Kwon, HyosangWoo, JusunOh, Jae-RyongJoo, Young Ji...
11页
查看更多>>摘要：The late Paleozoic was characterized by a series of continental collisions and ice ages. Despite the drastic environmental changes, sparse sulfur isotope data hinder our understanding of the late Paleozoic biogeochemical sulfur cycle, especially during the Early Permian. To overcome this potential bias, we present a high-resolution sulfur isotope record of carbonate-associated sulfate (CAS) and pyrite from the Carboniferous-Permian successions of the Svalbard archipelago. Throughout the Carboniferous, our results are largely consistent with the global trend, although the development of restricted environments resulted in a regionally observed delta S-34(CAS) peak of +20 parts per thousand during the Gzhelian. The Early Permian delta S-34(CAS) data in Svalbard bridge the gap in the existing record, showing a steady increase contemporaneous with the closure of the Ural Seaway and Gondwana glaciation, albeit superimposed by short-term oscillations. The enhanced incorporation of diagenetic sulfate into authigenic carbonates may have caused small-scale oscillations during the regional regression in the Artinskian, but the long-term increasing trend of delta S-34(CAS) and its relation to known geological events can be best explained by the enhanced pyrite burial flux driven by a major shift in the locus of organic carbon burial from the continent to the ocean, with a lesser contribution from the dissolution of epicontinental seaway evaporites. Since the onset of the Middle Carboniferous Bashkirian delta S-34(CAS) excursion also corresponds in timing to the major glaciation event and the closure of the Rheic Seaway, the sulfur isotope record in the course of the consolidation of Pangea is apparently punctuated by the episodes of increased pyrite burial and evaporite sulfate weathering, delineating the links between paleogeography, paleoclimate, and biogeochemical cycles. (C) 2022 The Author(s). Published by Elsevier B.V.
查看更多>>摘要：Quantifying tectonic-climatic interaction in shaping the margins of Tibetan Plateau is essential for understanding outward plateau growth. Here we investigate the histories of rock uplift and erosion along the northwestern margin of the Tibetan Plateau in the Altyn Shan, using low-relief high-elevation surfaces (LRHES) and combined bedrock and detrital apatite (U-Th)/He (AHe) analyses. Bedrock AHe dates and associated thermal modeling of samples collected from the mountain flank reveal a phase of very fast cooling starting at similar to 36 Ma, followed by subsequent moderate cooling since similar to 31 Ma. We argue that this pattern results from rock uplift caused by tectonic activity of the North Altyn fault (NAF), which separates the uplifted Altyn Shan from the low-lying Tarim Basin to the north. However, detrital AHe analysis and associated numerical modeling indicate that accelerated river incision in the Altyn Shan was delayed to as late as similar to 17 Ma merely similar to 10 km away from the NAF. Taken together, the data imply a long-lagged (similar to 19 Myr) response of accelerated river incision to tectonic-driven rock uplift. This delayed incision likely results from very low erosional efficiency associated with arid climate during the interval of similar to 36 - 17 Ma, with increased erosional efficiency during the relatively wet climate of the middle Miocene climate optimum (similar to 17 - 14 Ma). These findings illustrate the interplay between tectonics and climate in developing landforms on the northern margin of the Tibetan Plateau, and bear implications for both the Cenozoic evolution of this margin, and, more broadly, thermochronometer-based study of rock uplift and erosion. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Accurately reconstructing the temperature of the ocean through time carries implications for Earth's climate and early habitability. Attempts to build these reconstructions using oxygen isotope records have led to three end-member interpretations. Namely, that the observed enrichment over time in O-18 relative to O-16 in ancient chemical sediments reflects a change in sea-surface temperatures (SST), a change in the O-18 composition of the contemporaneous water, or that the primary signal has been subsequently overprinted. These questions become most salient in the Archean, where estimates of the isotopic composition of the ocean span similar to 20 parts per thousand, with a correspondingly wide range in estimated SSTs. Here, we introduce barite (BaSO4) as a robust new proxy for the oxygen isotope composition of the Archean ocean. We compile new and existing triple oxygen isotope and sulfur isotope data from the Fig Tree Group barite deposits in the Barberton Greenstone Belt, South Africa, with the goal of identifying the primary sources of sulfate to the Archean ocean. Using a simple Monte Carlo approach, we then constrain the possible isotopic composition of contemporaneous seawater. Our results suggest that microbial sulfur cycling played a limited role in setting the isotopic composition of Archean seawater sulfate. Additionally, it is likely that a significant flux of sulfate to the marine reservoir was atmospherically derived and carried a significant positive triple oxygen isotope signal. Importantly, our results support an Archean ocean with a somewhat enriched oxygen isotope composition (similar to 0-5 parts per thousand), with the exact composition dependent on the relative contribution from each sulfate production pathway. This result points either to the decreased significance of low-temperature weathering and/or to elevated SSTs in the early Archean. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：OSL-thermometry can be used to reconstruct the thermal structure in slowly denuded regions where infrared stimulated luminescence (IRSL) signals of samples obtained from deep boreholes are measured and evaluated with depth (e.g., 1.1-2.3 km depth, corresponding to similar to 40-75 ?; Guralnik et al., 2015a). Until now, only one study has explored this approach, using a target mineral of Na-feldspar. Therefore, in this study, we applied multi-OSL-thermometry to K-feldspar obtained from deep borehole core samples drilled at the Tono region, central Japan, which is a well-documented thermally stable crustal environment. The IRSL signals at 50, 100, 150, and 225 & DEG;C (IR50, IR100, IR150, and IR225, respectively) were measured. When a combination of four isothermal holding temperatures (ITL) between 190 and 250? was used for thermal kinetic parameter derivation, the inverted temperatures for the IR50 signals of the samples at a depth of -1 km (-40?) were most consistent with the in-situ temperature. However, the inverted temperatures for IR100, IR150, and IR225 signals were inconsistent with the in-situ temperatures even though the apparent geothermal gradients estimated from these IR signals are close to the modern geothermal gradient. These results suggest that the application of OSL-thermometry to K-feldspar in a borehole is useful to reconstruct the paleothermal conditions when adopting appropriate thermal kinetic parameters.(c) 2022 Elsevier B.V. All rights reserved.
Zhu, GaohuaYang, HongfengTan, Yen JoeJin, Mingpei...
10页
查看更多>>摘要：Foreshocks may provide valuable information on the nucleation process of large earthquakes. The 2021 Ms 6.4 Yangbi, Yunnan, China, earthquake was preceded by abundant foreshocks in the similar to 75 hours leading up to the mainshock. To understand the space-time evolution of the foreshock sequence and its relationship to the mainshock nucleation, we built a high-precision earthquake catalog using a machinelearning phase picker-EQTransformer and the template matching method. The source parameters of 17 large foreshocks and the mainshock were derived to analyze their interaction. Observed "back-and-forth" spatial patterns of seismicity and intermittent episodes of foreshocks without an accelerating pattern do not favor hypotheses of pre-slip in the nucleation region of the mainshock. The ruptured patches of most large foreshocks were adjacent to one another with little overlap, and the mainshock eventually initiated near the edge of the foreshocks' ruptured area where there had been a local increase in shear stress. These observations are consistent with a triggered cascade of stress transfer, where previous foreshocks load adjacent fault patches to rupture as additional foreshocks, and eventually the mainshock. (c) 2022 Elsevier B.V. All rights reserved.
Stepancikova, PetraRockwell, Thomas K.Stemberk, JakubRhodes, Edward J....
12页
查看更多>>摘要：We studied the southern part of the NW-SE trending Sudetic Marginal fault (SMF), situated at the northeastern limit of the Bohemian Massif in central Europe, to assess its Quaternary activity. Eighteen trenches and thirty-four electric resistivity profiles were performed at Bila Voda to study the fault zone and 3-dimensional distribution of a beheaded alluvial fan on the NE side of the fault. We interpret a small drainage, located about 29-45 m to the SE of the fan apex, as the only plausible source channel implying a similar amount of left-lateral offset. The alluvial fan deposits' radiometric ages range between about 24 and 63 ka, but postglacial deposits younger than 11 ka are not displaced, indicating that all motion occurred in the late Pleistocene. The site lies similar to 150 km south of the late Pleistocene Weichselian maximum (similar to 20 ka) ice sheet front. We model the effects of the ice load on lithospheric flexure and resolved fault stresses, and show that slip on the SMF was promoted by the presence of the ice sheet, resulting in a late Pleistocene slip rate of similar to 1.1(+2.3)/(-0.6) mm/yr. As the most favorable time for glacial loading-induced slip would be during the glacial maximum between about 24 and 12 ka, it is doubtful that the slip rate remained constant during the entire period of activity, and if most slip occurred during this period, the short-term rate may have been even higher. Considering that the modern maximum principal stress (sigma(1)) is oriented nearly parallel to the Sudetic Marginal fault (NNW-SSE) and is thus unfavorable for fault motion, our observations suggest that the likelihood of continued motion and earthquake production is much lower in the absence of an ice sheet. (C) 2022 Elsevier B.V. All rights reserved.
Duan, Wen-YongLi, Xu-PingSchertl, Hans-PeterWillner, Arne P....
16页
查看更多>>摘要：Metamorphic soles within ophiolite melanges record key information on subduction initiation and evolution of paleo-oceans. Mafic granulite and amphibolite occur in metamorphic soles within the Saga and Bairang ophiolitic melanges of the Yarlung Tsangbo suture zone, southern Tibet. In fresh mafic granulite, the early prograde assemblage (M1) is preserved as inclusions in the core of garnet. Minerals in matrix and garnet mantle define the peak metamorphic assemblage (M2). Near-isothermal decompression (M3) is recorded by the garnet rim and a symplectic corona. The mineral assemblage of the fresh amphibolite only records one major stage. Many samples were overprinted by strong metasomatism at sub-greenschist-facies conditions (M4). According to geochemical fingerprints, the soles originate from a mid-ocean-ridge environment with strong affinities to the non-metamorphic oceanic crust of the Yarlung Tsangbo ophiolites. P-T calculations of the granulites by pseudosection techniques, Zr-in-rutile and REE-based thermobarometry show similar to 690-760 degrees C/9.5-12.5 kbar for the prograde (M1) stage, 900-970 degrees C/14-16 kbar for the peak (M2) stage followed by 902-983 degrees C/9.5-12.6 kbar for the retrograde (M3) stage. From the amphibolite P-T conditions of < 700-880 degrees C/7-12.5 kbar were derived. This results in a clockwise trajectory with peak-high pressure to ultrahigh-temperature conditions characterizing a "hot" subduction environment. U-Pb dating of magmatic zircon yields similar to 133-127 Ma as protolith ages of the soles, almost coeval with the igneous ages of the unmetamorphosed oceanic crust. U/Pb ages of metamorphic zircon show a similar range within uncertainties (similar to 131-119 Ma) indicating that initiation of subduction subsequently followed the protolith crystallisation. The metamorphic soles were subducted to a depth of 50 km triggering partial melting in the mantle wedge by dehydration reactions and formation of supra-subduction-zone magma. The mantle wedge became cooler and more buoyant when the subduction zone matured, which caused exhumation of the metamorphic soles and surrounding mantle rocks as well as cooling. A new model for a "hot" subduction initiation close to a mid-ocean ridge near the Asian margin is proposed based on the data from this study and previous studies. The relict mid-ocean-ridge basalts after subduction initiation and the subsequent supra-subduction-zone basalts formed the YTSZ ophiolites during similar to 130-120 Ma. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Seismic cycles emerge in a broad range of rupture styles, from slow-slip events to pulse-like earthquake sequences. Meanwhile, large earthquakes in paleoseismic and instrumental catalogues exhibit various recurrence patterns going from periodic to chaotic cycles with characteristic or dissimilar ruptures. The potential connection between these observations is still poorly known. Here, we investigate the link between rupture styles and recurrence patterns in quasi-dynamic models of seismicity in twodimensional faults embedded in a compliant zone, exploring a wide range of frictional and fault zone properties. The recurrence patterns evolve from purely periodic to multiple-periodic time-and slip predictable cycles, to chaotic sequences of super-cycles with full and partial ruptures with an increasing number of aftershocks. This transition is accompanied by changes of rupture styles from crack-like to pulse-like ruptures. These behaviors can be obtained either by a more compliant fault zone or a reduced characteristic weakening distance of friction. The effects of the compliant zone and other physical characteristics can be conflated into a single non-dimensional number, such that seismic cycles with similar behaviors can be obtained with or without a compliant fault zone in quasi-dynamic simulations. The connection between recurrence patterns and rupture styles implies that the paleoseismic record can bring useful constraints to rupture characteristics and fault zone properties.(C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The 15 January 2022 Hunga, Tonga, volcano's explosive eruption produced the most powerful blast recorded in the last century, with an estimated equivalent TNT yield of 100-200 megatons. The blast energy was propagated through the atmosphere as various wave types. The most prominent wave was a long-period (> 2000 s) surface-guided Lamb wave with energy comparable to that of the 1883 Krakatoa Lamb wave; both were clearly observed by pressure sensors (barometers) worldwide. Internal gravity, acoustic-gravity, and infrasound waves were captured in great detail by the entire infrasound component of the International Monitoring System (IMS). For instance, infrasound waves (< 300 s period) were seen to circumnavigate Earth up to eight times. Atmospheric waves captured by the IMS infrasound network and selected barometers near the source provide insight on Earth's impulse response at planetary scales. (C) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
查看更多>>摘要：The dynamic behaviour of crystals in convecting fluids determines how magma bodies solidify. In particular, it is often important to estimate how long crystals stay in suspension in the host liquid before being deposited at its bottom (or top, for light crystals and bubbles of volatiles). We perform a systematic 3D numerical study of particle-laden Rayleigh-Benard convection, and derive a robust model for the particle residence time. For Rayleigh numbers higher than 107, inertial particles' trajectories exhibit a monotonic transition from fluid tracer-like to free-fall dynamics, the control parameter being the ratio between particle Stokes velocity and the mean amplitude of the fluid velocity. The average settling rate is proportional to the particle Stokes velocity in both the end-member regimes, but the distribution of residence times differs markedly from one to the other. For lower Rayleigh numbers (< 107), an interaction between large-scale circulation and particle motion emerges, increasing the settling rates on average. Nevertheless, the mean residence time does not exceed the terminal time, i.e. the settling time from a quiescent fluid, by a factor larger than four. An exception are simulations with only a slightly super-critical Rayleigh number (similar to 104), for which stationary convection develops and some particles become trapped indefinitely. 2D simulations of the same problem overestimate the flow-particle interaction - and hence the residence time - for both high and low Rayleigh numbers, which stresses the importance of using 3D geometries for simulating particle-laden flows. We outline how our model can be used to explain the depth changes of crystal size distribution in sedimentary layers of magmatic intrusions that are thought to have formed via settling of a crystal cargo, and discuss how the microstructural observations of solidified intrusions can be used to infer the past convective velocity of magma. (c) 2022 Elsevier B.V. All rights reserved.
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