查看更多>>摘要：The Mongolian Plateau located between the Siberian Craton and the North China Craton developed after multiple tectonic evolutions. It is proposed to be related to the far-field effect of the Indo-Asian collision in the Cenozoic. In this study, we inverted for high-resolution S wave velocity structures of Mongolia using Rayleigh wave tomography to constrain the plateau evolution. In particular, we obtained crustal and upper mantle seismic structures under Gobi Desert by combining Mongolian and Chinese datasets. The study reveals strong lowvelocity anomalies in the lower crust immediately beneath the Hangay Dome, while the low-velocity zones are imaged beneath the dome margins in the upper mantle. The results imply that the Hangay Dome was formed by mantle upwelling into the crust from major faults following lithospheric delamination. Under the South Gobi Desert, we imaged several inclined high-velocity patches in the upper mantle, indicating the subducted slabs formed in the Paleozoic. The ancient structures in the upper mantle led the Indo-Asian collision to propagate further to southern Mongolia.
查看更多>>摘要：An unexpectedly large uplift of 91 mm was detected by geodetic observations during the rupture of 2016 Mw 6.4 Meinong earthquake, Taiwan, which has been attributed as either a triggered anelastic and hydrologic related deformation from a proposed duplex/mud diapir or a triggered aseismic slip on a proposed backthrust. Here, using both high-rate GNSS and free-field strong motion data, we first estimated the coseismic source model. The locations of high PGV were inferred to explain the unexpected distribution of damaged buildings approximately 25-30 km west of the epicenter. Then, the aseismic surface displacements during the earthquake was differentiated using the coseismic source model. The aseismic extension of 3.8 mu strain is inferred at the unexpectedly large uplift region. Combining with local geology, residual gravity anomaly, seismic tomography, interseismic leveling vertical velocities, coseismic leveling uplifts and proposed Coulomb stress changes, the accelerated mud diapirism during the earthquake triggered by slip on the deep seismogenic fault was identified as the cause of unexpectedly large coseismic uplift.
查看更多>>摘要：The geoid over the north Indian Ocean has a significantly large negative amplitude, even if the excess flattening of the Earth beyond its equilibrium shape is considered. The various mechanisms proposed for this geoid anomaly vary and acceptable geoid predictions are obtained for specific tomographic models only. In this study, we identified model-independent features in the mantle beneath the Indian Ocean and Ross Sea region by analyzing eight recent global tomographic models. We standardized each of the models and applied cluster analysis to regionalize geophysically significant features in various depth ranges. These regionalizations are compared grid-by-grid to construct vote-maps. They highlight the anomalous features consistent across models and their approximate dimensions. Low velocity anomalies of dV(S) similar to-1.1% in the similar to 400-680 km depth range are consistent in almost all the models beneath the Indian Ocean and Ross Sea. High velocity anomalies of dV(S) >= 1% at depths below 1600 km, incoherent in dimension and orientation, are also observed. High velocity anomalies are most likely subducted slabs while low velocity anomalies could be partial melts generated by hydration of mantle. Additionally, a consistent low velocity structure is seen throughout the mantle beneath the southwestern Indian Ocean and east Africa. It is mostly likely a plume rising from the African LLSVP. It connects to the probable partial melts beneath the Indian Ocean via a remnant trail. Forward modelling of the geoid using votemaps reveals that the E-W extent of the Indian Ocean Geoid Low is precisely reproduced by the consistent low velocity anomalies in the upper mantle. However, the N-S extent, most likely dependent on lower mantle anomalies, is not expressed since the dimension, orientation and dV(S) characteristics of high velocity structures are inconsistent in different models. The inter-model agreement is insufficient to identify structure(s) seen across models that can explain the geoid low over the Ross Sea.
查看更多>>摘要：Located in the western Northpatagonian region, Argentina, the Lower Jurassic Can??ad??on Chileno Complex (CCHC) provides a remarkable opportunity to assess the roles of pre-, syn-, and post-eruptive faulting in felsic diatremes complexes evolution. The structural analyses of fractures, dikes, and folds allow recognition of the occurrence of four different strain partitions (SP1-SP4) developed during the Lower to Middle Jurassic. Recognized strain configurations show equivalent temporal and structural relationships throughout the Jurassic backarc system of Patagonia and contemporary basins of southern South America. The stratigraphical criteria allow inferring an Upper Sinemurian to Lower Pliensbachian time interval for the initial strain configurations (SP1, SP2, and SP3). WNW, NNE, and NE-oriented extensional phases were defined and correlated with adjoining areas. Particularly, the third strain partition phase is characterized by a significant transpressive deformation. A NE contractional episode characterizes the post-eruptive deformation stage (SP4) during the Bajocian to Callovian interval. Tectonic interpretations were elaborated concerning subduction dynamics, continental drift, and rotation that controlled the regional and local stress configuration throughout the Jurassic Period of Patagonia and central Argentina.
查看更多>>摘要：Knowledge of the regional crustal deformation and stress field is fundamental to understanding and constrain the ongoing evolution of Hovsgol basin, northwest Mongolia. The 2021 Mw 6.7 Turt earthquake provides an unprecedented opportunity to probe the local tectonic stress field and upper crust deformation. We investigate the coseismic surface displacements and invert fault slip models using Interferometric Synthetic Aperture Radar observations and teleseismic data. The mainshock occurred as a result of normal faulting with a right-lateral strike-slip component on an NW striking plane, which is consistent with the transtensive local stress field inverted from regional focal mechanisms. It is surrounded by transpressive and strike-slip stress fields proposed by previous studies indicating regional stress heterogeneity probably controlled by the distinct structure geometries in and around Hovsgol basin. Our results also suggest that the current deformation of the Hovsgol basin is dominated by half-graben forming. Seven historical strong earthquakes (M 7) may advance the 2021 Turt earthquake by-12% recurrence interval, based on the assumption of equal stress release from recurrence earthquakes, meanwhile, the 2021 Turt earthquake may increase the potential seismic hazard on the neighbor Mondy and South Hovsgol faults, which deserves more attention.
查看更多>>摘要：Near-continuous monitoring both of gas emissions (CO2, CH4 and H2S) and of water temperature at Santa Venera al Pozzo thermal springs (SE foot of Mt. Etna volcano, Sicily, Italy) was conducted from December 2017 to April 2019, using a novel and cheaper Chromatography Monitoring System (CMS) coupled with a water temperature sensor. The results showed methane as predominant gas and temporal changes in gas concentrations that were in part due to daily fluctuations, which caused small amplitude variations, and in part due to non-environmental causes. These latter were correlated with the occurrence of strong earthquakes and slow tectonic events related to magmatic intrusions, but not with input of magmatic gases into the thermal aquifer, given the nonmagmatic origin of all monitored gases. Methane spikes were observed during many volcano-tectonic events and call for a deep source of this gas. H2S was detected only during the strongest local tectonic events, including a Mw 4.9 earthquake, suggesting that this gas has a common origin as CH4 (i.e., mixing between microbial and thermogenic gas), but it is released only when tectonic stress is applied for sufficiently long periods as to cause H2S oversaturation in the hydrothermal aquifer. Water temperature decreases were also observed immediately after the two strongest earthquakes in the area, which helped us produce a comprehensive model to explain the observed geochemical variations. Our approach allowed revealing the great sensitivity of gases such as CH4 and especially H2S to tectonic stress, thus making them valuable indicators of impending strong tectonic or volcano-tectonic events.
Galland, Olivierde la Cal, HernanMescua, JoseRabbel, Ole...
18页
查看更多>>摘要：Laccolith emplacement and growth are controlled by doming of overburden rocks. Understanding the mechanics and structural evolution of laccolith-induced doming is therefore essential for revealing the emplacement dynamics and growth of laccoliths. In this paper, we present a 3D reconstruction of a subsurface laccolithic intrusion through the structural reconstruction of a well-exposed dome at Pampa Amarilla, Neuquen Basin, southern Mendoza province, Argentina. The 3D reconstruction was made possible by the unique integration of surface geological data and subsurface 3D seismic and borehole data. We estimate that the Pampa Amarilla laccolith is similar to 400 m thick, similar to 3 km and 2 km long in the E-W and N-S directions, respectively. Along an E-W cross section, the laccolith exhibits a wedge shape with maximum thickness near its western edge and gradual thinning toward the east. The structure of the dome is typical of a trapdoor, with faulting along the western, northwestern and southwestern edges, and tilting of the overburden to the east. The trapdoor tilting of the laccolith's overburden was the main mechanism controlling the thickening and growth of the Pampa Amarilla laccolith, which exhibits a relatively high thickness-to-length ratio T/D similar to 0.13. Numerous laccolithic intrusions exhibit similar values of T/D, and our study suggests that faulting commonly controls emplacement of laccoliths with T/D > 0.1; conversely, our study suggests that the established mechanical models of laccolith emplacement based on elastic bending of the overburden applies only to thin laccoliths. Finally, our study highlights the necessity and value of integrating field geological measurements with subsurface 3D seismic and borehole data for structural reconstructions of subsurface laccolith intrusions.
Serck, Christopher SaeboBraathen, AlvarHassaan, MuhammadFaleide, Jan Inge...
18页
查看更多>>摘要：The Utsira High (North Sea) records rift faulting that culminates with Jurassic-Cretaceous crustal-scale rollover towards the Viking Graben. This deformation is superimposed on Paleozoic fault-bounded basins on a substrate of Caledonian nappes. The latter contains multilevel crustal-scale shear systems that domed under the Utsira High during the Devonian, as indicated by mapping and interpretation of a large long-offset 2D seismic reflection dataset. Restorations show that isostatically driven doming from excision of overthickened crust caused uplift and erosion of basins and the underlying nappe stack. Doming took place above a crustal rollback system as a symmetrical metamorphic core complex formed. The dome discloses vertical flattening kinematics below bidirectional shear systems, evident by opposite shear-fabric kinematics on opposite dome flanks. A major detachment marks the upper boundary of a transition between upper and lower plate strain regimes, coinciding with low-reflective granitic units above strongly reflective Caledonian nappes. This detachment hosts transportparallel corrugations that strike E-W to NE-SW. A series of deeply eroded half-grabens on top of the upper plate are bounded by pre-Permian faults exhibiting top-NE extensional kinematics. Faults sole out in the fundamental detachment level, locating the brittle-ductile transition, with all structures subsequently rotated during doming. A new localized detachment formed at a shallower level above the region of maximum crustal uplift, seen as upwards detachment migration driven by heating. Later faulting locates to the dome flanks, either rejuvenating rotated shear zones or cutting to deeper crustal levels while recording predominantly down-eastward transport. During Jurassic-Cretaceous rifting, deformation localized to the Viking Graben Boundary Fault, giving room for thick growth wedges in the Viking Graben and establishing the Utsira High as a crustal-scale rollover structure.
Munch, JessicaUeda, KosukeSchnydrig, StephanieMay, Dave A....
22页
查看更多>>摘要：Surface processes and sediments have been suggested to play a crucial role in subduction initiation and to speed up subduction and plate tectonics. The exact roles of sediments and surface processes and the way they influence slab retreat dynamics has however not been constrained yet. Here, we analyse these roles by using 3D numerical thermo-mechanical modelling code coupled to surface processes model in order to investigate large scale dynamics of retreating subduction zones. We focus on two regional-scale geodynamic scenarios: a slab retreating in a homogeneous oceanic domain and a slab retreating along a continental margin before entering an oceanic domain. We study the influence of the thickness of the sediment cover on the oceanic crust and the intensity of surface processes. We show that the sediment thickness and the surface processes both affect the retreat dynamics in a distinct manner, and, when the slab retreats along a continental margin, also influence its trajectory. A thick sediment cover leads to the building of a large accretionary prism which acts as a lock on the system and slows down the slab retreat. When the slab retreats along a continental margin, the thicker the sediment cover, the stronger the slab deviation from that margin. Surface processes have a more complex role which depends on the amount of sediments available. In systems where little sediments are available, a higher efficiency of surface processes leads to a slow down of slab retreat by accumulating sediments in the accretionary wedge. In systems where a lot of sediments are available, a higher efficiency of surface processes slightly speeds up the retreat, by eroding the overriding plate and the subducting plate respectively at the front and the back of the accretionary wedge, as well as the prism itself when reaching a high enough elevation, thereby decreasing the mechanical locking caused by the accumulation of sediments.
查看更多>>摘要：The Daiyunshan volcanic field is one of the largest volcanic fields in the volcanic-plutonic complex belt along the coast of SE China, which records a long volcanic activity history from the Late Jurassic to the Late Cretaceous. In this paper, we conduct comprehensive petrological, geochemical, isotopic and zircon trace element analyses for two representative calderas (Shiniushan and Yunshan) to reveal the crystal-melt segregation and magma recharge processes of the Daiyunshan volcanic field. Systematic LA-ICP-MS zircon U-Pb dating and isotope analyses reveal that the porphyritic quartz monzonite, porphyritic granite and rhyolite of the Shiniushan caldera have identical crystallization ages (97???94 Ma) and consistent Nd-Hf isotope compositions [??Nd(t) = -3.6 to -2.8; zircon ??Hf(t) = -2.7 to 1.8], which are consistent with those of the porphyritic quartz monzonite and rhyolites in the nearby Yunshan caldera, indicating that the magmas of the two calderas were derived from a common magma source region. Volcanic-plutonic rocks from two calderas display metaluminous to peraluminous features and have low MgO, FeOT, Ni and Cr contents. We thus suggest that their parental magmas were derived by remelting of pre-existing crust with contributions of juvenile components. The Shiniushan porphyritic granite and rhyolite and the Yunshan rhyolites are characterized by distinctly negative Eu anomalies and depletions of Ba, Sr, P and Ti, while the porphyritic quartz monzonites from both calderas show complementary geochemical signatures, such as positive Ba anomalies and neglectable Eu anomalies. The back-scattered electron (BSE) images and energy-dispersive X-ray spectrometry (EDS) phase mapping of the Shiniushan porphyritic quartz monzonite reveal textural indicators of crystal accumulation, such as imbrication and synneusis of plagioclase phenocrysts. Their interstitial assemblages of K-feldspar, quartz and plagioclase commonly resemble the phenocryst assemblages of porphyritic granite. We believe that the Shiniushan porphyritic granite and rhyolite and Yunshan rhyolites represent extracted melts from the mush reservoir, while porphyritic quartz monzonites in both calderas are inherent cumulates that have lost interstitial melts. Therefore, our study shows that the Late Cretaceous volcanic-plutonic rocks in the Daiyunshan volcanic field should be connected by crystal-melt segregation processes. Furthermore, a typical zigzag variation in zircon ??Hf(t) values is shown by the Late Jurassic to Late Cretaceous volcanic-plutonic rocks from the Daiyunshan volcanic field, indicating variable contributions of asthenospheric mantle-derived melts and the multistage slab rollback of the subducting paleoPacific plate beneath SE China.
NSTL
Elsevier