查看更多>>摘要：Based on field geology, seismic reflection profiling data and isopach maps, the structural deformation pattern, timing of deformation, and mechanism of formation of the western part of the NE Qaidam Basin (including the Pingtai Uplift, Lenghu and Eboliang structural belts) during the Mesozoic and Cenozoic eras have been investigated. Several anticlines in the Lenghu and Eboliang structural belts are generally characterized by double fault systems at different structural levels. At shallower crustal levels, a thrust fault system dominates and at lower levels positive flower structures accommodate oblique shortening, and these are mainly separated by weak strata layers in the Upper Xiaganchaigou Formation, of late Eocene age. Left-step en echelon distributed normal faults and trailing extensional imbricate fan structures consistently demonstrate that the Lenghu and Eboliang structural belts are dominated by dextral transpressional deformation. The western part of the NE Qaidam Basin experienced an initial stage of extension in the Jurassic, which was associated with the formation of several NWstriking normal faults. We hypothesize that most of the deep compressional structures and shallow anticlines were formed due to the SW-directed thrusting of the Qilian Shan since the early Eocene, as a far-field effect of the Indo-Asian "hard" collision. The NNE-directed shortening was associated with dextral transpressional deformation within the western part of the NE Qaidam Basin that took place after the deposition of the Shangyoushashan Formation, of middle-late Miocene age. We interpret this phase of deformation to have been an integral part of the pulsed growth of the whole Tibetan Plateau.
查看更多>>摘要：The Indian Ocean geoid low (IOGL) is one of the lowest geoid anomalies on Earth. Several theories have been proposed to explain this geoid low, including past subduction (Nerlich et al., 2016; Rao and Kumar, 2014), subduction coupled with low velocity anomalies in the upper mantle (Spasojevic et al., 2010) and hot, low density anomaly in the upper to mid mantle depths (Reiss et al., 2017; Ghosh et al., 2017). It was also argued by Ghosh et al. (2017) that subducted slabs in the lower mantle have minimal role to play in contributing to this geoid signal. We further investigate that claim here by looking at the geoid contributed from various processes (density vs dynamic topography) as well as by inspecting the contribution from different spherical harmonic degrees. Our current findings substantiate the earlier claim that lower mantle slabs indeed play a minimal role in creating this anomalous geoid low.
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.
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).
查看更多>>摘要：The Kalabagh Fault Zone in the western Sub-Himalayas is a dextral strike slip fault zone that exhibits a push-up block in the stepover zone of the two fault segments. The inception of the push-up block occurred along the restraining faults that form two morphotectonic bends along the mountain front at Zaluch and in the South of Thathi. The landform was further developed by en-echelon fold and thrust sequence up to Khairabad in the North and Ghundi village in the South. The aseismically moving fault zone has experienced earthquakes during late Quaternary forming surface expressions in the West of the push-up block at Khairabad, Larkakki and Ghundi. The Khairabad and Ghundi sections are the active tectonic fronts of the stepover zone. Displacements caused by these seismic activities has deformed Quaternary sediments creating stream deflections, surface ruptures, pressure ridges, uplifted sediments at the mountain front, foreland ridges and uplifted alluvial fan. Offsets in the late Quaternary sediments indicate the Kalabagh Fault is active and seismic events of M-w >= 6 has formed these ground effects. Furthermore, stratigraphic correlations of fluvial sediments indicate the Indus River has been flowing in the NS direction along the northern segment of the Kalabagh Fault. Uplift of the push-up block in the Kalabagh Fault Zone and subsequent deposition of the alluvial fans has caused westward diversion of the Indus River.
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.
Gileva, Nadezhda A.Filippova, Alena, IBukchin, Boris G.Fomochkina, Anastasiya S....
15页
查看更多>>摘要：We study the M-w 5.6 Bystraya earthquake, occurred on September 21, 2020 at the SW flank of the Baikal rift zone in the area, in which only few small seismic events have been detected during the whole period of instrumental observations. Source parameters of the mainshock and its largest aftershock (M-w 4.7) are inverted from intermediate-period surface wave amplitude spectra. Hypocentral depths and seismic moment tensors in a double-couple approximation are calculated for both earthquakes, while integral source characteristics, describing its spatio-temporal development, are estimated only for the mainshock. For the Bystraya earthquake, directivity effects (rupture direction and velocity) are also modelled. The obtained results show that the study seismic event can be associated with activation of the SE segment of the Main Sayan fault. The faults of the mainshock and its largest aftershock are formed under the influence of the NW-SE extension and NE-SW compression. The predominance of left-lateral strike-slip motions agrees well with previous studies at the SW flank of the Baikal rift zone. A small thrust-fault component could reflect the inversion uplift of some blocks of the Bystraya basin bottom as well as the Bystrinskaya Sopka massif. The dipping of the earthquake fault plane could indicate flattening of the considered fault segment at some depth or the existence of differently oriented structural discontinuities inside the fault zone of a finite width. The long rupture of the Bystraya earthquake could be connected with its almost pure strike-slip focal mechanism and orientation of the rupture plane approximately along the Main Sayan fault strike.
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.
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).
Zakharov, V. S.Lubnina, N., VStepanova, A., VGerya, T., V...
13页
查看更多>>摘要：Available data suggest that the breakup of the Neoarchean Kenorland supercontinent at 2.5-2.4 Ga was likely triggered by a large mantle plume upwelling that caused significant magmatism. Here, we present 2D high-resolution magmatic-thermomechanical numerical models of extension of the continental crust underplated by a hot mantle plume material. Using this model, it is demonstrated that mantle plume underplating generates a large amount of mafic melt by decompression melting. This melt penetrates into the extending continental crust along normal faults thereby forming multiple generations of mafic dyke-like intrusions along normal faults. In case of extension velocity of 0.2-1 cm/yr, lower crustal heating and hot mafic melt emplacement may cause partial melting of the continental crust that can generate significant volume of felsic melts. This in turn triggers emplacement of felsic intrusions that temporarily and spatially associate with the mafic dyke-like intrusions. The modeling results agree well with geological data from the Karelian Craton and provide possible explanation for the observed association of Paleoproterozoic mafic dykes and felsic intrusions which formed in a relatively short time interval (up to 20 Myrs) in the early stages of the supercontinent breakup.
NSTL
Elsevier