On the dextral offset of a Variscan shear zone across the Mérens fault in the central Pyrenees (Andorra, France)

2014 ◽  
Vol 185 (2) ◽  
pp. 131-143 ◽  
Author(s):  
Bas van den Eeckhout ◽  
Hans de Bresser
Keyword(s):  
Shear Zone ◽  
Geographical Location ◽  
Structural Data ◽  
Shear Zones ◽  
Fault Activity ◽  
Horizontal Movement ◽  
Tectonic Significance ◽  
Dextral Shear ◽  
North And South ◽  
Central Pyrenees

AbstractThis paper contributes to the understanding of the offset on the 80 km long E-W striking Mérens fault in the central Pyrenees. Parameters such as amount and sense of offset are a prerequisite for a better understanding of the evolution of the fault, its tectonic significance and for reconstruction of the pre-existing configuration of its wall rocks.In the western Aston massif, north of the Mérens fault, an over 5 km long, N125E striking steep dextral shear zone occurs. This shear zone is characterized by medium-grade assemblages of metamorphic minerals and is considered to be of late Variscan age. The presence of such a shear zone in this area was deduced from i) published structural data on the Mérens fault, and ii) its cut off relation with an over 40 km long late Variscan shear zone to the south. In this study it is shown that the shear zones north and south of the Mérens fault initially formed a single late Variscan shear zone, cut and displaced by the younger Mérens fault. The exact geographical location of the shear zone in the Aston massif constrains the finite dextral horizontal movement on the Mérens fault to at least 10,4 ± 0,5 km. Finite uplift of the Aston massif exceeds 4 km. Extrapolation of the arguments to the eastern Aston and Hospitalet massifs indicates that the NE terminations of both gneiss cores also lined up along one single steep (W)NW striking shear zone prior to Mérens fault activity. Dextral horizontal offset is 8,5 ± 1 km in that area. Restoration of the late Variscan configuration of the Aston and Hospitalet massifs reveals an elongate WNW trending mantled gneiss antiform, bordered by steep dextral shear zones with similar trend.

Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW Anatolia

2020 ◽  
Author(s):  
Salim Birkan Bayrak ◽  
Işıl Nur Güraslan ◽  
Alp Ünal ◽  
Ömer Kamacı ◽  
Şafak Altunkaynak ◽  
...  
Keyword(s):  
Shear Zone ◽  
Boundary Migration ◽  
Microstructural Analysis ◽  
Structural Data ◽  
Ductile Deformation ◽  
Brittle Deformation ◽  
Deformation History ◽  
Shear Sense ◽  
History Of ◽  
Dextral Shear

<p>Marmara granitoid (47 Ma) is a representative example of the Eocene post-collisional magmatism which produced several granitic plutons in NW Anatolia, Turkey. It is a W-E trending sill-like magmatic body which was concordantly emplaced into the metamorphic basement rocks of Erdek Complex and Saraylar Marble. The granitoid is represented by deformed granodiorite which displays well-developed lineation and foliation in meso-scale defined by the elongation of mica and feldspar crystals and recrystallization of quartz however, in some places, magmatic textures are preserved. Deformed granodiorite is broadly cut by aplitic and pegmatitic dikes and contains mafic enclaves which display the same deformation indicators with the main granitoid.</p><p>Microstructural analysis shows that the solid-state deformation of the Marmara granitoid is classified as ductile deformation with high temperatures and ductile-to-brittle deformation with relatively lower temperatures. Evidence for the ductile deformation of the granitoid is represented by chessboard extinction of quartz, grain boundary migration (GBM) and subgrain rotation recrystallisation (SGR) which exhibits that the deformation temperature changed from 600 <sup>o</sup>C to 400<sup>o</sup>C. Bulging recrystallization (BLG), grain size reduction of amphibole, biotite and plagioclases and microcracks on plagioclases were considered as overlying ductile-to-brittle deformation signatures which develop between 300-<250 <sup>o</sup>C temperatures.</p><p>All of these field and micro-structural data collectively suggest that the shear sense indicators such as micafish structures and δ type mantled porphyroclasts displayed stair-steppings pointing out to a right lateral movement, indicating that the structural evolution and deformation history of Marmara granitoid was controlled by a dextral shear zone.</p>

The Ailao Shan–Red River shear zone revisited: Timing and tectonic implications

2019 ◽  
Vol 132 (5-6) ◽  
pp. 1165-1182 ◽  
Author(s):  
Junlai Liu ◽  
Xiaoyu Chen ◽  
Yuan Tang ◽  
Zhijie Song ◽  
Wei Wang
Keyword(s):  
Shear Zone ◽  
Structural Data ◽  
Shear Zones ◽  
Red River ◽  
Plate Convergence ◽  
Ductile Shearing ◽  
Magma Sources ◽  
T Values ◽  
Tectonic Extrusion ◽  
Lower Crustal

Abstract Continental strike-slip shear zones that may bear important information about the evolution of convergent tectonics often occur to accommodate plate convergence. When and how shearing along the shear zones responds to plate interactions, however, are often debated. In this study, we investigated the Oligocene–Miocene leucocratic dikes from the Ailao Shan–Red River shear zone, which was active during India-Eurasia plate convergence, to constrain the timing and mechanism of ductile shearing along the shear zone. The dikes are structurally grouped into pre-, syn-, and postkinematic types with respect to ductile shearing. Prekinematic dikes from ca. 41 to 30 Ma have low whole-rock 87Sr/86Sr(i) values (0.707–0.710), generally high εNd(t) values (–3.31∼–7.98), and variable εHf(t) values (–7.9∼+5.7). Their magma sources involved high thermal perturbation inducing partial melting of the lower crust, and contributions from the mantle that were possibly related to extensional collapse of the orogenic belt prior to tectonic extrusion of the Sundaland block. Syn- and postkinematic dikes from ca. 28 to 20 Ma dominantly have high whole-rock 87Sr/86Sr(i) (0.707–0.725) and low εNd(t) (–5.83 to –9.76) values, and either negative or positive zircon εHf(t) values (broadly in the range of –12 to + 7.6) for coeval but separate crustal magma sources. The results imply that major shearing accompanying retrograde metamorphism along the Ailao Shan–Red River shear zone was localized to crustal level. A synthesis of regional structural data suggests that Oligocene–Miocene shearing along the Ailao Shan–Red River shear zone and lateral tectonic extrusion of the Sundaland block proceeded in response to progressive India-Eurasia plate convergence. Distributed and inhomogeneous middle- to lower-crustal flow along the boundaries of and within the Sundaland block occurred during the tectonic extrusion.

Exploring the emplacement of Cretaceous arc granites and dextral shear zones in northwestern Nevada, USA, using the StraboSpot data system

2021 ◽  
pp. 221-251
Author(s):  
S.F. Trevino* ◽  
B. Tikoff ◽  
N. Van Buer ◽  
S.J. Wyld ◽  
H. McLachlan
Keyword(s):  
Solid State ◽  
Shear Zone ◽  
Shear Zones ◽  
Power Line ◽  
Field Trip ◽  
Data System ◽  
Intrusive Complex ◽  
Dextral Shear ◽  
Magnetic Lineations ◽  
Intrusive Suite

ABSTRACT This field trip traverses the Sahwave and Nightingale Ranges in central Nevada, USA, and northward to Gerlach, Nevada, to the Granite, northern Fox, and Selenite Ranges. Plutonic bodies in this area include the ca. 93–89 Ma Sahwave nested intrusive suite of the Sahwave and Nightingale Ranges, the ca. 106 Ma Power Line intrusive complex of the Nightingale Range, the ca. 96 Ma plutons in the Selenite Range, and the ca. 105–102 Ma plutons of the Granite and Fox Ranges. Collectively these plutons occupy nearly 1000 km2 of bedrock exposure. Plutons of the Sahwave, Nightingale, and Selenite Ranges intrude autochthonous rocks east of the western Nevada shear zone, while plutons of the Granite and Fox Ranges intrude displaced terranes west of the western Nevada shear zone. Integrated structural, geochemical, and geochronological studies are used to better understand magmatic and deformation processes during the Early Cretaceous, correlations with Cretaceous plutons in adjacent areas of Idaho and California, and regional implications. Field-trip stops in the Sahwave and Nightingale Ranges will focus on: (1) microstructure and orientation of magmatic and solid-state fabrics of the incrementally emplaced granodiorites-granites of the Sahwave intrusive suite; and (2) newly identified dextral shear zones hosted within intrusions of both the Sahwave and Nightingale Ranges. The Sahwave intrusive suite exhibits moderate to weak magnetic fabrics determined using anisotropy of magnetic susceptibility, with magnetic foliations that strike NW-NE and magnetic lineations that plunge moderately to steeply. Microstructural analysis indicates that these fabrics formed during magmatic flow. The older Power Line intrusive complex in the Nightingale Range is cross-cut by the Sahwave suite and contains a N-S–trending solid-state foliation that reflects ductile dextral shearing. Field-trip stops in the plutons of the Gerlach region will focus on composition, texture, and emplacement ages, and key differences with the younger Sahwave suite, including lack of evidence for zoning and solid-state fabrics. The field trip will utilize StraboSpot, a digital data system for field-based geology that allows participants to investigate the relevant data projects in the study areas.

scholarly journals The Variscan Millares granite (central Pyrenees): Pluton emplacement in a T fracture of a dextral shear zone

2006 ◽  
Vol 19 (3-4) ◽  
pp. 197-211 ◽  
Author(s):  
Teresa Román-Berdiel ◽  
Antonio M. Casas ◽  
Belén Oliva-Urcia ◽  
Emilio L. Pueyo ◽  
Carlos Liesa ◽  
...  
Keyword(s):  
Shear Zone ◽  
Pluton Emplacement ◽  
Dextral Shear ◽  
Central Pyrenees

The Cer massif in the internal Dinarides: Exhumation triggered as a far-field effect of the Carpathian slab roll-back

2021 ◽  
Author(s):  
Georg Löwe ◽  
Susanne Schneider ◽  
Blanka Sperner ◽  
Philipp Balling ◽  
Jörg Pfänder ◽  
...  
Keyword(s):  
Shear Zone ◽  
Late Cretaceous ◽  
Pannonian Basin ◽  
Structural Data ◽  
Shear Zones ◽  
White Mica ◽  
Step Heating ◽  
Type Granite ◽  
Single Grain ◽  
Internal Dinarides

<p>Extension across the southern Pannonian Basin and the internal Dinarides is characterized by the occurrence of a chain of Oligo-Miocene metamorphic core complexes (MCCs) exhumed along mylonitic low-angle extensional shear zones which in part represent former suturing thrusts. Cer MCC at the transition between the internal Dinarides and the Pannonian Basin occupies a structural position within the distal-most Adriatic thrust sheet and originates from two different tectonic processes: Late Cretaceous-Paleogene nappe-stacking during continent-continent collision between Adria and fragments of European lithosphere with Adria residing in a lower plate position, followed by Miocene exhumation. Structural data and a balanced cross section through the Cer massif show that the exhuming shear zone links to a breakaway fault, which reactivated the early Late Cretaceous most internal nappe contact between the two distal-most Adriatic thrust sheets. At Cer MCC, Paleozoic greenschist- to amphibolite-grade lithologies surround a polyphase intrusion composed of I- and S-type granites. These lithologies were exhumed along the shear zone by top-N transport. Thermobarometric analyses indicate an intrusion depth of 7-8 km of the Oligocene I-type granite; cooling below ~500°C occurred at 25.4±0.6 Ma (1σ) yielded by <sup>40</sup>Ar/<sup>39</sup>Ar dating of hornblende. Biotite and white mica from this intrusion as well as from the mylonitic shear zone yield <sup>40</sup>Ar/<sup>39</sup>Ar ages of 17-18 Ma independent of the used techniques (in-situ laser ablation, single-grain total fusion, single-grain step heating, and multi-grain step heating). White mica from the S-type granite yield an <sup>40</sup>Ar/<sup>39</sup>Ar age of 16.7±0.1 Ma (1σ). Associated dikes intruding the shear zone were also affected by N-S extension, indicating that deformation was still ongoing at that time. Our data suggests that exhumation of the MCC was related to the opening of the Pannonian back-arc basin in response to the Carpathian slab-rollback and triggered extensional reactivation of thrusts in the internal Dinarides.</p>

scholarly journals Whole-lithosphere shear during oblique rifting

Geology ◽  
2021 ◽  
Author(s):  
Brandon M. Lutz ◽  
Gary J. Axen ◽  
Jolante W. van Wijk ◽  
Fred M. Phillips
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Shear Zones ◽  
Death Valley ◽  
Necessary Condition ◽  
Middle Crust ◽  
Metamorphic Core Complexes ◽  
Dextral Shear ◽  
Depth Gradients ◽  
Metamorphic Core

Processes controlling the formation of continental whole-lithosphere shear zones are debated, but their existence requires that the lithosphere is mechanically coupled from base to top. We document the formation of a dextral, whole-lithosphere shear zone in the Death Valley region (DVR), southwest United States. Dextral deflections of depth gradients in the lithosphere-asthenosphere boundary and Moho are stacked vertically, defining a 20–50-km-wide, lower lithospheric shear zone with ~60 km of shear. These deflections underlie an upper-crustal fault zone that accrued ~60 km of dextral slip since ca. 8–7 Ma, when we infer that whole-lithosphere shear began. This dextral offset is less than net dextral offset on the upper-crustal fault zone (~90 km, ca. 13–0 Ma) and total upper-crustal extension (~250 km, ca. 16–0 Ma). We show that, before ca. 8–7 Ma, weak middle crust decoupled upper-crustal deformation from deformation in the lower crust and mantle lithosphere. Between 16 and 7 Ma, detachment slip thinned, uplifted, cooled, and thus strengthened the middle crust, which is exposed in metamorphic core complexes collocated with the whole-lithosphere shear zone. Midcrustal strengthening coupled the layered lithosphere vertically and therefore enabled whole-lithosphere dextral shear. Where thick crust exists (as in pre–16 Ma DVR), midcrustal strengthening is probably a necessary condition for whole-lithosphere shear.

scholarly journals The Borborema Strike-Slip Shear Zone System (NE Brazil): Large-Scale Intracontinental Strain Localization in a Heterogeneous Plate

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 6) ◽  
Author(s):  
Sergio P. Neves ◽  
Andréa Tommasi ◽  
Alain Vauchez ◽  
Thais Andressa Carrino
Keyword(s):  
Shear Zone ◽  
Large Scale ◽  
Shear Zones ◽  
Strike Slip ◽  
Northeastern Brazil ◽  
Main Stage ◽  
Plate Boundaries ◽  
Deformation Localization ◽  
Continental Scale ◽  
Dextral Shear

Abstract Large-scale strike-slip faults are fundamental tectonic elements of the continental lithosphere. They constitute plate boundaries (continental transforms), separate terranes with contrasting geological histories within accretionary orogens, or accommodate heterogeneous deformation in intracontinental settings. In ancient orogens, where deeper levels of the crust are exposed, these faults are expressed as shear zones materialized by up to tens of km-wide mylonitic belts. The Borborema shear zone system in northeastern Brazil is one of the largest and best-exposed intracontinental strike-slip shear zone systems in the world, cropping out over 250,000 km2. Here, we review its main geophysical, structural, petrologic, and geochronologic characteristics and discuss the factors controlling its development. This complex continental scale shear zone system is composed of a set of NE- to NNE-trending dextral shear zones from which there are two major E-trending dextral shear zones with horse-tail terminations into the transpressional belt branch, as well as several smaller E-trending dextral and NE-trending dextral and sinistral shear zones. The major shear zones are marked by extensive linear or curvilinear magnetic gradients, implying their continuation at depth. The major shear zones are materialized by migmatite to amphibolite-facies mylonites, but the entire system shows evidence of late deformation at lower temperatures. The system developed during the late stages of the Neoproterozoic Brasiliano (Pan-African) orogeny (mainly from 590 to 560 Ma), postdating by more than 20 Ma the main stage of contractional deformation. Localization of strike-slip shearing in this intraplate setting was controlled by rheological contrasts between blocks with distinct Paleoproterozoic histories, the presence of preorogenic Neoproterozoic rifts, the craton geometry, and zones of enhanced magmatic activity, highlighting the importance of rheological heterogeneity in controlling shear zone nucleation and evolution.

scholarly journals Kinematics and Geochronology of Late Paleozoic–Early Mesozoic Ductile Deformation in the Alxa Block, NW China: New Constraints on the Evolution of the Central Asian Orogenic Belt

Lithosphere ◽  
2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Beihang Zhang ◽  
Jin Zhang ◽  
Heng Zhao ◽  
Junfeng Qu ◽  
Yiping Zhang ◽  
...  
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Late Paleozoic ◽  
Ductile Shear Zone ◽  
Early Mesozoic ◽  
Central Asian ◽  
Ductile Shear Zones ◽  
Dextral Shear ◽  
Ductile Shear

Abstract Strike-slip faults are widely developed throughout the Central Asian Orogenic Belt (CAOB), one of the largest Phanerozoic accretionary orogenic collages in the world, and may have played a key role in its evolution. Recent studies have shown that a large number of Late Paleozoic–Early Mesozoic ductile shear zones developed along the southern CAOB. This study reports the discovery of a NW–SE striking, approximately 500 km long and up to 2 km wide regional ductile shear zone in the southern Alxa Block, the Southern Alxa Ductile Shear Zone (SADSZ), which is located in the central part of the southern CAOB. The nearly vertical mylonitic foliation and subhorizontal stretching lineation indicate that the SADSZ is a ductile strike-slip shear zone, and various kinematic indicators indicate dextral shearing. The zircon U-Pb ages and the 40Ar/39Ar plateau ages of the muscovite and biotite indicate that the dextral ductile shearing was active during Middle Permian to Middle Triassic (ca. 269–240 Ma). The least horizontal displacement of the SADSZ is constrained between ca. 40 and 50 km. The aeromagnetic data shows that the SADSZ is in structural continuity with the coeval shear zones in the central and northern Alxa Block, and these connected shear zones form a ductile strike-slip duplex in the central part of the southern CAOB. The ductile strike-slip duplex in the Alxa Block, including the SADSZ, connected the dextral ductile shear zones in the western and eastern parts of the southern CAOB to form a 3000 km long E-W trending dextral shear zone, which developed along the southern CAOB during Late Paleozoic to Early Mesozoic. This large-scale dextral shear zone was caused by the eastward migration of the orogenic collages and blocks of the CAOB and indicates a transition from convergence to transcurrent setting of the southern CAOB during Late Paleozoic to Early Mesozoic.

scholarly journals Monazite U–Th–Pb geochronology of the Central Metasedimentary Belt Boundary Zone (CMBbz), Grenville Province, Ontario Canada

2018 ◽  
Vol 55 (9) ◽  
pp. 1063-1078 ◽  
Author(s):  
Michelle J. Markley ◽  
Steven R. Dunn ◽  
Michael J. Jercinovic ◽  
William H. Peck ◽  
Michael L. Williams
Keyword(s):  
Shear Zone ◽  
Crustal Thickening ◽  
Boundary Zone ◽  
Grenville Province ◽  
Metamorphic History ◽  
Crustal Thinning ◽  
Tectonic Significance ◽  
History Of ◽  
Central Gneiss Belt ◽  
Scale Shear

The Central Metasedimentary Belt boundary zone (CMBbz) is a crustal-scale shear zone that juxtaposes the Central Gneiss Belt and the Central Metasedimentary Belt of the Grenville Province. Geochronological work on the timing of deformation and metamorphism in the CMBbz is ambiguous, and the questions that motivate our study are: how many episodes of shear zone activity did the CMBbz experience, and what is the tectonic significance of each episode? We present electron microprobe data from monazite (the U–Th–Pb chemical method) to directly date deformation and metamorphism recorded in five garnet–biotite gneiss samples collected from three localities of the CMBbz of Ontario (West Guilford, Fishtail Lake, and Killaloe). All three localities yield youngest monazite dates ca. 1045 Ma; most of the monazite domains that yield these dates are high-Y rims. In comparison with this common late Ottawan history, the earlier history of the three CMBbz localities is less clearly shared. The West Guilford samples have monazite grain cores that show older high-Y domains and younger low-Y domains; these cores yield a prograde early Ottawan (1100–1075 Ma) history. The Killaloe samples yield a well-defined prograde, pre- to early Shawinigan history (i.e., 1220–1160 Ma) in addition to some evidence for a second early Ottawan event. In other words, the answers to our research questions are: three events; a Shawinigan event possibly associated with crustal thickening, an Ottawan event possibly associated with another round of crustal thickening, and a late Ottawan event that resists simple interpretation in terms of metamorphic history but that coincides chronologically with crustal thinning at the base of an orogenic lid.

scholarly journals The Dabie Extensional Tectonic System: Structural Framework

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Quanlin Hou ◽  
Hongyuan Zhang ◽  
Qing Liu ◽  
Jun Li ◽  
Yudong Wu
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Ultrahigh Pressure ◽  
Metamorphic Complex ◽  
The South ◽  
Magma Intrusion ◽  
The North ◽  
Extensional Tectonic ◽  
Mechanism Transition ◽  
Tectonic System

A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56 km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12 km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190 Ma and ~124 Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later.

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