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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]

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 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]

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]

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.