查看更多>>摘要：Volatiles play a pivotal role in subduction zone evolution, yet their pathways remain poorly constrained. Studying the Lesser Antilles subduction zone can yield new constraints, where old oceanic lithosphere formed by slow-spreading subducts slowly. Here we use local earthquakes recorded by the temporary VoiLA (Volatile recycling in the Lesser Antilles) deployment of ocean-bottom seismometers in the fore-and back-arc to characterize the 3-D seismic structure of the north-central Lesser Antilles subduction zone. Along the slab top, mapped based on seismicity, we find low Vp extending to 130-150 km depth, deeper than expected for magmatic oceanic crust. The slab's most prominent, elevated Vp/Vs anomalies are beneath the fore- and back-arc offshore Guadeloupe and Dominica, where two subducted fracture zones lie with the obliquely subducting boundary between Proto-Caribbean and Equatorial Atlantic lithosphere. These structures, therefore, enhance hydration of the oceanic lithosphere as it forms and evolves and the subsequent dehydration of mantle serpentinite when subducted. Above the slab, we image the asthenosphere wedge as a high Vp/Vs and moderate Vp feature, indicating slab-dehydrated fluids rising through the overlying cold boundary layer that might induce melting further to the west. Our results provide new evidence for the impact of spatially-variable oceanic plate formation processes on slab dehydration and mantle wedge volatile transfer that ultimately impact volcanic processes at the surface, such as the relatively high magmatic output observed on the north-central islands in the Lesser Antilles. (C) 2022 The Author(s). Published by Elsevier B.V.
查看更多>>摘要：In the Mexican subduction zone, the heterogeneous spatial density of the GNSS network is limiting the capability to measure and study the variability of the surface deformation field all along the subduction zone. To improve the spatial coverage of interseismic deformation estimates, we combine InSAR and GNSS data. We use four Sentinel-1 descending tracks covering a large part of the Mexican Pacific coast from Jalisco to Oaxaca, over the period from 2016 to 2019.5. The InSAR and GNSS time series, over the same 3.5-year period, are corrected for the coseismic deformations of two M-w > 7 earthquakes but not for slow slip events (SSE) and postseismic surface displacements. We present estimates of mean surface velocities over the study period, which combine the linear inter-SSE trend and transient aseismic slip. By inverting these velocities, we estimate the short term coupling at the plate interface, which shows large lateral variations. InSAR data significantly improves the resolution of the inversion, compared to a model based only on GNSS data. Although not representative of long-term coupling in areas with large transient events, the short-term coupling estimates highlight the role of transient signals, such as slow slip events, on the coupling variability measured by geodesy. In agreement with GNSS times series over longer time period, the data also suggest that the Jalisco area (longitude from -106 degrees E to -104 degrees E), where no large transient events are observed, is highly coupled with a coupling ratio higher than 0.8. (C) 2022 Elsevier B.V. All rights reserved.
Li, Ka LokBean, Christopher J.Bell, Andrew F.Hernandez, Stephen...
8页
查看更多>>摘要：Seismic tremor observed near active volcanoes is an important tool for volcano monitoring as it often appears shortly before eruptions. Although tremor can be generated by a variety of physical processes it is usually interpreted as direct evidence for flowing magma in the sub-surface. These interpretations typically feed into risk assessments for potential eruptions. Using the temporal evolution of tremor amplitude and spectral data from a distributed seismic network that captured the 2018 eruption at Sierra Negra in Galapagos, we determine that tremor is not directly related to sub-surface fluid movement. Instead at Sierra Negra tremor likely indicates a slowly propagating fracture, which is later exploited as a pathway for silent magma flow. Distinct differences in the source migration and the spectral character of pre-eruptive and co-eruptive tremor allow both a location estimate of the future eruption site and a precise timing of the eruption onset. (C) 2022 The Authors. Published by Elsevier B.V.
查看更多>>摘要：The origin, evolution, and the state of Earth's hydrosphere are relevant for the timing, style, and intensity of plate tectonics, continental and submarine weathering, and the emergence of the continents. We here present a study of triple oxygen isotopes of hydrothermally altered oceanic crust from the Nuvvuagittuq greenstone belt (NGB) in Canada (4.3-3.8 Ga), which provides a rare snapshot of the Earth's earliest hydrosphere on a planet without modern-style plate tectonics. High delta O-18 = 8-12%o, delta O-iota 17=-0.02 to -0.05%o, and 8D of -30-40%o values measured in the NGB metavolcanic rocks are interpreted to indicate that they represent the upper section of ancient oceanic crust (pillows, sediments) altered at low temperature by seawater similar to modern submarine oceanic sections. Hydrothermal alteration was accompanied by silicification at low temperature (50-150?C) as evidenced by a positive correlation of delta O-18 with silica, elevated delta O-iota 17 values, and triple oxygen isotope thermometry. We discuss the effects of 2.7 Ga metamorphism on the preservation of triple oxygen isotope compositions and show that the hydrothermal alteration is protolithic and predated metamorphism. Triple oxygen isotopes allow reconstruction of the isotopic compositions of seawater and suggest that the 818O of the early oceans could have been comparable to that of the modern to perhaps -5%o but silica-saturated. Models with an ancient ocean with delta O-18 of +3%o or < -5%o seawater result in worse fits to the data. Submarine weathering and hydrothermal silicification could have played a more important role in Eoarchean world with subdued role of subaerial weathering due to insignificant continental exposure that helped balancing seawater delta O-18 values to near modern values. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The Eastern Block of the North China Craton preserves a Neoarchean greenstone-granite rock association with typical dome-and-keel structures. Metamorphic data for these rock assemblages record both anticlockwise P-T paths involving near-isobaric cooling (IBC) and clockwise paths with nearly isothermal decompression (ITD) from nearby locations leading to controversial and contradictory interpretations. To resolve the presence of coexisting diverse P-T paths, and to place them within a viable geodynamic regime, we conducted 2D thermomechanical numerical models with the initial and boundary conditions similar to that of the Neoarchean eastern North China Craton. Our model results reveal that heat transferred from the high-temperature lower boundary and crustal density inversion leads to crustal-scale sagduction that generates the observed dome-and-keel architecture and results in four major types of P-T-t paths: (1) an anticlockwise IBC-type P-T-t path in which the supracrustal rocks progressively sink to a deep crustal level through sagduction, and experience a long-lived residence followed by ambient mantle cooling without significant exhumation; (2) an clockwise ITD-type P-T-t path where the supracrustal rocks sink to the deep crust and are partly captured by upwelling felsic magmas, resulting in rapid exhumation to a middle crustal level; (3) a newly identified crescent-type P-T-t path that reveals an integrated burial-exhumation cycle characterized by an initial high dT/dP burial stage, followed by the rapid exhumation to the upper crust and extensive low dT/dP cooling; (4) a hairpin-type P-T-t path in which deeply buried supracrustal rocks experience a slow exhumation rate. The dome-and-keel architecture and P-T-t paths produced by the numerical model conform to the structural, metamorphic and geochronological data of the Eastern Block. We propose that the geological complexity of eastern China and temporally coexisting diverse P-T-t paths most likely developed under a mantle plume related crustal-scale sagduction geodynamic regime in Neoarchean. (C) 2022 Elsevier B.V. All rights reserved.
Van Breedam, JonasHuybrechts, PhilippeCrucifix, Michel
10页
查看更多>>摘要：It is generally believed that a large scale Antarctic ice sheet formed at the Eocene-Oligocene transition (34.44-33.65 Ma). However, oxygen isotope excursions during the late Eocene (38-34 Ma) and geomorphic evidence of glacial erosion suggest that there were ephemeral continental scale glaciations before the Oi-1 event. Here, we investigate the Antarctic ice sheet evolution over a multi-million year timescale during the late Eocene up to the early Oligocene with the most recent estimates of carbon dioxide evolution over this time period and different bedrock elevation reconstructions. A novel ice sheet-climate modelling approach is applied where the Antarctic ice sheet model VUB-AISMPALEO is coupled to the emulated climate from HadSM3 using the coupler CLISEMv1.0. Our modelling results show that short-lived continental scale Antarctic glaciation might have occurred during the late Eocene when austral summer insolation reached a minimum in a narrow range of carbon dioxide concentrations. The Antarctic ice sheet first reached the coast in Prydz Bay and later in the Weddell Sea region, supporting the glaciomarine sediments dated prior to the EOT. (C) 2022 The Author(s). Published by Elsevier B.V.
NSTL
Elsevier