scholarly journals Transpressive dextral shear in the Italva-Itaperuna section, Northern State of Rio de Janeiro, Brazil

2008 ◽  
Vol 80 (3) ◽  
pp. 565-577 ◽  
Author(s):  
Tiago R. Karniol ◽  
Rômulo Machado ◽  
Nolan M. Dehler
Keyword(s):  
Structural Control ◽  
Shear Zones ◽  
Continental Collision ◽  
Southeastern Brazil ◽  
Ductile Shear Zones ◽  
Shear Sense ◽  
Dextral Shear ◽  
Northern State ◽  
Map Scale ◽  
Shear Sense Indicators

Structural analysis carried out on a segment of the Neoproterozoic Ribeira Belt, southeastern Brazil, show that it represents part of the transpressive dextral orogen related to the Central Mantiqueira Province. NNE-trending and steeply dipping regional mylonitic belts form anastomosed geometry, and describe a map-scale, S-C-like structure that is characterized by their deflection towards NE near the Além Paraíba Lineament. Lithological and structural control related to deformation partition were responsible for the formation of felsic mylonitic granulites with S-type granites lenses developed in ductile shear zones, alternated with less deformed intermediate to basic granulites associated with charnockites. The dextral shear sense indicators are consistent with transpressive deformation in the region and are common especially at the border of the main shear zones. The presence of S-type leucogranite may lead to variations of linear and planar relationships, which result in local extension zones. These elements are consistent with oblique continental collision considering the São Francisco Craton as a stable block.

Regional setting and kinematic features of the Needle Falls Shear Zone, Trans-Hudson Orogen

1993 ◽  
Vol 30 (7) ◽  
pp. 1338-1354 ◽  
Author(s):  
Mel R. Stauffer ◽  
John F. Lewry
Keyword(s):  
Shear Zone ◽  
Simple Shear ◽  
Country Rock ◽  
Shear Zones ◽  
Small Scale ◽  
Lake Zone ◽  
Shear Sense ◽  
Regional Tectonic ◽  
Ductile Shear ◽  
Shear Sense Indicators

Needle Falls Shear Zone is the southern part of a major northeast-trending ductile shear system within the Paleoproterozoic Trans-Hudson Orogen in Saskatchewan. Throughout its exposed length of ~400 km, the shear zone separates reworked Archean continental crust and infolded Paleoproterozoic supracrustals of the Cree Lake Zone, to the northwest, from mainly juvenile Paleoproterozoic arc terrains and granitoid plutons of the Reindeer Zone, to the southeast. It also defines the northwest margin of the ca. 1855 Ma Wathaman Batholith, which forms the main protolith to shear zone mylonites. Although not precisely dated, available age constraints suggest that the shear zone formed between ca. 1855 and 1800 Ma, toward the end of peak thermotectonism in this part of the orogen.In the Needle Falls study area, shear zone mylonites exhibit varied, sequentially developed, ductile to brittle fabric features, including C–S fabrics, winged porphyroclasts (especially delta type), small-scale compressional and extensional microfaults ranging from thin ductile shear zones to late brittle faults, early isoclinal and sheath folds, later asymmetric folds related to compressional microfaults, and variably rotated and (or) folded quartz veins. All ductile shear-sense indicators suggest dextral displacement, as do most later ductile–brittle transition and brittle features. In conjunction with a gently north–northeast-plunging extension lineation, such data indicate oblique east-side-up dextral movement across the shear zone. However, preexisting structures in country rock protoliths rotate into the shear zone in a sense contrary to that predicted by ideal dextral simple shear, a feature thought to reflect significant flattening across the shear zone. Other ductile to brittle fabric elements in the mylonites are consistent with general noncoaxial strain, rather than ideal simple shear. Amount of displacement cannot be measured but indirect estimates suggest approximately 40 ± 20 km.The Needle Falls Shear Zone is too small and has developed too late in regional tectonic history to be considered a crustal suture. Rather, it is interpreted as either a late-tectonic oblique collisional structure or as the result of counterclockwise oroclinal rotation of the southern part of the orogen.

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.

Metamorphism and diachronous cooling in a contractional orogen: the Strandja Massif, NW Turkey

2011 ◽  
Vol 148 (4) ◽  
pp. 580-596 ◽  
Author(s):  
G. SUNAL ◽  
M. SATIR ◽  
B. A. NATAL'IN ◽  
G. TOPUZ ◽  
O. VONDERSCHMIDT
Keyword(s):  
Shear Zones ◽  
Structural Features ◽  
Amphibolite Facies ◽  
The South ◽  
The North ◽  
Ductile Shear Zones ◽  
Shear Sense ◽  
Nw Turkey ◽  
Northward Propagation ◽  
Peak Metamorphism

AbstractThe southern part of the Strandja Massif, northern Thrace, Turkey, comprises a basement of various gneisses, micaschists and rare amphibolite, and a cover of metaconglomerate and metasandstone, separated from each other by a pre-metamorphic unconformity. Metamorphic grade decreases from the epidote–amphibolite facies in the south to the albite–epidote–amphibolite/greenschist-facies transition in the north. Estimated P–T conditions are 485–530°C and 0.60–0.80 GPa in the epidote–amphibolite facies domain, and decrease towards the transitional domain between greenschist- and epidote–amphibolite facies. Rb–Sr muscovite ages range from 162.9 ± 1.6 Ma to 149.1 ± 2.1 Ma, and are significantly older (279–296 Ma) in the northernmost part of the study area. The Rb–Sr biotite ages decrease from 153.9 ± 1.5 Ma in the south to 134.4 ± 1.3 Ma in the north. These age values in conjunction with the attained temperatures suggest that the peak metamorphism occurred at around 160 Ma and cooling happened diachronously, and Rb–Sr muscovite ages were not reset during the metamorphism in the northernmost part. Structural features such as (i) consistent S-dipping foliation and SW to SE-plunging stretching lineation, (ii) top-to-the-N shear sense, and (iii) N-vergent ductile shear zones and brittle thrusts suggest a N-vergent compressional deformation coupled with exhumation. We tentatively ascribe this metamorphism and subsequent diachronous cooling to the northward propagation of a thrust slice. The compressional events in the Strandja Massif were most probably related to the coeval N-vergent subduction/collision system in the southerly lying Rhodope Massif.

Structure and shear-sense indicators of the Mesoproterozoic basement of the North Tianshan microcontinent: Example of granitoid gneisses of the Karadjilga pluton, NW Kyrgyzstan

2021 ◽  
Author(s):  
Anastasia Kushnareva ◽  
Andrey Khudoley ◽  
Dmitriy Alexeiev ◽  
Eugeny Petrov
Keyword(s):  
Granite Gneiss ◽  
Shear Zones ◽  
Magmatic Complex ◽  
Thin Sections ◽  
Metasedimentary Rocks ◽  
The North ◽  
Rock Types ◽  
Shear Sense ◽  
Granitoid Gneisses ◽  
Shear Sense Indicators

&lt;p&gt;The Mesoproterozoic Karadjilga pluton is a poorly studied fragment of the North Tianshan microcontinent located in the western Central Asian Orogenic Belt. Metasedimentary rocks surrounding the pluton consist of marbles and mica schists of the Mesoproterozoic Ortotau Group. These rocks constitute a major west-northwest trending syncline with steep to subvertical limbs. The hinge of the fold is well expressed in the west part of the syncline and plunges east with 30-40&amp;#176; angle of plunge. Eastern termination of the syncline is cut by faults. Granitoid gneisses and granites of the Karadjilga pluton crop out in the core of the syncline. The contacts of the pluton are sub-parallel to bedding and schistosity in surrounding rocks. Primary magmatic contacts are locally reworked by reverse faults and thrusts. Our detailed mapping and structural study revealed inhomogeneous deformation of rocks of the Karadjilga pluton. The following rock types are identified: 1) undeformed granite 2) foliated granite 3) granite-gneiss and 4) mylonite. Undeformed granites form &lt;25-30% of total volume of the pluton and are most widespread in the northeast part of the pluton. On some geological maps they are shown as Ordovician or Devonian. However, U-Pb dating of 9 zircon grains by SHRIMP-II (VSEGEI, St. Petersburg, Russia) yielded a 1125&amp;#177;5 Ma concordant age. It agrees with previously reported U-Pb SHRIMP ages for deformed granites and gneisses (Degtyarev et al., 2011; Kr&amp;#246;ner et al., 2013) and indicates that undeformed granites belongs to the same Mesoproterozoic magmatic complex. Foliated granites and gneisses prevail and constitute up to 60-70% of total volume. They form west-northwest trending zones alternating with mylonites or undeformed granite. Mylonites are subordinate and occur mainly along the contacts of the pluton. Shear zones seem to be approximately parallel to the schistosity of deformed granites, but their geometry needs more study and mapping. Shear-sense indicators were studied in the oriented thin sections and are represented mainly by sigma and delta structures and oblique foliation with rare folds and other indicators. In all but one sample only strike-slip displacement has been identified. In the northern part of the pluton sinistral displacement predominates, whereas dextral displacement prevails in the southern part of the pluton. Shear zones are most widespread on the margins of the Karadjilga pluton, but locally also occur in the central part of the pluton, where they form narrow west-northwest trending zones. According to shear-sense indicators, displacement within the Karadjilga pluton occurred mainly in the approximately west-east direction that strongly differs from the north-south sense of displacement in the Paleozoic thrust and fold belts of Tianshan.&lt;/p&gt;&lt;p&gt;The study was supported by the RFBR project 20-05-00252.&lt;/p&gt;

A reinterpretation of the Snow Lake gold camp, Trans-Hudson Orogen, Canada: The use of cleavages as markers to correlate structures across deformed terranes

2020 ◽  
Author(s):  
Kate Elizabeth Rubingh ◽  
Bruno Lafrance ◽  
Harold L. Gibson
Keyword(s):  
Boundary Conditions ◽  
Time Lag ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Thrust Faults ◽  
Volcanic Stratigraphy ◽  
Shear Sense ◽  
Flin Flon ◽  
Shear Sense Indicators ◽  
Superior Craton

The Snow Lake gold camp is located within amphibolite facies volcanic rocks of the ca. 1.88 – 1.87 Ga Flin Flon-Glennie Complex (FFGC) in the Trans-Hudson Orogen, Manitoba. During thrusting and collision with the Archean Sask craton, volcanic rocks were interleaved with turbidites of the ca. 1.855 - 1.84 Ga Burntwood Group and sandstone and conglomerate of the ca. 1.845 - 1.835 Ga Missi Group. The main cleavage in the turbidites was previously attributed to thrusting and used as a marker for correlating structures across the camp. A re-examination of this cleavage suggests that it overprints the thrust faults and formed during later collision between the FFGC and the Archean Superior craton. This has important implications as it further suggests that (1) previously unrecognized, early brittle thrust faults repeat volcanic stratigraphy and may have created the boundary conditions that enabled the formation of ductile thrust faults, fold nappes, and mega sheath folds; (2) shear sense indicators along ductile thrust faults formed during their reactivation as sinistral shear zones rather than during thrusting; and (3) peak metamorphic conditions were caused by thrusting and stacking during collision with the Sask craton but were attained later during collision with the Superior craton due to the time lag between orogenesis and the re-equilibration of regional isotherms. Results from this study may be applicable to other complexly deformed terranes where the dominant regional cleavage differs in expression in mixed volcanic and sedimentary successions and has been used as a marker for correlating structures.

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.

LONGEVITY OF DUCTILE SHEAR ZONES FROM DIFFUSION GEOSPEEDOMETRY OF KINEMATICALLY-SENSITIVE MINERAL INCLUSIONS

2019 ◽  
Author(s):  
William O. Nachlas ◽  
◽  
Christian Teyssier ◽  
Donna L. Whitney ◽  
Greg Hirth
Keyword(s):  
Shear Zones ◽  
Mineral Inclusions ◽  
Ductile Shear Zones ◽  
Ductile Shear

scholarly journals Geology of the orogenic Cheminis gold deposit along the Larder Lake – Cadillac deformation zone, Ontario

2015 ◽  
Vol 52 (12) ◽  
pp. 1093-1108 ◽  
Author(s):  
Bruno Lafrance
Keyword(s):  
Deformation Zone ◽  
Volcanic Rocks ◽  
Tholeiitic Basalt ◽  
Hydrothermal Fluids ◽  
South Side ◽  
Shear Sense ◽  
Abitibi Subprovince ◽  
Deformation Features ◽  
Shear Sense Indicators ◽  
Host Rocks

The Larder Lake – Cadillac deformation zone (LLCDZ) is one of two major, auriferous, deformation zones in the southern Abitibi subprovince of the Archean Superior Province. It hosts the Cheminis and the giant Kerr Addison – Chesterville deposits within a strongly deformed band of Fe-rich tholeiitic basalt and komatiite of the Larder Lake Group (ca. 2705 Ma). The latter is bounded on both sides by younger, less deformed, Timiskaming turbidites (2674–2670 Ma). The earliest deformation features are F1 folds affecting the Timiskaming rocks, which formed either during D1 extensional faulting or during early D2 north–south shortening related to the opening and closure, respectively, of the Timiskaming basin. Continued shortening during D2 imbricated the older volcanic rocks and turbidites and produced regional F2 folds with an axial planar S2 cleavage. D2 deformation was partitioned into the weaker band of volcanic rocks, producing the strong S2 foliation, L2 stretching lineation, and south-side-up shear sense indicators, which characterize the LLCDZ. Gold is present in quartz–carbonate veins in deformed fuchsitic komatiites (carbonate ore) and turbiditic sandstone (sandstone-hosted ore), and in association with disseminated pyrite in altered Fe-rich tholeiitic basalts (flow ore). All host rocks underwent strong mass gains in CO2, S, K2O, Ba, As, and W, during sericitization, carbonatization, and sulphidation of the host rocks, suggesting that they interacted with the same hydrothermal fluids. Textural relationships between alteration minerals and S2 cleavage indicate that mineralization is syn-cleavage. Thus, gold was deposited as hydrothermal fluids migrated upward along the LLCDZ during contractional, D2 south-side-up shearing. The gold zones were subsequently modified during D3 reactivation of the LLCDZ as a dextral transcurrent fault zone.

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