scholarly journals Kinematics of the Central Alpine Fault Mylonite  Zone, Tatare Stream, South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Benjamin G Gillam
Keyword(s):  
Shear Band ◽  
Shear Strain ◽  
Shear Zone ◽  
Late Cenozoic ◽  
Finite Shear ◽  
Alpine Fault ◽  
Mylonite Zone ◽  
The Pacific ◽  
Ductile Shearing ◽  
The Mean

<p>The hanging wall of the Alpine Fault (AF) near Franz Josef Glacier has been exhumed during the past ~3 m. y. providing a sample of the ductilely deformed middle crust via obliquereverse slip on the AF. The former middle crust of the Pacific Plate occurs as an eastward-tilted slab that has been upramped from depths of ~25–35 km. A mylonitic high strain zone abuts the eastern edge of the AF in Tatare Stream. This ductile shear zone is locally ~2 km thick. The Tatare Stream locality is remarkable along the AF in the Central Southern Alps for the apparent lack of near surface segmentation of the fault there; instead its mylonitic shear zone appears uniformly inclined by ~63° to the SE. I infer this foliation is parallel to the shear zone boundary (SZB). In the distal part of the mylonite zone in extensional C' shear bands cross-cut the older non-mylonitic Alpine foliation (S3), and deflect that pre-existing fabric in a dextral-reverse sense. Based on the attitude of these shears the ductile shearing direction in the Alpine mylonite zone (AMZ) during extensional shear band activity is inferred to have trended 090 ± 6° (2σ), which is ~20° clockwise of sea floor spreading based estimates for the azimuth of the Pacific Plate motion. This indicates that slip on this central part of the AF is not fully “unpartitioned”. Measurements of the mean spacing, per-shear offset, C’ orientation, and per-shear thickness on >1000 extensional C’ shears provides perhaps the largest field-based data set of extensional shear band geometrical parameters so far compiled for a natural shear zone. The mean spacing between C’ shears decreases towards the AF from ~6 cm to ~0.2 cm. The per-shear offsets (8.2 ± 5 mm 1σ) and thickness (128 ± 20 1σ) of the extensional shears remains consistent despite a finite shear strain gradient. Using shear offset data I calculate a bulk finite shear strain accommodated by slip on C’ shears of 0.4 ± 0.3 (1σ), and a mean intra-shear band (C’ local) finite shear strain of 12.6 ± 5.4 (1σ). Consistency in the intra-shear band finite shear strain throughout the mylonite zone, together with increased C’ density implies that the quartzose rocks have behaved with a strain hardening rheology as the shears evolved. The dominant C’ (synthetic) extensional shears are disposed at a mean dihedral angle of 30° ± 2.2 (2σ), whereas the C’’ (antithetic) shears are 135 ± 3° (2σ) to the foliation (SZB). The C’ and C’’ shears appear to lie approximately parallel to planes of maximum instantaneous shear strain rate from which I obtain an estimate for Wk of 0.5 for the AMZ. I have measured the geometrical orientation of Mesozoic Alpine Schist garnet inclusion trails and tracked these pre-mylonitic age porphyroblastic garnets through the distal and main mylonite zones to determine their rotational response to late Cenozoic shearing. Electron microprobe analysis indicates that all the garnets examined in Tatare Stream are prograde from the regional (M2) Barrovian metamorphism. The mean inclusion trail orientations in the distal mylonite zone have been forward rotated by 35° relative to their equivalent orientation in the adjacent, less deformed non-mylonitic Alpine Schist. This rotation is synthetic to the dextralreverse shear of the AF zone. The rotation of approximately spherical shaped garnet porphyroblasts in the distal mylonite implies a finite shear strain of 1.2 in that zone. In the main part of the mylonite zone an additional forward rotation of 46° implies a finite shear strain there of 2.8. The inclusion trail rotational axis measured trends approximately perpendicular to the shear direction and parallel to the inferred late Cenozoic vorticity vector of ductile shearing. Using GhoshFlow, a program for simulating rotation of rigid passive objects in plane strain general shear a new kinematic vorticity number (Wn) estimate of 0.5 – 0.7 is established for the AMZ. The transition zone between the distal mylonite and the main mylonite zone, though little described in the literature, is well exposed in Tatare Stream. A distinct quartz rodding lineation, inherited from the non-mylonitic schist as an object into the mylonite zone, is distorted in the plane of the foliation across the transition from SW plunges to NE plunges. Because the foliation plane is here parallel to the SZB and by special reference to strongly curved lineation traces I have been able to isolate the pure shear component of deformation considering a simple 2D deformation on that slip plane; by modeling the distortional reorientation of inherited lineations in that plane. The direction of maximum finite elongation that I calculate in this plane trends 89 ± 3.8° (2σ). I believe this records the finite strain related to the co-axial component only. The parallelism of the previously calculated mylonitic ductile shearing direction to this stretching direction (also trending 090) indicates that the late Cenozoic ductile flow path in the central AMZ has been approximately monoclinic. I estimate a Wn of 0.8 ± 0.06 (2σ) based on the observed finite shearing in the mylonite zone (garnet rotation) and on the co-axial strain observed deforming the inherited lineations.</p>

scholarly journals Kinematics of the Central Alpine Fault Mylonite  Zone, Tatare Stream, South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Benjamin G Gillam
Keyword(s):  
Shear Band ◽  
Shear Strain ◽  
Shear Zone ◽  
Late Cenozoic ◽  
Finite Shear ◽  
Alpine Fault ◽  
Mylonite Zone ◽  
The Pacific ◽  
Ductile Shearing ◽  
The Mean

<p>The hanging wall of the Alpine Fault (AF) near Franz Josef Glacier has been exhumed during the past ~3 m. y. providing a sample of the ductilely deformed middle crust via obliquereverse slip on the AF. The former middle crust of the Pacific Plate occurs as an eastward-tilted slab that has been upramped from depths of ~25–35 km. A mylonitic high strain zone abuts the eastern edge of the AF in Tatare Stream. This ductile shear zone is locally ~2 km thick. The Tatare Stream locality is remarkable along the AF in the Central Southern Alps for the apparent lack of near surface segmentation of the fault there; instead its mylonitic shear zone appears uniformly inclined by ~63° to the SE. I infer this foliation is parallel to the shear zone boundary (SZB). In the distal part of the mylonite zone in extensional C' shear bands cross-cut the older non-mylonitic Alpine foliation (S3), and deflect that pre-existing fabric in a dextral-reverse sense. Based on the attitude of these shears the ductile shearing direction in the Alpine mylonite zone (AMZ) during extensional shear band activity is inferred to have trended 090 ± 6° (2σ), which is ~20° clockwise of sea floor spreading based estimates for the azimuth of the Pacific Plate motion. This indicates that slip on this central part of the AF is not fully “unpartitioned”. Measurements of the mean spacing, per-shear offset, C’ orientation, and per-shear thickness on >1000 extensional C’ shears provides perhaps the largest field-based data set of extensional shear band geometrical parameters so far compiled for a natural shear zone. The mean spacing between C’ shears decreases towards the AF from ~6 cm to ~0.2 cm. The per-shear offsets (8.2 ± 5 mm 1σ) and thickness (128 ± 20 1σ) of the extensional shears remains consistent despite a finite shear strain gradient. Using shear offset data I calculate a bulk finite shear strain accommodated by slip on C’ shears of 0.4 ± 0.3 (1σ), and a mean intra-shear band (C’ local) finite shear strain of 12.6 ± 5.4 (1σ). Consistency in the intra-shear band finite shear strain throughout the mylonite zone, together with increased C’ density implies that the quartzose rocks have behaved with a strain hardening rheology as the shears evolved. The dominant C’ (synthetic) extensional shears are disposed at a mean dihedral angle of 30° ± 2.2 (2σ), whereas the C’’ (antithetic) shears are 135 ± 3° (2σ) to the foliation (SZB). The C’ and C’’ shears appear to lie approximately parallel to planes of maximum instantaneous shear strain rate from which I obtain an estimate for Wk of 0.5 for the AMZ. I have measured the geometrical orientation of Mesozoic Alpine Schist garnet inclusion trails and tracked these pre-mylonitic age porphyroblastic garnets through the distal and main mylonite zones to determine their rotational response to late Cenozoic shearing. Electron microprobe analysis indicates that all the garnets examined in Tatare Stream are prograde from the regional (M2) Barrovian metamorphism. The mean inclusion trail orientations in the distal mylonite zone have been forward rotated by 35° relative to their equivalent orientation in the adjacent, less deformed non-mylonitic Alpine Schist. This rotation is synthetic to the dextralreverse shear of the AF zone. The rotation of approximately spherical shaped garnet porphyroblasts in the distal mylonite implies a finite shear strain of 1.2 in that zone. In the main part of the mylonite zone an additional forward rotation of 46° implies a finite shear strain there of 2.8. The inclusion trail rotational axis measured trends approximately perpendicular to the shear direction and parallel to the inferred late Cenozoic vorticity vector of ductile shearing. Using GhoshFlow, a program for simulating rotation of rigid passive objects in plane strain general shear a new kinematic vorticity number (Wn) estimate of 0.5 – 0.7 is established for the AMZ. The transition zone between the distal mylonite and the main mylonite zone, though little described in the literature, is well exposed in Tatare Stream. A distinct quartz rodding lineation, inherited from the non-mylonitic schist as an object into the mylonite zone, is distorted in the plane of the foliation across the transition from SW plunges to NE plunges. Because the foliation plane is here parallel to the SZB and by special reference to strongly curved lineation traces I have been able to isolate the pure shear component of deformation considering a simple 2D deformation on that slip plane; by modeling the distortional reorientation of inherited lineations in that plane. The direction of maximum finite elongation that I calculate in this plane trends 89 ± 3.8° (2σ). I believe this records the finite strain related to the co-axial component only. The parallelism of the previously calculated mylonitic ductile shearing direction to this stretching direction (also trending 090) indicates that the late Cenozoic ductile flow path in the central AMZ has been approximately monoclinic. I estimate a Wn of 0.8 ± 0.06 (2σ) based on the observed finite shearing in the mylonite zone (garnet rotation) and on the co-axial strain observed deforming the inherited lineations.</p>

Interdecadal changes in the interannual variability of the summer temperature over Northeast Asia

2021 ◽  
pp. 1-50
Author(s):  
Ruidan Chen ◽  
Zhiping Wen ◽  
Riyu Lu ◽  
Wenjun Liu
Keyword(s):  
Interannual Variability ◽  
Northeast Asia ◽  
Tropical Indian Ocean ◽  
Summer Temperature ◽  
Atmospheric Variability ◽  
The Pacific ◽  
The Mean ◽  
Southeastern Tropical Indian Ocean ◽  
Interdecadal Changes ◽  
Mean State

AbstractThis study reveals the interdecadal changes in the interannual variability of the summer temperature over Northeast Asia (NEA), which presents an enhancement around the early 1990s and a reduction after the mid-2000s. The stronger NEA temperature variability after the early 1990s is favored by the enhanced influence of the Pacific–Japan (PJ) teleconnection, which is remotely modulated by the southeastern tropical Indian Ocean (SETIO). After the early 1990s, the mean state over the SETIO presents relatively warmer SST and ascending motion, favoring a good relationship between the local SST and convection. Therefore, the SETIO SST could prominently influence the local convection and subsequently modulate the convection over the western North Pacific (WNP) via a cross-equatorial overturning circulation. The abnormal convection over the WNP further triggers the PJ teleconnection to influence NEA. However, these ocean–atmosphere processes disappear before the early 1990s. In this period, the mean state over the SETIO features relatively colder SST and subsiding motion, accompanied by a poor relationship between the local SST and convection. Therefore, the variability of convection over the SETIO is weak, thus the atmospheric variability over the WNP is also weakened and the PJ teleconnection presents a different distribution that could not influence NEA. The reduced variability of NEA temperature after the mid-2000s is related to the feeble influence of the PJ teleconnection and the reduced variability of the SETIO SST, which is modulated by the SST over the tropical central–eastern Pacific during the preceding winter to spring.

scholarly journals Insights into Machining of a β Titanium Biomedical Alloy from Chip Microstructures

Metals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 710 ◽  
Author(s):  
Damon Kent ◽  
Rizwan Rahman Rashid ◽  
Michael Bermingham ◽  
Hooyar Attar ◽  
Shoujin Sun ◽  
...  
Keyword(s):  
Shear Band ◽  
Shear Zone ◽  
Biomechanical Properties ◽  
Temperature Fields ◽  
Large Strains ◽  
Shear Direction ◽  
Grain Sizes ◽  
Β Phase ◽  
Secondary Shear Zone ◽  
Cutting Speeds

New metastable β titanium alloys are receiving increasing attention due to their excellent biomechanical properties and machinability is critical to their uptake. In this study, machining chip microstructure has been investigated to gain an understanding of strain and temperature fields during cutting. For higher cutting speeds, ≥60 m/min, the chips have segmented morphologies characterised by a serrated appearance. High levels of strain in the primary shear zone promote formation of expanded shear band regions between segments which exhibit intensive refinement of the β phase down to grain sizes below 100 nm. The presence of both α and β phases across the expanded shear band suggests that temperatures during cutting are in the range of 400–600 °C. For the secondary shear zone, very large strains at the cutting interface result in heavily refined and approximately equiaxed nanocrystalline β grains with sizes around 20–50 nm, while further from the interface the β grains become highly elongated in the shear direction. An absence of the α phase in the region immediately adjacent to the cutting interface indicates recrystallization during cutting and temperatures in excess of the 720 °C β transus temperature.

scholarly journals Fishing effects on elasmobranchs from the Pacific Coast of Colombia

2016 ◽  
Vol 21 (1) ◽  
pp. 9 ◽  
Author(s):  
Andrés Felipe Navia ◽  
Paola Andrea Mejía-Falla
Keyword(s):  
Species Composition ◽  
Pacific Coast ◽  
Trophic Levels ◽  
Functional Level ◽  
The Pacific ◽  
The Mean ◽  
The Stability ◽  
Large Predators ◽  
Average Catch ◽  
Index Of Diversity

<p>During 1995, 2001, 2003, 2004 and 2007; we studied the temporal variation in the structure of the elasmobranch assemblage along the Colombian Pacific coast using: the community index of diversity, heterogeneity, equitability, species composition, average catch sizes, and mean trophic levels. A total of 1 711 specimens from 19 species<br />(7 sharks and 12 rays) were collected during the 90 trawling operations. The number of species captured varied between 7 (1995) and 12 (2007) demonstrating a trend towards an imbalance in the assemblage attributes. In 1995, the mean trophic level (TLm) of the assemblage was 3.60, but in 2007 it decreased to 3.55 when the functional level of large predators was absent (TL ≥ 4). These results suggest changes in species composition, structural attributes, and a reduction of the highest functional level. Alterations to the catch proportions were also found: i.e. a greater abundance of rays of lower trophic levels. This study suggests an effect of trawling on the stability of this tropical coastal ecosystem.</p>

scholarly journals Effect of Red tilapia (Oreochromis mossambicus × Oreochromis niloticus) on growth and survival of the pacific shrimp (Litopenaeus vannamei) in simultaneous polyculture under marine conditions//Efecto de la tilapia roja (Oreochromis mossambicus × Oreochromis niloticus) en el crecimiento y supervivencia del camarón (Litopenaeus vannamei) en policultivo simultáneo bajo condiciones marinas

Biotecnia ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 5-12
Author(s):  
Alejandro Mcdonal-Vera ◽  
Wilfrido M. Contreras-Sánchez ◽  
Neil J. Duncan ◽  
Kevin Fitzsimmons ◽  
Maria J. Contreras- García ◽  
...  
Keyword(s):  
Litopenaeus Vannamei ◽  
Oreochromis Niloticus ◽  
Oreochromis Mossambicus ◽  
Pacific White Shrimp ◽  
White Shrimp ◽  
Average Weight ◽  
Growth And Survival ◽  
Red Tilapia ◽  
The Pacific ◽  
The Mean

In the present investigation, we evaluated if the presence of tilapia affects growth and survival of shrimp during pre-growth and grow-out phases. In both experiments, we used a random-blocks design in a single earth pond (0.75 ha) that was prepared and divided into nine (7 x 30 m) enclosures that were considered to be three blocks of three enclosures each. Each randomly stocked block consisted on Pacific white shrimp Litopenaeus vannamei (30 shrimp/m2) and three different densities (0.0, 0.25 and 0.50 fish/m2) of red tilapia hybrids (Oreochromis mossambicus x Oreochromis niloticus) to give three different treatments with three replicates. The results from the pre-growth and grow-out experiments followed the same trend. In both cases, we found no significant statistical differences (P>0.05) in the final average weight of the shrimp. However, the experimental blocks had a significant (P<0.05) effect on the mean sample weight of shrimp. Shrimp in blocks B and C were significantly bigger than shrimp from block A (P<0.05). For both experiments, we found no effect of the presence of tilapias on survival or growth of shrimp.RESUMENEvaluamos si la presencia de tilapias libres afecta el crecimiento y la supervivencia de camarones en fase de preengorda y engorda. Para ambos experimentos, utilizamos un diseño de bloques al azar en un estanque rústico (0.75 ha) que fue preparado y dividido en nueve encierros (7 x 30 m), se formaron tres bloques con tres encierros cada uno. Cada encierro dentro de cada bloque fue aleatoriamente seleccionado para sembrar camarón blanco del Pacífico, Litopenaeus vannamei (30 camarones/m2) y tres diferentes densidades (0.0, 0.25 y 0.50 peces/m2) de híbrido de tilapia roja (Oreochromis mossambicus x Oreochromis niloticus) para formar tres tratamientos con tres réplicas. Los resultados del experimento de pre-engorda y engorda siguieron la misma tendencia. En ambos experimentos no encontramos diferencias estadísticamente en el crecimiento de los camarones ni en las tilapias. Sin embargo, los bloques experimentales presentaron diferencias significativas (P<0.05) en el peso promedio final. Los camarones de los bloques B y C fueron estadísticamente más grandes (P<0.05) que los del bloque A. Para las dos etapas de crecimiento de los camarones, no se observó un efecto de la presencia de tilapias sobre la sobrevivencia o crecimiento de los camarones.

scholarly journals Relations between Annular Modes and the Mean State: Southern Hemisphere Winter

2007 ◽  
Vol 64 (9) ◽  
pp. 3328-3339 ◽  
Author(s):  
Francis Codron
Keyword(s):  
Southern Hemisphere ◽  
Low Frequency ◽  
Stationary Waves ◽  
Annular Modes ◽  
The Pacific ◽  
Latitudinal Shift ◽  
The Indian Ocean ◽  
The Mean ◽  
Hemisphere Winter ◽  
Mean State

Abstract In a zonally symmetric climatology with a single eddy-driven jet, such as prevails in the Southern Hemisphere summer, the midlatitude variability is dominated by fluctuations of the jet around its mean position, as described by the Southern Hemisphere annular mode (SAM). To study whether this result holds for a zonally asymmetric climatology, the observed variability of the Southern Hemisphere winter is analyzed. The mean state in this case is characterized by relatively weak stationary waves; yet there exist significant zonal variations in the mean strength and meridional structure of the subtropical jet stream. As in summer, the winter SAM signature is annular in shape and the corresponding wind anomalies are dipolar; but it is associated with two different behaviors of the eddy-driven jet in different longitudinal ranges. Over the Indian Ocean, the SAM is associated primarily with a latitudinal shift of the jet around its mean position. Over the Pacific sector, it is instead characterized by a seesaw in the wind speed between two distinct latitudes, corresponding to the positions of the midlatitude and subtropical jets. Composites of eddy forcing and baroclinicity over both sectors appear consistent with the two different behaviors. As in the zonal-mean case, high-frequency eddies both force and maintain the low-frequency wind anomalies associated with the SAM. The positive feedback by eddies is, however, not local: changes in the eddy forcing are influenced most strongly by zonal wind anomalies located upstream.

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