查看更多>>摘要：Collisional shortening in the external Western Alps was first accommodated by internal (distributed) deformation in the External Crystalline Massifs (ECM) and then on frontal crustal ramps (localized deformation). However, the timing of transition between these two periods is still under-constrained, mainly because the available dataset is incomplete in the Western Alps. We here provide new zircon and apatite fission-track (ZFT and AFT) and zircon (U-Th-Sm)/He (ZHe) data that constrain the early stages of cooling hence exhumation of the external Alpine wedge, as well as new Raman Spectroscopy of Carbonaceous Material (RSCM) data from the Belledonne massif. ZFT ages mainly range between 15 and 20 Ma, ZHe ages between 5 and 12 Ma, AFT ages between 2 and 10 Ma. Those data are integrated within inverse and forward thermal history modelling (HeFTy) along with literature data to constrain the late Oligocene-Miocene cooling history and suggest that exhumation of the Belledonne and the Pelvoux massifs may have started as early as ca. 27 Ma. This early exhumation was rather slow (similar to 50 m.Myrs(-1) +/- 2 m.Myrs(-1)) and may date the transition between the distributed and the localized mode of shortening, i.e., the initiation of the crustal ramps below these massifs. Further north, in the Mont Blanc and Aiguilles Rouges massifs, exhumation was active around 18 Ma, and started possibly earlier, around 20-25 Ma. From this time on (18 Ma), exhumation rates increased in all external massifs (similar to 500 +/- 40 m.Myrs(-1), both North and South). This age most likely corresponds to the end of the transition period between distributed and localized shortening with localisation along the frontal crustal ramps and the rapid associated exhumation, then cooling of the hangingwall (even considering that cooling may start a few Myrs later than exhumation if isoterms are advected). This timing notably corresponds to a transition between the two molasse mega-sequences in the foreland basin (Lower Marine/Freshwater Molasse and Upper Marine/Freshwater Molasse).
Loncke, Liesde Lepinay, Marion MercierBasile, ChristopheMaillard, Agnes...
21页
查看更多>>摘要：The Demerara and Guinea plateaus are conjugate Transform Marginal Plateaus (TMPs) formed at the junction of the Jurassic Central Atlantic Ocean and the Cretaceous Equatorial Atlantic Ocean. We compare their structure and evolution through a combined industrial/academic seismic dataset tied by well data. We show that these TMPs record a complete evolution history from the Jurassic Central Atlantic to the Equatorial Atlantic breakup and seafloor spreading phases. Both plateaus first formed as volcanic margins displaying successive SDR wedges migrating towards the newly forming Central Atlantic domain. In this context, Demerara and Guinea, conjugates of the Bahamas, seem to have formed in relation to plume activity at the southern end of the Central Atlantic domain. Our dataset suggests that the Demerara and Guinea plateaus initially represented two distinct extrusive centres separated by a crustal basement high. Later, during the Cretaceous Equatorial opening phase, both plateaus separated in a transform mode following this discontinuity. Deformation is notably asymmetric during this phase: Aptian to Albian folding, strike-slip, transtensive deformation and complex vertical movements on the Demerara side and only minor deformation on the Guinean side, except on its divergent Sierra Leone termination. The deformation is sealed on both plateaus by a regional upper Albian erosion unconformity. Extensional reactivation occurs on the Guinea side (probably through a general collapse?). To conclude, this study provides new insights into the nature and origin of TMPs and the key tectono-sedimentary archives they may contain to understand the polyphase breakup conditions of Gondwana.
查看更多>>摘要：Crustal deformation due to the 2016 earthquake sequence in Kumamoto, Japan, that culminated in a preceding earthquake of magnitude M6.5 and a subsequent M7.3 earthquake 28 h later, caused stress perturbation on and around the causative Futagawa-Hinagu fault zone. Monitoring changes in seismicity pattern along this zone plays a role in understanding the process before and after major earthquakes. For this purpose, stress-dependent laws in statistical seismology can be used: the Gutenberg-Richter frequency-size law and the Omori-Utsu aftershock-decay law. We review the results obtained by using these laws in previous studies to show a zone of high stress near the eventual epicenters of the M6.5 and M7.3 earthquakes before the start of the Kumamoto sequence, and after it, showing a decreasing trend in stress along the Futagawa-Hinagu fault zone. Detailed analysis suggests aseismic slips along the causative fault zone. The aseismic preslip locally reduced stress just prior to the M7.3 earthquake near its epicenter. Recently, a system was proposed by Gulla and Wiemer (2019) that utilizes the Gutenberg-Richter frequency-size law to judge, immediately after a large earthquake, whether it was the mainshock or a foreshock to a future event. Based on the reviewed results and our new results, further research that takes into account the spatial variation of frequency-size distribution, allowing the exploration of the possibility of a local preslip of a future nearby earthquake, is needed to improve this system.
查看更多>>摘要：Knowledge of the crustal stress state is important for understanding tectonic processes and seismic hazard assessment as well as for various practical applications. In this study, we present a model describing the contemporary 3D crustal background stress field of the eastern Tibetan Plateau. The model incorporates a complex fault system and an appropriate initial stress state that matches both model-independent stress observations and kinematic data well. Our results show that the modeled maximum horizontal stress SH is generally oriented in NW-SE direction. The Bayan Har Block and the Chuan-Dian Block are dominated by a strike-slip faulting stress regime. However, in some local areas, the crust is governed by a normal faulting regime. We infer that the local normal faulting stress regime in the Bamei-Kangding area is caused by the clockwise rotation of the strike of the Xianshuihe fault at Kangding. This normal faulting stress regime would promote the ascent of intrusions and provide the space necessary for the emplacement of the Zheduoshan granite. The stress state on the Longmen Shan fault zone is rather inhomogeneous. For the Yingxiu-Beichuan fault, the northeastern segment has a lower normal stress but a higher shear stress than the southwestern segment. This inhomogeneous stress state on the Yingxiu-Beichuan fault could provide an explanation for the northeastward propagation of the ultralong unilateral rupture in the Wenchuan Ms8.0 earthquake. According to the stress state on the Xianshuihe fault, we conclude that the Kangding-Shimian segment has a high potential to produce a strong earthquake due to its high normal stress and a fast slip rate and should be carefully monitored. On the Bamei-Kangding segment, which is governed by a normal faulting stress regime and may be lubricated by fluids, slip seems to be facilitated favoring more frequent small to moderate magnitude earthquakes to occur on this segment.
查看更多>>摘要：Continental rifts are the expression of regional horizontal stretching and are in modelling studies often assumed to be the result of orthogonal or oblique extension. However, naturally occurring V-shaped rift geometries infer an underlying rotational component, resulting in a divergence velocity gradient. Here we use such analogue models of rifting in rotational settings to investigate and quantify the effect of such a divergence velocity gradient on normal fault growth and rift propagation towards a rotation pole. Particularly, we apply different divergence velocities and use different brittle-ductile ratios to simulate different crustal configurations and analyse its effect on rift propagation and surface deformation. Surface deformation is captured using stereoscopic 3D Digital Image Correlation, which allows for quantifying topographic evolution and surface displacement including vertical displacement. In combination with X-Ray computed tomography, we gain insights into the three-dimensional structures in our two-layer models. Based on our models, we present a novel characterisation of normal fault growth under rotational extension which is described by 1) an early stage of bidirectional stepwise growth in length by fault linkage with pulses of high growth rates followed by a longer and continuous stage of unidirectional linear fault growth; 2) segmented rifting activity which promotes strain partitioning among competing conjugate faults and 3) along-strike segmented migration of active faulting from boundary faults inwards to intra-rift faults allowing different fault generations to be simultaneously active over the entire rift length. For models with higher divergence velocities, inward migration is delayed but other first-order observations are similar to models with lower divergence velocities. Our quantitative analysis provides insights on spatiotemporal fault growth and rift propagation in analogue models of rotational rifting. Although natural rifts present complex systems, our models may contribute to a better understanding of natural rift evolution with a rotational component.
查看更多>>摘要：Constraining the shortening rate, timing, and deformation pattern in the frontal parts of the southern Qilian Shan (China) is helpful to further understand the strain distribution model and the tectonic deformation mechanism of the Qilian Shan. The Santai fold belt is one of the active thrust and fold belts parallel to southern Qilian Shan in the northern margin of the Qaidam Basin. It has experienced the structural evolution and interactions between itself and surrounding areas throughout the Late Cenozoic. Based on the geological and geomorphic mapping, landform profile surveys, and seismic line interpretations, the Santai anticline is considered to be a fault-propagation fold that is controlled by basement-involved faulting and limb rotation. In the late Quaternary, the shortening rate of the Santai anticline was almost 0.4 +/- 0.17 mm/a, accounting for about 8% of the crustal shortening across Qilian Shan, and with the assumption of a constant shortening rate, latest rapid deformation occurred at about 3 +/- 1.1 Ma. This indicates that the loci of deformation sequentially migrated southward in the foreland.
Austria, Rurik S. P.Parcutela, Nathaniel E.Reyes, Edd Marc L.Armada, Leo T....
12页
查看更多>>摘要：The Macolod Corridor (MC) is a NE-SW trending zone of Quaternary volcanism which perpendicularly bisects the Luzon Arc. This peculiar zone of volcanism is in a junction of different tectonic elements. This led to several models of formation associated with subduction or crustal extension-related processes. New information about its subsurface structure can provide constraints in resolving outstanding questions on its tectonic development. However, elucidating the origin and deep structure of the MC has been problematic due to the extensive young volcanic deposits that blanket the area. In this study, ground magnetic and aeromagnetic datasets are merged to characterize the magnetic signature in the MC. Short wavelength and high amplitude anomalies suggest complex interactions of magnetic bodies within the region. Edge detection techniques reveal linear magnetic anomalies with NE-SW, NW-SE, and E-W trends in the Corridor. These may indicate rift structures at depth. Analytic signals show maximum amplitudes over volcanic centers suggesting maximum magnetic property contrasts due to deep structural controls. Euler solutions cluster in the NE-SW, NW-SE, and E-W trends. These may correspond to conjugate structures at depth suggesting the primary role of the NW-SE shearing between the bounding Philippine Fault and the Sibuyan Verde Passage Fault. Clustering of solutions in a graben-like pattern is also observed beneath volcanic complexes indicating an extensional regime. The MC is also characterized by a shallow magnetic basement as reflected in the Curie point depths. This may be attributed to high heat flow associated with active volcanism and probably crustal thinning. These results skew our interpretation to a rift-related origin of the MC. Thus, it is interpreted to be the manifestation of the continuum of tectonic processes including near-field influences (shearing between the two bounding faults) and far-field influences (arc-continent collision and resulting northwestward translation of the Philippine Mobile Belt).
查看更多>>摘要：As an active intracontinental omgenic belt within the far field influence of the India-Eurasia collision, the Tien Shan is a natural laboratory to study the mechanisms of the large-scale mountain building. In this study, we image crustal seismic structures beneath the central Tien Shan using the H-kappa-c method with the harmonic corrections on Ps and its crustal multiples (PpPs, PpSs + PsPs) in P-wave receiver functions (RFs). The RFs are calculated from three-component seismograms recorded by 43 broadband stations located in central Tien Shan and surrounding areas. The robust and high-resolution images of the crustal thickness (H) and average Vp/Vs ratio (kappa) are finally obtained. From our observations, the crustal thickness beneath the central Tien Shan is larger (50- 65 km) than those beneath the Kazakh Shield (similar to 45 km) and Tarim Basin (similar to 42 km). The x image denotes a general distribution of kappa which is higher than 1.73 in most parts of the central Tien Shan, as well as the margins of the Kazakh Shield and Tarim Basin, while lower than 1.73 only in some sporadic areas of this orogenic belt. Our seismic results suggest the complex intracontinental collision with the inhomogeneous crustal thickening in the mountain building. Moreover, the kappa image implies the partial melting within the crust beneath the central Tien Shan. Combining with previous seismic studies, we infer that the magmatic intrusion of the hot upwelling mantle materials induces the partial melts within the crust, and also contributes to the rejuvenation of the Tien Shan orogenic belt.
查看更多>>摘要：Geological observations have revealed a rapid evolution and obvious east-west differential evolution in the North Sulawesi subduction zone. The Celebes Sea plate has inserted itself under the north arm of Sulawesi Islands, which has simultaneously rotated clockwise. The rotation of the north arm of the Sulawesi Islands might be critical in facilitating tectonic processes, such as the slab subduction and rollback of the Celebes Sea plate. For the east-west differences along the North Sulawesi subduction zone, a numerical model with the convergence rate of the plates as the basic variable is established to quantitatively describe the evolution process of the North Sulawesi subduction zone. Our results reproduced the east-west differences of the subducting Celebes Sea plate, showing a shallow-deep-shallow subduction style. We propose that the variable velocity ratio of the overriding plate to the subducting slab could be the principal reason for the differential subduction along the strike of the North Sulawesi subduction zone. We conclude that the residual slab and the rate of the eastern continental plate limit the downward movement of the subducted slabs of the eastern Sulawesi. Furthermore, the reason for the shorter subducted slab at the extreme western Sulawesi is the fact that subduction occurs outside the rotation radius. Moreover, the widespread extension at the western Sulawesi has a limited correlation with the clockwise rotation.
查看更多>>摘要：Deformation localization is a widely observed, but rarely quantified process in the crust. Recent observations suggest that the localization of seismicity and fracture networks can help identify the approach to catastrophic failure. Here, we quantify the localization processes of the volumetric and deviatoric strain components in twelve triaxial compression experiments imaged with X-ray tomography. We capture three-dimensional images of the rock cores during triaxial compressing toward failure, and then calculate the local strain components using digital volume correlation. The divergence and curl of the incremental displacement vector field provide the volumetric and deviatoric components of the strain field. We quantify localization using the proportion of the rock occupied by high magnitudes of the volumetric and deviatoric strains, and the Gini coefficient of these high magnitude strains, which measures the deviation from a uniform process. We find that the vast majority, but not all, of the experiments experience strain localization toward failure. The rocks typically experience their maximum degree of strain localization not immediately preceding failure, but on average at 90% of the failure stress. The volumetric strain tends to localize more than the deviatoric strain. These observations support using the localization of the volumetric strain, along with the deviatoric strain, to identify the evolution of the precursory phase preceding earthquakes.
NSTL
Elsevier