Loveless, Stephan R.Klimczak, ChristianCrane, Kelsey T.Byrne, Paul K....
1.1-1.14页
查看更多>>摘要：Mercury hosts thousands of shortening landforms that are widespread across the entire planet. The shortening is widely accepted to be caused by a combination of thrust faulting and folding, resulting from the global contraction of Mercury caused by long, sustained cooling. Most shortening landforms on Mercury's surface have been classified into one of two groups: lobate scarps or wrinkle ridges. There is no distinct statistical difference in the surface morphology of these shortening landform classifications. Only a small subset of shortening landforms are clear-endmember wrinkle ridges and lobate scarps. The difference between geomorphic manifestations of shortening landforms may be governed entirely by the thrust systems and associated folding that form them. We therefore model thrust systems associated with 55 lobate scarp and wrinkle ridge endmember shortening landforms found across the surface of Mercury. Structures were modeled in 2D sections below the topographic profiles of landforms with the greatest structural relief. Models utilized the fault-bend fold algorithm in the MOVE geologic modeling software. Once models matched the observed topography and shortening strain, fault geometric parameters, such as number of structures, dip, depth extent of faulting, height, etc., were extracted and compiled for all structures. Our modeling shows that Mercury hosts a wide range of complex thrust systems, including single, listric faults, imbricate thrusts, and pop-up structures. In particular, the morphologies of lobate scarps endmember structures are best explained by models of a single, listric fault, whereas most wrinkle ridge endmember structures require more than one fault. We identify a large overlap in the variation of fault geometric parameters for both wrinkle ridge and lobate scarp archetypes, confirming the results of our previous geomorphic analysis that shortening landforms do not comprise two distinct categories. The overlap in geometric parameters suggests that the formation mechanisms of lobate scarp and wrinkle ridge endmember structures are the same.
查看更多>>摘要：In the northern Tibetan Plateau, a series of northeast-striking faults have developed within the Xijianquan-Jiujing transtensional fault system (XJTFS), located approximately 150 km north of the Altyn Tagh Fault along the southern Beishan Block. Among these, the easternmost Jiujing-Bantan Fault (JBF) is the most active. Field mapping, unmanned aerial vehicle-derived digital topography, Google Earth imagery, and audio-magnetotelluric profiles reveal that the JBF, approximately 28 km in length, comprises four linear branches forming a negative flower structure. Displacement of landforms, such as terminal facets, terraces, small gullies, and ridges, indicates that the fault exhibits left-lateral strike-slip movement with a normal component. The vertical slip rate has been estimated at similar to 0.02 mm/yr since similar to 125 ka BP. Trenching research along the JBF identified four paleoseismic events, dated using optically stimulated luminescence (OSL) to approximately 20, 27-31, 34, and 76-78 ka BP. The potential seismic magnitude along the fault is estimated at M 6.3- 6.5. These findings, combined with regional geodetic data, suggest that late Quaternary deformation in the northern Tibetan Plateau has propagated into the southern Beishan Block. This deformation is inferred to be influenced by the clockwise transpressional deformation and northeastward movement of the Tashi micro-Block, located north of the Altyn Tagh Fault. The observed deformation pattern demonstrates strain partitioning and transfer between the northern Tibetan Plateau and the southern Mongolian Plateau.
查看更多>>摘要：Shallow crustal faulting involves complex processes, including brittle and ductile deformation, frictional heating, and fluid interaction, which may all leave distinct geological signatures. However, deciphering these mechanisms is challenging. This study investigates the deformation near two faults in northern Israel: the active Nahef East fault and the Qiryat Shemona fault, a major strand of the Dead Sea Fault (DSF) system, both cutting through diamagnetic carbonate rocks. We employ a range of methods, including anisotropy of magnetic susceptibility (AMS), magnetic properties, electron backscatter diffraction (EBSD), and geochemical analyses to target specific faulting processes. Both faults exhibit magnetic fabrics with foliations formed by AMS maximum (K-1) and intermediate (K-2) axes which are scattered on a plane sub-parallel to fault surfaces, extending similar to 0.5 m from these fault surfaces. In the Nahef East fault, slight changes in magnetic properties, overall mineralogy and microstructures such as lobate calcite grains, indicate moderate temperatures (<200-250 degrees C), and fluid interaction, which constrains grain reorientation and the development of crystallographic preferred orientation (CPO). Conversely, in the Qiryat Shemona fault, the small (similar to 5 mu m) twinned calcite grains indicate moderate to high temperatures (>250-300 degrees C), high stress (>= 100 MPa) and dry conditions, potentially reflecting the fault's maturity. Distinct deformation fabrics and microstructural features around these faults reveal localized plastic deformation. The results underscore a potential gap between the extent of deformation observed in natural faults and those replicated in laboratory experiments, likely due to limited sample size and timescale considerations in laboratory settings.
Chukwuma, KennethHarris, Nicholas B.Konstantinovskaya, Elena
1.1-1.31页
查看更多>>摘要：Mudstone formations (shales) are increasingly recognized as targets of hydrocarbon exploration and production, sites for CO2 storage, and repositories for nuclear and other waste. Due to their low matrix permeability, considerable amount of fluid flow in shales may occur within fractures, and consequently significant effort is placed on the characterization of fracture networks. We report results of a multidisciplinary field and borehole study of a fracture network in Permian organic-rich shales of the Whitehill Formation in the Karoo Basin, South Africa, developed in proximity to Lower Jurassic dolerite intrusive sills. The goal was to systematically document the different fracture types, differentiate the underlying fracturing mechanisms, and quantify their contribution to fracture networks in intrusion-related organic-rich shales. Our observations comprise high-resolution digital outcrop models constructed from ground- and drone-based photogrammetry, and petrographic and geochemical data from fracture cements and fluid inclusions contained in them. Our results indicate that the fracture network in the studied shale developed from a suite of processes related to intrusion of the sills. These resulted in the formation of five distinctive fracture types, with varying orientation and fracture-filling material: (i) vertical solid bitumen veins; (ii) sub-vertical to horizontal solid bitumen-calcite veins; (iii) closely-spaced subvertical calcite veins; (iv) horizontal bitumen and calcite veins; and (v) sub-vertical joints. Based on the spatial distribution of these fracture types, three fracture domains are identified: upper, central, and lower domains, where the upper and lower domains are near the intrusions and the central domain at a greater distance. The upper and lower domains are dominated by solid bitumen and solid bitumen-calcite veins that exhibit a strong vertical orientation with a N-S strike. In contrast, the central domain comprises nearly horizontal solid bitumen-calcite veins. The vertical tensile fractures in the upper and lower domains likely developed in response to increased pore fluid pressure associated with the mobilization hydrocarbon and other hydrothermal fluids caused by intrusive heating. The horizontal tensile fractures in the central domain may be related to the thermal maturation and poroelastic deformation of the organic-rich shales. The development of the N-S tensile fractures is consistent with the normal fault regime associated with the E-W Early Jurassic extensive tectonics that led to the breakup of Gondwana. The relative contributions of the vertical and horizontal tensile fracture types in the Karoo shale to spatial variation of fracture orientation, intensity, and connectivity were evaluated using digital fracture network quantification. All observed fracture types contributed to hydrocarbon and fluid migration and storage. Our observations demonstrate that outcrops containing natural fracture sets can be used to characterize crucial fracture attributes such as fracture length, spatial arrangement, and connectivity and contribution of different fracturing mechanisms to fluid flow and storage in organic-rich shales impacted by igneous intrusions.
查看更多>>摘要：The Qilian-Haiyuan fault is a boundary fault with strike slipping in the Qilian Shan (Shan means mountain or mountain range in Chinese) on the northeastern Tibetan Plateau. Several strong earthquakes (M >= 7) have occurred in this fault zone, and the risk of future major earthquakes is highly concerning. We identified a seismic surface rupture zone of unknown age at the Halahu fault, which is located at the western end of the Qilian- Haiyuan fault. The Halahu fault plays a crucial role in structural transformation at the westernmost point of the Qilian-Haiyuan fault zone, and historical seismic records are vital for assessing the future seismic risk associated with the fault. We found via field investigation that the existing length of the rupture zone is more than 24 km, which is characterized mainly by cracks, the offset of the trench, and the offset of terrace edges. Twenty-eight left-lateral coseismic offsets were determined using field measurements and UAV image analysis, with a minimum offset of 0.6+0.1 m and a maximum offset of 2.5+0.2 m. Historical earthquake records confirm that the surface rupture zone was caused by the M61/2 earthquake that occurred east of Hala Lake on July 14, 1930 east of Hala Lake; however, the magnitude of that earthquake should be revised to be approximately M63/4 on the basis of field survey data. Research has shown that major earthquakes have shifted from the Bayan Har active block to the Qinghai-Tibet block boundary fault zone. This study identified and dated earthquake surface rupture zones, offering essential guidance for future research and assessments of fault earthquake risk. Our results indicate that the Halahu, Tuolaishan, and Jinqianghe-Laohushan faults have high potential for strong future earthquakes.
查看更多>>摘要：This study presents a detailed microstructural analysis of salt samples collected from the exposed mountain glacier in Iran, the Kuh-e-Namak (Dashti). Our goal is to pinpoint the different deformation mechanisms leading to grain size reduction and, how these, together with the influx of rainwater and development of porosity, affect the creep of the polycrystalline halite. We investigated 17 gamma-irradiated thin sections by transmitted and reflected light microscopy, quantitative grain and subgrain statistics, and crystallographic-preferred orientation (CPO) mapping using Electron Back Scattered Diffraction (EBSD). The microstructural evidence suggests a combination of solution-precipitation accompanied by grain-boundary sliding and dynamic recrystallization. The grain size decreases by subgrain rotation recrystallization, microcracking, and grain boundary migration by three different mechanisms: 1) grain boundary bulging into grains, 2) nucleation of new grains and, 3) segmentation of porphyroclasts by planar domains of dynamic recrystallization. The mean grain size ranges from 118 to 508 mu m and subgrain sizes from 14 to 99 mu m from which differential stresses between 1.9 and 10.2 MPa were calculated. Inferred strain rates for the glacier are in the order of magnitude of 10-10-10-8 s-1. The increasing shape-preferred orientation of halite grains from the crestal domal part of the diapir towards the frontal parts of extrusive glaciers is interpreted as a result of dominant solution-precipitation creep and salt flow. Rainwater influx rendering this important deformation mechanism switch is attributed to the development of porosity along microcracks and grain boundaries.
查看更多>>摘要：Preferred orientation of pyrrhotite by crystal lattice in varied mineralized rocks was investigated by means of the anisotropy of magnetic susceptibility. The study area is mineralized contact of Neo-Proterozoic meta-volcanics with Variscan Sa<acute accent>zava tonalite in the Central Bohemia. The contact crops out in the Josef Gallery located in the Mokrsko-West gold deposit. Magnetism of the investigated rocks is dominantly carried by pyrrhotite associated with the Mokrsko-West gold mineralization. In meta-volcanics, pyrrhotite basal planes are parallel to the cleavage and were preferably oriented through recrystallization or neocrystallization in an anisotropic stress field and/or through mechanical reorientation due to ductile deformation of the host rock. In tonalite, pyrrhotite basal planes are parallel to dominating steep joints. This preferred orientation evidently originated through oriented crystallization from mineralizing fluids into microcracks hosting quartz veinlets. Steep to vertical intersections come from differently striking vertical joints hosting mineralizations.
Polanski, Clara CostaTrzaskos, BarbaraRodrigues, Merolyn Camila Naves de LimaVesely, Fernando Farias...
1.1-1.18页
查看更多>>摘要：Soft-sediment deformation structures (SSDS) are the result of deformation in sedimentary material before significant diagenesis or lithification, and they can result from various triggers, including mass transport (slides, slumps and debris flows). There are several previous works on SSDS within mass-transport deposits (MTDs) and their deformation mechanisms, however most of them consider only macro-to mesoscale data (outcrops and hand specimens), resulting in a lack of microanalysis of deformation mechanisms. In this work we investigate microstructures aiming to interpret deformation mechanisms involved in the formation of folds commonly found in MTDs, aiming to create a compendium of these structures. Using samples from two evolved (highly homogeneized) MTDs in the Permo-Carboniferous Itarare<acute accent> Group, Parana<acute accent> Basin, southern Brazil, we analyze structural styles in thin sections and discuss their occurrence, geometry and deformation mechanisms. Structural analysis reveals a diverse range of folds resulted from buckling-dominated and bending-dominated folding processes, whose formation was influenced by variations in sediment cohesion, layer thickness and rheology. The absence of cataclasis and early diagenetic minerals, along with grain alignment to fault planes and fold axial surfaces, indicates that deformation occurred under low confining stress prior to lithification, driven by granular flow. Local variations in cohesion within sand- and silt-rich layers are attributed to pore-fluid pressure fluctuations. The findings suggest that the primary deformation mechanism involves progressive shearing of water-saturated sediment, enhanced by liquefaction and fluidization processes.
查看更多>>摘要：This study investigates slip behaviour on overlapping, en echelon normal faults by analysing the slip histories of the Skinos and Pisia active normal faults over the past similar to 20 kyrs using in situ Cl-36 cosmogenic dating. New Cl-36 data from the Skinos Fault and published Pisia Fault Cl-36 data were modelled, with both sample sites located within an overlap zone and separated by an across-strike distance of 1-2 km. Our analysis reveals fluctuating slip rates, with the two faults alternating between out-of-phase and simultaneous slip. The Pisia Fault exhibited a slip rate of similar to 0.5-0.75 mm/yr from similar to 20 ka to similar to 9.6 ka, increasing to similar to 1.25 mm/yr until similar to 5.2 ka. It then slowed to similar to 0.25 mm/yr or less until similar to 2.0 ka, before accelerating again to similar to 1.25-1.5 mm/yr to the present day. The Skinos Fault maintained a low slip rate of similar to 0.25 mm/yr or less from similar to 20 ka to similar to 6.4 ka, before accelerating to similar to 2.0-3.0 mm/yr, persisting to similar to 1.0 ka or possibly the present-day. Comparing their slip histories, the faults show periods of simultaneous slip between similar to 6.4 ka to similar to 5.2 ka and similar to 2.0 ka to similar to 1.0-0.0 ka, and out-of-phase slip occurred between similar to 9.6 ka and similar to 6.4 ka, and from similar to 5.2 ka to similar to 2.0 ka. Out-of-phase behaviour on faults across strike has now been observed on faults spaced across-strike at distances of 1-2 km, 10-20 km, and similar to 100 km, raising the question of why it occurs. Possible mechanism(s), including rheological fluctuations within fault/shear-zone structures linked between the brittle upper crust and viscous lower crust and stress interactions, are discussed to explain the out-of-phase and simultaneous slip behaviour.
NETL
NSTL
Elsevier