U–Pb geochronology of deformed metagranites in central Sutherland, Scotland: evidence for widespread late Silurian metamorphism and ductile deformation of the Moine Supergroup during the Caledonian orogeny

ABSTRACTThe Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238–lead-206 (238U–206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U–Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium–osmium (Re–Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U–Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5–10 km Ma−1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50–100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.

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The Nusfjord exhumed earthquake source (Lofoten, Norway): deep crustal seismicity driven by bending of the lower plate during continental collision

10.5194/egusphere-egu2020-7129 ◽

2020 ◽

Author(s):

Luca Menegon ◽

Lucy Campbell ◽

Åke Fagereng ◽

Giorgio Pennacchioni

Keyword(s):

Shear Zone ◽

Lower Crust ◽

Tectonic Setting ◽

Shear Zones ◽

Continental Collision ◽

Earthquake Source ◽

Ductile Deformation ◽

Lower Plate ◽

Caledonian Orogeny ◽

Lower Crustal

The origin of earthquakes in the lower crust at depth of 20-40 km, where dominantly ductile deformation is expected, is highly debated. Exhumed networks of lower crustal coeval pseudotachylytes (quenched frictional melt produced during seismic slip) and mylonites (produced during the post- and interseismic viscous creep) provide a snapshot of the earthquake cycle at anomalously deep conditions in the crust. Such natural laboratories offer the opportunity to investigate the origin and the tectonic setting of lower crustal earthquakes.The Nusfjord East shear zone network (Lofoten, northern Norway) represents an exhumed lower crustal earthquake source, where mutually overprinting mylonites and pseudotachylytes record the interplay between coseismic slip and viscous creep (Menegon et al., 2017; Campbell and Menegon, 2019). The network is well exposed over an area of 4 km2 and consists of three main intersecting sets of ductile shear zones ranging in width from 1 cm to 1 m, which commonly nucleate on former pseudotachylyte veins. Mutual crosscutting relationships indicate that the three sets were active at the same time. Amphibole-plagioclase geothermobarometry yields consistent P-T estimates in all three sets (700-750 &#176;C, 0.7-0.8 GPa). The shear zones separate relatively undeformed blocks of anorthosite that contain pristine pseudotachylyte fault veins. These pseudotachylytes link adjacent or intersecting shear zones, and are interpreted as fossil seismogenic faults representing earthquake nucleation as a transient consequence of ongoing, localised aseismic creep along the shear zones (Campbell et al., under review).The coeval activity of the three shear zone sets is consistent with a local extensional setting, with a bulk vertical shortening and a horizontal NNW-SSE extension. This extension direction is subparallel to the convergence direction between Baltica and Laurentia during the Caledonian Orogeny, and with the dominant direction of nappe thrusting in the Scandinavian Caledonides. 40Ar&#8208;39Ar dating of localized upper amphibolite facies shear zones in the Nusfjord area with similar orientation to the Nusfjord East network yielded an age range of 433&#8211;413 Ma (Fournier et al., 2014; Steltenpohl et al., 2003), which indicates an origin during the collisional (Scandian) stage of the Caledonian Orogeny.We propose that the Nusfjord East brittle-viscous extensional shear zone network represents the rheological response of the lower crust to the bending of the lower plate during continental collision. (Micro)seismicity in the lower crust in collisional orogens is commonly localized in the lower plate and has extensional focal mechanisms. This has been tentatively correlated with slab rollback and bending of the lower plate (Singer et al., 2014). We interpret the Nusfjord East shear zone network as the geological record of this type of lower crustal seismicity.

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Application Of Electron Probe Analyses Of Minerals In Discussing The Relationship Between Ductile Deformation And Metamorphism

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134855 ◽

1990 ◽

Vol 48 (2) ◽

pp. 250-251

Author(s):

Fan Guochuan ◽

Sun Zhongshi

Keyword(s):

Chemical Composition ◽

Shear Deformation ◽

Electron Probe ◽

General Rule ◽

Granulite Facies ◽

Ductile Deformation ◽

Higher Temperature ◽

Ductile Shear ◽

The Relationship ◽

Ductile Shear Deformation

Under influence of ductile shear deformation, granulite facies mineral paragenesis underwent metamorphism and changes in chemical composition. The present paper discusses some changes in chemical composition of garnet in hypers thene_absent felsic gnesiss and of hypersthene in rock in early and late granulite facies undergone increasing ductile shear deformation .In garnet fetsic geniss, band structures were formed because of partial melting and resulted in zoning from massive⟶transitional⟶melanocrate zones in increasing deformed sequence. The electron-probe analyses for garnet in these zones are listed in table 1 . The Table shows that Mno, Cao contents in garnet decrease swiftly from slightly to intensely deformed zones.In slightly and moderately deformed zones, Mgo contents keep unchanged and Feo is slightly lower. In intensely deformed zone, Mgo contents increase, indicating a higher temperature. This is in accord with the general rule that Mgo contents in garnet increase with rising temperature.

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DUCTILE DEFORMATION OF THE DIANA COMPLEX ALONG THE SOUTH-CENTRAL CARTHAGE-COLTON MYLONITE ZONE: RECONCILING NORTHWEST OVER SOUTHEAST OBLIQUE-SINISTRAL THRUST KINEMATICS WITH TECTONIC COLLAPSE

10.1130/abs/2018ne-311250 ◽

2018 ◽

Author(s):

Graham B. Baird ◽

Keyword(s):

Ductile Deformation ◽

The South ◽

South Central ◽

Mylonite Zone

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Statherian (ca. 1714–1680 Ma) Extension-Related Magmatism and Deformation in the Southwestern Korean Peninsula and Its Geological Significance: Constraints from the Petrological, Structural, Geochemical and Geochronological Studies of Newly Identified Granitoids

Minerals ◽

10.3390/min11060557 ◽

2021 ◽

Vol 11 (6) ◽

pp. 557

Author(s):

Byung-Choon Lee ◽

Weon-Seo Kee ◽

Uk-Hwan Byun ◽

Sung-Won Kim

Keyword(s):

Korean Peninsula ◽

Tectonic Setting ◽

Alkali Feldspar ◽

Ductile Deformation ◽

Southwestern Part ◽

The North ◽

Deformation Event ◽

Geochemical Analyses ◽

A Minor ◽

T Values

In this study, petrological, structural, geochemical, and geochronological analyses of the Statherian alkali feldspar granite and porphyritic alkali feldspar granite in the southwestern part of the Korean Peninsula were conducted to examine petrogenesis of the granitoids and their tectonic setting. Zircon U-Pb dating revealed that the two granites formed around 1.71 Ga and 1.70–1.68 Ga, respectively. The results of the geochemical analyses showed that both of the granites have a high content of K2O, Nb, Ta, and Y, as well as high FeOt/MgO and Ga/Al ratios. Both granites have alkali-calcic characteristics with a ferroan composition, indicating an A-type affinity. Zircon Lu-Hf isotopic compositions yielded negative εHf(t) values (−3.5 to −10.6), indicating a derivation from ancient crustal materials. Both granite types underwent ductile deformation and exhibited a dextral sense of shear with a minor extension component. Based on field relationships and zircon U-Pb dating, it was considered that the deformation event postdated the emplacement of the alkali feldspar granite and terminated soon after the emplacement of the porphyritic alkali feldspar granite in an extensional setting. These data indicated that there were extension-related magmatic activities accompanying ductile deformation in the southwestern part of the Korean Peninsula during 1.71–1.68 Ga. The Statherian extension-related events are well correlated with those in the midwestern part of the Korean and eastern parts of the North China Craton.

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Fault reactivation and strain partitioning across the brittle-ductile transition

Geology ◽

10.1130/g46516.1 ◽

2019 ◽

Vol 47 (12) ◽

pp. 1127-1130 ◽

Cited By ~ 8

Author(s):

Gabriel G. Meyer ◽

Nicolas Brantut ◽

Thomas M. Mitchell ◽

Philip G. Meredith

Keyword(s):

Fault Slip ◽

Fault Reactivation ◽

Ductile Deformation ◽

Tectonic Deformation ◽

Gradual Change ◽

Bulk Rock ◽

Total Deformation ◽

Bulk Strain ◽

Brittle Ductile Transition ◽

Ductile Flow

Abstract The so-called “brittle-ductile transition” is thought to be the strongest part of the lithosphere, and defines the lower limit of the seismogenic zone. It is characterized not only by a transition from localized to distributed (ductile) deformation, but also by a gradual change in microscale deformation mechanism, from microcracking to crystal plasticity. These two transitions can occur separately under different conditions. The threshold conditions bounding the transitions are expected to control how deformation is partitioned between localized fault slip and bulk ductile deformation. Here, we report results from triaxial deformation experiments on pre-faulted cores of Carrara marble over a range of confining pressures, and determine the relative partitioning of the total deformation between bulk strain and on-fault slip. We find that the transition initiates when fault strength (σf) exceeds the yield stress (σy) of the bulk rock, and terminates when it exceeds its ductile flow stress (σflow). In this domain, yield in the bulk rock occurs first, and fault slip is reactivated as a result of bulk strain hardening. The contribution of fault slip to the total deformation is proportional to the ratio (σf − σy)/(σflow − σy). We propose an updated crustal strength profile extending the localized-ductile transition toward shallower regions where the strength of the crust would be limited by fault friction, but significant proportions of tectonic deformation could be accommodated simultaneously by distributed ductile flow.

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Pressure-dependent flow behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass

Journal of Materials Research ◽

10.1557/jmr.2003.0287 ◽

2003 ◽

Vol 18 (9) ◽

pp. 2039-2049 ◽

Cited By ~ 93

Author(s):

Jun Lu ◽

Guruswami Ravichandran

Keyword(s):

Metallic Glass ◽

Bulk Metallic Glass ◽

Inelastic Deformation ◽

Shear Failure ◽

Flow Behavior ◽

Shear Bands ◽

Ductile Deformation ◽

Multiaxial Compression ◽

Dependent Flow ◽

Tresca Criterion

An experimental study of the inelastic deformation of bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10Be22.5 under multiaxial compression using a confining sleeve technique is presented. In contrast to the catastrophic shear failure (brittle) in uniaxial compression, the metallic glass exhibited large inelastic deformation of more than 10% under confinement, demonstrating the nature of ductile deformation under constrained conditions in spite of the long-range disordered characteristic of the material. It was found that the metallic glass followed a pressure (p) dependent Tresca criterion τ = τ0 + βp, and the coefficient of the pressure dependence β was 0.17. Multiple parallel shear bands oriented at 45° to the loading direction were observed on the surfaces of the deformed specimens and were responsible for the overall inelastic deformation.

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Ductile deformation of K-feldspar in dry eclogite facies shear zones in the Bergen Arcs, Norway

Tectonophysics ◽

10.1016/s0040-1951(00)00048-2 ◽

2000 ◽

Vol 320 (2) ◽

pp. 107-121 ◽

Cited By ~ 33

Author(s):

U. Altenberger ◽

S. Wilhelm

Keyword(s):

Shear Zones ◽

Ductile Deformation ◽

Eclogite Facies

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Structural deformation-metamorphism and exhumation processes of Yuanmou metamorphic complex, Yunnan, China

10.5194/egusphere-egu21-10483 ◽

2021 ◽

Author(s):

Xuemei Cheng ◽

Shuyun Cao

Keyword(s):

High Temperature ◽

Electron Backscatter Diffraction ◽

Early Stage ◽

Structural Features ◽

Detachment Fault ◽

Ductile Deformation ◽

Structural Deformation ◽

Subsequent Stage ◽

Metamorphic Complex ◽

South Central

Within orogenic zone and continental extensional area, it often developed metamorphic complex or metamorphic gneiss dome that widely exposed continental mid-lower crustal rocks, which is an ideal place to study exhumation processes of deep-seated metamorphic complex and rheology. The Yuanmou metamorphic complex is located in the south-central part of the "Kangdian Axis" in the western margin of Qiangtang Block and Yangtze Block, which is a part of the anticline of the Sichuan-Yunnan platform. Many research works mainly focus on the discussion of intrusion ages, aeromagnetic anomalies, and polymetallic deposits. However, the exhumation process and mechanism of the Yuanmou metamorphic complex are rarely discussed and still unclear. This study, based on detailed field geological observations, optical microscopy (OM), cathodoluminescence (CL), electron backscatter diffraction (EBSD) and electron probe (EMPA) were performed to illustrate the geological structure features, deformation-metamorphic evolution process and its tectonic significance of Yuanmou metamorphic complex during the exhumation process. All these analysis results indicate that the Yuanmou metamorphic complex generally exhibits a dome structure with deep metamorphic rocks and deformed rocks of varying degrees widely developed. Mylonitic gneiss and granitic intrusions are located in the footwall of the Yuanmou, which have suffered high-temperature shearing. The mylonitic fabrics and mineral stretching lineations in the deformed rock are strongly developed, forming typical S-L or L-shaped structural features. The high-temperature ductile deformation-metamorphism environment is high amphibolite facies, that is, the temperature range is between 620 ~ 690 &#8451; and the pressure is between 0.8 ~ 0.95 Gpa. In the deformed rocks closed to the detachment fault, some of the mylonite fabric features are retained, but most of them have experienced a strongly overprinted retrogression metamorphism and deformation. At the top of the detachment fault zone, it is mainly composed of cataclasites and fault gouge. The comprehensive macro- and microstructural characteristics, geometry, kinematics, and mineral (amphibole, quartz and calcite) EBSD textures indicate that the Yuanmou metamorphic complex has undergone a progressive exhumation process during regional extension, obvious high-temperature plastic deformation-metamorphism in the early stage, and superimposed of low-temperature plastic-brittle and brittle deformation in the subsequent stage, which is also accompanied by strong fluid activities during the exhumation process.

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The influence of backstop geometry in the structural style of the Eastern Cordillera of Colombia: A sandbox modeling approach

10.5194/egusphere-egu21-13914 ◽

2021 ◽

Author(s):

Camilo Andrés Conde Carvajal ◽

Cristhian Bolívar Riascos Rodríguez ◽

Michael Andres Avila Paez ◽

Andreas Kammer

Keyword(s):

Kink Band ◽

Ductile Deformation ◽

High Plains ◽

Angle Of Internal Friction ◽

Eastern Cordillera ◽

Surface Uplift ◽

Structural Style ◽

Mountain System ◽

Mountain Front ◽

Structural Relief

Among the foreland belts of the Andean mountain system, the Eastern Cordillera of Colombia (EC) represents a unique example of an isolated, bi-vergent mountain belt. In contrast, to block tectonics of broken foreland basins, it displays a ductile deformation style which involves two mountain fronts with a structural relief of the order of 10 km. Internal parts of the EC have been shortened by buckling at high and a homogeneously strained basement at deeper structural levels. These deformation patterns likely attest to conditions of a thermally weakened backarc setting. Two opposed scenarios have been postulated for its surface uplift and consequent exhumation: 1) an E-migrating deformation front and the formation of progressively forward breaking faults; and 2) the pop-up of a weak crustal welt enclosed by strong foreland blocks. In this latter setting, a synchronous early formation of marginal mountain fronts and a late-stage surface uplift of a central domain may be anticipated. These two constellations compare, in terms of a contrasting model setup, to a foreland migrating orogenic wedge or a relatively stable, doubly vergent wedge formed above a structural discontinuity or rheologic boundaries that acted as sites for the nucleation of the marginal faults.In this contribution, we opt to examine the &#8220;boundary&#8221; conditions for the development of a doubly vergent wedge formed at the tip line of a rigid tapering backstop, that simulates a rigid foreland block. With respect to the shape of this backstop, we examine the effects of tip angles less than the angle of internal friction (<30&#176;) and find, that at a low tip angle of 10&#176; the pop-up evolves above a forward-breaking principal kink-band with the synchronous formation of a sequence of conjugate back-kinks that cut into the sand pack, as it is pushed toward the backstop. At a moderate tip angle of 20o the forward-breaking kink-band is slightly steeper than the backstop and gives rise to a frontal fold with an overturned limb. This latter geometrical configuration loosely compares to the structural relations of a structural section through the high plains of Bogot&#225;, where the eastern mountain front defines a strongly deformed antiform, that is juxtaposed against an undeformed margin of the adjacent Guyana shield.

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