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>

scholarly journals Burial-deformation History of Folded Rocks Unraveled by Fracture Analysis, Stylolite Paleopiezometry and Vein Cement Geochemistry: A Case Study in the Cingoli Anticline (Umbria-Marche, Northern Apennines)

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 135
Author(s):  
Aurélie Labeur ◽  
Nicolas E. Beaudoin ◽  
Olivier Lacombe ◽  
Laurent Emmanuel ◽  
Lorenzo Petracchini ◽  
...  
Keyword(s):  
Isotope Geochemistry ◽  
Central Italy ◽  
Microstructural Analysis ◽  
Northern Apennines ◽  
Foreland Basins ◽  
Deformation History ◽  
The North ◽  
Regional Tectonic ◽  
History Of ◽  
Clumped Isotope

Unravelling the burial-deformation history of sedimentary rocks is prerequisite information to understand the regional tectonic, sedimentary, thermal, and fluid-flow evolution of foreland basins. We use a combination of microstructural analysis, stylolites paleopiezometry, and paleofluid geochemistry to reconstruct the burial-deformation history of the Meso-Cenozoic carbonate sequence of the Cingoli Anticline (Northern Apennines, central Italy). Four major sets of mesostructures were linked to the regional deformation sequence: (i) pre-folding foreland flexure/forebulge; (ii) fold-scale layer-parallel shortening under a N045 σ1; (iii) syn-folding curvature of which the variable trend between the north and the south of the anticline is consistent with the arcuate shape of the anticline; (iv) the late stage of fold tightening. The maximum depth experienced by the strata prior to contraction, up to 1850 m, was quantified by sedimentary stylolite paleopiezometry and projected on the reconstructed burial curve to assess the timing of the contraction. As isotope geochemistry points towards fluid precipitation at thermal equilibrium, the carbonate clumped isotope thermometry (Δ47) considered for each fracture set yields the absolute timing of the development and exhumation of the Cingoli Anticline: layer-parallel shortening occurred from ~6.3 to 5.8 Ma, followed by fold growth that lasted from ~5.8 to 3.9 Ma.

Deformation textures in pyrite from the Vangorda Pb-Zn-Ag deposit, Yukon, Canada

1993 ◽  
Vol 57 (386) ◽  
pp. 55-66 ◽  
Author(s):  
D. Brown ◽  
K. R. McClay
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Ductile Deformation ◽  
Mining District ◽  
Strain Partitioning ◽  
Triple Junctions ◽  
Brittle Deformation ◽  
Deformation Textures

AbstractThe Vangorda Pb-Zn-Ag orebody is a 7.1 M tonne, polydeformed stratiform massive sulphide deposit in the Anvil mining district, Yukon, Canada. Five sulphide lithofacies have been identified within the desposit with a typical mineralogy of pyrite, sphalerite, galena, and barite. Pyrrhotite-sphaleritemagnetite assembalges are locally developed. Etched polished sections of massive pyrite ores display relict primary depositional pyrite textures such as colloform growth zoning and spheroidal/framboidal features. A wide variety of brittle deformation, ductile deformation, and annealing textures have been identified. Brittle deformation textures include thin zones of intense cataclasis, grain indentation and axial cracking, and grain boundary sliding features. Ductile deformation textures include strong preferred grain shape orientations, dislocation textures, grain boundary migration, dynamic recrystallisation and pressure solution textures. Post deformational annealing has produced grain growth with lobate grain boundaries, 120° triple junctions and idioblastic pyrite porphyroblasts. The distribution of deformation textures within the Vangorda orebody suggests strong strain partitioning along fold limbs and fault/shear zones, it is postulated that focussed fluid flow in these zones had significant effects on the deformation of these pyritic ores.

scholarly journals Fluid-mediated, brittle–ductile deformation at seismogenic depth – Part 2: Stress history and fluid pressure variations in a shear zone in a nuclear waste repository (Olkiluoto Island, Finland)

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 489-511 ◽  
Author(s):  
Francesca Prando ◽  
Luca Menegon ◽  
Mark Anderson ◽  
Barbara Marchesini ◽  
Jussi Mattila ◽  
...  
Keyword(s):  
Shear Zone ◽  
Nuclear Waste ◽  
Strain Localization ◽  
Microstructural Analysis ◽  
Fluid Pressure ◽  
Rheological Parameters ◽  
Nuclear Waste Repository ◽  
Brittle Deformation ◽  
Differential Stress ◽  
Brittle Ductile Transition

Abstract. The microstructural record of fault rocks active at the brittle–ductile transition zone (BDTZ) may retain information on the rheological parameters driving the switch in deformation mode and on the role of stress and fluid pressure in controlling different fault slip behaviours. In this study we analysed the deformation microstructures of the strike-slip fault zone BFZ045 in Olkiluoto (SW Finland), located in the site of a deep geological repository for nuclear waste. We combined microstructural analysis, electron backscatter diffraction (EBSD), and mineral chemistry data to reconstruct the variations in pressure, temperature, fluid pressure, and differential stress that mediated deformation and strain localization along BFZ045 across the BDTZ. BFZ045 exhibits a mixed ductile–brittle deformation, with a narrow (<20 cm thick) brittle fault core with cataclasites and pseudotachylytes that overprint a wider (60–100 cm thick) quartz-rich mylonite. Mylonitic deformation took place at 400–500 ∘C and 3–4 kbar, typical of the greenschist facies metamorphism at the base of the seismogenic crust. We used the recrystallized grain size piezometry for quartz to document a progressive increase in differential stress, from ca. 50 to ca. 120 MPa, towards the shear zone centre during mylonitization and strain localization. Syn-kinematic quartz veins formed along the mylonitic foliation due to transiently high pore fluid pressure (up to lithostatic value). The overprint of the veins by dynamic recrystallization and mylonitic creep is further evidence of the occurrence of brittle events under overall ductile conditions. We propose a conceptual model in which the ductile–brittle deformation cycle was controlled by transient oscillations in fluid pressure and progressively higher differential stress, possibly occurring in a narrowing shear zone deforming towards the peak strength of the crust at the BDTZ.

Structural evolution of the Hemlo greenstone belt in the vicinity of the world-class Hemlo gold deposit

2003 ◽  
Vol 40 (3) ◽  
pp. 395-430 ◽  
Author(s):  
T L Muir
Keyword(s):  
Gold Deposit ◽  
Greenstone Belt ◽  
Structural Evolution ◽  
Small Scale ◽  
Structural Elements ◽  
Shear Sense ◽  
History Of ◽  
Brittle Fractures ◽  
World Class ◽  
Dextral Shear

A complex history of volcano-sedimentary deposition, polyphase strain, multiple intrusive events, and various stages of porphyroblastesis is indicated for the Hemlo gold deposit area within the Hemlo greenstone belt. Structural elements can be assigned to at least six stages of development (D1–D6). D1 generated small-scale folds and low-angle faults (thrusts?) with no planar fabric, except within strain aureoles around the earliest intrusions. D2 was a progressive event resulting from northeast-directed compression, which generated regional, predominantly S-shaped folds (early D2); penetrative planar and linear fabrics, overturned stratigraphy, and formation of an inflection in the strike of the greenstone belt (mid-D2); and development of high-strain zones with dominant sinistral and local dextral shear sense (late D2). D3 was a distinctly separate progressive event resulting from northwest-directed transpression, which generated variably penetrative east- to northeast-striking foliation (S3), ductile dextral shear fabrics, and small-scale Z-shaped folds (early D3), followed by brittle–ductile to brittle development of cataclasite and pseudotachylite in layer-parallel zones (late D3). D4 resulted in contractional kinks and brittle fractures, locally in conjugate sets. D5 and D6 are represented by brittle to brittle–ductile faults, which overprint Paleoproterozoic and Mesoproterozoic dikes, respectively. Four granitoid magmatic events span the interval 2720–2677 Ma, with emplacement mainly during D2, between ca. 2690 and ca. 2684 Ma. A protracted period of regional medium-grade metamorphism likely spanned the D2–D3 stages. The Hemlo gold deposit was emplaced during mid-D2 and was largely controlled by D2 structural elements and competency contrast between rock units.

scholarly journals Strain Pattern Analysis of Mylonites From Sitampundi-Kanjamalai Shear Zone, Thiruchengode, South India

2019 ◽  
Vol 1 (1) ◽  
pp. 25-34
Author(s):  
Thirukumaran V ◽  
Biswal T.K ◽  
Sundaralingam K ◽  
Sowmya V ◽  
Boopathi S ◽  
...  
Keyword(s):  
Shear Zone ◽  
Simple Shear ◽  
Pure Shear ◽  
Strain Analysis ◽  
Strain Pattern ◽  
Shear Sense ◽  
Shear Component ◽  
Deep Crustal Level ◽  
Dextral Shear ◽  
Shear Sense Indicators

This study aims to investigate the petrography and strain pattern of mylonites from parts of N-S trending Sitampundi-Kanjamalai Shear Zone (SKSZ) around Thiruchengode. The petrographic study indicates the presence of recrystallized quartz, K-feldspar, plagioclase, biotite and some hornblende. The kinematic analysis of Mylonites was done with the help of shear sense indicators such as recrystallized type quartz (quartz ribbon) around the cluster of feldspar, S-C fabric shows dextral shear sense and some sinisterly shear sense in some parts of SASZ which can be considered as a product of partitioning of both strain and vorticity between domains. These all indicates the simple shear extension along E-W direction and the mylonitic foliation shows the pure shear compression along N-S direction. Further the study of bulk strain analysis by Flinn plot method using L and T section of mylonite shows k<1 which lies in the field of flattening zone of finite strain. The kinematic vorticity number is calculated by Rxz/β method which gives the value of 0.36 indicating the general shear. The rigid grain graph shows that the pure shear component is more ­­­­dominant than the simple shear component. The analysis leads to the conclusion that the mylonite has experienced a high temperature shearing of above 700°cat deep crustal level.

scholarly journals Deformation conditions during syn-convergent extension along the Cordillera Blanca shear zone, Peru

Geosphere ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 1342-1367 ◽  
Author(s):  
Cameron A. Hughes ◽  
Micah J. Jessup ◽  
Colin A. Shaw ◽  
Dennis L. Newell
Keyword(s):  
Shear Zone ◽  
Microstructural Analysis ◽  
Convergent Extension ◽  
Brittle Deformation ◽  
Cordillera Blanca ◽  
Peruvian Andes ◽  
Fine Grained ◽  
Brittle Ductile Transition ◽  
Tectonically Active ◽  
Lower Temperature

AbstractStrain localization across the brittle-ductile transition is a fundamental process in accommodating tectonic movement in the mid-crust. The tectonically active Cordillera Blanca shear zone (CBSZ), a ∼200-km-long normal-sense shear zone situated within the footwall of a discrete syn-convergent extensional fault in the Peruvian Andes, is an excellent field laboratory to explore this transition. Field and microscopic observations indicate consistent top-down-to-the-southwest sense of shear and a sequence of tectonites ranging from undeformed granodiorite through mylonite and ultimately fault breccia along the detachment.Using microstructural analysis, two-feldspar and Ti-in-quartz (TitaniQ) thermometry, recrystallized quartz paleopiezometry, and analysis of quartz crystallographic preferred orientations, we evaluate the deformation conditions and mechanisms in quartz and feldspar across the CBSZ. Deformation temperatures derived from asymmetric strain-induced myrmekite in a subset of tectonite samples are 410 ± 30 to 470 ± 36 °C, consistent with TitaniQ temperatures of 450 ± 60 to 490 ± 33 °C and temperatures >400 °C estimated from microstructural criteria. Brittle fabrics overprint ductile fabrics within ∼150 m of the detachment that indicate that deformation continued to lower-temperature (∼280–400 °C) and/or higher-strain-rate conditions prior to the onset of pervasive brittle deformation. Initial deformation occurred via high-temperature fracturing and dissolution-precipitation in feldspar. Continued subsolidus deformation resulted in either layering of mylonites into monophase quartz and fine-grained polyphase domains oriented subparallel to macroscopic foliation or the interconnection of recrystallized quartz networks oriented obliquely to macroscopic foliation. The transition to quartz-controlled rheology occurred at temperatures near ∼500 °C and at a differential stress of ∼16.5 MPa. Deformation within the CBSZ occurred predominantly above ∼400 °C and at stresses up to ∼71.4 MPa prior to the onset of brittle deformation.

Microstructures and deformation temperature of carbonate mylonites in Shajigami shear zone at eastern margin of Abukuma Mountains, Northeastern Japan

2021 ◽  
Author(s):  
Hiroaki Yokoyama ◽  
Jun Muto ◽  
Hiroyuki Nagahama
Keyword(s):  
Grain Size ◽  
Shear Zone ◽  
Deformation Temperature ◽  
Microstructural Analysis ◽  
Shear Plane ◽  
Strike Slip ◽  
Eastern Margin ◽  
Northeastern Japan ◽  
Shear Sense ◽  
Shear Component

&lt;p&gt;&amp;#12288;&amp;#12288;Microstructural analysis is essential for estimating the deformation conditions of plastically deformed rocks. In this study, we analyze the microstructures of carbonate mylonites and deformation conditions in natural shear zone to reconstruct tectonics. Carbonate mylonites originated from late Carboniferous Tateishi Formation and mylonitized in middle Cretaceous by the strike-slip motion of Shajigami shear zone in the eastern margin of the Abukuma Mountain, Northeastern Japan.&lt;br&gt;&amp;#12288;&amp;#12288;Microstructural analysis was carried out by optical microscope and electron backscattered diffraction (EBSD) mapping to determine grain size, aspect ratio, shape preferred orientation (SPO) and crystallographic preferred orientation (CPO) of calcite aggregates.&lt;br&gt;&amp;#12288;&amp;#12288;Pervasive deformation twins and dynamically recrystallized grains are observed. Although most porphyroclasts show symmetric structure, some show asymmetric structure that indicates dextral shear sense. Mean dynamically recrystallized grain size is 16-67 &amp;#181;m, and it decreases close to the shear zone. CPOs show that &lt;em&gt;c&lt;/em&gt;-axes concentrate normal to the shear plane or slightly rotate to the shear sense. The strong CPOs suggest that the dominant deformation mechanism is dislocation creep. SPOs show the foliation which is slightly oblique or almost parallel to the shear plane. However, we observed the SPOs parallel to the shear plane at the location 150 m away from the shear zone. &amp;#160;The 3D dynamically recrystallized grain shapes are between plane-strain ellipsoid and oblate ellipsoid. The grain shapes tend to be relatively polygonal close to the shear zone, while more elongated further away from the shear zone. The distribution of the carbonate mylonite originated from same Tateishi Formation is known to be about 5 km apart from the Shajigami shear zone (Tateishi location). However, based on many aspects of differences in microstructures among both locations such as SPOs of recrystallized grains, we infer that the deformation of Shajigami shear zone was not related to one at Tateishi location. The pervasive dynamic recrystallization suggests that the deformation temperature was at least 200&amp;#176;C. Observed type &amp;#8545; and type &amp;#8546; twin morphologies (Burkhard, 1993) of calcite grains suggest deformation temperature below 300&amp;#176;C.&amp;#160;&lt;br&gt;&amp;#12288;&amp;#12288;These results indicate that the deformation of the Shajigami shear zone was in the range from 200 to 300&amp;#8451; and deformation was stronger near the shear zone. In addition, the polygonal grain shape close to the shear zone suggests that the deformation temperature is higher close to the shear zone. Furthermore, SPOs show that pure shear component is larger than simple shear component in terms of SPOs that almost parallel to the shear plane away from the shear zone. This study including several additional results will provide the microstructural development of carbonate mylonites in natural strike-slip shear zones deformed near the brittle-ductile condition of the upper crust.&lt;/p&gt;

Structural petrology along a transect across the Thompson Belt, Manitoba: dip slip at the western Churchill–Superior boundary

1989 ◽  
Vol 26 (10) ◽  
pp. 1976-1989 ◽  
Author(s):  
Frank Fueten ◽  
Pierre-Yves F. Robin
Keyword(s):  
Structural Study ◽  
Metamorphic Grade ◽  
Ductile Deformation ◽  
Superior Province ◽  
Deformation History ◽  
Tectonic Model ◽  
Kinematic Indicators ◽  
Metamorphic History ◽  
Structural Style ◽  
History Of

Early Proterozoic rocks and Archean gneisses of the Thompson Belt, east of the Churchill Province – Superior Province boundary, record the history of the Hudsonian Orogeny in this area. A structural study has been undertaken along a 45 km long corridor cutting across the width of the belt.Three blocks are defined along this transect, each characterized by a specific structural style and metamorphic history, Foliation and lineation data and the analysis of kinematic indicators from these blocks show that (i) the Thompson Belt has been an area of predominantly dip-slip movement for its recognizable ductile deformation history; (ii) the sense of shear for most of that history corresponds to the Superior side moving up with respect to the Churchill side; (iii) the shearing emplaced rocks of progressively higher metamorphic grade towards the southeast, away from the Churchill–Superior boundary; and (iv) there appears to have been a period of movement at the later stages of the Hudsonian Orogeny during which the sense of movement was Churchill side up.Structural and metamorphic data support a tectonic model in which the Superior Province has been thrust over the Churchill Province, with a convergence direction approximately perpendicular to the Thompson Belt.

Multiphase brittle tectonic evolution of the Mid-Norwegian margin, central Norway, reconstructed by remote sensing, paleostress inversion and K-Ar fault rock dating

2020 ◽  
Author(s):  
Giulia Tartaglia ◽  
Giulio Viola ◽  
Alberto Ceccato ◽  
Stefano Bernasconi ◽  
Roelant van der Lelij ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Field Work ◽  
Brittle Deformation ◽  
Deformation History ◽  
Fault Rock ◽  
Calcite Veins ◽  
History Of ◽  
Norwegian Margin ◽  
Clumped Isotope ◽  
Paleostress Inversion

&lt;p&gt;Basement terranes commonly contain complex fault networks developed during repeated episodes of brittle deformation. The Mid-Norwegian margin (from 62 to 63.8 &amp;#176;N) exposes a complexly fractured terrane formed mainly by Caledonian basement rocks. The margin recorded a prolonged brittle deformation history spanning the Devonian to Paleogene time interval. It is characterised by a pervasive NE-SW structural grain due to the ductile-brittle multiphase activity of the M&amp;#248;re-Tr&amp;#248;ndelag Fault Complex (MTFC).&lt;/p&gt;&lt;p&gt;In order to develop a time-constrained tectonic model of the area, we applied a multidisciplinary approach combining remote sensing, field work, paleostress inversion, microstructural analysis, mineralogical characterization, clumped isotope thermometry on carbonates and K-Ar dating of fault rocks from key representative faults. We present herein the preliminary structural-geochronological data of a still ongoing study of two regions along the Mid-Norwegian margin, the Hitra-Fr&amp;#248;ya and Kr&amp;#229;kenes-Runde areas. These key areas represent the intersection regions between the Mid-Norwegian- and the other sectors of the margin.&lt;/p&gt;&lt;p&gt;The brittle structural record of the entire Mid-Norwegian margin was analysed by remote sensing of lineaments using high resolution LiDAR data followed by ground-truthing of the obtained results during field work. Three main sets of lineaments were identified: i) (E)NE-(W)SW-trending lineaments, parallel to the coastline and to the MTFC; ii) N(NW)-S(SE)-trending lineaments; iii) WNW-ESE-trending lineaments. The main sets of faults and fractures were further characterised by their fault rock association and coating. All generations of faults contain thin coatings of chlorite, variably thick epidote and quartz mineralisations and calcite veins and coatings, locally associated with acicular zeolite. Samples of calcite and related gouges were collected from different sets of faults. Carbonate clumped isotope thermometry constrains the range of temperature of calcite growth between 140 and 30 &amp;#176;C, indicating that calcite precipitated at different thermal conditions during a multiphase structural evolution. K-Ar data collected so far from synkinematic illite separated from fault gouges yield Jurassic-Paleogene ages.&lt;/p&gt;&lt;p&gt;The structural network of the margin is interpreted as reflecting a sequence of different deformation episodes. In order to resolve the orientation of the stress field for each recorded event, we applied paleostress inversion with the Win-Tensor software [1]. The preliminary results suggest that at least three tectonic stages affected the margin. A NE-SW strike-slip dominated transpression possibly reflects the late stages of the Caledonian orogenic cycle. A pure and oblique extensional (E)NE-(W)SW stage is associated with the Jurassic North Sea rifting, followed by a NW-SE Paleogene extensional reactivation observable throughout the margin.&lt;/p&gt;&lt;p&gt;To conclude, a new multidisciplinary database for the reconstruction of the brittle deformation history of the Mid-Norwegian margin is presented. The proposed approach aims to define the temporal and structural characterisation of each single tectonic episode. Such an approach is also pivotal toward the correlation with the deformation history of the corresponding offshore domains, as well as the comparison in time with other segments of the Norwegian margin.&lt;/p&gt;&lt;p&gt;[1] Delvaux, D. and Sperner, B. (2003). Stress tensor inversion from fault kinematic indicators and focal mechanism data: the TENSOR program. Geological Society, London, Special Publications, 212: 75-100&lt;/p&gt;

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