scholarly journals Structural and rheological evolution of the Laramide subduction channel in southern California

2016 ◽  
Author(s):  
Haoran Xia ◽  
John P. Platt
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Southern California ◽  
Microstructural Analysis ◽  
Carbonaceous Material ◽  
Dislocation Creep ◽  
Return Flow ◽  
Pressure Solution ◽  
Subduction Channel ◽  
San Gabriel Mountains

Abstract. The Pelona schist in the San Gabriel Mountains, southern California, formed in the Laramide subduction channel, exhibits multiple phases of deformation/metamorphism and provides valuable insights into the rheological properties of the subduction channel. Petrological and microstructural analysis indicates that the Pelona schist has undergone three major deformational/metamorphic events. Subduction of volcanic and sedimentary protoliths during D1 was recorded by aligned mineral inclusions in albite and epidote porphyroblasts. Metamorphic temperature and pressure at the end of subduction yielded by Raman spectroscopy of carbonaceous material and Si-in-muscovite barometry were 518.9 ± 19.6 °C and 10.5 ± 0.4 kbar, respectively. During D1 the dominant deformation mechanism was quartz pressure solution, and the estimated shear stress and strain rate were less than 10 MPa and 5.8×10−13 s−1. D2, the first stage exhumation of the Pelona schist along the upper section of the subduction channel during return flow, was recorded by retrogressive metamorphism, isoclinal folding, and a pervasive schistosity that wraps around earlier porphyroblasts. Metagreywacke was deformed mainly by quartz pressure solution and metachert was deformed dominantly by dislocation creep during D2. The shear stress in metagreywacke was less than 10 MPa and that in metachert was between 8.6 and 13.3 MPa, resulting in a strain rate of 1.4×10−13 to 5.5×10−13 s−1. A topography driven model is proposed as the main driving force of D2 exhumation. D3 records normal-sense movement on the Vincent fault, which separates the schist from overlying arc and continental basement. This resulted in the second stage of exhumation, creating a major synform and associated mylonitic fabric in the upper section of the Pelona schist. Conditions at the beginning of D3 were 390°C and 5.8 kbar given by the TitaniQ thermometer and phengite barometer. The deformation was dominated by quartz dislocation creep with a strain rate of ~5.1 ×10−13 s−1 at a shear stress of ~22 MPa.

scholarly journals Structural and rheological evolution of the Laramide subduction channel in southern California

Solid Earth ◽  
2017 ◽  
Vol 8 (2) ◽  
pp. 379-403 ◽  
Author(s):  
Haoran Xia ◽  
John P. Platt
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Southern California ◽  
Microstructural Analysis ◽  
Carbonaceous Material ◽  
Dislocation Creep ◽  
Return Flow ◽  
Pressure Solution ◽  
Subduction Channel ◽  
San Gabriel Mountains

Abstract. The Pelona Schist in the San Gabriel Mountains, southern California, formed in the Laramide subduction channel, exhibits multiple phases of deformation/metamorphism and provides valuable insights into the rheological properties of the subduction channel. Petrological and microstructural analysis indicates that the Pelona Schist has undergone three major deformational/metamorphic events. Subduction of volcanic and sedimentary protoliths during D1 was recorded by aligned mineral inclusions in albite and epidote porphyroblasts. Metamorphic temperature and pressure at the end of subduction yielded by Raman spectroscopy of carbonaceous material and phengite barometry were 519 ± 20 °C and 10.5 ± 0.4 kbar, respectively. During D1 the dominant deformation mechanism was quartz pressure solution, and the estimated shear stress at the end of D1 was less than 10 MPa. D2, the first stage exhumation of the Pelona Schist along the upper section of the subduction channel during return flow, was recorded by retrogressive metamorphism, isoclinal folding, and a pervasive schistosity that wraps around earlier porphyroblasts. Metagreywacke was deformed mainly by quartz pressure solution and metachert was deformed dominantly by dislocation creep during D2. The shear stress in metagreywacke was less than 10 MPa and that in metachert was between 8.3 + 2.7/− 1.5 and 12.9 + .9/− 2.3 MPa, resulting in a strain rate of 1.4  ×  10−13 to 5.5  ×  10−13 s−1. A topography driven model is proposed as the main driving force of D2 exhumation. D3 records normal-sense movement on the Vincent Fault, which separates the schist from overlying arc and continental basement. This resulted in the second stage of exhumation, creating a major synform and associated mylonitic fabric in the upper section of the Pelona Schist. Conditions at the beginning of D3 were 390 ± 13 °C and 5.8 ± 0.8 kbar given by the TitaniQ thermometer and phengite geobarometer. The deformation was dominated by quartz dislocation creep with a strain rate of 4.5 ± 1.2  ×  10−13 s−1 at a shear stress of 20.1 + 7.3/− 4.0 MPa.

Grain-scale deformation in the Palaeoproterozoic Dongargarh Supergroup, central India: implications for shallow crustal deformation mechanisms from microstructural analysis

2006 ◽  
Vol 143 (4) ◽  
pp. 531-543 ◽  
Author(s):  
GAUTAM GHOSH ◽  
SUKANYA CHAKRABORTY ◽  
JOYDIP MUKHOPADHYAY ◽  
ARIJIT RAY
Keyword(s):  
Grain Size ◽  
Crustal Deformation ◽  
Finite Strain ◽  
Microstructural Analysis ◽  
Central India ◽  
Vital Role ◽  
Deformation Mechanisms ◽  
Dislocation Creep ◽  
Pressure Solution ◽  
Volume Loss

Analysis of the grain-scale deformation mechanisms in folded rocks of the Dongargarh Supergroup, central India, reveals that deformation was accomplished by a combination of pressure solution, microfracturing and dislocation creep processes. The finite strain was assessed using the Rf/ϕ method (X/Z ≈ 2). Partitioning of strain into various deformation mechanisms revealed that dislocation creep and pressure solution were the major contributors to the finite strain, followed by microfracturing. Analyses of microstructures suggest a sequence of dislocation creep followed by pressure solution and microfracturing, that ultimately gave way to microfracturing and limited crystallization or recrystallization. Overall constancy in volume during deformation is suggested from the balance between fracture-related grain-scale dilatancy and solution-related volume loss. Observations on cleavage spacing within various lithologies in a specific structural setting suggest that lithology played a vital role in cleavage development. Cleavage development in sandstones of the Dongargarh Supergroup required thin shale interbeds (for competency contrast) and grain size <0.036 mm (4.75 ϕ).

scholarly journals Application of the Strain Compensation Model and Processing Maps for Description of Hot Deformation Behavior of Metastable β Titanium Alloy

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2021
Author(s):  
Oleksandr Lypchanskyi ◽  
Tomasz Śleboda ◽  
Aneta Łukaszek-Sołek ◽  
Krystian Zyguła ◽  
Marek Wojtaszek
Keyword(s):  
Titanium Alloy ◽  
Strain Rate ◽  
Flow Behavior ◽  
Microstructural Analysis ◽  
Calculated Data ◽  
Processing Temperature ◽  
Processing Maps ◽  
Compression Tests ◽  
Strain And Strain Rate ◽  
Average Absolute Relative Error

The flow behavior of metastable β titanium alloy was investigated basing on isothermal hot compression tests performed on Gleeble 3800 thermomechanical simulator at near and above β transus temperatures. The flow stress curves were obtained for deformation temperature range of 800–1100 °C and strain rate range of 0.01–100 s−1. The strain compensated constitutive model was developed using the Arrhenius-type equation. The high correlation coefficient (R) as well as low average absolute relative error (AARE) between the experimental and the calculated data confirmed a high accuracy of the developed model. The dynamic material modeling in combination with the Prasad stability criterion made it possible to generate processing maps for the investigated processing temperature, strain and strain rate ranges. The high material flow stability under investigated deformation conditions was revealed. The microstructural analysis provided additional information regarding the flow behavior and predominant deformation mechanism. It was found that dynamic recovery (DRV) was the main mechanism operating during the deformation of the investigated β titanium alloy.

scholarly journals Longitudinal Stress Gradients and Basal Shear Stress of a Temperate Valley Glacier

1979 ◽  
Vol 24 (90) ◽  
pp. 507-508 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Field Data ◽  
Numerical Models ◽  
Lateral Strain ◽  
Longitudinal Stress ◽  
Base Shear ◽  
Stress Gradients ◽  
Valley Glacier ◽  
Image Position

AbstractFor the first time field data from a temperate valley glacier, the Variegated Glacier, are used to investigate the behavior of longitudinal stress gradients predicted by the relation(1)whereHis the local depth, andysandybare the surface and bed elevations respectively. This equation is similar to one derived by Budd (1970) for plane strain-rate, to evaluate the importance of longitudinal stress gradients, but a shape factorfis included to account approximately for lateral strain-rate gradients. Predictive numerical models of valley glaciers require the local base shear stress to be known as accurately as possible. It has been argued on theoretical grounds that whenTis averaged over distances of more than five to ten times the depth, this term is negligible. At larger averaging scales, 2Gcan then be considered a correction to the simple geometric expression of base stress due to the presence of longitudinal stress gradients. Field data of velocity and geometry are used to evaluate the terms of Equation (1), whereτband 2Gare estimated asandat intervals of 100 m,Usis the measured surface center-line velocity,Aandnare the flow-law parameters, andis the surface longitudinal strain-rate. The expression for 2Gis an approximation proposed by Budd (1970).

Hot working of SP-700 titanium alloy with lamellar α + β starting structure using a processing map

2020 ◽  
Vol 111 (4) ◽  
pp. 297-306
Author(s):  
Amir Hosein Sheikhali ◽  
Maryam Morakkabati
Keyword(s):  
Titanium Alloy ◽  
Strain Rate ◽  
Hot Deformation ◽  
Processing Map ◽  
Microstructural Analysis ◽  
Shear Bands ◽  
Alpha Phase ◽  
Strain Rates ◽  
Compression Tests ◽  
Temperature Range

Abstract In this study, hot deformation behavior of SP-700 titanium alloy was investigated by hot compression tests in the temperature range of 700-9508C and at strain rates of 0.001, 0.1, and 1 s-1. Final mechanical properties of the alloy (hot compressed at different strain rates and temperatures) were investigated using a shear punch testing method at room temperature. The flow curves of the alloy indicated that the yield point phenomenon occurs in the temperature range of 800- 9508C and strain rates of 0.1 and 1 s-1. The microstructural analysis showed that dynamic globularization of the lamellar α phase starts at 7008C and completes at 8008C. The alpha phase was completely eliminated from b matrix due to deformation- induced transformation at 8508C. The microstructure of specimens compressed at 8508C and strain rates of 0.001 and 0.1 s-1showed the serration of beta grain boundaries, whereas partial dynamic recrystallization caused a necklace structure by increasing strain rate up to 1 s-1. The specimen deformed at 7008C and strain rate of 1 s-1was located in the instability region and localized shear bands formed due to the low thermal conductivity of the alloy. The processing map of the alloy exhibited a peak efficiency domain of 54% in the temperature range of 780-8108C and strain rates of 0.001- 0.008 s-1. The hot deformation activation energy of the alloy in the α/β region (305.5 kJ mol-1) was higher than that in the single-phase β region (165.2 kJ mol-1) due to the dynamic globularization of the lamellar a phase.

Elastic strains of quartz inclusions and microstructures from pressure solution in garnet reveal orientation and low magnitude of differential stress during subduction metamorphism

2021 ◽  
Author(s):  
Hugo van Schrojenstein Lantman ◽  
David Wallis ◽  
Mattia Gilio ◽  
Marco Scambelluri ◽  
Matteo Alvaro
Keyword(s):  
Microstructural Analysis ◽  
Strain Analysis ◽  
Fluid Phase ◽  
Mineral Dissolution ◽  
Ultrahigh Pressure ◽  
Garnet Growth ◽  
Pressure Solution ◽  
Differential Stress ◽  
Aspect Ratios ◽  
Elastic Strains

&lt;p&gt;Determining the stress state during metamorphism is a key challenge in metamorphic petrology as the effect of differential stress on metamorphic reactions is currently debated. Conventional piezometry generally gives stresses that correspond to overprinting deformation rather than to mineral growth of high-grade metamorphism, so an alternative approach is required. Garnetite lenses from the ultrahigh-pressure, low-temperature metamorphic Lago di Cignana unit (Western Alps, Italy) record compaction by a high degree of mineral dissolution in the fluid-rich environment of a cold subduction zone. This work combines microstructural analysis of deformed garnet with elastic strains of quartz inclusions to study the stresses in these metasedimentary rocks.&lt;/p&gt;&lt;p&gt;Garnet exhibits abundant evidence for incongruent pressure solution (IPS), most notably as truncated zones that mismatch across grain boundaries, interlocking structures, and shape-preferred orientation (SPO). The gap in garnet compositions represented by overgrown truncated zonation corresponds to undeformed garnet with inclusions of quartz and coesite, indicating that IPS operated during prograde to peak metamorphism. The distribution of aspect ratios in the garnet grain population suggests that pressure solution preferentially affected smaller grains. SPO analysis of many subregions across a garnetite sample reveals a complex distribution, however the local SPO is consistent with the stress orientation expected for local microstructures such as layering, garnet stacks, or fine-grained internal fluid pathways. Locally, two different preferential orientations are observed, interpreted as the result of two subsequent deformation stages under different stress configurations.&lt;/p&gt;&lt;p&gt;Quartz inclusions in prograde euhedral garnet, grown on the outer margin of coevally deformed garnetite, were analysed with Raman spectroscopy. Elastic strains obtained for these inclusions are in agreement with predicted strains for entrapment along the prograde &lt;em&gt;P&lt;/em&gt;-&lt;em&gt;T&lt;/em&gt; path for the Lago di Cignana unit (~1.5&amp;#8211;2.0 GPa; ~450&amp;#8211;500 &amp;#176;C), whereas significant differential stress during entrapment is expected to result in deviating strain components.&lt;/p&gt;&lt;p&gt;By combining microstructural analysis of garnet with elastic-strain analysis of quartz inclusions, stress orientations obtained from deformed garnet are combined with the stress magnitude for coeval garnet growth. The results indicate that the garnetite lenses were deformed and metamorphosed under low differential stress of variable orientation during subduction. These results are in agreement with a system where garnet is wet by a fluid phase that allows IPS.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgements: This project has received funding from the European Research Council under the H2020 research and innovation program (N. 714936 TRUE DEPTHS to M. Alvaro)&lt;/p&gt;

scholarly journals Erebus Glacier Tongue, Mcmurdo Sound, Antarctica

1974 ◽  
Vol 13 (67) ◽  
pp. 27-35 ◽  
Author(s):  
G. Holdsworth
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Shear Strain ◽  
Longitudinal Strain ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
Mcmurdo Sound ◽  
Glacier Tongue ◽  
The Past ◽  
Image Position

Examination of the past and present behaviour of the Erebus Glacier tongue over the last 60 years indicates that a major calving from the tongue appears to be imminent. Calculations of the regime of the tongue indicate that bottom melt rates may exceed 1 m a−1. By successive mapping of the ice tongue between the years 1947 and 1970, longitudinal strain-rates were determined using the change in distance between a set of 15 teeth, which are a prominent marginal feature of the tongue. Assuming a flow law for ice of the form where τ is the effective shear stress and is the effective shear strain-rate, values of the exponent n = 3 and B = 1 × 108 N m−2 are determined. These are in fair agreement with published values.

Sign in / Sign up

Export Citation Format

Share Document