Journal of Geodynamics最新文献

The origin, tectonic development, and lithosphere structure of the East Black Sea Basin (EBSB) are governed by the evolution of the northern branch of the Tethys ocean. The most spectacular features of its evolution could retain their imprints in geophysical fields and models, which we used to constrain a geophysical transect for the crust and upper mantle crossing the EBSB and the Shatsky Ridge (SR) from the Eastern Pontides to the Northern Caucasus. 2D gravity and magnetic modeling, constrained by wide-angle seismic data, revealed thin high-density and high-velocity sub-oceanic crust of the EBSB with the Moho shallowing up ~20 km depth. A spectacular feature of the Black Sea magnetic field is the Alushta-Batumi anomaly (ABA) above the SR that could be an imprint of subduction-related Middle Jurassic magmatic arc, whereas the Cretaceous (in Eastern Pontides) magmatic arc manifests itself by a chain of magnetic anomalies on the southern shoreline of the Black Sea. The high-velocity heterogeneity, revealed by seismic tomography, could be an image of a slab due to Mesozoic (Middle Jurassic and Cretaceous) subduction of the northern branch of Neotethys ocean. It shows rather a flat subduction slab that plunges northwards from subcrustal depths south of Eastern Pontide to the depth of > 70–80 km below the SR. Middle Jurassic and Cretaceous subduction fronts are located closely in the region of Eastern Pontides, whereas the related magmatic arcs are spaced differently – over the SR for the Middle Jurassic arc and along the southern coastline for Cretaceous Eastern Pontide magmatic arc correspondingly. The latter could be caused by the opening of the EBSB in the Cretaceous that separated the eastern segment of the BS onto the Eastern Pontides – Arkhangelsky Ridge and the SR – Northern Caucasus domains.

In a recent paper published in the Journal of Geodynamics (vol. 137, June 2020, 101733), Fonseca et al. (2020) proposed a thought-provoking model aiming to elucidate the exhumation history of the Neoproterozoic Brasília Fold Belt (BFB) between the Devonian and Cretaceous periods. Exclusively based on information from the literature and new thermochronological data, Fonseca et al. (2020) presented an alternative model that tries to bind tectonic uplift, erosion, and the influx of clastic material coming from the BFB into the intracratonic Paraná Basin. Although the welcome proposal and reliable quality of the analytical data, the hypothesis presented diverges from several previously published works. In the light of the presented apatite fission-track ages, we disagree with their paleogeographical model, which puts the Brasília Fold Belt as a major source for clastic detritus to the Paraná Basin between the Devonian to Permian. The primary goal of our comments is to clarify the state-of-art of the intricate source-to-sink system of the Paraná Basin. Secondarily, we try to demonstrate why the model proposed by Fonseca et al. (2020) presents some geodynamic and interpretative problems and do not characterize an adequate paleogeographic scenario for southwest Gondwana between the Devonian to Permian periods.

The 2017 Chiapas earthquake with moment magnitude M_w = 8.2, caused seismic induced surface motion which has been well recorded and analyzed globally using broadband seismometers. In contrast, Global Navigation Satellite System (GNSS) measurements of absolute receiver positions at cm accuracy have been marginally used for seismic wave analysis. We show that GNSS station displacement measurements, located in North America, can detect traveling seismic surface waves through a GNSS network for the 2017 Chiapas earthquake with a single station precise point positioning (PPP) measurement accuracy of 1–2 cm, evaluating 1 Hz data. We found that the network data show a total amplitude in temporal filtered horizontal displacement data of up to 5 cm, which is in good agreement with absolute measurements of a broadband seismometer. The multi constellation (primarily GPS and GLONASS) GNSS measurements are most sensitive to seismic surface waves such as e.g. given by Love and Rayleigh wave components in the frequency range of 20–35 s determined by FTAN (Frequency Time Analysis) where the Rayleigh component dominates the measured GNSS signals. We provide estimates of phase velocities and epicenter location determined by a cross-correlation procedure and evaluate its accuracy within the framework of a comparison to state-of-the-art seismic models. Hereby GNSS station data suffer from double measurement noise in the vertical displacement component, which results in a low signal to noise ratio that deny proper pressure wave analysis. While the derived phase velocities have typical uncertainties of 200 m/s in standard deviation, which may seem inappropriate for geophysical interpretation of a single station they might be appropriate in a large and dense GNSS network (spatial distance < 25 km). Determination of the seismic source location is possible and even offers the ability to provide tsunami early warning. Consequently, we see GNSS network station data may be a complementary and independent observation type – prior to well established geophone or accelerometer measurements – which is suited for seismic wave detection and analysis, although limited in accuracy.

The Vardar Zone is a product of the Triassic-Jurassic opening of the Neotethys, Jurassic obduction, Late Cretaceous/Paleogene consumption of the oceanic crust and continental collision. During the last process, the Eastern Vardar Zone was thrust over the Central and eventually both onto the Western Vardar Zone. The present paleomagnetic and structural study provided new results from the first two zones in the Belgrade area. The younger set of data, together with published ones from the third zone, provide firm evidence for about 30° clockwise vertical axial rotation of the Vardar Zone between 23 and 18 Ma, connected to extension driven by the roll-back of the Carpathians lithosphere.

Earlier, the Vardar Zone was affected by intensive compression generating a nappe pile, comprising the Eastern, Central and Western Vardar Zones. This assembly was eventually thrusted over CCW rotating Adriatic elements in the Paleogene. The rotation triggered a system of right lateral strike slip faults between different tectonic slices in the Vardar Zone. This tectonic model offers a plausible explanation for the paleomagnetic directions of post-folding age of the Upper Cretaceous flysch of the Central Vardar Zone. Nevertheless, the possibility of remagnetization of the magnetite bearing flysch during Late Neogene uplift can not be excluded.

The position of the middle-upper Miocene volcanic arc, encompassing the Maghrebides, the Sardinia Channel and the Sardinia-Corsica block, implies that the Algerian and Tyrrhenian basins developed, respectively, as backarc and forearc extensional zones in the Western-Central Mediterranean. The opening of the Western-Central Mediterranean Neogene extensional basin has been commonly interpreted as a two-step process: the opening of the Provençal-Algerian basin during the early-middle Miocene, followed, in the late Miocene, by the formation of the Tyrrhenian Basin. This article is an attempt to synthesize knowledge about the hinge zone between Algerian and Tyrrhenian basins by combining the analysis of seismic reflection profiles with dredge and borehole data in order to investigate how the transition between the eastern Algerian backarc and Tyrrhenian forearc geodynamic settings took place. We identified three sectors: the western Tyrrhenian characterized by a Tortonian forearc extension; the Sardinia Channel, which preserves the architecture of the lower Miocene Maghrebian thrust belt formed during the collision between Europe and Africa plates; and the easternmost Algerian basin-Sicily Channel where a backarc–thrust belt system developed during the Tortonian stage. During the extensional events, we hypothesize the re-activation of inherited structures during Tortonian rifting, (that is a negative tectonic inversion of pre-existing Eocene and early Miocene thrust faults). The contemporaneity of two different geodynamic environments, the forearc extension in the northern area and backarc–thrust belt system in the southern area, can be directly related with a lateral variation of the lower plate paleogeography of the Africa continental margin. This evidence contributes to the understanding of how the paleogeography of the lower plate can control, to a certain extent, the tectonic evolution of the upper plate in a subduction setting.

The ability to mitigate and predict volcanic risk is a long-standing question in the Geosciences’ community, while the extent of volcanic activity may be regulated by a predictable and periodic external excitation induced by seasonal rainfall, hydrological loading, or Moon-Sun gravitational force. Moreover, the complex stress-triggering, hydro-mechanical coupling in response to seasonal rainfall, and associated feedback mechanism with deep magmatic process remains enigmatic and indeed deserves more attention in view of recent climate change scenario. In this letter, a compelling scenario of seasonal rainfall-triggered eruption cycles of Mount Etna (Italy) is found and presented on the eastern coast of Sicily which continuously erupting since last 200 kyr. Results show that the seasonal rainfall significantly weakened the Mount Etna edifice and initiated mechanical tensile failure in the complex magmatic plumbing system and adjacent flank surface by changing the pore pressure build-up, probably promoting dyke intrusion and eventual triggering of eruptive cycle. Further, the possibility of seasonal hydrological loading on the Mount Etna volcano and adjacent flank region, hydrological load-induced sliding along the impermeable outer ‘shell’ of the flank are discussed, and the effect of tidal stress perturbations on the eruptions cycle cannot be ruled out completely.

The Raohe accretionary complex (RHC) is located at the eastern of northeast China and adjacent to Russian Far East. As a part of the Circum-Pacific Orogenic Belt, it is the unique region of the accretionary orogenic belt, which is associated with the subduction process of the Panthalassic-Pacific Plate (PPP). We synthesize the detrital zircon ages of terrigenous clastic rocks of the RHC and tectonic units along the East Asian Continental Margin (EACM) to clarify its provenance. Then we place the docking position of the RHC adjacent to the South China Block, and determine that the final accretion of the RHC occur during the later Late Jurassic (~150 Ma) according to combination for ages of stitching plutons and terrigenous clastic rock. Integrating with the published global-scale plate kinematic frame, we restored the pre-docking motion path of the RHC using the Gplates software. The reconstructed scenario shows that it is a long distance of at least 1000 km between the proto-RHC and continent margin when the basaltic volcanism occurred subaqueously within the abyssal basin of the PPP. This model also provides a probability that the proto-RHC and the proto-Yuejingshan accretionary complexes have the same drift history, before their simultaneous emplacement into the continental margin.

Here we reply to the comment by Alessandretti and Warren, (2021) on the paper “Devonian to Permian post-orogenic denudation of the Brasília Belt of West Gondwana: insights from apatite fission track thermochronology” by Fonseca et al. (2020). We have the impression that many of the remarks, at least to some extent stem from a misunderstanding of our manuscript, also considering that they did not propose any alternative hypothesis for interpretation of our results presented in the aforementioned paper. We, thus, reiterate our interpretations from our low-temperature thermochronology data. The basement of the Brasilia Belt was subject to a significant exhumation during the Devonian to the Permian through erosion, and was likely a source area for detrital sediments deposited in parts of the northeastern Paraná Basin at that time. Apatite fission-track data show that Meso-Cenozoic events had limited effect on post-orogenic exhumation of the Brasília Belt, in contrast to e.g. the Araçuaí Belt.

The character of arcs varies over time with significant temporal fluctuations in the quantity and spatiotemporal patterns of magmatism. However, the driving mechanisms for this episodic behavior of arcs need more constraints. This paper analyzed the published data along with our new zircon U-Pb dating and Hf isotopic and whole-rock geochemical data of plutonic rocks in the Gangdese belt in southern Tibet to explore the features, potential drivers, and tectonic implications of episodic arc activity in the Gangdese arc. A comprehensive compilation of U-Pb ages and Lu-Hf isotopic analyses of zircon grains from igneous rocks in the Gangdese belt, sedimentary rocks in trench fill sequences, forearc basins and foreland basins, and sands from modern river reveals that: 1) Gangdese arc activity was episodic during Late Cretaceous to Middle Eocene, displaying two magmatic flare-ups (ca. 100–80 and 65–45 Ma) and one magmatic lull (ca. 80–65 Ma), and 2) both flare-up magmas show relatively positive ε_Hf(t) values (+5 ~ +15) indicative of juvenile sources suggesting these magmas are dominated by contributions from the depleted mantle. In contrast, the magmatic lull between these two magmatic flare-ups could be caused by flat subduction of the Neotethyan slab beneath the southern margin of the Lhasa terrane. These flare-ups likely contributed greatly to the crustal thickening of the Gangdese belt. Constraints from paleo-elevation and geochemical proxies for crustal thickness showed that the ~100–80 Ma flare-up was accompanied by the formation of a thick arc root while the ~65–45 Ma flare-up likely developed in a thinner crust without an arc root.