Structural Features of the Central Labrador Trough: A Model for Strain Partitioning, Differential Exhumation and Late Normal Faulting in a Thrust Wedge under Oblique Shortening

The west-verging fold and thrust belt of the Central Labrador Trough originated as a part of the New Quebec Orogen from rift inversion as a result of oblique collision and dextral transpression between the Archean Superior craton and the Archean block of the Core Zone during the Trans-Hudson orogeny (1.82−1.77 Ga). The structures associated with dextral transpression are well established in the northern segment of the orogen but not in the central part. We present new field structural observations along the ca. 70 km long W−E Minowean-Romanet transect that include not only elements of thrust tectonics but also previously undocumented examples of strike-slip shear zones and late brittle, semi-brittle and ductile extensional structures which occurred both in the frontal and rear parts of the thrust wedge. The newly described low-angle mineral lineation, axes of cylindrical folds and dextral mylonitic shear zones in the footwall of the Romanet Fault are oriented subparallel to the orogen and reflect the early phase of oblique convergence. Mineral lineations and striations on planes of normal faults in the hanging wall of the Romanet Fault are oriented orthogonal to the orogen and correspond to a later phase of exhumation driven by the combined effects of erosion and underplating. To explain the increase in the degree of exhumation along the orogen in the study area from NW to SE, we propose a model of strain partitioning and differential exhumation that resulted from longitudinal variations of shortening and erosion under an oblique convergence setting.RÉSUMÉLa partie centrale de la ceinture de plissement et de chevauchement de la Fosse du Labrador de vergence vers l’ouest fait partie intégrante de l’Orogène du Nouveau-Québec, et résulte de la collision oblique avec transpression dextre entre le craton Supérieur archéen et le bloc archéen de la Zone noyau pendant l’Orogenèse trans-hudsonienne (1.82−1.77 Ga). Les structures associées à la transpression dextre sont bien établies dans la partie nord de l’orogène mais pas dans la partie centrale. Nous présentons de nouvelles observations structurales de terrain le long de la traverse ouest−est Minowean-Romanet d’environ 70 km de long, qui comprennent non seulement des évidences de tectonique de chevauchement, mais également des exemples encore non documentés de zones de cisaillement ductile et de structures d’extension fragiles, demi-fragiles et ductiles à la fois dans les parties frontales et arrière du prisme d’accrétion tectonique. La linéation minérale à faible plongement récemment décrite, les axes de plis cylindriques et les zones de cisaillement mylonitique dextre dans le compartiment inférieur de la faille de Romanet sont subparallèles à l’orogène et reflètent une phase précoce de la convergence oblique. La linéation et les stries minérales sur les plans des failles normales dans le compartiment supérieur de la faille de Romanet sont orientées orthogonalement à l’orogène et correspondent à la phase ultérieure d’exhumation induite par les effets combinés de l’érosion et de l’accrétion basale. Pour expliquer l’augmentation du degré d’exhumation le long de l’orogène du nord-ouest au sud-est dans la zone d’étude, nous proposons un modèle de partitionnement de la déformation et de l’exhumation différentielle résultant des variations longitudinales du raccourcissement et de l’érosion dans un contexte de convergence oblique.

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ANÁLISE TECTÔNICA DA PORÇÃO NORDESTE DA FAIXA SERGIPANA, PROVÍNCIA BORBOREMA: DUPLA VERGÊNCIA EM RESPOSTA A COLISÃO OBLÍQUA ENTRE O CRÁTON DO SÃO FRANCISCO E O TERRENO PERNAMBUCO-ALAGOAS

Revista Geonomos ◽

10.18285/geonomos.v25i2.1078 ◽

2018 ◽

Author(s):

Haroldo Monteiro Lima ◽

Márcio Martins Pimentel ◽

Lauro Cezar Montefalco de Lira Santos ◽

Vanildo Almeida Mendes

Keyword(s):

Geometric Analysis ◽

Shear Zones ◽

Strain Partitioning ◽

Fold Belt ◽

Oblique Collision ◽

Borborema Province ◽

Thrust Tectonics ◽

Late Neoproterozoic ◽

Orogenic Belts ◽

Belo Monte

Estruturas de dupla vergência são reconhecidas em cinturões orogênicos pré-cambrianos e fanerozoicos em resposta à partição da deformação entre componentes contracionais e transcorrentes em zonas transpressionais. A Faixa Sergipana é um importante segmento crustal localizado no sul da Província Borborema, NE do Brasil. Análise cinemática e geométrica em escala meso e microscópica realizadas na porção Nordeste da Faixa Sergipana revelou a existência de quatro fases deformacionais: Dn, D1, D2 e D3 que resultaram em inversão de transporte tectônico e imbricamento de complexos metavulcanossedimentares abundantes na região. O Domo Jirau do Ponciano representa o embasamento gnáissico migmatítico que preserva a trama mais antiga Dn. As fases posteriores (D1 e D2) representam tectônica contracional manifestada pelas zonas de cisalhamento de Jacaré dos Homens, Belo Monte-Jeremoabo e Palmeira dos Índios, e transcorrente/transpressional, respectivamente. Todo esse conjunto foi deformado por último por um episódio rúptil-dúctil (D3) responsável pela formação de fraturas, falhas e brechas de falhas. A combinação de dados estruturais e análise litoestratigráfica sugere que este arcabouço deve ter se desenvolvido em episódios contracionais distintos e retrabalhado durante o final do Neoproterozoico em resposta à colisão oblíqua entre o Terreno Pernambuco-Alagoas e o Cráton do São Francisco.Palavras Chave: Cinturões orogênicos, dupla vergência, Faixa SergipanaAbstract:TECTONIC ANALYSIS OF THE NORTHEAST SERGIPANA BELT, BORBOREMA PROVINCE: DOUBLE VERGENCE IN RESPONSE TO OBLIQUE COLLISION BETWEEN THE SÃO FRANCISCO CRATON AND PERNAMBUCO-ALAGOAS TERRANE. Double-vergent structures are recognized in Precambrian and Phanerozoic orogenic belts due strain partitioning in thrust and transcurrent components in transpressional sites. The Sergipano Fold Belt is an important crustal segment, located in the southern Borborema Province, NE Brazil. Meso and microscopic kinematic and geometric analysis in the northeastern portion of the Sergipano Fold Belt revealed the presence of four deformation stages (Dn, D1, D2 e D3). They resulted in inversion of tectonic vergence and imbrication of the metavolcanosedimentary sequences. The Jirau do Ponciano Dome represents the gneissic-migmatitic basement, preserving the older fabric. The later stages (D1 and D2), corresponds to thrust tectonics, represented by the Jacaré dos Homens, Belo Monte-Jeremoabo and Palmeira dos Índios shear zones and the transcurrent/transpressional stage, respectively. All this set is later affected by a ductile-brittle phase (D3), responsible for fractures, faults and formation of breccias. The integration of the obtained data suggest that the area framework was developed in distinct contractional episodes and reworked in the Late Neoproterozoic, in response to oblique collision between the Pernambuco-Alagoas terrane/block and the São Francisco Craton.Keywords: Orogenic belts, double vergence, Sergipana belt

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Oblique collision and deformation partitioning in the SW Iberian Variscides

Solid Earth ◽

10.5194/se-7-857-2016 ◽

2016 ◽

Vol 7 (3) ◽

pp. 857-872 ◽

Cited By ~ 9

Author(s):

Irene Pérez-Cáceres ◽

José Fernando Simancas ◽

David Martínez Poyatos ◽

Antonio Azor ◽

Francisco González Lodeiro

Keyword(s):

Finite Strain ◽

Lateral Displacement ◽

Point Of View ◽

Variscan Orogeny ◽

Strain Partitioning ◽

Complex Deformation ◽

Oblique Collision ◽

Deformation Partitioning ◽

Oblique Convergence ◽

Deformation Patterns

Abstract. Different transpressional scenarios have been proposed to relate kinematics and complex deformation patterns. We apply the most suitable of them to the Variscan orogeny in SW Iberia, which is characterized by a number of successive left-lateral transpressional structures developed in the Devonian to Carboniferous period. These structures resulted from the oblique convergence between three continental terranes (Central Iberian Zone, Ossa-Morena Zone and South Portuguese Zone), whose amalgamation gave way to both intense shearing at the suture-like contacts and transpressional deformation of the continental pieces in-between, thus showing strain partitioning in space and time. We have quantified the kinematics of the collisional convergence by using the available data on folding, shearing and faulting patterns, as well as tectonic fabrics and finite strain measurements. Given the uncertainties regarding the data and the boundary conditions modeled, our results must be considered as a semi-quantitative approximation to the issue, though very significant from a regional point of view. The total collisional convergence surpasses 1000 km, most of them corresponding to left-lateral displacement parallel to terrane boundaries. The average vector of convergence is oriented E–W (present-day coordinates), thus reasserting the left-lateral oblique collision in SW Iberia, in contrast with the dextral component that prevailed elsewhere in the Variscan orogen. This particular kinematics of SW Iberia is understood in the context of an Avalonian plate salient currently represented by the South Portuguese Zone.

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Migration of deformation, subsidence, and basin formation in the SW Pannonian Basin (central Europe) and the change to contractional deformation

10.5194/egusphere-egu21-13300 ◽

2021 ◽

Author(s):

László Fodor ◽

Attila Balázs ◽

Gábor Csillag ◽

István Dunkl ◽

Gábor Héja ◽

...

Keyword(s):

Pannonian Basin ◽

Numerical Models ◽

Hanging Wall ◽

Shear Zones ◽

Normal Faults ◽

Rift System ◽

Distal Margin ◽

Late Middle Miocene ◽

Basin Scale ◽

Basin Formation

The Pannonian Basin is a continental extensional basin system with various depocentres within the Alpine&#8211;Carpathian&#8211;Dinaridic orogenic belt. Along the western basin margin, exhumation along the Rechnitz, Pohorje, Kozjak, and Baj&#225;n detachments resulted in cooling of diverse crustal segments of the Alpine nappe stack (Koralpe-W&#246;lz and Penninic nappes); the process is constrained by variable thermochronological data between ~25&#8211;23 to ~15 Ma. Rapid subsidence in supradetachment sub-basins indicates the onset of sedimentation in the late Early Miocene (Ottnangian? or Karpatian, from ~19 or 17.2 Ma). In addition to extensional structures, strike-slip faults mostly accommodated differential extension between domains marked by large low-angle normal faults. Branches of the Mid-Hungarian Shear Zone (MHZ) also played the role of transfer faults, although shear-zones perpendicular to extension also occurred locally.During this period, the distal margin of the large tilted block in the hanging wall of the detachment system, the pre-Miocene rocks of the Transdanubian Range (TR) experienced surface exposure, karstification, and terrestrial sedimentation. The situation changed after ~15&#8211;14.5 Ma when faulting, subsidence, and basin formation shifted north-eastward. Migration of normal faulting resulted in fault-controlled basin subsidence within the TR which lasted until ~8 Ma.3D thermo-mechanical lithospheric and basin-scale numerical models predict similar spatial migration of the depocenters from the orogenic margin towards the basin center. The reason for this migration is found in the interaction of deep Earth and surface processes. A lithospheric and smaller crustal-scale weak zones inherited from a preceding orogenic structure localize initial deformation, while their redistribution controls asymmetric extension accompanied by the upraising of the asthenopshere and flexure of the lithosphere. Models suggest ~4&#8211;5 Myr delay of the onset of sedimentation after the onset of crustal extension and ~150&#8211;200 km of shift in depocenters during ~12 Myr. These modeling results agree well with our robust structural and chronological data on basin migration.Simultaneously with or shortly after depocenter migration, the southern part of the former rift system, mostly near the MHZ, underwent ~N&#8211;S shortening; the basin fill was folded and the boundary normal faults were inverted. The style of deformation changed from pure contraction to transpression. The Baj&#225;n detachment could be slightly folded, although its synformal shape could also be considered a detachment corrugation. Deformation was dated to ~15&#8211;14 Ma (middle Badenian) in certain sub-basins while in other sub-basins deformation seems to be continuous throughout the late Middle Miocene from ~15 Ma to ~11.6 Ma.Another contractional pulse occurred in the earliest Late Miocene, between ~11.6 and ~9.7 Ma while the western part of the TR was still affected by extensional faulting and subsidence. All these contractional deformations can be linked to the much larger fold-and-thrust belt that extends from the Southern and Julian Alps through the Sava folds region in Slovenia. Contraction is still active, as indicated by recent earthquakes in Croatia.Mol Ltd. largely supported the research. The research is supported by the scientific grant NKFI OTKA 134873 and the Slovenian Research Agency (research core funding No. P1-0195).

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Extension and transtension associated with strike-slip faults and its relation with aquifer potentials: a case study in Aravalli terrane (North Gujarat), India

10.5194/egusphere-egu2020-18625 ◽

2020 ◽

Author(s):

Rudra Mohan Pradhan ◽

Tapas Kumar Biswal

Keyword(s):

Complex Geometry ◽

Fractured Rock ◽

Primary Source ◽

Structural Data ◽

Shear Zones ◽

Structural Features ◽

Strike Slip ◽

Normal Faults ◽

Fold Belt ◽

North Gujarat

Fractured rock aquifers are one of the most difficult aquifers to characterize due to complex geometry and fracture network. In Aravalli terranes of North Gujarat, communities depend on basement rock aquifers as the primary source of water supply. The hydrogeology of these aquifers is poorly understood and the drinking/irrigation wells are frequently placed in this area with little appreciation of the fracture systems. Increasing water demand puts stress to explore groundwater from less reliable sources of basement rocks and hence, makes it vital to identify potential hydrogeological zones. Lineament studies are commonly used for targeting groundwater bearing zones in hard rock terrane and very often ignore the other important structural settings viz. extension, transtension etc. For the present study, structural data pertaining faults and fractures have been mapped through fieldwork and Electrical resistivity imaging (ERT) technique. The key objective of the study is to correlate the structural features (extensional and transtensional settings) with geophysical profiles and to find out potential hydrogeological zones from where water can be explored economically. The study area comes under the Ambaji basin of Aravalli-Delhi fold belt which is a Proterozoic fold belt running 700-800 km in NE-SW direction and situated in NW India. The Aravalli-Delhi fold belt had undergone multiple phases of deformation. In this area, three major sets of fractures are present and are oriented largely in WNW-ESE, NE-SW, and NW-SE direction. The WNW-ESE fracture is dextral in nature which has interpreted from the displacement of fold limbs. Further, these are right lateral en-echelon normal faults where NE-SW extension has been taken place. There is another set of fracture i.e. NW-SE which is due to stretching of strike-slip fault. The ductile shear zones in the area are also parallel to the NW-SE fracture set. The shear zones are opened-up due to extension and formed potential aquifers. ERT has been carried out along and across the fractures to understand the subsurface fracture geometry. The ERT shows deep sited fractures and low resistivity values at the cross-section of WNW-ESE faults with the shear zone. This concludes a strong correlation between different structural settings with potential aquifers which could be used for pumping as well as artificial recharge sites for long term sustainability.Keywords- Aravalli terrane, Aquifer, Extension, Fracture, ERT

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Acadian deformation in the shallow crust: an example from the Siluro-Devonian Arisaig Group, Avalon terrane, mainland Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e05-106 ◽

2006 ◽

Vol 43 (1) ◽

pp. 71-81 ◽

Cited By ~ 6

Author(s):

James A Braid ◽

J Brendan Murphy

Keyword(s):

Nova Scotia ◽

Shear Zones ◽

Thrust Fault ◽

Structural Features ◽

Strike Slip ◽

Normal Faults ◽

Progressive Deformation ◽

Acadian Orogeny ◽

Shallow Crust ◽

Dextral Strike Slip

The Silurian Early Devonian Arisaig Group of the Avalon terrane in northern mainland Nova Scotia consists mainly of thinly bedded sandstones, siltstones, and shales deposited in a near shore environment. These strata were deformed in the middle Devonian to form regional northeast- to NNE-trending folds and record deformation processes in the shallow crust during the Acadian orogeny, one of the most regionally extensive orogenic events in the Canadian Appalachians. Structural features in the Arisaig Group are consistent with fold propagation associated with thrust fault geometry and coeval local extension recorded by a set of conjugate normal faults. Many outcrop-scale folds have sheared limbs and show evidence of a complex progressive deformation. Folding was predominantly accomplished by bulk rotation and flattening above thrust fault tips. Early structures (D1D2) produced regional cylindrical folds, whereas later (D3a, D3b, D3c) structures produced conical folds. D1D3 fold orientations show high variability, but are consistent with progressive deformation related to reactivation and coeval dextral strike-slip movement along the Hollow Fault. The style of deformation is compatible with models in which strain is partitioned into preexisting shear zones in the basement, with folds in the overlying Arisaig Group initiated above the tips of upward-propagating thrusts as second-order structures related to movement along those shear zones. Taken together, these data indicate that fold mechanisms and geometry in the shallow crust during the Acadian orogeny in mainland Nova Scotia may be related to dextral strike-slip along major faults in the basement and co-genetic upward-propagating thrusts that rotated and flattened overlying strata.

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Bivergent extension in the overriding plate above a slab tear (Dodecanese, Greece)

10.5194/egusphere-egu2020-3167 ◽

2020 ◽

Author(s):

Bernhard Grasemann ◽

David A. Schneider ◽

Konstantinos Soukis ◽

Vincent Roche

Keyword(s):

Eastern Mediterranean ◽

Hanging Wall ◽

Finite Extension ◽

Normal Fault ◽

Vertical Axis ◽

Normal Faults ◽

Low Grade ◽

Thrust Belt ◽

Fold And Thrust Belt ◽

Variscan Basement

Tearing in the Hellenic slab below the transition between the Aegean and Anatolian plate is considered to have significantly affected Miocene tectonic and magmatic evolution of the eastern Mediterranean by causing a toroidal flow of asthenosphere and a lateral gradient of extension in the upper plate. Some studies suggest that this lateral gradient is accommodated by a distributed sinistral lithospheric-scale shear zone whereas other studies favor a localized NE-SW striking transfer zone. Recent studies in the northern Dodecanese demonstrate that the transition zone between the Aegean and Anatolian plate is characterized by Miocene extension with a constant NNE-SSW sense of shear accommodating the difference in finite extension rates in the middle-lower crust. Neither localized or distributed strike-slip faults nor rotation of blocks about a vertical axis have been observed. In this work we focus on the geology Kalymnos located in the central Dodecanese. Based on our new geological map, three major tectonic units can be distinguished: (i) Low-grade, fossil-rich late Paleozoic marbles, which have been deformed into S-vergent folds and out-of-sequence thrusts. This fold-and-thrust belt is sealed by an up to 200 m thick wildflysch-type deposit consisting of low-grade metamorphic radiolarites and conglomerates with tens of meters-scale marbles and ultramafics blocks. (ii) Above this unit, amphibolite facies schists, quartzites and amphibolites are tectonically juxtaposed along a several meter-thick thrust fault with low-grade ultramylonites and cohesive ultracataclasites/pseudotachylites with top-to-N kinematics. (iii) At highest structural levels, a major cataclastic low-angle normal fault zone localized in Verrucano-type violet slates separates Mesozoic unmetamorphosed limestones in the hanging wall. The sense of shear of the normal fault is top-to-SSW. All units are cut by brittle high-angle normal faults shaping the geomorphology of Kalymnos, which is characterized by three major NNW-SSE trending graben systems. New white mica Ar-Ar ages suggests that the middle units represent relics of a Variscan basement, which was thrusted on top of a fold-and-thrust belt during an Eo-Cimmerian event. Zircon (U-Th)/He ages from the Variscan basement are c. 28 Ma, indicating that the lower units were exhumed below the Mesozoic carbonates during the Oligocene-Miocene. Since Miocene extension in the northern Dodecanese records top-to-NNE kinematics, we suggest that back-arc extension in the whole Aegean realm and transition to the Anatolian plate is bivergent, and tearing in the Hellenic slab did not significantly affected the extension pattern in the upper crust.

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Structural and thermal evolution of the eastern Aar Massif: insights from structural field work and Raman thermometry

Swiss Journal of Geosciences ◽

10.1186/s00015-020-00381-3 ◽

2021 ◽

Vol 114 (1) ◽

Cited By ~ 1

Author(s):

Lukas Nibourel ◽

Alfons Berger ◽

Daniel Egli ◽

Stefan Heuberger ◽

Marco Herwegh

Keyword(s):

Shear Zone ◽

Hanging Wall ◽

Shear Zones ◽

Swiss Alps ◽

Normal Faults ◽

En Bloc ◽

Temperature Conditions ◽

Kinematic Evolution ◽

Structural Style ◽

Aar Massif

AbstractThe thermo-kinematic evolution of the eastern Aar Massif, Swiss Alps, was investigated using peak temperature data estimated from Raman spectroscopy of carbonaceous material and detailed field analyses. New and compiled temperature-time constraints along the deformed and exhumed basement-cover contact allow us to (i) establish the timing of metamorphism and deformation, (ii) track long-term horizontal and vertical orogenic movements and (iii) assess the influence of temperature and structural inheritance on the kinematic evolution. We present a new shear zone map, structural cross sections and a step-wise retrodeformation. From $$\text{ca.\;26\,Ma}$$ ca.\;26\,Ma onwards, basement-involved deformation started with the formation of relatively discrete NNW-directed thrusts. Peak metamorphic isograds are weakly deformed by these thrusts, suggesting that they initiated before or during the metamorphic peak under ongoing burial in the footwall to the basal Helvetic roof thrust. Subsequent peak- to post-metamorphic deformation was dominated by steep, mostly NNW-vergent reverse faults ($$\text{ca.}$$ ca. 22–14 Ma). Field investigations demonstrate that these shear zones were steeper than $$50^{\circ}$$ 50 ∘ already at inception. This produced the massif-internal structural relief and was associated with large vertical displacements (7 km shortening vs. up to 11 km exhumation). From 14 Ma onwards, the eastern Aar massif exhumed “en bloc” (i.e., without significant differential massif-internal exhumation) in the hanging wall of frontal thrusts, which is consistent with the transition to strike-slip dominated deformation observed within the massif. Our results indicate 13 km shortening and 9 km exhumation between 14 Ma and present. Inherited normal faults were not significantly reactivated. Instead, new thrusts/reverse faults developed in the basement below syn-rift basins, and can be traced into overturned fold limbs in the overlying sediment, producing tight synclines and broad anticlines along the basement-cover contact. The sediments were not detached from their crystalline substratum and formed disharmonic folds. Our results highlight decreasing rheological contrasts between (i) relatively strong basement and (ii) relatively weak cover units and inherited faults at higher temperature conditions. Both the timing of basement-involved deformation and the structural style (shear zone dip) appear to be controlled by evolving temperature conditions.

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Neogene kinematics and structural evolution of the Giudicarie Belt and eastern Southern Alpine orogenic front (Northern Italy)

10.5194/egusphere-egu2020-7840 ◽

2020 ◽

Author(s):

Vincent Verwater ◽

Mark R. Handy ◽

Eline Le Breton ◽

Vincenzo Picotti ◽

Azam Jozi Najafabadi ◽

...

Keyword(s):

Cross Sections ◽

Hanging Wall ◽

Structural Evolution ◽

Leading Edge ◽

Strike Slip ◽

Southern Alps ◽

Normal Faults ◽

Strain Partitioning ◽

The North ◽

Thickness Variations

The eastern Southern Alps are part of the deformed leading edge of the Adriatic plate indenting the European plate to the north. Neogene deformation in the eastern Southern Alps is partitioned into three, kinematically linked fold-and-fault systems: (1) The Giudicarie Belt, (2) the Valsugana Thrust System and (3) the external fold-and-thrust systems of the orogenic front, including the strike-slip Schio-Vicenza Fault. We aim to constrain fault kinematics from the Southern Alpine orogenic front to the Northern Giudicarie Fault to better understand deformation of the Adriatic indenter since Miocene time.The Giudicarie Belt is a sinistral transverse zone characterized by NNE-oriented faults. Some of these faults originated in the Mesozoic as NNE-SSW trending normal faults, which were inverted during Alpine orogeny. Most of the Mesozoic normal faults are oriented oblique to sub-parallel to the main Neogene shortening direction, which led to strain partitioning between thrust and strike-slip faults. This significant strike-slip component complicates kinematic and structural restoration of geological cross-sections in 2-D because rock units moved into and out of the section trace, distorting in-section shortening estimates.To assess lateral variations in shortening and quantify strain partitioning along and across the strike of the Giudicarie Belt, we constructed and balanced a network of closely spaced cross-sections perpendicular to the main structural trend. Seven 2-D NNW-SSE cross-sections from the Northern Giudicarie Fault to the Southern Alpine orogenic front reveal that the amount of Neogene NNW-SSE shortening varies from 11 km in the vicinity of the Adige embayment to 27 km further NE, with most shortening (20 to 26 km) accommodated within the Valsugana and Giudicarie systems. Shortening differs on either side of the Trento-Cles, Schio-Vicenza (4 km difference) and Ballino-Garda (7 km difference) strike-slip faults. These faults are inherited Mesozoic faults that coincide with significant stratigraphic thickness variations, which we constrained along orogen-parallel cross-sections. The SW-NE variation in shortening is inferred to have been taken up by these sinistral strike-slip faults, but also including the Northern Giudicarie Fault, for which we estimate the minimum amount of slip to be 19 km.Exposure of Pre-Permian basement in the hanging wall of thrusts indicates a thick-skinned style of deformation. Forward modelling using the MOVE Suite Software indicates that the depth of the detachments within the Pre-Permian basement is no greater than 20 km. A recently located cluster of minor seismic events (2017-2018) within the study area is aligned between 5 and 15 km along the modelled detachments. These earthquake clusters occur within the external fold-and-thrust systems of the orogenic front, suggesting that ongoing shortening is taken up within this system and that the Valsugana and Giudicarie systems are inactive today.

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Oblique collision and deformation partitioning in the SW Iberian Variscides

Solid Earth Discussions ◽

10.5194/sed-7-3773-2015 ◽

2015 ◽

Vol 7 (4) ◽

pp. 3773-3815 ◽

Cited By ~ 2

Author(s):

I. Pérez-Cáceres ◽

J. F. Simancas ◽

D. Martínez Poyatos ◽

A. Azor ◽

F. González Lodeiro

Keyword(s):

Finite Strain ◽

Lateral Displacement ◽

Point Of View ◽

Variscan Orogeny ◽

Strain Partitioning ◽

Complex Deformation ◽

Oblique Collision ◽

Deformation Partitioning ◽

Oblique Convergence ◽

Deformation Patterns

Abstract. Different transpressional scenarios have been proposed to relate kinematics and complex deformation patterns. We apply the most suitable of them to the Variscan orogeny in SW Iberia, which is characterized by a number of successive left-lateral transpressional structures developed at Devonian to Carboniferous times. These structures resulted from the oblique convergence between three continental terranes (Central Iberian Zone, Ossa-Morena Zone and South Portuguese Zone), whose amalgamation gave way to both intense shearing at the suture-like contacts and transpressional deformation of the continental pieces in-between, thus showing strain partitioning in space and time. We have quantified the kinematics of the collisional convergence by using the available data on folding, shearing and faulting patterns, as well as tectonic fabrics and finite strain measurements. Given the uncertainties regarding the data and the boundary conditions modeled, our results must be considered as a semi-quantitative approximation to the issue, though very significant from a regional point of view. The total collisional convergence surpasses 1000 km, most of them corresponding to left-lateral displacement parallel to terrane boundaries. The average vector of convergence is oriented E–W (present-day coordinates), thus reasserting the left-lateral oblique collision in SW Iberia, in contrast with the dextral component that prevailed elsewhere in the Variscan orogen. This particular kinematics of SW Iberia is understood in the context of an Avalonian plate promontory currently represented by the South Portuguese Zone.

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Relationships between oblique convergence partitioning and plate kinematics. A case study from the western Betics external zones and foreland (southern Spain)

10.5194/egusphere-egu2020-6104 ◽

2020 ◽

Author(s):

Manuel Díaz-Azpiroz ◽

Inmaculada Expósito ◽

Alejandro Jiménez-Bonilla ◽

Juan Carlos Balanyá

Keyword(s):

Foreland Basin ◽

Strike Slip ◽

Southern Spain ◽

Thrust Belt ◽

Strain Partitioning ◽

Seismic Profiles ◽

Tectonic Plates ◽

Upper Miocene ◽

Fold And Thrust Belt ◽

Oblique Convergence

Displacement between tectonic plates is normally partitioned into different tectonic domains accommodating specific components of the bulk strain, such that no single domain can possibly be regarded as representative of the overall kinematics. Eventually, this partitioning can be produced at different scales. Therefore, plate kinematic motion estimations based on the surface geological record should ideally rely on detailed multiscale, structural analyses of all different tectonic domains involved.The Betic-Rif orogen was formed during the Cenozoic by the convergence and subsequent collision of the Alboran domain and the South Iberian and Maghrebian paleomargins. After the main Miocene event, oblique convergence has been still active up to present times in both branches of the resulting Gibraltar Arc. In this work we analyze how dextral oblique convergence in the northern Betic branch is partitioned into different tectonic domains of the orogen external zones and foreland, where contrasting strain fields are deduced. These domains present distinctive rheologies, thus showing also specific structural styles. As such, we present data of upper Miocene-Present structures from four different tectonic domains along a complete transect of the western Betics (southern Spain), from the internal-external zones boundary outwards. In the inner fold and thrust belt, the detached South Iberian paleomargin and Flysch trough units (mostly limestones and other carbonatic rocks) are deformed mainly by upright and double-verging folds as well as reverse faults, both registering mostly orthogonal shortening. The outer fold and thrust belt progressed toward the foreland incorporating block-in-matrix formations, with evaporite-rich marly matrix, formed ahead the mountain front; its main deformation is resolved at a strike-slip dominated, dextral transpressional zone. The upper Miocene deposits of the foreland basin (calcarenites and marls) are affected by weak deformation combining some shortening and an unconstrained strike-slip component, as deduced from seismic profiles. Finally, Paleozoic structures of the foreland, formerly developed at non- to medium-grade metamorphic conditions, were likely reactivated under a dextral transpressional strain field, which acts in combination with forebulge bending.The strongly arcuate shape of the Gibraltar Arc likely imposes contrasting kinematics along strike within the same tectonic domain. Indeed, the inner fold and thrust belt shows nearly orthogonal shortening to the west, in a more frontal position, and a strike-slip dominated high-strain zone (the so-called Torcal shear zone) to the east. By contrast, preliminary studies show no significant differences in the kinematics of the foreland eastward from the analyzed transect.All of our kinematic results from the studied domains are compatible with an overall dextral oblique convergence. However, more accurate strain estimations are needed to constrain the plate displacements responsible for the upper Miocene-Recent deformation in the Gibraltar Arc northern branch. Moreover, detailed analyses of strain partitioning modes will shed light into the relationships between these plate displacements and the resulting strain patterns.

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