Radial Faults Research Articles

Analog modeling of normal faulting above Middle East domes during regional extension

We study the effects of planform dome shape on fault patterns developing with and without concurrent regional extension oriented oblique to the long axis of the dome. The motivation was the need to understand fault and fracture patterns in two adjacent mature hydrocarbon fields in the Middle East: one, an elliptical dome, and one, an irregularly shaped dome. The largest faults have throws of approximately 30 m (98 ft), which is close to the resolution limit of older two-dimensional seismic reflection data. The known fault trends are not parallel to the highest transmissivity direction but could form compartment boundaries. Fault and fracture patterns developed over the modeled domes provide insight into the populations of faults and fractures that are likely to exist in the reservoirs but have been undetected because they are at or below the resolution limit of reflection seismic data. Major domal structural elements, crestal fault systems, end splay systems, and radial faults are observed in modeled domes rising both with and without concurrent regional extension. Experimental results indicate that fault and fracture patterns are influenced by the effects of dome shape, regional extension, and relative timing of uplift with respect to regional extension. The expression of particular sets of faults and fractures associated with concurrent doming and regional extension depends on the interaction among regional extension, outer arc extension over the dome, and tangential extension around the dome margins. Our results also indicate that the two adjacent natural domes possibly experienced different kinematic histories from those previously interpreted.

Magmatism and metallogeny associated with mantle upwelling: Zircon U–Pb and Lu–Hf constraints from the gold-mineralized Jinchang granite, NE China

The Jinchang gold deposit is located in the easternmost portion of the Central Asian Orogenic Belt (CAOB), and represents one of the major gold districts in eastern Jilin–Heilongjiang provinces of China. The gold ore bodies are hosted mainly in altered Mesozoic granitoids, breccia pipes and ring and radial faults. Gold mineralization consists of alteration (stockwork in hydrothermally altered granites), breccia, and quartz-sulfide vein-types. Alteration assemblages around the alteration-style ore body show a vertical sequence of potassic, phyllic, and propylitic zones.In this study, we present U–Pb and Lu–Hf isotope data on zircons derived from mineralized granophyric granite, biotite monzogranite, granodiorite, and granite porphyry, and sericite Rb–Sr ages from the Jinchang gold deposit. The results show 206Pb/238U ages of 201±3Ma (MSWD=1.1), 203±4Ma (MSWD=1.4), 201±5Ma (MSWD=2.1), and 110±3Ma (MSWD=1.6), respectively. Sericite from the gold-mineralized phyllic-altered granodiorite and granite porphyry returns Rb–Sr isochron ages of 110±4Ma (MSWD=1.04) and 107±5Ma (MSWD=0.91), respectively. Our new data indicate that the gold mineralization at Jinchang took place at ca. 110Ma and was temporally related to intrusion of the granite porphyry. Zircon ε Hf (200Ma) values of the ca. 200Ma granites vary from −4.8 to +8.1, with TCDM model ages of 727–1535Ma, reflecting their derivation mainly by partial melting of juvenile Proterozoic crust. The gold-bearing 110Ma granite porphyry returns ε Hf (110Ma) values in the range of −1.6 to +9.8, with TCDM model ages of 542–1069Ma, suggesting partial melts of juvenile Proterozoic crust with notable input of mantle components as compared to the ca. 200Ma granites. Compiled oxygen (δ18OSMOW=−0.7–10.1) and hydrogen (δDSMOW=−99 to −70) stable isotopic values of quartz from ores indicate that the ore-forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz-sulfide veins at the late stage. The Hf isotope data from the granite porphyry, integrated with the results from previous data on S and Pb isotopic composition of ores, constrain the source of ore-forming components as lower crust with discernible mantle inputs and wall rock assimilation. Our results have implications bearing on the widespread magmatism and metallogenic event during the Early Cretaceous time in East China, and link them to mantle upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas.

Functioning of natural and natural-engineering systems formation conditions and natural state of the hydrothermal system in the Valley of Geysers (Kronotsky Nature Reserve, Kamchatka)

The formation of the hydrothermal system in the Valley of Geysers is shown to be governed by a structure of radial and circular faults of above-intrusion zone of a partially melted magmatic body with an epicenter near the Upper-Geyser Field, while the hydrothermal system is shown to receive its water from elevations of +500 to +900 m abs (according to isotopic data). The catastrophic landslide of June 3, 2007, was just a stage in the general scenario of the gradual hydrothermal transformation of the inclined Geyser unit (Q34grn), building up the roof of the hydrothermal reservoir, with a gradual decline of slide resistance. The slide was triggered by the increased pressure in the hydrothermal and magmatic systems and the saturation of the Geyser unit by moisture during spring flood. According to the data of continuous regime thermohydrodynamic observations carried out in the Valley of Geysers with the use of HOBO-loggers of temperature and pressure since July 2007 to April 2010, the mean time between eruptions of Velikan geyser was 348 minutes. The intensification of precipitation input directly into the geyser pool causes a short-time increase in the time between eruptions (up to the maximum of 32 h). According to observations at the “Plotina” gage, the total estimated mean annual discharge of thermal springs (by chlorine ion) in the Valley of Geysers is 263 kg/s; the discharge of thermal springs is governed by the level of Poldprudnoe Lake and its seasonal variations exceed 40%.

Talundilly, Western Queensland, Australia: geophysical and petrological evidence for an 84 km-large impact structure and an Early Cretaceous impact cluster

The Talundilly Structure, southwestern Queensland, Australia, is represented on 2D seismic reflection transects as a major seismic anomaly disrupting the consistent ‘C’ seismic–stratigraphic horizon above the early Cretaceous Bulldog Wallumbilla Formation throughout the Eromanga Basin. The seismic anomalous zone, estimated at 84 km in diameter from the maximum extent of horizon disruption, coincides with a prominent aeromagnetic (TMI) high which is centrally located within a near-circular seismic anomaly of the ‘C’ horizon. The structure consists of a raised central area, with radial faults extending from the central high, an annular synform with disrupted seismic elements dipping at low angles towards the central uplift, and an outer faulted rim. Cuttings from the Talundilly-1 well, drilled ∼30 km northwest from the central high, contain quartz grains with planar deformation features (PDF) indicative of shock metamorphism. The age of the structure, as determined from seismic correlation and sparse palynology, post-dates the ‘C’ seismic horizon and is determined as approximately 125 Ma, coinciding with a marine transgression. Correlation of seismic profiles suggest that the Talundilly impact structure is a possible twin of the Tookoonooka impact structure, dated as 125 ± 1 Ma and located 328 km to the south.

Fault Location in Distribution Systems Considering the Non-Liner Profile Characteristic of Voltage Sag on the Bus

The bus will experience different voltage sag when fault occurs at different location. Based on the non-liner profile characteristic of voltage sag measured at the bus, the paper proposes a new fault location method. Firstly, it obtains the analytical expression of each section based on the relationship between voltage sag and fault location. Then calculate the fault distance using chord secant method and identify the faulted section through the minimal deviation of fault distance. The combined two results of fault distance and faulted section make fault location accurately. It overcomes the difficulty of radial power distribution systems fault location. Through simulating for the IEEE 13 node test feeder with different faults, including various fault resistance, loading variation and the connected distributed generation, it proves the method’s accuracy and effectiveness.

Interpretation of Nisyros volcanic terrain using land surface parameters generated from the ASTER Global Digital Elevation Model

To model the morphotectonic evolution of Nisyros stratovolcano in the Aegean Volcanic Arc (36° 35′ N, 27° 10′ E), a 30 m resolution ASTER GDEM was used. Nisyros is characterized by a relative pristine volcanic terrain. Elevation, slope and aspect images, the corresponding frequency distributions and rose diagrams enabled the geomorphometric analysis of Nisyros revealing the major geomorphological structures that are associated to both endogenetic and exogenetic processes acting on the island either new or previously reported in the literature. New elements include the number, loci of issue, relative age, ogive structures of the voluminous precalderan Nikia flows and their contact relationships with the Avlaki flows. The tectonic control, fine feature morphology and flow paths of lavas and smaller domes associated with the main postcalderan domes become visually apparent. Particularities of the hydrographic network accentuate and bring forward non-mapped radial faults. Intense landslide scarring and the volcanic stratigraphy of the intact units were revealed in the northeastern quadrant of Nisyros. Major, new volcano-tectonic features include the division of the island into three northwesterly trending sectors and the dipping of Nisyros towards the southeast as a result of segmentation by two major ring faults the Kos Ring Fault (KRF) and Perigussa Ring trapdoor Fault (PRF) which represent ring faults of the Kos sagging-caldera. The ASTER GDEM has provided suitable thematic information content in the geomorphometric analysis of Nisyros and therefore it offers a reconnaissance tool in the geomorphological analysis of a volcanic landscape.

Remote Sensing Analysis of Selected Terrestrial Impact Craters and a Suspected Impact Structure in South Korea using Space Shuttle Photographs

Typical morphological elements for impact craters were detected on all analyzed Shuttle photographs. Features with diameters smaller than 2 km could not be successfully analyzed. The search for suitable Shuttle scenes was successfully performed using on-line Internet databases. Image enhancement and lineament analysis were also performed on the acquired Shuttle, Landsat and SPOT images of a suspected impact feature in South Korea. A fault bounded polygonal rim and a central uplift were identified on all images. A distinct system of annular and radial faults was not detected. The results of the study do not exclude the possibility of a meteoritic origin of this structure.

Erosional modification and gully formation at Meteor Crater, Arizona: Insights into crater degradation processes on Mars

Hydrogeological modification of Meteor Crater produced a spectacular set of gullies throughout the interior wall in response to rainwater precipitation, snow melting, and possible groundwater discharge. The crater wall has an exceptionally well-developed centripetal drainage pattern consisting of individual alcoves, channels, and fans. Some of the gullies originate from the rim crest and others from the middle crater wall where a lithologic transition occurs; broad gullies occur along the crater corner radial faults. Deeply incised alcoves are well developed on the soft Coconino Sandstone exposed on the middle crater wall, beneath overlying dolomite. In general, the gully locations are along crater wall radial fractures and faults, which are favorable locales of erosion due to preferential rock breakup from faulting, and groundwater flow/discharge; these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow, causing erosion and crater degradation. Channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor. Caves exposed on the lower crater level point to percolation of surface runoff and selective discharge through fractures on the crater wall. In addition, lake sediments on the crater floor provide significant evidence of a past pluvial climate, when the water table was higher, and groundwater may have seeped from springs on the crater wall. Although these hydrological processes continue at Meteor Crater today, conditions at the crater are much more arid than they were soon after impact, reflecting a climatic shift. This climate shift and the hydrological modifications observed at Meteor Crater provide insights for landscape sculpturing on Mars during various parts of its history.

A 3D model of first-order structural elements of the Vredefort Dome, South Africa — Importance for understanding central uplift formation of large impact structures

Based on detailed structural mapping, geophysical information and structural consideration, we generated a 3D structural model of a segment of the Vredefort Dome. This model provides insight into the mechanism of mass transfer during central uplift formation of large impact structures. The model consists of geometrically and kinematically linked km-scale radial and concentric faults that affected the overturned limb of the rim syncline to the Vredefort Dome. The faults accomplished constrictional (centripetal) rock flow followed by radial spreading of uplifted and gravitationally unstable rocks in the crater centre. More specifically, concentric faults formed likely as normal faults during transient crater rim collapse, steepened and were transformed to reverse faults during central rock uplift and finally, were overturned during gravitational collapse of the central uplift. Radial faults, by contrast, formed at a later stage of convergent rock flow towards the crater centre and retained largely their orientation during central uplift formation. Displacement on individual faults is up to 2 km. Cumulative displacement, notably on concentric faults, can account for the large displacement magnitudes predicted by numerical models.

The geology of Hotei Regio, Titan: Correlation of Cassini VIMS and RADAR

Joint Cassini VIMS and RADAR SAR data of ∼700-km-wide Hotei Regio reveal a rich collection of geological features that correlate between the two sets of images. The degree of correlation is greater than anywhere else seen on Titan. Central to Hotei Regio is a basin filled with cryovolcanic flows that are anomalously bright in VIMS data (in particular at 5 μm) and quite variable in roughness in SAR. The edges of the flows are dark in SAR data and appear to overrun a VIMS-bright substrate. SAR-stereo topography shows the flows to be viscous, 100–200 m thick. On its southern edge the basin is ringed by higher (∼1 km) mountainous terrain. The mountains show mixed texture in SAR data: some regions are extremely rough, exhibit low and spectrally neutral albedo in VIMS data and may be partly coated with darker hydrocarbons. Around the southern margin of Hotei Regio, the SAR image shows several large, dendritic, radar-bright channels that flow down from the mountainous terrain and terminate in dark blue patches, seen in VIMS images, whose infrared color is consistent with enrichment in water ice. The patches are in depressions that we interpret to be filled with fluvial deposits eroded and transported by liquid methane in the channels. In the VIMS images the dark blue patches are encased in a latticework of lighter bands that we suggest to demark a set of circumferential and radial fault systems bounding structural depressions. Conceivably the circular features are tectonic structures that are remnant from an ancient impact structure. We suggest that impact-generated structures may have simply served as zones of weakness; no direct causal connection, such as impact-induced volcanism, is implied. We also speculate that two large dark features lying on the northern margin of Hotei Regio could be calderas. In summary the preservation of such a broad suite of VIMS infrared color variations and the detailed correlation with features in the SAR image and SAR topography evidence a complex set of geological processes (pluvial, fluvial, tectonic, cryovolcanic, impact) that have likely remained active up to very recent geological time (<10 4 year). That the cryovolcanic flows are excessively bright in the infrared, particularly at 5 μm, might signal ongoing geological activity. One study [Nelson, R.M., and 28 colleagues, 2009. Icarus 199, 429–441] reported significant 2-μm albedo changes in VIMS data for Hotei Arcus acquired between 2004 and 2006, that were interpreted as evidence for such activity. However in our review of that work, we do not agree that such evidence has yet been found.

Faulting of salt-withdrawal basins during early halokinesis: Effects on the Paleogene Rio Doce Canyon system (Espírito Santo Basin, Brazil)

Three-dimensional seismic-reflection data are used in the analysis of submarine channel systems in the Espirito Santo Basin, Brazil. The exceptional quality of the studied data set allows the detailed documentation of the geometry, regional distribution, and statistical parameters of salt-related normal faults, and their effect on the Rio Doce Canyon system (RDCS). On the Espirito Santo continental slope, normal faulting was triggered during early halokinesis (stage A) but barely controlled the initial evolution of the RDCS, which incised the continental slope axially within a salt-withdrawal basin. However, in a second stage (stage B), crestal or radial faults controlled erosion over growing salt structures, whereas synclinal and channel-margin fault sets dissected overbank strata to the RDCS. In the later part of stage B, channel sinuosity decreased sharply in response to fault activity and associated sea-floor destabilization. Vertical propagation of blind faults was triggered in a third stage (stage C), in association with crestal collapse of buried salt anticlines and regional diapirism, but synclinal and channel-margin faults did not propagate vertically above a regional unconformity marking the base of stage C strata. Statistical analyses of observed fault sets demonstrate that synclinal faults are in average 2.3 times longer than the crestal or radial types but record 60% of the throw (average 83 m [272 ft]) experienced by the latter. In addition, the fault sets are shown to have contributed to local cannibalization of the sea floor, vertical stacking of channel-fill strata, and structural and depositional compartmentalization of potential reservoir successions. As a result, channel systems show marked differences in mean values for sinuosity, height, and width in relation to five main phases of channel development. The structural setting in the study area differs from productive areas offshore Espirito Santo (e.g., Golfinho field), west Africa, and Gulf of Mexico, revealing in distal parts of the Brazilian margin the existence of local controls on submarine channel architecture and structural compartmentalization prior to the main stages of diapirism.

Cinder cones of Mount Slamet, Central Java, Indonesia

http://dx.doi.org/10.17014/ijog.vol4no1.20096The Mount Slamet volcanic field in Central Java, Indonesia, contains thirty five cinder cones within an area of 90 sq. km in the east flank of the volcano. The cinder cones occur singly or in small groups, with diameter of the base ranges from 130 - 750 m and the height is around 250 m. Within the volcanic field, the cinder cones are spread over the volcanic area at the distance of 4 to 14 km from the eruption center of the Slamet Volcano. They are concentrated within latitudes 7°11’00” - 7°16’00” S,, and longitudes 109°15’00” - 109°18’00” E. The density of the cinder cones is about 1.5 cones/km2. Most of the cinder cones lie on the Tertiary sedimentary rocks along the NW-trending fault system and on radial fractures. The structural pattern may be related to the radial faults in this region. The cone surfaces are commonly blanketed by Slamet air-falls and lava flows. The deposits consist of poorly bedded, very coarse-grained, occasionally overlain by oxidized scoria, and large-sized of ballistic bombs and blocks. There are various kind of volcanic bombs originating from scoriae ballistic rock fragments. The other kind of volcanic bombs are breadcrust bomb, almond seed or contorted shape. All of the cinder cones have undergone degradation, which can be observed from the characters of gully density and surface morphology. By using Porter parameters, Hco is equal to 0.25 Wco, whilst Wcr is equal to 0.40 Wco. The Hco/Wco ratio is higher than Hco = 0.2 Wco reference line. A radiometric dating using K-Ar method carried out on a scoria bomb yields the age of 0.042 + 0.020 Ma.

Rim uplift and crater shape in Meteor Crater: Effects of target heterogeneities and trajectory obliquity

We have analyzed the rim structure of Meteor Crater, Arizona, in order to understand the mechanism of rim uplift in simple craters and the causes of the shape of polygonal impact craters. For this purpose, we systematically determined bedding orientation of the autochthonous crater wall and overturned flap and analyzed the kinematics of major radial faults. We found that rim uplift correlates with the crater shape and increases in the corners of the crater. The two main mechanisms of differential uplift are the formation of horizontal interthrust wedges, leading to the doubling of strata in the rim, and radial corner faults, or tear faults, that vertically displace bedrock. The development of Meteor Crater's quadrangular shape is caused by more effective crater excavation flow parallel to major joint sets. Additionally, we infer the impact direction with a newly developed technique, the two corners model, and review the arguments in favor of an oblique trajectory. While the data set is ambiguous, several indicators suggest an impact direction from the NNW. We conclude that oblique impacts should have an effect on early cratering and excavation flow, whereas target heterogeneities like joints start to play a prominent role in later stages when the stresses induced by the excavation flow are in the same order of strength as the material involved.

Characteristics of mantle branch structure in western Shandong and its roles in mine-rogenesis and ore-controlling

This work deals with the characteristics of mantle branch structure in western Shandong Province, China, with respect to the distribution characteristics and ages of the regional strata, the development of ring-like and radial faults, the development of gently inclined detachment-slip structures in the axial part, mantle-source magmatic activities, regional petrology, petrochemistry and isotope geology. The study indicated that the N-W sharply plunged ductile shear zone in the region of western Shandong cuts through the mantle rocks detached from the deep-seated North China mantle sub-plume, hence leading to unloading in response to depressurization and thereafter the formation of anatexis magma. The intense and complete magmatic evolution series not only manifests a variation trend of alkalinity of magma from high to low and its intrusive depth from deep to shallow, but also reflects that the wall-rock alteration shows a general evolution trend from strong to weak. The evolution of mantle structure played an important role in controlling endo-mineralogenesis, accompanied with the rise of the country rocks. As a result, typical mantle branch structures were formed as observed in western Shandong. At the top of the mantle branch structure was developed an obvious detachment-tilt fault block, and some endogenic ores, at the same time, were uplifted onto the shallow levels.

Implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults

Reservoirs associated with salt diapirs that are circular or elliptical in plan view can be segmented by radial faults, concentric faults, both or neither. Explanations for this variation are offered based on integration of fault kinematics, published studies and seismic examples. Strata around diapirs can be divided into three structural domains with characteristic fault styles. (1) Roof zone between the present day depositional surface and crest of a buried, inactive diapir. This zone is characterised by doming, radial faults and occasionally, conic graben. Doming is usually caused by differential compaction and increases with depth. (2) A steeply-dipping sheath of strata surrounds the diapir out to a distance of less than one diapir radius, recording near-surface diapir growth in poorly-lithified sediments. These contain early gravity slumps and late concentric extensional faults. Regional layer-bound polygonal fault systems form radial faults within approximately one diapir radius—the only significant radial faulting mechanism below the roof zone. (3) Diapir root zone of strata whose structural architecture records the diapirs’ initiating mechanism, typically rim synclines or graben that detach on the salt source layer. Concentric faults at radial distances of a kilometre or more have been found only in root zone rim synclines and sheared sheath strata. These models and observations can assist seismic interpretation and structural model building in areas of poor geophysical imaging, for instance below overhanging salt.

Structural record of an oblique impact

Most impactors strike their target at an oblique angle. The common criterion for identifying craters formed by an oblique impact is the pattern of the ejecta blanket. On Earth, however, ejecta blankets are rarely preserved and other morphological, structural or geophysical criteria are needed. Here, we present structural details from the central uplift of the Upheaval Dome impact structure that are diagnostic of the kinematics during crater collapse and central uplift formation. A characteristic imbrication of thrust slices towards the SE, the pattern of strata orientation within the central uplift, dominant radial faults that accommodated NW–SE shortening and an elliptical bedding outline indicate that the displacement field during crater collapse has not been axial symmetric. Instead, an additional lateral component, roughly towards the SE, is preserved in the internal structure of the central uplift. The structural asymmetries are largest in the core of the central uplift and disappear outwards, thereby preserving the large-scale circular shape of the main structural elements (rim monocline, ring syncline). Comparison with numerical models of oblique impacts suggests that the additional lateral displacement component reflects a downrange material transport during the initial stages of central uplift formation. Similar patterns are identified in other impact structures and may serve as general criteria for identifying the impact direction of deeply eroded impact structures in sedimentary targets.

State of the hydrothermal activity of Soufrière of Guadeloupe volcano inferred by VLF surveys

La Soufrière (1467 m) is the active island arc volcano of Guadeloupe Island in the Lesser Antilles arc. Its historical eruptions are more or less violent phreatic outbursts the last of which, in 1976–1977, led to the evacuation of nearly 70 000 persons. The subsurface structure of the volcano consists of calderas, craters, and avalanche amphitheatres nested within the composite pile of eruptive products. Since the last magmatic eruption, dated ca. 1440 AD, the four phreatic eruptions have developed radial fractures on Soufrière dome favouring the development of a huge active hydrothermal system emphasized by a tropical environment. After the eruptions, the thermal state and the stable ground water flow are completely disorganised during several years during which the slow mineralization of rocks is becoming again preponderant. Sealing of fractures and decay of rocks permeability act as a cap for upward thermal transfers. Therefore Soufrière dome operates as a valve, resealing the hydrothermal system underlying the volcano thus providing over pressurization that could lead to the next phreatic eruption. In 1992 new small seismic swarms have appeared. Several of them are recorded every year while the emission of acid gas slowly increases. In order to recognise the superficial electrical resistive and conductive zones (less than 100 m depth) as well as the cavities on Soufrière volcano, we have made Very Low Frequency (VLF) surveys in 2000. Electrical conductive zones are clearly associated with major radial faults starting from the summit in which the hydrothermal activity takes place. In the continuation of these active hydrothermal fractures hot springs are located down slope. Conversely some of the resistive zones are associated with inactive clayed and sealed or opened faults. The distribution of the conductive zones allows detailing the state of the superficial part of the hydrothermal system of La Soufrière. The distribution of vertical clayed zones associated with major faults supposes Soufrière dome constituted of more or less consolidated blocks joined side by side and lying on the hydrothermally floor of crater Amic.

Collapse of large complex impact craters: Implications from the Araguainha impact structure, central Brazil

The 40-km-wide Araguainha impact structure in central Brazil provides extensive outcrops to study the structural evolution of all parts of a complex crater, including the central uplift, annular trough, and crater rim. While most craters of comparable size are buried by impact-related or postimpact sedimentary deposits, Araguainha is deeply eroded and it exposes in detail outcrop-scale structural features that can be used to understand the structural evolution of large impact craters. This study explores evidence from structural features across the entire impact structure in order to provide constraints on the target rock movement during the crater collapse. Most of the structural features described here are consistent with folding and bedding-parallel shearing during several kilometers of lateral inward movement of the target rocks. Vertical movement was, in contrast, restricted to distances of less than a few hundred meters along radial and concentric fault zones around the crater rim.

Tectonics of complex crater formation as revealed by the Haughton impact structure, Devon Island, Canadian High Arctic

The results of a systematic field mapping campaign at the Haughton impact structure have revealed new information about the tectonic evolution of mid-size complex impact structures. These studies reveal that several structures are generated during the initial compressive outward-directed growth of the transient cavity during the excavation stage of crater formation: (1) sub-vertical radial faults and fractures; (2) sub-horizontal bedding parallel detachment faults; and (3) minor concentric faults and fractures. Uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift. Compressional inward-directed deformation results in the duplication of strata along thrust faults and folds. It is notable that Haughton lacks a central topographic peak or peak ring. The gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults. While the outermost concentric faults dip in toward the crater center, the majority of the innermost faults at Haughton dip away from the center. Complex interactions between an outward-directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted, intensely faulted (sub-) vertical and/or overturned strata at a radial distance from the crater center of ∼5.0-6.5 km. Converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures: (1) sub-vertical radial faults and folds; (2) positive flower structures and chaotically brecciated ridges; (3) rollover anticlines in the hanging-walls of major listric faults; and (4) antithetic faults and crestal collapse grabens. Oblique strike-slip (i.e., centripetal) movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage. It is clear that deformation during collapse of the transient cavity walls at Haughton was brittle and localized along discrete fault planes separating kilometer-size blocks.

3D seismic reflection mapping of the Silverpit multi-ringed crater, North Sea

Research Article| March 01, 2005 3D seismic reflection mapping of the Silverpit multi-ringed crater, North Sea S.A. Stewart; S.A. Stewart 1BP Azerbaijan, c/o Chertsey Road, Sunbury on Thames, Middlesex TW16 7LN, UK Search for other works by this author on: GSW Google Scholar P.J. Allen P.J. Allen 2Production Geoscience Ltd, Banchory AB31 5YR, UK Search for other works by this author on: GSW Google Scholar Author and Article Information S.A. Stewart 1BP Azerbaijan, c/o Chertsey Road, Sunbury on Thames, Middlesex TW16 7LN, UK P.J. Allen 2Production Geoscience Ltd, Banchory AB31 5YR, UK Publisher: Geological Society of America Received: 17 Feb 2004 Revision Received: 22 Jun 2004 Accepted: 29 Jun 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2005) 117 (3-4): 354–368. https://doi.org/10.1130/B25591.1 Article history Received: 17 Feb 2004 Revision Received: 22 Jun 2004 Accepted: 29 Jun 2004 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S.A. Stewart, P.J. Allen; 3D seismic reflection mapping of the Silverpit multi-ringed crater, North Sea. GSA Bulletin 2005;; 117 (3-4): 354–368. doi: https://doi.org/10.1130/B25591.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The first comprehensive mapping of the Silverpit multi-ringed crater is presented, based on five adjoining 3D seismic surveys that together provide 78% (216 km2) areal coverage of the structure with spatial and depth sampling of ∼10 m. The top Cretaceous surface shows an excavated crater 3 km in diameter surrounded by 10–15 concentric ring structures out to a radius of 9.4 km. Seismic sequence stratigraphy and drilled wells indicate the lower age bound is a disconformity spanning 74–54 Ma. The upper bound is Eocene termination of concentric ring fault growth (ca. 45 Ma). The inner rings are extensional faults defining rotated fault blocks that would be considered part of the crater in an impact structure interpretation, giving a final impact crater diameter of 8 km. The outer rings show a surprising variation in style, from graben in the west to compressional structures in the east. This may be explained by postcratering gravity spreading on easterly dipping intra-Cretaceous detachments. Within the crater, the top Cretaceous seismic reflector is disrupted and blocky, but defines a central uplift with a slight crestal depression. Below this uplift, the prominent base Cretaceous seismic reflector shows Jurassic strata rising into a cone 300 m high and 1 km wide, characterized by radial faults. This central uplift within the crater may structurally balance the inner ring fault blocks via a slumping model, but we also identify low seismic velocity in the uplifted Jurassic, so fracturing may have contributed to growth of the central peak. At a radius of 2.5 km, base Cretaceous shows a dish-shaped depression that we interpret as marking either the extent of slumping toward the crater at this structural level or the limit of shockwave-induced porosity collapse. Seismic reflectors above the top Cretaceous excavated crater show differential compaction during the Eocene, accommodated by drape structure plus two conical faults that define narrow ring graben and represent the final phase of crater-related tectonics. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.