Complex Deformation Zone Research Articles

Distribution of Permian and Triassic strata in the Laoshan Uplift, Southern Yellow Sea, using seismic attributes

The Laoshan Uplift (LSU) in the South Yellow Sea Basin of the Lower Yangtze Plate is a potential site for hydrocarbon exploration; thus, determining the strata attributes and distribution is imperative. Tracking a wide range of seismic reflection horizons for lateral comparisons is challenging because the first well (CSDP-2) encountered in the Paleozoic strata of the LSU is located in a structurally complex deformation zone and has yielded poor seismic data quality. In this study, we present a novel approach to seismic horizon tracking in areas with few or no wells and adopt a cross-regional analogy and inverse analysis method to track the seismic horizon. Seismic attribute characteristics of the marine strata of the LSU were compared with the seismic horizons calibrated in the Wx1 well in the stable Qingdao Depression (QDD), and horizontal tracking was performed. An inverse analysis was then performed on the CSDP-2 well area to predict the distribution of marine strata in the LSU. The results revealed that the Permian and Triassic strata of the LSU and QDD have similar seismic attributes. Finally, the seismic horizon of the LSU was tracked horizontally based on a comparison of the seismic attributes of the LSU and QDD. Previous studies showed that seismic reflection horizons are difficult to calibrate, and the marine strata attributes in the LSU remain controversial. This study adopted a cross-regional comparison and inversion analysis method to perform a seismic multi-attribute comparison based on the calibrated results of the QDD for the Wx1 well. The remaining Permian and Triassic strata lie almost entirely within the LSU. Moreover, the maximum reported thicknesses of the Upper Permian and Lower-Middle Triassic strata in the LSU were approximately 500 and 2750 m, respectively. Our findings will aid in the exploration and evaluation of early hydrocarbon resources in the LSU.

Mechanical Properties of 6061 Aluminum Alloy under Cyclic Tensile Loading

During the service process of an aluminum alloy structure, its complex deformation zone experiences repeated loading problems such as repeated tension, compression, bending and reverse bending. At the same time, the cyclic loading and heat treatment process also have a certain impact on the mechanical properties of aluminum alloy extruded tubes. Therefore, the study of heat treatment process parameters has important engineering and practical value for the mechanical properties of aluminum alloy extrusion tubes under cyclic loading conditions. The experiment takes 6061-T6 aluminum alloy extruded tubes as the research objects. In the study, heat treatment and cyclic tensile tests were carried out on 26 aluminum alloy specimens to study the effects of different heat treatment parameters (such as heating temperature, holding time, and cooling method) on the stress–strain hysteresis curves, stress characteristics, hysteretic energy, skeleton curves and failure characteristics of the alloy under the same loading system. In addition, different cyclic tensile tests were carried out on 20 aluminum alloy samples without secondary heat treatment to discuss the effects of different cyclic loading regimes on the mechanical properties of the alloy. The research results indicate that the effect of heating temperature on the cyclic loading performance of the alloy is greater than that of the holding time, and the effect of the cooling method on the cyclic loading performance of the alloy is not obvious. A cyclic tensile loading regime has a significant impact on the strength, elongation and hysteresis energy of the alloy. The hysteretic behavior of the alloy during cyclic tensile loading depends on the applied stress level and loading history. As the number of cycles increases, the shape of the hysteresis curve tends to be stable, but there is no monotonic relationship between the number of cycles loaded and the hysteresis energy.

Mapping the near‐surface trace of the seismically active Kachchh Mainland Fault and its lateral extension in the blind zone, Western India

ABSTRACTThe W–WNW‐striking Kachchh Mainland Fault (KMF) is the largest intra‐basinal fault in the Kachchh Rift Basin (KRB) located at the western continental margin of the Indian plate, and is responsible for several historic earthquakes, including the 2001 Bhuj earthquake and the 1956 Anjar earthquake. The objective of the study is to constrain the precise location and near‐surface characteristics of the KMF using field and ground penetrating radar (GPR) studies. Efforts were also made to ascertain and map the eastward continuity of the KMF. The fault has a prominent geomorphic expression up to the east of Devisar, where the KMF scarp finally dies out. The KMF marks the lithotectonic contact between Mesozoic rocks in the south and Tertiary rocks in the north. The segmented nature of the KMF has been previously attributed to transverse faults, complex deformation zones and heterogeneous assemblages of unconformable Quaternary deposits. Eight survey sites between Nirona and Sikra were chosen for near‐surface investigation of KMF using GPR. Comparatively, high‐amplitude radar reflections were received from well‐compacted sand‐ and shale‐rich Mesozoic rocks, whereas low‐amplitude weak reflections were observed from softer and clay‐rich Tertiary rocks. In the upper section of the GPR profiles, Quaternary deposits display low‐ to moderate‐amplitude semi‐continuous to wavy reflections. The traceable length of the KMF has been extended eastward by ∼20 km through the current study, which is considered a blind zone as feeble surficial evidence is present, but the fault trace is confirmed near the surface using GPR. The eastern part of the KMF is inferred to be a near‐vertical north‐dipping normal fault based on GPR data analysis. The tendency of the KMF to transform into a reverse fault in the vicinity of the intersection with transverse faults implies zones of relatively higher stress accumulation that might activate and trigger devastating earthquakes in the future.

Towards Automated/Semiautomated Extraction of Faults from Lidar Data

The Pajarito fault system is a complex zone of deformation and a seismically active region nestled within the Rio Grande rift in north-central New Mexico. Numerous laterally discontinuous faults and associated folds and fractures interact in a manner that has important implications for seismic hazards and risk mitigation. Previous efforts have established a foundation for the location of lineaments and structures in the Pajarito fault system; however, ensuring the completeness of the current lineament mapping is required for identifying areas for field validation, evaluating the potential for future seismic activity, and better understanding fault interaction. Assistance with this fault-mapping task via automated or semiautomated techniques as applied to lidar data over a large area of interest is highly desirable. A proof-of-concept processing flow which transforms lidar point-cloud data into a raster of surficial fault candidates is described and illustrated herein. These initial results hold great promise toward achieving our ultimate goal.

Statement of the Task of Studying Multidimensional Dynamic Objects with Complex Deformation Zones of Fibrous Materials

Statement of the Task of Studying Multidimensional Dynamic Objects with Complex Deformation Zones of Fibrous Materials

Calculating Power Parameters of Rolling Mill Based on Model of Deformation Zone with Four-Roll Passes

Making “digital twins” for rolling processes and mill equipment should begin with the development of mathematical models of the deformation zone. The deformation zone of two-high flat mill rolling have been studied in detail, relevant models are available in many academic papers. However, the same cannot be said about the most complex deformation zones in stands with multi-roll gauge. Therefore, the task of their reliable mathematical description is of immediate interest. The development of mathematical models is necessary for the design of new wire mills and rolling-drawing units. The combination of rolling in stands with multi-roll gauge and drawing is a promising direction in the production of wire from difficult-to-form steels and alloys. Digital models for pressure-based metal treatment are also necessary for calculating the rolling-mill power parameters during the development of new assortments at the operating mills. The models of deformation zones present the basis for developing the multivariable control systems of process conditions of continuous mills. This research is devoted to the study of the deformation zone and the development of a procedure for calculating the power parameters of rolling in a stand with four-roll passes. The solution of these challenges is given using the example of an operating five-stand wire mill. The authors analysed the known analytical dependencies for calculating the rolling mill force and torque. A mathematical model of the deformation zone and a program for calculating the power parameters have been developed. The paper compares the results obtained from calculations based on analytical dependence and on modelling. A comparison with the experimental parameters obtained at the mill is given. The authors assess the feasibility of using the known formulas and analyse the impact of the front and rear tensions on the power parameters of rolling mill. The problem of developing an automatic tension control system for continuous mills with multi-roll groove is substantiated.

Lithospheric Structure of Northwestern Venezuela From Wide‐Angle Seismic Data: Implications for the Understanding of Continental Margin Evolution

AbstractNorthwestern Venezuela is located in the complex deformation zone between the Caribbean and South American plates. Several models regarding the lithospheric structure of the Mérida Andes have been proposed. Nevertheless, they lack relevant structural information in order to support the interpretation of deeper structures. Therefore, a 560‐km‐long refraction profile across the northern part of Mérida Andes, oriented in a NNW direction, covering areas from the Proterozoic basement in the south, to both Paleozoic and Meso‐Cenozoic terranes of northwestern Venezuela to the north, is analyzed in this contribution. Thirteen land shots were recorded by 545 short‐deployment seismometers, constraining P wave velocity models from first‐arrival seismic tomography and layer‐based inversion covering the whole crust in detail, with some hints to upper mantle structures. The most prominent features imaged are absence of a crustal root associated to the Mérida Andes, as the Northern Andes profile is located marginal to the Andean crustal domain, and low‐angle subduction of the Caribbean oceanic slab (~10–20°) beneath northwestern South America. Further crustal structures identified in the profile are (a) crustal thinning beneath the Falcón Basin along the western extension of the Oca‐Ancón fault system interpreted as a back‐arc basin; (b) suture zones between both the Proterozoic and Paleozoic provinces (Ouachita‐Marathon‐related suture?), and Paleozoic and Meso‐Cenozoic terranes (peri‐Caribbean suture) interpreted from lateral changes in seismic velocity; and (c) evidence of a deep Paleozoic(?) extensional basin, underlying thick Mesozoic and Cenozoic sequences (beneath the Guárico area).

Historical coseismic surface deformation of fluvial gravel deposits, Schafberg fault, Lower Rhine Graben, Germany

Intraplate earthquakes pose a significant seismic hazard in densely populated rift systems like the Lower Rhine Graben in Central Europe. While the locations of most faults in this region are well known, constraints on their seismogenic potential and earthquake recurrence are limited. In particular, the Holocene deformation history of active faults remains enigmatic. In an exposure excavated across the Schafberg fault in the southwestern Lower Rhine Graben, south of Untermaubach, in the epicentral region of the 1756 Duren earthquake (M L 6.2), we mapped a complex deformation zone in Holocene fluvial sediments. We document evidence for at least one paleoearthquake that resulted in vertical surface displacement of 1.2 ± 0.2 m. The most recent earthquake is constrained to have occurred after 815 AD, and we have modeled three possible earthquake scenarios constraining the timing of the latest event. Coseismic deformation is characterized by vertical offset of sedimentary contacts distributed over a 10-m-wide central damage zone. Faults were identified where they fracture and offset pebbles in the vertically displaced gravel layers and fracture orientation is consistent with the orientation of the Schafberg fault. This study provides the first constraint on the most recent surface-rupturing earthquake on the Schafberg fault. We cannot rule out that this fault acted as the source of the 1756 Duren earthquake. Our study emphasizes the importance of, and the need for, paleoseismic studies in this and other intracontinental regions, in particular on faults with subtle geomorphic expression that would not typically be recognized as being potentially seismically active. Our study documents textural features in unconsolidated sediment that formed in response to coseismic rupturing of the underlying bedrock fault. We suggest that these features, e.g., abundant oriented transgranular fractures in their context, should be added to the list of criteria used to identify a fault as potentially active. Such information would result in an increase of the number of potentially active faults that contribute to seismic hazards of intracontinental regions.

The Eurekan deformation in the Arctic: an outline

The evolution of the Eurekan deformation zones in the Arctic is closely related to the development of the circum-Greenland plate boundaries in Early Cenozoic times (53 – 34 Ma). Mostly, the Eurekan Orogeny or deformation has been interpreted as a predominantly compressive tectonic event, but the Eurekan deformational history in the Arctic was not the result of a single tectonic episode. It rather represents a complex sequence of successive tectonic stages, which produced a number of intra-continental deformation zones with changing, sometimes opposing, lateral, oblique and convergent kinematics in the Canadian Arctic Archipelago, north and NE Greenland, and Svalbard. The interaction between the continental plates, especially in combination with the development of transform faults, resulted onshore in the formation of several complex deformation zones and areas of Eurekan deformation. The Eurekan deformation can be divided into two major tectonic stages: the first phase in the Early Eocene was dominated by orthogonal compression in the West Spitsbergen Fold-and-Thrust Belt along the west margin of the Barents Shelf and contemporaneous sinistral strike-slip tectonics along the Wegener Fault and on Ellesmere Island, whereas the second phase in the Late Eocene was characterized by dextral strike-slip and compression on Ellesmere Island and contemporaneous dextral transpression and transtension along the De Geer Fracture Zone or Hornsund Fault Complex between NE Greenland and Spitsbergen.

Fracture-fluid relationships: implications for the sealing capacity of clay layers – Insights from field study of the Blue Clay formation, Maltese islands

Abstract Sealing capacity of clay layers is a key parameter in many fields of geoscience, such as CO2 storage, hydrocarbons trapping, and waste disposal. In the context of deep geological disposal of radioactive waste, clayey formations are studied as potential host rocks. This work deals with tectonic fracturing, fluid flow, and the sealing capacity of clay layers in an outcropping formation sharing similarities to these potential host rocks. The Blue Clay formation (Maltese islands) outcrops between two limestones affected by slight extensional tectonics. Zones of oxidation around fractures are interpreted as evidence of palaeofluid circulation, and are used to assess the role of joints and faults in controlling the hydrological communication between adjacent layers. Joints and small faults (displacement < 5 m) seem to die out quickly up-section within the Blue Clays, and appear to have played an insignificant role in the palaeohydrology of the area. In contrast, large faults (displacement > 50 m) display clay smear structures, and the lack of oxidized zones around them suggests they served as barriers to fluid flow. Intermediate-sized faults die out up-section into complex deformation zones comprised of irregular joints that are filled with gypsum and surrounded by oxidation zones. These observations indicate that these intermediate-sized faults, usually considered as sealed by classical predictive methods such as “Shale Smear Factor”, may have played a significant role in the local palaeohydrology.

The geologic evolution of Venus: Insights into Earth history

Through the clever use of stereo radargrammetric techniques on images from the Magellan mission to Venus in the 1990s, combined with recent quantitative analyses of magma reservoirs on Earth, McGovern et al. (2014, p. 59 in this issue of Geology) resolve an important outstanding question dating from that era: What forces are responsible for the graben extending radially from large shield volcanoes? They show that, in addition to radial dike emplacement, the larger graben are readily accounted for by magma reservoir infl ation, providing new insight into processes of magma ascent and eruption on Venus, and their relation to globally interconnected rift systems on Earth’s sibling planet. This new contribution serves as a reminder of the importance of Venus to our understanding of geological processes and history on Earth, and the need for new data to resolve some of the most fundamental problems in comparative planetology. HISTORY OF VENUS EXPLORATION The liftoff of Sputnik in 1957 launched a vigorous international program of planetary exploration and the fi eld of comparative planetology. How do our neighboring terrestrial (Earth-like) planets look, and what insights can they provide in understanding our own planet? Early missions to the Moon, Mercury, and Mars showed that these terrestrial planets with one-half or less the diameter of Earth looked very different from Earth. Their high surface area/volume ratio lets them conduct internal heat to the surface effi ciently and cool rapidly, becoming “one-plate planets” with thick, stable lithospheres. Their surfaces preserve evidence of geological processes from the fi rst half of solar system history. Intensely pockmarked by impact craters and resurfaced by volcanism, they reveal the roles of external forces (early accretion and high impact fl ux) and internal thermal evolution (conduction, convection, hot spot formation, magmatism, advection, and surface volcanism). But what about Venus, similar to Earth in size, density, and position in the Solar System? Is it Earth-like, with a young surface, plate tectonics, and tracks of hot-spot volcanoes, or like the smaller planets, with a heavily cratered surface? When imagination outstripped data, Venus was thought to have an Earth-like hot swampy surface, but we now know that its CO 2 atmosphere, sulfuric acid clouds, surface temperatures hot enough to melt lead, and very slow and retrograde rotation, are nothing like Earth. What about its surface and interior geology? Venera (Soviet Union) atmospheric probes and landers showed that the surface was littered with generally basaltic rocks and patchy soils (Hunten et al., 1983). A radar altimeter on the Pioneer Venus (PV, United States) orbiter (1978) provided a global topographic map, with a resolution of ~100 km, low by today’s standards. Its analysis showed many Earth-like features: evidence for continent-like highlands with marginal linear mountain belts, broad Iceland-like rises and plateaus, circular basins, and very long, linear lowlands, but with a global hypsometry different from that of current Earth. Instead of the latter’s bimodal distribution of global topography, the hypsometry of Venus was unimodal, skewed to higher elevations. Increasingly higher-resolution radar data provided additional evidence for Earth-like features. One of the rises in the PV data (Beta Regio) was cleaved by a rift zone, surmounted by volcanoes. The mountain belts surrounding a large continent-like plateau (Ishtar Terra) were composed of multiple parallel linear features analogous to Earth’s folded mountain belts. Often-circular features (coronae) were not impact structures, but complex deformation zones, more consistent with internal deformation origins. Higher-resolution radar imaging and more coverage were needed to fi out whether Venus was Earth-like. In 1983, Soviet Union orbiters Venera 15 and 16 surveyed the northern hemisphere (~30% of Venus), with radar imaging resolution of 1‐2 km (Barsukov et al., 1992), showing that many highlands consist of very highly deformed terrain (tesserae), and that organized linear folded mountain belts surround highland plateaus. Large volcanoes exist in abundance, but show little evidence for hot spot traces or convergent plate boundaries. Coronae looked like the fi ngerprints of mantle processes. Most remarkably, there were few impact craters, indicating an age on the order of only hundreds of millions of years. These results raised signifi cant, fundamental questions: Where is the ancient billions-of-years-old continent-like terrain on Venus? What is the average age of the surface? Is Venus characterized by Earth-like plate tectonics, or do its thermal regimes suggest another manifestation of plate tectonics? Is internal heat transferred mainly by conduction, advection, or plate tectonics? Are the fold belts global and if so, where is the corresponding extension and divergence? These questions guided the 1989 United States Magellan mission to Venus. THE MAGELLAN MISSION PROVIDES GLOBAL COVERAGE

Complex rupture mechanism and topography control symmetry of mass-wasting pattern, 2010 Haiti earthquake

The 12 January 2010 Mw 7.0 Haiti earthquake occurred in a complex deformation zone at the boundary between the North American and Caribbean plates. Combined geodetic, geological and seismological data posited that surface deformation was driven by rupture on the Léogâne blind thrust fault, while part of the rupture occurred as deep lateral slip on the Enriquillo–Plantain Garden Fault (EPGF). The earthquake triggered >4490 landslides, mainly shallow, disrupted rock falls, debris-soil falls and slides, and a few lateral spreads, over an area of ~2150km2. The regional distribution of these slope failures defies those of most similar earthquake-triggered landslide episodes reported previously. Most of the coseismic landslides did not proliferate in the hanging wall of the main rupture, but clustered instead at the junction of the blind Léogâne and EPGF ruptures, where topographic relief and hillslope steepness are above average. Also, low-relief areas subjected to high coseismic uplift were prone to lesser hanging wall slope instability than previous studies would suggest. We argue that a combined effect of complex rupture dynamics and topography primarily control this previously rarely documented landslide pattern. Compared to recent thrust fault-earthquakes of similar magnitudes elsewhere, we conclude that lower static stress drop, mean fault displacement, and blind ruptures of the 2010 Haiti earthquake resulted in fewer, smaller, and more symmetrically distributed landslides than previous studies would suggest. Our findings caution against overly relying on across-the-board models of slope stability response to seismic ground shaking.

Shallow subsurface structure of the Wasatch fault, Provo segment, Utah, from integrated compressional and shear-wave seismic reflection profiles with implications for fault structure and development

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Fault interaction and along-strike variation in throw in the Pajarito fault system, Rio Grande rift, New Mexico

The seismically active Pajarito fault system (PFS) of northern New Mexico, United States, is a complex zone of deformation made up of many laterally discontinuous faults and associated folds and fractures that interact in ways that have important implications for seismic hazards. Mapping and drilling projects in the PFS provide new insights into the structural geometry and paleoseismic history of the fault system. A 1.25 Ma old datum (the Bandelier Tuff) and high-resolution digital elevation data allow construction of throw-length profiles along the entire length of the PFS, revealing primary geometric features previously unrecognized. The fault system as a whole consists of numerous closely spaced overlapping sections ~8–14 km long. Slip maxima in some cases occur near the centers of these sections, and in others they are shifted toward one end. Along-strike asymmetrical throw profiles and throw deficits indicate fault branching, merging, and strain transfer. This pattern results from processes of fault linkage and conservation of strain on diverse structures of a large fault system. New mapping reveals that the northern end of the Pajarito fault terminates in a wide zone of extensional monoclines and discontinuous, small-displacement faults, and interacts with nearby antithetic faults. New paleoseismic data from a normal fault splay, interpreted in light of previous paleoseismic work, argue for three Holocene surface-rupturing earthquakes; one ca. 1.4 thousand calendar years ago (1.4 cal ka) on the Pajarito fault, a second 6.5–5.2 ka ago on the Pajarito fault that is consistent with an event 6.5–4.2 ka ago on the Guaje Mountain fault, and a third ca. 9 ka ago on both the Pajarito and the Rendija Canyon faults. This paleoseismic event chronology demonstrates that the Pajarito fault often ruptures alone, but sometimes ruptures either with the Rendija Canyon or the Guaje Mountain fault. When this occurs, the resultant seismic moment and therefore the earthquake magnitude are larger than when the main Pajarito fault ruptures alone. Evidence for fault interaction, and the presence of prominent bends in the Pajarito fault system, imply structural control of paleoseismicity and neoseismicity and suggest the potential for stress concentrations and earthquake triggering in complex linking fault systems.

40Ar–39Ar biotite and hornblende geochronology from the Oskarshamn area, SE Sweden: discerning multiple Proterozoic tectonothermal events

AbstractTwelve40Ar–39Ar biotite and four hornblende age determinations have been carried out to constrain the cooling history of the Proterozoic bedrock near Oskarshamn, SE Sweden, an area identified as a possible site for long-term nuclear waste storage. The bedrock hostsc.1.80 Ga granites and diorites of the Transscandinavian Igneous Belt and two 1.45–1.44 Ga granite intrusions, the Götemar and Uthammar plutons. Biotite was selected from three surface samples, representing both the older rocks and the younger granites, and from three cored boreholes at nine different depth levels. Hornblende was extracted from samples at the top and bottom of one borehole and at two sub-surface levels of another borehole. Three age groups were distinguished: ≥1.62 Ga, 1.51–1.47 Ga and 1.43–1.42 Ga. In the first group, two hornblende analyses yielded ages of 1799±4 Ma and 1773±13 Ma, which indicate initial fast cooling after emplacement of 1.80 Ga rocks of the Transscandinavian Igneous Belt. Two biotite ages of 1618±7 Ma and 1621±3 Ma are interpreted to date final cooling, through 300 °C, after the youngest suite (1.68–1.67 Ga) of the Transscandinavian Igneous Belt in south-central Sweden. Seven biotite ages, in the range 1.51–1.47 Ga, are enigmatic to interpret but largely coincide in age with the end of widespread rapakivi magmatism in Fennoscandia and the initiation of the Danopolonian event. The 1.43–1.42 Ga biotite and hornblende ages reflect cooling after thermal heating from the 1.45–1.44 Ga Götemar and Uthammar plutons. Later events thermally affected the bedrock in the Oskarshamn area as indicated by a poorly defined biotite age of 928±6 Ma and other disturbed40Ar–39Ar ages of samples bordering a complex deformation zone.

Curie Point Depth variations to infer thermal structure of the crust at the African-Eurasian convergence zone, SW Turkey

Abstract We examined the thermal structure of the crust across complex deformation zones in SW Turkey using the Curie Point Depth (CPD) estimates and made comparisons of the thermal state of the crust with the seismic activity to provide insights for spatial limits of brittle failure in this region. The CPD estimates of SW Turkey from 80 overlapping blocks vary from 9 to 20 km. SW Turkey has two regions of shallow CPD. The shallow CPD region in the Uşak-Afyon zone in western part of the study area is caused by upper crustal thinning and shallowing of high conductivity lower crust. The other shallow CPD region is in the Central Anatolian Volcanic Province in the eastern part of the study area and is thought to be related to the presence of silicate melts in the shallow-level crust. A NNW-SSE trending belt of deep CPD region separates these two zones and is located along the boundary of high (west) and low (east) seismic activities. It is interpreted that the regional thermal structure in SW Turkey is mainly controlled by the processes associated with the African-Eurasian plate convergence zone. The N-S lithospheric extension above the subducting slab created a thermal dome in Western Anatolia in response to upwelling of asthenosphere. Post-collisional magmatism of Neogene-Quaternary age generated another thermal dome in the eastern area. Comparison of the CPD variations with the seismic activity has shown that large earthquakes occur near the margins of the inferred regional thermal domes. Low seismic activity within the regionally active seismic areas seems to be associated with shallow CPD and high heat flow.

Enhanced recovery in a particulate-reinforced aluminium composite

The microstructural development during cold rolling and static recovery of an Al alloy (AA 2014) and an AA 2014 particulate-reinforced metal matrix composite (PMMC) was investigated. The composite contained 20 vol.% of 15 μm diameter Al 2O 3 particulates. Both materials were rolled at room temperature and subsequently annealed to determine the effect of the reinforcement on static recovery. The addition of the ceramic reinforcement affected the matrix deformation microstructure by refining the cellular substructure near Al 2O 3 particles and generating shear bands and complex deformation zones in the vicinity of particle clusters. Following deformation, room temperature storage was sufficient to decrease the hardness of the composite, and annealing at 200 °C resulted in a more rapid rate of recovery compared with the alloy. This enhanced recovery was attributable to a larger driving force brought about by the finer cell size near the particles, but internal stress relaxation and interfacial diffusion may also be important factors, particularly at ambient temperature. The Al 2O 3 particles, particularly those in clusters, enhanced considerably the rate of subgrain growth of the matrix. Based on models of various stages of recovery, the enhanced rate of softening in the composite is not likely to be associated with a particular mechanism but involves a number of separate, but overlapping mechanisms.

Transition from strike-slip faulting to oblique subduction: active tectonics at the Puysegur Margin, South New Zealand

South of New Zealand the Pacific–Australia (PAC–AUS) plate boundary runs along the intracontinental Alpine Fault, the Puysegur subduction front and the intraoceanic Puysegur Fault. The Puysegur Fault is located along Puysegur Ridge, which terminates at ca. 47°S against the continental Puysegur Bank in a complex zone of deformation called the Snares Zone. At Puysegur Trench, the Australian Plate subducts beneath Puysegur Bank and the Fiordland Massif. East of Fiordland and Puysegur Bank, the Moonlight Fault System (MFS) represents the Eocene strike-slip plate boundary. Interpretation of seafloor morphology and seismic reflection profiles acquired over Puysegur Bank and the Snares Zone allows study of the transition from intraoceanic strike-slip faulting along the Puysegur Ridge to oblique subduction at the Puysegur Trench and to better understand the genetic link between the Puysegur Fault and the MFS. Seafloor morphology is interpreted from a bathymetric dataset compiled from swath bathymetry data acquired during the 1993 Geodynz survey, and single beam echo soundings acquired by the NZ Royal Navy. The Snares Zone is the key transition zone from strike-slip faulting to subduction. It divides into three sectors, namely East, NW and SW sectors. A conspicuous 3600 m-deep trough (the Snares Trough) separates the NW and East sectors. The East sector is characterised by the NE termination of Puysegur Ridge into right-stepping en echelon ridges that accommodate a change of strike from the Puysegur Fault to the MFS. Between 48°S and 47°S, in the NW sector and the Snares Trough, a series of transpressional faults splay northwards from the Puysegur Fault. Between 49°50′S and 48°S, thrusts develop progressively at Puysegur Trench into a decollement. North of 48°S the Snares Trough develops between two splays of the Puysegur Fault, indicating superficial extension associated with the subsidence of Puysegur Ridge. Seismic reflection profiles and bathymetric maps show a series of transpressional faults that splay northwards across the Snares Fault, and terminate at the top of the Puysegur trench slope. Between ca. 48°S and 46°30′S, the relative plate motion appears to be distributed over the Puysegur subduction zone and the strike-slip faults located on the edge of the upper plate. Conversely, north of ca. 46°S, a lack of active strike-slip faulting along the MFS and across most of Puysegur Bank indicates that the subduction in the northern part of Puysegur Trench accounts for most of the oblique convergence. Hence, active transpression in the Snares fault zone indicates that the relative PAC–AUS plate motion is transferred from strike-slip faulting along the Puysegur Fault to subduction at Puysegur Trench. The progressive transition from thrusts at Puysegur Trench and strike-slip faulting at the Puysegur Fault to oblique subduction at Puysegur Trench suggests that the subduction interface progressively developed from a western shallow splay of the Puysegur Fault. It implies that the transfer fault links the subduction interface at depth. A tectonic sliver is identified between Puysegur Trench and the Puysegur Fault. Its northwards motion relative to the Pacific Plate implies that is might collide with Puysegur Bank.

Abstract: Implications of 3D Structural Restoration in Complex Deformation Zone: Example of an Albian Rafted Structure in the Congo Basin

Abstract: Implications of 3D Structural Restoration in Complex Deformation Zone: Example of an Albian Rafted Structure in the Congo Basin

Structural Style of the Warburton Basin and Control in the Cooper and Eromanga Basins, South Australia

Deep-seated structures within the Warburton Basin have been intermittently reactivated during development of the overlying Cooper and Eromanga Basins. Four major deep structures preceding deposition of the Cooper Basin succession are described. 1) A complex deformation zone occurs on the eastern flank of the Birdsville Track Ridge near Kalladeina 1. 2) Simple reverse faults are common and widespread in the Warburton Basin strata. 3) Gentle folds occur in the Coongie area and become increasingly tight towards the Birdsville Track Ridge. 4) Imbricate thrust faults form the cores of structures along the northeast-southwest trending Gidgealpa–Merrimelia–Innamincka Ridge. Warburton Basin structural control in the overlying basins is characterised by reactivation and propagation of thrust faults along the Gidgealpa–Merrimelia–Innamincka Ridge, and by further folding and faulting of the complex deformation zone on eastern flank of the Birdsville Track Ridge. The episodic, compressive reactivation has controlled depositional and erosional patterns of the Cooper and Eromanga Basins, and hence controlled hydrocarbon occurrence in these two basins. Potential footwall traps may be formed by propagation of the thrust faults.