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：One major critical issue in seismic hazard analysis deals with the computation of the maximum earthquake magnitude expected for a given region. Its estimation is usually based on the analysis of past seismicity that is incomplete by definition, or derived from the dimension of faults through empirical relationships with the intrinsic uncertainty in source characterization. Here, we propose a workflow aimed at providing a timeindependent estimate for the maximum possible magnitude based on geological and geophysical evidence. Our estimate is also source unrelated as it is constrained by the seismic brittle volume of the crust that scales with the effective seismic energy. The seismic brittle volume is calculated considering fault kinematics and rock rheology (i.e., the brittle-ductile transition depth) over a grid that covers the entire study area. The maximum earthquake magnitude is calculated at each point of the grid based on a volume/magnitude empirical relationship. We apply this model to Italy for which we propose a map of the maximum possible magnitudes. Maximum predicted magnitudes are 7.3 ?? 0.25 for thrust faulting, 7.6 ?? 0.77 for normal faulting and 7.6 ?? 0.37 for strike-slip faulting (?? deviation from the mean value calculated at each node). These magnitudes are locally higher than the historical record. This could be due to an overestimation of the involved volumes; smaller volumes and lower magnitudes may occur where faults are detached at decollements shallower than the brittle ductile transition or where they behave aseismically. Alternatively, strong or major earthquakes could be possible, but they have longer recurrence time and they have never been recorded yet in Italy. Regardless these values are fully reliable or not, the recurrence of earthquakes with the predicted magnitude is related to current strain rates. We conclude that a large part of the Italian territory is prone to trigger Mw > 5 earthquakes.
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：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.
查看更多>>摘要：Deformation in oblique convergent margins, especially non-plane deformation in de??collement belts within such a margin, is not fully understood. The northern Zhangbaling tectonic belt represents an oblique convergent margin to the east of the NNE???SSW-striking Tan???Lu Fault Zone that separates the Yangtze Block to the east from the North China Craton to the west, and it provides a good opportunity to understand deformation in the margin. The tectonic belt consists of a fold-and-thrust belt in the east and a low-angle ductile de??collement belt in the west. The fold-and-thrust belt in the marginal cover rocks indicates a pure shear-dominated deformation, and the fold axes rotated with the long axis of the horizontal finite strain ellipse. The underlying de??collement belt was involved in a non-plane deformation owing to the superposition of wrenching along the Tan???Lu Fault Zone and horizontal de??collement shearing. The horizontal de??collement shearing dominated in the development of the flat-lying foliation, whereas the wrenching mostly dominated in the development of stretching lineations. Top-to-theSSW sense of shear dominates in the central to southern parts of the de??collement belt, whereas top-to-the-SSE sense of shear is widely present in the northern part of the belt and locally in other parts. Partitioning of the non-plane deformation is shown by kinematic partitioning within the originally flat-lying de??collement belt, and it is different from the strain partitioning in a transpressional zone involved in plane deformation. The structural and geochronological data for the oblique convergent margin are consistent with sinistral faulting of the initial Tan???Lu Fault Zone during the Triassic.
查看更多>>摘要：We analyzed a set of 11 slow slip events occurred during the 2006-2016 period and affecting the GNSS (Global Navigation Satellite System) stations of the unstable flank of Mt. Etna volcano. Observed surface deformation for most of the detected slow slip events, concentrates on the south-eastern edge of the unstable flank while the slow slip events involving the north-eastern edge are less frequent. Such a pattern highlights the existence of two distinct families of events, involving two contiguous sectors of the unstable flank, which occasionally slip together in large slow slip events. The modelled slips also highlight that both contiguous sectors extend similar to 10-12 km offshore, on areas where active tectonic lineaments such as the ESE (northward of Catania Canyon) and the N102 degrees (along the southern slope of the Riposto Ridge) ones have been recently discovered. Equivalent seismic moments of slow slip events occurred in the last ten years (corresponding to magnitudes in the range 5.4-5.9) are larger than those associated to seismic events observed in the last 200 years, suggesting that most of the deformation affecting the eastern flank occurs aseismically.
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.
NSTL
Elsevier