Journal of Geodynamics最新文献

The Valley of the Volcanoes is a representative area of the extension of the Quaternary Andahua Group with which it overlaps. Some of its eruption centres have renewed activity after more than 500 ka. Recreating the history of the Valley of the Volcanoes activity required satellite data and remote sensing-based methods for visualizing the terrain surface. We used SRTM 30 m DEM, channels 4, 3, 2; Landsat 7, 8 and ASTER images. We verified and refined the obtained data during field works using Structure-from-Motion (SfM) to create of 3D models of selected geoforms. Satellite data allowed us to create: Red Relief Image Map, Topographic Position Index and Normalised Difference Vegetation Index (NDVI) maps. In the Valley of the Volcanoes, we analysed 12 lava fields with a total area of 326.3 km² and a volume of approx. 20 km³. We determined the number of eruption centres that yielded to 41 small lava domes and 23 scoria cones. This domes are classified as monogenetic volcanoes, however five of them can be considered polygenetic e.g. Puca Mauras. We used NDVI to develop chronology map of lavas. This allowed us to extract same-age eruption centres and associated volcanoes that represent the same eruptive time phase connected by fault lines: first generation (0.5–0.27 Ma) NW-SE and NE-SW, second (Pleistocene/Holocene) NNW-SSE and third (Holocene-Historical) again NW-SE and NE-SW. We carried out the reconstruction of the central part of the Valley of the Volcanoes because only there repeated phases of volcanic activity can be inferred with remote sensing and geological mapping. The results of this study led us to indicate that this area should be observed since it is very likely that future eruptions will occur.

High-resolution structural analysis of stratigraphically-controlled units within North Dobrogea (ND), based on fieldwork and the production of new cross-sections as well as a reconstruction of the Mesozoic paleo-stress regimes, has resulted in a revision of the tectonic events across the region as well as demonstrating the significance of tectonic inheritance. The observed structures are closely related to the major strike-slip faults of the Teisseyre-Tornquist Zone (TTZ) a lithospheric structure active during the early and middle Mesozoic. The significance of this zone has been underestimated in previous kinematic reconstructions examining the opening of the continental back-arc basin of the Black Sea. Integrating the present results with existing knowledge on the tectonic evolution of the Black Sea, suggests a new conceptual kinematic model for further testing, one that involves movement of the continental fragment of Moesia NW along the TTZ during the early and middle Mesozoic. Such a displacement would represent the westernmost occurrence of the Cimmerian orogeny in the region of the western Black Sea. The escape of Moesia to the NW could possibly explain the polyphase extension of the western Black Sea crust, which developed on the continental Eurasian Plate as a back-arc basin due to the N-directed subduction of Tethys.

Seismic anisotropy in the East Japan arc has been extensively investigated by conducting shear-wave splitting measurements, receiver-function analyses, and tomographic inversions of body-wave travel times and surface-wave dispersion data, which have provided a wealth of information on dynamic processes associated with active subduction of the Pacific plate. Measuring shear-wave splitting is popular and effective to detect seismic anisotropy, but it has poor depth resolution. This problem has been overcome by conducting 3-D anisotropic tomography, which has high-resolution in both lateral and vertical directions. Both P and S wave anisotropies are revealed in the crust, which are caused by alignment or preferred orientation of crustal minerals and stress-induced microcracks related to active faults. Trench-normal fast-velocity directions (FVDs) of azimuthal anisotropy are revealed in the back-arc mantle wedge, reflecting subduction-driven convection there. Trench-parallel FVDs appear in the forearc mantle wedge under the land area, which may reflect deformation that results in B-type olivine fabric. The forearc mantle wedge offshore may lack anisotropy, suggesting that it is stagnant and decoupled from the subducting slab and does not participate in the viscous flow, in sharp contrast with the rest of the mantle wedge. The most significant findings of the body-wave anisotropic tomography are its constraints on the slab anisotropy. The subducting Pacific slab exhibits mainly trench-parallel FVDs, which reflect shape-preferred orientation of crystals and cracks related to normal faults produced in the outer-rise area before the plate subduction, overprinting the fossil anisotropy that the Pacific plate gained when it was produced at the mid-ocean ridge. Trench-parallel intraslab fast velocity planes of anisotropy intersect the slab upper surface at high angles (∼45–90°), reflecting aligned hydrated faults in the slab. Ruptures of the hydrated faults in the upper part of the slab may cause large intraslab earthquakes (M ≥7.0) that take place frequently beneath the forearc area. Trench-normal FVDs also appear in the subslab mantle, which may reflect asthenospheric shear deformation associated with the overlying slab subduction.

Plate kinematic models of the Pyrenees have been extensively debated due to discrepancies between plate kinematic constraints for the Iberian plate and Atlantic/Tethyan related plate motions. Recently, the morphology of the Iberian plate and its partitioning into several continental blocks has been proposed as a solution towards reconciling discrepancies between previously published reconstructions that treat Iberia as a single, rigid, tectonic plate. Herein, the first deformable plate tectonic modeling study of the Pyrenean realm is presented using previously published and newly presented reconstructions of Iberia. Special emphasis is given to the kinematics of the Ebro Block, a continental block situated between the Pyrenees and Iberian Ranges, whose kinematics are considered to play a key role in the extensional deformation experienced within the Pyrenean realm. Temporal variations in strain rate and crustal thickness calculated by deformable plate models provide insights regarding the pre-orogenic template of the Pyrenees and the variability in regional stress directions along the Iberia-Eurasia plate boundary from the Triassic to Cenomanian. Models that propose transtensional rift phases within the Pyrenean realm induced by the Landes High and Ebro Block kinematics since the Triassic are successful in deriving crustal thicknesses indicative of a pre-orogenic hyperextended rifted margin within the Pyrenean realm. The results of this study demonstrate the importance of continental block kinematics during rift-related deformation and their impact on the evolution and partitioning of rift domains. Furthermore, this study also highlights potential avenues to consider for improving future plate kinematic models of Iberia, and regions elsewhere.

The tectonics of southwestern Canada are dominated by the Cascadia subduction zone. The northern Cascadia backarc encompasses a > 400 km wide region of the Southern Canadian Cordillera. Geophysical observations, including seismic tomography and surface heat flow, show that the backarc is characterized by a hot, thin lithosphere (60–70 km). The eastern limit of the backarc approximately underlies the Rocky Mountain Trench, where there is an abrupt eastward increase in lithosphere thickness to the ∼250 km thick North American (Laurentian) Craton. Seismic tomography studies show that the transition in lithosphere thickness occurs over a horizontal distance of 50–100 km, resulting in a subvertical to west-dipping lithosphere step, with a dip angle of 75–90°. Using numerical models, we show that such a structure can be readily destabilised by internal buoyancy forces, edge-driven convection, and shearing by regional mantle flow. To maintain a subvertical step for > 50 Myr, the lowermost craton mantle lithosphere must be both dry and moderately chemically depleted. The observed westward dip may reflect partial lateral extrusion of the lowermost craton lithosphere, as well as shearing from west-directed mantle flow associated with the Cascadia subduction zone. The models also show that the backarc mantle must be relatively weak, such that vigorous convection maintains the hot, thin lithosphere. This also provides a mechanism to explain the observed lateral seismic gradient between the low-velocity backarc mantle and high-velocity craton. Our models demonstrate that the eastern limit of the Cascadia backarc is a region of active mantle flow, including possible slow deformation of the craton edge.

Aravalli craton of central Rajasthan comprises Mangalwar Complex and Sandmata Complex with Archean to Proterozoic basement, well known for the mineralization. Recent geological studies have also revealed that the Aravalli mountains of the Banded Gneiss Complex are composed of Paleoproterozoic granulite and amphibolite-facies. Extensive geophysical surveys comprising gravity and magnetic were conducted to assess the occurrence of potential mineral sources in the uplifted crustal blocks of the Aravalli Fold belt. The calculated Bouguer gravity anomalies trending in a NE-SW direction and three broad gravity highs (∼7–10 mGal) were observed. These gravity highs may be due to the uplifting of the basement or the presence of high-density contrast material near the subsurface. A gradient in the gravity contours at the northwestern part of the study area is due to the fault/structural contact trending along the NE-SW direction. The 2D inversion technique is used to model the gravity data perpendicular to fault/contact. The horizontal gradient reflects the distribution of structures and intrusive bodies, which will give new insight for further future mineral exploration. The spectral analysis depicts the three depth interfaces, ∼7, ∼3.1, and ∼1.1 km, representing the basement and shallow depth interfaces. Further, the subsurface ore bodies geometry was obtained through 2D modelling of gravity data incorporating the constraints from the rock sample's physical property (density). We established that the structure and lithology of the host rocks were responsible for controlling mineralization by integrating the geochemical findings with geophysical measurements. In addition, the Archean to the Proterozoic basement of the study area is undulating at a depth of ∼3–5 km.

Geophysical methods, especially the gravity method, are very helpful in ore and mineral explorations. Here, gravity modeling and interpretation for the subsurface geologic structures generally assumes either homogenous or spatially varying densities within target source rocks and surrounding structures. Therefore, the use of simple-geometric bodies helps in the validation of the subsurface ore and mineral targets. A Bat optimization algorithm is a recently developed metaheuristic algorithm that is used in various geophysical applications to explore and explain the parameters of buried ore and mineral targets. Using the Bat optimization algorithm, we were elucidating gravity anomaly profiles for ore and mineral cases. To perform global optimization, the Bat optimization algorithm is based on the echolocation behavior of bats. The global optimum solution in the Bat optimization algorithm reached the suggested minimum value of the objective function. The Bat optimization algorithm is applied to gravity data to estimate the target parameters (e.g., amplitude coefficient, depth, origin location, and geometric shape). The stability and efficiency of the introduced optimizing algorithm have been checked on two synthetic models represented in a spherical model and an infinitely horizontal cylinder model using two different kinds of noise. Furthermore, successful applications of the proposed algorithm for discovering the ore and minerals in Canada, Cuba, and India were presented. The results match well with the available geological and borehole information and other results from the published literature.

During 2008–2020, four strong earthquakes occurred in Yutian, Xinjiang Uygur Automous Region, northwest China, in particular, two M7 + and two M6 + earthquakes demonstrating the high tectonic activity of this region. We systematically use multiple electromagnetic data from satellites and ground, such as GIM TEC (Global Ionospheric Mapping Total Electron Content) published by JPL (Jet Propulsion Laboratory), and the ULF (Ultra Low Frequency) electromagnetic waves and plasma parameters onboard DEMETER (Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions), Swarm and CSES (China Seismo-Electromagnetic Satellite) satellites. The ionospheric perturbations were revealed frequently around the four case studies, but mostly within 10 days before, over the epicentral area, and sometimes over its conjugate region at southern hemisphere. The abnormal amplitude is quite larger in years with high solar activity than in those with low solar activity. We employ the SAMI2 model to simulate the variations from the effects of E × B under different plasma background in 2008 and 2014 to explain the great difference in different solar years. The similarity of the anomalies in this region demonstrates the higher electromagnetic and chemical emissions, implying that the electric field is possibly generated by the preparation of the seismic events in the epicentral area inducing the ionospheric disturbances above this area and its conjugate region through this coupling channel.

3D inversion of broad band MT data present variation of electrical signatures across the subducting Indian crust in Sikkim Himalaya. The vertical and horizontal geoelectric cross-sections are dominated by north-east dipping conductive zones. Two high conductivity zones (4–8 Ω m) at a depth of 5–18 km in Lesser Himalayan Domain (LHD) are explained by conductive mineral assemblage associated with abundant low saline and entrapped fluids. Another conductive feature (6–16 Ω m) in Main Himalayan Thrust Zone close to Main Himalayan Thrust ramp could have arisen from entrapment of CO₂-H₂O fluids and fluids released by metamorphic reactions. The high conductive anomaly (4–10 Ω m) at a depth of 5–16 km in Greater Himalayan Sequence (GHS) is caused by the presence of partial melts/aqueous fluids derived by present day fluid-absent melting of leucogranite source rocks. A combination of leucogranite intrusion, shear heating, and radiogenic heat production (4–17 μW/m³) are the heat sources for inferred partial melting. Though, the constrained melt fractions of 1.4–3.8% in GHS are lower than the estimation in south Tibet that might be due to the less intrusion of leucogranites. The obtained moderate viscosities of (10^4.19-10^5.49 Pa.s) from empirical relation with low melt and fluid fractions of 5–6 wt% in high conductive zone suggest viscous/ductile deformation and weakening mid-crust beneath northern Sikkim Himalaya. However, the estimated values of melt fractions and viscosities at mid-crustal depth of GHS are insufficient to develop a melt channel to flow southward between Main Central Thrust-1(MCT-1) and South Tibet Detachment (STD) envisaged by channel flow model.

The lithospheric structure of the on-shore Potiguar Basin has been investigated through velocity-depth profiles developed from the joint inversion of receiver functions and surface-wave dispersion at 16 seismic stations in and around the basin. The Potiguar Basin is an aborted rift basin that formed during the opening of the South Atlantic Ocean in the Lower Cretaceous, and is characterized by an unusual surface heat-flow with values as high as 101 mW/m². Our results reveal: (i) A relatively thin crust of ∼30 km below the on-shore Potiguar Basin and a relatively thicker crust of ∼32 km around the basin; (ii) the existence of an anomalous uppermost mantle of ∼4.3 km/s at 30–40 km depth under most seismic stations; and (iii) the presence of a negative velocity gradient centered at ∼125 km depth, which probably represents a shallow Lithosphere Asthenosphere Boundary (LAB). We argue that the anomalous uppermost mantle is associated with magmatic intrusions just below the Moho, deeper than previously postulated from independent heat-flow studies, and that those intrusions result from heating by an active, hot sublithospheric mantle under the basin that keeps the lithosphere thin. We further argue that heating from the magmatic intrusions, along with direct heating from the sublithospheric mantle, may explain the unusually elevated heat flow observed at the surface.