Ductile shearing and LA-ICP MS zircon U-Pb dating of Sa'erqiaoke ductile shear belt in the Bogda orogen: Constraints on the process of mountain building of eastern Tianshan

2018 ◽  
Vol 53 ◽  
pp. 206-222 ◽  
Author(s):  
Wanshan Lei ◽  
Junfeng Guo ◽  
Danli Chen ◽  
Jianpeng Chu ◽  
Yong Li
Keyword(s):  
Mountain Building ◽  
Eastern Tianshan ◽  
Icp Ms ◽  
Ductile Shearing ◽  
Ductile Shear ◽  
Shear Belt

A geochronological framework for sedimentation and Mesoproterozoic tectono-magmatic activity in lower Belt–Purcell rocks exposed west of Kimberley, British Columbia

2015 ◽  
Vol 52 (7) ◽  
pp. 444-465 ◽  
Author(s):  
Christopher R.M. McFarlane
Keyword(s):  
British Columbia ◽  
Minor Component ◽  
Structural Level ◽  
Peraluminous Granite ◽  
Icp Ms ◽  
Ductile Shearing ◽  
History Of ◽  
Metamorphic Zone ◽  
A Minor ◽  
Plate Reconstruction

The Matthew Creek Metamorphic Zone (MCMZ) exposes what is inferred to be the lowest structural level of the lower Aldridge Formation in the Canadian portion of the Belt–Purcell Supergroup. Zircon, monazite, and titanite were dated using the U–Pb system by LA–ICP–MS. The detrital zircon populations of quartzite layers in these rocks define a provenance dominated by sources of Laurentian affinity with a minor component of non-North American ages between 1600 and 1490 Ma. Special attention was paid to monazite in sillimanite-grade metapelitic schists that was analyzed using in situ LA–ICP–MS techniques guided by BSE imaging and compositional mapping. Textural and geochronological evidence indicate that coupled dissolution–reprecipitation affected detrital monazite at 1413 ± 10 Ma. This was followed by prograde monazite growth at 1365 ± 10 Ma, synchronous with crystallization of the nearby Hellroaring Creek peraluminous granite at 1365 ± 5 Ma. Late-stage pegmatite emplacement and ductile shearing along the contact of the MCMZ and overlying rocks occurred at 1335 ± 5 Ma, interpreted as a period of post-collisional extension, core complex formation, exhumation, and decompression melting. The entire package was subsequently affected by a pervasive ∼1050 Ma hydrothermal overprint that partially reset U–Pb dates in monazite, zircon, and titanite contained in all lithologies examined. The lowermost Belt–Purcell stratigraphy in southeast British Columbia preserves a detailed record of sedimentary provenance and a long history of episodic collision and extension that must be reconciled with plate reconstruction models for the break-up of the Nuna supercontinent and assembly of Rodinia.

Structural characteristics and LA–ICP-MS U–Pb zircon geochronology of the deformed granitic rocks from the Mesozoic Xingcheng-Taili ductile shear zone in the North China Craton

2015 ◽  
Vol 650 ◽  
pp. 80-103 ◽  
Author(s):  
Chenyue Liang ◽  
Yongjiang Liu ◽  
Franz Neubauer ◽  
Wei Jin ◽  
Zuoxun Zeng ◽  
...  
Keyword(s):  
Shear Zone ◽  
North China Craton ◽  
North China ◽  
Structural Characteristics ◽  
Granitic Rocks ◽  
Zircon Geochronology ◽  
Ductile Shear Zone ◽  
The North ◽  
Icp Ms ◽  
Ductile Shear

Exhumation of HP/UHP rocks by normal ductile shearing on top of the Eocene extruding wedge

2020 ◽  
Author(s):  
Michel Ballèvre ◽  
Paola Manzotti
Keyword(s):  
Shear Zone ◽  
Kinematic Model ◽  
Geological Mapping ◽  
Greenschist Facies ◽  
Western Boundary ◽  
Frontal Part ◽  
Ductile Shearing ◽  
Shear Sense ◽  
Eclogite Facies ◽  
Ductile Shear

<p>A popular model for the exhumation of HP-UHP rocks is the ‘extruding wedge’ model, where a crustal slice is bounded at its base by a ‘thrust shear-sense’ fault and to the top by a ‘normal shear-sense’ fault. In the Western Alps, the late Eocene Combin Shear Zone (CSZ) allowed extrusion of a wedge made by the Briançonnais-Piemonte-Liguria (‘Penninic’) stack.</p><p>Geological mapping has established the geometry and continuity of the CSZ from the frontal part of the Dent Blanche Tectonic System to the western boundary of the Sesia Zone. The CSZ has been cut during the Miocene by the brittle Aosta-Ranzola Fault, with an estimated downthrow of the northern block of c. 2.5 km with respect to the southern block. Consequently, the sections observed north (Monte Rosa) and South (Gran Paradiso) of the Aosta Fault display different structural levels in the Alpine nappe stack. The CSZ has been folded (Vanzone phase) during the final part of its history (i.e. when displacement along the CSZ was no more taking place), due to the indentation of the Adriatic mantle. This offers us the unique opportunity to study the change in deformation mechanisms along the shear zone (for a distance parallel to its displacement of about 50 km).</p><p>Salient characteristics of the CSZ are the following. (i) The thickness of the ductile shear zone increases from NW (frontal part of the Dent Blanche) to SE (frontal part of the Sesia Zone), from a few hundred metres to several kilometres. The type of lithologies pervasively reworked by the ductile shear changes along strike (dominantly calcschists from the topmost oceanic units in the Combin Zone, possibly up to the whole of the ‘Gneiss Minuti’ in the frontal Sesia Zone). (ii) The main ductile deformation along the CSZ was taking place at greenschist-facies conditions, overprinting eclogite-facies to greenschist-facies deformations of Cretaceous to Middle Eocene age. The CSZ is cutting and reworking eclogite-facies structures developed in its hangingwall (Sesia) as well as in its footwall (Zermatt). (iii) Ductile displacement along the CSZ is associated with the development in its footwall of south-east-verging, kilometre-scale, folds (Mischabel phase). The sedimentary sequences of the Pancherot-Cime Bianche-Bettaforca Unit may be used to estimate the minimum amount of ‘normal shear sense’ displacement of the order of 15-20 km.</p><p>A kinematic model integrating slab roll-back, ‘thrust shear-sense’ at the base and ‘normal shear-sense’ displacement on top of the Eocene eclogite-facies stack will be presented.</p>

scholarly journals Evolution of Quartz and Calcite Microstructures Exhumed From Deep Brittle-Ductile Shear Zones in the Southern Alps of New Zealand

2021 ◽  
Author(s):  
◽  
Matthew P Hill
Keyword(s):  
New Zealand ◽  
Grain Boundary ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Differential Stress ◽  
Alpine Fault ◽  
Ductile Shearing ◽  
Boundary Sliding ◽  
Ductile Shear

<p><b>Arrays of brittle-ductile shears exposed in the Southern Alps of New Zealand, haveprovided a superb natural laboratory for insight into the microstructural evolution of lowercrustal shear zones during exhumation. Shears are exposed in the central section of theSouthern Alps at Sam Peak, Chancellor Ridge, and Baumann Glacier in a zone ~2 kmwide that is located 6–8 km structurally above the Alpine Fault. An array ofsystematically spaced shear zones that formed by embrittlement and faulting ofquartzofeldspathic schist took place at the same time as ductile shearing of quartzcarbonateveins embedded within the schist. This study has used field-based structuralmapping along with optical microscopy and universal stage measurements ofcrystallographic preferred orientations (CPO) to resolve the shear zone kinematics andrheology. On the basis of these data, the strain path can be reconstructed for the shearedveins during their progressive deformation. This began with their incidence as backshearsat the base of the Alpine Fault ramp and ended with their subsequent recrystallisation,uplift, and exhumation.</b></p> <p>The near-vertical shear planes have mean orientation of 221@89 NW ± 1o (n =780). They are inferred to have formed as backshears accommodating uplift of the PacificPlate as it was translated onto the oblique footwall ramp of the Alpine Fault during lateCenozoic oblique convergence. Detailed fault offset transect surveys across the shears atChancellor Ridge and Baumann Glacier reveal a mean spacing between the shear zones of25 ± 5 cm (n = 410). Quartz-carbonate marker veins are displaced in a dextral west-sideupshear sense. Fault offset geometry and a consistent arrangement of mineral fibrelineations that decorate fault surfaces, indicate that the mean displacement vector pitches35o SW in the shear plane (trend and plunge of: 262, 35 ± 7o). Ductilely deformed markerveins have been subject to a mean displacement of 9.9 ± 1.4 cm (n = 344) and a meanfinite ductile shear strain of 4.8 ± 0.3 (n = 219). A strain-rate for the ductile deformationof the veins is estimated at 3 x 10-11 sec-1 based on the observed finite ductile shear strain,an escalator kinematic model, and assumptions about the width of the deforming zone.</p> <p>Five deformation phases have affected the sheared veins during their transport upthe fault ramp: 1) initial brittle faulting and ductile shearing; 2) grain boundary sliding ofmylonitic quartz in response to a post-ramping differential stress drop; 3) recrystallisationand grain growth; 4) renewed late-stage dislocation creep; and 5) semibrittle deformationand exhumation. In the schist, the shears initiated as planar brittle faults at lower crustal depths of~21 km at a temperature of 450 ± 50oC. They developed in a zone of transiently highshear strain-rates near the base of the Alpine Fault ramp. Dislocation creep caused a CPOof quartz and calcite to develop in sheared veins. Using the flow law of Hirth et al. (2001)and the estimated strain-rate, a differential stress of ~165 MPa is inferred for ductiledeformation of the veins. Near-lithostatic (λ = 0.85) fluid pressures would have causedthe rocks to undergo brittle failure, a situation that is confirmed by a late component ofbrittle deformation that over prints the ductilely sheared veins. Syntectonic quartz-calciteveins infill the shear fractures, and these themselves have been sheared. The deformationof the veins was not a simple shear process but one with triclinic flow symmetry. This isinferred from discordance between the shear direction and the near-vertical principleextension direction that is revealed by the pattern and symmetry of quartz and calcite CPOfabrics.</p> <p>After the shears move away from the ramp-step, grain boundary sliding (GBS)accommodated by solid-state diffusion creep is inferred to have affected quartz veins.</p> <p>This deformation mechanism takes place because of 1) the small 8 μm grain size inheritedfrom Phase 1; 2) the presence of fluid in the shear zone; and 3) a stress drop to ~22 MPathat followed the initial up-ramping. Quartz CPO fabrics in the sheared veins areremarkably weak considering their large shear strains. GBS is inferred to have been achief deformation mechanism that caused the weakening of quartz CPO fabrics in thehighly sheared sections of deformed veins. Calcite has also affected the quartz fabricstrength as those veins containing >5% calcite have very weak quartz CPO fabrics. Incontrast to quartz, the CPO fabrics for the co-existing calcite remained strong andcontinued to develop by dislocation creep.</p> <p>The third phase of deformation, a process that may have contributed to subsequentweakening of quartz CPO fabrics, was recrystallisation and grain growth to 126 μm and anequigranular-polygonal grain shape fabric. This fabric was overprinted by late-stagedislocation creep microstructures in the fourth deformation phase in response increaseddifferential stress encountered by the rocks at lower temperatures in the upper crust. Thefinal phase of deformation to affect the sheared veins was semibrittle deformation atdifferential stresses of <189 MPa and temperatures of 200–280oC as the rocks passedthrough the steady-state brittle-ductile transition zone at depths of 8–10 km before beingexhumed at the surface.</p>

Record of a Palaeogene syn-collisional extension in the north Aegean region: evidence from the Kemer micaschists (NW Turkey)

2007 ◽  
Vol 144 (2) ◽  
pp. 393-400 ◽  
Author(s):  
LAURENT BECCALETTO ◽  
NIKOLAY BONEV ◽  
DELPHINE BOSCH ◽  
OLIVIER BRUGUIER
Keyword(s):  
Early Eocene ◽  
Extensional Deformation ◽  
Aegean Region ◽  
The North ◽  
Upper Limit ◽  
Early Tertiary ◽  
Icp Ms ◽  
Ductile Shearing ◽  
Nw Turkey ◽  
North Aegean

In NW Turkey, the medium-grade Kemer micaschists of the Biga Peninsula record NE-directed extension related to ductile to brittle–ductile shearing during the Palaeogene period: a lower limit for their exhumation is given by the Late Maastrichtian age of the HP–LT metamorphism of a similar nearby area (Çamlıca micaschists); an upper limit is given by the Early Eocene intrusion age of the post-kinematic Karabiga granitoid, dated as 52.7 ± 1.9 Ma using the U–Pb LA–ICP–MS method on xenotime. Correlations with the northeasterly Rhodope region and integration into the geodynamic regional frame indicate that the Kemer micaschists experienced an extensional deformation connected to a collisional context in latest Cretaceous–early Tertiary times. The Kemer micaschists therefore represent a new area (the first in Turkey), which suffered synorogenic extension in the north Aegean domain at the very beginning of Tertiary times.

scholarly journals Evolution of Quartz and Calcite Microstructures Exhumed From Deep Brittle-Ductile Shear Zones in the Southern Alps of New Zealand

2021 ◽  
Author(s):  
◽  
Matthew P Hill
Keyword(s):  
New Zealand ◽  
Grain Boundary ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Differential Stress ◽  
Alpine Fault ◽  
Ductile Shearing ◽  
Boundary Sliding ◽  
Ductile Shear

<p><b>Arrays of brittle-ductile shears exposed in the Southern Alps of New Zealand, haveprovided a superb natural laboratory for insight into the microstructural evolution of lowercrustal shear zones during exhumation. Shears are exposed in the central section of theSouthern Alps at Sam Peak, Chancellor Ridge, and Baumann Glacier in a zone ~2 kmwide that is located 6–8 km structurally above the Alpine Fault. An array ofsystematically spaced shear zones that formed by embrittlement and faulting ofquartzofeldspathic schist took place at the same time as ductile shearing of quartzcarbonateveins embedded within the schist. This study has used field-based structuralmapping along with optical microscopy and universal stage measurements ofcrystallographic preferred orientations (CPO) to resolve the shear zone kinematics andrheology. On the basis of these data, the strain path can be reconstructed for the shearedveins during their progressive deformation. This began with their incidence as backshearsat the base of the Alpine Fault ramp and ended with their subsequent recrystallisation,uplift, and exhumation.</b></p> <p>The near-vertical shear planes have mean orientation of 221@89 NW ± 1o (n =780). They are inferred to have formed as backshears accommodating uplift of the PacificPlate as it was translated onto the oblique footwall ramp of the Alpine Fault during lateCenozoic oblique convergence. Detailed fault offset transect surveys across the shears atChancellor Ridge and Baumann Glacier reveal a mean spacing between the shear zones of25 ± 5 cm (n = 410). Quartz-carbonate marker veins are displaced in a dextral west-sideupshear sense. Fault offset geometry and a consistent arrangement of mineral fibrelineations that decorate fault surfaces, indicate that the mean displacement vector pitches35o SW in the shear plane (trend and plunge of: 262, 35 ± 7o). Ductilely deformed markerveins have been subject to a mean displacement of 9.9 ± 1.4 cm (n = 344) and a meanfinite ductile shear strain of 4.8 ± 0.3 (n = 219). A strain-rate for the ductile deformationof the veins is estimated at 3 x 10-11 sec-1 based on the observed finite ductile shear strain,an escalator kinematic model, and assumptions about the width of the deforming zone.</p> <p>Five deformation phases have affected the sheared veins during their transport upthe fault ramp: 1) initial brittle faulting and ductile shearing; 2) grain boundary sliding ofmylonitic quartz in response to a post-ramping differential stress drop; 3) recrystallisationand grain growth; 4) renewed late-stage dislocation creep; and 5) semibrittle deformationand exhumation. In the schist, the shears initiated as planar brittle faults at lower crustal depths of~21 km at a temperature of 450 ± 50oC. They developed in a zone of transiently highshear strain-rates near the base of the Alpine Fault ramp. Dislocation creep caused a CPOof quartz and calcite to develop in sheared veins. Using the flow law of Hirth et al. (2001)and the estimated strain-rate, a differential stress of ~165 MPa is inferred for ductiledeformation of the veins. Near-lithostatic (λ = 0.85) fluid pressures would have causedthe rocks to undergo brittle failure, a situation that is confirmed by a late component ofbrittle deformation that over prints the ductilely sheared veins. Syntectonic quartz-calciteveins infill the shear fractures, and these themselves have been sheared. The deformationof the veins was not a simple shear process but one with triclinic flow symmetry. This isinferred from discordance between the shear direction and the near-vertical principleextension direction that is revealed by the pattern and symmetry of quartz and calcite CPOfabrics.</p> <p>After the shears move away from the ramp-step, grain boundary sliding (GBS)accommodated by solid-state diffusion creep is inferred to have affected quartz veins.</p> <p>This deformation mechanism takes place because of 1) the small 8 μm grain size inheritedfrom Phase 1; 2) the presence of fluid in the shear zone; and 3) a stress drop to ~22 MPathat followed the initial up-ramping. Quartz CPO fabrics in the sheared veins areremarkably weak considering their large shear strains. GBS is inferred to have been achief deformation mechanism that caused the weakening of quartz CPO fabrics in thehighly sheared sections of deformed veins. Calcite has also affected the quartz fabricstrength as those veins containing >5% calcite have very weak quartz CPO fabrics. Incontrast to quartz, the CPO fabrics for the co-existing calcite remained strong andcontinued to develop by dislocation creep.</p> <p>The third phase of deformation, a process that may have contributed to subsequentweakening of quartz CPO fabrics, was recrystallisation and grain growth to 126 μm and anequigranular-polygonal grain shape fabric. This fabric was overprinted by late-stagedislocation creep microstructures in the fourth deformation phase in response increaseddifferential stress encountered by the rocks at lower temperatures in the upper crust. Thefinal phase of deformation to affect the sheared veins was semibrittle deformation atdifferential stresses of <189 MPa and temperatures of 200–280oC as the rocks passedthrough the steady-state brittle-ductile transition zone at depths of 8–10 km before beingexhumed at the surface.</p>

Strain-induced mineral growth in ductile shear zones and a preliminary study of ductile shearing in western Newfoundland

1988 ◽  
Vol 25 (12) ◽  
pp. 2118-2129 ◽  
Author(s):  
M. A. J. Piasecki
Keyword(s):  
Growth Characteristic ◽  
Shear Zones ◽  
The North ◽  
Mineral Growth ◽  
Inclined Surfaces ◽  
Ductile Shear Zones ◽  
Ductile Shearing ◽  
Preliminary Study ◽  
Ductile Shear ◽  
North And South

In the Fleur de Lys and the Central Gneiss terranes the presence of strain-induced mineral growth characteristic of ductile shear zones within zones of rocks with mylonitic fabrics indicates the existence of major belts of layer-parallel ductile shearing with complex evolutionary sequences. Kinematic markers in several of these shear belts indicate that shearing movements on initially probably gently inclined surfaces, directed not normal to the axial trend of the orogen but parallel to it, are tectonically important in western Newfoundland. The shear belts are in excess of 1 km thick, and one well-exposed example exhibits a pattern in which zones of the highest strain anastomose on the map scale.The base of the Fleur de Lys Supergroup is marked by one such major zone of shearing (décollement) in which kinematic indicators record movements directed to the north and to the south, before the regional attitude of the rocks was steepened. Along the Baie Verte Line, earlier north- and south-directed movements in the Fleur de Lys were succeeded by reverse movements towards the east, over the Dunnage Terrane.

The timescale of the aseismic to seismic deformation in a cooling pluton: 40Ar-39Ar ages of the solid-state deformation in the Adamello (Southern Italian Alps)

2021 ◽  
Author(s):  
Silvia Mittempergher ◽  
Stefano Zanchetta ◽  
Federico Caldiroli ◽  
Andrea Bistacchi ◽  
Andrea Zanchi ◽  
...  
Keyword(s):  
Thermal Anomaly ◽  
Shear Zones ◽  
Wall Rock ◽  
Deformation Phase ◽  
Ductile Shear Zones ◽  
Ductile Shearing ◽  
Two Samples ◽  
Ductile Shear ◽  
Magma Pulses ◽  
Absolute Age

&lt;p&gt;The northern Adamello is crosscut by ductile shear zones and pseudotachylyte-bearing faults, both compatible with the same stress field, with ductile shear zones crosscut by brittle faults. These relations are coherent with the re-equilibration of the pluton-related thermal anomaly to temperatures typical of the base of the seismogenic continental crust (T = 250 &amp;#8211; 300&amp;#176;). Our new &lt;sup&gt;40&lt;/sup&gt;Ar-&lt;sup&gt;39&lt;/sup&gt;Ar ages help to constrain the absolute age and duration of each deformation phase.&lt;/p&gt;&lt;p&gt;Samples included wall-rock biotite, bulk ultramylonites and pseudotchylytes. Before stepwise heating &lt;sup&gt;40&lt;/sup&gt;Ar-&lt;sup&gt;39&lt;/sup&gt;Ar measurements, samples were characterized by microstructural, geochemical and petrological analyses.&lt;/p&gt;&lt;p&gt;The wall-rock biotite is 33.4&amp;#177;0.1 Ma old, independently of grainsize. Mylonites feature complex age spectra between 28-31 Ma, including biotite and altered feldspar. Four pseudotachylyte matrices are clustered around 30-31.5 Ma, and two samples have 25-26 Ma ages.&lt;/p&gt;&lt;p&gt;Ductile shearing active 2 Ma after wall-rock emplacement indicates either low strain rates, or a long-lasting thermal anomaly, which might be due to high emplacement depth, and/or the progressive assemblage of adjacent plutons through small magma pulses. Seismogenic faulting overlaps with mylonitization around 31 Ma; younger pseudotachylyte ages may be due to late-stage reactivation.&lt;/p&gt;

scholarly journals Supplemental Material: From Ordovician nascent to early Permian mature arc in the southern Altaids: Insights from the Kalatage inlier in the Eastern Tianshan, NW China

2020 ◽  
Author(s):  
Q.G. Mao ◽  
et al. ◽  
W.J. Xiao
Keyword(s):  
Trace Element ◽  
Trace Element Data ◽  
Early Permian ◽  
Eastern Tianshan ◽  
Nw China ◽  
Element Data ◽  
Icp Ms ◽  
Geochronological Dating

<div>Zircon SIMS, LA-ICP-MS, and SHRIMP U-Pb geochronological dating, major, and trace element data (listed in Supplemental Tables S1 to S5, respectively).<br></div>

scholarly journals Supplemental Material: From Ordovician nascent to early Permian mature arc in the southern Altaids: Insights from the Kalatage inlier in the Eastern Tianshan, NW China

2020 ◽  
Author(s):  
Q.G. Mao ◽  
et al. ◽  
W.J. Xiao
Keyword(s):  
Trace Element ◽  
Trace Element Data ◽  
Early Permian ◽  
Eastern Tianshan ◽  
Nw China ◽  
Element Data ◽  
Icp Ms ◽  
Geochronological Dating

<div>Zircon SIMS, LA-ICP-MS, and SHRIMP U-Pb geochronological dating, major, and trace element data (listed in Supplemental Tables S1 to S5, respectively).<br></div>

Sign in / Sign up

Export Citation Format

Share Document