New Articles for Geosphere Posted Early Online
Boulder, Colo., USA: GSA’s dynamic online journal, Geosphere,
posts articles online regularly. Topics this month include an analysis of
geoscience job applications; Uturuncu volcano, Bolivia; Picture Gorge
Basalt; and the Red Bluff Granite Suite. You can find these articles at
https://geosphere.geoscienceworld.org/content/early/recent
.
Critical workforce skills for bachelor-level geoscientists: An
analysis of geoscience job advertisements
G.W. Shafer; K. Viskupic; A.E. Egger
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.
Picture Gorge Basalt: Internal stratigraphy, eruptive patterns, and
its importance for understanding Columbia River Basalt Group
magmatism
Emily B. Cahoon; Martin J. Streck; Anthony A.P. Koppers
The Picture Gorge Basalt (PGB) of the Columbia River Basalt Group (CRBG)
has been previously thought to be limited in its eruptive volume (<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. The geochemical identifiers used to differentiate PGB from other
main-phase CRBG formations include lower TiO2 (<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.
Multiple spatial and temporal scales of deformation from geodetic
monitoring point to active transcrustal magma system at Uturuncu
volcano, Bolivia
Elizabeth Eiden; Patricia MacQueen; Scott Henderson; Matthew Pritchard
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.
Tectonomagmatic evolution of southwestern Laurentia: Insights from
zircon U-Pb geochronology and hafnium isotopic composition of the
Red Bluff Granite Suite, west Texas, USA
Munazzam Ali Mahar; Philip C. Goodell; Jason W. Ricketts; Eric J. Kappus;
James L. Crowley ...
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.
GEOSPHERE articles are available at
https://geosphere.geoscienceworld.org/content/early/recent
. Representatives of the media may obtain complimentary copies of GEOSPHERE
articles by contacting Kea Giles at the address above. Please discuss
articles of interest with the authors before publishing stories on their
work, and please refer to GEOSPHERE in articles published. Non-media
requests for articles may be directed to GSA Sales and Service, gsaservice@geosociety.org.
https://www.geosociety.org
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