Geodynamic effects of subducted seamount at the Manila Trench: Insights from numerical modeling

Abstract We used numerical modeling to investigate the geodynamic effects of subducted seamounts at the Manila Trench. A series of numerical modeling experiments were conducted with variable parameters, including the activation volume (Vact) and cohesion (C), which influence lithospheric rheology, the plate convergence velocity, and the age of subducting slab. Modeling results indicate that varying the Vact and C within an appropriate range have limited effects on the geodynamic process of subduction. A lower Vact allows the slab to sink more easily and results in a steeper dip angle. A slab break-off is more likely to occur under subduction at depths of 100–300 km, while the existence of a seamount further promotes the break-off process. The convergence rate is a key parameter affecting the break-off timing and depth. In contrast, under subduction where subducted oceanic plate move faster upper plate, the model results exhibit non-break-off, steady subduction. Slab age is another factor controlling break-off, where break-off time extends with slab age. A subduction without seamount will cause a ~2 Myr delay in break-off timing. We suggest that the low-velocity zone under the Manila Trench at 17o N is the result of a break-off event due to subduction of the Zhenbei-Huangyan Seamount Chain. Further to the north, such as the location at 19o N, the absence of seamount and an older oceanic crust would favor a delay in break-off timing during subduction

Drivers of cropland abandonment in mountainous areas: A household decision model on farming scale and a case study of Southwest China

Cropland abandonment has emerged as a prevalent phenomenon in the mountainous areas of China.While there is a general understanding that this new trend is driven by the rising opportunity cost of rural labor, rigorous theoretical and empirical analyses are largely absent. This paper first develops a theoretical model to investigate household decisions on farming scale when off-farm labor market is accessible and there is heterogeneity of farmland productivity and distribution. The model is capable of explaining the hidden reasons of cropland abandonment in sloping and agriculturally less-favored locations. The model also unveils the impacts of heterogeneity of household labor on fallow decisions and the efficiency loss due to an imperfect labor market. The model is empirically tested by applying the Probit and Logit estimators to a unique household and land-plot survey dataset which contains 5258 plots of599 rural households in Chongqing, a provincial level municipality, in Southwest China. The survey shows that more than 30% of the sample plots have been abandoned, mainly since 1992. The econometric results are consistent with our theoretical expectations. This work would help policy-makers and stakeholders to identify areas with a high probability of land abandonment and farming practice which is less sustainable in the mountainous areas

Influence of syntectonic sedimentation on kinematic evolution of fold‐and‐thrust belts with lateral changes in shallow décollement properties and basement inherited structures: insights from analogue modeling

International audienceStructural deformation of fold-and-thrust belts is influenced by the properties of décollements (number, rheology, thickness, etc.), the presence of inherited structures in the basement as well as the amount of syntectonic sedimentation, among others. Although the effect of each of these parameters has been well constrained with a series of numerical and experimental works in the literature, few sandbox models comprehensively consider all these parameters together, and particularly investigate the effect of their lateral variation. In this context, we carried out several 3-D sandbox models to investigate the effect of increasing syntectonic sedimentation rate on kinematic evolution of fold‐and‐thrust systems which contain a basal brittle detachment layer and a shallow detachment layer that changed from a brittle to a viscous domain along the mountain strike. The influence of different basement width structures, affecting the kinematics and geometry of the interbedded viscous décollement, has been also tested.Results indicate that the rate of syntectonic sedimentation exerts a first-order control on the kinematic evolution of fold‐and‐thrust belts since increasing syntectonic sedimentation rate stops (in the brittle domain) or delays (in the viscous domain) the propagation of deformation towards the foreland. Moreover, syntectonic sedimentation prohibits the propagation of deformation in the deep décollement level due to the modification of the taper angle. Structural evolution of the transfer zone in between the brittle and viscous domain is also affected since if becomes narrower and more orthogonal to the mountain front at higher sedimentation rates. Specifically, in the brittle domain, the fault dip angle increases with the increase in syn-sedimentation rate and its cross-sectional geometry becomes straighter. In the viscous domain, syntectonic sedimentation affects the partitioning of deformation with development of long-lived and complex 3-D salt structures near the hinterland (such as squeezed diapirs, salt welds and salt tongue), whereas frontal structure becomes more cylindrical. Toward the hinterland, syntectonic sedimentation increases backthrust activity, which becomes increasingly different between the brittle and viscous domain. For instance, the increase in backthrust displacement in the ductile domain is greater than the one in the brittle domain. About the basement high, our study reveals that it has a strong controlling effect on the viscous domain, dominating the development of structural belt on the top of the basement high and promoting the propagation of deformation front to the pinch-out of the salt layer. Besides, syntectonic sedimentation simplifies the structural style between the basement high and the hinterland. It strengthens the structural influence of the transfer zone, which localizes into a single strike-slip transfer fault which increases the frontal fault displacement.Our experimental results are compared with structures in the Wushi-Kuqa fold-and-thrust belts in Southern Tianshan (Central Asia) and help better understanding interaction between syntectonic sedimentation, décollement properties and basement configuration

Imaging Velocity Fields Analysis of Space Camera for Dynamic Circular Scanning

Compared with traditional push-broom imaging, the space camera that performs the new circular scanning imaging can effectively enlarge the imaging area and obtain high-resolution images. However, the imaging velocity fields of space camera will seriously deteriorate the image quality in the circular scanning imaging process. And the velocity fields are anisotropically distributed due to various factors, including attitude maneuvering, satellite precession, earth curvature, and earth rotation. Therefore, this paper proposes a mathematical model of the velocity field to analyze the effect of circular scanning imaging. Based on the principle of ray tracing, the expression of the instantaneous velocity field on the ground is first derived, and then the corresponding image velocity field is obtained by mapping the velocity vector to the focal plane. In addition, numerical simulations and image simulations are performed to analyze the anisotropy distribution of the velocity vectors. Moreover, the dynamic characteristics of the space camera are analyzed to evaluate the performance of this new imaging. The simulation results show that the higher velocity leads to worse imaging quality. The study of this paper provides guidance for attitude planning and imaging assessment for new remote sensing imaging of space cameras

Analogue modeling of the kinematic evolution of fold-and-thrust belts under various syntectonic sedimentation rates, shallow décollement properties and basement inherited structure configurations

International audienceStructural deformation of fold-and-thrust belts is influenced by the properties of décollements (number, rheology, thickness, etc.), the presence of inherited structures in the basement as well as the amount of syntectonic sedimentation, among others. Although the effect of each of these parameters has been well constrained with a series of numerical and experimental works in the literature, few sandbox models consider all these parameters together, and particularly investigate the effect of their lateral variation.To gain insight on this issue, we carried out several 3-D sandbox models and investigated the effect of increasing syntectonic sedimentation rate on the kinematic evolution of fold-and-thrust systems. Models contain a basal brittle detachment layer and a shallow detachment layer that changed from a brittle to a viscous domain along the model strike. The effect of basement high and syntectonic sedimentation are also considered meanwhile. Model results are compared with field data from the Wushi-Kuqa fold-and-thrust belt (FTB) in Southern Tianshan, Tarim basin, Central Asia.The Wushi-Kuqa is one of the south-vergent FTBs that developed in the southern Tian Shan orogen, within the Tarim basin (Fig. 1). The Wushi (W) and Kuqa (E) FTBs are separated by the Kalayuergun right-lateral strike- slip fault. According to geological maps and drilling data, the shallow décollement involved in the deformation of both FTBs changes laterally in rheological properties. The Neogene Jidike mudstones in the Wushi FTB (W) are considered as frictional, whereas the Paleogene evaporites in the Kuqa FTB (E) are viscous. This leads to different deformation styles along the strike, single fault and fold to the W, and salt nappe and folds to the E.In both FTB, two basement high structures, the Wensu (to the W) and Xiqiu (to the E) basement high, have been interpreted from seismic profiles and affected the décollement continuity and thickness (Fig. 1.c). Thus, the Jidike mudstones in the Wushi FTB decreases in thickness toward the south (Line-1, Fig. 1.c). In the Kuqa FTB, the Xiqiu basement high is closer to the mountain front to the west than to the east. Its arcuate shape is likely responsible for the similar shape of the Qiulitage belt (Line-2 and 3, Fig. 1.c).Analogue modeling approachWe set up two series of experimental models at Lille University, France, to test the influence of syntectonic sedimentation rate magnitude and basement high configuration on FTB development. In Series 1, we test variable syntectonic sedimentation rates, including low (0.3 mm/h), medium (0.6 mm/h) and high (0.9 mm/h) rates. Then we combined basement high and syntectonic sedimentation together in Series 2, and we particularly tested the along-strike change in the width of the basement high.The experimental models were typically made up of three materials that simulate different lithologies of rocks, including: (1) quartz sand, simulating the frictional behavior of brittle sedimentary rocks, (2) glass microbeads, simulating frictional brittle décollement and (3) silicone, simulating a viscous décollement, like salt layers.Modeling results and conclusionModeling results of Series 1 show that the rate of syntectonic sedimentation exerts a first-order control on the kinematic evolution of fold-and-thrust belts which concentrates deformation along the mountain front and delays the propagation of both deep and shallow deformation in the brittle and viscous domains.Modeling results of Series 2 (Fig. 2), indicate that: (1) syntectonic sedimentation reduced the number of fore- thrusts that nucleate between the basement high and the hinterland, in the viscous domain, and reduced the shallow thrust in the brittle domain; (2) basement high controlled the deformation process and distribution of deformation only in the viscous domain. Besides, modeling results can be used to explain salt-influenced deformations on the Xiqiu basement high and in Wushi-Kuqa FTB, which shows that Xiqiu basement high acts as a weak stress zone in the deformation process resulting in localized deformation in the Qiulitage structural belt

Analogue modeling of the kinematic evolution of fold-and-thrust belts under various syntectonic sedimentation rates, shallow décollement properties and basement inherited structure configurations

International audienceStructural deformation of fold-and-thrust belts is influenced by the properties of décollements (number, rheology, thickness, etc.), the presence of inherited structures in the basement as well as the amount of syntectonic sedimentation, among others. Although the effect of each of these parameters has been well constrained with a series of numerical and experimental works in the literature, few sandbox models consider all these parameters together, and particularly investigate the effect of their lateral variation.To gain insight on this issue, we carried out several 3-D sandbox models and investigated the effect of increasing syntectonic sedimentation rate on the kinematic evolution of fold-and-thrust systems. Models contain a basal brittle detachment layer and a shallow detachment layer that changed from a brittle to a viscous domain along the model strike. The effect of basement high and syntectonic sedimentation are also considered meanwhile. Model results are compared with field data from the Wushi-Kuqa fold-and-thrust belt (FTB) in Southern Tianshan, Tarim basin, Central Asia.The Wushi-Kuqa is one of the south-vergent FTBs that developed in the southern Tian Shan orogen, within the Tarim basin (Fig. 1). The Wushi (W) and Kuqa (E) FTBs are separated by the Kalayuergun right-lateral strike- slip fault. According to geological maps and drilling data, the shallow décollement involved in the deformation of both FTBs changes laterally in rheological properties. The Neogene Jidike mudstones in the Wushi FTB (W) are considered as frictional, whereas the Paleogene evaporites in the Kuqa FTB (E) are viscous. This leads to different deformation styles along the strike, single fault and fold to the W, and salt nappe and folds to the E.In both FTB, two basement high structures, the Wensu (to the W) and Xiqiu (to the E) basement high, have been interpreted from seismic profiles and affected the décollement continuity and thickness (Fig. 1.c). Thus, the Jidike mudstones in the Wushi FTB decreases in thickness toward the south (Line-1, Fig. 1.c). In the Kuqa FTB, the Xiqiu basement high is closer to the mountain front to the west than to the east. Its arcuate shape is likely responsible for the similar shape of the Qiulitage belt (Line-2 and 3, Fig. 1.c).Analogue modeling approachWe set up two series of experimental models at Lille University, France, to test the influence of syntectonic sedimentation rate magnitude and basement high configuration on FTB development. In Series 1, we test variable syntectonic sedimentation rates, including low (0.3 mm/h), medium (0.6 mm/h) and high (0.9 mm/h) rates. Then we combined basement high and syntectonic sedimentation together in Series 2, and we particularly tested the along-strike change in the width of the basement high.The experimental models were typically made up of three materials that simulate different lithologies of rocks, including: (1) quartz sand, simulating the frictional behavior of brittle sedimentary rocks, (2) glass microbeads, simulating frictional brittle décollement and (3) silicone, simulating a viscous décollement, like salt layers.Modeling results and conclusionModeling results of Series 1 show that the rate of syntectonic sedimentation exerts a first-order control on the kinematic evolution of fold-and-thrust belts which concentrates deformation along the mountain front and delays the propagation of both deep and shallow deformation in the brittle and viscous domains.Modeling results of Series 2 (Fig. 2), indicate that: (1) syntectonic sedimentation reduced the number of fore- thrusts that nucleate between the basement high and the hinterland, in the viscous domain, and reduced the shallow thrust in the brittle domain; (2) basement high controlled the deformation process and distribution of deformation only in the viscous domain. Besides, modeling results can be used to explain salt-influenced deformations on the Xiqiu basement high and in Wushi-Kuqa FTB, which shows that Xiqiu basement high acts as a weak stress zone in the deformation process resulting in localized deformation in the Qiulitage structural belt