Frank, Tracy D.Xu, YilunFielding, Christopher R.Gong, Yizhe...
8页
查看更多>>摘要：Throughout Earth history, large volcanic eruptions that inject sulfur-bearing gases are believed to have imparted strong forcings on global climates and ecosystems. Sulfur outgassing by the Siberian Traps Large Igneous Province (STLIP) is hypothesized to have catalyzed environmental catastrophe associated with the end-Permian extinction (EPE). However, there is as yet only sparse evidence for dispersal of atmospheric sulfate aerosols that precisely coincided with the EPE on land. Here we report S-isotopic compositions of pyrite (delta S-34) from the Sydney Basin in SE Australia, where we find a sharp delta S-34 decrease from 0.04 parts per thousand to -21.52 parts per thousand coinciding with the stratigraphic level of the terrestrial extinction. The negative delta S-34 values in the extinction interval provide new evidence for a significant increase in atmospheric sulfate concentrations linked to fallout of sulfate aerosols originating from the Siberian Traps eruptions. We suggest that climatic perturbations of short-term cooling caused by the sulfate aerosols, along with longer-term global warming, and their interactions, may have contributed to the EPE on land. Our data suggest that sulfuric acid rain and ozone depletion may have greatly deteriorated global environments, leading to the terrestrial EPE. (C) 2022 Elsevier B.V. All rights reserved.
Liou, PengWang, ZaicongMitchell, Ross N.Doucet, Luc S....
11页
查看更多>>摘要：Tonalite-trondhjemite-granodiorite (TTG) rocks consitute the dominant felsic lithology of the Archean crust in most cratons, but their petrogenesis and geodynamic setting are still matters of great debate. Here, we report new Fe isotopic analyses for ca. 2.5 Ga diorites and TTGs with compositions typically interpreted to reflect a high-pressure affinity in eastern Hebei Province of the North China craton. Whole-rock Fe3+/ sigma Fe and delta Fe-56 of the trondhjemites show strong correlations with MgO and Fe2O3T, both indices of igneous differentiation, supporting the radical reinterpretation that the apparent "high pressure " signatures in the trondhjemites instead formed by amphibole-dominated fractionation at low pressure. Likewise, for the tonalites, their light Fe isotopes make them unlikely to be the melting products of enriched mafic rocks at high pressure within the garnet stability range. Thus, Fe isotopes support that "high pressure " TTGs in verity formed at lower pressure with little involvement of residual garnets. Our results thus challenge the evidence once purported to infer Archean subduction. (C) 2022 Elsevier B.V. All rights reserved.
Jackson, VPearson, D. G.Timmerman, S.Reimink, J. R....
11页
查看更多>>摘要：When and how Earth's ancient crust - the cratons - became underpinned by cool, thick lithospheric mantle roots capable of hosting diamonds are among the most controversial aspects of Archean geology. Alluvial diamonds in cratonic sedimentary cover rocks, whose minimum age is determined by detrital-zircon geochronology, provide a unique perspective on this topic. A new discovery of a diamond-bearing quartz-pebble conglomerate from the northern Slave craton, Canada contains detrital zircon with a restricted U-Pb age distribution that has a dominant peak at -2.94 Ga and depositional age of -2.83 Ga. Pressure-temperature constraints derived from an olivine-diamond host pair lie on a conductive Mesoarchean geotherm of -36-38 mW/m(2), comparable to the coolest modern lithospheric geotherms. This result is at odds with a hotter geothermal gradient related to nearby Mesoarchean komatiites. We propose a model whereby early building blocks for cratons were small but with deep cool roots that formed by slab-stacking, and were subsequently juxtaposed with regions of thinner, hotter lithosphere. This heterogeneous initial architecture later amalgamated and thickened through lateral accretion forming the more uniformly thick cratonic lithosphere observed today. Thermal modelling indicates that stacking/thickening of cool initial lithosphere into a lithospheric keel thick enough to stabilise diamonds is the most likely way of generating the observed geotherm by Mesoarchean times. (C) 2022 Elsevier B.V. All rights reserved.
Bouvier, Anne-SophieRose-Koga, Estelle F.Nichols, Alexander R. L.Le Lay, Clemence...
12页
查看更多>>摘要：Melt inclusions are often used to infer melting processes or to determine source magmas that are usually overprinted in bulk rocks due to late stage mixing or near surface contamination. Here we present the first investigation of oxygen (O) isotope equilibrium between melt inclusions and their host olivines from arc samples. Olivines in all but one sample record either magma mixing or fractional crystallization. All six melt inclusions from Vulcano, 83% of seven from Sukumoyama, 44% of 21 from St Vincent, 37% of four from Iwate, and 21% of 13 from Aoba are not in isotopic equilibrium with their olivine host, despite the other major elements being in apparent equilibrium. A detailed study of some of the olivines shows that only a small volume around the melt inclusions is in equilibrium with its host. This strongly suggests that in these olivines melt inclusions are trapped in partly recrystallized olivines, highlighting the importance of magma mixing and crystal recycling in the magmatic plumbing system of these volcanoes. Oxygen isotope fractionation between melt inclusions and their host olivines, as well as phosphorus -delta O-18 systematics, could be used to better understand the formation of melt inclusions and crystal history. It could also provide valuable information to help characterize the magmatic plumbing system that the inclusions and their olivine hosts formed in (e.g., crystal rich-mush versus crystal poor melt lenses). (C) 2022 The Author(s). Published by Elsevier B.V.
查看更多>>摘要：Astronomical solutions provide insight into the Solar System's dynamical evolution and are indispensable tools in cyclostratigraphy and astrochronology. Constructing an absolute, fully calibrated astronomical time scale (ATS) has hitherto been hindered beyond -50 Ma because orbital calculations disagree before that age due to solar system chaos. We have recently developed a new approach that allows extending the fully calibrated astronomical time scale to -58 Ma. Here, we present geologic data and new astronomical solutions, extending our approach across the Paleocene epoch (-66 to -56 Ma). New astronomical solutions were generated using numerical solar system integrations following our earlier work, which now provides geologically constrained astronomical solutions for the Cenozoic era (66-0 Ma). The orbital solutions are available to 300 Ma - we caution, however, that the time interval 30066 Ma is unconstrained due to dynamical chaos in the solar system. We have tested the sensitivity of our new solutions to various parameters, including numerical stepsize, solar quadrupole moment, number of asteroids included, initial positions, and tidal dissipation. We demonstrate that our new solutions yield improved agreement with the geologic record across the Paleocene epoch, compared to previously available astronomical solutions for that period. Furthermore, we discuss implications of our results for solar system chaos and resonance transitions. We have also obtained K/T boundary (KTB) ages based on our new solutions, which suggest slightly younger KTB ages than those inferred from most recent 40Ar/39Ar radiometric dating.
Li, ZhenyuDing, Linvan Hinsbergen, Douwe J. J.C.Lippert, Peter...
13页
查看更多>>摘要：Paleomagnetic data constrain paleogeographic motion of rocks relative to the Earth's spin axis, which is a sum of plate motion relative to the mantle and true polar wander. Discerning between these effects is challenging for studies aiming to reconstruct paleo-plate motions from deformed orogenic terranes. Here, we study the paleolatitudinal drift history of the Lhasa terrane of southern Tibet that migrated from the northern Gondwana to the southern Eurasian margin between late Triassic and early Cretaceous time. Previous work identified a 180 Ma near-equatorial Lhasa latitude and assumed near-constant paleolatitudinal drift. Large-scale true polar wander at this time, however, which has been argued for in previous work, requires highly variable Lhasa plate motion rates relative to Gondwana. Here, we test whether the alternative interpretation of constant plate motion rates provides a better prediction of paleomagnetic data. To this end, we present a new paleomagnetic pole from similar to 155 Ma volcanics (here dated by U/Pb zircon) of the Lhasa terrane. Our pole comprises site mean directions from 46 lavas, passes a fold test, and is supported by an extensive rock magnetic and microscopic analysis that reveals no evidence of remagnetization. Our results give an average direction of D +/- ADx = 337.1 degrees +/- 2.6 degrees, I +/- AIx = -13.8 degrees +/- 4.9 degrees, and a corresponding paleopole position at lambda p = 45.3 degrees N, phi p = 295.3 degrees E with K=69.8 and A95 = 2.5 degrees, predicting a similar near-equatorial, paleolatitude as at 180 Ma. This paleolatitudinal standstill is consistent with predicted paleolatitudes from global APWPs that account for Jurassic TPW and assume a constant Lhasa-Gondwana (India) oceanic spreading rate of similar to 8 cm/a during the 215-130 Ma opening of the Neotethys and closure of the Mesotethys oceans. Contemporaneous arc magmatism on the Lhasa terrane was previously interpreted to indicate that the Lhasa terrane was located above a subduction zone during its northward journey to Tibet: our results show that if our reconstruction is accurate, then trench migration rates also must have been similar to 8 cm/a. Our results are consistent with the range of rates of global long-lived trench migration that have been reconstructed in other studies, but they are much higher than measured in most modern systems. Our results more completely document the Lhasa terrane's separation from Gondwana and provide a straightforward methodology of using paleomagnetic data to test plate kinematic scenarios, overcoming the problem of the unknown effect of true polar wander on paleomagnetic data from deformed terranes.
Thompson, James O.Contreras-Arratia, RodrigoBefus, Kenneth S.Ramsey, Michael S....
10页
查看更多>>摘要：High temporal resolution, geostationary, thermal infrared data from the Advanced Baseline Imager combined with seismic data of La Soufriere Volcano, St. Vincent provide empirical insights into the volcanic processes and mechanisms that occurred from November 2020 until the explosive phase in April 2021. An overall increase in intensity of thermal output and seismicity are observed during the effusive phase; however, the intensity of the thermal data increased -20 days earlier than the seismicity. During the effusive phase, the daily radiant heat flux increased from 0.01 to > 100 MW and the seismicity increased from 1 to 647 events. The climax of both records occurred during the explosive eruptions on April 9-14, 2021. Strong correlations are observed between these datasets in the weeks leading to the explosive eruptions. A significant (-5 day) decrease in thermal and seismic activity is observed -12 days prior to the explosive phase, which could reveal a hiatus in magma migration prior to the eruption. Periods of decoupling between these datasets are also observed and are attributed to different mechanisms during the volcanic unrest. Occurrences with high seismicity and low heat flux may indicate deeper magmatic migration where no significant surface thermal response could be detected, for example. Recognizing correlations, or lack thereof, between high-temporal resolution thermal infrared and seismic data expands potential insights to subsurface volcanic processes by providing a second, complementary vantage. Such seismic-thermal analysis can improve our community's capability to monitor and evaluate new volcanic eruptions. Indeed, extensive seismic networks (local and regional) and multiple geostationary weather satellites now provide near global coverage. A similar analysis to our work at La Soufriere Volcano, St. Vincent is feasible, and should become routine, at other volcanoes worldwide using combined high-temporal, ground and orbital data where available. The 2022 eruption at Hunga-Tonga-Hunga-Ha'apai volcano, Tonga, illustrates the important potential for these high cadence data and subsequent analysis even at extremely remote volcanoes.(C) 2022 The Author(s). Published by Elsevier B.V.
Johnson, Sarah E.Swallom, Meredith L.Thigpen, RyanMcGlue, Michael...
13页
查看更多>>摘要：This study examines the role of topography as a dynamic boundary condition that limits the efficiency of fluvial erosion in the post-glacial Teton Range landscape. The volume of sediment currently stored in two major catchments was estimated using high-resolution LiDAR and geometric reconstructions of depth to bedrock. Seismic reflection data in Moran Bay reveals post-glacial sediment preserved behind a submerged moraine, which isolates the bay from the larger Jackson Lake depocenter. The volume of post-glacial sediment stored in the canyons and bay totals 173.82 +/- 19.5336.0 (x10-3 km3), which translates to a catchment-wide sediment production rate of 0.17 +/- 0.02 mm/yr. The rock-equivalent sediment volume in Moran Bay is 4.4 +/- 0.9 (x10-3 km3), only similar to 2.6% of the total post-glacial volume. While the estimated sediment production rate in the canyons is similar to the uplift rate, the denudation rate derived from Moran Bay sediment is 0.004 +/- 0.001 mm/yr, implying highly inefficient post-glacial sediment transport. The fluvial system has been disequilibrated by glacial erosion such that interglacial valley profiles lack the steepness needed to transport sediment, delaying sediment evacuation until the next glacial advance, or until uplift sufficiently steepens the fluvial system so that it regains efficiency. Furthermore, colluvial production rates in the deglaciated valleys are close to long-term denudation and uplift rates, suggesting that once topography has been equilibrated to glacial erosion processes, subsequent glaciers do not need to produce much bedrock erosion, but mainly sweep out accumulated sediment to maintain equilibrium.
Clendenen, Ashley R.Aleksandrov, AleksandrJones, Brant M.Loutzenhiser, Peter G....
8页
查看更多>>摘要：Water and molecular hydrogen evolution from Apollo sample 14163 and lunar regolith simulants LMS-1 and LHS-1 were examined using Temperature Programmed Desorption (TPD) in ultra-high vacuum. LMS-1, LHS-1, and Apollo 14163 released water upon heating, whereas only the Apollo sample directly released measurable quantities of molecular hydrogen. The resulting H2O and H-2 TPD curves were fit using a model which considers desorption at the vacuum grain interface, transport in the void space between grain-grain boundaries, molecule formation via recombination reactions and sub-surface diffusion. The model yielded a most probable H2O formation and desorption effective activation energy of ~150 kJ mol(-1) for all samples. The probability distribution widths were ~100 - 400, ~100 - 350, and ~100 - 300 kJ mol(-1) for LMS-1, LHS-1, and Apollo 14163, respectively. In addition to having the narrowest energy distribution width, the Apollo sample released the least amount to water (103 ppm) relative to LMS-1 (176 ppm) and LHS-1 (195 ppm). Since essentially no molecular hydrogen was observed from the simulants, the results indicate that LMS-1 and LHS-1 display water surface binding and transport interactions similar to actual regolith but not the desorption chemistry associated with the implanted hydrogen from the solar wind. Overall, these terrestrial surrogates are useful for understanding the surface and interface interactions of lunar regolith grains, which are largely dominated by the terminal hydroxyl sites under both solar wind bombardment and terrestrial preparation conditions. (C) 2022 Elsevier B.V. All rights reserved.
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