Search

We present the results of remote sensing analysis of U.S. Geological Survey digital elevation models, Landsat spectral data, and National Agriculture Imagery Program orthophotos to generate a preliminary geologic map that significantly aided our boots-on-the-ground geologic mapping of the southwest portion of the Three Peaks 7.5ʹ quadrangle in southwest Utah. Sedimentary rocks, intrusive rocks, and a variety of geologic contacts, including unconformities and faults, as well as unconsolidated alluvium are recognized in the study area. We constructed a series of geologic maps using remote sensing data and analysis techniques that are readily available to geoscientists. These techniques include band-ratioing, random forest analysis, and these analyses. Resolution of the resulting geologic maps generated by random forest analysis and principal component analysis were greatly improved by incorporating both the high resolution orthophoto and the 1/3 arc second digital elevation model into the principal component analysis. Our final remotely sensed geologic map integrated results from each technique. We used this remotely sensed geologic map to develop our preliminary plan for the field campaign. We preselected high priority targets (e.g., previously unrecognized units and faults) for in-person field analysis. We also identified highly accessible areas that allowed for efficient use of in-person field time needed for evaluation of large areas covered by relatively homogeneous units. The authors spent 25 days in the field over a seven-week field season, mapping the same area. Here, we compare the remote-sensed geologic maps with the final in-person field checked geologic map and discuss the utility of remote sensing data for detailed geologic field investigations. Preparing a remote sensing geologic map prior to field work has several advantages, including identification of mappable units, recognition of geologic contacts, and selection of priority target areas for direct evaluation of hypothesized field relationships, thereby promoting more efficient geologic mapping.

The temporal and spatial distribution of strain associated with the Sevier orogeny in western North America is significantly different in the southern end of the belt, at the latitude of Las Vegas, Nevada, than farther to the north at the latitude of Salt Lake City, Utah. Reasons for these differences have been speculative as a lack of temporal constraints on thrusting in the intervening region hindered along-strike correlation across the belt. We determined a crystallization age of 100.18 ± 0.04 Ma for zircons extracted from a recently recognized dacite lapilli ash-fall tuff near the base of the synorogenic Iron Springs Formation. We propose the name “Three Peaks Tuff Member” for this unit, and identify a type stratigraphic section on the western flank of the “Three Peaks,” a topographic landmark in Iron County, Utah. Field relationships and this age constrain movement on the Iron Springs thrust and the end of the sub-Cretaceous unconformity in the critical intervening area to latest Albian/earliest Cenomanian. Movement on the Iron Springs thrust was synchronous with movement on multiple Sevier thrusts at ~100 Ma, indicating that the mid-Cretaceous was a period of extensive thrust-fault movement. This mid-Cretaceous thrusting event coincided with a period of global plate reorganization and increased convergence, and hence an increased subduction rate for the Farallon Plate beneath North America. The accelerated subduction contributed to a Cordilleran arc flare-up event and steepening of the orogenic wedge, which triggered widespread thrusting across the retroarc Sevier deformation belts. Additionally, based on temporal constraints and the strong spatial connection of mid-Cretaceous thrusts to lineaments interpreted as pre-orogenic transform faults, we suggest that temporal and spatial variations along the strike of the orogenic belt reflect tectonic inheritance of basement structures associated with the edge of the rifted Precambrian craton.

Reliance on π-diagrams and tangent plots to describe fold geometry has created an unwarranted status for conical folds at the expense of periclines. Analysis of virtual periclines using synthetic stereograms, tangent diagrams, and geologic curvature analysis demonstrates small portions of periclines are “cylindrical.” The more significant “non-cylindrical” portion of periclines allows for a mathematically permissible, but unrealistic, geometrical representation as portions of cones. We demonstrate cones are an extremely poor geometric representation of both the virtual periclines and examples of natural non-cylindrical folds. “Conical folds,” if they exist, terminate at a point; the amplitude to width ratio and the plunge of the crestal line must remain constant towards the fold terminus, with a Gaussian curvature of zero. In contrast, the amplitude to width ratio, plunge along the crestal line, and Gaussian curvature of periclines vary towards the fold terminus. These differences have important implications for the rheological modeling of folds, and while realistic dynamic models for periclines exist, models for conical fold formation remain conceptual. We suggest that in order to advance our understanding of how folds form, it may be “pointless” to continue the misconception of conical folds as an accurate geometric representation of how folds end.

Graphical abstract, High-resolution visualization of surfaces of geologic interest, at a multitude of scales, using 3D point cloud technologies provides an opportunity to analyze spatial relationships of surfaces using orientation data. We present a MATLAB® script that produces planar geologic attitude data (e.g., strike, dip, and dip-direction data) from 3D datasets (e.g., point clouds, 3D scanning). The method utilizes Cartesian coordinates of triangular planar surfaces and converts them into matrices of conventional geologic attitude data. Spatial relationships among data points can be investigated, using polar tangent diagrams, stereographic analysis, or geologic curvature analysis. We utilize this script to create “synthetic” graphical plots (e.g., stereograms, tangent diagrams) from geomechanically realistic, virtual, folded surfaces produced by dynamic modeling. Synthetic graphical diagrams are of considerable usefulness in interpreting graphical plots (e.g., stereograms) of attitude data from natural folded rock surfaces, particularly in locations with poor exposure. • This script outputs attitude data (strike, dip, and dip direction) in a spreadsheet and as a text file for use in other visualization software. • A tangent diagram is created and displayed in this script for rapid visualization and fold shape assessment. • The MATLAB script is readily modified to accept multiple data formats for input (e.g., MATLAB variables, *.csv files, etc.) and output (e.g., *.csv files, *.txt files, etc.).

The characterization of folds is often limited to two-dimensional cross-sectional views where folds are approximated as cylindrical. This enables simplification of fold shape analysis (using principles such as dip isogons, stereographs, tangent diagrams, and Bezier curve analysis), allows for a simplified analysis of the distribution of stress and strain, and enables and the analysis and visualization of folding associated fractures. However, in a heterogenous medium folds have to terminate somewhere, resulting in more complex three-dimensional geometries. In this study, a 3D finite element modeling approach using a Maxwell visco-elastic rheology is utilized to simulate 3D periclinal folds resulting from single layer buckle folding. With respect to fold shape analysis, we use the forward modeled pericline geometries to demonstrate that geometrical attitude data collected for various cross sections and plotted using traditional 2D methods such as stereographs and tangent diagrams may lead to the misinterpretation of the fold shape as conical. In contrast 3D geometric data such as Gaussian curvature can describe and quantify the 3D fold geometry in its entirety. With respect to folding associated fracture analysis, the 3D modeling results show that shear fractures of various orientations in the fold limb, which cannot be intuitively explained by the strain/stress regimes during 2D buckling and require unrealistic boundary conditions, are feasible to occur during a single deformation event during the development of a pericline. In summary, accounting for the true 3D geometry of buckle fold structures will lead to a better classification of folds, a better understanding of the processes and parameters affecting their development, and enable post-folding failure analysis.

In the southeast Western Desert of Egypt, a prominent set of E-W faults and co-located domes and basins involve sedimentary cover rock as young as the early Eocene. Although earlier Mesozoic slip on faults in southern Egypt has been widely mentioned in the literature and attributed to repeated reactivation of basement faults, evidence is indirect and based on the idea that regional stresses associated with tectonic events in the Syrian Arc would likely have reactivated basement faults in south Egypt in dextral strike slip during the Mesozoic as well as the Cenozoic. Here, we present direct evidence from the rock record for the sequence of development of features along these faults. Southwest of Aswan, a small structural dome in Mesozoic Nubia facies rocks occurs where the Seiyal Fault bends northward from west to east. The dome is cut by strands of the Seiyal Fault and a related set of cataclastic deformation bands showing dominantly right lateral strike slip, as well as by younger calcite veins with related patchy poikilotopic cement. High resolution satellite image analysis of the remote southwest Kharga Valley shows a similar sequence of events: older structural domes and basins located where E-W faults bend northward from west to east, right lateral offset of domes and basins along the E-W faults, and two sets of deformation band faults that lack co-located domes and basins. We suggest that field data, image analysis, and burial depth estimates are best explained by diachronous development of features along the E-W fault system. We propose that Late Mesozoic right lateral strike slip produced domes and basins in Nubia facies rocks in stepover regions above reactivated basement faults. We further suggest that the extensively linked segments of the E-W fault system in Nubia facies rocks, plus the deformation band systems, formed during the late Eocene when basement faults were again reactivated in dominantly right lateral strike slip.

The Jefferson Lab 12 GeV Upgrade in Hall B will need CLAS12 detector that requires two superconducting magnets. One is a magnet system consisting of six superconducting trapezoidal racetrack-type coils assembled in a Toroidal configuration (Torus) and the second is an actively shielded solenoidal magnet (Solenoid). Both the torus and solenoid are located in close proximity to one another and are surrounded by sensitive detectors. This paper investigates the electromagnetic interactions between the two systems during normal operation as well as during various fault scenarios as part of a Risk Assessment and Mitigation (RAM).

Although polygonal fault systems and related features are common in fine-grained sediments in modern submarine basins and have been studied in basins worldwide using three-dimensional (3-D) seismic data, extensive on-land exposures have remained elusive. We report here on the discovery of a polygonal fault system occurring in nearly continuous surface exposure over ∼900 km 2 in chalk of the Cretaceous Khoman Formation near Farafra Oasis, Egypt. Field exposures reveal polygon boundaries defined by clusters of dozens of normal faults with strongly grooved fault surfaces and coarse calcite veins along faults with evidence for multiple fluid flow events. Geometric patterns and fault intersections reveal that mechanically interacting normal faults with multiple orientations were active contemporaneously in a horizontal strain field that was essentially isotropic and extensional. We interpret the very steep dips (∼80°) to reflect fault initiation in response to elevated pore fluid pressures. In the uppermost part of the Khoman Formation, a terrain of isolated circular structures displaying shallow inward dips overlies the polygonal fault network. The spatial relationship to the underlying faults is consistent with these small circular basins having formed as fluid escape structures as the polygonal fault system evolved. Outcrops in the Khoman Formation provide an unprecedented look into the 3-D geometry of a polygonal fault system, providing context for the analysis of analogous systems in marine basins and other on-land exposures.

The isotopic composition of lead (Pb) in fugitive dust suspended by a vehicle from 13 unsurfaced roads in Missouri was measured to identify the source of Pb within an established long-term mining area. A three end-member model using 207 Pb/ 206 Pb and concentration as tracers resulted in fugitive dust samples plotting in the mixing field of well characterized heterogeneous end members. End members selected for this investigation include the 207 Pb/ 206 Pb for 1) a Pb-mixture representing mine tailings, 2) aerosol Pb-impacted soils within close proximity to the Buick secondary recycling smelter, and 3) an average of soils, rock cores and drill cuttings representing the background conditions. Aqua regia total concentrations and 207 Pb/ 206 Pb of mining area dust suggest that 35.4–84.3% of the source Pb in dust is associated with the mine tailings mixture, 9.1–52.7% is associated with the smelter mixture, and 0–21.6% is associated with background materials. Isotope ratios varied minimally within the operational phases of sequential extraction suggesting that mixing of all three Pb mixtures occurs throughout. Labile forms of Pb were attributed to all three end members. The extractable carbonate phase had as much as 96.6% of the total concentration associated with mine tailings, 51.8% associated with smelter deposition, and 34.2% with background. The next most labile geochemical phase (Fe + Mn Oxides) showed similar results with as much as 85.3% associated with mine tailings, 56.8% associated with smelter deposition, and 4.2% associated with the background soil.

Aeromagnetic and gravity data collected across the Okavango rift zone, northwest Botswana are used to map the distribution of faults, provide insights into the two-dimensional shallow subsurface geometry of the rift, and evaluate models for basin formation as well as the role of pre-existing basement fabric on the development of this nascent continental rift. The structural fabric (fold axes and foliation) of the Proterozoic basement terrane is clearly imaged on both gravity and magnetic maps. The strike of rift-related faults (030–050° in the north and 060–070° in the south) parallels fold axes and the prominent foliation directions of the basement rocks. These pre-existing fabrics and structures represent a significant strength anisotropy that controlled the orientation of younger brittle faults within the stress regime present during initiation of this rift. Northwest dipping faults consistently exhibit greater displacements than southeast dipping faults, suggesting a developing half-graben geometry for this rift zone. However, the absence of fully developed half-grabens along this rift zone suggests that the border fault system is not fully developed consistent with the infancy of rifting. Three en-echelon northeast trending depocenters coincide with structural grabens that define the Okavango rift zone. Along the southeastern boundary of the rift, developing border faults define a 50 km wide zone of subsidence within a larger 150 km wide zone of extension forming a rift-in-rift structure. We infer from this observation that the localization of strain resulting from extension is occurring mostly along the southeastern boundary where the border fault system is being initiated, underscoring the important role of border faults in accommodating strain even during this early stage of rift development. We conclude that incipient rift zones may provide critical insights into the development of rift basins during the earliest stages of continental rifting.

The Devonian Deer Isle granite complex, Penobscot Bay, Maine, exhibits complex and highly diverse textures of minerals and rocks that are the result of thermal perturbations related to injections of new magma during the crystallization history of the pluton. The pluton-wide systematic spatial variation in the abundance of minerals, plagioclase-mantled alkali feldspar, schlieren, enclaves, and rock textures allows us to define four facies. Their spatial distribution across the Deer Isle granite complex reflects crystallization within a zoned magma-chamber. Lithological and textural variations were produced by a combination of the open-system behavior and crystal–melt fractionation during evolution of the magma chamber. The Flye Point and Oak Point facies are basal cumulates formed by crystal accumulation during emplacement and growth of the chamber. Both subsequently matured by compaction and filter pressing of residual melts. The transition from the relatively static cumulate-rich base into a dynamic magmatic flow regime is preserved by the texturally variable Settlement Quarry facies. The overlying leucocratic Crotch Island facies represents an evolved felsic cap that was modified by addition of low-density melts derived from the growing pile of cumulates. The decreasing abundance of mafic enclaves from the Flye Point facies toward the Crotch Island facies indicates that the importance of replenishments of mafic magma, in terms of adding heat and material to the chamber, waned during crystallization. As crystallization proceeded, convection ceased and texturally distinct granite domains were preserved.

Large facial tissue defects are traditionally treated with staged conventional reconstruction. Facial allograft transplantation has emerged as a treatment modality. Facial allografts are procured from a dead donor and transplanted to the recipient. Recipients are then subjected to lifelong global immunosuppression to prevent immunologic rejection. This study analyzes the cost of facial allograft transplantation in comparison with conventional reconstruction.Hospital billing records from facial allograft transplantation (2009 to 2011) and conventional reconstruction (2000 to 2010) patients were compiled. Comparative 1-year costs were calculated, segregated by physician, hospital, and hospital's department costs. Because most conventional reconstruction patients had smaller facial deficits than their facial allograft transplantation counterparts, regression models were used to estimate costs of conventional reconstruction for full facial defects, mirroring the facial transplantation cohort. All costs were adjusted using the medical consumer price index.One-year costs for facial allograft transplantation were significantly higher than those for conventional reconstruction (mean/median, $337,360/$313,068 versus $70,230/$64,451, respectively). One-year costs for a hypothetical full-face conventional reconstruction were $184,061 (95 percent CI, $89,358 to $278,763). The per-patient cost in a hypothetical cohort of conventional reconstruction patients with deficits identical to four facial allograft transplantation recipients was $155,475 (95 percent CI, $69,021 to $241,929).Initial cost comparison portrays facial allograft transplantation as significantly more costly than conventional reconstruction. However, after adjustments for case severity, the cost profiles are similar. Gains in efficiency and experience are expected to lower costs. Additional unmeasured benefits may also positively influence the cost-to-benefit ratio of facial allograft transplantation.

A-type felsic magmatism associated with the Cambrian Southern Oklahoma Aulacogen began with eruption of voluminous rhyolite to form a thick volcanic carapace on top of an eroded layered mafic complex. This angular unconformity became a crustal magma trap and was the locus for emplacement of later subvolcanic plutons. Rising felsic magma batches ponding along this crustal magma trap crystallised first as fine-grained granite sheets and then subsequently as coarser-grained granite sheets. Aplite dykes, pegmatite dykes and porphyries are common within the younger coarser-grained granite sheets but rare to absent within the older fine-grained granite sheets. The older fine-grained granite sheets typically contain abundant granophyre.The differences between fine-grained and coarse-grained granite sheets can largely be attributed to a progressive increase in the depth of the crustal magma trap as the aulacogen evolved. At low pressures (2O in felsic magmas. This is a direct consequence of the shape of the H2O-saturated granite solidus. The effect of this slight increase in total pressure on the crystallisation of felsic magmas is to delay vapour saturation, increase the H2O content of the residual melt fractions and further depress the solidus temperature. Higher melt H2O contents, and an extended temperature range over which crystallisation can proceed, both favour crystallisation of coarser-grained granites. In addition, the potential for the development of late, H2O-rich, melt fractions is significantly enhanced. Upon reaching vapour saturation, these late melt fractions are likely to form porphyries, aplite dykes and pegmatite dykes.For the Southern Oklahoma Aulacogen, the progressive increase in the depth of the crustal magma trap at the base of the volcanic pile appears to reflect thickening of the volcanic pile during rifting, but may also reflect emplacement of earlier granite sheets. Thus, the change in textural characteristics of granite sheets of the Wichita Granite Group may hold considerable promise as an avenue for further investigation in interpreting the history of this rifting event.

The level of emplacement and final form of felsic and mafic igneous rocks of the Wichita Mountains Igneous Province, southwestern Oklahoma, U.S.A. are discussed in light of magma driving pressure, lithostatic load, and crustal magma traps. Deposition of voluminous A-type rhyolites upon an eroded gabbroic substrate formed a subhorizontal strength anisotropy that acted as a crustal magma trap for subsequent rising felsic and mafic magma. Intruded along this crustal magma trap are the A-type sheet granites (length/thickness 100:1) of the Wichita Granite Group, of which the Mount Scott Granite sheet is typical, and smaller plutons of biotite bearing Roosevelt Gabbro. In marked contrast to the subhorizontal granite sheets, the gabbro plutons form more equant stocks with flat roofs and steep side walls. Late Diabase dikes cross-cut all other units, but accompanying basaltic flows are extremely rare in the volcanic pile. Based on magmastatic calculations, we draw the following conclusions concerning the level of emplacement and the shape of these intrusions. (1) Magma can rise to a depth at which the magma driving pressure becomes negligible. Magma that maintains a positive driving pressure at the surface has the potential to erupt. (2) Magma ascent may be arrested at a deeper level in the crust by a subhorizontal strength anisotropy (i.e. crustal magma trap) if the magma driving pressure is greater than or equal to the lithostatic load at the depth of the subhorizontal strength anisotropy. (3) Subhorizontal sheet-intrusions form along crustal magma traps when the magma driving pressure greatly exceeds the lithostatic load. Under such conditions, the magma driving pressure is sufficent to lift the overburden to create the necessary space for the intrusion. (4) Thicker steep-sided stocks or batholiths, with flat roofs, form at crustal magma traps when the magma driving pressure approximates that of the lithostatic load. Under these conditions, the necessary space for the intrusion must be created by other mechanisms (e.g. stoping). (5) Subvertical sheets (i.e. dikes) form when the magma driving pressure is less than the lithostatic load at the level of emplacement.

Petrological investigations of granite commonly reveal multiple periods of growth punctuated by resorption for many of the constituent minerals. Complementary to such textures are mineral compositional heterogeneity manifested by zoning or grain to grain variability. These features ultimately reflect changes in the intensive parameters or activities of components during melt solidification. Such complexities of granite crystallisation can be simultaneously modelled in a reaction space constructed from the set of linearly independent reactions describing the equilibria among all phases and components in the system of interest.The topology of the linearly independent reactions that define the reaction space for garnetmuscovite-biotite granites yields the following insights: (1) there is no one unique reaction that produces or consumes aluminous minerals (e.g. garnet); (2) minerals can alternate as reactants or products in different reactions accounting for textures indicating multiple periods of crystallisation separated by resorption; (3) mineral compositions are regulated by the reaction(s) producing them and vary as the stoichiometry of the reaction(s) producing them varies; (4) resorption of early crystallising garnet is likely to reflect decreasing pressure, presumably during magma ascent; (5) late crystallisation of garnet, at the expense of biotite, reflects an increase in melt aluminosity and does not necessarily require high Mn activities for the melt and (6) increasing melt H2O, at H2Oundersaturated conditions, favours the formation of biotite–muscovite granite.Application of the reaction space method to other granite types holds considerable promise for elucidating reactions that regulate mineral assemblages and compositions during crystallisation.

The presence of rapakivi feldspar and of distinctive porphyritic texture of Mount Scott Granite indicates a period of crystallization prior to final emplacement beneath an extensive penecontemporaneous rhyolite volcanic pile. Final crystallization conditions are interpreted to have been

Errors in projection position arise when the resolution required by tomographic systems approaches the tolerance of the translational stage. These shifts in the projection data, commonly known as backlash, appear as jagged edges in a sinogram. If these random shifts are not removed, the resulting reconstruction is blurred. This reduces the effective resolution of the system preventing viewing of single pixel events within the sample. An iterative method is presented for removing the translational backlash from projection data. The proposed method finds the center of gravity for all projections within a fixed window of the projection. The center of gravity of the projection will follow a sinusoidal path through the sinogram. A minimum mean square error (MMSE) fit to a sinusoid is made. If the center of gravity of a projection does not match the fit value, the entire projection is shifted into the correct position using linear interpolation. Since the shift of a projection introduces new data (that includes random noise) into the fixed calculation window, the center of gravity is again calculated, and the appropriate shift is made. This process is repeated until an acceptable error is reached. Since each shift uses linear interpolation, the data is blurred with each iteration. In order to minimize the amount of blurring, the shift values for each iteration are saved. The saved values are added and single shifts of the original projection data are made. An example of translational stage error removal is included.

Monomineralic aggregates or glomerocrysts are a distinctive feature of many igneous rocks. Those with crystals joined along prominent euhedral crystal faces form by synneusis while the mineral is crystallizing. Other glomerocrysts, comprised of crystals joined along irregular, embayed margins, arguably formed while the crystals were being resorbed. A model for glomerocryst formation during mineral resorption is described. During resorption, a boundary-layer melt, which envelops the dissolving crystals, is produced. When two or more dissolving crystals come into close proximity, the intervening portion their respective boundary-layer melts becomes isolated from chemical communication with the surrounding granitic liquid. Contributions from both dissolving crystals to this isolated portion of the boundary layer melt creates a melt composition that eventually becomes supersaturated with respect to the dissolving crystals. This results in crystallization of new material from the intervening melt that bonds th...

The initial Pb isotopic composition of anatectic granites is modelled as a mixture of Pb derived from major minerals that have characteristically low 238 U 204 Pb and 232 Th 204 Pb ratios (i.e., feldspars, biopyroboles, etc.) with Pb contributed from dissolved accessory minerals with characteristically high 238 U 204 Pb and 232 Th 204 Pb ratios (i.e., zircon, monazite, etc.). The initial Pb isotopic composition of anatectic granites is a function of (a) the age, type, modal distribution and heterogeneity in the initial U and Th content of the accessory minerals, (b) variation in melt composition and temperature during anatexis (c) the fraction of the source melted, and (d) the extent to which the melt was homogenized prior to crystallization. The differential behavior of accessory minerals during anatexis can explain the common yet enigmatic decoupling of the Pb isotopes from other chemical and isotopic systems in granite rocks. Granitic plutons derived by anatexis of the same source material are not required to have the same initial Pb isotopic composition. Low temperature, peraluminous granites are more likely to exhibit homogeneous initial Pb isotopic compositions dominated by the Pb contained within the major mineral assemblage of the source material. In contrast, the initial Pb isotopic composition of higher temperature, metaluminous or peralkaline anatectic granites is more likely to be heterogeneous, unless the melts are homogenized during emplacement, and will record a larger fraction of the radiogenic Pb component contained in the accessory mineral assemblage of the source material. Heterogeneity in the initial Pb isotopic composition of individual granites or granitic suites can preserve the weighted average age of the radiogenic Pb present in the accessory mineral assemblage of the source region even if these minerals are entirely dissolved during anatexis. The use of isotopic tracer studies in terrane analysis will be optimized by the isotopic characterization of granitic suites.