Contrasting Geomorphic and Stratigraphic Responses to Normal Fault Development During Single and Multi-Phase Rifting

Understanding the impact of tectonics on surface processes and the resultant stratigraphic evolution in multi-phase rifts is challenging, as patterns of erosion and deposition related to older phases of extension are overprinted by the subsequent extensional phases. In this study, we use a one-way coupled numerical modelling approach between a tectonic and a surface processes model to investigate topographic evolution, erosion and basin stratigraphy during single and multi-phase rifting. We compare the results from the single and the multi-phase rift experiments for a 5 Myr period during which they experience equal amounts of extension, but with the multi-phase experiment experiencing fault topography inherited from a previous phase of extension. Our results demonstrate a very dynamic evolution of the drainage network that occurs in response to fault growth and linkage and to depocentre overfilling and overspilling. We observe profound differences between topographic and depocenter development during single and multi-phase rifting with implications for sedimentary facies architecture. Our quantitative approach, enables us to better understand the impact of changing extension direction on the distribution of sediment source areas and the syn-rift stratigraphic development through time and space.

Experimental Study on Crack Extension Rules of Hydraulic Fracturing Based on Simulated Coal Seam Roof and Floor

Hydraulic fracturing can increase the fracture of coal seams, improve the permeability in the coal seam, and reduce the risk of coal and gas outburst. Most of the existing experimental specimens are homogeneous, and the influence of the roof and floor on hydraulic fracture expansion is not considered. Therefore, the hydraulic fracturing test of the simulated combination of the coal seam and the roof and floor under different stress conditions was carried out using the self-developed true triaxial coal mine dynamic disaster large-scale simulation test rig. The results show that (1) under the condition of triaxial unequal pressure, the hydraulic fractures are vertical in the coal seam, and the extension direction of hydraulic fractures in the coal seam will be deflected, with the increase of the ratio of the horizontal maximum principal stress to the horizontal minimum principal stress. The angle between the extension direction of the hydraulic fracture and the horizontal maximum principal stress decreases. (2) Under the condition of triaxial equal confining pressure, the extension of hydraulic fractures in the coal seam are random, and the hydraulic fracture will expand along the dominant fracture surface and form a unilateral expansion fracture when a crack is formed. (3) When the pressure in one direction is unloaded under the condition of the triaxial unequal pressure, the hydraulic fractures in the coal seam will reorientate, and the cracks will expand in the direction of the decreased confining pressure, forming almost mutually perpendicular turning cracks.

Ultrastructure and Function of Setae of a Planktonic Diatom, Chaetoceros Coarctatus

Silica frustules of most planktonic diatoms have many shallow holes in which the length (L) is smaller than the width (W). The present study focuses on a silicic ultrastructure of the setae of a planktonic diatom having deep (L/W > 1) holes. Here, we characterized nanoholes on the silica walls of hollow setae of a colony of Chaetoceros coarctatus. Basically, tetragonal poroid arrangements with and without a costa pattern are observed on the inner and outer surfaces, respectively, for three kinds of curving hollow setae. Deep nanoholes ∼90 nm wide are elongated from 150 to 1500 nm (L/W ∼17) with an increase in the wall thickness of the polygonal tubes of the setae. The inside poroid array, with a period of 190 nm in the extension direction of setae, is lined by parallel plates of the costae. However, the poroid arrangement on the outer surface is disordered, with several holes obstructed with increasing wall thickness of the posterior terminal setae. According to the movement of a colony in a fluid microchannel, the thick curving terminal setae is suggested to involve attitude control and mechanical protection. Using an optical simulation, the patterned deep through-holes on the intercalary setae were inferred to contribute anti-reflection of blue light for the promotion of photosynthesis in seawater.

Effect of Leading-Edge Bulges on Aerodynamic Characteristics of Bionic Wingsail

The leading-edge bulges along the extension direction are designed on the marine wingsail. The height and the spanwise wavelength of the protuberances are 0.1c and 0.25c, respectively. At Reynolds number Re=5×105, the Reynolds Averaged Navier-Stokes equations are applied to the simulation of the wingsail with the bulges thanks to ANSYS Fluent finite-volume solver based on the SST K-ω models. The grid independence analysis is carried out with the lift and drag coefficients of the wingsail at AOA = 8° and AOA=20°. The results show that while the efficiency of the wingsail is reduced by devising the leading-edge bulges before stall, the bulges help to improve the lift coefficient of the wingsail when stalling. At AOA=22° under the action of the leading-edge tubercles, a convective vortex is formed on the suction surface of the modified wingsail, which reduces the flow loss. So the bulges of the wingsail can delay the stall.

The Interrelationships between Faulting and Volcanism in the Okataina Volcanic Centre, New Zealand

<p>Continental rifts show close spatial relations between faulting and volcanism, however the interrelations between each process and their roles in the accommodation of regional extension are not well understood. The geometric and kinematic relations between an active silicic caldera complex and active faults in the upper 3-4 km of the crust (i.e. Taupo Rift) are investigated using regional gravity data, digital elevation models, outcrop mapping, seismic reflection lines, focal mechanisms and an historical account of the 1886 AD Tarawera eruption adjacent to, and within, the Okataina Volcanic Centre, New Zealand.The location and geometry of the Okataina Caldera were influenced by pre-existing faults. The caldera is elongate north-south, has a maximum subsidence of 3 +/- 0.5 km at the rift axis and occupies a 10 km hard-linked left step in the rift. The principal rift faults (55-75 degrees dip) define the location and geometry of the northwest and southeast margins and locally accommodate piecemeal caldera collapse. Segments of the east and west margins of the caldera margin are near vertical (70-90 degrees dip), trend north-south, and are inferred to be faults formed by the reactivation of a pervasive Mesozoic basement fabric (i.e. bedding, terrane boundaries, and/or faults). Measured displacements along the Paeroa and Whirinaki Fault zones in, and adjacent to, the Okataina Volcanic Centre took place over time periods ranging from 60 to 220 ka (together with historical accounts of the 1886 AD Tarawera eruption). These indicate that neither dike intrusion nor caldera collapse have a measurable influence on fault displacement rates outside the volcanic complex. Within the volcanic complex, vertical displacement along the Whirinaki Fault zone increases by up to 50% between the caldera topographic margin and inner collapse boundary. This increase in vertical displacement is predominantly due to the collapse of the caldera 60 ka ago. In the Okataina Volcanic Centre, extension is accommodated by a combination of tectonic faulting, dike intrusion, and gravitational caldera collapse. Gravitational caldera collapse is however, superimposed on regional extension without contributing to it. Rift-orthogonal extension dominates across the Taupo Rift with a minor (</= 20 degrees) component of right-lateral slip increasing northwards. The regional principal horizontal extension direction rotates 30 degrees clockwise south to north along the rift. The modal principal horizontal extension direction for the Okataina Volcanic Centre trends ~145 degrees, approximately normal to northeast striking rift faults and intra-caldera linear vent zones, and oblique to north-south faults. Zones of crustal weakness, brittle deformation, and dilation at the intersections of northeast-southwest dip slip and north-south oblique slip active fault sets are inferred to locally promote the ascent of magma. Preliminary examination of volcanism outside the Okataina Volcanic Centre suggests that intersecting northeast-southwest and north-south fault sets may also play a role in defining the geometry of calderas and locations of volcanic centres throughout the Taupo Volcanic Zone. Outside these volcanic centres (e.g. Taupo and Okataina) active extension is primarily accommodated by normal faulting which is driven by tectonic processes (e.g. far-field plate motions) and is not attributed to dike intrusion. The Taupo Rift has not yet reached the stage where it is dominated by magma-assisted extension and is primarily a young tectonic rift in an arc environment.</p></p>

The Interrelationships between Faulting and Volcanism in the Okataina Volcanic Centre, New Zealand

<p>Continental rifts show close spatial relations between faulting and volcanism, however the interrelations between each process and their roles in the accommodation of regional extension are not well understood. The geometric and kinematic relations between an active silicic caldera complex and active faults in the upper 3-4 km of the crust (i.e. Taupo Rift) are investigated using regional gravity data, digital elevation models, outcrop mapping, seismic reflection lines, focal mechanisms and an historical account of the 1886 AD Tarawera eruption adjacent to, and within, the Okataina Volcanic Centre, New Zealand.The location and geometry of the Okataina Caldera were influenced by pre-existing faults. The caldera is elongate north-south, has a maximum subsidence of 3 +/- 0.5 km at the rift axis and occupies a 10 km hard-linked left step in the rift. The principal rift faults (55-75 degrees dip) define the location and geometry of the northwest and southeast margins and locally accommodate piecemeal caldera collapse. Segments of the east and west margins of the caldera margin are near vertical (70-90 degrees dip), trend north-south, and are inferred to be faults formed by the reactivation of a pervasive Mesozoic basement fabric (i.e. bedding, terrane boundaries, and/or faults). Measured displacements along the Paeroa and Whirinaki Fault zones in, and adjacent to, the Okataina Volcanic Centre took place over time periods ranging from 60 to 220 ka (together with historical accounts of the 1886 AD Tarawera eruption). These indicate that neither dike intrusion nor caldera collapse have a measurable influence on fault displacement rates outside the volcanic complex. Within the volcanic complex, vertical displacement along the Whirinaki Fault zone increases by up to 50% between the caldera topographic margin and inner collapse boundary. This increase in vertical displacement is predominantly due to the collapse of the caldera 60 ka ago. In the Okataina Volcanic Centre, extension is accommodated by a combination of tectonic faulting, dike intrusion, and gravitational caldera collapse. Gravitational caldera collapse is however, superimposed on regional extension without contributing to it. Rift-orthogonal extension dominates across the Taupo Rift with a minor (</= 20 degrees) component of right-lateral slip increasing northwards. The regional principal horizontal extension direction rotates 30 degrees clockwise south to north along the rift. The modal principal horizontal extension direction for the Okataina Volcanic Centre trends ~145 degrees, approximately normal to northeast striking rift faults and intra-caldera linear vent zones, and oblique to north-south faults. Zones of crustal weakness, brittle deformation, and dilation at the intersections of northeast-southwest dip slip and north-south oblique slip active fault sets are inferred to locally promote the ascent of magma. Preliminary examination of volcanism outside the Okataina Volcanic Centre suggests that intersecting northeast-southwest and north-south fault sets may also play a role in defining the geometry of calderas and locations of volcanic centres throughout the Taupo Volcanic Zone. Outside these volcanic centres (e.g. Taupo and Okataina) active extension is primarily accommodated by normal faulting which is driven by tectonic processes (e.g. far-field plate motions) and is not attributed to dike intrusion. The Taupo Rift has not yet reached the stage where it is dominated by magma-assisted extension and is primarily a young tectonic rift in an arc environment.</p></p>

Tectonic Transport Directions, Shear Senses and Deformation Temperatures Indicated by Quartz c-Axis Fabrics and Microstructures in a NW-SE Transect across the Moine and Sgurr Beag Thrust Sheets, Caledonian Orogen of Northern Scotland

Moine metasedimentary rocks of northern Scotland are characterized by arcuate map patterns of mineral lineations that swing progressively clockwise from orogen-perpendicular E-trending lineations in greenschist facies mylonites above the Moine thrust on the foreland edge of the Caledonian Orogen, to S-trending lineations at higher structural levels and metamorphic grades in the hinterland. Quartz c-axis fabrics measured on a west to east coast transect demonstrate that the lineations developed parallel to the maximum principal extension direction and therefore track the local tectonic transport direction. Microstructures and c-axis fabrics document a progressive change from top to the N shearing in the hinterland to top to the W shearing on the foreland edge. Field relationships indicate that the domain of top to the N shearing was at least 55 km wide before later horizontal shortening on km-scale W-vergent folds that detach on the underlying Moine thrust. Previously published data from the Moine thrust mylonites demonstrate that top to the W shearing had largely ceased by 430 Ma, while preliminary isotopic age data suggest top to the N shearing occurred at ~470–450 Ma. In addition, data from the east coast end of our transect indicate normal-sense top down-SE shearing at close to peak temperatures at ~420 Ma that may be related to the closing stages of Scandian deformation, metamorphism and cooling/exhumation.

Contrasting geomorphic and stratigraphic responses to normal fault development during single and multi-phase rifting

Understanding the impact of tectonics on surface processes and the resultant stratigraphic evolution in multi-phase rifts is challenging, as patterns of erosion and deposition related to older phases of extension are overprinted by the subsequent extensional phases. In this study, we use a one-way coupled numerical modelling approach between a tectonic and a surface processes model to investigate topographic evolution, erosion and basin stratigraphy during single and multi-phase rifting. We compare the results from the single and the multi-phase rift experiments for a 5 Myr period during which they experience equal amounts of extension, but with the multi-phase experiment experiencing fault topography inherited from a previous phase of extension. Our results demonstrate a very dynamic evolution of the drainage network that occurs in response to fault growth and linkage and, to depocentre overfilling and overspilling. However, we observe profound differences between topographic and depocenter development during single and multi-phase rifting with implications for sedimentary facies development. Our quantitative approach, enables us to better understand the impact of changing extension direction on the distribution of sediment source areas and the syn-rift stratigraphic development through time and space.

Looking beyond kinematics: 3D thermo-mechanical modelling reveals the dynamics of transform margins

Transform margins represent ∼ 30 % of non-convergent margins worldwide. Their formation and evolution have traditionally been addressed through kinematic models that do not account for the mechanical behaviour of the lithosphere. In this study, we use high-resolution 3D numerical thermo-mechanical modelling to simulate and investigate the evolution of intra-continental strain localization under oblique extension. The obliquity is set through velocity boundary conditions that range from 15∘ (high obliquity) to 75∘ (low obliquity) every 15∘ for rheologies of strong and weak lower continental crust. Numerical models show that the formation of localized strike-slip shear zones leading to transform continental margins always follows a thinning phase during which the lithosphere is thermally and mechanically weakened. For low- (75∘) to intermediate-obliquity (45∘) cases, the strike-slip faults are not parallel to the extension direction but form an angle of 20∘ to 40∘ with the plate motion vector, while for higher obliquities (30∘ to 15∘) the strike-slip faults develop parallel to the extension direction. Numerical models also show that during the thinning of the lithosphere, the stress and strain re-orient while boundary conditions are kept constant. This evolution, due to the weakening of the lithosphere, leads to a strain localization process in three major phases: (1) initiation of strain in a rigid plate where structures are sub-perpendicular to the extension direction; (2) distributed deformation with local stress field variations and formation of transtensional and strike-slip structures; (3) formation of highly localized plate boundaries stopping the intra-continental deformation. Our results call for a thorough re-evaluation of the kinematic approach to studying transform margins.

Preparation of Long Sisal Fiber-Reinforced Polylactic Acid Biocomposites with Highly Improved Mechanical Performance

Green biodegradable plastics have come into focus as an alternative to restricted plastic products. In this paper, continuous long sisal fiber (SF)/polylactic acid (PLA) premixes were prepared by an extrusion-rolling blending process, and then unidirectional continuous long sisal fiber-reinforced PLA composites (LSFCs) were prepared by compression molding to explore the effect of long fiber on the mechanical properties of sisal fiber-reinforced composites. As a comparison, random short sisal fiber-reinforced PLA composites (SSFCs) were prepared by open milling and molding. The experimental results show that continuous long sisal fiber/PLA premixes could be successfully obtained from this pre-blending process. It was found that the presence of long sisal fibers could greatly improve the tensile strength of LSFC material along the fiber extension direction and slightly increase its tensile elongation. Continuous long fibers in LSFCs could greatly participate in supporting the load applied to the composite material. However, when comparing the mechanical properties of the two composite materials, the poor compatibility between the fiber and the matrix made fiber’s reinforcement effect not well reflected in SSFCs. Similarly, the flexural performance and impact performance of LSFCs had been improved considerably versus SSFCs.