Weak Horizon Research Articles

A Fast Horizon Detector and a New Annotated Dataset for Maritime Video Processing

Accurate and fast sea horizon detection is vital for tasks in autonomous navigation and maritime security, such as video stabilization, target region reduction, precise tracking, and obstacle avoidance. This paper introduces a novel sea horizon detector from RGB videos, focusing on rapid and effective sea noise suppression while preserving weak horizon edges. Line fitting methods are subsequently employed on filtered edges for horizon detection. We address the filtering problem by extracting line segments with a very low edge threshold, ensuring the detection of line segments even in low-contrast horizon conditions. We show that horizon line segments have simple and relevant properties in RGB images, which we exploit to suppress noisy segments. Then we use the surviving segments to construct a filtered edge map and infer the horizon from the filtered edges. We propose a careful incorporation of temporal in- formation for horizon inference and experimentally show its effectiveness. We address the computational constraint by providing a vectorized implementation for efficient CPU execution, and leveraging image downsizing with minimal loss of accuracy on the original size. Moreover, we contribute a public horizon line dataset to enrich existing data resources. After extensive tests, we report the following major findings: 1) thanks to its filter, our algorithm accurately detects horizon lines with low or weak edge response, 2) the vectorized filter takes no more than 1.71% of the overall computations, while most of the computations are taken by the Line Segment Detection (LSD) algorithm we integrated into our pipeline, 3) our strategy of incorporating the temporal information avoids outlier detections, mitigates the effect of strong noisy lines, and exhibits high robustness when using incorrect detections as a temporal reference. Our algorithm’s performance is rigorously evaluated against state-of-the-art methods, and its core components are validated through ablation experiments.

The Flims rock avalanche: structure and consequences

The Flims rock avalanche has a gliding surface that cuts down section in a limestone sequence and does not follow a weak horizon. The gliding surface is parallel to bedding and/or to the penetrative Alpine foliation in the limestone that is characterized by a shape-preferred orientation of calcite grains. Predisposition was governed by structural weaknesses in form of sub-vertical fault zones within solid limestone. Faults controlled the orientation of lateral scarps of the rock avalanche. The main body of the rock avalanche behaved as semi-coherent mass, which preserved the original overall structure. The internal deformation occurred by dynamic fragmentation, which was distributed rather heterogeneously. Fragmentation starts by the formation of veins consisting of comminuted limestone. In a later stage crosscutting veins coalesce to form a texture with entirely comminuted limestone (“rock flour”) containing angular shattered fragments of limestone of variable sizes. The involvment of the post-glacial water-saturated substrate contributed to the long-runout of the Flims rock avalanche. The substrate was plowed bulldozer-wise at the front of the rock avalanche and escaped upward through the moving rock avalanche as clastic dikes and blow-out pipes. Bulldozing raised the valley floor in front of the rock avalanche by more than 100 m and, on the margins, entrained pieces of the valley flank and the neighboring, older Tamins rock avalanche deposit. The liquefied substrate breached the Tamins rock avalanche at Reichenau and entrained fragments thereof down the valley. The fragments now form the famous tumas of Domat/Ems, Felsberg and Chur. Lake Ilanz, dammed the by Flims rock avalanche, experienced a first major outburst shortly after its formation.

Modes and geometry of crustal-scale detachment folding in hot orogens—Insights from physical modeling

Detachment folding can be defined as the displacement and buckling of a competent layer above a rheologically weak horizon during tectonic shortening, frequently addressed in the context of salt tectonics. More recent studies have focused on influence of detachments in large-scale lithospheric deformation where the detachment horizon is represented by partially molten lower crust.This study addresses the geometric, kinematic and dynamic behavior of crustal-scale detachment folds using heated paraffin wax as an analogue for partially molten lower crust. Various thermal and shortening rate scenarios were tested in order to characterize deformation patterns within hot orogens in general, and to find an appropriate range of temperature gradients and shortening rates for the detachment folding regime. Five different regimes of lower crustal deformation were identified: 1. Homogeneous thickening or bulging, 2. Short-wavelength folding, 3. Development of diapir-shape folds or ductile faults, 4. Detachment folding and 5. Formation of lower crustal finger-like protrusions.Models are compared to various natural prototypes worldwide, in particular a series of metamorphic domes in the Central Asian Orogenic Belt (CAOB). Detailed analysis of the kinematic-dynamic evolution of the detachment folding scenario revealed an asymmetrical evolution of the folds associated with rotation of the limbs, as well as flexural flow of the lower weak mushy crust around the molten core. Pressure gradients in the fold cores saturated by melt controlled the sequential injections and outflows of partially/molten material between folds’ cores and the melt source layer at the base of the system. This resulted in accumulation of melt in the foreland of the accretionary zone, with higher melt absorption potential for newly developed folds. These observations may have significant implications for the development of pseudo-symmetrical metamorphic domes in the CAOB.

Exhibition Review: Every Day. Art. Solidarity. Resistance

Exhibition Review: <i>Every Day. Art. Solidarity. Resistance</i>

A tectonic carpet of Variscan flysch at the base of a rootless accretionary prism in northwestern Iberia: U–Pb zircon age constrains from sediments and volcanic olistoliths

Abstract. The allochthonous complexes of Galicia–Trás-os-Montes Zone (NW Iberia) are part of a rootless tectonic stack which preserves part of a Variscan accretionary prism. They are formed by individual tectonic slices marked by specific tectonometamorphic evolutions, which were piled up in a piggy-back mode onto its relative autochthon, the Central Iberian Zone (CIZ). Allochthony decreases from the structurally upper thrust sheets towards the lower ones. The lowermost unit of the stack is known as the Parautochthon or Schistose Domain. It is characterized by a low metamorphic grade in contrast with higher temperatures and/or pressures estimated for the overlying allochthonous units and shares the stratigraphic sequence with the underlying autochthon. The Parautochthon is divided in two structural and stratigraphic sub-units: (i) the Lower Parautochthon (LPa) is made of synorogenic flysch-type sediments with varied turbiditic units and olistostrome bodies, showing Upper Devonian–lower Carboniferous age according to the youngest zircon populations and fossiliferous content; (ii) the Upper Parautochthon (UPa) is composed of highly deformed preorogenic upper Cambrian–Silurian volcano-sedimentary sequence comparable with the nearby autochthon and to some extent, also with the high-P and low-T Lower Allochthon laying structurally above. The UPa was emplaced onto the LPa along the Main-Trás-os-Montes Thrust, and the LPa became detached from the CIZ relative autochthon by a regional-scale structure, the Basal Lower Parautochthon Detachment, which follows a weak horizon of Silurian carbonaceous slates. A review on the detrital zircon studies on the synorogenic LPa complemented by zircon dating of 17 new samples is presented here. The results support the extension of the LPa underneath the NW Iberian allochthonous complexes, from Cabo Ortegal, to Bragança and Morais massifs. Its current exposure follows the lowermost tectonic boundary between the Galicia–Trás-os-Montes (allochthon) and Central Iberian (autochthon) zones. The youngest zircon age populations point to a maximum sedimentation age for the LPa formations ranging from Famennian to Serpukhovian and supports the piggy-back mode of emplacement of the Galicia–Trás-os-Montes Zone, of which it represents the latest imbricate. The zircon age populations in the LPa allow the sedimentary provenance areas to be constrained, showing the intervention of nearby sources (mostly the UPa) and/or multiply recycled and long-transport sediments with a typically north-central Gondwana age fingerprint, also found in the Lower Allochthon, UPa and Autochthon. Complementary geochronology of volcanic olistoliths trapped in the LPa sediments and of late Cambrian to Upper Ordovician rhyolites from the UPa is also presented. It shows a direct relationship between the major blocks source area (UPa) and the setting place (LPa). Old zircon age patterns show that the LPa sedimentary rocks were recycled from detrital rocks of the allochthon (advancing wedge) and the nearby autochthon (peripheral bulge).

THE ROLE OF MULTIPLE WEAK LITHOLOGIES IN THE DEFORMATION OF COVER UNITS IN THE NORTHWESTERN SEGMENT OF THE ZAGROS FOLD‐AND‐THRUST BELT

The geometry, kinematics and dynamics of fold‐and‐thrust belts are strongly influenced by the mechanical behaviour of the basal décollement. However, many fold‐and‐thrust belts also include mechanically weak lithologies such as evaporites and marls or mudstones at different levels within the shortened stratigraphy. The kinematics and dynamic evolution of these thrust belts are controlled by the mechanical behaviour both of the basal décollement and of the weak units embedded within the overlying stratigraphic succession. In the Zagros fold‐and‐thrust belt (ZFTB), the shortened sedimentary cover is between 7 and 12 km thick and mechanically weak lithologies compartmentalize the stratigraphic column at shallow and intermediate levels. In this paper, satellite, field and seismic data from the Kurdistan Region of Iraq are used to identify structures of different sizes and surface traces. The observations are used to underline the role of mechanically weak horizons within the Zagros stratigraphy and the decoupling of deformation both laterally and with depth in the belt.The decoupling between shallow and deeper structures observed in seismic profiles from the Kurdistan Region of Iraq is also reported from field observations from the Iranian part of the Zagros fold‐and‐thrust belt, where folds with different surface traces occur. Decoupling between shallow and deep layers by incompetent lithologies at intermediate depths (e.g. marls, mudstones and evaporites) results in the formation of disharmonic folds. The geometry, size and location of such folds may differ between outcropping and subsurface structures. Decoupling may have a significant impact on hydrocarbon exploration in different parts of the Zagros fold‐and‐thrust belt due to potential offsets between outcropping and subsurface structures and their associated traps.

Control on frontal thrust progression by the mechanically weak Gondwana horizon in the Darjeeling-Sikkim Himalaya

This study integrates field evidence with laboratory experiments to show the mechanical effects of a lithologically contrasting stratigraphic sequence on the development of frontal thrusts: Main Boundary Thrust (MBT) and Daling Thrust (DT) in the Darjeeling-Sikkim Himalaya (DSH). We carried out field investigations mainly along two river sections in the DSH: Tista-Kalijhora and Mahanadi, covering an orogen-parallel stretch of ~20 km. Our field observations suggest that the coal-shale dominated Gondwana sequence (sandwiched between the Daling Group in the north and Siwaliks in the south) has acted as a mechanically weak horizon to localize the MBT and DT. We simulated a similar mechanical setting in scaled model experiments to validate our field interpretation. In experiments, such a weak horizon at a shallow depth perturbs the sequential thrust progression, and causes a thrust to localize in the vicinity of the weak zone, splaying from the basal detachment. We correlate this weak-zone-controlled thrust with the DT, which accommodates a large shortening prior to activation of the weak zone as a new detachment with ongoing horizontal shortening. The entire shortening in the model is then transferred to this shallow detachment to produce a new sequence of thrust splays. Extrapolating this model result to the natural prototype, we show that the mechanically weak Gondwana Sequence has caused localization of the DT and MBT in the mountain front of DSH.

Role of Late Jurassic intra-oceanic structural inheritance in the Alpine tectonic evolution of the Monviso meta-ophiolite Complex (Western Alps)

AbstractThe eclogite-facies Monviso meta-ophiolite Complex in the Western Alps represents a well-preserved fragment of oceanic lithosphere and related Upper Jurassic – Lower Cretaceous sedimentary covers. This meta-ophiolite sequence records the evolution of an oceanic core complex formed by mantle exhumation along an intra-oceanic detachment fault (the Baracun Shear Zone), related to the opening of the Ligurian–Piedmont oceanic basin (Alpine Tethys). On the basis of detailed geological mapping, and structural, stratigraphic and petrological observations, we propose a new interpretation for the tectonostratigraphic architecture of the Monviso meta-ophiolite Complex, and discuss the role played by structural inheritance in its formation. We document that subduction- and exhumation-related Alpine tectonics were strongly influenced by the inherited Jurassic intra-oceanic tectonosedimentary physiography. The latter, although strongly deformed during a major Alpine stage of non-cylindrical W-verging folding and faulting along exhumation-related Alpine shear zones (i.e. the Granero–Casteldelfino and Villanova–Armoine shear zones), was not completely dismembered into different tectonic units or subduction-related mélanges as suggested in previous interpretations. The present-day architecture of the Monviso meta-ophiolite Complex results from nappe-scale folding with a significant component of shearing, and strain partitioning of the Alpine deformation, which were controlled by the inherited occurrence of (i) lateral and vertical variations of facies and thickness of sediments, (ii) an intra-oceanic fault-rock assemblage, which acted as weak horizons in concentrating deformation, and (iii) remnants of a volcanic ridge, which consists of massive metabasalt. Thus, the recognition of pre-collisional, intra-oceanic, tectonostratigraphic inheritance represents an important step in reconstructing the tectonic evolution of meta-ophiolite units in orogenic belts.

Recognizing seamount-forearc collisions at accretionary margins: Insights from discrete numerical simulations

We conducted discrete numerical simulations to examine the effects of seamount collisions with forearcs along actively accreting subduction margins. Modeled seamount interactions leave behind distinctive structures in overriding forearcs that differ from those found at non-accreting margins. Whereas accretion above a planar decollement produces evenly spaced thrust faults with uniform displacements, seamounts activate one or more large-offset splay faults that accommodate substantial offset. Locally oversteepened slopes develop above the seamounts, but in contrast to non-accreting margins, the steep slopes are transient. Renewed accretion following seamount passage allows the equilibrium surface slopes to recover. Seamounts also protect incoming strata in their wake, delaying formation of new thrust faults and increasing fault spacing. Weak horizons within accreting strata allow the decollement to step up above the seamount, further protecting deeper strata and vertically partitioning wedge deformation. Notably, all modeled faults form in sequence, in contrast to out-of-sequence faults found at non-accreting margins. Similar structures found at many accretionary margins, including Nankai (offshore Japan), suggest that we may underestimate the role of seamount interactions in many locations, with implications for our assessment of subduction hazards in these settings.

Sandbox modelling of sequential thrusting in a mechanically two-layered system and its implications in fold-and-thrust belts

Many fold-and-thrust belts display multi-storied thrust sequences, characterizing a composite architecture of the thrust wedges. Despite dramatic progress in sandbox modelling over the last three decades, our understanding of such composite thrust-wedge mechanics is limited and demands a re-visit to the problem of sequential thrusting in mechanically layered systems. This study offers a new approach to sandbox modelling, designed with a two-layered sandpack simulating a mechanically weak Coulomb layer, resting coherently upon a stronger Coulomb layer. Our experimental models reproduce strikingly similar styles of the multi-storied frontal thrust sequences observed in natural fold-and- thrust belts. The upper weak horizon undergoes sequential thrusting at a high spatial frequency, forming numerous, closely spaced frontal thrusts, whereas the lower strong horizon produces widely spaced thrusts with progressive horizontal shortening. This contrasting thrust progression behaviour gives rise to composite thrust architecture in the layered sandpack. We show the evolution of such composite thrust sequences as a function of frictional strength (μb) at the basal detachment and thickness ratio (Tr) between the weak and strong layers. For any given values of Tr and μb, the two thrust sequences progress at different rates; the closely-spaced, upper thrust sequence advances forelandward at a faster rate than the widely-spaced, lower thrust sequence. Basal friction (μb) has little effects on the vergence of thrusts in the upper weak layer; they verge always towards foreland, irrespective of Tr values. But, the lower strong layer develops back-vergent thrusts when μb is low (∼0.36). In our experiments, closely spaced thrusts in the upper sequence experience intense reactivation due to their interaction with widely spaced thrusts in the lower sequence. The interaction eventually affects the wedge topography, leading to two distinct parts: inner and outer wedges, characterised by steep and gentle surface slopes, respectively.

Deep plate serpentinization triggers skinning of subducting slabs

Research Article| August 01, 2014 Deep plate serpentinization triggers skinning of subducting slabs Katharina Vogt; Katharina Vogt * 1Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584CD Utrecht, Netherlands *E-mail: katharina.vogt@erdw.ethz.ch. Search for other works by this author on: GSW Google Scholar Taras Gerya Taras Gerya 2Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092 Zurich, Switzerland Search for other works by this author on: GSW Google Scholar Author and Article Information Katharina Vogt * 1Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584CD Utrecht, Netherlands Taras Gerya 2Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092 Zurich, Switzerland *E-mail: katharina.vogt@erdw.ethz.ch. Publisher: Geological Society of America Received: 11 Feb 2014 Revision Received: 01 Jun 2014 Accepted: 02 Jun 2014 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2014 Geological Society of America Geology (2014) 42 (8): 723–726. https://doi.org/10.1130/G35565.1 Article history Received: 11 Feb 2014 Revision Received: 01 Jun 2014 Accepted: 02 Jun 2014 First Online: 09 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 Katharina Vogt, Taras Gerya; Deep plate serpentinization triggers skinning of subducting slabs. Geology 2014;; 42 (8): 723–726. doi: https://doi.org/10.1130/G35565.1 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 SocietyGeology Search Advanced Search Abstract Most of the present-day ocean floor is continuously being consumed in subduction zones, but large fragments of oceanic crust (ophiolites) have also been recognized on land. The process by which oceanic crust is separated from the subducting slab remains enigmatic, and several competing hypothesis have been proposed in the past.Based on numerical experiments we suggest that serpentinized mantle, formed in the outer rise regions of subduction zones, may provide a mechanically weak horizon within which basal detachment of the oceanic crust is feasible. Deformation of this serpentinized layer may lead to decoupling and separation of oceanic crust from the downgoing slab. Fragments of the former oceanic crust can underplate the accretionary wedge or be exposed on continental crust, whereas the skinned lithospheric part of the slab subducts into the mantle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Analogue modeling of the collapse of non-homogeneous granular slopes along weak horizons

In this study, we use results of analogue models to investigate the effect of the dip, location and thickness of a weak horizon on the stability/failure, kinematics and internal deformation of a granular slope. The models are systematically designed to simulate the collapse of non-homogeneous granular slopes by focusing on the spatial and temporal distribution of their internal deformation. Model results show that the presence of a weak horizon embedded within the granular slope has a significant influence on the granular failure, which is accommodated through different generation pulses that successively decrease in volume. However, the dip and stratigraphic location of the weak horizon dictate whether the weak horizon play a role during the failure or not. When the main failure surface is contained within a weak horizon, the dip and thickness of the weak horizon have a positive effect on the displacement of the failure mass, whereas a shallow-located weak horizon causes larger displacement of the failure mass during the collapse of granular slopes. In addition, the collapse of granular slopes results in the formation of different-generation normal faults and shortening structures (folds and thrusts) within the failure mass. The first-generation normal faults with a steep dip (about 60°) cut across the entire stratigraphy of the slope, whereas the later-generation normal faults with a gentle dip (about 40°) cut across the shallow units. The distribution of these internal structures within the failure mass is affected significantly by the dip, location and thickness of the weak horizon.

Stress inversion and basement-cover stress transmission across weak layers in the Paris basin, France

We investigate the source of non-purely gravitational horizontal stresses in the Paris basin, a nowadays tectonically quiet intracratonic basin, in its eastern border of which outstandingly dense stress measurements are available. Based on a synthesis of published data, the stress state in the basin is first shown to be very close to the one that may be extrapolated for the underlying basement, in terms of principal stress orientations and horizontal to vertical stress ratios. This is in favour of a mechanical coupling between the basement and its sedimentary cover, which may seem contradictory to the presence of several weak rock layers in the basin fill, e.g. an argillite layer that was shown to bear low deviatoric stresses, and salt layers that are implicated in a major decollement elsewhere. To unravel this apparent contradiction, a 3D-numerical modelling is performed, following a rigorous inverse problem approach, to determine the long-term elastic properties of both the basement and the basin rocks. The objective is to find the set of elastic constants that provides the best fit between the calculated stress state in the basin and the in situ data, by assuming that the stress state in the basement is known. This methodology provides a realistic set of mechanical parameters, in agreement with previous studies, which leads to the conclusion that the horizontal stresses in the basin constitute its mechanical response to the stresses that developed in the underlying basement during and since the last tectonic event (Alpine phase). The fact that horizontal stresses could be transmitted across the weak horizons, contrary to what may be expected at first glance, is explained both by the geometry of the basin and the fact that, over the long term, the stiffnesses of the various sedimentary rocks are only slightly different from each other.

How Much Does the Stock Market Risk Decline with the Investment Horizon? A Cross-Country Comparison

We perform a cross-country comparison of stock market risk. Stock market risk is defined as the standard deviation of cumulative stock market returns. We model stock market returns in a VAR(1) system jointly with bond returns and a set of predictive variables. Our results provide evidence of a strong negative horizon effect for US stock market returns and a weak negative horizon effect for Germany and France. When an open economy VAR(1) is considered, we find that stock market risk increases for the United States and Germany, while the evidence for France is mixed.

The impact of a weak horizon on kinematics and internal deformation of a failure mass using discrete element method

Weak horizons within slopes may induce and/or accelerate failure of slopes. In this study, we focus on the effect of orientation, location and dimension of a weak horizon on the mode and kinematics of downslope movement of a failure mass using discrete element method. Two kinds of cases with weak horizons were studied, one unstable homogeneous slope with low shear strength (c=50 kPa, μ=0.57) and two stable homogeneous slopes with high shear strength (c=60 kPa, μ=0.57 or c=50 kPa, μ=0.7). In the three sets of slope models, there was a weak horizon with a finite thickness embedded within the slope. In each set of slope models, two different thicknesses and locations for the weak horizons were considered to systematically investigate the effect of these parameters on the mass movement. In addition, the dip of the weak horizon was changed where in some models, it was parallel to the slope and in others it was dipping either steeper or gentler than the slope. We analyzed both kinematics and internal deformation of the failure mass in all models and conclude that the presence and geometry (i.e., thickness, location and dip) of a weak horizon changes the mode and kinematics of mass movement and governs the location of the failure surface.

New Method of Horizon Recognition in Seismic Data

Horizon recognition is a valuable tool in the interpretation of seismic data. In this letter, we present a new method which uses the combination of horizontal derivative and mathematical morphology to identify horizons. We first use a threshold value to filter the horizontal derivative of seismic data and then use the ratio of the erosion of the filtered derivative to the dilation of the filtered derivative to balance the amplitudes of strong and weak horizons. Finally, we move the strong amplitude to the position of the actual horizon. This method is demonstrated on both synthetic and real data. The resolving power of the new method is evaluated by comparing the results with those obtained by other similar methods. The new method can display the horizons more clearly.

Failure mechanism of overhanging slopes in sedimentary rocks with dissimilar mechanical properties

The paper discusses a slope failure which occurred in December 2009 adjacent to a road in northern Greece. Thick Miocene limestone horizons are interbedded with relatively thin weak horizons of silty to sandy clays and loams which are more easily eroded, resulting in the formation of notches. The weak horizon acts as an aquitard, inhibiting downward percolation from both rainfall and house discharges. The two main areas of failure occurred where the notches were particularly deep (hence the overhang was greatest) at a time when heavy rainfall created a hydrostatic head within the bedrock to the west of the slope face. The stability of the notched benches is controlled by the tensile strength of rock bridges in the limestone’s discontinuities. The analysis showed that the limestone’s in situ tensile strength and cohesion are on average three times lower than those obtained from laboratory tests, hence their application in the failure analysis would lead to an overestimation of the slope stability.

Interconnected sills and inclined sheet intrusions control shallow magma transport in the Ferrar large igneous province, Antarctica

Research Article| January 01, 2012 Interconnected sills and inclined sheet intrusions control shallow magma transport in the Ferrar large igneous province, Antarctica James D. Muirhead; James D. Muirhead † 1School of Environment, University of Auckland, Private Bag 92019, Auckland, New Zealand †E-mail: jmuirhead@ymail.com Search for other works by this author on: GSW Google Scholar Giulia Airoldi; Giulia Airoldi 2Geology Department, University of Otago, Leith Street, P.O. Box 56, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar Julie V. Rowland; Julie V. Rowland 1School of Environment, University of Auckland, Private Bag 92019, Auckland, New Zealand Search for other works by this author on: GSW Google Scholar James D.L. White James D.L. White 2Geology Department, University of Otago, Leith Street, P.O. Box 56, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar GSA Bulletin (2012) 124 (1-2): 162–180. https://doi.org/10.1130/B30455.1 Article history received: 20 Nov 2010 rev-recd: 25 Mar 2011 accepted: 06 Apr 2011 first online: 08 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 James D. Muirhead, Giulia Airoldi, Julie V. Rowland, James D.L. White; Interconnected sills and inclined sheet intrusions control shallow magma transport in the Ferrar large igneous province, Antarctica. GSA Bulletin 2012;; 124 (1-2): 162–180. doi: https://doi.org/10.1130/B30455.1 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 Field observations and structural data from intrusive complexes at Allan Hills and Terra Cotta Mountain, South Victoria Land, Antarctica, demonstrate that interconnected sills and inclined sheets transported magma through the shallow subsurface. These sills and sheets represent the upper-crustal (top 4 km) plumbing system of the 183 Ma Ferrar large igneous province. The sheets are short in length (<1500 m), are moderately inclined (47° and 51° means), and show meter-scale variations in attitude; in places, they intruded bedding planes, resulting in stepped sheet-sill geometries. Sheet geometries and their relationship to the surrounding country rock are consistent with peripheral sheet intrusion under local magmatic stresses arising from roof-lift during sill injection. The sheet intrusions thus reflect the intrusive process itself rather than a far-field tectonic stress regime. The sills and sheets, together with local dolerite masses, formed the intrusive network that supplied magma to the Mawson Formation pyroclastic rocks in various parts of South Victoria Land and, by inference, the Kirkpatrick flood basalt lavas. The predominance of inclined sheets rather than steeply dipping dikes indicates a magmatic environment that is unlike the Jurassic rift arm inferred by previous authors. This could be explained using any of the following three scenarios. (1) The axis of the rift, and hence any rift-hosted dikes, lies beyond the current exposure area. (2) The regionally extensive Ferrar sills may have provided rheologically weak horizons that limited mechanical coupling of the basement rocks and overlying Beacon Supergroup, locally detaching the upper 4 km of the crust from possible synmagmatic basement extension below. (3) The Ferrar large igneous province was emplaced in a neutral tectonic setting. In this scenario, broad-scale distribution of magma through the province was controlled by preexisting structure in the basement, and local intrusion geometries reflect the physical interaction of intruding magma with bedding anisotropy of the Beacon Supergroup. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Centrifuge modelling of deformation of a multi-layered sequence over a ductile substrate: 1. Style and 4D geometry of active cover folds during layer-parallel shortening

Centrifuge analogue modelling illustrates the progressive development of active folds in multilayers upon a ductile substrate during layer-parallel shortening. Models simulate folding of a mechanically stratified sedimentary sequence upon migmatitic gneisses in a large hot orogen, or upon a thick basal evaporite ± shale sequence in deeper levels of fold belts. The absence of a weak low-viscosity and low-density layer at the interface promotes infolding of the cover sequence and ductile substrate, whereas a planar upper surface to the basal ductile substrate is preserved when it is present. Whilst fold style, wavelength, and deformation of the interface with the ductile substrate differ depending on whether a low-viscosity and low-density layer is present at the base of the cover sequence, there is no marked systematic curvature of fold axes as seen in previous sandbox models for fault-bend or fault propagation folding during bulk shortening. Bulk shortening of a layered sequence with relatively thick individual layers above a ductile substrate promotes a regular and upright train of buckle folds, whereas thinner layers promote a more irregular distribution of buckle folds with variable vergence, style, and amplitude. Buckle folds above a ductile substrate progressively develop during bulk shortening from open and upright, to angular and tight, and may further develop into cuspate structures above relatively weak horizons. Relatively thick weak horizons within the layered sequence during bulk shortening interrupt regular fold patterns up structural section and allow out-of-phase folds to develop above and below the weak horizon.

Bowl-shaped basin related to low-angle detachment during continental extension: The case of the controversial Neogene Siena Basin (central Italy, Northern Apennines)

This paper deals with the tectonic evolution of a bowl-shaped Neogene basin (Siena Basin) located in the inner Northern Apennines and developed during an articulated tectonic evolution. This basin was controversially interpreted by different authors as graben, half-graben or thrust-top basin. Structural and stratigraphic data from the basin substratum and filling sediments, integrated with the interpretation of reflection seismic profiles and borehole logs, highlight that the Siena Basin consists of a tectonic depression with a complex internal architecture. Such a basin developed on a multilayered substratum deeply affected by extensional tectonics since the Middle Miocene. Extensional detachments produced a widespread thinning of the basin substratum and superimposed on contractional structures developed during the Northern Apennines collisional events. Extensional detachments accommodated within weak horizons and gave rise to the lateral segmentation of most competent stratigraphic horizons. Sediments filling the Siena Basin mainly deposited on the Ligurian Units (the topmost tectonic units forming the tectonic pile) in the gap between two laterally segmented geological bodies made up of the Triassic siliciclastic succession of the Verrucano Group. Such a lateral segmentation produced a synformal structural depression, not delimited by faults, filled by Late Serravallian–Late Messinian marine to continental sediments which deposited during the extensional faulting. From the latest Early Pliocene to the Middle Pliocene the architecture of the basin was modified by an high-angle normal fault system which affected the eastern side of the basin and produced new accommodation space for marine sediments. In sum, the Siena Basin consists of a sin-tectonic basin developed on the hanging wall of staircase extensional detachments, later affected by high angle normal to oblique faults. The latter faults defined a half-graben during the latest evolution of the basin. The tectonic evolution of the Siena Basin made it possible to point out some differences with respect to the types of bowl-shaped basins related to extensional detachments and named as supradetachment basins.