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Observational scientists use data—either qualitative or quantitative—to construct conceptual models but do not indicate which data are particularly important for the building of that model. We propose the use of salience to denote the relevance of data in supporting a particular model. Salience is effectively a weighting factor for observational data with respect to a model. We propose a scale to characterize the salience of data (from low to high): no attribution, negligible, peripheral, pertinent, important, and paramount. Data that are inconsistent with a given model are categorized with negative salience values. For fields in which the spatial distribution of salience can be visually displayed, we introduce the concept of salience maps. We provide an example of the use of salience rankings and construction of a salience map for the Sage Hen Flat pluton in the White Mountains in eastern California. The use of salience and salience maps is a way to provide increased reliability and trustworthiness of models, facilitate communication, promote inclusiveness, and allow for scientists to more effectively build off prior data in the observational sciences. [ABSTRACT FROM AUTHOR]

Understanding and communicating uncertainty is a key skill needed in the practice of science. However, there has been little research on the instruction of uncertainty in undergraduate science education. Our team designed a module within an online geoscience field course which focused on explicit instruction around uncertainty and provided students with an uncertainty rating scale to record and communicate their uncertainty with a common language. Students then explored a complex, real-world geological problem about which expert scientists had previously made competing claims through geologic maps. Provided with data, expert uncertainty ratings, and the previous claims, students made new geologic maps of their own and presented arguments about their claims in written form. We analyzed these reports along with assessments of uncertainty. Most students explicitly requested geologists' uncertainty judgments in a post-course assessment when asked why scientists might differ in their conclusions and/or utilized the rating scale unprompted in their written arguments. Through the examination of both pre- and post-course assessments of uncertainty and students' course-based assessments, we argue that explicit instruction around uncertainty can be introduced during undergraduate coursework and could facilitate geoscience novices developing into practicing geoscientists. [ABSTRACT FROM AUTHOR]

The Paleoarchean Mt Edgar dome in the East Pilbara Terrane has long been studied as an archetypal dome within Archean dome‐and‐keel terranes, but the history of its formation is debated. Kinematic data presented in this study provide new insights into the late‐stage development of the Mt Edgar dome and East Pilbara Terrane. Quartz crystallographic preferred orientation (CPO), optical microstructures, and field structures all indicate that the granite‐greenstone contact of the Mt Edgar dome experienced reverse (greenstone‐up, dome‐down) sense of shear after the formation of the dominant schistosity. This reverse sense of shear is observed at localities along the entire extent of the sheared margin that rings most of the Mt Edgar dome, but is best documented along the southwest margin in the Warrawoona Greenstone Belt. Additionally, quartz CPO data from a dome triple junction outside of the sheared margin dominantly indicate a constrictional strain geometry, consistent with the previous interpretation that this area represents a zone of vertical foundering in a buoyancy‐instability driven system. However, buoyancy‐instability models do not necessarily predict the occurrence of greenstone‐up sense of shear preserved in solid‐state fabrics along the dome margin. Several geologic explanations are considered, including dome expansion or post‐doming deformation. The data are most consistent with explanations that directly relate to dome formation, especially when considered in tandem with recently published structural data from within the Mt Edgar dome. These kinematic data suggest that late dome development occurred in a near‐static crustal environment rather than an extensional or contractional setting. Key Points: The granite‐greenstone interface at the margin of the granitic Mt Edgar dome is characterized by a late‐stage greenstone‐up sense of shearStrain geometry within the Warrawoona Greenstone Belt varies from constrictional to flatteningThe East Pilbara Terrane domes likely formed as diapiric structures in a near‐static crust [ABSTRACT FROM AUTHOR]

Recent structural and geodetic data define the Guatemala City graben region as the continental triple junction between the North American plate, Caribbean plate, and the Central American Forearc sliver. We present minor fault analysis, geochronological and geochemical analyses, and newly updated GPS velocities in western Guatemala, west of the Guatemala City graben, to characterize the magnitude and timing of extensional deformation in this poorly understood area. Elongations estimated from fault data are parallel (∼east‐west) and perpendicular to the Polochic‐Motagua fault system to the north, similar to geodetically measured active deformation observed east of the Guatemala City graben. Four new 40Ar/39Ar dates and correlation of tephra deposits suggest that faulting was active during the Pliocene, but ceased eastward toward the Guatemala City graben over time. From west to east, fault cessation occurred before the deposition of the Los Chocoyos ash (75 ka) and E tephra (51 ka). Faulting just west of the Guatemala City graben appears to be active, where a major fault cuts the most recent Amatitlán tephras. Based on this data, we propose a time‐progressive strain model for deformation related to North America‐Caribbean plate interactions, whereby distributed elongation of the westernmost Caribbean plate occurred during the Pliocene but localized mostly within the Guatemala City graben and nearby faults during the Pleistocene. Our model supports that: (a) The Guatemala City graben is effectively the western limit of the Caribbean plate; and (b) Western Guatemala, which was the trailing edge of the Caribbean plate, has been transferred to the forearc region. Key Points: Distributed deformation once extended across Guatemala and into Honduras and has localized into the Guatemala City graben region over timeThe Guatemala City graben region is the current North America, Central American Forearc, and Caribbean plate triple junctionFaulting in western Guatemala, representing internal deformation of the Caribbean plate, ceased in an eastward direction over the past ∼4 Ma [ABSTRACT FROM AUTHOR]

Managing uncertainty is fundamental to geoscience practice, yet geoscience education generally does not incorporate explicit instruction on uncertainty. To the extent that students are exposed to scientific uncertainty, it is through in-person field experiences. Virtual field experiences - which rely on pictures, maps, and previously collected measurements - should therefore explicitly address uncertainty or risk losing this critical aspect of students' experience. In this paper we present a framework for teaching students to assess and communicate their uncertainty, which is grounded in best expert practices for conveying uncertainty and familiar terms-of-art in geology. The starting point of our framework is the recognition of uncertainty in both geologic data and models, the latter of which we use as an encompassing term to refer to potential geological processes and structures inferred on the basis of incomplete information. We present a concrete application of the framework to geological mapping and discuss how it could enhance student learning in both traditional in-person and virtual experiences. Our framework is extensible in that it can be applied to a variety of geologic features beyond those where uncertainty is traditionally assessed, and can also be applied to geological subdisciplines. [ABSTRACT FROM AUTHOR]

The rhyolite‐producing Laguna del Maule volcanic field (LdMVF), Chile, has had numerous post‐glacial eruptions that produced large explosions and voluminous lava flows. During the Holocene ∼60 m of surface uplift is recorded by paleo‐shorelines of the fresh‐water Laguna del Maule, with an inflation source near the Barrancas volcanic complex. Rhyolites from the Barrancas complex erupted over ∼14 ka including some of the youngest (1.4 ± 0.6 ka) lava flows in the field. New gravity data collected on the Barrancas complex reveals a residual gravity low (−6 mGal, "Barrancas anomaly") that is distinct from the pronounced gravity low (−19 mGal; "Lake anomaly") associated with present‐day ground uplift to the northwest. Three‐dimensional inversion of the Barrancas anomaly indicates the presence of a magma body with a maximum density contrast with the host rock of −250 kg/m3 centered at a depth of ∼3 km below surface. Nearby Miocene high‐silica granites represent frozen remnants of highly evolved rhyolitic magma. Comparison of the densities measured from samples of these plutons with the geophysical model densities, and integration of thermodynamic modeling of silicic melt evolution, provide constraints on our interpretation. We propose a magma body, containing <30% melt phase and low volatile content, exists beneath Barrancas. The Barrancas and Lake gravity lows represent magma in different physical states, associated with past and present‐day storage beneath LdMVF. The gravity model mirrors geochemical observations which independently indicate that at least two distinct rhyolites were generated and stored as discrete magma bodies within the broader LdMVF. Plain Language Summary: The Laguna del Maule volcanic field (LdMVF) in Chile, has a long history of eruptions that produced large explosions and voluminous lava flows. Lava emitted during these eruptions comes from shallow sources of partially molten rock (magma) located a few kilometers below the surface. Magma pushing from below and into these shallow regions has caused the ground around the lake to rise over the last 10,000 years. To understand the causes of deformation and assess the likelihood of future eruptions, it is essential to know the location and present‐day state of magma within Earth's crust. Magma is typically less dense than the surrounding rock and these density variations cause small changes in the local gravity field, detectable with geophysical instruments. We collected a new set of gravity measurements at the Barrancas volcanic complex to determine if magma is present beneath the volcano that last erupted about 2000 years ago. Our data reveal a shallow magma body at depth beneath the Barrancas complex. This new magma body is separate from another magma body located in a different part of the LdMVF, which has important implications for the assessment of future volcanic hazards in the region. Key Points: At least two separate magma storage regions in different physical states exist beneath the Laguna del Maule volcanic fieldA −6 mGal gravity anomaly below the Barrancas complex is close to a postulated inflation source which produced ∼62 m of Holocene upliftComparing model densities to nearby plutons and seismic models indicates Barrancas magma is above solidus with a small melt proportion [ABSTRACT FROM AUTHOR]

In comparison to the six spinel end‐members in the spinel prism, magnetic information on the intermediate spinel compositions is relatively poorly established. To investigate magnetic properties of intermediate compositions of Cr‐rich spinel, we collected 12 samples that might contain potentially magnetic Cr‐rich spinel. On the basis of chemical composition analysis and physical magnetic behavior, magnetic Group A Fe‐rich spinel (i.e., magnetite), magnetic Group B Cr‐rich spinel, and paramagnetic Group C Cr‐Al‐rich spinel were identified. Magnetite is solely responsible for the natural remanent magnetization (NRM) in severely serpentinized samples from intraoceanic island arcs, orogenic exposures of ultramafics, and back‐arc continental lithosphere settings. Magnetic Group B Cr‐rich spinel shows maximum unblocking temperatures of 200–280°C. Such temperatures permit Cr‐rich spinel to contribute to magnetic anomalies up to about 8–12 km in terrestrial lithosphere settings, given a normal geothermal gradient of 25 K/km. The existence of magnetic Cr‐rich spinel requires certain compositional conditions including a cation ratio of [Cr]/[Fe2+ + Fe3+] from 1.33 to 1.56 as well as a low oxide ratio of (Al2O3 + MgO)/(Cr2O3 + FeO + Fe2O3) less than 10%. It is evident that compositions of spinels are related with the degree of serpentinization as Group A spinel is observed along the fractures between/among olivine grains in heavily serpentinized rocks. Spinels in Groups B and C seem to experience less severe metasomatic or hydrothermal alteration during serpentinization. Distribution of magnetic Cr‐rich spinel along the fractures of silicates (mostly olivine) may support a chemical origin of the NRM. Thus, Cr‐rich spinel is a potential NRM carrier and a source of magnetic anomalies in ultramafic complexes. Key Points: Cr‐rich spinel with unblocking temperatures up to 200–280°C can contribute to magnetic anomalies in terrestrial lithosphere up to 8–12 kmMagnetic remanence carriers reflect the degree of metasomatic reaction associated with serpentinizationIntermediate compositions of Cr‐rich spinel with a cation ratio of [Cr]/[Fe2+ + Fe3+] ranging from 1.33 to 1.56 can be magnetic [ABSTRACT FROM AUTHOR]

The Laguna del Maule volcanic field (LdMVF) in Chile, a rapidly inflating silicic volcanic system without historical eruption, is intersected by active regional faults. The LdMVF provides an opportunity to observe how faults influence, accommodate, or are driven by an actively deforming large silicic system. Here we use Compressed High Intensity Radar Pulse (CHIRP) acoustic reflection data to map the fault network in sediments captured within the eponymous lake at the LdMVF and combine our fault maps with the volcanic history, earthquake locations, focal mechanisms, and lacustrine magnetic data to interpret how faults and magmatism interact. Our seismic data image dominantly dip‐slip faults forming grabens within the lake, subparallel to regional faults. No indications exist in the seismic data to suggest that fault patterns were created by the volcanic system, either ring or radial faults. Fault strikes interpreted from seismic and magnetic data are consistent with mapped dike and fault orientations on land. We therefore interpret that active faults at the LdMVF are tectonic rather than volcanic in origin, forming a transtensional zone that hosts the magmatic system. However, vertical motion along a NS‐striking fault near the center of uplift suggests trapdoor‐style faulting above the volcanic center in which tectonic faults are reactivated to accommodate magmatic inflation and overlying deformation. Magnetic anomalies follow regional faults, suggesting that faults also provide migration pathways. Depositional patterns indicate a prior episode of uplift followed by quiescence, indicating that significant magmatically related uplift at the LdMVF can occur without an associated major eruption. Key Points: Active normal faults subparallel to regional faults are imaged in the upper 20 m of lake sediments in the Laguna del Maule volcanic fieldGrabens within the lake are on trend with magnetic lineations and faults mapped on land, consistent with normal offset focal mechanismsFault‐facilitated localized doming and venting are present near the center of magmatic inflation [ABSTRACT FROM AUTHOR]

The abrupt boundary between accreted terranes and cratonic North America is well exposed along the Salmon River suture zone in western Idaho and eastern Oregon. To constrain the post-suturing deformation of this boundary, we assess the cooling history using zircon and apatite (U-Th)/He thermochronology. Pre-Miocene granitic rocks, along a regional transect, were sampled from accreted terranes of the Blue Mountains Province to cratonic North America (Idaho batholith). Each sample was taken from a known structural position relative to a paleotopographic surface represented by the basal unit of the Miocene Columbia River basalts. An isopach map constructed for the Imnaha Basalt, the basal member of the Columbia River Basalt Group (CRBG), confirms the presence of a Miocene paleocanyon parallel to the northern part of Hells Canyon. The (U-Th)/He zircon dates indicate mostly Cretaceous cooling below 200°C, with the ages getting generally younger from west to east. The (U-Th)/He apatite dates indicate Late Cretaceous-Paleogene cooling, which post-dates tectonism associated with the western Idaho shear zone (WISZ). However, (U-Th)/He apatite dates younger than the Imnaha Basalt, with one date of 3.4 ± 0.6 Ma, occur at the bottom of Hells Canyon. These young (U-Th)/He apatite dates occur along the trend of the Miocene paleocanyon, and cannot be attributed to local exhumation related to faults. We propose that burial ofMesozoic basement rocks by the Columbia River basalts occurred regionally. However, the only samples currently exposed at the Earth's surface that were thermally reset by this burial were at the bottom of the Miocene paleocanyon. If so, exhumation of these samples must have occurred by river incision in the last 4 million years. Thus, the low-temperature thermochronology data record a combination of Late Cretaceous- Paleogene cooling after deformation along the WISZ that structurally overprinted the suture zone and Neogene cooling associated with rapid river incision. [ABSTRACT FROM AUTHOR]

Sketching is a valuable but underutilized tool for science education. Sketch worksheets were developed to help change this, by using artificial intelligence technology to give students immediate feedback and to give instructors assistance in grading. Sketch worksheets use automatically computed visual representations combined with conceptual information to give feedback to students, by computing analogies between students' sketches and an instructor's solution sketch. This enables domain experts to develop sketch worksheets, to facilitate dissemination. We describe our experiences in deploying them in geoscience and artificial intelligence classes. The geoscience worksheets, authored by geoscientists at University of Wisconsin-- Madison, were used at both Wisconsin and Northwestern University. The artificial intelligence worksheets were developed and used at Northwestern. Our experience indicates that sketch worksheets can provide helpful on-thespot feedback to students, and significantly improve grading efficiency, to the point where sketching assignments can be more practical to use broadly in science, technology, engineering, and mathematics education. [ABSTRACT FROM AUTHOR]

We describe a new elastic-kinematic model for the present tectonics of northern Central America and southern Mexico, where the Motagua-Polochic fault zone, Middle America subduction zone and faults in the Central America volcanic arc pose significant seismic hazards. The new model, which consists of the angular velocities for eight plates and blocks, interseismic locking solutions for some of the block-bounding faults and strain-rate tensors for three blocks with significant internal deformation, optimizes the fit to regional fault azimuths and earthquake slip directions and a new 200+ station GPS velocity field that has been corrected for the coseismic and post-seismic effects of three large regional earthquakes in 2009 and 2012. From our new observations and modelling thereof, we find evidence for the following: (1) 13±1 mm yr−1 of ≈E-W stretching between undeformed Caribbean plate in central Honduras and a location ≈50 km west of the Guatemala City graben; (2) accommodation of the above extension via slow W-to-WNW motions of newly defined Chortis and Ipala blocks and distributed ENE-WSW stretching within both blocks; (3) 80 per cent of Chortis-North America plate motion in eastern Guatemala occurs on the Motagua fault versus only 20 per cent on the Polochic fault; (4) Motagua fault slip rates that decrease westwards from 14 ± 1.5 mm yr−1 to 9–10 ± 2 mm yr−1 to less than 2 mm yr−1 in eastern Guatemala, central Guatemala and west of the Guatemala City graben, respectively; (5) Slip rates along Central America volcanic arc faults that decrease from 12.5 ± 1.0 mm yr−1 in Nicaragua to 10 ± 1.3 mm yr−1 in central El Salvador to 7.6 ± 2.1 mm yr−1 on the Jalpatagua fault of southern Guatemala to 2-3 mm yr−1 or less across the volcanic arc west of Guatemala City; (6) a transition near the Mexico–Guatemala border from moderate-to-high locking of the subduction interface offshore from southern Mexico to low locking below the Central America forearc sliver; (7) Subduction of the Cocos plate beneath the Central America forearc sliver up to 10 mm yr−1 faster than and 7–8° clockwise from all previous estimates; (8) 12 ± 6 mm yr−1 of E–W extension across the newly defined Fonseca block. A pattern of misfits to the velocities of sites in northern Guatemala and southern Mexico may be caused by distributed deformation in this region or shortcomings with our model and/or assumptions. The primary factors that control the regional deformation appear to include the arcuate geometry of the Motagua fault, low locking of the Middle America subduction interface, slow-to-no motion between the leading edge of the Central America forearc sliver and North America plate and a rheologically weak volcanic arc. [ABSTRACT FROM AUTHOR]

The physical process of rhyolite segregation from crystal mushes remains elusive as microstructural evidence of conventional segregation mechanisms is not available. This study provides direct fabric evidence for deformation‐assisted segregation of eruptible rhyolite in the Chilean Andean arc. The shallow (<7 km), 6.4–6.2 Ma Huemul pluton comprises domains of quartz monzonite, granite, and high‐silica granite. Compositional modeling shows that rhyolitic melt (high‐silica granite) was extracted from a granitic parent, leaving behind silicic cumulates (quartz monzonite). To understand mechanisms of rhyolite segregation, we investigate magmatic fabrics in the pluton. Anisotropy of Magnetic Susceptibility analyses reveal oblate magnetic fabrics and NNW‐striking, subvertical magnetic foliations throughout Huemul. Within the high‐silica granite, magnetic lineations are subvertical and parallel to elongate miarolitic cavities. Magnetic lineations in the quartz monzonite plunge moderately to the NNW, away from the high‐silica granite. In the quartz monzonite, the Shape‐Preferred Orientation of early feldspars is parallel to the magnetic lineation and developed while suspended in melt. Estimations of early feldspar clustering and crystallinity yield ~38% of interstitial volume loss in the quartz monzonite and no volume loss in the granite. These fabric data suggest ENE tectonic shortening coeval with rhyolite extraction. We explain these observations with a model of tectonic filter pressing in which shortening is accommodated by interstitial melt flow at slow (10−5 km3/yr) rates, segregating moderate volumes of rhyolite in Myr time scales. These interactions link plutonism, tectonic deformation, and upward mobility of eruptible rhyolite in tectonically active margins. Key Points: Granitic fabrics in a silicic pluton show rhyolite segregation, accumulation, and extraction coeval with tectonic shorteningWe interpret that a portion of tectonic shortening is accommodated by displaced interstitial melt, that is, tectonic filter pressingTectonic filter pressing may be the key connecting segregation of rhyolite in volcanic and tectonic time scales in active arcs [ABSTRACT FROM AUTHOR]

Research from cognitive science and geoscience education has shown that sketching can improve spatial thinking skills and facilitate solving spatially complex problems. Yet sketching is rarely implemented in introductory geosciences courses, due to time needed to grade sketches and lack of materials that incorporate cognitive science research. Here, we report a design-centered, collaborative effort, between geoscientists, cognitive scientists, and artificial intelligence ( AI) researchers, to characterize spatial learning challenges in geoscience and to design sketch activities that use a sketch-understanding program, CogSketch. We developed 26 CogSketch worksheets that use cognitive science-based principles to scaffold problem solving of spatially complex geoscience problems and report observations of an implementation in an introductory geoscience course where students used CogSketch or human-graded paper worksheets. Overall, this research highlights the principles of interdisciplinary design between cognitive scientists, geoscientists, and AI researchers that can inform the collaborative design process for others aiming to develop effective educational materials. [ABSTRACT FROM AUTHOR]

This study documents the geochemical heterogeneity introduced into mantle lithosphere at the onset of subduction, where an essentially homogeneous mantle asthenosphere is converted into a compositionally heterogeneous mantle lithosphere as a result of increasingly focused melt ascent at shallower levels. We report field observations and geochemical results from the Red Hills ultramafic massif, part of the Dun Mountain ophiolite belt of New Zealand. In the east, the Red Hills massif contains geochemically homogeneous harzburgites (Two Tarns Harzburgite). On its western and southern edge, the harzburgites are overprinted by a petrologically zoned sequence of foliated plagioclase lherzolite and plagioclase harzburgite on the periphery (Plagioclase Zone), and banded harzburgite and dunite (Plateau Complex) in the interior. The various lithological units of the Red Hills massif are interpreted to have formed as a result of a polygenetic, multi-stage melting and refertilization history. The Two Tarns Harzburgite is interpreted to record c. 10-15% melting in the garnet stability field followed by an additional 10% melting in the spinel stability field. Early garnet field melting is defined as Stage 1, and probably occurred in a mid-ocean ridge setting in a relatively reduced environment of around log fO2 (ΔFMQ) -1.5 (where FMQ is the fayalite-magnetite-quartz buffer) or lower. Stage 2 is defined as spinel field melting and melt interaction. Melt interaction trends for Stage 2 indicate that Stage 2 melts were relatively oxidized, at around log fO2 (ΔFMQ) +1, and boninitic in composition, suggesting a forearc subduction initiation setting for Stage 2. In the western massif, later Stage 3 melts petrologically overprinted rocks once part of the Two Tarns Harzburgite. The plagioclase-rich contact (Plagioclase Zone) between the Two Tarns Harzburgite and the Plateau Complex is interpreted to represent a refertilization front between the Two Tarns Harzburgite and an upper mantle melt transport network (Plateau Complex; Stage 3), where melts became focused into kilometer-scale conduits at shallow depths in the plagioclase stability field. Highly anorthitic plagioclase suggests that Stage 3 melts were also associated with a forearc, subduction-zone setting. Within the Stage 3 melt network, pervasive major element and cryptocrystalline metasomatism altered peridotite originally similar to the Two Tarns Harzburgite. Our results indicate that pulses of pervasively migrating melts (Stage 2) rose and were focused into narrower conduits (Stage 3) towards the surface in a forearc suprasubduction-zone setting. Because shallow melt migration is localized into narrow zones, a significant percentage of the mantle lithosphere in forearcs may be relict from earlier pervasive mid-ocean ridge melting or deeper forearc melting, as seen in the Red Hills. [ABSTRACT FROM AUTHOR]

Capturing the nature of students' mental representations and how they change with learning is a primary goal in science education research. This can be challenging in spatially intense domains, such as geoscience, architecture, and engineering. In this research, we test whether sketching can be used to gauge level of expertise in geoscience, using new technology designed to facilitate this process. We asked participants with differing levels of geoscience experience to copy two kinds of geoscience images-photographs of rock formations and causal diagrams. To permit studying the process of sketching as well as the structure and content of the sketches, we used the CogSketch system (Forbus et al. , Topics in Cognitive Science 3:648-666) to record the time course of sketching and analyze the sketches themselves. Relative to novices, geoscience students included more geological structures and relational symbols in their sketches of geoscience materials and were more likely to construct their sketches in a sequence consistent with the order of causal events. These differences appear to stem from differences in domain knowledge, because they did not show up in participants' sketches of materials from other fields. The findings and methods of this research suggest new ways to promote and assess science learning, which are well suited to the visual-spatial demands of many domains. [ABSTRACT FROM AUTHOR]

Spatial thinking skills are critical to success in many subdisciplines of the geosciences. We tested students' spatial skills in geoscience courses at three institutions (a public research university, a comprehensive university, and a liberal arts college, all in the midwest) over a two-year period. We administered standard psychometric tests of spatial skills to students in introductory geology, mineralogy, sedimentology and stratigraphy, hydrogeology, structural geology, and tectonics courses. In addition, in some courses we administered a related spatial skills test with geoscience content. In both introductory and upper level undergraduate geology courses, students' skills vary enormously as measured by several spatial thinking instruments. Additionally, students' spatial skills generally improve only slightly during one academic term, in both introductory and advanced geoscience classes. More unexpectedly, while there was a tendency for high-performing students to be adept at multiple spatial skills, many individual students showed strong performance on tests of one spatial skill (e.g., rotation) but not on others (e.g., penetrative thinking). This result supports the contention that spatial problem solving requires a suite of spatial skills, and no single test is a good predictor of "spatial thinking." [ABSTRACT FROM AUTHOR]

Cognitive science has primarily studied the mental simulation of spatial transformations with tests that focus on rigid transformations (e.g., mental rotation). However, the events of our world are not limited to rigid body movements. Objects can undergo complex non-rigid discontinuous and continuous changes, such as bending and breaking. We developed a new task to assess mental visualization of non-rigid transformations. The Non-rigid Bending test required participants to visualize a continuous non-rigid transformation applied to an array of objects by asking simple spatial questions about the position of two forms on a bent transparent sheet of plastic. Participants were to judge the relative position of the forms when the sheet was unbent. To study the cognitive skills needed to visualize rigid and non-rigid events, we employed four tests of mental transformations-the Non-rigid Bending test (a test of continuous non-rigid mental transformation), the Paper Folding test and the Mental Brittle Transformation test (two tests of non-rigid mental transformation with local rigid transformations), and the Vandenberg and Kuse (Percept Motor Skills 47:599-604, ) Mental Rotation test (a test of rigid mental transformation). Performance on the Mental Brittle Transformation test and the Paper Folding test independently predicted performance on the Non-rigid Bending test and performance on the Mental Rotation test; however, mental rotation performance was not a unique predictor of mental bending performance. Results are consistent with separable skills for rigid and non-rigid mental simulation and illustrate the value of an ecological approach to the analysis of the structure of spatial thinking. [ABSTRACT FROM AUTHOR]

The Idaho batholith and spatially overlapping Challis intrusive province in the North American Cordillera have a history of magmatism spanning some 55 Myr. New isotopic data from the ∼98 Ma to 54 Ma Idaho batholith and ∼51 Ma to 43 Ma Challis intrusions, coupled with recent geochronological work, provide insights into the evolution of magmatism in the Idaho segment of the Cordillera. Nd and Hf isotopes show clear shifts towards more evolved compositions through the batholith's history and Pb isotopes define distinct fields correlative with the different age and compositionally defined suites of the batholith, whereas the Sr isotopic compositions of the various suites largely overlap. The subsequent Challis magmatism shows the full range of isotopic compositions seen in the batholith. These data suggest that the early suites of metaluminous magmatism (98–87 Ma) represent crust–mantle hybrids. Subsequent voluminous Atlanta peraluminous suite magmatism (83–67 Ma) results primarily from melting of different crustal components. This can be attributed to crustal thickening, resulting from either subduction processes or an outboard terrane collision. A later, smaller crustal melting episode, in the northern Idaho batholith, resulted in the Bitterroot peraluminous suite (66–54 Ma) and tapped different crustal sources. Subsequent Challis magmatism was derived from both crust and mantle sources and corresponds to extensional collapse of the over-thickened crust. [ABSTRACT FROM PUBLISHER]

Mount Hay ridge, Arunta Region, central Australia, exposes a 10 km scale, antiformal sheath fold formed in the deep crust (P ≈ 0.6-0.9 GPa) in Proterozoic time. Tilting and exhumation during the Devonian Alice Springs orogeny resulted in an oblique cross section, such that the once subhorizontal sheath fold now has a moderately dipping, gently folded axial plane and overturned southern limb. Fabric types (e.g., S = L, L > S) were mapped in the field, and finite strain data were collected from a widely distributed gabbroic granulite unit. Fabric and finite strain data sets exhibit remarkable correspondence and confirm the common assumption that fabric type is directly related to finite strain type for deep crustal rocks. Both data sets reveal a distinct pattern of oblate strain on fold limbs grading into prolate strain in the fold hinge. There is no field evidence for significant strain localization, and measured strain magnitudes are consistent across the fold. Thus, we infer that different structural domains record different though coeval strain paths and that strain compatibility was maintained across domain boundaries. The uniformity of foliation, lineation, and mesoscale fold orientations across Mount Hay and the consistent magnitude of maximum stretch across structural domains indicate that the sheath fold and subsidiary structures formed during a single, progressive deformational event. Based on its geometry, the inferred scale of the enclosing shear zone (≥8 km in thickness), and regional tectonic correlations, we infer that the Mount Hay sheath fold formed in a subhorizontal, crustal-scale flow zone during the Paleoproterozoic Strangways orogeny (1740-1690 Ma). The record of deformation is consistent with fold formation either on one side of a channel or through detachment flow. [ABSTRACT FROM AUTHOR]

In the Twin Sisters ultramafic massif, NW Washington, an ∼0·5 cm thick, isolated ultramafic ultramylonitic shear zone displaces orthopyroxenite and clinopyroxenite dikes, by a minimum of 21 cm. The shear zone exists only adjacent to the orthopyroxenite and clinopyroxenite dikes, with deformation distributed along strike into the wall-rock less than 10 cm from the dikes in the outcrop face. Microstructurally, the shear zone contains domains of different grain sizes and phase proportions. A marginal domain of almost pure olivine displays a mean grain size of ∼30–100 μm and an olivine lattice preferred orientation (LPO) indicating that glide occurred on (010)[100] and (010)[001]. A central domain of mixed olivine, pyroxene and amphibole displays a finer grain size, ranging down to ∼5 μm. Aligned grain and phase boundaries and weak olivine and pyroxene LPOs indicate that this zone deformed by a grain-size-sensitive deformation mechanism (e.g. grain boundary sliding accompanied by diffusion creep). Geothermometry indicates that shearing occurred at temperatures in the range 650–750°C. We interpret the formation of this ultramylonitic shear zone as a shear instability caused by the presence of compositional heterogeneity. Localization was promoted by a deformation mechanism switch from dislocation creep to grain-size-sensitive creep as a result of syn-deformational grain-size reduction. Mineral compositions indicate that this grain-size reduction was associated with reaction. The fine grain size was stabilized by the presence of multiple phases, particularly pyroxene, within the central shear zone domain. The shear zone did not propagate beyond the vicinity of the pyroxenite dikes because the fine grain sizes necessary for the deformation mechanism switch to occur could not be maintained in the monophase olivine forming the surrounding dunite. [ABSTRACT FROM PUBLISHER]

Geoscience instructors and textbooks rely on analogy for teaching students a wide range of content, from the most basic concepts to highly complicated systems. The goal of this paper is to connect educational and cognitive science research on analogical thinking with issues of geoscience instruction. Analogies convey that the same basic relationships hold in two different examples. In cognitive science, analogical comparison is understood as the process by which a person processes an analogy. We use a cognitive framework for analogy to discuss what makes an effective analogy, the various forms of analogical comparison used in instruction, and the ways that analogical thinking can be supported. Challenges and limitations in using analogy are also discussed, along with suggestions about how these limitations can be addressed to better guide instruction. We end with recommendations about the use of analogy for instruction, and for future research on analogy as it relates to geoscience learning. [ABSTRACT FROM AUTHOR]

This paper describes three mid-Tertiary intrusions from the Henry Mountains (Utah, USA) that were assembled from amalgamation of multiple horizontal sheet-like magma pulses in the absence of regional deformation. The three-dimensional intrusion geometries are exceptionally well preserved and include: (1) a highly lobate sill; (2) a laccolith; and (3) a bysmalith (a cylindrical, fault-bounded, piston-like laccolith). Individual intrusive sheets are recognised on the margins of the bodies by stacked lobate contacts, and within the intrusions by both intercalated sedimentary wallrock and formation of solid-state fabrics. Finally, conduits feeding these intrusions were mostly sub-horizontal and pipe-like, as determined by both direct observation and modelling of geophysical data.%The intrusion geometries, in aggregate, are interpreted to reflect the time evolution of an idealised upper crustal pluton. These intrusions initiate as sills, evolve into laccoliths, and eventually become piston-like bysmaliths. The emplacement of multiple magma sheets was rapid and pulsed; the largest intrusion was assembled in less than 100 years. The magmatic fabrics are interpreted as recording the internal flow of the sheets preserved by fast cooling rates in the upper crust. Because there are multiple magma sheets, fabrics may vary vertically as different sheets are traversed. These bodies provide unambiguous evidence that some intrusions are emplaced in multiple pulses, and that igneous assembly can be highly heterogeneous in both space and time. The features diagnostic of pulsed assembly observed in these small intrusions can be easily destroyed in larger plutons, particularly in tectonically active regions. [ABSTRACT FROM PUBLISHER]

We present results from a natural deformed shear zone in the Turon de Técouère massif of the French Pyrenees that directly addresses the processes involved in strain localization, a topic that has been investigated for the last 40 years by structural geologists. Paleopiezometry indicates that differential stresses are variable both spatially across the zone, and temporally during exhumation. We have, however, also calculated strain rate, which remains constant despite changes in stress. This result appears to be at odds with recent experimental deformation on monophase (olivine) rocks, which indicate that strain localization occurs dominantly as a result of constant stress. We hypothesize that in the Turon de Técouère massif—and many natural shear zones—strain localization occurs as a result of reactions, which decrease the grain size and promote the activation of grain size sensitive deformation mechanisms. From a tectonics perspective, this study indicates that the deformation rate in a particular plate boundary is relatively uniform. Stress, however, varies to accommodate this deformation. This viewpoint is consistent with deformation at a plate boundary, but it is not the typical way in which we interpret strain localization. [ABSTRACT FROM AUTHOR]

The Rock Springs uplift of Wyoming and the Douglas Creek arch of Colorado are intrabasinal, Laramide-age basement uplifts within the Rocky Mountain foreland, and are currently separated by the east-west-trending Uinta Mountains. The geometry, timing, and progressive development of these uplifts were investigated using a combined geophysical and geological approach. New gravity surveys were combined with existing regional data to provide a regional Bouguer gravity anomaly map of these two uplifts and the intervening Uinta uplift. The gravity data show a distinct and continuous north south-striking gravity high along the trend of the two uplifts that crosses the east-west-trending Uinta uplift. The relatively constant amplitude (∼40 mGal) of the gravity anomaly indicates that the inferred basement relief is similar for both arches (∼4 km). Sedimentation patterns indicate that the Rock Springs uplift and Douglas Creek arch formed simultaneously in the Late Cretaceous. The intrabasinal setting of the uplifts records aspects of foreland deformation that are overprinted or obscured in better-developed uplifts. On the local scale, neither the Rock Springs or Douglas Creek uplift apparently reactivates a pre-existing structure. On a regional scale, there is no change in structural style or timing of the two uplifts, despite their formation in different crustal provinces. The Rock Springs uplift occurs within the Archean Wyoming province north of the Cheyenne belt, whereas the Douglas Creek arch occurs in Proterozoic crust south of this boundary. Timing relations, available floor the basinal stratigraphy, indicate the uplifts were initiated as broad arches in the Late Cretaceous before developing into more concentrated uplifts. Thus, large-scale folding, and not reactivation of pre-existing structures, may be the primary control on the initial pattern of north- to northwest-trending foreland deformation. [ABSTRACT FROM AUTHOR]

Most rocks contain both ferromagnetic and paramagnetic minerals that contribute to their bulk magnetic susceptibility and the anisotropy of magnetic susceptibility. Anisotropy of magnetic susceptibility techniques typically measure the net susceptibility and are not able to separate paramagnetic and ferromagnetic contributions. Since different minerals may form at various times and/or under different conditions, examination of their individual contributions provides unique information related to the rock's formation and evolution. By subjecting a sample to high magnetic fields, the ferromagnetic minerals become saturated and the contribution of the paramagnetic minerals can be evaluated (the slope of the line at high field values, on a field vs magnetization plot). Using this approach, we developed a new technique that separates the ferromagnetic and paramagnetic components of standard I inch cylindrical samples using a Vibrating Sample Magnetometer. This separation is tested by artificially combining separate samples with known paramagnetic-only and ferromagnetic-only behaviour. By comparing the high-field results of a combined paramagnetic and ferromagnetic signal to the classic low field alternating current susceptibility of the paramagnetic-only signal, we demonstrate that the high field anisotropy is the result solely of the paramagnetic fabric even when the low field anisotropy of magnetic susceptibility is dominated by the ferromagnetic minerals. A ferromagnetic-only fabric is calculated for the combined paramagnetic and ferromagnetic rock, by tensor subtraction of the high field (paramagnetic-only) and low field (paramagnetic plus ferromagnetic) measurements on the same sample. Application of this technique to natural samples of combined paramagnetic and ferromagnetic behaviour is discussed. [ABSTRACT FROM AUTHOR]

Explores the relationship between crustal finite strain and seismic anisotropy in the mantle of the Pacific-Australia plate boundary zone in South Island, New Zealand. Distribution of the dextral shear between the Pacific and Australian plates in the Cenozoic; Broad coupling of the lithospheric mantle and upper crustal deformation; Characterization of the infinitesimal displacement field.

Foreland deformation, in the form of arches or uplifts, occurred throughout the eastern Rocky Mountains region during the Laramide orogeny (75-50 Ma). Arches with the same structural style developed in the mid-continent region, east of the Rocky Mountains, although these were subsequently buried by Tertiary sedimentary rocks. We attribute deformation in the Rocky Mountain foreland and continental interior to folding of the entire lithosphere (lithospheric buckling) as a result of horizontal endload on the western edge of North America. The observed wavelength of arches in the western United States is ca. 190 kin, a spacing consistent with a lithospheric buckling interpretation. This buckling model provides a mechanical explanation for the distinction between "thin-skinned" Sevier-style and "thick-skinned" Laramide-style deformation, which depends respectively upon the decoupling or coupling of lithospheric layers. Additionally, the buckling model explains concurrent tectonism east of the Rocky Mountains during Late Cretaceous time. Dextral shearing within the block uplifts indicates that the deformation was broadly transpressional during the Laramide orogeny. [ABSTRACT FROM AUTHOR]

Presents evidence of dextral transpression during the youngest magmatism in the Sierra Nevada, California magmatic arc. Analysis of geological data from the Rosy Finch shear zone (RFSZ); Mapped extent of the dextral Rosy Finch shear zone; Stereonets of shear bands and lineation orientations within RFSZ; Structures within the RFSZ in the Mono Creek granite.