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<jats:p>We provide laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) and high-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb ages and Hf isotopic compositions of zircons from the Red Bluff Granite Suite and mafic dikes in the Franklin Mountains of El Paso, Texas, USA. Granitoids exposed in the Franklin Mountains were previously divided into five magmatic stages based on cross-cutting relationships. Major and trace element compositions showed that these granitoids are ferroan, alkaline, and A2 type. Homogeneity in the whole-rock geochemistry suggests that the granite stages are genetically related and share similar petrogenetic histories. Weighted mean zircon 206Pb/238U dates from the older magmatic stage 1 alkali-feldspar quartz syenite and stage 2 alkali-feldspar granite are 1112.36 ± 0.35 and 1112.46 ± 0.37 Ma, respectively. The weighted mean εHf(t) values varying from +5.3 to +7.2 are similar to those of other regional ca. 1.1 Ga magmatic rocks throughout south- western Laurentia. Geochemical characteristics, petrological modeling, and enriched Hf isotopic composition suggest fractional crystallization of a basaltic magma that was produced by melting of an enriched mantle reservoir. However, zircon inheritance ages of ca. 1.3 Ga and 1.26–1.15 Ga are consistent with a minor contribution from felsic crustal basement. Our data and regional geology are consistent with a post-collisional slab break-off that facilitated asthenospheric upwelling and partial melting of the enriched mantle, possibly subcontinental lithospheric mantle, extending from Llano Uplift, Texas, in the southeast to California to the northwest. Magma thus generated upon differentiation produced ferroan and A-type granitoids.</jats:p>

<jats:p>The Picture Gorge Basalt (PGB) of the Columbia River Basalt Group (CRBG) has been previously thought to be limited in its eruptive volume (&amp;lt;3000 km3) 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.</jats:p> <jats:p>The geochemical identifiers used to differentiate PGB from other main-phase CRBG formations include lower TiO2 (&amp;lt;2 wt%) 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.</jats:p>

<jats:p>Uturuncu volcano in southern Bolivia last erupted around 250 ka but is exhibiting signs of recent activity, including over 50 yr of surface uplift, elevated seismic activity, and fumarolic activity. We studied the spatial and temporal scales of surface deformation from 1992 to 2021 to better understand subsurface activity. We tracked Uturuncu’s recent deformation using interferometric synthetic aperture radar (InSAR) data and the global navigation satellite system (GNSS) station UTUR, located near Uturuncu’s summit. We observed a spatially coherent signal of uplift from 2014 to 2021 from Sentinel-1 A/B satellites that indicates the Altiplano-Puna magma body, located 19–24 km below ground level, and previously noted as the source of the large region of deformation, is still active. The ground is now uplifting at a rate of ~3 mm/yr compared to prior rates of ~10 mm/yr. We corroborated this waning uplift with in situ data from station UTUR. We combined the Sentinel-1 data with TerraSAR-X interferograms to constrain an ~25 km2 region of subsidence located 11 km SSW of Uturuncu, with a source depth of 2.1 km below ground level to an active period of ~2.5 yr with ~5 mm/yr subsidence. We developed a conceptual model that relates these varying depths and time scales of activity in a transcrustal magmatic system. We associate the surface uplift with pressurization from ascending gases and brines from magmatic reservoirs in the midcrust. We infer the existence of brine lenses in the shallow hydrothermal system based on low subsurface resistivity correlated with surface subsidence.</jats:p>

<jats:p>Understanding the skills bachelor-level geoscientists need to enter the workforce is critical to their success. The goal of this study was to identify the workforce skills that are most requested from a broad range of geoscience employers. We collected 3668 job advertisements for bachelor-level geoscientists and used a case-insensitive, code-matching function in Matlab to determine the skills geoscience employers seek. Written communication (67%), field skills (63%), planning (53%), and driving (51%) were most frequently requested. Field skills and data collection were frequently found together in the ads. Written communication skills were common regardless of occupation. Quantitative skills were requested less frequently (23%) but were usually mentioned several times in the ads that did request them, signaling their importance for certain jobs. Some geoscience-specific skills were rarely found, such as temporal understanding (5%) and systems thinking (0%). We also subdivided field skills into individual tasks and ranked them by employer demand. Site assessments and evaluations, unspecified field tasks, and monitoring were the most frequently requested field skills. This study presents the geoscience community with a picture of the skills sought by employers of bachelor-level geoscientists and provides departments and programs with data they can use to assess their curricula for workforce preparation.</jats:p>

<jats:p>Deep-marine two-part strata consisting of a sand-rich basal part overlain sharply by a mud-rich upper part have been termed linked debrites, hybrid event beds, transitional flow deposits, and bipartite facies. In continental slope and proximal basin floor strata of the Neoproterozoic Windermere Supergroup (western North America) and distal basin-floor strata of the Ordovician Cloridorme Formation (eastern North America), bipartite facies form the middle of a depositional continuum hundreds of meters long consisting upflow of thick-bedded, matrix-poor sandstone (&amp;lt;20% detrital mud matrix) to thin-bedded, sandy mudstone (50%–90% mud matrix). This consistent lithofacies change is interpreted to reflect particle settling in a rapidly but systematically evolving, negligibly sheared sand-mud suspension developed along the margins (Windermere) and downflow terminus (Cloridorme) of a high-energy, mud-enriched avulsion jet.</jats:p> <jats:p>In both study areas, beds of similar lithofacies type succeed one another vertically and transform to the next facies in the depositional continuum at about the same along-strike position, forming stratal units two to nine beds thick whose grain-size distribution gradually decreases upward. This spatial and temporal regularity is interpreted to be caused by multiple surges of a single, progressively waning turbidity current, with sufficient lag between successive surges for the deposition of a traction-structured sandstone overlain by mudstone cap. Furthermore, the systematic back-stepping or side-stepping recognized at the stratal unit scale is interpreted to have been driven by a combination of knickpoint migration and local topographic steering of the flows, which continued until the supply of mud from local seafloor erosion became exhausted, the main channel avulsed elsewhere, or a new stratal element developed.</jats:p>

<jats:p>The Northwestern Hawaiian Ridge is an age-progressive volcanic chain sourced from the Hawaiian mantle plume. Proximal to the Northwestern Hawaiian Ridge are several clusters of smaller seamounts and ridges with limited age constraints and unknown geodynamic origins. This study presents new bathymetric data and 40Ar/39Ar age determinations from lava flow samples recovered by remotely operated vehicle (ROV) from two east–west-trending chains of seamounts that lie north of the Pūhāhonu and Mokumanamana volcanoes. The previously unexplored Naifeh Chain (28°48′N,167°48′W) and Plumeria Chain (25°36′N, 164°35′W) contain five volcanic structures each, including three guyots in the Naifeh Chain. New 40Ar/39Ar age determinations indicate that the Naifeh Chain formed ca. 88 Ma and the Plumeria Chain ca. 85 Ma. The Cretaceous ages, coupled with a perpendicular orientation of the seamounts relative to absolute Pacific plate motion at that time, eliminate either a Miocene Hawaiian volcanic arch or Cretaceous mantle-plume origin. The seamounts lie on oceanic crust that is modeled to be 10–15 Ma older than the corresponding seamounts. Here, two models are put forth to explain the origin of these enigmatic seamount chains as well as the similar nearby Mendelssohn Seamounts. (1) Diffuse lithospheric extension results in the formation of these seamounts until the initiation of the Kula-Pacific spreading center in the north at 84–79 Ma, which alleviates the tension. (2) Shear-driven upwelling of enriched mantle material beneath young oceanic lithosphere results in an age-progressive seamount track that is approximately perpendicular to the spreading ridge. Here we show that all sampled seamounts proximal to the Northwestern Hawaiian Ridge are intraplate in nature, but their formations can be attributed to both plume and plate processes.</jats:p>

<jats:p>Fluid inclusion microthermometry of synkinematic veins is used to estimate the maximum syntectonic load that was deposited on the wedge top in the central Appalachians (northeastern United States) during the Alleghanian orogeny. The restored loads indicate two major depocenters during the Alleghanian orogeny: one above Broadtop synclinorium, with as much as 7 km of Pennsylvanian–Permian load probably sourced by the erosion of rocks uplifted by the growing Blue Ridge massif and emplacement of the North Mountain thrust sheet; the other above the Anthracite belt, with as much as 16 km of syntectonic load likely sourced by the erosion of rocks uplifted by the growing Reading Prong massif. The loads were generally &amp;lt;3 km in the intervening Juniata culmination. In areas of high load, the structural architecture of the basin is that of widely spaced thrusts (~17–22 km) with large leading-edge anticlines in the Cambrian–Ordovician lithotectonic unit, while in areas of low load, thrusts are more closely spaced (~15 km) and deformed into an imbricate stack. The relationship between observed syntectonic loads, thrust spacing, and structural style reflect modeled relationships.</jats:p>

<jats:p>The Walker Lane belt and Eastern California shear zone of California, USA, are active, plate boundary–related dextral systems with transtensional and transpressional deformation, respectively. They are separated by the sinistral Garlock fault, creating a complex system without an overall integrated formation and evolution model. We examine the deformation within the eastern segment of the Garlock fault zone over geologic timescales by determining the slip history of faults. We assess the progression of faulting and associated deformation along the WSW-striking Garlock fault zone and how it applies to the overall NNW-directed dextral system. Previous studies found that large synthetic fault strands take up 30% of the slip of the Garlock fault zone and have proposed multiple mechanisms to explore how to accommodate regional NNW-directed shear across the Garlock fault without cutting its trace.</jats:p> <jats:p>We analyze an unstudied section of faulting in one of the more complex areas of regional deformation via compiled and reinterpreted published geologic data for an analysis of total and incremental slip on the main faults of the eastern Garlock fault zone. We identify geologic offset features to interpret total slip, timing, and deformation evolution. We find that 30% of the total slip of the Garlock zone occurs on strands other than the Garlock fault sensu stricto, with the locus of main slip sidestepping during the evolution of accommodation of through-going, regional dextral shear. Our results support ideas of the creation and evolution of the regional dextral system via stress concentration on a sub-Garlock lithospheric anisotropy with a resulting lowering of the plastic yield stress. Our results also show an eastward increase in fault system complexity, which may imply an underappreciated seismic hazard of the eastern Garlock fault zone.</jats:p>

<jats:p>An occurrence of blueschist-facies metamorphism in the Appalachian orogen is newly recognized in northwestern New England, United States. Inclusions of glaucophane and omphacite occur in a relict garnet core from a retrogressed garnet-barroisite amphibolite of the Belvidere Mountain Complex in Vermont. Pressure-temperature pseudosection and mineral composition isopleth calculations demonstrate that the Belvidere Mountain Complex blueschist-facies mineral assemblage of glaucophane–magnesio-hornblende–omphacite–chlorite–rutile–quartz–clinozoisite–garnet was stable at ~1.65–2.0 GPa and ~450–480 °C. Garnet-absent amphibolite with barroisite and chlorite inclusions in clinozoisite records high-pressure epidote-amphibolite–facies metamorphism at ~1.0–1.4 GPa and ~515–550 °C. These new findings quantify deep subduction of the Belvidere Mountain Complex during the Cambrian to Ordovician Taconic orogenic cycle and suggest that more blueschist-facies mineral assemblages could be revealed in the Appalachians with detailed analysis of retrogressed rocks.</jats:p>

<jats:p>Volcanic islands export clastic material to their surrounding oceans by explosive eruptions, lava emissions, biogenic production on their shelves, and failure of their slopes, amongst other processes. This raises the question of whether geological events (in particular, eruptions and landslides) can be detected offshore and dated, and whether any relationships (for example, with climate changes) can be revealed using sediment cores. The volcanically active central Azorean islands (Faial, Pico, São Jorge, and Terceira), with their neighboring submarine basins, are potentially good candidates for such an analysis. Here, chronostratigraphies of four gravity cores collected amongst the islands are constructed based on twelve radiocarbon dates and two dates derived by geochemically correlating primary volcaniclastic turbidites with ignimbrites on Faial and Terceira Islands. Age-depth models are built from the hemipelagic intervals to estimate individual turbidite dates. Volumes of turbidites are modeled by multiplying basin areas with bed thickness, allowing for various turbidite thinning rates and directions. The volumes of landslide-generated turbidites are only comparable with the largest volumes of their adjacent upper-slope submarine landslide valleys; therefore, such turbidites in the cores likely derive from these largest landslides.</jats:p> <jats:p>Emplacement intervals between turbidites originating from both landslides and pyroclastic density currents are found to be mostly a few thousand years. Frequencies of landslide-generated turbidites and hemipelagic sedimentation rates were both highest in the past 8 k.y. compared to preceding periods up to 50 k.y. High hemipelagic sedimentation rates are interpreted to be related to sea-level rise, allowing more shelf bioproduction and release of particles by coastal erosion. The coincident increased frequencies of submarine landslides may also be associated with the increased sediment supply from the islands, resulting in a more rapid build-up of unstable sediments on submarine slopes. Notably, the emplacement frequencies of turbidites of pyroclastic density current origins do not suggest the decreased eruption frequency toward the Holocene that has been found elsewhere.</jats:p>