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.
查看更多>>摘要：The east-west (E-W) trending South Tibetan Detachment System (STDS) and the north-south (N-S) trending normal faults and detachments have played significant roles in the Himalayan tectonic evolution since the Miocene. The Ama Drime Massif (ADM), which is bounded by the STDS in the north as well as the Dinggye and Kharta N-S trending detachments in the east and west, respectively, is a rare place where N-S and E-W extensions interacted and thus contains key information to detect the evolution of Himalayan extensional structures. Aiming at fully reconstructing the exhumation process of the ADM and figuring out the mid-Miocene evolution of Hi-malayan extensional structures, this contribution provides detailed field investigations and geochronological, petrological, as well as mineral compositional studies to constrain the activity of the detachments surrounding the ADM, the metamorphic process, and the thermal state of the ADM. The geochronological results suggest that both the STDS and the Dinggye detachment were active at 13 Ma. Unlike the Dinggye detachment, whose ductile deformation terminated at-10 Ma, the Kharta detachment maintained its ductile deformation until at least 8.5 Ma. Geochronological, petrological, and mineral compositional analyses show that the ADM paragneiss under-went muscovite dehydration melting and garnet breakdown from at least 20 Ma to 12.5 Ma, indicating a long-term exhumation of the ADM. Importantly, biotite dehydration melting and garnet growth in the ADM orthogneiss suggest a heating event in the ADM at 15???13 Ma. Based on the temporal relationship of different extensional structures, the exhumation of the ADM was dominated by the STDS before 15 Ma, and subsequently by the E-W extension of the Dinggye and Kharta detachments since 15???13 Ma. The E-W extension led to sig-nificant uplift and melting of the ADM gneisses, which made the STDS reactivate as a passive stretching detachment after its-15 Ma cessation. In the mid-Miocene E-W extensional regime, the ADM had exhumed asymmetrically with decreasing time and amount of the exhumation from its eastern side to the western side. Together with the heating event, the asymmetric exhumation indicates the lateral delamination of the subducted Indian lithosphere beneath the ADM in the middle Miocene. From a wider perspective, the mid-Miocene E-W extensions in the Himalayan Orogen were intrinsically controlled by the deep geodynamic process of the sub-ducted Indian lithosphere and played a important role in the diachronous cessation of the STDS.
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：Arclogites are an important part of the continental arc root architecture. When overlooked, the crustal structure could be misinterpreted, assuming that the seismically defined Moho necessarily coincides with the crust-mantle boundary. Evaluating the possible presence of lower crustal rocks below the seismic Moho with physical properties resembling those of the underlying mantle, is therefore, of major importance. Through a multi-approach receiver function assessment, which includes shear wave velocity inversion, and determination of plausible crustal seismic velocity distributions from forward modeling, we present new constraints on the seismic structure of the arc root beneath the Colombian Andes magmatic arc. Results suggest a high-velocity arc root with a latitudinally variable thickness, from 13.5 to 20 km. The arc root is composed of a 4 to 6 km thick upper domain with seismic wave speeds 5% slower, and 8.5 to 14 km thick lower domain 5% faster, relative to the underlying uppermost mantle. This lower crustal structure, coupled with documented garnet pyroxenitic xenoliths, supports an arclogite nature for the Colombian Andes arc root.
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.
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.
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.
查看更多>>摘要：The uplift mechanism and geodynamic model of the northeastern (NE) Tibetan Plateau remain controversial. Two competing models have been proposed for the uplift of the NE Tibetan Plateau, including crustal shortening through folding or thrust faulting and the middle-lower crustal flow model. Here, we applied the joint inversion of surface wave dispersions and receiver functions with P-wave velocity constraints on a dense linear broadband seismic array to obtain the Vs and Vp/Vs profiles of the crust and uppermost mantle across northeastern Tibet. The inversion yields robust structural images that show stark Vs and Vp/Vs jumps across the West Qinling fault from the Songpan-Ganzi and Kunlun-West Qinling terranes (south) to the Qilian and North China terranes (north). The results reveal that regional low-Vs/high-Vp/Vs anomalies present in the middle-to-lower crust, which may be the signature of viscous flow, are distinctly limited south of the West Qinling fault. In contrast, the imaged physical properties of the crust and mantle lithosphere north of this fault manifest a rigid pattern, which is inferred to be originated from the North China craton underthrust below the northern margin of the Tibetan plateau. Our seismic imaging indicates that the NE corner of the Tibetan Plateau does not currently serve as the flow channel of the ductile material from the central and northern Tibet.
查看更多>>摘要：The origin of the high-elevation and neotectonism of western Mongolia remains enigmatic. Several studies suggested that the mechanisms might, at least in part, lurk in the mantle, but little consensus was reached on its pattern and contributions to the surface topography. Geophysical and geodynamical studies indicated that the viscous stresses exerted by mantle flow can maintain a substantial proportion of topography and gravity anomaly, resulting in a high long-wavelength free-air admittance and dynamic topography. These two estimates are commonly used as indicators to detect mantle flow. In this study, we provided evidence for mapping mantle flow beneath western Mongolia by lithospheric flexure analysis in terms of the relationship between gravity anomaly and topography. Our results show a significant dynamic topography of an amplitude over 500 m and a high long-wavelength free-air admittance of value over 35 mGal/km in the southwestern part of western Mongolia, leading to a reliable argument for mantle upwelling beneath western Gobi Altai. We also reveal that the long-wavelength free-air admittance deviates from lithospheric flexure isostasy in the Hangai Dome. Combined with other studies, we infer that horizontal flow fed by the upwelling from western Gobi Altai supports the Hangai Dome uplift. Our results demonstrate the significant role of mantle flow in shaping the present-day anomalous topography and tectonism in western Mongolia, central Asia.
Bagdasaryan, Tatyana E.Thomson, Stuart N.Latyshev, Anton, VVeselovskiy, Roman V....
14页
查看更多>>摘要：We present results of apatite fission-track analysis of seven intrusions located within the Permian-Triassic Siberian Traps Large Igneous Province (LIP): (1) alkaline-ultramafic central type plutons of Odikhincha, Yessey and Magan, (2) intrusions of Norilsk-1 and Kontay, (3) Padunsky sill, and (4) Kotuy dike. Additionally, we also present a set of new geochmnological data for some of studied intrusions: (a) LA-ICPMS U-Pb apatite ages of the Odikhincha pluton (266 +/- 29 Ma) and the Padunsky sill (241 +/- 12); (b) Rb-Sr ages from the Odikhincha (258.0 +/- 0.6 Ma), Magan (242.8 +/- 6.8 Ma) and Yessey (243.1 +/- 2.7 Ma) plutons; and (c) Ar-40/Ar-39 mica ages from the Odikhincha (264.3 +/- 3.0 Ma) and Magan (254.7 +/- 3.1 Ma) plutons. Most of these intrusions, probably with the exception of the Odikhincha, were emplaced during the most voluminous phase of the Siberian Traps magmatism ca. 252-251 Ma, but their AFT ages are distributed from 207 +/- 17 to 173 +/- 13 Ma and much younger than Late Permian to Early Triassic isotopic ages from these and other Siberian Traps LIP intrusions. Available AFT, U-Pb, Rb-Sr and Ar-40/Ar-39 data and time-temperature modeling has allowed us to create the first model of the post-Paleozoic tectono-thermal history of the Siberian Traps. After their emplacement ca. 251 Ma the studied rocks underwent a later phase of rapid cooling to below 120-60 degrees C during the time interval similar to 207-173 Ma and have remained near the surface until present. We propose this later cooling event is linked to exhumation associated with coeval Late Triassic-Early Jurassic large-scale uplift of the Siberian platform caused by collisional processes at its periphery. Our new results also indicate that at least a 1-2 km thickness of Siberian Traps lavas have been removed by erosion in the north of the Siberian platform since eruption, implying the total volume of the Permian-Triassic lavas was much greater than that currently preserved today.
NSTL
Elsevier