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The Haast Schist of South Island, New Zealand, consisting of the Otago, Alpine, and Marlborough Schist components, is the most deeply buried and strongly metamorphosed part of an accretionary complex above a westward-dipping subduction zone on the eastern margin of Gondwana. Conventional wisdom is that the schist formed in the Jurassic (ca. 170 Ma) by collision between Carboniferous to Triassic graywacke sequences of the exotic eastern Torlesse composite terrane and the western Caples terrane. However, extensive areas of Alpine Schist in the west, rich in metabasite, and in part overlying a metamorphosed ophiolitic sequence, have anomalously young, mid-Cretaceous, ca. 108 Ma, detrital zircon ages. Their deposition and subsequent deformation occurred approximately synchronous with the cessation of westward-directed subduction in the Eastern Province of New Zealand, the onset of regional extension, and deposition of terrestrial and volcanic sediments on the exhumed erosion surface of the eastern schist basement. These Cretaceous schist protoliths are interpreted to form the exotic Pounamu terrane, accreted and interfolded with Otago Schist on the western margin of the Haast Schist. The Alpine Schist metamorphism is dated from zircon overgrowths on detrital grains at ca. 70 Ma (although over an extended period, 98-64 Ma, regionally). This thermal event is unknown further east. The Haast Schist is therefore a polygenetic unit formed by the amalgamation of metamorphic components accreted from both the east and west sides of the SE Zealandia microplate. Existence of the Pounamu terrane requires a major revision to the Cretaceous tectonic history of southern New Zealand. [ABSTRACT FROM AUTHOR]

Many recent thrust fault earthquakes have involved coseismic surface faulting and surface folding strains. This multifaceted nature of active thrust sheet deformation can make attempts to quantify slip and slip rates from surface strains challenging and uncertain. We present new methods for integrating records of surface deformation, subsurface structure, and geochronology to investigate active deformation over multiple rupture cycles across the Southern Junggar Thrust in the southern Junggar Basin, NW China, from ~225 ka to present. Fluvial terraces preserve records of surface faulting as a prominent fault scarp where the Southern Junggar Thrust is surface-emergent. Terraces also exhibit progressive folding strains across fold scarps that are spatially coincident with subsurface fault-bend folds--constrained by seismic reflection data--along the Southern Junggar Thrust. We quantify the fault slip at depth implied by fold scarp relief along Holocene-aged terraces, and the results are corroborated by independent estimates of slip implied by fault scarp relief for the same terraces. Older terraces exhibit a distinct fanning of dips across fold scarps, suggesting active fault-bend folding kinematics involving a component of limb rotation. We developed quantitative relations for fault-bend folds between fault slip and fold dip using a mechanical, forward modeling approach. Using this novel method, we show how Southern Junggar Thrust slip rate has decelerated markedly, from ~4.1 mm/yr in the middle Quaternary to ~1.2 mm/yr throughout the Holocene. These results provide new insight into natural fault-bend folding kinematics and define innovative methods for elucidating accurate estimates of fault slip and slip rates from terrace folds in active thrust sheets. [ABSTRACT FROM AUTHOR]

The combination of structural data from the source area and descriptive data from the deposit's carapace, as well as remote sensing and statistical analysis, allows a better understanding of the collapse, fragmentation, and propagation processes of the Frank Slide rock avalanche. The in situ observed conservation of the stratigraphic sequence of the Turtle Mountain anticline's normal limb in the deposit is interpreted as the consequence of the collapse mode, involving simple shearing of the mass accompanied by a rotational movement, i.e., a "simple shear" parallel to the topography, and a breakage of the hinge, followed by overthrusting of the normal limb on the inverse limb. Coherence between the block size distributions of the source area and the deposit carapace is interpreted as a demonstration of the primary control of preexisting fracturing on the fragmentation processes. Remote-sensing indexes allow us to uncover a priori hidden morphological features preserved on the surface of the deposit, i.e., longitudinal and compressional features, as well as lobes. Their location on the carapace provides evidence of lateral heterogeneity in the propagation, highlighted by three different types of propagation behaviors. This comprehensive study not only provides elements that contribute to an understanding of the Frank Slide rock avalanche, but it also provides insight into essential parameters to take into account in further modeling of these types of phenomena. [ABSTRACT FROM AUTHOR]

The study of shock pressure indicators can provide important clues for understanding the cratering process, though the estimation of shock pressures in weakly shocked rocks is commonly difficult. In this study, we selected a very young and well-preserved impact structure, the Lonar crater in India. The crater, devoid of any tectonic overprint, can be assumed as pristine. We used a combination of rock magnetic and microfracture studies to estimate shock pressure in the crater rim. On the basis of present results, the magnetic fabrics are interpreted to be of magmatic origin related to the Deccan basalt emplacement. The high-coercivity component of the natural remnant magnetization in the crater rim basalt is similar to that in the unshocked basalt. The lack of any shock-related magnetic overprint on the crater rim basalt is, therefore, evident in the Lonar crater. In contrast, radial and concentric microfractures observed in basalts at the crater rim and farther away show symmetric distribution with respect to the crater. The concentric microfractures consistently overprint the radial microfractures. We infer that the radial and concentric microfractures were developed during propagation of the early compressional and the late decompressional shock wave components, respectively. The results of our rock magnetic and microfracture studies, when interpreted in light of published experimental and numerical simulation studies on the Lonar basalt, reveal that the shock pressure in the Lonar crater rim was less than 0.5 GPa but greater than 0.2 GPa. This shock pressure was high enough to produce fractures but too low to affect the magnetic fabrics. These results give new information on the relationship between shock pressure and resulting microfractures. [ABSTRACT FROM AUTHOR]

New mapping of the southern McDoogle pluton, an early intrusion in the John Muir suite in the central Sierra Nevada, California, has resolved important details of incremental assembly by magmatic crack-seal. The tabular McDoogle pluton concordantly intruded the steeply dipping mylonitic Sawmill Lake shear zone around 95 Ma. The pluton was previously divided into three phases based on wall-rock screen abundance and lithology. The earliest central phase consists of steep dikes separated by abundant wall-rock screens. These screens are largely absent from border phases located on either side of the central phase. The inferred relative ages of intrusive phases and the wall-rock screen distribution signify a change from antitaxial (addition at the margins of the central phase) to syntaxial (addition at the center of each border phase) assembly during pluton growth. Interaction among the effects of preexisting foliation, older nondeformed intrusions, and synintrusive static recovery of shear zone rocks likely caused the transition from antitaxial to syntaxial growth. The trend from antitaxial to syntaxial growth during emplacement has been observed in other intrusions and intrusive suites and may be a general pattern of incremental intrusion associated with the feedback between preexisting deformation and thermal addition in magmatic arcs. [ABSTRACT FROM AUTHOR]

The Andean fold-and-thrust belts of west-central Argentina (33°S and 36°S), above the normal subduction segment, present important along-strike variations in mean topographic uplift, structural elevation, amount and rate of shortening, and crustal root geometry. To analyze the controlling factors of these latitudinal changes, we compare these parameters and the chronology of deformation along 11 balanced crustal cross sections across the thrust belts between 70°W and 69°W, where the majority of the upper-crustal deformation is concentrated, and reconstruct the Moho geometry along the transects. We propose two models of crustal deformation: a 33º40'S model, where the locus of upper-crustal shortening is aligned with respect to the maximum crustal thickness, and a 35º40'S model, where the upper-crustal shortening is uncoupled from the lower-crustal deformation and thickening. This degree of coupling between brittle upper crust and ductile lower crust deformation has strong influence on mean topographic elevation. In the northern sector of the study area, an initial thick and felsic crust favors the coupling model, while in the southern sector, a thin and mafic lower crust allows the uncoupling model. Our results indicate that interplate dynamics may control the overall pattern of tectonic shortening; however, local variations in mean topographic elevation, deformation styles, and crustal root geometry are not fully explained and are more likely to be due to upper-plate lithospheric strength variations. [ABSTRACT FROM AUTHOR]

The active dextral-reverse Wairarapa fault in the North Island, New Zealand, cuts ca. 12 ka, post-Last Glacial Maximum (post-LGM) fluvial gravels with a highly segmented fault trace. This <350-m-wide fault zone displaces the gravels laterally by ∼130 m and warps them into elongate deformational bulges in the left-stepover regions between overlapping synthetic fault strands. Aerial photography, field observations, and global positioning system surveying were used to map the structural geology of a central section of this major oblique-slip fault zone. Topographic data collected at two particularly well-expressed and exposed pressure bulges of contrasting size were used to undertake a kinematic-volumetric analysis and to calculate the likely vertical extent of the bulge-related distributed deformation. In the near-surface, the Wairarapa fault zone is characterized by a two-order hierarchy of en echelon fault segments. Type A segments are the longest (2-7 km) and are separated by the largest stepover widths (250-350 m). Volumetric calculations suggest that these splays converge downward into a master fault plane at depths of ∼100-260 m, well below the base of the post-LGM gravels. Accordingly, we infer that type A faults and the bulges that form in their stepovers had already developed in the lithified basement rock prior to deposition of the surficial gravels. Type B segments are shorter (500 m to ∼4 km long) and are separated by 30-150-m-wide stepovers. We calculate that these splays converge at shallow depths of <20 m near the base of the poorly consolidated gravels, where they developed in response to distributed deformation of that surficial cover during the past ∼12 k.y. The segmented surface trace of the Wairarapa fault in some ways resembles that produced in analogue models of deformation above a strike-slip fault in basement rock; however, the synthetically slipping fault segments of the Wairarapa fault zone strike at a smaller angle (2°-18°) to the overall strike of the fault than do most analogue models (typically, 10°-30°), raising questions about the angles at which "R-shears" may develop along natural strike-slip faults that slip with a convergent component. Also, the natural fault zone is narrower (350 m wide) than equivalent scaled widths of most analogue models (typically 1-2 km). These differences are interpreted to reflect the shallow depth of splaying of the natural Wairarapa fault zone in comparison to thickly sedimented analogue models. Based on our field data, we present a general model for (1) the relationship between an oblique-slip fault and the asymmetry of its near-surface synthetic fault splays and pressure bulges that deform gravel, and (2) the along-strike partitioning of strike- and dip-slip components of slip between adjacent splays in the near-surface in relation to the oblique slip accumulating on the main fault at depth. [ABSTRACT FROM AUTHOR]

The article discusses the late Miocene to early Pleistocene sedimentary rocks in the Fish Creek-Vallecito basin in southern California that records late Cenozoic subsidence and basin filling due to deformation in the San Andreas fault system. Data reportedly show that the section ranges in age from circa 8.0-0.4 million years (Ma). The article states that the onset of sedimentation at circa 8.0-0.4 million years (Ma) preserves the earliest extension or transtension in the area.

The article evaluates the hypothesis that porous sedimentary rocks subjected to high strain may not form deformation band zones (DBDZs). The accessible faults planes at the Upheaval Dome impact structure in southeastern Utah reportedly yielded no DBDZ formation evidence and instead pulverized quartz grains in the adjacent Navajo structure were found. The article states that strain rates at Upheaval Dome are consistent with seismic slip rates along faults like the San Andreas fault.

The article presents a case study of the four structural deformation stages in the Western Hills of Beijing in China during the Mesozoic time. These include the East-West-trending folds, North-East trending, Fangshan granitic pluton intrusion and East-dipping normal faulting in 70-60 million years (Ma). The article states that the structure of the hills in eastern China are related to complex imprinting of tectonic regimes that involved time-space deformation and various tectonic stresses.

The article reports on the development of a crenulation cleavage in a Mooselookmeguntic igneous complex roof due to intrusion resulting to mechanical thinning by complex thermal, chemical and mechanical interaction. This deformation gradient may reportedly mirror the steeply dipping of the pre-emplacement foliation that might be expected for nonlinear creep mechanisms. The article states that the cleavage may be important in the spatial distribution of localized strain in evolving orogens.

The article presents a study on the interactions of tectonic deformation, climate, eustasy and isostasy on forearc basin sedimentation in the Pleistocene sedimentary record of Hawke Bay, New Zealand. Eleven depositional sequences that developed during the last 1.1 million years are reportedly preserved into four controlled basins. The article states that the major uncorformity S5 separates megasequences M1 and M2 and that an overall retrogradational pattern of sequences were identified.

This paper addresses the contribution of extension in the upper crust during syncollisional exhumation of subducted material. We present structural data based on the analysis of ductile, brittle-ductile, and brittle deformation features in meta-pelitic schists and meta-basalts from the Schistes lustrés nappe stack in the Piedmont zone of the western Alps. To link the structures with synkinematic pressure and temperature estimates, geothermobarometry was performed using fluid inclusion investigation in quartz together with temperature estimations based on metamorphic chlorite composition. Samples used for geothermobarometry were collected taking into account the structural framework within veins associated with extensional structures observed at the regional scale. The early generation of veins associated with boudinage occurred at 415-345 °C and 6-2.5 kbar, and subsequent incipient normal faulting occurred at temperatures of 315-235 °C and pressures <1.7 kbar. The transition from ductile to brittle extension occurred between ca. 27 Ma and ca. 10 Ma. These results indicate a continuous extension in the upper crust during exhumation and continuous deformation associated with regional-scale tilting of the exhumed Schistes lustrés tectonic pile. The extensional tectonic regime in greenschist-facies conditions remains active today in most of the internal Alpine zones as the Alpine collision continues. [ABSTRACT FROM AUTHOR]

Most structural/kinematic models are inherently two-dimensional; even several recent three-dimensional models are "pseudo-three-dimensional" in that they consist of a series of parallel two-dimensional cross sections. Lack of a true three-dimensional formulation hampers our abilities to simulate three-dimensional structures such as oblique- and strike-slip faulting and displacement gradients perpendicular to the slip vector. The mathematical formulation of trishear deformation using incompressibility of flow is well suited to a solution in three dimensions. We derive one plausible velocity field for true three-dimensional flow in a triangular shear zone. This formulation allows us to simulate the deformation in oblique-slip deformation zones as well as flower structures associated with strike-slip fault zones. The strain distribution in flower structures combined with some simple mechanical assumptions suggests that faults in these zones would have a helicoidal geometry. The results of the kinematic model compare well to well-described structures in the Colorado Plateau, Andaman Sea, and Death Valley, as well as to data from analogue experiments. [ABSTRACT FROM AUTHOR]

This study addresses some aspects of the kinematics and structural setting of the Mediterranean Ridge accretionary complex, particularly those aspects related to the occurrence and distribution of Messinian evaporites. The approach is by (1) identification of the geometry of deformation through reprocessing of existing multichannel seismic reflection data from the Levantine Basin, aimed at the definition of the velocity field and depth imaging; (2) physical modeling in the laboratory, aimed at the study of the kinematics of shortening of sedimentary sequences detaching on viscous deco-elements; and (3) comparison between the results of the two approaches. We conclude that the thick Messinian sequence of the Levantine Basin is composed primarily of salt, so that the entire evaporitic sequence can be expected to behave as a viscous material. It follows that the main detachment of the post-Messinian wedge is located at the base of the Messinian salt layer. A viscous (salt) décollement would produce thrusting trending normal to the shortening direction, but boundary conditions affect structural trends even more than stress and/or movement direction. Both strain partitioning and the formation of major strike-slip faults within the post-Messinian wedge are prevented by the high angle of convergence between the African and Aegean plates as well as by the Iow intraplate friction. In addition, we show that curved and anastomosing thrust fronts are reflected in the cobblestone topography of the Mediterranean Ridge. We finally postulate that extension may occur in the central Mediterranean Ridge as a result of the geometry of the plate boundaries. This extension is considered as a possible cause of mud volcanism and mud diapirism. [ABSTRACT FROM AUTHOR]

Discusses the reactivation of Proterozoic structures during Laramide tectonism in Grand Canyon, Arizona. Geologic setting; Age of the Grand Canyon Supergroup; Tilting and normal faulting of the Unkar Group; Unconformities and intraformational faults in the Nankoweap Formation; Geometry and style of deformation.

Studies the late Cenozoic to Holocene deformation found in southwestern Sichuan and Yunnan, both in China, and their role in forming the southeastern portion of the Tibetan Plateau. Indication of a common evolution based on the similarity of structural development between the sites; Evidence for a complex, homogenous and diachronous plateau formation.

Investigates the deformational history of the Appalachian plateau detachment sheet during the Alleghanian orogeny in New York State. Identification of three types of fringe cracks; Twist angle of the fringe cracks and the abutting relationships of parent joints; Documentation of the spatial distribution and nature of fringe cracks.

Studies the distribution and characteristics of Taconian and Acadian deformation in the southern Quebec Appalachians. Subdivision of Taconian orogen; Structural relationships of Cambro-Ordovician rocks; Structural synthesis and interpretation; Tectonic zonation of the Quebec Appalachians.

The propagation of deformation bands into compressive and extensional stepover geometries is investigated by integrating field observations with numerical model simulations of the effective stress state due to shear along the bands. Deformation bands are tabular discontinuities, with mm- to cm-scale thicknesses, of localized volumetric strain and shear. Deformation bands are precursors to frictional slip (i.e., faulting) in porous granular rocks and soils. Systematic rotations in near-tip principal stress orientation due to shear along the overlapping deformation bands are shown to predict band propagation paths that are consistent with characteristic stepover geometries as viewed in the mode II direction, the orientation in which the observation plane is parallel with the displacement direction. Therefore, propagation paths for deformation bands can be predicted from knowledge of the effective near-tip stress state. These results establish a mechanics-based framework for investigations of fault growth and fault-controlled fluid flow in porous granular rocks and soils. [ABSTRACT FROM AUTHOR]