Lithosphere Dynamics Research Articles

Pengembangan Bahan Ajar E-Magazine dengan Pendekatan SAVI pada Materi Dinamika Litosfer dan Dampaknya Terhadap Kehidupan

The development of 21st century education affects the use of learning media. In learning activities, digital teaching materials are needed that support the student's learning process. The development of e-magazine teaching materials for lithosphere dynamics materials is carried out because digital teaching materials are minimally used in learning. The purpose of this research is to produce e-magazine teaching materials with the SAVI approach. This study used the ADDIE (Analyze, Design, Development, Implementation, and Evaluation) model procedure. The types of data used are quantitative and qualitative. In the process of collecting data using questionnaires, interviews, as well as documentation of activities with percentage descriptive data analysis techniques. Teaching material products are tested for feasibility at SMA Negeri 2 Malang class XI IPS 3. Based on the results of product feasibility tests by media expert validators, material experts, linguists and test results in schools, e-magazine teaching materials are very feasible and valid for geography learning.

Synthetic seismicity obtained by block movements modeling for the territory of Bulgaria: preliminary results

The Bulgarian Region is located in the Southeastern Europe, with not so frequent recent seismicity. Several strong seismic events in the beginning of the XX century evidenced the capability of the main faults to accumulate significant energy. In this study, we investigate the seismicity in the region using the numerical block-and-fault dynamics (BAFD) model of lithosphere dynamics and seismicity. The morphostructural zoning outlines major crustal blocks, and external driving motions are prescribed using GPS data. We performed preliminary test for the simplified block structure to compile the synthetic earthquake catalogue for the Bulgarian region.

Exploring rift geodynamics in Ethiopia through olivine-spinel Al-exchange thermometry and rare-earth element distributions

Understanding the process of continental break-up requires knowledge of the geodynamics of mature rift systems close to the point of plate rupture. In Ethiopia, late-stage continental rifting occurs in a magma-rich setting where extensional processes correlate closely with magmatic and volcanic activity. Unravelling the role that mantle and lithospheric dynamics play in sustaining rifting in Ethiopia is key to improving models of late-stage continental rift evolution. In this study we provide petrological constraints on the physical characteristics of magma production using volcanic samples from the northern Main Ethiopian Rift (MER) and central Afar. Olivine crystallisation temperatures provide information about the thermal state of mantle-derived magmas generated by the mantle during upwelling and melting. These temperatures, determined by Al-exchange thermometry, are used in conjunction with other geochemical and geophysical constraints in inversion models of melting a multi-lithology mantle to find the best-fitting geodynamic parameters that can reproduce observed magma compositions and melt volumes. Our model results suggest that the potential temperature of the Ethiopian mantle is hotter than ambient mantle by ≥ 150∘C, and is elevated to a similar degree across the MER and Afar. We predict significant variations in lithospheric thickness between the MER (90 km) and Afar (50-70 km), with Afar also likely to have a higher portion of fusible mantle domains. This thinner lithosphere and/or more productive mantle is required to generate the larger volumes of magma inferred to have been intruded into the Afar crust. The geodynamic differences between these two settings can be attributed to the more-evolved state of the Afar rift and its proximity to the centre of the Afar plume.

Plateau archives of lithosphere dynamics, cryosphere and paleoclimate: The formation of Cretaceous desert basins in east Asia

Southeastern Eurasia is a global window to the Cretaceous paleoclimate and lithosphere coupling. China contains one of the most complete and complex sedimentary records of Mesozoic desert basins on planet Earth. In this study, we perform the spatio-temporal tracking of 96 Cretaceous palaeoclimate indicators during 79 Myr which reveal that the plateau paleoclimate archives from East Asia resulted from an Early to Mid-Cretaceous ocean–atmosphere coupling and a shift to a preponderant role of Late Cretaceous lithosphere dynamics and tectonic forcing on high-altitude depositional systems linked to the subduction margins of the Tethys and Paleo-Pacific realms beneath the Eurasian plate. The crustal response to tectonic processes linked with the spatio-temporal evolution of the Tethyan and Paleo-Pacific margins defined the configuration of major sedimentary basins on this region. The significant increase and decrease in the number of active sedimentary basins that occur during the Cretaceous, from 16 in the Early Cretaceous, to 28 in the Mid-Cretaceous, and a decreasing to 20 sedimentary basins in the Late Cretaceous, is a direct response of lithospheric dynamics associated with the two main subduction zones (Tethys and Pacific domains). A shift in subduction style from an Early Cretaceous Paleo-Pacific Plate slab roll back to a Late Cretaceous flat-slab mode might have triggered regional plateau uplift, blocked intraplate volcanism, thus enhancing the denudation and sediment availability, and created wind corridors that led to the construction and accumulation of extensive Late Cretaceous aeolian sandy deserts (ergs) that covered Mid-Cretaceous plateau salars. At the same time, plateau uplift associated with crustal thickening following terrane assembly in the Tethyan margin triggered altitudinal cryospheric processes in sandy desert systems. Evidence of an active Cretaceous cryosphere in China include Valanginian-Hauterivian glacial debris flows, Early Aptian geochemical signature of melt waters from extensive ice sheets, and Cenomanian–Turonian ice-rafted debris (IRD). These cryospheric indicators suggest an already uplifted plateau in southeastern Eurasia during the Cretaceous, and the marked correlation between cold plateau paleoclimate archives and marine records suggests a strong ocean-atmosphere coupling during Early and Mid-Cretaceous cold snaps. We thus conclude that lithospheric tectonics during Cretaceous played a fundamental role in triggering high-altitude basin desertification and spatio-temporal plateau paleohydrology variability in the Cretaceous of south-eastern Eurasia.

Coupled influence of tectonics, climate, and surface processes on landscape evolution in southwestern North America

The Cenozoic landscape evolution in southwestern North America is ascribed to crustal isostasy, dynamic topography, or lithosphere tectonics, but their relative contributions remain controversial. Here we reconstruct landscape history since the late Eocene by investigating the interplay between mantle convection, lithosphere dynamics, climate, and surface processes using fully coupled four-dimensional numerical models. Our quantified depth-dependent strain rate and stress history within the lithosphere, under the influence of gravitational collapse and sub-lithospheric mantle flow, show that high gravitational potential energy of a mountain chain relative to a lower Colorado Plateau can explain extension directions and stress magnitudes in the belt of metamorphic core complexes during topographic collapse. Profound lithospheric weakening through heating and partial melting, following slab rollback, promoted this extensional collapse. Landscape evolution guided northeast drainage onto the Colorado Plateau during the late Eocene-late Oligocene, south-southwest drainage reversal during the late Oligocene-middle Miocene, and southwest drainage following the late Miocene.

Mercury isotopic composition of igneous rocks from an accretionary orogen: Implications for lithospheric recycling

Abstract Mercury (Hg) provides critical information on terrestrial planet formation and evolution due to its unique physicochemical properties and multiform isotopic compositions. Current knowledge of Hg is mainly limited to Earth's surface environments, and the understanding of Hg in the Earth's interior remains unclear. Accretionary orogens are major settings for continental crustal growth and crust-mantle interactions. We studied the Hg concentration and isotopic composition of igneous rocks in the eastern Central Asian orogenic belt, using Hg as a proxy to trace the recycling of surface materials in Earth's lithosphere. Our results show low Hg abundances in mafic through felsic igneous rocks (4.93 ± 4.35 ppb, standard deviation [SD], n = 267). Mafic rocks show slightly lower δ202Hg (−2.9‰ ± 0.5‰, SD, n = 24) than intermediate (−2.4‰ ± 0.8‰, SD, n = 58) and felsic (−1.5‰ ± 0.8‰, SD, n = 185) rocks, indicating a chemical stratification of Hg isotopic composition in the continental crust with isotopically lighter Hg in the lower part and heavier Hg in the upper part. Slightly positive Δ199Hg values are observed in mantle-derived mafic (0.07‰ ± 0.06‰, SD) and intermediate (0.06‰ ± 0.07‰, SD) rocks, which agree well with those reported for marine sediments, indicating the involvement of fluids or melts from the oceanic crust. Larger variations of Δ199Hg values (−0.26‰ to +0.21‰, average: 0.01‰ ± 0.08‰, SD, n = 185) are observed in felsic rocks, further indicating recycling of surface Hg from the marine reservoir via slab subduction (reflected by positive values) plus magmatic assimilation of terrestrial Hg (reflected by negative values). Our study demonstrates that Hg isotopes can be a promising tracer for the chemical dynamics of Earth's lithosphere.

Abnormally low heat flow in Southeast China resulted from remnant slab subducted beneath the east Asian lithosphere

AbstractSubducted remnant slabs play an important role in the geodynamics and evolution of the Earth, but their behaviour in the mantle is not well understood. Terrestrial heat flow and thermal lithosphere structure provide crucial constraints on lithospheric dynamics. Based on whole‐well steady‐state temperature logs and conductivity measurements of core samples from a scientific borehole, we obtained a new high‐quality terrestrial heat flow values for East Asia. The heat flow was calculated at 60.6 ± 16.0 mW/m2 with a high crust/mantle heat flow ratio of 1.41, suggesting a hot‐crust‐cold‐mantle lithospheric structure. The thermal lithospheric thickness of eastern Fujian is estimated to be 152–166 km, indicating a thick and cold lithosphere. We demonstrate that the cooling of the lithosphere is caused by a remnant palaeo‐slab of the Palaeo‐Pacific plate subducted beneath SE China. The remnant slab blocked heat convection into the bottom of the lithosphere of the Eurasian Plate.

Anatomy and kinematic evolution of an ancient passive margin involved into an orogenic wedge (Western Southern Alps, Varese area, Italy and Switzerland)

We make use of own geological mapping, interpretations of seismic reflection profiles and deep geophysical data to build a lithospheric-scale cross-section across the European Western Southern Alps (Varese area) and to model a progressive restoration from the end of Mesozoic rifting to present-day. Early phases of Alpine orogeny were characterized by Europe-directed thrusting, whereas post-Oligocene shortening led to basement-involving crustal accretion accompanied by backfolding, and consistent with the kinematics of the adjoining Ivrea Zone. Wedging was favored by a significant component of reactivation of the inherited Adriatic rifted margin. Our results also suggest that, during the collisional and post-collisional tectonics, lithosphere dynamics drove diachronically the onset of tectonic phases (i.e., wedging and slab retreat), from east to west, across the Western Southern Alps.

Terrestrial heat flow and its geodynamic implications in the northern Songliao Basin, Northeast China

SUMMARY Heat flow data are essential for understanding lithospheric dynamics. As a petroliferous basin, a large number of boreholes have been drilled during hydrocarbon exploration and production in the northern part of Songliao Basin, Northeast China. Meanwhile, the data on crustal structures, core samples and formation temperatures have been accumulated, which provide an opportunity for understanding the thermal state of the basin. Based on the temperature data from both Drilling Stem Test and continuous steady-state logging profiles, together with the systematic analysis of the thermal properties of rock samples, we present a new heat flow map of the northern Songliao Basin with significantly increased number of heat flow sites. The northern Songliao Basin is characterized by relatively high geothermal gradients and high heat flow for sedimentary basins. The heat flow values range from 44.4 to 95.0 mW m–2 with an average of 67.2 ± 12.8 mW m–2, and the geothermal gradients range from 21 to 59 °C km–1 with an overall average of 41.7 °C km–1. Heat production from sedimentary covers accounts for about 4.5 mW m–2 at the site of Well SK-2. Furthermore, based on the crustal structures revealed by previous seismic studies, lithospheric thermal structures are analysed and compared among different structural units of the basin. A thinned thermal lithosphere with a thickness of ∼65 km is found beneath the Central downwarp and the Southeast uplift in which a large part of the heat flow is mantle derived. The Western Slope exhibits a moderate heat flow value and a thicker thermal lithosphere with thickness greater than 110 km. From the perspective of the geothermal state of the lithosphere, the regional geodynamics related to the Mesozoic lithosphere stretching and the subduction of the Pacific Plate are discussed.

The lithospheric effective elastic thickness and its tectonic implications in the Ordos Block and adjacent areas

The Ordos Block, located at the western edge of the North China Block, is a stable rigid block. It is characterized by inactive tectonic activity and rare earthquakes, while the south‐west margin of this block and adjacent areas present the opposite features. There is still considerable ambiguity with regard to the lithospheric mechanical strength in these areas. The effective elastic thickness (Te), widely used for comprehending the mechanism of cratonic deformation and lithospheric dynamics, is a proxy of the lithospheric strength. This study provided detailed two‐dimensional lithospheric Te spatial variations in the Ordos and adjacent areas by using coherence analysis of the topography and Bouguer anomaly. The result showed that the higher Te values in the Ordos Block varied from 80 to 100 km and implied that it is capable of strong rigidity. The lower Te values were distributed over the Qinling Block (20–45 km), the Qilian Block and Haiyuan arcuate tectonic region (20–40 km), as well as the Baryan‐Har Block (15–30 km). By comparing the Te values with the geophysical results, we believe that the higher Te value in the Ordos Block was supported not only by the crust, but also by the upper mantle. In contrast, the mechanical strength of the south‐west margin, especially the Baryan‐Har Block and western Qinling Block, was mainly borne by the brittle upper crust, but the tectonic activity and brittle failure likely resulted in a lower Te. Furthermore, we found that a large number of shallow earthquakes were located above low‐velocity and low‐resistivity layers, most of which probably occurred in the brittle upper crust with small mechanical strength.

Miocene tuffs from the Dinarides and Eastern Alps as proxies of the Pannonian Basin lithosphere dynamics and tropospheric circulation patterns in Central Europe

Tuffaceous layers are regularly preserved in Miocene carbonate and siliciclastic sediments of the Dinarides and Eastern Alps in southeastern and central Europe. Detailed mineralogical and geochemical analyses of 13 tuffs of known ages acquired from sedimentary successions of the intramontane Dinarides basins and the southwestern Pannonian Basin were carried out to infer on plausible source areas, relative strengths of volcanism, and ash distribution patterns. Studied tuffs were altered to various degrees with illite–smectite and smectite as dominant phases while volcanic glass, carbonates and other silicates are minor constituents. Tuffs’ compositions range from andesite through trachyandesite to rhyolite and trachyte. Trace-element-based correlation with regional data reveal that Lower Miocene (LM) and Lower Middle Miocene (LMM) tuffs (17.0–14.0 Ma) likely originated in the Western Carpathians (the Bükkalja volcanic field) while source areas of Upper Middle Miocene (UMM) tuffs (13.8–12.5 Ma) were in the Apuseni Mountains and/or Eastern Carpathians. The spatial relation of LM/LMM and UMM tuffs with respect to their source areas (the Bükkalja volcanic field and Apuseni Mountains, respectively) is most consistent with tropospheric easterly trade winds that carried ash hundreds of kilometres to the SW toward an azimuth of c. 200–250°. Supplementary material: Annotated X-ray diffractograms of the global and clay fraction of studied tuffs and AFM classification diagram are available at https://doi.org/10.6084/m9.figshare.c.5429592

The transition from ancient to modern-style tectonics: Insights from lithosphere dynamics modelling in compressional regimes

Orogens are traditionally classified according to their tectonic style. Paleoproterozoic tectonics is referred to as “ancient-style tectonics” while Proterozoic tectonics is referred to as “modern-style tectonics”. Ancient-style tectonics is characterised by distributed vertical structures and low topography gradients, often associated with diapirism and partial melting. In contrast, modern-style tectonics involve prominent strain localisation and the formation of thrusts, nappes and high topographic gradients. However, the parameters controlling the transition from ancient to modern-style tectonics are poorly understood. To quantify this transition, a combination of 1D and 2D high resolution lithospheric-scale thermo-mechanical models was conducted. The parameters controlling the strength of the lithosphere (i.e., Moho temperature, strain rate, crustal rheology, crustal radiogenic heat production and role of shear heating) were investigated in detail. Our results show that tectonic style is controlled by the maximum of crustal strength (shear stress). Modern-style tectonics is observed to occur when the maximum of crustal strength is greater than 300 MPa. At the opposite, a maximum crustal strength lower than 300 MPa leads to ancient style tectonic structures. Therefore, crustal rheology, temperature and background strain rate significantly influence the transition from ancient to modern-style tectonics. Shear heating remains a key factor in promoting strain localisation in modern-style tectonics. Crustal radiogenic heat production has a moderate influence by increasing/decreasing the tendency for faulting within the crust. This crustal strength criterion also provides an excellent fit for a second potential proxy: a localisation criterion of ca. 225°C. These two proposed proxies can be used interchangeably to predict the transition from ancient to modern-style tectonics.

Pressure‐Driven Poiseuille Flow Inherited From Mesozoic Mantle Circulation Led to the Eocene Separation of Australia and Antarctica

AbstractThe separation between Australia and Antarctica occurred during the final stages of the break‐up of Pangea. Reconstructions of the rifting of the Australian plate away from Antarctica show fast spreading rates since Mid‐Eocene (45 Ma). These reconstructions can be used to understand and quantify the forces driving the Australia/Antarctica separation, and to test hypotheses on mechanisms that may be of shallow (i.e., lithosphere) or deep (i.e., mantle) origin. Analytical calculations indicate that plate‐boundary forces are highly unlikely to be a plausible candidate to explain such a separation. Thus, we use a recently developed global coupled models of mantle and lithosphere dynamics, here we show that this event, whose kinematics are reproduced in our models within the bounds of the reconstruction uncertainties, owes to a significant degree to the pressure‐driven asthenospheric Poiseuille flow associated with the mantle buoyancy field inherited from viscous circulation history throughout the Mesozoic. On the contrary, in simulations when such a buoyancy field is replaced by another one resulting from a random distribution of mantle temperature–thus not representative of Earth’s mantle circulation history–the rapid northward motion of Australia does not occur. Similarly, suppressing contemporaneous plate‐boundary processes (i.e., subduction of the Pacific ridge at the Aleutians and healing of the India‐Australia ridge) from our models does not have a noticeable effect on the Australia‐Antarctica kinematics. Thus, a pressure‐driven Poiseuille mantle flow must be considered, at least in this example and possible elsewhere, as a main driver of plate tectonics.

Presence of hydrocarbons on Mars: A possibility

There exists a fair degree of geological similarity between the internal structure of Mars, its orbital cycle, and axis tilt with that of Earth. The early plate tectonics along with subaerial volcanism have emitted oxygen as evident in the geological history of Earth during the Archaean–Proterozoic transition. The ancient Valles Marineris equatorial rift basin of Mars could have resulted because of lithospheric dynamics. The associated large-scale transtensional strike-slip during the Late Amazonian Period further implies manifestation of possible plate tectonics on Mars. The presence of the earliest organic species, 3.7 billion years ago, had been established on Earth. The presence of lake and ocean and evidence of glaciation infer probable evolution of life in early Mars. The depositional morphology like alluvial fans, debris flow fans, deltas, and lacustrine fans implies possible sedimentation processes active on early Mars. Organic matters on Mars could be in situ or could have been delivered by meteorites. The presence of organic molecules of benzene and propane in 3-billion-year-old rock samples has been evidenced in Gale crater. Deposition of source rock and subsequent decomposition of organic matter could have generated hydrocarbons in early Mars. A comparative geological phenomenon between Meso-Neoproterozoic petroleum geology of Earth and the equivalent Amazonian and older periods has been analyzed in the light of the envisaged hydrocarbon generation and entrapment on early Mars. Possible martian petroleum systems of the ancient Valles Marineris rift basin and crater-induced basins including prevalence of gas hydrate and abiotic origin of methane have been studied.

Research progress of Yarlung Zangbo ophiolite

Ophiolite is a relic of the paleo oceanic crust preserved on the earth continent. It preserves a lot of important evidences in the process of crust-mantle interaction and records information about oceanic lithospheric dynamics and geotectonics. It has always been a research hotspot in the field of geology. Especially in recent years, the ophiolite has made a lot of important progress in the global lithospheric evolution, ocean-continent transition history in different geological periods and geodynamics, which has aroused great research enthusiasm in the field of geology. The Yarlung Zangbo ophiolite is the most important ophiolite in China.However, the tectonic setting, rock composition and genesis of the Yarlung Zangbo ophiolite are still controversial. This paper expounds the Yarlung Zangbo ophiolite from three aspects: brief history, characteristics and existing problems, so as to promote the Yarlung Zangbo ophiolite to the international academic circles.

Impact of upper mantle convection on lithosphere hyperextension and subsequent horizontally forced subduction initiation

Abstract. Many plate tectonic processes, such as subduction initiation, are embedded in long-term (>100 Myr) geodynamic cycles often involving subsequent phases of extension, cooling without plate deformation and convergence. However, the impact of upper mantle convection on lithosphere dynamics during such long-term cycles is still poorly understood. We have designed two-dimensional upper-mantle-scale (down to a depth of 660 km) thermo-mechanical numerical models of coupled lithosphere–mantle deformation. We consider visco–elasto–plastic deformation including a combination of diffusion, dislocation and Peierls creep law mechanisms. Mantle densities are calculated from petrological phase diagrams (Perple_X) for a Hawaiian pyrolite. Our models exhibit realistic Rayleigh numbers between 106 and 107, and the model temperature, density and viscosity structures agree with geological and geophysical data and observations. We tested the impact of the viscosity structure in the asthenosphere on upper mantle convection and lithosphere dynamics. We also compare models in which mantle convection is explicitly modelled with models in which convection is parameterized by Nusselt number scaling of the mantle thermal conductivity. Further, we quantified the plate driving forces necessary for subduction initiation in 2D thermo-mechanical models of coupled lithosphere–mantle deformation. Our model generates a 120 Myr long geodynamic cycle of subsequent extension (30 Myr), cooling (70 Myr) and convergence (20 Myr) coupled to upper mantle convection in a single and continuous simulation. Fundamental features such as the formation of hyperextended margins, upper mantle convective flow and subduction initiation are captured by the simulations presented here. Compared to a strong asthenosphere, a weak asthenosphere leads to the following differences: smaller value of plate driving forces necessary for subduction initiation (15 TN m−1 instead of 22 TN m−1) and locally larger suction forces. The latter assists in establishing single-slab subduction rather than double-slab subduction. Subduction initiation is horizontally forced, occurs at the transition from the exhumed mantle to the hyperextended passive margin and is caused by thermal softening. Spontaneous subduction initiation due to negative buoyancy of the 400 km wide, cooled, exhumed mantle is not observed after 100 Myr in model history. Our models indicate that long-term lithosphere dynamics can be strongly impacted by sub-lithosphere dynamics. The first-order processes in the simulated geodynamic cycle are applicable to orogenies that resulted from the opening and closure of embryonic oceans bounded by magma-poor hyperextended rifted margins, which might have been the case for the Alpine orogeny.

Lithospheric dynamics in the vicinity of the Tengchong volcanic field (southeastern margin of Tibet): an investigation usingPreceiver functions

SUMMARYTengchong volcanic field (TVF) in the northern Indochina block lies in a critical area for understanding complex regional dynamics associated with continent–continent convergence between the Indian and Eurasian plates, including northeastward compression generated by subduction of the Indian Plate beneath the Burma Arc, and southeastward lateral extrusion of the crust from below central Tibet. We gathered 3408 pairs of P receiver functions with different frequencies and calculated the splitting parameters of the Moho-converted Pms phase. An anisotropic H-κ stacking algorithm was used to determine crustal thickness and Vp/Vs ratios. We also inverted for the detailed S-velocity structure of the crust and upper mantle using a two-step inversion technique. Finally, we mapped the topography of the lithosphere–asthenosphere boundary. Results show fast-wave polarization directions with a dominant NE–SW orientation and delay times varying between 0.19 and 1.22 s, with a mean of 0.48 ± 0.07 s. The crustal Vp/Vs ratio varies from 1.68 to 1.90 and shows a maximum value below the central part of the TVF, where there is relatively thin crust (∼35–39 km) and a pronounced low-velocity anomaly in the middle–lower crust. The depth of the lithosphere–asthenosphere boundary ranges from 53 to 85 km: it is relatively deep (∼70–85 km) in the vicinity of the TVF and relatively shallow in the south of the study area. In the absence of low shear wave velocity in the upper mantle below the TVF, we propose that the low-velocity anomaly in the lower crust beneath the TVF derives from the upper mantle below the neighbouring Baoshan block.

Normal Faulting in the 2020 Mw 6.2 Yutian Event: Implications for Ongoing E–W Thinning in Northern Tibet

Extensional earthquakes in the Tibetan Plateau play an important role in the plateau’s orogenic evolution and cause heavy seismic hazard, yet their mechanisms remain poorly known, in particular in harsh northern Tibet. On 25 June 2020, a Mw 6.2 earthquake struck Yutian, Xinjiang, offering us a rare chance to gain insights into its mechanism and implications in the Tibetan extension. We used both descending and ascending Sentinel-1 images to generate coseismic deformation associated with this event, which indicates a typical extensional mechanism with a maximum subsidence displacement of 25 cm and minor uplift. The causative fault constrained with interferometric synthetic aperture radar (InSAR) data based on a finite fault model suggests that the fault plane has a strike of 186.4° and westward dip of 64.8°, and the main rupture is concentrated at a depth of 3.6–10.8 km with a peak slip of 0.85 m. Our source model indicates that the 2020 Yutian event ruptured an unknown high-angle blind normal fault with N–S striking. The total released geodetic moment yields 2.69 × 1018 N·m, equivalent to Mw 6.23. We used dense interseismic global positioning system (GPS) measurements to reveal an approximate 7 mm/yr extensional motion in the Yutian region, but it still does not seem large enough to support high local seismicity for normal events within 12 years, i.e., Mw 7.1 in 2008, Mw 6.2 in 2012, and this event in 2020. Combined with Coulomb stress change modeling, we speculate that the seismicity in Yutian is related to the lower lithospheric dynamics.

Seismic anisotropy reveals crustal flow driven by mantle vertical loading in the Pacific NW.

Buoyancy anomalies within Earth's mantle create large convective currents that are thought to control the evolution of the lithosphere. While tectonic plate motions provide evidence for this relation, the mechanism by which mantle processes influence near-surface tectonics remains elusive. Here, we present an azimuthal anisotropy model for the Pacific Northwest crust that strongly correlates with high-velocity structures in the underlying mantle but shows no association with the regional mantle flow field. We suggest that the crustal anisotropy is decoupled from horizontal basal tractions and, instead, created by upper mantle vertical loading, which generates pressure gradients that drive channelized flow in the mid-lower crust. We then demonstrate the interplay between mantle heterogeneities and lithosphere dynamics by predicting the viscous crustal flow that is driven by local buoyancy sources within the upper mantle. Our findings reveal how mantle vertical load distribution can actively control crustal deformation on a scale of several hundred kilometers.

Active crustal deformation and rotations in the southwestern Balkans from continuous GPS measurements

The western limb of the Hellenic Arc defines the boundary of a large intracontinental active extensional domain covering the Aegean and the southwestern part of the Balkan peninsula. Along this boundary a transition from collision in the north to subduction in the south is associated with post-Miocene clockwise rotations of ∼50∘. We present a new GPS velocity field that, with new permanent station velocities in Albania, Bulgaria, Kosovo, Montenegro, and Northern Macedonia, provides insights into previously unresolved aspects on the large-scale dynamics of continental lithosphere and on the relation between long and short-term kinematics. In particular we address (1) the kinematic description of the collision/subduction transition, (2) the relation between long-term finite rotations with geodetically-measured instantaneous rotations, (3) the forces maintaining and resisting the deformation of the extensional domain and (4) the extent of its northern boundary. We use the analogy of rigid elongate inclusions in the velocity field to predict the senses and approximate rates of rotation of crustal blocks in the deforming continental region. Across the collision/subduction transition zone a large rotational pattern in the velocity field is found whose spatial pattern and sense of rotation is compatible with the observed paleomagnetic rotations through the occurrence of fault-bounded block rotations. Geodetic observations show that clockwise vertical axis rotation of the western limb of the Hellenic margin is active today, with distribution and rates that are essentially the same as that defined by the paleomagnetic data for the last 5 Ma. The maximum rates of the rotational component of the velocity field is found along the wide arrangement of fault-bounded blocks in central Greece that accomodate the NE-SW dextral shear transferred from the northern Aegan trough. The northern limit of the rotating margin defines a hinge (Scutari-Pec transverse zone) that has remained stationary throughout the Middle Miocene (relative to the upper plate of the collision/subduction system) with important implications for the distribution of strength of the western margin of the Hellenic Arc. The distribution and style of deformation along the western boundary of the extensional domain is controlled by the relation between gravitational forces, driving the flow of crustal material towards the low-lying adjacent regions sea floor, and heterogeneous resistive forces along the collision/subduction boundary.