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Landscape evolution modeling and global compilations of exhumation data indicate that a wetter climate, mainly through orographic rainfall, can govern the spatial distribution of erosion rates and crustal strain across an orogenic wedge. However, detecting this link is not straightforward since these relationships can be modulated by tectonic forcing and/or obscured by heavy-tailed frequencies of catchment discharge. This study combines new and published along-strike average rates of catchment erosion constrained by 10 Be and river-gauge data in the Central Andes between 28°S and 36°S. These data reveal a nearly identical latitudinal pattern in erosion rates on both sides of the range, reaching a maximum of 0.27 mm/a near 34°S. Collectively, data on topographic and fluvial relief, variability of rainfall and discharge, and crustal seismicity suggest that the along-strike pattern of erosion rates in the southern Central Andes is largely independent of climate, but closely relates to the N–S distribution of shallow crustal seismicity and diachronous surface uplift. The consistently high erosion rates on either side of the orogen near 34°S imply that climate plays a secondary role in the mass flux through an orogenic wedge where the perturbation to base level is similar on both sides. [ABSTRACT FROM AUTHOR]

Climatic or geologic controls, such as tectonics or glacial drainage, might impose constraints on landscape self-organization resulting in spatial patterns of rivers and valleys which do not obey the typical self-similar relationships found in most landscapes. The goal of this study is to quantify how such geologic constraints express themselves on channel network topology, spatial heterogeneity of drainage patterns, and emergence of preferred scales of landscape dissection. We use as an example a basin located in the Upper Midwestern United States where successive glaciations over the past thousand years have led to a pronounced spatially anisotropic channel network structure which defeats most scaling laws of fluvial landscapes. This is contrasted with another river basin in the North-Central U.S. which has been organized under the absence of major geologic influences and follows a typical self-similar channel network organization. We show how the geologic constraints have imposed a competition for space which is captured in the slope–local drainage density probabilistic structure, in the failure of self-similarity in basin-wide river network topology, and in the length-area scaling relationship being not typical of fluvial landscapes. Via a two-dimensional wavelet analysis and synthesis, we demonstrate the occurrence of a gap in the power spectrum which corresponds to the presence of preferred scales of organization, and characterize them through multi-scale detrending. The developed methodologies can be useful in advancing our geomorphologic understanding of how external controls might manifest themselves in creating a landscape dissection that is outside the norm and how this dissection can be studied objectively for understanding cause and effect. [ABSTRACT FROM AUTHOR]

Long period (10-20,000 s) magnetotelluric (MT) data are being acquired across the continental USA on a quasi-regular grid of ~70 km spacing as an electromagnetic component of the National Science Foundation EarthScope/USArray Program. These data are sensitive to fluids, melts, and other orogenic indicators, and thus provide a valuable complement to other components of EarthScope. We present and interpret results of 3-D MT data inversion from 325 sites acquired from 2006-2011 to provide a regional scale view of electrical resistivity from the middle crust to nearly the mantle transition zone, covering an area from NW Washington to NW Colorado. Beneath the active extensional subprovinces in the south-central region, on average we see a resistive upper crust, and then extensive areas of low resistivity in the lower crust and uppermost mantle. Further below, much of the upper half of the upper mantle appears moderately resistive, then subsequently the lower upper mantle becomes moderately conductive. This column suggests a dynamic process of moderately hydrated and fertile deeper upper mantle upwelling during extension, intersection of that material with the damp solidus causing dehydration and melting, and upward exodus of generated mafic melts to pond and exsolve saline fluids near Moho levels. Lithosphere here is very thin. To the east and northeast, thick sections of resistive lithosphere are imaged under the Wyoming and Medicine Hat Cratons. These are punctuated with numerous electrically conductive sutures presumably containing graphitic or sulfide-bearing meta-sediments deeply underthrust and emplaced during ancient collisions. Below Cascadia, the subducting Juan de Fuca and Gorda lithosphere appears highly resistive. Suspected oceanic lithosphere relicts in the central NW part of the model domain also are resistive, including the accreted "Siletzia" terrane beneath the Coast Ranges and Columbia Embayment, and the seismically fast "slab curtain" beneath eastern Idaho interpreted by others as stranded Farallon plate. Upwelling of deep fluid or melt in the Cascade volcanic arc region manifests as conductive features at several scales. These include quasi-horizontal conductive patches under the arc and fore-arc, likely denoting fluids evolved via breakdown of hydrous minerals in the current down-going slab. In the backarc, low resistivities concentrate in "plumes" connecting into a deeper aesthenospheric layer to the east, consistent with subduction-driven upwelling of hot, hydrated or melted, aesthenospheric mantle. Low resistivities <10 Ωm deep beneath the stable cratons suggest higher levels of hydration there, and/or influence of poorly resolved structures outside the array. [ABSTRACT FROM AUTHOR]

This study explores the properties of the lithosphere-asthenosphere boundary (LAB) and other shallow mantle discontinuities across the diverse geologic provinces of the northwest United States. Sp phases were used to image three-dimensional discontinuity structure by common conversion point stacking with data from 804 temporary and permanent broadband stations, including 247 from EarthScope's USArray Transportable Array. Substantial variations in mantle discontinuity structure are apparent over a variety of spatial and temporal scales. To the west of the Sevier Thrust Belt, a coherent Sp negative phase coincides with the LAB depth range inferred from tomographic models. To the east, within the stable craton, multiple negative phases typically occur in the high velocity lithospheric layer, although in places a single mid-lithospheric discontinuity is imaged. Sub-cratonic LAB phases are often absent, indicating an LAB velocity gradient that is distributed over >50 km and that is consistent with effects of temperature alone. Where weak and intermittent LAB phases appear, they suggest more vertically localized velocity gradients produced by other factors such as bulk composition, volatile content, or contrasts in grain size or melt. In the tectonically active west, a positive Sp phase at depths consistent with the base of the asthenospheric low velocity zone in tomography models is intermittently observed. Beneath magmatic provinces in the west, the LAB Sp discontinuity deepens by ?10 km from the High Lava Plains, where magmatism has occurred from 0-10.5 Ma, to the northern region of the Columbia River Basalts, which has been magmatically quiet since 15 Ma. Here we suggest a model in which the negative LAB velocity gradient is created by a layer of partial melt ponding beneath a solidus-defined boundary. This model predicts that higher temperatures associated with more recent magmatism would result in a shallowing of the intersection of the geotherm with the solidus. Beneath the Yellowstone Caldera, the absence of an LAB Sp phase suggests that the contrast in seismic velocity between the lithosphere and asthenosphere has been erased by intrusion of partial melt and heat into the lithosphere. [ABSTRACT FROM AUTHOR]

The magnetotelluric component of the EarthScope USArray program has covered over 35% of the continental United States. Resistivity tomography models derived from these data image lithospheric structure and provide constraints on the distribution of fluids and melt within the lithosphere. We present a three-dimensional resistivity model of the northwestern United States which provides new insight into the tectonic assembly of western North America from the Archean to present. Comparison with seismic tomography models reveals regions of correlated and anti-correlated resistivity and velocity that help identify thermal and compositional variations within the lithosphere. Recent (Neogene) tectonic features reflected in the model include the subducting Juan de Fuca-Gorda plate which can be traced beneath the forearc to more than 100 km depth, high lithospheric conductivity along the Snake River Plain, and pronounced lower-crustal and upper-mantle conductivity beneath the Basin and Range. The latter is abruptly terminated to the northwest by the Klamath-Blue Mountains Lineament, which we interpret as an important structure during and since the Mesozoic assembly of the region. This boundary is interpreted to separate hot extended lithosphere from colder, less extended lithosphere. The western edge of Proterozoic North America, as indicated by the Cretaceous initial 87Sr/86Sr = 0.706 contour, is clearly reflected in the resistivity model. We further image an Archean crustal block ("Pend Oreille block") straddling the Washington/Idaho border, which we speculate separated from the Archean Medicine Hat block in the Proterozoic. Finally, in the modern Cascades forearc, the geometry and internal structure of the Eocene Siletz terrane is reflected in the resistivity model. The apparent eastern edge of the Siletz terrane under the Cascades arc suggests that pre-Tertiary rocks fill the Washington and Oregon back-arc. [ABSTRACT FROM AUTHOR]

Abstract: Although the northwest-striking Saline River fault system of southeastern Arkansas is not defined by microseismicity, it is associated with sand blows and shows evidence of Pleistocene and Holocene surface ruptures, suggesting a significant seismogenic potential. This fault system is within the northern Gulf of Mexico interior coastal plain, a region only recently recognized as containing seismogenic faults. To better characterize this active fault system, we reconstructed its post-Paleozoic history using petroleum and coal industry wire-line well log and seismic reflection subsurface data. The Saline river fault system initiated as a series of northwest-striking grabens during Triassic/Jurassic uplift and incipient Gulf of Mexico rifting along the basement Alabama–Oklahoma transform margin of the North American Proterozoic craton. During post-rift subsidence, these grabens were buried by Gulf sediments until mid-Cretaceous uplift and igneous activity resulted in minor extensional reactivation of graben faults. Faulting style changed from extension to transpression during the Late Cretaceous due to compression of eastern North America as the North Atlantic rapidly widened and due to thermal weakening of the Alabama–Oklahoma transform lithospheric discontinuity as it obliquely crossed a mantle hot spot. In the Late Cretaceous, graben faults experienced contractional reactivation and steep, deeply-rooted transpressional faults developed within and parallel to the graben system. These transpressional faults locally displace Eocene, Pleistocene, and Holocene sediments. Fault activity continues on the Saline River fault system due to thin crust along the Alabama–Oklahoma transform and to high heat flow, which act together to weaken the crust and promote seismogenic tectonism. The fault system may lack appreciable microseismicity because the aftershock sequence of the last large earthquake has had time to dissipate. [Copyright &y& Elsevier]

Abstract: Giant duplexes called mushwads in the southern Appalachian thrust belt are estimated to contain a natural gas resource base of about 17.7Tcm (625Tcf). Early development efforts in mushwads of the Cambrian-age Conasauga Formation encountered significant challenges and highlight the need for an integrated, multidisciplinary approach to shale gas exploration. To facilitate development of this gigantic resource, an integrated geological analysis of stratigraphy, sedimentation, structural geology, basin hydrodynamics, petrology, geochemistry, gas storage and mobility, and reservoir volumetrics was conducted. The results of this analysis demonstrate the myriad geological factors that need to be considered when developing shale gas resources and suggest that the greatest reservoir potential lies deep in the mushwads, where free gas is concentrated. Meeting the challenges posed by deformed shale masses in thrust belts is a major frontier for hydrocarbon exploration that could result in a major expansion of natural gas reserves. [Copyright &y& Elsevier]

Abstract: The paper studies the relationship between the earthquake and spatio-temporal changes of the addictive tectonics stress caused by the celestial tide-generating force (ATSCTF) about the M7.3 earthquake of Japan at 38.5°N, 142.8°E, and extracts the abnormal temperature increment before and after the earthquake by using the National Centers for Environmental Prediction (NCEP) data according to the ATSCTF''s time cycle. The analysis reveals that the time when the ATSCTF''s absolute value on P-axis and N-axis reached peak is same to the time of the earthquake''s occurrence, the abnormal temperature increment before the earthquake is obvious and the area of abnormal temperature increment mostly locates to the east of the epicenter, the minimum values’ spatial distribution of the ATSCTF on P-axis and N-axis mostly focused to the east of epicenter on the day earthquake occurred, at the same time, the unbalanced spatial distribution was similar to the abnormal temperature increment distribution, this phenomena testifies the ATSCTF''s inducing effect to the earthquake''s occurrence from another perspective. [Copyright &y& Elsevier]

Abstract: During a trip to the Hall of the White Giant, Carlsbad Caverns (NM, USA) cigar-shaped vertically upward developing holes were observed on the ceiling at different heights of the passages. They have a circular cross-section with diameters of 1 to some centimetres and taper out towards their upper end. Their walls are smooth and their bottom edges are sharp, while their length can reach several decimetres. Sometimes gypsum can be found inside. They often occur randomly distributed in groups and their development is not necessarily controlled by fractures or other bedrock structures. We name these peculiar karren-like cave microforms “zenithal ceiling tube-holes” because of their origin by H2S environment corrosion processes and their vertical (zenithal) upward growth in ceilings. A comparison is made between zenithal ceiling tube-holes and other karstic or non karstic similar forms such as bell holes, oxidation vents, snailholes, Korrosionskolke (mixture-solution hollows) or pockets, röhrenkarren, light-oriented photokarren, borings of (often marine) organisms and negative stalactites. Zenithal ceiling tube-holes are created by the corrosive effect of sulphuric acid. H2S(g) dissolves in water giving rise to widespread sulphuric acid corrosion. When H2S bubbles are trapped underneath overhanging surfaces or ceilings and water level rises steadily the corrosive effect is concentrated vertically upwards, drilling vertical holes that can also completely pass overhanging rock ledges. [Copyright &y& Elsevier]

Abstract: New field observations and cross section restoration from the Jurassic White Horse pluton–host rock system, Goshute Range, eastern Nevada, USA, indicate a sequential variation of host rock rheology attending magma emplacement. The pluton intruded weakly to nondeformed Devonian–Mississippian limestone, argillite and quartzite at shallow crustal levels (ca. 7km). The contact aureole is well exposed along the southern, eastern and northern margin of the intrusive body and is less than 1km wide. Rocks outside of the aureole are sub-horizontal and do not contain a penetrative fabric or are gently folded (interlimb angles >120°) about sub-vertical axial planes. Within the contact aureole, continuous and discontinuous spaced, axial planar foliations and harmonic to disharmonic, tight to isoclinal folds wrap around the eastern margin of the pluton. Folds verge toward and away from the pluton and rim anticlines, synclines, and monoclines with wavelength in excess of 250m are preserved along the pluton margin. The spatial proximity of these ductile structures to the pluton and the apparent increase in intensity of structure development approaching the pluton is compatible with contraction within the aureole attending pluton emplacement. However, all of the above structures are truncated by the intrusive contact at various scales. Granodioritic dikes ranging in thickness from 1m up to ∼10m emanate from the intrusion and cut host rock structure at high angles and turn to propagate towards one another, parallel to the pluton margin and host rock anisotropy. Such features are interpreted to reflect the last stages of diking and brittle deformation that modified the pluton contact after emplacement-related folding of the carbonate rocks, but before final solidification of the pluton. Eight serial geologic cross sections were constructed and evaluated to place geometric constraints on the shape and growth of the White Horse intrusion. Based on line-length restoration of serial cross sections oriented perpendicular to the pluton contact, the aureole was shortened approximately 54% during emplacement. Extrapolating this shortening value over the exposed area of the pluton indicates that approximately 48% of the exposed pluton area may be accounted for by the restoration. Therefore, host rocks must have been displaced out of the map plane and likely downward based on geometrical constraints provided by the cross sections. The preferred emplacement model requires in-situ chamber dilation accommodated by ductile deflection of host rocks followed by fracturing and removal of the aureole rocks via cauldron subsidence and/or stoping. [Copyright &y& Elsevier]

Abstract: During the Early Cretaceous Australia''s eastward passage over sinking subducted slabs induced widespread dynamic subsidence and formation of a large epeiric sea in the eastern interior. Despite evidence for convergence between Australia and the paleo-Pacific, the subduction zone location has been poorly constrained. Using coupled plate tectonic–mantle convection models, we test two end-member scenarios, one with subduction directly east of Australia''s reconstructed continental margin, and a second with subduction translated ~1000km east, implying the existence of a back-arc basin. Our models incorporate a rheological model for the mantle and lithosphere, plate motions since 140Ma and evolving plate boundaries. While mantle rheology affects the magnitude of surface vertical motions, timing of uplift and subsidence depends on plate boundary geometries and kinematics. Computations with a proximal subduction zone result in accelerated basin subsidence occurring 20Myr too early compared with tectonic subsidence calculated from well data. This timing offset is reconciled when subduction is shifted eastward. Comparisons between seismic tomography and model temperature cross-sections, and an absence of subduction zone volcanism in eastern Australia in the Early Cretaceous provide support for the back-arc basin scenario. [Copyright &y& Elsevier]

Abstract: Faults and associated fracture networks can significantly influence regional flow of groundwater, hydrocarbons and other fluids. The distribution of CO2 springs and seeps along the Little Grand Wash fault and Salt Wash faults in central Utah is controlled by along-fault flow of CO2-charged groundwater from shallow aquifers (<1 km deep). The same faults are the likely conduits that charge the shallow aquifers with CO2 from depth. We document fault zone trace geometry and architecture, and evidence for palaeo-fluid flow within the footwalls of both faults. Evidence for palaeo-fluid flow consists of extensive bleaching of sandstones and some siltstones, mineralisation of carbonates and celestine veins and minor hydrocarbon staining. The field evidence shows that the pathways for multiple phases of fluid flow were structurally controlled utilising the fracture network developed in the damage zone of the faults. To investigate the likely effect of these faults on the regional fluid-migration pathways at depth, a 3D model of the faulted system was generated and a fault seal analysis applied to predict the cross-fault sealing capabilities of the studied faults. Due to the scarcity of subsurface data, the results are not conclusive but suggest probable multiple cross-fault leak points for fluids to migrate across the fault, in contrast to the field observations that indicate fault-parallel flow. This comparison of field observations to the modelling approach demonstrates the inability of conventional seal analysis techniques to predict fault-parallel fluid leakage and highlight the effects fracture networks in the damage zone, especially at structural complexities along the fault, have in producing pathways for vertical flow. Multiple fluids have utilised similar fault-parallel pathways over geological time demonstrating that such pathways have the potential to cause long-term leakage from hydrocarbon reservoirs and CO2 storage sites. [Copyright &y& Elsevier]

Abstract: Despite how common folds are as structural features, along-strike fold propagation has proven elusive to document. However, if a fold grows laterally along its axis, early-formed fold-related joints may differ significantly in orientation from joints that form later. In this paper, we integrate mechanical stratigraphy with joint pattern analysis to determine relative timing of jointing. Additionally, we demonstrate that joint patterns can be related to stresses on both the top and bottom of the bed during flexure. We present joint data from eight sedimentary beds on the fold terminus at Sheep Mountain Anticline, Wyoming, USA. The joint patterns around the terminus show two distinct patterns: joints in six of the beds show a radial pattern around the terminus whereas joint patterns in the two remaining beds differ from proximal units, despite being in the same structural position. Fracture resistance calculations confirm that the beds with mis-oriented fractures are less resistant to fracturing than other units in the study, and therefore would have fractured earlier in fold growth history. We present a plate bending model that illustrates potential joint patterns around a plunging fold nose from stresses along both the top and bottom of the bed. The joint strike predictions for the area in front of the inflection line on the fold nose match the orientations in our less resistant beds, which are now positioned behind the inflection line, suggesting that the fold grew laterally. The combined analysis of fracture pattern and mechanical stratigraphy provides a new way to investigate fold evolution. [ABSTRACT FROM AUTHOR]

Abstract: For some time, onset of the Antarctic Circumpolar Current (ACC) was considered to have caused or stabilised full Antarctic glaciation. Recently, however, the importance of the ACC in this role has been questioned. In order to understand the relationship between the ACC and Antarctic glaciation, and thence the importance of ocean circulation to palaeoclimate, we need to determine the development history of both processes. To this end, we summarise all published estimates of ACC onset. The time of onset, of shallow circulation or deep, is uncertain, whether based on tectonic studies or the interpretation of changes in the sediment record. Two potential final barriers to circumpolar flow have been identified; south of Tasmania and south of South America. The former is well constrained by tectonics and marine geology to before 32Ma for a deep gap, with a shallow gap in place by 35.5Ma at the latest. These ages fit nicely with the onset of full Antarctic glaciation at 33–34Ma, although some workers question the causality. Estimates of the time of opening of the latter range widely, whether based on tectonics or sedimentary geology, from as recently as 6Ma to as early as 41Ma, with the gap depth uncertain also. Resolution of the tectonics-based uncertainties by additional survey being most probably both time-consuming and inconclusive, and the geological estimates being open to alternative interpretations, we define an optimal strategy for additional sampling and measurement, designed to resolve the time of onset more certainly, possibly also resolving between deep and shallow opening, and thereby constraining the ACC role. Sample sites would have to be close to likely final barriers, to avoid extraneous influence, and within modern zones of ACC influence, ideally would form a depth transect, and would have continuous, mixed terrigenous and biogenic sections. A wide range of carefully selected parameters would be measured at each. [Copyright &y& Elsevier]

Abstract: Fault slip and fault separation are generally not equal to each other, however, they are geometrically related. The fault slip (S) is a vector with a magnitude, a direction, and a sense of the movement. In this paper, a series of approaches are introduced to estimate quantitatively the magnitude and direction of the fault slip using fault separations. For calculation, the known factors are the pitch of slip lineations (γ), the pitch of a cutoff (β), the dip separation (S md) or the strike separation (S mh) for one marker. The two main purposes of this work include: (1) to analyze the relationship between fault slip and fault separation when slickenside lineations of a fault are known; (2) to estimate the slip direction when the parameters S md or S mh, and β for two non-parallel markers at a place (e.g., a point) are known. We tested the approaches using an example from a mainly strike-slip fault in East Quantoxhead, United Kingdom, and another example from the Jordan Field, Ector County, Texas. Also, we estimated the relative errors of apparent heave of the normal faults from the Sierra de San Miguelito, central Mexico. [Copyright &y& Elsevier]

Abstract: In the western Churchill Province, Canadian Shield, Neoarchean supracrustal and plutonic rocks, intruded by Paleoproterozoic mafic dykes and granitic rocks, comprise the MacQuoid supracrustal belt and the structurally overlying Cross Bay plutonic complex. They form part of the northwestern Hearne subdomain that occupies an intermediate position between the continental Rae domain to the north and west, and the oceanic central Hearne subdomain to the south and east. New geological mapping and supporting geoscience are compatible with the presence of 2550–2500Ma, southeast-directed, mid-crustal, thick-skinned thrusting that juxtaposed the plutonic complex over the supracrustal belt. The structural contact between the MacQuoid supracrustal belt and the Cross Bay plutonic complex potentially represents a fundamental boundary between isotopically distinct crustal blocks. The ∼2190Ma MacQuoid mafic dyke swarm cuts across Neoarchean deformation fabrics, but records ∼1.9Ga, deep-crustal, regional metamorphism that affected both the supracrustal belt and the plutonic complex. Other Paleoproterozoic deformation events that occurred at ∼1850–1810Ma are of local extent and appear to be relatively minor manifestations of more important events elsewhere, related to the Trans-Hudson orogen. [Copyright &y& Elsevier]

Abstract: The Tehuantepec Ridge is one of the most prominent lithospheric structures of the Cocos Plate, yet its tectonic evolution has remained poorly constrained until now. Calculated ocean floor ages and spreading rates, morphostructural analysis of the ridge and the surrounding ocean floor are used to infer the tectonic evolution and pattern of the Tehuantepec Ridge and associated structures. The ocean floor age estimates south of the Tehuantepec Ridge suggest an age of ∼26 Ma at the Middle America trench. A mean age difference across the Tehuantepec Ridge of ∼7 Ma suggests that the Tehuantepec Ridge would be formed as a long transform fault on the Guadalupe plate, prior to 15 Ma. The full-spreading rate estimates show that there might be a differential full-spreading rate across the transform fault between 15 and 5 Ma, when the oceanic plate just south of Clipperton Fracture Zone was decelerating between 15 and 10 Ma, then accelerating for the next 5 Ma. We propose a model in which between 13 and 8 Ma temporarily transpressional intratransform-spreading centers would have been existing as a consequence of the East Pacific Rise onset with an angle of ∼10° clockwise with respect to the ceased Mathematician ridge. Our model estimates indicate that between 21 and 15 Ma a prominent pseudofault was formed south of the Tehuantepec Ridge due to an unstable offset on the Mathematician ridge that migrated northward. The Tehuantepec Ridge and the pseudofault trace bound a deeper oceanic basin than the surrounding area, with no corresponding anomalous depth on the western side of the East Pacific Rise. The complete absence of a pseudofault trace and a deeper oceanic basin on the western side of the East Pacific Rise, as well as the spreading rate changes, suggest the existence of a microplate embedded into the Cocos Plate just south of the Tehuantepec Ridge. Also, the asymmetric and sharp morphology of the Tehuantepec Ridge suggests that it may be the expression of a major transpressional structure along the former transform fault on the Guadalupe plate 15–20 Ma ago. [Copyright &y& Elsevier]

Yucca Mountain, Nevada, is the sole candidate site for underground disposal of high-level radioactive waste in the United States. The mountain is composed of Tertiary (12.8–11.6 Ma) volcanic tuff, cut by west-dipping normal faults that divide the mountain into north-trending, east-dipping cuestas. Geologic characterization of Yucca Mountain by the U.S. Department of Energy (DOE) has focused on mapping lithostratigraphic units, faults (including single plane, small-displacement surfaces of discontinuity, and large-displacement fault zones), and fractures (quasi-planar zones that have experienced loss of cohesion, including joints, partially mineralized joints, veins, and small-displacement faults). Faults and fractures are important to repository design because they affect seismic hazard, rockfall, and fluid transmissivity in the surrounding rock mass. Geologic maps and detailed studies of rock pavements and tunnel walls reveal that faults and fractures within Yucca Mountain are not uniform in orientation or intensity. We investigate two aspects of distributed deformation arising from fault displacement patterns at Yucca Mountain. First, fault-parallel strains (elongation parallel to cutoff lines where stratigraphic horizons intersect fault planes) develop as a result of lateral fault displacement gradients. Using existing data, we analyze the likely state of strain in fault blocks at Yucca Mountain. Second, fault-strike-perpendicular strains can develop where two normal faults propagate past each other. A component of the total strain is distributed into the surrounding rock to produce synthetic layer dip or a network of smaller faults and fractures. We find that small-scale faulting and fracturing at Yucca Mountain is variable and is strongly controlled by larger scale fault system architecture. [Copyright &y& Elsevier]

Clay mineral assemblages have been investigated in a sequence of Late Quaternary age sediments (160 ka) from the Santa Barbara Basin off California. These predominantly terrigenous sediments contain an assemblage of clay minerals dominated by smectite mostly derived from discharges of the Santa Clara River, together with illite and kaolinite from adjacent relief. Besides its characteristic clay mineral signature, the Santa Clara River has the largest drainage basin in this region and contributes most of the terrigenous load to the Santa Barbara Basin. Smectite contents of the sediments in the basin may therefore be used as a proxy for precipitation and run-off. Distinct changes in the relative abundance of smectite allow reconstruction of the pattern of precipitation, and its relations with regional environments and global climate. This showed that major intervals of precipitation coincide with local development of pine during glacials, and oak during terminations and interglacials; some expansion of mountain glaciers in the Sierra Nevada, especially when they occur during local minima of insolation; and lacustrine developments in the now arid continental interior of California. Major precipitation intervals started during glacials, and persisted during terminations and early interglacials, associated with a weak California Current and subsequent expansion of warm Pacific surface waters. In detail, major precipitation intervals consist of alternating episodes of higher and lower rainfall modulated by orbital precession, with a significant correlation between episodes of high rainfall and minima in precession, which were times of increased meridional gradients, enhanced poleward heat transfer and northward expansion of tropical waters. [Copyright &y& Elsevier]

Appalachian Deep Core Hole 2 (ADCOH-2) penetrated part of one of the most persistent and important tectonostratigraphic belts in the southern Appalachians—the Brevard-Chauga belt in South Carolina. The Brevard-Chauga belt is a subdivision of the Inner Piedmont and it includes the Brevard fault zone. The 307 m core contains four imbricated slices of Early Ordovician Henderson Gneiss and metasedimentary rocks of the Chauga River Formation. Aqueous (NaCl–CaCl2) inclusions and CO2–CH4-rich inclusions present in syntectonic quartz veins in the metasedimentary units, together with garnet-biotite geothermometry, provide information on the P-T conditions during uplift. Garnet-biotite geothermometry in the Brevard metasiltstone indicates a crystallization temperature of 466±52 °C, which together with published 40Ar/39Ar hornblende data from the Chauga belt, are interpreted as a Neoacadian (late Devonian) garnet crystallization age. High-density CO2-rich fluid inclusion isochores indicate a pressure of ∼4.5 kbar at 466±52 °C at this time. A Rb–Sr muscovite model age of 302 Ma in retrograde mylonitic Henderson Gneiss is interpreted as an Alleghanian recrystallization age. Fluid inclusions record a 2.5 kbar decompression event at this time, consistent with thrust assembly of the tectonostratigraphic units in the core. [Copyright &y& Elsevier]

A case study from southern California illustrates the value of detailed geologic data for understanding the kinematics of complex fault systems. The neotectonic behavior of faults at the junction of the Eastern California shear zone (ECSZ) and Transverse Ranges has implications for the interaction of intersecting, segmented fault systems and regional plate boundary evolution. Paleoseismic observations indicate that the North Frontal thrust system (NFTS) has ruptured once in the Holocene with 1.7-m displacement, despite previous speculations of inactivity based on its dissection by younger strike-slip faults. Simple polyphase deformation, in which dextral shear has replaced and overprinted thrusting, is thus not a valid explanation for this system of intersecting faults. This illustrates the limitations of inferring rupture behavior from mapped fault patterns alone. Neotectonic and geomorphic observations along the thrust system also suggest that the thrust segment west of the intersection with the dextral Helendale fault is significantly more active than the segment to the east. This is consistent with a simple block velocity model, in which dextral slip on the Helendale fault is balanced by convergence on the western thrust segment, dextral motion on the poorly studied Pipes Creek fault to the southeast, and inactivity on the eastern thrust segment. This divides the San Bernardino Mountains into domains dominated by thrusting (west) and strike-slip (east), the union of which is a quasi-stable triple junction. We speculate that this union has migrated to the west as the Mojave Desert has been translated southwards along the San Andreas fault. [Copyright &y& Elsevier]

We developed a simple quantitative framework based on crustal thickness estimations along the Carnegie, Cocos and Malpelo ridges, to place first-order constraints on the tectonic evolution of the Galapagos Volcanic Province and on the along-axis intensity of the Galapagos melt anomaly during the last 20 m.y. Our results suggest that the Cocos–Nazca spreading centre has migrated northwards at 26±4 km/m.y. with respect to the Galapagos hotspot (GHS) during this period of time. At ∼20 m.y., the GHS was approximately ridge-centered, and thus the along-axis intensity of the melt anomaly at this time was the maximum. At ∼11.5 m.y. the hotspot was located 106±27 km north of the spreading center, and the along-axis intensity of the melt anomaly was 0.54±0.04 of that estimated at 20 Ma. At present day it is located at ∼190 km south of the spreading center and the along-axis intensity is only 0.19±0.03 of that estimated at 20 Ma. These results are used to reconstruct the relative position between the GHS and the Cocos–Nazca Spreading Center. The spreading center passed over the GHS for the last time at 7.4±1.3 Ma. The Panama fracture zone was initiated at 8.9±1.6 Ma, leading to the separation between the Cocos and Malpelo ridges. The present configuration of the Galapagos Volcanic Province and the plate velocities are consistent with symmetric spreading with a mean full spreading rate of ∼60 km/m.y. along the CNSC during the last 20 m.y. A melt flux for excess crustal production of 9.4±5.1 m3/s is obtained for the Galapagos melt anomaly at 20 Ma, implying that the maximum potential intensity of the Galapagos plume is similar to that of the Icelandic plume and twice smaller than the Hawaiian one. [Copyright &y& Elsevier]

High Re abundances in mid-ocean ridge basalts (MORB) relative to primitive mantle (ave. MORB[Re]&ap;930 ppt; PM[Re]&ap;260 ppt) indicate that Re behaves as an incompatible element during MORB generation. However, contrary to expectations for an incompatible element, average Re abundances in subaerial ocean island and arc lavas (∼330 ppt and ∼190 ppt, respectively) are much lower than in MORB. Previous studies have argued that the low Re abundances in ocean island and arc lavas reflect greater Re compatibility during melt generation, caused by higher modal abundances of garnet and sulfide. However, available partitioning data for Re suggest that reasonable variations in the modal abundances of these phases cannot fully account for the observed differences in Re abundance in different tectonic settings. Higher modal garnet in the sources of ocean island and arc lavas cannot produce the observed low Re/Yb ratios (relative to MORB), because available data suggest that Re is less compatible in garnet than Yb. High sulfide abundances can in principle produce the observed Re depletions, but would require extremely high sulfur contents in the sources of ocean island and arc lavas (>1000 ppm). Large differences in modal sulfide abundance in different tectonic settings are also contradicted by the similarity of MgO–Os trends in ocean island, arc, and mid-ocean ridge samples. An alternative explanation for the low Re abundances in ocean island and arc settings is that much of the Re initially contained in these (largely subaerial) lavas escaped as volatile Re-oxide or Re-chloride species during magma degassing prior to or during subaerial eruption. The ∼3 km deep HSDP-2 Mauna Kea drillcore on Hawaii provides a unique opportunity to examine the effects of magma degassing on Re abundances. The upper ∼800 m of the Mauna Kea portion of the drillcore is composed of subaerial lavas, whereas the lower 2 km is submarine. Os-isotopes are nearly constant throughout the core (187Os/188Os=0.128–0.130), so large variations in source composition (e.g. Re content) over the period sampled by the core are unlikely. Rhenium abundances in the subaerial lavas are consistently low (ave. Re&ap;180 ppt). In contrast, Re abundances in the submarine lavas increase systematically with increasing depth, ranging from an average of ∼300 ppt in samples emplaced at <1000 m below sea level (mbsl) up to ∼755 ppt in lavas from >1000 mbsl. Rhenium/ytterbium ratios also increase with core depth, ranging to values significantly exceeding those observed in MORB. These trends are best explained by progressive Re loss in the subaerial and shallow submarine lavas during melt degassing. Assuming that the deepest submarine lavas are unaffected by Re loss during degassing, the subaerial Mauna Kea lavas appear to have lost on average ∼80% of their initial Re. The systematic differences in Re abundance in ocean island, arc, and mid-ocean ridge lavas may therefore reflect the fact that most analyzed ocean island and arc samples are subaerial and therefore degassed, whereas MORB retain a greater fraction of their volatile inventory. [Copyright &y& Elsevier]

We identify two surfaces in the shallow subsurface on the Eel River margin offshore northern California, a lowstand erosion surface, likely formed during the last glacial maximum, and an overlying surface likely formed during the most recent transgression of the shoreline. The lowstand erosion surface, which extends from the inner shelf to near the shelfbreak and from the Eel River to Trinidad Head (∼80 km), truncates underlying strata on the shelf. Above the surface, inferred transgressive coastal and estuarine sedimentary units separate it from the transgressive surface on the shelf. Early in the transgression, Eel River sediment was likely both transported down the Eel Canyon and dispersed on the slope, allowing transgressive coastal sediment from the smaller Mad River to accumulate in a recognizable deposit on the shelf. The location of coastal Mad River sediment accumulation was controlled by the location of the paleo-Mad River. Throughout the remainder of the transgression, dispersed sediment from the Eel River accumulated an average of 20 m of onlapping shelf deposits. The distribution and thickness of these transgressive marine units was strongly modified by northwest–southeast trending folds. Thick sediment packages accumulated over structural lows in the lowstand surface. The thinnest sediment accumulations (0–10 m) were deposited over structural highs along faults and uplifting anticlines. The Eel margin, an active margin with steep, high sediment-load streams, has developed a thick transgressive systems tract. On this margin sediment accumulates as rapidly as the processes of uplift and downwarp locally create and destroy accommodation space. Sequence stratigraphic models of tectonically active margins should account for variations in accommodation space along margins as well as across them. [Copyright &y& Elsevier]

Reprocessing and interpretation of seismic profiles from the Gulf of Alaska in the vicinity of the St. Elias Mountains indicate that over 3000 km3 of sediment were deposited on the ocean shelf since the end of the last glacial epoch, approximately 10,000 years ago. This estimate of the sediment volume does not include material moved out of the region by long shore currents, transportation from the shelf to deeper waters, or material trapped in fiords and basins on and near land. Thus, an estimated sedimentation rate offshore of 7.9 mm/year and the average erosion rate of 5.1 mm/year from the St. Elias Mountains, derived from the estimated sedimentation rate, represent minimum estimates. We infer that these estimated rates are not typical of the approximately 5 m.y. history of mountain building in the area, but rather, they represent the result of efficient erosion by glaciers during this interglacial period. [Copyright &y& Elsevier]

Understanding the way fluids flow in fault zones is of prime importance to develop correct models of earthquake mechanics, especially in the case of the abnormally weak San Andreas Fault (SAF) system. Because fluid flow can leave detectable signatures in rocks, geochemistry is essential to bring light on this topic. The present detailed study combines, for the first time, C–O isotope analyses with a comprehensive trace element data set to examine the geometry of fluid flow within a significant fault system hosted by a carbonate sequence, from a single locality across the Little Pine Fault–SAF system. Such a fault zone contains veins, deformation zones, and their host rocks. Stable isotope geochemistry is used to establish a relative scale of integrated fluid–rock ratios. Carbonate δ18O varies between 28‰ and 15‰ and δ13C between 5‰ and −7‰. From highest to lowest delta values, thus from least to most infiltrated, are the host rocks, the vein fillings, and the deformation zone fillings, respectively. Infiltration increases toward fault core. The fluids are H2O–CO2 mixtures. Two fluid sources, one internal and the other external, are found. The external fluid is inferred to come essentially from metamorphism of the Franciscan formation underneath. The internal (local) fluid is provided by a 30% volume reduction of the host limestones resulting from pressure solution and pore size reduction. Most trace elements, including the lanthanides, show enrichment at the 100-m scale in host carbonate rocks as fluid–rock ratios increase toward the fault core. In contrast, the same trace element concentrations are low, relative to host rocks, in veins and deformation zone carbonate fillings, and this difference in concentration increases as fluid–rock ratio increases toward the fault core. We suggest that the fluid trace elements are scavenged by complexation with organic matter in the host rocks. Elemental complexation is especially illustrated by large fractionation of Y–Ho and Nb–Ta geochemical pairs. Complexation associated with external fluid flow has a significant effect on trace element enrichment (up to 700% relative enrichment) while concentration by pressure solution associated with volume decrease of host rocks has a more limited effect (up to 40% relative enrichment). Our observations from the millimeter to the kilometer scale call for the partitioning of fluid sources and pathways, and for a mixed focused–pervasive fluid flow mechanism. The fluid mainly flows within veins and deformation zones and, simultaneously, within at least 10 cm from these channels, part of the fluid flows pervasively in the host rock, which controls the fluid composition. Scavenging of the fluid rare earth elements (REE) by host rocks is responsible for the formation of REE-depleted vein and deformation zone carbonate fillings. Fluid flow is not only restricted to veins or deformation zones as commonly believed. An important part of fluid flow takes place in host rocks near fault zones. Hence, the nature of the lithologies hosting fault zones must be considered in order to take into account the role of fluids in the seismic cycle. [Copyright &y& Elsevier]

The Wetumpka structure, an arcuate, 7.6 km diameter, rimmed feature of the inner Coastal Plain, Alabama, is a Late Cretaceous shallow-marine impact crater. In this paper, we show unequivocal evidence of Wetumpka’s impact origin. Within and about this structure, pre-existing Upper Cretaceous stratigraphy was resedimented and(or) deformed, thus creating distinctive intra-structure and extra-structure terrains. These terrains are located, respectively, within Wetumpka’s crystalline-rim terrain and adjacent to the structure on the southern side. Core drilling near the structure’s geographic center revealed that Wetumpka’s basin-filling sequence has two distinctive units, suggestive of a two-stage filling process consisting of (1) fall-back plus resurge followed by (2) a later secondary seawater resurge event. Wetumpka’s lower subsurface unit includes polymict impact breccias, which contain quartz grains displaying shock-characteristic multiple sets of planar deformation features. Selected subsurface samples of this breccia also contain elevated Ir, Co, Ni and Cr concentrations indicative of a minor extraterrestrial component. [Copyright &y& Elsevier]

The Permian Basin is one of the most important petroleum-producing regions in the United States. The structural history of the Permian Basin is extremely complex. Most of the structural traps in the Permian Basin are associated with the strike-slip fault system, which presented challenges for past structural interpretation completed primarily using well log and 2D seismic data. We utilized a 3D seismic survey, a part of the Midland Basin and eastern margin of the Central Basin Platform (CBP), to identify the Early Paleozoic structural elements to study its influence on the HC production from the Permian strata. We computed volumetric seismic attributes including, coherence which can identify faults with a significant amount of throw, along with curvature which can detect flexure and folds. We also used, recently developed aberrancy attribute, which illuminates subtle faults and flexures. We observed several strong lineations on seismic attributes extracted along the Woodford surface. Lineations have three different trends. Trend 1 lineations are drag folds associated with the Andrews shear zone (ASZ). Trend 2 lineations, which show a left-lateral strike-slip motion, are R' Riedel Shear, are oriented N 65° W truncating against the CBP. The trend 2 lineations continue upward to the shallower surfaces, as well as they are parallel to the surface lineations identified on the satellite images, which indicates the continued movement of the pre-existing faults. The trend 3 lineations, which show a right-lateral strike-slip motion, are R Riedel Shear and align with the ASZ. The formation micro image (FMI) shows the fracture orientations in trend 2 and trend 3 directions. The aberrancy lineation anomalies are indicative of highly fractured areas; wells drilled in these areas display lower oil-water ratio, as well as a higher amount of production, which may be due to the increase in permeability due to the fractures. • Permian Basin is one of most producing basin in the US. • Paleozoic aged strike slip fault system influence the accumulation and production of oil and gas. • Seismic attribute analysis displays three primary directions of lineations. • Surface lineations correlates to the deeper subsurface lineations. [ABSTRACT FROM AUTHOR]