Textural Investigation into Rapid Welding Transitions in the Tuff of Leslie Gulch along Succor Creek at the Mahogany Mountain-Three Fingers Rhyolite Field, Southeastern Oregon

The Mahogany Mountain-Three Fingers Rhyolite Field (MM-TFrf) in southeastern Oregon, associated with mid-Miocene rhyolite activity and Columbia River flood basalts, has been the subject of geological scrutiny. Previous studies proposed separate origins for the tuff of Leslie Gulch (LGT) and Spring Creek, but Benson and Mahood (2006) suggested a single ignimbrite event at 15.8 Ma, prompting a reassessment of MM-TFrf\u27s history. This research focuses on LGT, investigating textural disparities between welded and non-welded tuff formations. Petrographic examinations delve into the transformation stages of pyroclastic tuff deposition, revealing the dynamic influences of volcanological and magmatic processes on welded and non-welded tuff development. Using light microscopy, thin sections are meticulously analyzed, with a focus on pyroclastic grain characteristics such as size, vesicularity, and shape. Vesicularity serves as a crucial indicator of eruption dynamics, aiding in the differentiation of pyroclastic clasts. Preliminary findings suggest partially welded ignimbrites contain a higher abundance of visible glass shards. Further investigations aim to elucidate the volcanic dynamics shaping MM-TFrf\u27s history

Volcanology and petrology of the Rattlesnake Ash-Flow Tuff, eastern Oregon

The Rattlesnake Ash-Flow Tuff erupted 7.05±0.01 Ma from the western Harney Basin, southeastern Oregon. The location of the vent area is inferred based on vent-ward increases in size of pumices, in degree of welding, and in degree of post-emplacement crystallization. Today's outcrops cover 9000 km2 and estimated original outcrop coverage was ca. 35000 km2. Tuff thickness is uniform ranging mainly between 5 and 30 in with maxima up to 70 in. Estimated eruption volume is 280 km3 dense rock equivalent (DRE). Lithological variations include vitric non- to densely welded tuff, vapor-phase, devitrified, spherulitic, lithophysal, and rheomorphic tuff. Lithological zoning characteristics of the tuff change locally at nearly constant tuff thickness over distances of 1 to 3 km grading from incipiently welded tuff to highly zoned sections. Regional variations become apparent by integrating many sections from one area. A three-dimensional facies model is developed describing the local and regional facies variations. The Rattlesnake Tuff consists of high-silica rhyolite (HSR) erupted as pumices and glass shards. Dacite pumices make up less than 1% of the total volume and quenched basalt and basaltic andesite inclusions inside dacite pumices constitute << 0.1 volume %. HSR pumices cluster in 4 to 5 compositional groups which are discerned best by La, Eu, Ba, Hf(Zr), Ta(Nb). Major element variations are minor but consistent between groups with Si02 increasing and FeO*, MgO, Ti02, and CaO decreasing with differentiation. Modal mineralogy, mineral chemistry, and partition coefficients also change progressively. The diversity of HSR is likely the product of crystal fractionation processes. A model is proposed by which a stratified magma chamber is generated from the roof of the chamber downward by progressively more evolved HSR. Least evolved HSR is likely the product of dehydration melting of high-grade intermediate to mafic protoliths. High Ba/Rb ratios of 30 in the least evolved HSR limit the potential protoliths to lithologies with equal or higher Ba/Rb. Dacite pumices and mafic inclusions reveal the nature of the mafic root zone to the Rattlesnake Tuff magma chamber. Quenching and mingling textures with the host pumice indicate that basaltic andesite and basalt inclusions are cognate. Dacite formed at the interface between HSR and underlying enriched basaltic andesite and was generated by mixing of these two components. Basaltic andesite is fractionated and enriched in trace elements compared to regional primitive tholeiite (HAOT). Basaltic andesite has evolved from HAOT's mainly through fractionation and recharge while being stalled underneath a silicic cap

Picture Gorge Basalt: Internal stratigraphy, eruptive patterns, and its importance for understanding Columbia River Basalt Group magmatism

The Picture Gorge Basalt (PGB) of the Columbia River Basalt Group (CRBG) has been previously thought to be limited in its eruptive volume (\u3c3000 \u3ekm3) and thought to not extend far from its type locality. At present, PGB represents only 1.1 vol% of the CRBG with a relatively limited spatial distribution of ~10,000 km2. New age data illustrate that the PGB is the earliest and longest eruptive unit compared to other main-phase CRBG formations and that some dated basaltic flows reach far (~100 km) beyond the previously mapped extent. This study focuses on extensive outcrops of basaltic lavas and dikes south of the type locality at Picture Gorge, in order to reassess the spatial distribution and eruptive volume of the PGB. Field observations coupled with geochemical data indicate that PGB lava flows and mafic dikes covered a significantly greater area than shown on the published geologic maps. We find that additional mafic dikes located farther south of the original mapped distribution have geochemical compositions and northwest-trending orientations comparable to the dikes of the Monument dike swarm. We also identify new lava flows that can be correlated where stratigraphic control is well defined toward the original mapped PGB distribution. Our analyses and correlations are facilitated by comparison of 20 major- and trace-element abundances via a principal component analysis. This statistical comparison provides a new detailed distribution of PGB with stratigraphic significance that more than doubles the total distribution of PGB lavas and dikes and brings the eruptive volume to a new minimum of at least ~4200 km3. Geochemically correlated basaltic lavas and dikes in the extended distribution of PGB represent the earlier and later sections of the internal PGB stratigraphy. This is an intriguing observation as new geochronological data suggest an eruptive hiatus of ~400 k.y. during PGB volcanic activity, which occurred from 17.23 Ma to 15.76 Ma. The geochemical identifiers used to differentiate PGB from other main-phase CRBG formations include lower TiO2 (\u3c2 \u3ewt%) concentrations, lower incompatible trace-element (i.e., La, Th, and Y) abundances, and a more pronounced enrichment in large- ion- lithophile elements (LILEs) on a primitive mantle–normalized trace-element diagram (Sun and McDonough, 1989). Geochemical characteristics of PGB are interpreted to represent a magmatic source component distinct from the other main-phase CRBG units, possibly a localized backarc-sourced mantle melt. However, this source cannot be spatially restricted as there are observed PGB lava flows and dikes extending as far east as Lake Owyhee and as far south as Hart Mountain, covering at least 15,000 km2. In context with the existing stratigraphy and the new extent of PGB lavas and dikes, these ages and coupled geochemical signatures demonstrate this mantle component was not spatially localized but rather tapped across a wide region

Filling Critical Gaps in the Space-Time Record of High Lava Plains and co-Columbia River Basalt Group rhyolite Volcanism

Miocene rhyolitic volcanism of eastern Oregon, USA, can be divided into two main episodes. Mantle plume upwelling is thought to have generated Columbia River Basalt Group (CRBG) lavas and coeval \u3e16.5−15 Ma silicic volcanism trending north−south from northeast Oregon to northern Nevada. Rhyolite volcanism of the 12−0 Ma High Lava Plains province has been ascribed to either buoyancy-driven westward plume spreading or to slab rollback and mantle convection spanning from southeast Oregon to Newberry Volcano to the west. The apparent ca. 15−12 Ma eruptive hiatus suggests that rhyolites of these provinces were a product of separate processes, yet this gap was based on incomplete data. The lack of data on ∼33 of the total ∼50 rhyolitic eruptive centers in the area where the two provinces overlap (117−119°W, 43−44°N) yields only tenuous relationships between these two provinces

Mantle Sources and Geochemical Evolution of the Picture Gorge Basalt, Columbia River Basalt Group

The Columbia River Basalt Group (CRBG) is the youngest continental flood basalt province, proposed to be sourced from the deep-seated plume that currently resides underneath Yellowstone National Park. If so, the earliest erupted basalts from this province, such as those in the Picture Gorge Basalt (PGB), aid in understanding and modeling plume impingement and the subsequent evolution of basaltic volcanism. Using geochemical and isotopic data, this study explores potential mantle sources and magma evolution of the PGB. Long known geochemical signatures of the PGB include overall large ion lithophile element (LILE) enrichment and relative depletion of high field strength elements (HFSE) typical of other CRBG main-phase units. Basaltic samples of the PGB have 87Sr/86Sr ratios on the low end of the range displayed by other CRBG lavas and mantle-like δ18O values. The relatively strong enrichment of LILE and depletion of HFSE coupled with depleted isotopic signatures suggest a metasomatized upper mantle as the most likely magmatic source for the PGB. Previous geochemical modeling of the PGB utilized the composition of two high-MgO primitive dikes exposed in the northern portion of the Monument Dike swarm as parental melt. However, fractionation of these dike compositions cannot generate the compositional variability illustrated by basaltic lavas and dikes of the PGB. This study identifies a second potential parental PGB composition best represented by basaltic flows in the extended spatial distribution of the PGB. This composition also better reflects the lowest stratigraphic flows identified in the previously mapped extent of the PGB. Age data reveal that PGB lavas erupted first and throughout eruptions of main-phase CRBG units (Steens, Imnaha, Grande Ronde Basalt). Combining geochemical signals with these age data indicates cyclical patterns in the amounts of contributing mantle components. Eruption of PGB material occurred in two pulses, demonstrated by a ~0.4 Ma temporal gap in reported ages, 16.62 to 16.23 Ma. Coupling ages with observed geochemical signals, including relative elemental abundances of LILE, indicates increased influence of a more primitive, potentially plume-like source with time

Columbia River Rhyolites: Age-Distribution Patterns and Their Implications for Arrival, Location, and Dispersion of Continental Flood Basalt Magmas in the Crust

Columbia River province magmatism is now known to include abundant and widespread rhyolite centers even though the view that the earliest rhyolites erupted from the McDermitt Caldera and other nearby volcanic fields along the Oregon–Nevada state border has persisted. Our study covers little-studied or unknown rhyolite occurrences in eastern Oregon that show a much wider distribution of older centers. With our new data on distribution of rhyolite centers and ages along with literature data, we consider rhyolites spanning from 17.5 to 14.5 Ma of eastern Oregon, northern Nevada, and western Idaho to be a direct response to flood basalts of the Columbia River Basalt Group (CRBG) and collectively categorize them as Columbia River Rhyolites. The age distribution patterns of Columbia River Rhyolites have implications for the arrival, location, and dispersion of flood basalt magmas in the crust. We consider the period from 17.5 to 16.4 Ma to be the waxing phase of rhyolite activity and the period from 15.3 to 14.5 Ma to be the waning phase. The largest number of centers was active between 16.3–15.4 Ma. The existence of crustal CRBG magma reservoirs beneath rhyolites seems inevitable, and hence, rhyolites suggest the following. The locations of centers of the waxing phase imply the arrival of CRBG magmas across the distribution area of rhyolites and are thought to correspond to the thermal pulses of arriving Picture Gorge Basalt and Picture-Gorge-Basalt-like magmas of the Imnaha Basalt in the north and to those of Steens Basalt magmas in the south. The earlier main rhyolite activity phase corresponds with Grande Ronde Basalt and evolved Picture Gorge Basalt and Steens Basalt. The later main phase rhyolite activity slightly postdated these basalts but is contemporaneous with icelanditic magmas that evolved from flood basalts. Similarly, centers of the waning phase span the area distribution of earlier phases and are similarly contemporaneous with icelanditic magmas and with other local basalts. These data have a number of implications for long-held notions about flood basalt migration through time and the age-progressive Snake River Plain Yellowstone rhyolite trend. There is no age progression in rhyolite activity from south-to-north, and this places doubt on the postulated south-to-north progression in basalt activity, at least for main-phase CRBG lavas. Furthermore, we suggest that age-progressive rhyolite activity of the Snake River Plain–Yellowstone trend starts at ~12 Ma with activity at the Bruneau Jarbidge center, and early centers along the Oregon–Nevada border, such as McDermitt, belong to the early to main phase rhyolites identified here

Temporal and crustal effects on differentiation of tholeiite to calcalkaline and ferro-trachytic suites, High Lava Plains, Oregon, USA

Strongly bimodal, basalt-rhyolite volcanism of the High Lava Plains Province of Oregon followed the Middle Miocene flood basalts of the Pacific Northwest and extends to recent time. During the 8 m.y. of volcanism recorded in the central High Lava Plains, in western Harney Basin, three distinct mafic magmatic trends originate from primitive high-alumina olivine tholeiites (HAOT); they are tholeiitic, calcalkaline and ferro-trachytic. Tholeiitic basalts occur throughout the history and their compositions are derived by crystal fractionation while traversing the crust and mixing with evolved mafic magmas. Scavenging of apatite from crustal rocks and minor contamination with felsic melts accounts for P, incompatible element enrichments and increasing tilts of incompatible element patterns with differentiation. The calcalkaline mafic suite occurs in temporal association with abundant silicic volcanism and is the only suite with Fe decreasing with Mg. Calcalkaline compositions are derived from evolved tholeiitic basalt by crystal fractionation coupled with assimilation of felsic crust or crustal melts. The ferro-trachytic suite occurs mainly late, is highly enriched in incompatible element with patterns parallel to tholeiites from which it is derived by protracted fractionation and recharge. The three suites primarily reflect changes in magma flux and crustal interactions in time. High magma flux promotes crustal melting and contamination of tholeiite to make the calcalkaline suite. On the other hand, ferrotrachytic magmas erupted mainly late in the sequence, during magmatic waning and after significant basaltification of the crust.Keywords: basalt differentiation, calcalkaline trend, phosphorus enrichment, HAOT, trachyandesite, high lava plain

Characteristics and Predictors of Intensive Care Unit Admission in Pediatric Blunt Abdominal Trauma

BACKGROUND: Pediatric trauma patients sustaining blunt abdominal trauma (BAT) with intra-abdominal injury (IAI) are frequently admitted to the intensive care unit (ICU). This study was performed to identify predictors for ICU admission following BAT. METHODS: Prospective study of children (\u3c 16 years) who presented to 14 Level-One Pediatric Trauma Centers following BAT over a 1-year period. Patients were categorized as ICU or non-ICU patients. Data collected included vitals, physical exam findings, laboratory results, imaging, and traumatic injuries. A multivariable hierarchical logistic regression model was used to identify predictors of ICU admission. Predictive ability of the model was assessed via tenfold cross-validated area under the receiver operating characteristic curves (cvAUC). RESULTS: Included were 2,182 children with 21% (n = 463) admitted to the ICU. On univariate analysis, ICU patients were associated with abnormal age-adjusted shock index, increased injury severity scores (ISS), lower Glasgow coma scores (GCS), traumatic brain injury (TBI), and severe solid organ injury (SOI). With multivariable logistic regression, factors associated with ICU admission were severe trauma (ISS \u3e 15), anemia (hematocrit \u3c 30), severe TBI (GCS \u3c 8), cervical spine injury, skull fracture, and severe solid organ injury. The cvAUC for the multivariable model was 0.91 (95% CI 0.88-0.92). CONCLUSION: Severe solid organ injury and traumatic brain injury, in association with multisystem trauma, appear to drive ICU admission in pediatric patients with BAT. These results may inform the design of a trauma bay prediction rule to assist in optimizing ICU resource utilization after BAT. STUDY DESIGN: Prognosis study

Microplastics persist in an arable soil but do not affect soil microbial biomass, enzyme activities, and crop yield

Microplastics (MP, plastic particles <5 mm) are ubiquitous in arable soils due to significant inputs via organic fertilizers, sewage sludges, and plastic mulches. However, knowledge of typical MP loadings, their fate, and ecological impacts on arable soils is limited. We studied (1) MP background concentrations, (2) the fate of added conventional and biodegradable MP, and (3) effects of MP in combination with organic fertilizers on microbial abundance and activity associated with carbon (C) cycling, and crop yields in an arable soil. On a conventionally managed soil (Luvisol, silt loam), we arranged plots in a randomized complete block design with the following MP treatments (none, low‐density polyethylene [LDPE], a blend of poly(lactic acid) and poly(butylene adipate‐co‐terephthalate) [PLA/PBAT]) and organic fertilizers (none, compost, digestate). We added 20 kg MP ha-1 and 10 t organic fertilizers ha-1. We measured concentrations of MP in the soil, microbiological indicators of C cycling (microbial biomass and enzyme activities), and crop yields over 1.5 years. Background concentration of MP in the top 10 cm was 296 ± 110 (mean ± standard error) particles <0.5 mm per kg soil, with polypropylene, polystyrene, and polyethylene as the main polymers. Added LDPE and PLA/PBAT particles showed no changes in number and particle size over time. MP did not affect the soil microbiological indicators of C cycling or crop yields. Numerous MP occur in arable soils, suggesting diffuse MP entry into soils. In addition to conventional MP, biodegradable MP may persist under field conditions. However, MP at current concentrations are not expected to affect C turnover and crop yield.Ministry of Environment, Climate and Energy of Baden-WürttembergDeutsche ForschungsgemeinschaftProjekt DEA