Extreme ductile deformation of fine-grained salt by coupled solution-precipitation creep and microcracking: Microstructural evidence from perennial Zechstein sequence (Neuhof salt mine, Germany)

2012 ◽  
Vol 37 ◽  
pp. 89-104 ◽  
Author(s):  
Prokop Závada ◽  
Guillaume Desbois ◽  
Alexander Schwedt ◽  
Ondrej Lexa ◽  
Janos L. Urai
Keyword(s):  
Ductile Deformation ◽  
Salt Mine ◽  
Fine Grained ◽  
Coupled Solution

Use of pyrite microfabric as a key to tectono-thermal evolution of massive sulphide deposits – an example from Deri, southern Rajasthan, India

1998 ◽  
Vol 62 (2) ◽  
pp. 197-212 ◽  
Author(s):  
Anju Tiwary ◽  
Mihir Deb ◽  
Nigel J. Cook
Keyword(s):  
Thermal Evolution ◽  
Regional Metamorphism ◽  
Massive Sulphide ◽  
Ductile Deformation ◽  
Sulphide Deposit ◽  
Fine Grained ◽  
Thermal Metamorphism ◽  
Sulphide Ores ◽  
History Of ◽  
South Delhi Fold Belt

AbstractPyrite is an ubiquitous constituent of the Proterozoic massive sulphide deposit at Deri, in the South Delhi Fold Belt of southern Rajasthan. Preserved pyrite microfabrics in the Zn-Pb-Cu sulphide ores of Deri reveal a polyphase growth history of the iron sulphide and enable the tectono-thermal evolution of the deposit to be reconstructed.Primary sedimentary features in Deri pyrites are preserved as compositional banding. Regional metamorphism from mid-greenschist to low amphibolite facies is recorded by various microtextures of pyrite. Trails of fine grained pyrite inclusions within hornblende porphyroblasts define S1-schistosity. Pyrite boudins aligned parallel to S1 mark the brittle–ductile transformation of pyrite during the earliest deformation in the region. Isoclinal to tight folds (F1 and F2) in pyrite layers relate to a ductile deformation stage during progressive regional metamorphism. Peak metamorphic conditions around 550°C, an estimation supported by garnet–biotite thermometry, resulted in annealing of pyrite grains, while porphyroblastic growth of pyrite (up to 900 µm) took place along the retrogressive path. Brittle deformation of pyrite and growth of irregular pyritic mass around such fractured porphyroblasts characterize the waning phase of regional metamorphism. A subsequent phase of stress-free, thermal metamorphism is recorded in the decussate and rosette textures of arsenopyrite prisms replacing irregular pyritic mass. Annealing of such patchy pyrite provides information regarding the temperature conditions during this episode of thermal metamorphism which is consistent with the hornblendehornfels facies metamorphism interpreted from magnetite–ilmenite geothermometry (550°C) and sphalerite geobarometry (3.5 kbar). A mild cataclastic deformation during the penultimate phase produced microfaults in twinned arsenopyrite prisms.

Kosmochlor and chromian jadeite aggregates from the Myanmar jadeitite area

2005 ◽  
Vol 69 (6) ◽  
pp. 1059-1075 ◽  
Author(s):  
G. H. Shi ◽  
B. Stöckhert ◽  
W. Y. Cui
Keyword(s):  
Ductile Deformation ◽  
Coarse Grained ◽  
Variable Composition ◽  
Dislocation Creep ◽  
Minimum Pressure ◽  
Fine Grained ◽  
Terrestrial Rock ◽  
Miscibility Gaps ◽  
Creep Regime

AbstractFour distinct textures and related compositions of kosmochlor (Ko) and chromian jadeite in rocks from the Myanmar jadeitite area are described: (1) spheroidal or ellipsoidal aggregates with a corona texture surrounding relict chromite; (2) spheroidal or ellipsoidal aggregates with a core of jadeite; (3) granoblastic textures in undeformed coarse-grained clinopyroxene rocks; and (4) recrystallized fine-grained aggregates in deformed jadeitite. Nearly pure kosmochlor (97 mol.% NaCrSi2O6) was found in type 2 textures, closest to the end-member reported so far from a terrestrial rock. Sharp compositional boundaries between kosmochlor and chromian jadeite of variable composition are interpreted to be related to progressive crystallization or replacement at differing conditions. The compositions analysed plot along the kosmochlor-jadeite join. In contrast to conclusions of previous studies on the Myanmar clinopyroxenes there is no unequivocal evidence for miscibility gaps. The preservation of relict chromite in the centre of coronitic spheroidal or ellipsoidal aggregates of kosmochlor and jadeite indicates a metasomatic origin from a peridotite protolith at an inferred minimum pressure of 1.0 GPa and temperatures of 250—370°C. Recrystallization during later ductile deformation of the clinopyroxene rocks in the dislocation creep regime leads to fine-grained aggregates of chromian jadeite, which are of particular gemmological interest.

Direct observations of a dynamic earthquake rupture in the lower crust

2020 ◽  
Author(s):  
Arianne Petley-Ragan ◽  
Yehuda Ben-Zion ◽  
Håkon Austrheim ◽  
Benoit Ildefonse ◽  
Francois Renard
Keyword(s):  
Lower Crust ◽  
Damage Zone ◽  
Granulite Facies ◽  
Wall Rock ◽  
Ductile Deformation ◽  
Fine Grained ◽  
Seismic Slip ◽  
Sequence Of Events ◽  
Shear Rupture ◽  
Brittle Faulting

<p>A significant number of studies in recent years have demonstrated that earthquakes in the lower crust are more abundant than previously thought. Specifically in continental collision zones, earthquakes are suggested to play a crucial role in permitting fluid infiltration and driving metamorphic transformation processes in crustal portions that are typically considered dry and metastable. However, the mechanisms that trigger brittle failure in the lower crust remain debated and the sequence of events that ultimately lead to seismic slip is unclear. To further understand this process we performed field and microstructural observations on an amphibolite facies fault (0.9-1 GPa) in granulite facies anorthosite from the Bergen Arcs, Western Norway. The fault preserves an exceptional record of brittle deformation and frictional melting that allows us to constrain the temporal sequence of deformation events. Most notably, the fault is flanked on one side by a damage zone where wall rock minerals are fragmented with little to no shear strain (pulverization). The fault core consists of a zoned pseudotachylyte bound on both sides by fine-grained cataclasites. Spatial relationships between these structures reveal that asymmetric pulverization of the wall rock and comminution preceded the seismic slip required to produce melting. These observations are consistent with the propagation of a dynamic shear rupture. Our study implies that high differential stress levels may exist within the dry lower crust of orogens, causing brittle faulting and earthquakes in a portion of the crust that has long been assumed to be characterized by ductile deformation.</p>

Stress variations in space and time within the mantle section of an oceanic transform zone: Evidence for the seismic cycle

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 569-573 ◽  
Author(s):  
Vasileios Chatzaras ◽  
Basil Tikoff ◽  
Seth C. Kruckenberg ◽  
Sarah J. Titus ◽  
Christian Teyssier ◽  
...  
Keyword(s):  
New Caledonia ◽  
Stress Gradient ◽  
Oceanic Lithosphere ◽  
Temporal Variations ◽  
Ductile Deformation ◽  
Seismic Cycle ◽  
Fine Grained ◽  
Transform Zone ◽  
Stress Variations ◽  
Mantle Section

Abstract The Bogota Peninsula shear zone in New Caledonia (southwest Pacific Ocean) is the exhumed mantle section of an oceanic transform zone. Ductile fabrics in this zone formed at temperatures >820 °C, and differential stresses estimated from microstructures vary spatially and temporally. Along a transform-perpendicular transect, stresses increase toward the high-strain areas. We attribute this stress gradient to an increase in strain rate caused by imposed rather than intrinsic strain localization. Temporal stress variations are indicated by the formation of fine-grained microdeformation zones (MDZs) that truncate and offset coarser grains. We interpret the MDZs to result from zones of brittle deformation caused by earthquake fracture propagation downward in the upper mantle, which are in turn overprinted by ductile deformation at stresses 2–6 times higher (22–81 MPa) than their surrounding steady-state fabrics. We interpret the spatial and temporal variations in microstructures and stresses as reflecting different stages of the seismic cycle in oceanic lithosphere.

Mid-Cretaceous ductile deformation on the Eastern Palmer Land Shear Zone, Antarctica, and implications for timing of Mesozoic terrane collision

2002 ◽  
Vol 139 (4) ◽  
pp. 465-471 ◽  
Author(s):  
ALAN P. M. VAUGHAN ◽  
SIMON P. KELLEY ◽  
BRYAN C. STOREY
Keyword(s):  
Shear Zone ◽  
Antarctic Peninsula ◽  
Early Cretaceous ◽  
Lower Jurassic ◽  
Ductile Deformation ◽  
Fine Grained ◽  
Form Part ◽  
Tectonic Boundary ◽  
The Antarctic ◽  
Reverse Deformation

Ar–Ar dating of high-strain ductile mylonites of the Eastern Palmer Land Shear Zone in the southern Antarctic Peninsula indicates that reverse movement on the shear zone occurred in late Early Cretaceous times (Albian), and not latest Jurassic times as previously supposed. The Eastern Palmer Land Shear Zone forms a major tectonic boundary, separating suspect arc terranes from rocks of Gondwana continental affinity. The dated mylonites are developed in Lower Jurassic plutonic rocks at Mount Sullivan, eastern Palmer Land, and form part of a zone of ductile reverse deformation up to 25 km wide. Biotite from a fine-grained mafic mylonite yields an Ar–Ar cooling age of 102.8±3.3 Ma. Movement of this age on the Eastern Palmer Land Shear Zone is coeval with circum-Pacific deformation, possibly related to a mantle superplume event, and provides support for allochthonous-terrane models for the Antarctic Peninsula with accretion in post-Early Cretaceous times.

"Sudbury Breccia" at Whitefish Falls, Ontario: evidence for an impact origin

2002 ◽  
Vol 39 (6) ◽  
pp. 971-982 ◽  
Author(s):  
Andrew C Parmenter ◽  
Christopher B Lee ◽  
Mario Coniglio
Keyword(s):  
Host Rock ◽  
High Strain ◽  
Ductile Deformation ◽  
Impact Event ◽  
Fine Grained ◽  
Sudbury Igneous Complex ◽  
Matrix Rock ◽  
Penetrative Foliation ◽  
Impact Origin ◽  
East West

Sudbury breccias are unusual clast–matrix rock bodies formed in abundance around the Sudbury Igneous Complex, the most obvious manifestation of a major impact event at Sudbury. At Whitefish Falls, ~70 km southwest of Sudbury, similar breccias consisting of clasts of argillite and amphibolite dyke enclosed in a fine-grained matrix of host rock are developed in metamorphosed argillites of the Huronian Supergroup. Pre-brecciation brittle textures in the host argillite and breccia clasts, such as layer-parallel foliation offset by cataclastic fractures, suggest that the host rock was entirely competent prior to brecciation. One composite penetrative foliation and its associated ductile folding were also formed in the argillite host prior to brecciation. Post-brecciation ductile deformation produced a regionally dominant east–west-trending foliation, and two late-stage folding events, and indicate a syn-Penokean age of brecciation. The breccias at Whitefish Falls are enriched in ferromagnesian minerals compared to adjacent, embayed and partially digested, host rock. Flow-foliated breccia matrices surround a highly rounded clast phase. These features are characteristic of impact-related pseudotachylyte, formed during extreme cataclasis and friction melting of the impacted host rock. We propose that these breccias formed by injection of a high-strain, pseudotachylytic melt, triggered by the Sudbury impact event, and focused along a blind superfault, coincident with a post-Penokean high-strain zone.

Sulphide mylonites from the Renström VMS deposit, Northern Sweden

1993 ◽  
Vol 57 (386) ◽  
pp. 83-91 ◽  
Author(s):  
Rowena C. Duckworth ◽  
David Rickard
Keyword(s):  
Massive Sulphide ◽  
Ductile Deformation ◽  
Metamorphic Event ◽  
Pressure Solution ◽  
Northern Sweden ◽  
Sulphide Minerals ◽  
Fine Grained ◽  
Sulphide Ore ◽  
Sulphide Ores ◽  
Textural Evidence

AbstractSulphide mylonites are fine-grained massive sulphides which have deformed in a plastic manner. In the Renström Zn-Pb-Cu-Ag-Au VMS deposit, one of several operating mines in the Early Proterozoic Skellefte District in Northern Sweden, shear-zone metamorphism has resulted in the development of mylonitic fabrics within the sulphides. The massive sulphide ore is hosted in a shallow submarine to subaerial volcano-sedimentary sequence which has been variably metamorphosed and deformed. Initially, the sequence underwent burial metamorphism which was followed by an amphibolite grade regional metamorphic event at pressures of around 7.5 kbar and temperatures of 540-600°C This has been overprinted by a retrogressive metamorphic event at greenschist facies (at ca. 400°C with concomitant ductile deformation. Finally the area was uplifted to shallower crustal levels with associated cataclastic deformation.Both the regional and dynamic metamorphic events have resulted in the development of specific textures in the sulphide ores. Textural evidence indicates that pressure solution has been mainly responsible for the plastic deformation in pyrite, while the weaker sulphide minerals such as pyrrhotite, chalcopyrite and galena have generally recrystallised in response to the high strains.Sulphide mylonites are probably common rocks in many polydeformed massive sulphide deposits like Renström. They may have previously been misinterpreted as primary depositional textures.

Chemical and boron isotopic variations of deformed tourmaline in the Laojunshan metamorphic dome, Southwest China: Implication for magmatic-hydrothermal evolution during exhumation

2021 ◽  
Author(s):  
Wei Li ◽  
Shuyun Cao ◽  
Eizo Nakamura ◽  
Tsutomu Ota ◽  
Tak Kunihiro ◽  
...  
Keyword(s):  
Southwest China ◽  
Structural Evolution ◽  
Potassium Feldspar ◽  
Ductile Deformation ◽  
Brittle Deformation ◽  
Great Opportunity ◽  
Fine Grained ◽  
Multi Stage ◽  
Isotopic Variations ◽  
Hydrothermal Veins

<p>Multi-stage tourmalines are widely developed in granitic gneisses and hydrothermal veins from the Laojunshan metamorphic dome, Southwest China. These tourmalines exhibit variable petrographic characteristics and microstructures by ductile deformation to brittle deformation, which offers a great opportunity to understand the fluid and structural evolution during exhumation of the Laojunshan metamorphic dome. Three types of tourmalines have been recognized, including disseminated tourmaline distributed in granitic gneisses (Tur-G), elongated and broken tourmalines in quartz veins (Tur-QV), needle-columnar and fine-grained tourmaline with micro-shear zone in tourmaline veins (Tur-TV). All the tourmalines belong to the alkali group representing dravite-schorl solid solution series. The former two types belong to schorl and the latte type contains more Mg-rich components. Models of occurrence and chemical varieties including Al-occupation at the Y-site suggest that the Tur-G type and Tur-QV type tourmalines crystallized from magmatic fluids and the Tur-TV type tourmalines are hydrothermal origin. Hydrothermal tourmalines are characterized by higher Mg/(Mg + Fe) ratios, more pronounced positive Eu anomalies, higher Li, Sr, HREE contents and lower Na/(Na + Ca) ratios, lower Nb, Zr, Hf, LREE contents compared with magmatic tourmalines. The increase of Mg/(Mg+Fe) ratios from the Tur-QV to Tur-TV type tourmalines is associated with the crystallization of Fe-rich mineral during hydrothermal stage. In the Tur-QV types, the decrease of Mg/(Mg+Fe) ratios and increase of Al and LREE contents from core to rim suggest the contamination from surrounding strata. The δ<sup>11</sup>B values of Tur-G, Tur-QV, Tur-TV type tourmalines are ranging from -13~-7.9‰, -15.5~-7.5‰, -18.6~-11.6‰ respectively, which suggests that the boron was mainly derived from granitic melt and exsolved hydrothermal fluid. Boron isotopic variations of tourmaline are mainly controlled by temperature and exsolved fluid. All the results of observations from outcrop to thin section scales and chemical analysis indicate the formation of disseminated tourmaline distributed in granitic gneisses (Tur-G) should have been associated with late stage of magma evolution before regional exhumation, while tourmalines in hydrothermal veins (Tur-QV and Tur-TV) have been formed by the magmatic-hydrothermal events during exhumation of Laojunshan metamorphic dome. The primary tourmalines experienced shearing and fracturing, and then were replaced by chlorite, potassium feldspar and epidote. The ductile-brittle deformation of tourmalines was produced by progressive strain localization accompanied by the alkaline, B-undersaturated fluids, indicating episodes of brittle fracturing, possibly as a consequence of faulting at depths and subsequent fluid flow during exhumation of the dome.</p>

Application of an image management system in microscopy

1992 ◽  
Vol 50 (2) ◽  
pp. 1052-1053
Author(s):  
Richard S. Chemock
Keyword(s):  
Data Storage ◽  
Cost Savings ◽  
Image Data ◽  
Analytical Techniques ◽  
Operational Mode ◽  
Fine Grained ◽  
Image Recording ◽  
Primary Output ◽  
Capacity Data ◽  
Image Management System

One of the most common tasks in a typical analysis lab is the recording of images. Many analytical techniques (TEM, SEM, and metallography for example) produce images as their primary output. Until recently, the most common method of recording images was by using film. Current PS/2R systems offer very large capacity data storage devices and high resolution displays, making it practical to work with analytical images on PS/2s, thereby sidestepping the traditional film and darkroom steps. This change in operational mode offers many benefits: cost savings, throughput, archiving and searching capabilities as well as direct incorporation of the image data into reports.The conventional way to record images involves film, either sheet film (with its associated wet chemistry) for TEM or PolaroidR film for SEM and light microscopy. Although film is inconvenient, it does have the highest quality of all available image recording techniques. The fine grained film used for TEM has a resolution that would exceed a 4096x4096x16 bit digital image.

Use of fractals to describe microstructures of porous thick-film platinum electrodes

1992 ◽  
Vol 50 (1) ◽  
pp. 314-315
Author(s):  
Steven D. Toteda
Keyword(s):  
Fractal Dimension ◽  
Power Plants ◽  
Electrical Response ◽  
Cubic Phase ◽  
Platinum Electrodes ◽  
Fine Grained ◽  
Impedance Response ◽  
Platinum Particles ◽  
Energy Surfaces ◽  
Highly Porous

Zirconia oxygen sensors, in such applications as power plants and automobiles, generally utilize platinum electrodes for the catalytic reaction of dissociating O2 at the surface. The microstructure of the platinum electrode defines the resulting electrical response. The electrode must be porous enough to allow the oxygen to reach the zirconia surface while still remaining electrically continuous. At low sintering temperatures, the platinum is highly porous and fine grained. The platinum particles sinter together as the firing temperatures are increased. As the sintering temperatures are raised even further, the surface of the platinum begins to facet with lower energy surfaces. These microstructural changes can be seen in Figures 1 and 2, but the goal of the work is to characterize the microstructure by its fractal dimension and then relate the fractal dimension to the electrical response. The sensors were fabricated from zirconia powder stabilized in the cubic phase with 8 mol% percent yttria. Each substrate was sintered for 14 hours at 1200°C. The resulting zirconia pellets, 13mm in diameter and 2mm in thickness, were roughly 97 to 98 percent of theoretical density. The Engelhard #6082 platinum paste was applied to the zirconia disks after they were mechanically polished ( diamond). The electrodes were then sintered at temperatures ranging from 600°C to 1000°C. Each sensor was tested to determine the impedance response from 1Hz to 5,000Hz. These frequencies correspond to the electrode at the test temperature of 600°C.

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