the other extensional basins of the Ross Sea exhibit little variation and average approximately 35km. The relatively high Te values are interpreted to indicate that the lithosphere cooled and became mechanically stronger between late Cretaceous extension and Eocene-Neogene deposition.