Emplacement of unusual rhyolitic to basaltic ignimbrites during collapse of a basalt-dominated caldera: The Halarauður eruption, Krafla (Iceland)

Abstract Deposits of the ca. 110 ka Halarauður eruption of Krafla caldera (reconstructed volume = 7 ± 6 km3 dense rock equivalent) include the only spatter-rich ignimbrite known in Iceland, and an exceptionally rare lava-like basaltic ignimbrite. We present a revised stratigraphy and new whole-rock major-element data set for products of this unusual event, one of only three Quaternary ignimbrite eruptions identified in Iceland. Compositions of Halarauður products span a broad range (50.0–74.6 wt% SiO2), reflecting mixing of rhyolite with underplating basalt. Small-volume, valley-ponded, basal pumice- and spatter-bearing lithic breccias and ignimbrite (rhyolite to andesite) reflect rapid column collapse during early opening of ring-fault vents. A transition to voluminous, regionally dispersed spatter agglomerates (dacite to basaltic andesite) marks an abrupt eruptive intensification, as gas-poor magma was squeezed into a developing ring-fault system by the subsiding chamber roof. Spatial heterogeneities in ascent rates and outgassing through this variably dilated fault system caused coeval formation of collapsing plumes and spatter fountains at separate vents. Spatter was entrained into flows from the more explosive vents, which deposited proximal spatter agglomerates and more distal spatter-bearing ignimbrite. Overlying lava-like ignimbrite deposits (basaltic andesite to basalt) reflect a final opening of vents, as mafic magma from deep levels of the chamber was squeezed through a dilated ring-fault system by the subsiding roof block and erupted at uncharacteristically high mass flux. Development of a mature ring-fault conduit system during early tapping of silicic magma appears to be a prerequisite for the emplacement of welded basaltic ignimbrites, and it should be considered as a possible eruption scenario in basalt-dominated systems where silicic magma has been known to also accumulate. Poor preservation of the Halarauður deposits exemplifies the challenges of studying ignimbrite eruptions in frequently glaciated regions like Iceland, where they may be more common than the geological record suggests.

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Insights into productivity drivers for the Niobrara-equivalent horizontal play in the Piceance Basin, Colorado

The Mountain Geologist ◽

10.31582/rmag.mg.57.4.309 ◽

2020 ◽

Vol 57 (4) ◽

pp. 309-354

Author(s):

Jason Eleson ◽

Chip Oakes ◽

Graham McClave

Keyword(s):

Powder River Basin ◽

Fault System ◽

Piceance Basin ◽

Thermal Maturity ◽

Data Set ◽

Horizontal Drilling ◽

Child Effects ◽

Mancos Shale ◽

Low Degree ◽

Future Potential

Limited horizontal drilling has occurred within the Niobrara-equivalent section of the Mancos Shale in the Piceance Basin, and the results from individual wells are highly variable. Prior studies have suggested that thermal maturity and completion techniques were the primary drivers for the observed production trends, but further analysis of well results indicates there are more variables at play. This study leveraged a comprehensive data set from the Piceance Basin, including core analyses, pressure data, and drilling and completion methods to provide additional context for the production results. From this analysis, several key trends were identified. North/south variations in thermal maturity were confirmed, as well as additional trends were identified revealing later exhumation south of the Rangely fault system resulted in significant depressurization, particularly in the western Piceance Basin. The semi-regional depressurization was the result of decrease in overburden pressures that allowed vertical migration of hydrocarbons out of the Mancos Shale. In addition to the semi-regional depressurization, there were more local depressurization events that resulted from faulting in areas such as the Orchard Unit in the southern Piceance Basin where thrust faults allowed hydrocarbons to migrate vertically into overlying formations. Northwest to southeast production trends are present in the southern Piceance Basin and are interpreted to reflect structurally undeformed areas based on high formation pressures and better producing horizontal wells. Parent-child effects have been observed locally and are linked to lower initial production rates and faster decline rates. The northern Piceance Basin exhibits higher reservoir pressure in the liquids window than was observed to the south due to the relatively low degree of exhumation and/or faulting in areas where horizontal Niobrara wells were drilled. Horizontal well results in the northern Piceance Basin have been mixed, largely due to inefficient completion strategies. By comparing the northern Piceance Basin wells with similar horizontal Niobrara wells in the Powder River Basin of northeastern Wyoming, it is concluded that drilling into the over-pressured liquids rim and utilizing slickwater frac fluid with friction reducer and 100 mesh sand will yield improved economic results over those obtained so far in the Piceance Basin. Though relatively few laterals have been drilled in the Piceance Basin Niobrara play, the basin has great future potential.

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Empirical Relationship for Assessing the Near-Field Horizontal Coseismic Displacement Using GPS Seismology Data

Geofísica Internacional ◽

10.22201/igeof.00167169p.2021.60.1.2025 ◽

2021 ◽

Vol 60 (1) ◽

pp. 31-50

Author(s):

Ryad Darawcheh ◽

Riad Al Ghazzi ◽

Mohamad Khir Abdul-wahed

Keyword(s):

Near Field ◽

Empirical Relationship ◽

Active Faults ◽

Historical Earthquakes ◽

Dead Sea ◽

Fault System ◽

Coseismic Displacement ◽

Data Set ◽

Earthquake Parameters ◽

Gps Station

In this research, a data set of horizontal GPS coseismic displacement in the near-field has been assembled around the world in order to investigate a potential relationship between the displacement and the earthquake parameters. Regression analyses have been applied to the data of 120 interplate earthquakes having the magnitude (Mw 4.8-9.2). An empirical relationship for prediction near-field horizontal GPS coseismic displacement as a function of moment magnitude and the distance between hypocenter and near field GPS station has been established using the multi regression analysis. The obtained relationship allows assessing the coseismic displacements associated with some large historical earthquakes occurred along the Dead Sea fault system. Such a fair relationship could be useful for assessing the coseismic displacement at any point around the active faults.

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Use of Enterobacteriaceae Analysis Results for Predicting Absence of Salmonella Serovars on Beef Carcasses

Journal of Food Protection ◽

10.4315/0362-028x-72.2.260 ◽

2009 ◽

Vol 72 (2) ◽

pp. 260-266 ◽

Cited By ~ 6

Author(s):

JOHN R. RUBY ◽

STEVEN C. INGHAM

Keyword(s):

Small Volume ◽

Large Data ◽

Data Sets ◽

Data Set ◽

A Value ◽

Large Data Set ◽

Intervention Treatment ◽

Beef Carcasses ◽

Predictive Approach ◽

Potential Use

Previous work using a large data set (no. 1, n = 5,355) of carcass sponge samples from three large-volume beef abattoirs highlighted the potential use of binary (present or absent) Enterobacteriaceae results for predicting the absence of Salmonella on carcasses. Specifically, the absence of Enterobacteriaceae was associated with the absence of Salmonella. We tested the accuracy of this predictive approach by using another large data set (no. 2, n = 2,163 carcasses sampled before or after interventions) from the same three data set no. 1 abattoirs over a later 7-month period. Similarly, the predictive approach was tested on smaller subsets from data set no. 2 (n = 1,087, and n = 405) and on a much smaller data set (no. 3, n = 100 postintervention carcasses) collected at a small-volume abattoir over 4 months. Of Enterobacteriaceae-negative data set no. 2 carcasses, >98% were Salmonella negative. Similarly accurate predictions were obtained in the two data subsets obtained from data set no. 2 and in data set no. 3. Of final postintervention carcass samples in data set nos. 2 and 3, 9 and 70%, respectively, were Enterobacteriaceae positive; mean Enterobacteriaceae values for the two data sets were −0.375, and 0.169 log CFU/100 cm2 (detection limit = −0.204, and Enterobacteriaceae negative assigned a value of −0.505 log CFU/100 cm2). Salmonella contamination rates for final postintervention beef carcasses in data set nos. 2 and 3 were 1.1 and 7.0%, respectively. Binary Enterobacteriaceae results may be useful in evaluating beef abattoir hygiene and intervention treatment efficacy.

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A deep view into the nucleus of the Sagittarius dwarf spheroidal galaxy: M54

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007907 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 47-50

Author(s):

M. Alfaro-Cuello ◽

N. Kacharov ◽

N. Neumayer ◽

A. Mastrobuono-Battisti ◽

N. Lützgendorf ◽

...

Keyword(s):

Metal Complex ◽

Detailed Analysis ◽

Globular Clusters ◽

Milky Way ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Star Clusters ◽

High Mass ◽

Data Set

AbstractNuclear star clusters hosted by dwarf galaxies exhibit similar characteristics to high-mass, metal complex globular clusters. This type of globular clusters could, therefore, be former nuclei from accreted galaxies. M54 resides in the photometric center of the Sagittarius dwarf galaxy, at a distance where resolving stars is possible. M54 offers the opportunity to study a nucleus before the stripping of their host by the tidal field effects of the Milky Way. We use a MUSE data set to perform a detailed analysis of over 6600 stars. We characterize the stars by metallicity, age, and kinematics, identifying the presence of three stellar populations: a young metal-rich (YMR), an intermediate-age metal-rich (IMR), and an old metal-poor (OMP). The evidence suggests that the OMP population is the result of accretion of globular clusters in the center of the host, while the YMR population was born in-situ in the center of the OMP population.

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Detection of sharp lateral discontinuities through the analysis of surface-wave propagation

Geophysics ◽

10.1190/geo2013-0314.1 ◽

2014 ◽

Vol 79 (4) ◽

pp. EN77-EN90 ◽

Cited By ~ 19

Author(s):

Paolo Bergamo ◽

Laura Valentina Socco

Keyword(s):

Surface Wave ◽

Fault Location ◽

Synthetic Data ◽

Finite Element Method Simulation ◽

Fault System ◽

Energy Concentration ◽

Data Sets ◽

Data Set ◽

Shallow Subsurface ◽

Velocity Models

Surface-wave (SW) techniques are mainly used to retrieve 1D velocity models and are therefore characterized by a 1D approach, which might prove unsatisfactory when relevant 2D effects are present in the investigated subsurface. In the case of sharp and sudden lateral heterogeneities in the subsurface, a strategy to tackle this limitation is to estimate the location of the discontinuities and to separately process seismic traces belonging to quasi-1D subsurface portions. We have addressed our attention to methods aimed at locating discontinuities by identifying anomalies in SW propagation and attenuation. The considered methods are the autospectrum computation and the attenuation analysis of Rayleigh waves (AARW). These methods were developed for purposes and/or scales of analysis that are different from those of this work, which aims at detecting and characterizing sharp subvertical discontinuities in the shallow subsurface. We applied both methods to two data sets, synthetic data from a finite-element method simulation and a field data set acquired over a fault system, both presenting an abrupt lateral variation perpendicularly crossing the acquisition line. We also extended the AARW method to the detection of sharp discontinuities from large and multifold data sets and we tested these novel procedures on the field case. The two methods are proven to be effective for the detection of the discontinuity, by portraying propagation phenomena linked to the presence of the heterogeneity, such as the interference between incident and reflected wavetrains, and energy concentration as well as subsequent decay at the fault location. The procedures we developed for the processing of multifold seismic data set showed to be reliable tools in locating and characterizing subvertical sharp heterogeneities.

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Seismological Investigations in the Olduvai Basin and Ngorongoro Volcanic Highlands (Western Flank of the North Tanzanian Divergence)

Seismological Research Letters ◽

10.1785/0220200111 ◽

2020 ◽

Vol 91 (6) ◽

pp. 3286-3303 ◽

Cited By ~ 1

Author(s):

Laura Parisi ◽

Ian Stanistreet ◽

Jackson Njau ◽

Kathy Schick ◽

Nicholas Toth ◽

...

Keyword(s):

Sedimentary Basins ◽

Quality Analysis ◽

Fault System ◽

Conservation Area ◽

Data Set ◽

The North ◽

Western Flank ◽

Passive Seismic ◽

African Rift ◽

Western Side

Abstract We present data and results of a passive seismic experiment that we operated between June 2016 and May 2018 in the Ngorongoro Conservation Area (northern Tanzania), located on the western side of the eastern branch of the Eastern African Rift (EAR) system. The motivation for this experiment is twofold: (1) investigating the extension of the Olduvai basin, referred to also as the “Cradle of Human Mankind,” as it hosted a variety of paleoenvironments exploited by hominins during their evolution; and (2) studying the link between the fault system in the main EAR and in its western flank. We conduct detailed data-quality analysis of the seismic recordings based upon ambient noise characterization and numerical waveform simulations. Our data set is of good quality, and we observe that local magnitude can be overestimated up to at least 0.23, due to wave-amplifications effects occurring at sites with loose sedimentary material. Based on a new but simple approach using power spectral density measurements, we calculate the thickness of sedimentary basins. This allows us to map the bottom of the Olduvai paleolake confirming that its sedimentary record may be at least 200 m deeper than previously inferred from core drilling. We also map the bottom of the Olbalbal depression for the first time. In addition, we present a seismicity map of the Ngorongoro Conservation Area with unprecedented detail. The seismicity depicts the suture zone between the Tanzanian craton and the Mozambique belt and reveals that the fault system in the western flank of the rift merges at depth into a single detachment that joins the Manyara fault on the western side of the main rift valley.

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Re-exploring Molecular Complexity with ALMA (ReMoCA): interstellar detection of urea

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935428 ◽

2019 ◽

Vol 628 ◽

pp. A10 ◽

Cited By ~ 22

Author(s):

A. Belloche ◽

R. T. Garrod ◽

H. S. P. Müller ◽

K. M. Menten ◽

I. Medvedev ◽

...

Keyword(s):

Column Density ◽

High Mass ◽

Synthetic Spectrum ◽

Mass Star ◽

Methyl Isocyanate ◽

Vibrationally Excited ◽

Data Set ◽

Star Forming ◽

Order Of Magnitude ◽

Molecular Complexity

Context. Urea, NH2C(O)NH2, is a molecule of great importance in organic chemistry and biology. Two searches for urea in the interstellar medium have been reported in the past, but neither were conclusive. Aims. We want to take advantage of the increased sensitivity and angular resolution provided by the Atacama Large Millimeter/submillimeter Array (ALMA) to search for urea toward the hot molecular cores embedded in the high-mass-star-forming region Sgr B2(N). Methods. We used the new spectral line survey named ReMoCA (Re-exploring Molecular Complexity with ALMA) that was performed toward Sgr B2(N) with ALMA in its observing cycle 4 between 84 and 114 GHz. The spectra were analyzed under the local thermodynamic equilibrium approximation. We constructed a full synthetic spectrum that includes all the molecules identified so far. We used new spectroscopic predictions for urea in its vibrational ground state and first vibrationally excited state to search for this complex organic molecule in the ReMoCA data set. We employed the gas-grain chemical kinetics model MAGICKAL to interpret the astronomical observations. Results. We report the secure detection of urea toward the hot core Sgr B2(N1) at a position called N1S slightly offset from the continuum peak, which avoids obscuration by the dust. The identification of urea relies on nine clearly detected transitions. We derive a column density of 2.7 × 1016 cm−2 for urea, two orders of magnitude lower than the column density of formamide, and one order of magnitude below that of methyl isocyanate, acetamide, and N-methylformamide. The latter molecule is reliably identified toward N1S with 60 clearly detected lines, confirming an earlier claim of its tentative interstellar detection. We report the first interstellar detections of NH2CH18O and 15NH2CHO. We also report the nondetection of urea toward the secondary hot core Sgr B2(N2) with an abundance relative to the other four species at least one order of magnitude lower than toward the main hot core. Our chemical model roughly reproduces the relative abundances of formamide, methyl isocyanate, acetamide, and N-methylformamide, but it overproduces urea by at least one order of magnitude. Conclusions. Urea is clearly detected in one of the hot cores. Comparing the full chemical composition of Sgr B2(N1S) and Sgr B2(N2) may help understand why urea is at least one order of magnitude less abundant in the latter source.

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Shallow structural setting of an active normal fault zone in the 30 October 2016 Mw 6.5 central Italy earthquake imaged through a multidisciplinary geophysical approach.

10.5194/egusphere-egu2020-7242 ◽

2020 ◽

Author(s):

Fabio Villani ◽

Stefano Maraio ◽

Pier Paolo Bruno ◽

Lisa Serri ◽

Vincenzo Sapia ◽

...

Keyword(s):

Cluster Analysis ◽

Fault Zone ◽

Central Italy ◽

Normal Fault ◽

Alluvial Fan ◽

Fault System ◽

Depth Range ◽

Inversion Algorithm ◽

Data Set ◽

Refraction Tomography

We investigate the shallow structure of an active normal fault-zone that ruptured the surface during the 30 October 2016 Mw 6.5 Norcia earthquake (central Italy) using a multidisciplinary geophysical approach. The survey site is located in the Castelluccio basin, an intramontane Quaternary depression in the hangingwall of the SW-dipping Vettore-Bove fault system. The Norcia earthquake caused widespread surface faulting affecting also the Castelluccio basin, where the rupture trace follows the 2 km-long Valle delle Fonti fault (VF), displaying a ~3 m-high fault scarp due to cumulative surface slip of Holocene paleo-earthquakes. We explored the subsurface of the VF fault along a 2-D transect orthogonal to the coseismic rupture on recent alluvial fan deposits, combining very high-resolution seismic refraction tomography, multichannel analysis of surface waves (MASW), reflection seismology and electrical resistivity tomography (ERT).We acquired the ERT profile using an array of 64 steel electrodes, 2 m-spaced. Apparent resistivity data were then modeled via a linearized inversion algorithm with smoothness constraints to recover the subsurface resistivity distribution. The seismic data were recorded by&#160; a190 m-long single array centered on the surface rupture, using 96 vertical geophones 2 m-spaced and a 5 kg hammer source.Input data for refraction tomography are ~9000 handpicked first arrival travel-times, inverted through a fully non-linear multi-scale algorithm based on a finite-difference Eikonal solver. The data for MASW were extracted from common receiver configurations with 24 geophones; the dispersion curves were inverted to generate several S-wave 1-D profiles, subsequently interpolated to generate a pseudo-2D Vs section. For reflection data, after a pre-processing flow, the picking of the maximum of semblance on CMP super-gathers was used to define a velocity model (VNMO) for CMP ensemble stack; the final stack velocity macro-model (VNMO) from the CMP processing was smoothed and used for post-stack depth conversion. We further processed Vp, Vs and resistivity models through the K-means algorithm, which performs a cluster analysis for the bivariate data set to individuate relationships between the two sets of variables. The result is an integrated model with a finite number of homogeneous clusters.In the depth converted reflection section, the subsurface of the VF fault displays abrupt reflection truncations in the 5-60 m depth range suggesting a cumulative fault throw of ~30 m. Furthermore, another normal fault appears in the in the footwall. The reflection image points out alternating high-amplitude reflections that we interpret as a stack of alluvial sandy-gravels layers that thickens in the hangingwall of the VF fault. Resistivity, Vp and Vs models provide hints on the physical properties of the active fault zone, appearing as a moderately conductive (< 150 &#8486;m) elongated body with relatively high-Vp (~1500 m/s) and low-Vs (< 500 m/s). The Vp/Vs ratio > 3 and the Poisson&#8217;s coefficient > 0.4 in the fault zone suggest this is a granular nearly-saturated medium, probably related to the increase of permeability due to fracturing and shearing. The results from the K-means cluster analysis also identify a homogeneous cluster in correspondence of the saturated fault zone.

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Mafic-silicic layered intrusions: the role of basaltic injections on magmatic processes and the evolution of silicic magma chambers

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s0263593300006647 ◽

1996 ◽

Vol 87 (1-2) ◽

pp. 233-242 ◽

Cited By ~ 79

Author(s):

R. A. Wiebe

Keyword(s):

Basaltic Magma ◽

Mafic Magma ◽

Silicic Magma ◽

Granitic Magma ◽

Magma Chambers ◽

Mechanical Mixing ◽

Diffusive Convection ◽

Type Granite ◽

Mafic Magmas ◽

Silicic Magmas

ABSTRACT:Plutonic complexes with interlayered mafic and silicic rocks commonly contain layers (1–50 m thick) with a chilled gabbroic base that grades upwards to dioritic or silicic cumulates. Each chilled base records the infusion of new basaltic magma into the chamber. Some layers preserve a record of double-diffusive convection with hotter, denser mafic magma beneath silicic magma. Processes of hybridisation include mechanical mixing of crystals and selective exchange of H2O, alkalis and isotopes. These effects are convected away from the boundary into the interiors of both magmas. Fractional crystallisation aad replenishment of the mafic magma can also generate intermediate magma layers highly enriched in incompatible elements.Basaltic infusions into silicic magma chambers can significantly affect the thermal and chemical character of resident granitic magmas in shallow level chambers. In one Maine pluton, they converted resident I-type granitic magma into A-type granite and, in another, they produced a low-K (trondhjemitic) magma layer beneath normal granitic magma. If comparable interactions occur at deeper crustal levels, selective thermal, chemical and isotopic exchange should probably be even more effective. Because the mafic magmas crystallise first and relatively rapidly, silicic magmas that rise away from deep composite chambers may show little direct evidence (e.g. enclaves) of their prior involvement with mafic magma.

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