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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.).

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.

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...

[1] Digital Elevation Models (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data and high-resolution aeromagnetic data are used to characterize the growth and propagation of faults associated with the early stages of continental extension in the Okavango Rift Zone (ORZ), northwest Botswana. Significant differences in the height of fault scarps and the throws across the faults in the basement indicate extended fault histories accompanied by sediment accumulation within the rift graben. Faults in the center of the rift either lack topographic expressions or are interpreted to have become inactive, or have large throws and small scarp heights indicating waning activity. Faults on the outer margins of the rift exhibit either (1) large throws or significant scarp heights and are considered older and active or (2) throws and scarp heights that are in closer agreement and are considered young and active. Fault linkages between major fault systems through a process of “fault piracy” have combined to establish an immature border fault for the ORZ. Thus, in addition to growing in length (by along-axis linkage of segments), the rift is also growing in width (by transferring motion to younger faults along the outer margins while abandoning older faults in the middle). Finally, utilization of preexisting zones of weakness allowed the development of very long faults (>100 km) at a very early stage of continental rifting, explaining the apparent paradox between the fault length versus throw for this young rift. This study clearly demonstrates that the integration of the SRTM DEM and aeromagnetic data provides a 3-D view of the faults and fault systems, providing new insight into fault growth and propagation during the nascent stages of continental rifting.

WOS: 000257103800006, Very unusual rocks consisting of natrolite (>95 vol.%) pargasite (

New shear-wave splitting measurements at permanent broadband seismic stations in the south-central United States reveal the orien- tation and degree of polarization of mantle fabrics, and provide constraints on models for the formation of these fabrics. For stations on the stable North American craton, correspon- dence between observed polarization direc- tion of the fast wave and the trend of Protero- zoic and Paleozoic structures associated with rifts and orogenic belts implies a lithospheric origin for the observed anisotropy. The larg- est splitting times (up to 1.6 s) are observed at stations located in the ocean-continent transi- tion zone, in which the fast directions are par- allel to the Gulf of Mexico continental margin. The parallelism and the geometry of the keel of the craton beneath the study area suggest that asthenospheric fl ow around the keel of the North American craton, lithospheric fab- rics developed during Mesozoic rifting, or a combination of these factors are responsible for the observed anisotropy on stations above the transitional crust.

Titanite and fluorite stability in melt were experimentally evaluated at 850 °C, 200 MPa, f(O 2 ) ≈ NNO (nickel-nickel oxide oxygen buffer) as functions of total F and H 2 O content. Experiments employed the metaluminous Mount Scott Granite of the Wichita igneous province, Oklahoma. Over a large range of added H 2 O (∼1–7 wt%), melts containing 1 wt% F precipitated fluorite without titanite. In addition, at high F (≥ 1.2 wt%) plagioclase and hornblende reacted to form biotite. Thus, an increase in F during crystallization may explain the observed higher modal abundance of plagioclase and hornblende in titanite-dominant samples vs. higher modal biotite in fluorite-dominant samples within the Mount Scott Granite pluton. Coexistence of magmatic titanite and fluorite in the Mount Scott Granite pluton implies F m of ∼1 wt% at the point in its crystallization history where these minerals coprecipitated. We suggest that the presence of primary fluorite within high-temperature, shallowly emplaced, moderate f (O 2 ), subaluminous felsic rocks indicates high magmatic fluorine, whereas titanite without fluorite in such rocks indicates low initial fluorine.

A symposium entitled “;A-Type Granites and Rhyolites: Is A for Ambiguous?,” held last May at the AGU 1992 Spring Meeting in Montreal, Canada, provided a forum for continued discussion and scientific debate of the complexities inherent in A-type granites. The concept of A-type granites [Loiselle and Wones, 1979] originally distinguished granites that are relatively anhydrous, with alkaline affinities, and which are formed in anorogenic tectonic settings, commonly after a previous episode of crustal melting. These granites were noted for their distinctive mineralogy and chemistry. A-type granites commonly contain sodic pyroxenes and amphiboles, late crystallizing iron-rich amphiboles and biotites, fluorite, and exotic accessory minerals (for example, chevkinite). They have high SiO2, Na2O+K2O, Fe/Mg, F, and low CaO and Sr. They are enriched in high field strength elements (for example, zirconium, niobium, gallium, yttrium) and REEs except europian.