Tectonophysics最新文献

The Barreirinhas pull-apart system encompasses marginal basins in divergent and transform margin segments in the central sector of the Brazilian Equatorial Margin and its African conjugate counterpart. This ancient pull-apart system evolved through transtensional strike-slip motion within a highly heterogeneous crystalline basement affected by multiple rift phases. The geometry and development of pull-apart structural elements during the final rifting phase before continental breakup and the mechanisms and extent to which they were influenced by preexisting crustal heterogeneities are comprehensively addressed using an extensive database of potential field (magnetic and gravity) and 2D seismic reflection data. We also assess the lithospheric thermomechanical conditions and their influence on transtensional extension throughout Curie Point Depth, Heat Flow, and Moho depth, derived from potential field data and published seismological models. Plate reconstruction of Brazilian and African equatorial margins based on gravity patterns and comparison with sandbox analog models allow a 3D synoptic model to reveal the Barreirinhas pull-apart system evolution during the Equatorial Atlantic opening. During the rift phase I, the location of major grabens was controlled by favorably oriented Neoproterozoic shear zones, while the cooler, stronger, and thicker crust beneath cratonic areas formed the western barrier to strike-slip rift activity during rift phase II. This same geological domain anchored the onset of the pull-apart system in the last rift phase III, whose principal displacement zones developed along the extensive oceanic fracture zones linked by sigmoidal fault systems. Toward the end of the rift phase, a large asymmetric lozangle to a lazy-Z-shaped, pull-apart basin developed above low overlapping ∼90°, releasing stepover in oblique transtensional strike-slip motion.

On 22 May 2021, an M_W 7.4 earthquake occurred in Maduo County, Qinghai Province, China, which is located on the Kunlun Mountain Pass-Jiangcuo fault inside the Bayan Har block, providing a good opportunity to investigate seismogenesis of large intraplate earthquakes. We analyze two years of continuous seismic data from June 2021 to June 2023, which were recorded at 34 portable seismic stations of the MaduoArray deployed in the source zone by our group. The LOC-FLOW workflow of automatic detection and location is applied to construct a complete and high-precision seismic catalog for the region, which includes machine-learning phase picking (PhaseNet), earthquake phase association (REAL), velocity model updating and station correction (VELEST), absolute earthquake location (HypoInverse), and relative location (HypoDD). As a result, 78,832 Maduo aftershocks and other local earthquakes are detected and relocated precisely. Our results show that the length of the Maduo aftershock zone is ∼170 km, which is mainly distributed along the NWW-SEE oriented Kunlun Mountain Pass-Jiangcuo fault, and there is a horsetail bifurcation feature at the eastern end of the aftershock sequence. The seismogenic fault is nearly vertical, and local seismicity occurs on both sides of the fault. Our results also show that there is no seismic gap or aftershock sparse area in the region. Previous studies have revealed a low-velocity and high-conductivity anomaly below the source zone, reflecting fluids ascending from the lower crustal flow. These results provide new insights into the cause of the 2021 Maduo earthquake.

The Mexican subduction system is an ideal region to study 3-D mantle deformation patterns in response to changes in slab geometry and the presence of tears. Shear-wave splitting measurements were made using SKS, SKKS, and PKS waves in southern Mexico, where the Cocos slab subducts beneath the North American and western Caribbean plates. For most of southern Mexico, the results are consistent with predominantly trench-normal fast polarization directions that can be interpreted as a consequence of sub-slab entrained flow and 2-D corner flow in the mantle wedge in the presence of A-type olivine fabric (or similar). This pattern of trench-perpendicular fast axes extends northward to the region southeast of the Trans-Mexican Volcanic Belt. Beneath its eastern end, fast axes rotate ∼20° clockwise and are likely controlled by the absolute motion of the North American plate. In southeastern Mexico, along the coast and above the mantle wedge tip, the fast axes are trench-normal and the delay times are the shortest. They were interpreted to result from a possibly serpentinized mantle wedge tip. In the same region above the mantle wedge core, the splitting parameters appear to result from different flow patterns in the mantle wedge and the sub-slab mantle.

High-pressure and temperature deformation experiments interfaced with acoustic emission (AE) monitoring have been conducted to study transformational faulting in Mn₂GeO₄ olivine, which transforms to the β phase, isostructural to wadsleyite. Metastable Mn₂GeO₄ olivine exhibits a marked embrittlement behavior at temperatures between 800 and 1100 K, emitting numerous AEs. At each temperature, brittle deformation is characterized by a two-stage process: (1) a “preparation” stage with numerous diffusedly located low-magnitude AEs and large b values (>2), and (2) a failure stage where larger-magnitude AEs form a planar distribution with b values about 1. Microstructure analysis reveals extensive kink band development in olivine grains in the recovered samples. Kink band boundaries (KBBs), with a typical thickness of ∼100 nm, are filled with a nanometric β-Mn₂GeO₄ “gouge”. A dense array of secondary shear localizations is often present within the kink bands, suggesting significant shear deformation therein. The combined observations suggest that faulting in metastable Mn₂GeO₄ olivine is a self-similar process, from grain-scale to the sample-scale. Both observed embrittlement behavior and the microstructure of metastable Mn₂GeO₄ olivine are essentially identical to those in Mg₂GeO₄ olivine we have reported previously, indicating that the physical mechanism of faulting in metastable olivine is insensitive to the specific crystallographic structure of the high-pressure phase. The low b values (about 1) observed in the faulting process in our experiments are similar to those of deep focus earthquakes in cold subduction zones. Our observed mechanism explains deep focus seismicity in cold metastable mantle wedges, provided that the self-similarity assumption holds to geological scales.

An intraoceanic Trans-Tethyan subduction zone has been identified in both the Kohistan-Ladakh arc and the West Burma Terrane. This has significant implications for the India-Eurasia collision. Concurrently, the dismembered ophiolites within the Yarlung-Tsangpo Suture Zone likely originated from the intraoceanic Trans-Tethyan subduction zone or the Andean-type southern Eurasian continental margin. A paleomagnetic study was conducted on the Lower Cretaceous (∼120–130 Ma) mafic dykes in the Xiugugabu ophiolite to resolve the uncertainty of its origin. The characteristic remanent magnetization (ChRM) obtained through stepwise thermal demagnetization successfully passed consistency/fold and reversal tests. After tilt correction, the overall mean direction of the ChRM was D = 296.9°, I = −25.5°, k = 47.6, α₉₅ = 4.5°, and N = 22, indicating a paleolatitude of 13.4°N/S and a paleopole at 15.0° N, 326.6°E with A₉₅ = 3.8°. Compared with previous paleomagnetic data from the Trans-Tethyan subduction zone, our findings strongly support the involvement of the Xiugugabu ophiolite in the intraoceanic Trans-Tethyan subduction zone. This finding reinforces the hypothesis that there were two distinct subduction zones in the Neotethyan Ocean during the Early Cretaceous. One subduction zone was situated on the southern margin of the Gangdese Arc. The second was the intraoceanic subduction zone, located approximately 3500 km from the southern margin of Eurasia, in the southern hemisphere. Our results also support a multistage India–Eurasia collision process involving continental plates, intraoceanic arcs, and terranes within the Neo-Tethyan Ocean.

This study examines subsurface deformation at the northern end of the Wadi Araba Fault (WAF), focusing on the Amman-Hallabat Fault (AHF) and the Wadi Shueib Fault (WSF). While surface evidence shows their tectonic impact from the Late Cretaceous to the present, research on their subsurface structures, contributing to the WAF, is limited. Using seismic data and well report, five seismo-stratigraphic units with significant unconformities were identified. The seismo-structural interpretation reveals a complex deformational fault zone with numerous reverse and normal faults intersecting strata from post-Precambrian rocks to the uppermost Cretaceous deposits, forming a composite flower structure with positive and negative flower characteristics. These structures show significant folding and thrusting of deposits from the uppermost Cretaceous to recent times. Seismic evidence indicates that the AHF and WSF extend upward to the Earth's surface. Fault mechanism analysis suggests a NE-SW transpressional deformation pattern, with fault formation and associated structures influenced by the Syrian Arc stress field since the Turonian. Changes in stress field orientation have significantly affected their reactivation. At its northern termination, the WAF may intersect or terminate against pre-existing faults like the AHF and WSF, influencing the WAF's behavior by accommodating strain, dissipating energy, or being reactivated as restraining bends due to the NNW-SSE-trending Dead Sea stress, leading to a complex network of distributed movement.

The links between tectonics, surface processes and magmatism govern the evolution of rifted and transform margins. Quantifying the control of surface and deep Earth processes, lithosphere rheology and plate kinematics is challenging because of their non-linear interactions. We designed and conducted systematic 3D magmatic-thermo-mechanical numerical experiments coupled with surface processes modelling to better understand the formation of rifted and transform continental margins. Oceanic transform faults are formed by either the opposite polarity of oceanic detachment faults or their formation is linked to the gradual interaction between two propagating rift and spreading centers.

Lower divergence velocities, faster crustal and slower mantle thinning, lower surface processes (i.e. erosion and sedimentation) rates, and lower mantle potential temperature lead to the formation of magma-starved continental margins, mantle exhumation and eventually the formation of a stable transform fault zone with a magma-starved, deep transform valley. Suppressed melting and small-scale mantle instabilities govern the along-ridge variation of magmatic and non-magmatic segments, often leading to V-shaped zero-offset oceanic fracture zones. In contrast, faster divergence, lithospheric mantle inherited weak zones, enhanced erosion and sedimentation, result in enhanced mantle melting, and rift magmatism and the formation of a spreading center in the transform zone. Models simulating the temporal increase of divergence velocities show the evolution from an initial magma-poor to a final magma-rich oceanic basin.

In models without simulating mantle melting, enhanced surface processes lead to delayed break-up linked to a longer continental hyper-extended stage. However, enhanced surface processes and a more localized and accelerated lithospheric mantle thinning can promote earlier mantle melting and the formation of magma-chambers beneath the crust.

The tempo of subduction-related magmatic activity over geological time is episodic. Despite intense study and its importance to crustal growth, the fundamental drivers of this episodicity remains unclear. We demonstrate quantitatively a first order relationship between arc flare-up events and high subduction flux. The volume of oceanic lithosphere entering the mantle is the key parameter that regulates the proportion and rate of H₂O entering the sub-arc. New estimates of subduction zone H₂O flux over the last 150 million-years indicate a three- to five-fold increase in the proportion of H₂O entering the sub-arc during the most recent global pulse of magmatism. Step changes in H₂O flux enable proportionally greater partial melting in the sub-arc mantle leading to a flare-up episode. Similar magmatic flare-ups in the ancient Earth could be related to variability in slab flux associated with supercontinent cycles.

We identify possible sources of seismic anisotropy beneath India by synthesizing 2064 well-constrained shear-wave splitting parameters determined from a consistent analysis of waveforms recorded at 357 broadband seismic stations. Our effort includes compilation of previous results, reanalysis of old data, analysis of new data from previous networks and new stations. Our results reveal that the average delay time for entire India and its constituent tectonic provinces is $\sim$0.83 s suggesting moderate strength of anisotropy. Although the fast polarization azimuths (FPAs) are scattered, a NE trend appears dominant. Due to significant correlation of FPAs with the APM direction and lack of correlation between i) splitting parameters and backazimuths and ii) average delay times and lithospheric thickness, we conclude that the major contribution to anisotropy is from shearing in the upper part of the asthenosphere or a transitional layer from the base of the lithosphere to the upper part of the asthenosphere. Further, we postulate that a weakly anisotropic lithosphere in northern, central and south-eastern India is due to frozen anisotropy from past tectonic events. Northern and central India, Arunachal Himalaya and southern part of Burmese arc have simple anisotropy. Application of the spatial coherency technique reveals a source depth of 290 km for northern India. However, for south-eastern India and northern part of the Burmese arc, a two-layer model, with frozen-in and present-day anisotropy in the upper layer, and shearing and mantle flow in the lower layer, respectively, fits the anisotropy. In southern India, a large deviation of the FPAs from APM suggests imprints of deformation related to past tectonic events. A two-layer model, with frozen-in anisotropy in the upper and lower layers, is plausible. Variation in FPAs in the central part of the Indian shield is attributed to deflection in mantle flow at the northern edge of the lithospheric keel.

We employed shear-wave splitting analysis on both teleseismic SKS and S waves, and S waves from deep (150–250 km) local earthquakes collected from a dense array with 43 temporary broadband seismic stations and nine long-term seismic stations centered at Mount Taranaki to characterize the upper-mantle dynamics in the southwestern North Island of New Zealand, in areas previously unexamined for shear-wave splitting. We observed predominantly trench-parallel fast polarizations and strikingly large delay times over 3 s from teleseismic analysis. In contrast, local S analysis yielded a sharp transition of fast-polarization from trench-parallel in the northeast to trench-normal in the southwest. Trench-parallel fast-polarization from teleseismic analysis may be attributed to sub-slab trench-parallel flow or to trench-parallel fractures in the subducting slab. More importantly, we attribute large delay times to deep upper-mantle (200–400 km depth) deformation, possibly associated with the dynamic interaction between the downgoing slab and the 410-km discontinuity or with the lithosphere delamination near the Taranaki-Ruapehu line. In contrast, the trench-parallel anisotropy from the local S waves in the northeast could be caused by fluid-bearing cracks in the crust of the Taupō Volcanic Zone and/or by trench-parallel fractures in the subducting slab resulting from outer rise bending. The abrupt change to trench-normal may be related to stress variations in the downgoing slab at different depths.