Mittal, TusharJordan, Jacob S.Retailleau, LiseBeauducel, Francois...
13页
查看更多>>摘要：Despite significant advancements in understanding crustal melt transport, determining the shallow magmatic architecture at any given volcanic system remains a significant challenge with geophysical methods alone. In this study, we present a new conceptual model combining previously studied models for geomechanical magma reservoirs and dyke-shaped conduits. Supplementary to previous work, we include a model for porous mush adjacent to a visco-elastic magma reservoir during the eruption. This addition enables physically consistent magma recharge into the elastic magma reservoir by porous flow instead of employing an arbitrary mantle magma recharge parameterization. We compare our conceptual model with an illustrative test case -the submarine 2018 Mayotte eruption in the Comoros Islands (-6.55 km(3) Bulk Rock Volume, -3.5 km water depth, -35 km estimated deep magma reservoir). We estimate a magma effusion rate history using a new continuous-time inversion of surface deformation data. A single magma reservoir cannot match the observed eruptive history for any reservoir geometry or crustal and magmatic material properties. However, the presence of a porous mush adjacent to the magma reservoir helps to reconcile the model with the observations. The additional magma flux from the mush region sustains the long eruption at a low effusion rate, as is observed off Mayotte, with a decreasing effusion rate after few months of eruptions and a low persistent effusion rate since then. The mush flow dynamics are a direct consequence of reduced pressure in the magma reservoir during the eruption. Thus, our model provides a parsimonious and physically motivated explanation of the Mayotte eruptive history. Since many historical basaltic eruptions worldwide, such as sometime observed at Piton de la Fournaise, Volcan Arenal, and Laki, have a similar effusion rate history shape as Mayotte, magmatic mushes may be a key component for explaining long-lived basaltic eruptions.(C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Impact events on planetary surfaces can leave significant volumes of melt, archived in planetary regoliths, which provide important information regarding the timing and nature of these events. For example, an observed ca. 3.9-4.1 Ga age cluster within lunar samples has been interpreted as indicative of a significant Solar System-wide event: the so-called "Late Heavy Bombardment". Here, we report data from a laser ablation microprobe 40Ar/39Ar study of clasts within two unpaired howardite meteorites (NWA 1929 and Dho 485) to explore the impact history of their asteroid parent body - (4)Vesta. Laser microprobe dates for the howardites varied broadly between 3.5 to 4.5 Ga (NWA 1929) and 2.5 to 4.5 Ga (Dho 485), but show no clear cluster in ages at ca. 3.9-4.1 Ga. Consistent with previously reported U-Pb dates for HED meteorites, our data suggest an extended impact bombardment period on (4)Vesta as compared to the distribution of 40Ar/39Ar impactite dates for available samples from the Apollo and Luna sample archives. The impact history of Vesta revealed here highlights that current models of the impact flux in the inner Solar System based on the Late Heavy Bombardment hypothesis require refinement. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
McCarthy, A.Falloon, T. J.Danyushevsky, L. V.Sauermilch, I....
14页
查看更多>>摘要：The mostly submarine Hunter Ridge, located in the SW Pacific records a ~12 Myr to present history of magmatism related to the opening of the North Fiji Basin and subduction of oceanic lithosphere of the South Fiji Basin. Although the Hunter Ridge is probably composed primarily of an older Vitiazrelated basement, young volcanic features are present from Matthew Island to Kadavu Island. Some dredged volcanic rocks from these features have low-FeO and high-Mg# affinities, ranging from picrites to high-Mg# andesites and dacites. Elevated Sr (500 - 3400 ppm) and Sr/Y (50 - 240) coupled to fractionated (adakitic) rare-earth element patterns (La/Yb = 5 - 40, Gd/Yb = 1.5 - 5.7) indicate a garnet signature derived from the melting of eclogite-facies basalt. Pacific-type MORB Nd-Hf-Pb isotopic ratios of these rocks contrast with the Indian-type MORB nature of the underlying North Fiji mantle but match closely the subducted South Fiji ocean crust. Low values of Th/La (< 0.15), Ba/La (< 22), unradiogenic Sr-87/Sr-86 (0.7026 - 0.7032) and Pacific-MORB Nd-Hf-Pb isotopic ratios indicate that sediment is a minor contributor to the source. The isotopic data clearly connect Hunter Ridge arc rocks of all compositions (picrites, low-to medium K2O arc lavas, basalts, high-Mg# andesites and dacites) to source components predominantly within the subducting plate. Unradiogenic Sr-87/Sr-86 (0.7026 - 0.7029) at high Sr abundances (700 - 1400 ppm) are common in hot-slab localities and are interpreted to reflect flux melting of MORB under eclogite-facies conditions driven by dehydration in the underlying mantle of the subducting plate. Such an adakitic slab-melt component can be detected in more common (nonadakitic) arc rocks along the Hunter Ridge and Vanuatu arc as well. Evidence of slab melting along the western Pacific indicates that melting of subducting oceanic lithosphere is likely a common occurrence at convergent margins. (C) 2022 The Author(s). Published by Elsevier B.V.
查看更多>>摘要：Oxygenation of the oceans and atmosphere has been invoked to be the prerequisite for the early Cambrian radiation of animals. However, the temporal and causal relationships between oxygenation and metazoan proliferation have not been fully explored. Here we report sulfur and oxygen isotope compositions (delta 34Sanhy and delta 18Oanhy) of marine anhydrite deposited around 516 to 506 million years ago (Ma) from the Tarim Basin, NW China. Using a biogeochemical model, we propose that a paired negative delta 18Oanhy (-4.5%0) and delta 34Sanhy (-8700) excursion between 515 and 510 Ma can best be explained by decreased isotope fractionation factors during sulfate reduction related to a 45% to 100% increase in atmospheric oxygen level (pO2). Significantly, evidence from this interval infers an oxygenation event in the backdrop of the most rapid radiation stage (ca. 520 to 510 Ma) during the Cambrian explosion, confirming that oxygen availability was a crucial factor in accelerating the radiation of marine animals.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Magma buoyancy is a mechanism usually neglected with respect to magma overpressure in eruption models constrained with geophysical data. In this study we provide evidence for a buoyancy-driven mechanism of magma ascent during the effusive phase of the 2008-2009 Chaiten rhyolitic eruption. We also constrain the volcano plumbing system with source models from InSAR and teleseismic data. InSAR data did not detect unambiguous evidence of pre-eruptive ground deformation up to 1 year before the eruption. Teleseismic data indicate that a dike opened twice during the first two days of the eruption, while InSAR data show that three sources deflated during the eruption. These include one dike and a sill during the onset of the eruption, and a spherical source halfway through it, all located at depths between 3 and 12 km. 75% of the total ground deformation of -0.5 m occurred during the first three weeks of the eruption. A Pleiades DEM show that the dome has a bulk volume of 1 km3, and was extruded with an exponential trend, but the lack of deformation during most of the effusive phase of the eruption implies that the dome extrusion did not result in depressurization of a magma reservoir. Instead, we show that the time series of extruded volume can be explained by magma ascending due its buoyancy instead of its overpressure. Further, the end of the first pulse of dome effusion in September 2008 can be explained by an increase in the dome surface load that equals the effect of the magma buoyancy. These results imply that in some cases ground deformation data alone cannot be used to forecast the temporal evolution of an eruption. They also call for the acquisition of denser time series of extruded volume, as a way to better constrain their evolution through time.
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Elsevier