110 results found
Chrapkiewicz K, Paulatto M, Heath BA, et al., 2022, Magma Chamber Detected Beneath an Arc Volcano With Full‐Waveform Inversion of Active‐Source Seismic Data, Geochemistry, Geophysics, Geosystems, Vol: 23, ISSN: 1525-2027
Paulatto M, Hooft E, Chrapkiewicz K, et al., 2022, Advances in seismic imaging of magma and crystal mush, Frontiers in Earth Science, ISSN: 2296-6463
Seismic imaging methods have provided detailed three-dimensional constraints on the physical properties of magmatic systems leading to invaluable insight into the storage, differentiation and dynamics of magma. These constraints have been crucial to the development of our modern understanding of magmatic systems. However, there are still outstanding knowledge gaps resulting from the challenges inherent in seismic imaging of volcanoes. These challenges stem from the complex physics of wave propagation across highly heterogeneous low-velocity anomalies associated with magma reservoirs. Ray-based seismic imaging methods such as travel-time and surface-wave tomography lead to under-recovery of such velocity anomalies and to under-estimation of melt fractions. This review aims to help the volcanologist to fully utilize the insights gained from seismic imaging and account for the resolution limits. We summarize the advantages and limitations of the most common imaging methods and propose best practices for their implementation and the quantitative interpretation of low-velocity anomalies. We constructed and analysed a database of 277 seismic imaging studies at 78 arc, hotspot and continental rift volcanoes. Each study is accompanied by information about the seismic source, part of the wavefield used, imaging method, any detected low-velocity zones, and estimated melt fraction. Thirty nine studies attempted to estimate melt fractions at 22 different volcanoes. Only five studies have found evidence of melt storage at melt fractions above the critical porosity that separates crystal mush from mobile magma. The median reported melt fraction is 13% suggesting that magma storage is dominated by low-melt fraction crystal mush. However, due to the limits of seismic resolution, the seismological evidence does not rule out the presence of small (<10 km3) and medium-sized (<100 km3) high-melt fraction magma chambers at many of the studied volcanoes. The combination of multipl
Morgan J, Bralower TJ, Brugger J, et al., 2022, The Chicxulub impact and its environmental consequences, NATURE REVIEWS EARTH & ENVIRONMENT, Vol: 3, Pages: 338-354
Hernández-Terrones L, Martínez L, Szamotulski J, et al., 2022, Study of fluid circulation through the chicxulub crater using Rock-Eval pyrolysis and fluid inclusions, Applied Geochemistry, Vol: 137, Pages: 1-12, ISSN: 0883-2927
The aim of the study is to evaluate fluids circulation through the Chicxulub crater, and to determine the composition of hydrothermal fluids after the impact. Rock-Eval pyrolysis and fluid inclusion micro-thermometry analyses were performed. The technique has been routinely used for about fifteen years and has become a standard tool for hydrocarbon exploration. Rock-Eval pyrolysis reveals the distribution of organic and mineral carbon affected by the impact and later affected by hydrothermal activity. All measured inclusions are primary and were found in basement samples only. Both the fluid inclusions data and Rock-Eval pyrolysis show that composition and temperature of the fluids changed as the fluids migrated though crater rocks. An evolution of temperatures occurs (vertical, horizontal, or both), from the surface and from the center of the crater; this spatial evolution is consistent with model of Abramov and Kring, showing a thermal evolution of temperature with depth in the crater as well as its influence on the hydrothermal system. Post-impact fluid circulation modifies the temperature distribution.
Ross CH, Stockli DF, Rasmussen C, et al., 2022, Evidence of Carboniferous arc magmatism preserved in the Chicxulub impact structure, Geological Society of America Bulletin, Vol: 134, Pages: 241-260, ISSN: 0016-7606
Determining the nature and age of the 200-km-wide Chicxulub impact target rock is an essential step in advancing our understanding of the Maya Block basement. Few age constraints exist for the northern Maya Block crust, specifically the basement underlying the 66 Ma, 200 km-wide Chicxulub impact structure. The International Ocean Discovery Program-International Continental Scientific Drilling Program Expedition 364 core recovered a continuous section of basement rocks from the Chicxulub target rocks, which provides a unique opportunity to illuminate the pre-impact tectonic evolution of a terrane key to the development of the Gulf of Mexico. Sparse published ages for the Maya Block point to Mesoproterozoic, Ediacaran, Ordovician to Devonian crust are consistent with plate reconstruction models. In contrast, granitic basement recovered from the Chicxulub peak ring during Expedition 364 yielded new zircon U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) concordant dates clustering around 334 ± 2.3 Ma. Zircon rare earth element (REE) chemistry is consistent with the granitoids having formed in a continental arc setting. Inherited zircon grains fall into three groups: 400–435 Ma, 500–635 Ma, and 940–1400 Ma, which are consistent with the incorporation of Peri-Gondwanan, Pan-African, and Grenvillian crust, respectively. Carboniferous U-Pb ages, trace element compositions, and inherited zircon grains indicate a pre-collisional continental volcanic arc located along the Maya Block's northern margin before NW Gondwana collided with Laurentia. The existence of a continental arc along NW Gondwana suggests southward-directed subduction of Rheic oceanic crust beneath the Maya Block and is similar to evidence for a continental arc along the northern margin of Gondwana that is documented in the Suwannee terrane, Florida, USA, and Coahuila Block of NE México.
McCall N, Gulick SPS, Hall B, et al., 2021, Orientations of planar cataclasite zones in the Chicxulub peak ring as a ground truth for peak ring formation models, Earth and Planetary Science Letters, Vol: 576, Pages: 1-12, ISSN: 0012-821X
Hypervelocity impact cratering is an important geologic process but the rarity of large terrestrial impact craters on Earth and the limited technical options to study cratering processes in the laboratory hinders our understanding of large-scale impact processes. Drill core recovered from the peak ring of the Chicxulub impact crater during International Ocean Discovery Program (IODP)/International Continental scientific Drilling Program (ICDP) Expedition 364 provides an opportunity to examine target rock deformation and thus, to assess cratering models in this regard. Using oriented computer tomography (CT) scans and line scan images of the core, we present the orientations of mm-to-cm-scale planar cataclasite and ultracataclasite zones in the deformed granitoid target rock of the peak ring. In the upper 470 m of the target rock, the cataclasite zones dip towards the crater center, whereas the dip directions for the ultracataclasite zones are approximately tangential to the peak ring. These two orientations are consistent with deformation expected from hydrocode-modeled principal stress directions for the outward movement of rocks as the transient crater develops, and the inward movement of rocks associated with collapse of the transient crater. Near the base of the core is a 96 m-thick interval of highly-deformed target rock with impact melt rock and rock fragments not observed elsewhere in the core; this interval has previously been interpreted as an imbricate thrust zone within the peak ring. The cataclasite zones below this thrust zone have different orientations than those in the 470 m-thick block above. This observation implies a differential rotation from the overlying block during the final stages of peak-ring formation. Our results support an acoustic fluidization process, wherein blocks that vibrate or slide relative to each other allow the target rock to flow during transient crater collapse, and that the size of coherent rock blocks increases over the co
Davy R, Frahm L, Bell R, et al., 2021, Generating high‐fidelity reflection images directly from full‐waveform inversion: Hikurangi Subduction Zone case study, Geophysical Research Letters, Vol: 48, Pages: 1-10, ISSN: 0094-8276
Full-waveform inversion (FWI) can resolve subsurface physical properties to high resolutions, yet high-performance computing resources have only recently made it practical to invert for high frequencies. A benefit of high-frequency FWI is that recovered velocity models can be differentiated in space to produce high-quality depth images (FWI images) of a comparable resolution to conventional reflection images.Here, we demonstrate the generation of high-fidelity reflection images directly from the FWI process. We applied FWI up to 38 Hz to seismic data across the Hikurangi subduction margin. The resulting velocity models and FWI images reveal a complex faulting system, sediment deformation, and bottom-simulating reflectors within the shallow accretionary prism. Our FWI images agree with conventional reflection images and better resolve horizons around the Pāpaku thrust fault. Thus, FWI imaging has the potential to replace conventional reflection imaging whilst also providing physical property models that assist geological interpretations.
Wittmann A, Cavosie AJ, Timms NE, et al., 2021, Shock impedance amplified impact deformation of zircon in granitic rocks from the Chicxulub impact crater, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 575, ISSN: 0012-821X
Heath BA, Hooft EEE, Toomey DR, et al., 2021, Relationship Between Active Faulting/Fracturing and Magmatism Around Santorini: Seismic Anisotropy From an Active Source Tomography Experiment, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 126, ISSN: 2169-9313
Christeson GL, Morgan J, Gulick SPS, 2021, Mapping the Chicxulub Impact Stratigraphy and Peak Ring Using Drilling and Seismic Data, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 126, ISSN: 2169-9097
Zhao J, Xiao L, Xiao Z, et al., 2021, Shock-deformed zircon from the Chicxulub impact crater and implications for cratering process, Geology, Vol: 49, Pages: 755-760, ISSN: 0091-7613
Large impact structures with peak rings are common landforms across the solar system, and their formation has implications for both the interior structure and thermal evolution of planetary bodies. Numerical modeling and structural studies have been used to simulate and ground truth peak-ring formative mechanisms, but the shock metamorphic record of minerals within these structures remains to be ascertained. We investigated impact-related microstructures and high-pressure phases in zircon from melt-bearing breccias, impact melt rock, and granitoid basement from the Chicxulub peak ring (Yucatán Peninsula, Mexico), sampled by the International Ocean Discovery Program (IODP)/International Continental Drilling Project (IODP-ICDP) Expedition 364 Hole M0077A. Zircon grains exhibit shock features such as reidite, zircon twins, and granular zircon including “former reidite in granular neoblastic” (FRIGN) zircon. These features record an initial high-pressure shock wave (>30 GPa), subsequent relaxation during the passage of the rarefaction wave, and a final heating and annealing stage. Our observed grain-scale deformation history agrees well with the stress fields predicted by the dynamic collapse model, as the central uplift collapsed downward-then-outward to form the peak ring. The occurrence of reidite in a large impact basin on Earth represents the first such discovery, preserved due to its separation from impact melt and rapid cooling by the resurging ocean. The coexistence of reidite and FRIGN zircon within the impact melt–bearing breccias indicates that cooling by seawater was heterogeneous. Our results provide valuable information on when different shock microstructures form and how they are modified according to their position in the impact structure, and this study further improves on the use of shock barometry as a diagnostic tool in understanding the cratering process.
Cockell CS, Schaefer B, Wuchter C, et al., 2021, Shaping of the present-day deep biosphere at chicxulub by the impact catastrophe that ended the cretaceous, Frontiers in Microbiology, Vol: 12, Pages: 1-16, ISSN: 1664-302X
We report on the effect of the end-Cretaceous impact event on the present-day deep microbial biosphere at the impact site. IODP-ICDP Expedition 364 drilled into the peak ring of the Chicxulub crater, México, allowing us to investigate the microbial communities within this structure. Increased cell biomass was found in the impact suevite, which was deposited within the first few hours of the Cenozoic, demonstrating that the impact produced a new lithological horizon that caused a long-term improvement in deep subsurface colonization potential. In the biologically impoverished granitic rocks, we observed increased cell abundances at impact-induced geological interfaces, that can be attributed to the nutritionally diverse substrates and/or elevated fluid flow. 16S rRNA gene amplicon sequencing revealed taxonomically distinct microbial communities in each crater lithology. These observations show that the impact caused geological deformation that continues to shape the deep subsurface biosphere at Chicxulub in the present day.
Boddupalli B, Minshull TA, Morgan J, et al., 2021, Comparison of 2-D and 3-D full waveform inversion imaging using wide-angle seismic data from the Deep Galicia Margin, Geophysical Journal International, Vol: 227, Pages: 228-256, ISSN: 0956-540X
<jats:title>SUMMARY</jats:title> <jats:p>Full waveform inversion (FWI) is a data-fitting technique capable of generating high-resolution velocity models with a resolution down to half the seismic wavelength. FWI is applied typically to densely sampled seismic data. In this study, we applied FWI to 3-D wide-angle seismic data acquired using sparsely spaced ocean bottom seismometers (OBSs) from the Deep Galicia Margin west of Iberia. Our data set samples the S-reflector, a low-angle detachment present in this area. Here we highlight differences between 2-D, 2.5-D and 3-D-FWI performances using a real sparsely spaced data set. We performed 3-D FWI in the time domain and compared the results with 2-D and 2.5-D FWI results from a profile through the 3-D model. When overlaid on multichannel seismic images, the 3-D FWI results constrain better the complex faulting within the pre- and syn-rift sediments and crystalline crust compared to the 2-D result. Furthermore, we estimate variable serpentinization of the upper mantle below the S-reflector along the profile using 3-D FWI, reaching a maximum of 45 per cent. Differences in the data residuals of the 2-D, 2.5-D and 3-D inversions suggest that 2-D inversion can be prone to overfitting when using a sparse data set. To validate our results, we performed tests to recover the anomalies introduced by the inversions in the final models using synthetic data sets. Based on our comparison of the velocity models, we conclude that the use of 3-D data can partially mitigate the problem of receiver sparsity in FWI.</jats:p>
Ormö J, Gulick SPS, Whalen MT, et al., 2021, Assessing event magnitude and target water depth for marine-target impacts: Ocean resurge deposits in the Chicxulub M0077A drill core compared, Earth and Planetary Science Letters, Vol: 564, Pages: 1-14, ISSN: 0012-821X
The rim wall of water formed from even a modestly-sized marine impact may be kilometers in height.Although modeling has shown that this wave swiftly breaks and relatively rapidly loses energy duringoutwards travel from the impact site, the portion of the rim wall that collapses inwards may generatea resurge flow with tremendous transport energy. Here we compare the deposits generated by thisocean resurge inside one of the largest marine-target craters on Earth, the 200-km wide Chicxulubcrater, Yucatán Peninsula, México, with resurge deposits (breccias) in eight drill cores from five othermarine-target craters in Sweden and the United States. Examination of the wide range of cored locationswithin the craters, and target water depths (H) relative to modeled projectile diameters (d) reveal a highcorrelation between location, average clast frequency (N ), and d/H from which any of the four variablescan be obtained. The relationship shown here may provide an important tool for diagnosing marineimpact cratering processes where there is limited understanding of crater size and/or paleobathymetry
Schulte FM, Wittmann A, Jung S, et al., 2021, Ocean resurge-induced impact melt dynamics on the peak-ring of the Chicxulub impact structure, Mexico, International Journal of Earth Sciences, Vol: 110, Pages: 2619-2639, ISSN: 1437-3254
Core from Hole M0077 from IODP/ICDP Expedition 364 provides unprecedented evidence for the physical processes in effect during the interaction of impact melt with rock-debris-laden seawater, following a large meteorite impact into waters of the Yucatán shelf. Evidence for this interaction is based on petrographic, microstructural and chemical examination of the 46.37-m-thick impact melt rock sequence, which overlies shocked granitoid target rock of the peak ring of the Chicxulub impact structure. The melt rock sequence consists of two visually distinct phases, one is black and the other is green in colour. The black phase is aphanitic and trachyandesitic in composition and similar to melt rock from other sites within the impact structure. The green phase consists chiefly of clay minerals and sparitic calcite, which likely formed from a solidified water–rock debris mixture under hydrothermal conditions. We suggest that the layering and internal structure of the melt rock sequence resulted from a single process, i.e., violent contact of initially superheated silicate impact melt with the ocean resurge-induced water–rock mixture overriding the impact melt. Differences in density, temperature, viscosity, and velocity of this mixture and impact melt triggered Kelvin–Helmholtz and Rayleigh–Taylor instabilities at their phase boundary. As a consequence, shearing at the boundary perturbed and, thus, mingled both immiscible phases, and was accompanied by phreatomagmatic processes. These processes led to the brecciation at the top of the impact melt rock sequence. Quenching of this breccia by the seawater prevented reworking of the solidified breccia layers upon subsequent deposition of suevite. Solid-state deformation, notably in the uppermost brecciated impact melt rock layers, attests to long-term gravitational settling of the peak ring.
Goderis S, Sato H, Ferrière L, et al., 2021, Globally distributed iridium layer preserved within the Chicxulub impact structure., Science Advances, Vol: 7, Pages: 1-14, ISSN: 2375-2548
The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.
An expanded sedimentary section provides an opportunity to elucidate conditions in the nascent Chicxulub crater during the hours to millennia after the Cretaceous‐Paleogene (K‐Pg) boundary impact. The sediments were deposited by tsunami followed by seiche waves as energy in the crater declined, culminating in a thin hemipelagic marlstone unit that contains atmospheric fallout. Seiche deposits are predominantly composed of calcite formed by decarbonation of the target limestone during impact followed by carbonation in the water column. Temperatures recorded by clumped isotopes of these carbonates are in excess of 70°C, with heat likely derived from the central impact melt pool. Yet, despite the turbidity and heat, waters within the nascent crater basin soon became a viable habitat for a remarkably diverse cross section of the food chain. The earliest seiche layers deposited with days or weeks of the impact contain earliest Danian nannoplankton and dinocyst survivors. The hemipelagic marlstone representing the subsequent years to a few millennia contains a nearly monogeneric calcareous dinoflagellate resting cyst assemblage suggesting deteriorating environmental conditions, with one interpretation involving low light levels in the impact aftermath. At the same horizon, microbial fossils indicate a thriving bacterial community and unique phosphatic fossils including appendages of pelagic crustaceans, coprolites and bacteria‐tunneled fish bone, suggesting that this rapid recovery of the base of the food chain may have supported the survival of larger, higher trophic‐level organisms. The extraordinarily diverse fossil assemblage indicates that the crater was a unique habitat in the immediate impact aftermath, possibly as a result of heat and nutrients supplied by hydrothermal activity.
Whalen MT, Gulick SPS, Lowery CM, et al., 2020, Winding down the Chicxulub impact: The transition between impact and normal marine sedimentation near ground zero, Marine Geology, Vol: 430, Pages: 1-18, ISSN: 0025-3227
The Chicxulub impact led to the formation of a ~ 200-km wide by ~1-km deep crater on México's Yucatán Peninsula. Over a period of hours after the impact the ocean re-entered and covered the impact basin beneath several hundred meters of water. A suite of impactites were deposited across the crater during crater formation, and by the resurge, tsunami and seiche events that followed. International Ocean Discovery Program/International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub crater, and recovered ~130 m of impact deposits and a 75-cm thick, fine-grained, carbonate-rich “Transitional Unit”, above which normal marine sedimentation resumed. Here, we describe the results of analyses of the uppermost impact breccia (suevite) and the Transitional Unit, which suggests a gradual waning of energy recorded by this local K-Pg boundary sequence.The dominant depositional motif in the upper suevite and the Transitional Unit is of rapid sedimentation characterized by graded bedding, local cross bedding, and evidence of oscillatory currents. The lower Transitional Unit records the change from deposition of dominantly sand-sized to mainly silt to clay sized material with impact debris that decreases in both grain size and abundance upward. The middle part of the Transitional Unit is interrupted by a 20 cm thick soft sediment slump overlain by graded and oscillatory current cross-laminated beds. The uppermost Transitional Unit is also soft sediment deformed, contains trace fossils, and an increasing abundance of planktic foraminifer and calcareous nannoplankton survivors. The Transitional Unit, as with similar deposits in other marine target impact craters, records the final phases of impact-related sedimentation prior to resumption of normal marine conditions. Petrographic and stable isotopic analyses of carbon from organic matter provide insight into post-impact processes. δ13Corg values are bet
Smith V, Warny S, Grice K, et al., 2020, Life and death in the Chicxulub impact crater: a record of the Paleocene–Eocene Thermal Maximum, Climate of the Past, Vol: 16, Pages: 1889-1899, ISSN: 1814-9324
latitudes, with sea surface temperatures at some localities exceeding the 35 ∘C at which marine organisms experience heat stress. Relatively few equivalent terrestrial sections have been identified, and the response of land plants to this extreme heat is still poorly understood. Here, we present a new record of the PETM from the peak ring of the Chicxulub impact crater that has been identified based on nannofossil biostratigraphy, an acme of the dinoflagellate genus Apectodinium, and a negative carbon isotope excursion. Geochemical and microfossil proxies show that the PETM is marked by elevated TEXH86-based sea surface temperatures (SSTs) averaging ∼37.8 ∘C, an increase in terrestrial input and surface productivity, salinity stratification, and bottom water anoxia, with biomarkers for green and purple sulfur bacteria indicative of photic zone euxinia in the early part of the event. Pollen and plants spores in this core provide the first PETM floral assemblage described from Mexico, Central America, and the northern Caribbean. The source area was a diverse coastal shrubby tropical forest with a remarkably high abundance of fungal spores, indicating humid conditions. Thus, while seafloor anoxia devastated the benthic marine biota and dinoflagellate assemblages were heat-stressed, the terrestrial plant ecosystem thrived.
Bralower TJ, Cosmidis J, Heaney PJ, et al., 2020, Origin of a global carbonate layer deposited in the aftermath of the Cretaceous-Paleogene boundary impact, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 548, ISSN: 0012-821X
Lyons SL, Karp AT, Bralower TJ, et al., 2020, Organic matter from the Chicxulub crater exacerbated the K-Pg impact winter., Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 25327-25334, ISSN: 0027-8424
An asteroid impact in the Yucatán Peninsula set off a sequence of events that led to the Cretaceous-Paleogene (K-Pg) mass extinction of 76% species, including the nonavian dinosaurs. The impact hit a carbonate platform and released sulfate aerosols and dust into Earth's upper atmosphere, which cooled and darkened the planet-a scenario known as an impact winter. Organic burn markers are observed in K-Pg boundary records globally, but their source is debated. If some were derived from sedimentary carbon, and not solely wildfires, it implies soot from the target rock also contributed to the impact winter. Characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Chicxulub crater sediments and at two deep ocean sites indicate a fossil carbon source that experienced rapid heating, consistent with organic matter ejected during the formation of the crater. Furthermore, PAH size distributions proximal and distal to the crater indicate the ejected carbon was dispersed globally by atmospheric processes. Molecular and charcoal evidence indicates wildfires were also present but more delayed and protracted and likely played a less acute role in biotic extinctions than previously suggested. Based on stratigraphy near the crater, between 7.5 × 1014 and 2.5 × 1015 g of black carbon was released from the target and ejected into the atmosphere, where it circulated the globe within a few hours. This carbon, together with sulfate aerosols and dust, initiated an impact winter and global darkening that curtailed photosynthesis and is widely considered to have caused the K-Pg mass extinction.
Chiarenza A, Farnsworth A, Mannion PD, et al., 2020, Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction, Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 17084-17093, ISSN: 0027-8424
The Cretaceous/Paleogene mass extinction, 66 Ma, included the demise of non-avian dinosaurs. Intense debate has focused on the relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms for this event. Here, we combine fossil-occurrence data with paleoclimate and habitat suitability models to evaluate dinosaur habitability in the wake of various asteroid impact and Deccan volcanism scenarios. Asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats. Conversely, long-term forcing from Deccan volcanism (carbon dioxide [CO2]-induced warming) leads to increased habitat suitability. Short-term (aerosol cooling) volcanism still allows equatorial habitability. These results support the asteroid impact as the main driver of the non-avian dinosaur extinction. By contrast, induced warming from volcanism mitigated the most extreme effects of asteroid impact, potentially reducing the extinction severity.
Zhao J, Xiao L, Gulick SPS, et al., 2020, Geochemistry, geochronology and petrogenesis of Maya Block granitoids and dykes from the Chicxulub Impact Crater, Gulf of México: Implications for the assembly of Pangea, Gondwana Research, Vol: 82, Pages: 128-150, ISSN: 1342-937X
The Late Paleozoic tectono–magmatic history and basement of the Maya block are poorly understood due to the lack of exposures of coeval magmatic rocks in the region. Recently, IODP–ICDP Expedition 364 recovered drill core samples at borehole M0077A from the peak ring of the Chicxulub impact crater, offshore of the Yucatán peninsula in the Gulf of México, have been studied comprehensively. In the lowermost ~600 m of the drill core, impact–deformed granitoids, and minor felsite and dolerite dykes are intercalated with impact melts and breccias. Zircon U-Pb dating of granitoids yielded ages of around 326 ± 5 Ma, representing the first recovery of Late Paleozoic magmatic rocks from the Maya block, which could be genetically related to the convergence of Laurentia and Gondwana. The granitoids show the features of high K2O/Na2O, LaN/YbN and Sr/Y ratios, but very low Yb and Y contents, indicating an adakitic affinity. They are also characterized by slightly positive ԑNd(326Ma) of 0.17–0.68, intermediate initial 87Sr/86Sr(326Ma) of 0.7036–0.7047 and two–stage Nd model age (TDM2) of 1027–1069 Ma, which may indicate a less evolved crustal source. Thus, the adakitic granitoids were probably generated by partial melting of thickened crust, with source components similar to Neoproterozoic metagabbro in the Carolina block (Pan–African Orogeny materials) along Peri–Gondwana. Felsite dykes are shoshonitic with typical continental arc features that are sourced from a metasomatic mantle wedge by slab–fluids. Dolerite dykes display OIB–type features such as positive Nb and Ta anomalies and low ThNpm/NbNpm. In our interpretation, the Chicxulub adakitic granitoids of this study are formed by crustal anatexis due to asthenospheric upwelling resulting from slab breakoff. Through comparing sources and processes of Late Paleozoic magmatism along the Peri–Gondwanan realm, a tearing slab breakoff mode
Kring DA, Tikoo SM, Schmieder M, et al., 2020, Probing the hydrothermal system of the Chicxulub impact crater, Science Advances, Vol: 6, ISSN: 2375-2548
The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.
Collins G, Patel N, Davison T, et al., 2020, A steeply-inclined trajectory for the Chicxulub impact, Nature Communications, Vol: 11, Pages: 1-10, ISSN: 2041-1723
The environmental severity of large impacts on Earth is influenced by their impact trajectory. Impact direction and angle to the target plane affect the volume and depth of origin of vaporized target, as well as the trajectories of ejected material. The asteroid impact that formed the 66 Ma Chicxulub crater had a profound and catastrophic effect on Earth’s environment,but the impact trajectory is debated. Here we show that impact angle and direction can be diagnosed by asymmetries in the subsurface structure of the Chicxulub crater. Comparison of 3D numerical simulations of Chicxulub-scale impacts with geophysical observations suggests that the Chicxulub crater was formed by a steeply-inclined (45 -60° to horizontal) impact from the northeast; several lines of evidence rule out a low angle (< 30°) impact. Asteeply-inclined impact produces a nearly symmetric distribution of ejected rock and releases more climate-changing gases per impactor mass than either a very shallow or near-vertical impact.
Artemieva N, Morgan J, 2020, Global K‐Pg layer deposited from a dust cloud, Geophysical Research Letters, Vol: 47, Pages: 1-8, ISSN: 0094-8276
Although it is widely agreed that the distal K‐Pg clay layer contains ejecta from the Chicxulub impact site, no current models can explain how these ejecta travel from the impact site around the globe. A widely accepted hypothesis is that impact spherules and shocked minerals in the layer were ejected from an expanding impact plume and traveled to their final destination on a ballistic path. Shocked minerals, however, are ejected at too low a velocity to reach distal sites, and plausible ballistic ejection models cannot explain the observed ejecta distribution. Using a suite of numerical simulations, we find that intense interactions between the ejecta curtain and atmosphere generate a fast‐moving dust cloud traveling at speeds of a few kilometers per second, which carries a substantial fraction of ejecta, including shocked minerals, to distal sites. We conclude that ejecta curtain material must make a major contribution to the formation of the distal K‐Pg layer.
McVey BG, Hooft EEE, Heath BA, et al., 2020, Magma accumulation beneath Santorini volcano, Greece, from P-wave tomography, GEOLOGY, Vol: 48, Pages: 231-235, ISSN: 0091-7613
The Chicxulub crater was formed by an asteroid impact at ca. 66 Ma. The impact is considered to have contributed to the end-Cretaceous mass extinction and reduced productivity in the world’s oceans due to a transient cessation of photosynthesis. Here, biomarker profiles extracted from crater core material reveal exceptional insights into the post-impact upheaval and rapid recovery of microbial life. In the immediate hours to days after the impact, ocean resurge flooded the crater and a subsequent tsunami delivered debris from the surrounding carbonate ramp. Deposited material, including biomarkers diagnostic for land plants, cyanobacteria, and photosynthetic sulfur bacteria, appears to have been mobilized by wave energy from coastal microbial mats. As that energy subsided, days to months later, blooms of unicellular cyanobacteria were fueled by terrigenous nutrients. Approximately 200 k.y. later, the nutrient supply waned and the basin returned to oligotrophic conditions, as evident from N2-fixing cyanobacteria biomarkers. At 1 m.y. after impact, the abundance of photosynthetic sulfur bacteria supported the development of water-column photic zone euxinia within the crater.
Bell R, Gray M, Morgan J, et al., 2019, New Zealand 3D full waveform inversion (NZ3D-FWI) 2017-2018 field acquisition report
Paulatto M, Moorkamp M, Hautmann S, et al., 2019, Vertically extensive magma reservoir revealed from joint inversion and quantitative interpretation of seismic and gravity data, Journal of Geophysical Research. Solid Earth, Vol: 124, Pages: 11170-11191, ISSN: 2169-9356
Recent advances in our understanding of arc magmatic systems indicate that melt is stored for long periods in low‐melt fraction crystal mushes and that eruptible magma reservoirs are short‐lived and are assembled rapidly by buoyancy‐induced instabilities and draining of the crystal mush. Many aspects of their architecture remain unclear, particularly in relation to their geometry and shallow melt distribution. We investigate the storage of melt below the active Soufrière Hills Volcano (SHV), Montserrat, using joint geophysical inversion combined with a quantitative interpretation approach based on rock physics. We jointly inverted active‐source P‐wave traveltimes and gravity anomalies to derive coincident 3‐D models of P‐wave velocity and density to a depth of 8 km. Comparative analysis of the active SHV and extinct Centre Hills volcano and effective elastic medium computations allow us to constrain temperature, melt fraction, and melt geometry. A continuous column of partial melt is inferred beneath SHV, at 4–8 km depth. Melt fraction is ~6% (ranging from 3 to 13% depending on melt geometry) and is maximum at 5–6 km depth. When under‐recovery of the low‐vP volume is taken into account, the melt fraction is revised to ~17% (ranging from 11 to 28%). Analysis of vP/density cross plots indicates that the melt distribution is best represented by low‐aspect ratio geometries. These likely span a multiscale spectrum ranging from grain‐scale inclusions and fractures to 100‐m‐scale dykes and sills. Our results confirm the concept of vertically extensive crystal mush including one or multiple more melt‐rich layers.
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