Geochronology of Himalayan shear zones: unravelling the timing of thrusting from structurally complex fault rocks

2021 ◽  
Author(s):  
Igor M Villa ◽  
Chiara Montemagni
Keyword(s):  
Electron Probe ◽  
Shear Zones ◽  
The Other ◽  
Metamorphic Rocks ◽  
A Posteriori ◽  
Furnace Temperature ◽  
Fault Rocks ◽  
Mineral Phases ◽  
Complex Fault ◽  
Average Bond

<p>Dating structurally complex fault rocks often results in internally inconsistent ages, as several mineral generations are intergrown at scales << 10 µm and almost always altered to various degrees. We describe here <sup>39</sup>Ar-<sup>40</sup>Ar stepheating using the combination of two independent indicators that allow the discrimination of coexisting mica generations from each other and from the ubiquitous retrogression/alteration phases. A necessary first step is electron probe microanalysis to assess both inventory and spatial distribution of the mineral phases that need to be distinguished a posteriori by <sup>39</sup>Ar-<sup>40</sup>Ar systematics. One indicator is based on mica stoichiometry, which can be proxied by the <sup>39</sup>Ar concentration in combination with the <sup>37</sup>Ar/<sup>39</sup>Ar and <sup>38</sup>Ar/<sup>39</sup>Ar (i.e. Ca/K and Cl/K) ratios. The other indicator is the furnace temperature, at which a degassing peak accompanying dehydration and structural collapse is observed. As dehydration rates depend on the average bond strength in the crystal structure, it is predicted (and indeed observed) that the temperature of the differential Ar release peak is variable among different minerals. As the Ca/Cl/K signatures of pure micas coincide with the Ar release peak, their combination identifies the isochemical steps that correspond to the degassing of pristine micas. Only these should be used to date the activity of shear zones.</p><p>This procedure should become routine in analysing polydeformed metamorphic rocks.</p>

Geochronology of Himalayan shear zones: unravelling the timing of thrusting from structurally complex fault rocks

2021 ◽  
pp. jgs2020-235
Author(s):  
Chiara Montemagni ◽  
Igor M. Villa
Keyword(s):  
Shear Zones ◽  
Main Central Thrust ◽  
Fault Rocks ◽  
Isotopic Dating ◽  
Content Type ◽  
Link Type ◽  
Complex Fault ◽  
Thrust Zone ◽  
Supplementary Material ◽  
Average Bond

Dating structurally complex fault rocks often results in internally inconsistent ages, as several mineral generations are intergrown at scales << 10 µm and almost always altered to various degrees. Firstly, electron probe microanalysis is necessary to assess both inventory and spatial distribution of minerals and their retrogression/alteration phases. We then used 40Ar/39Ar stepheating combining two independent indicators that allow the discrimination of coexisting mica generations from each other: (i) mica stoichiometry, which is proxied by 39Ar concentration in combination with 37Ar/39Ar and 38Ar/39Ar (Ca/K and Cl/K) ratios; (ii) furnace temperature, at which the degassing peak accompanying dehydration and structural collapse is observed. As dehydration rates depend on average bond strength in the crystal structure, it is predicted and observed that the temperature of the differential Ar release peak is variable among different minerals. We observe that the Ca/Cl/K signatures of pure micas coincide with the Ar release peak. The Main Central Thrust zone in the Garhwal Himalaya records a protracted history. Foliation of Vaikrita Thrust formed at 15-8 Ma, followed by static decompression at 7 Ma; foliation of structurally lower Munsiari Thrust formed around 5 Ma. Our elaborate and time-consuming petrochronological procedure should become routine whenever analysing polydeformed metamorphic rocks.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5357212Thematic collection: This article is part of the Isotopic Dating collection available at: https://www.lyellcollection.org/cc/isotopic-dating-of-deformation

Microchemical imaging in biomedical research

1992 ◽  
Vol 50 (2) ◽  
pp. 1118-1119
Author(s):  
P. Ingram
Keyword(s):  
Data Analysis ◽  
Electron Probe ◽  
The Other ◽  
X Ray ◽  
Cell Element ◽  
Physiological Information ◽  
Functional States ◽  
Elemental Maps ◽  
Electron Energy Loss ◽  
Secondary Ion

It is well established that unique physiological information can be obtained by rapidly freezing cells in various functional states and analyzing the cell element content and distribution by electron probe x-ray microanalysis. (The other techniques of microanalysis that are amenable to imaging, such as electron energy loss spectroscopy, secondary ion mass spectroscopy, particle induced x-ray emission etc., are not addressed in this tutorial.) However, the usual processes of data acquisition are labor intensive and lengthy, requiring that x-ray counts be collected from individually selected regions of each cell in question and that data analysis be performed subsequent to data collection. A judicious combination of quantitative elemental maps and static raster probes adds not only an additional overall perception of what is occurring during a particular biological manipulation or event, but substantially increases data productivity. Recent advances in microcomputer instrumentation and software have made readily feasible the acquisition and processing of digital quantitative x-ray maps of one to several cells.

Practical Correction of Three Fold Astigmatism in the Philips CM TEM

1996 ◽  
Vol 54 ◽  
pp. 418-419
Author(s):  
Arno J. Bleeker ◽  
Mark H.F. Overwijk ◽  
Max T. Otten
Keyword(s):  
Optical Properties ◽  
Phase Contrast ◽  
The Other ◽  
Objective Lens ◽  
Symmetric Part ◽  
A Posteriori ◽  
Contrast Transfer Function ◽  
High Brightness ◽  
Rotationally Symmetric ◽  
Brightness Field

With the improvement of the optical properties of the modern TEM objective lenses the point resolution is pushed beyond 0.2 nm. The objective lens of the CM300 UltraTwin combines a Cs of 0. 65 mm with a Cc of 1.4 mm. At 300 kV this results in a point resolution of 0.17 nm. Together with a high-brightness field-emission gun with an energy spread of 0.8 eV the information limit is pushed down to 0.1 nm. The rotationally symmetric part of the phase contrast transfer function (pctf), whose first zero at Scherzer focus determines the point resolution, is mainly determined by the Cs and defocus. Apart from the rotationally symmetric part there is also the non-rotationally symmetric part of the pctf. Here the main contributors are not only two-fold astigmatism and beam tilt but also three-fold astigmatism. The two-fold astigmatism together with the beam tilt can be corrected in a straight-forward way using the coma-free alignment and the objective stigmator. However, this only works well when the coefficient of three-fold astigmatism is negligible compared to the other aberration coefficients. Unfortunately this is not generally the case with the modern high-resolution objective lenses. Measurements done at a CM300 SuperTwin FEG showed a three fold-astigmatism of 1100 nm which is consistent with measurements done by others. A three-fold astigmatism of 1000 nm already sinificantly influences the image at a spatial frequency corresponding to 0.2 nm which is even above the point resolution of the objective lens. In principle it is possible to correct for the three-fold astigmatism a posteriori when through-focus series are taken or when off-axis holography is employed. This is, however not possible for single images. The only possibility is then to correct for the three-fold astigmatism in the microscope by the addition of a hexapole corrector near the objective lens.

scholarly journals Are doomsday scenarios best seen as failed predictions or political detonators? The case of the ‘Theory of Himalayan Environmental Degradation’

2017 ◽  
Vol 10 ◽  
pp. 1-14
Author(s):  
Tor H. Aase
Keyword(s):  
Hypothesis Testing ◽  
Environmental Degradation ◽  
The Other ◽  
Mountain Range ◽  
Last Millennium ◽  
A Posteriori ◽  
Alarm Clock ◽  
Policy Initiatives ◽  
Ecological Variation ◽  
Other Hand

The so-called ‘Theory of Himalayan Environmental Degradation’ predicted an environmental collapse by the end of last millennium, threatening the life of millions of people. Fortunately, the all-encompassing crisis did not materialize. The article shows that the ‘Theory’ failed to take into account the vast ecological variation in Himalaya and thus generalized its contentions to the whole mountain range on the basis of deficient data. But, on the other hand, what would have happened if the prediction had not been made? A doomsday scenario like the Theory of Himalayan Degradation can, from the perspective of positivist hypothesis testing, be viewed a posteriori as a failed prediction; but from another perspective it can be seen as an alarm clock that triggered a series of policy initiatives and new knowledge.The Geographical Journal of Nepal Vol. 10: 1-14, 2017

Kripke on Epistemic and Metaphysical Possibility

2014 ◽  
Author(s):  
Scott Soames
Keyword(s):  
The Other ◽  
A Posteriori ◽  
Singular Proposition ◽  
Metaphysical Possibility ◽  
Frege’S Puzzle ◽  
Frege's Puzzle ◽  
Necessary A Posteriori ◽  
Errors And Confusions

This chapter discusses Saul Kripke’s treatment of the necessary a posteriori and concomitant distinction between epistemic and metaphysical possibility. It extracts the enduring lessons of his treatment of these matters and disentangles them from errors and confusions that mar some of his most important discussions. It argues that there are two Kripkean routes to the necessary a posteriori—one correct and philosophically far-reaching; the other incorrect, philosophically misleading, and the source of damaging errors that persist to this day. It connects two false principles involved in the second, unsuccessful, route to the necessary a posteriori with the plausible and potentially correct idea that believing a singular proposition that o is F always involves also believing a richer more descriptively informative proposition in which some further property plays a role in the agent’s thoughts about o. It explains why this idea will not save the failed second route to the necessary a posteriori and suggests that it may help reconcile Kripke’s insights with the lessons of Frege’s puzzle.

scholarly journals Stress fields of ancient seismicity recorded in the dynamic geometry of pseudotachylyte in the Outer Hebrides Fault Zone, UK

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-101
Author(s):  
L.R. Campbell ◽  
G.E. Lloyd ◽  
R.J. Phillips ◽  
R.C. Walcott ◽  
R.E. Holdsworth
Keyword(s):  
Fault Zone ◽  
Dynamic Geometry ◽  
Shear Zones ◽  
Stress Fields ◽  
Tectonic Activity ◽  
Sensitivity Testing ◽  
Fault Rocks ◽  
Outer Hebrides ◽  
Supplementary Material

Heterogeneous sequences of exhumed fault rocks preserve a record of the long-term evolution of fault strength and deformation behaviour during prolonged tectonic activity. Along the Outer Hebrides Fault Zone (OHFZ) in NW Scotland, numerous pseudotachylytes record palaeoseismic slip events within sequences of mylonites, cataclasites and phyllonites. To date, the kinematics and controls on seismicity within the long active history of the OHFZ have been poorly constrained. Additional uncertainties over the relative location of a meteorite impact and possible pre-OHFZ brittle faulting also complicate interpretation of the diffuse seismic record. We present kinematic analyses of seismicity in the OHFZ, combining observations of offset markers, en echelon injection veins and injection vein geometry to reconstruct slip directions and stress fields. This new dataset indicates that a range of fault orientations, slip directions and slip senses hosted seismicity in the OHFZ. Such complexity requires several stress field orientations, in contrast with the NW–SE Caledonian compression traditionally attributed to frictional melting along the OHFZ, indicating that seismicity had a long-term presence across the fault zone. Persistence of strong frictional failure alongside the simultaneous development of weak fault rocks and phyllonitic shear zones in parts of the OHFZ has significant implications for understanding seismic hazard along mature continental faults.Supplementary material: Tables listing analysed orientation measurements plus further information and sensitivity testing of palaeostress analysis parameters are available at https://doi.org/10.6084/m9.figshare.c.5134797

Ca10V5.2Fe0.8O24, a Novel Oxometalate with Discrete Complex Anions

2003 ◽  
Vol 58 (11) ◽  
pp. 1112-1116 ◽  
Author(s):  
Kurt O. Kleppa ◽  
Norbert A. Harringer ◽  
Hubert Preßlinger
Keyword(s):  
Crystal Structure ◽  
Single Crystals ◽  
Bond Distance ◽  
Structure Type ◽  
The Other ◽  
Nominal Composition ◽  
Average Bond ◽  
Complex Anions ◽  
Trigonal Prismatic ◽  
Discrete Complex

Abstract Lustrous needle shaped prismatic single crystals of the new compound Ca10V5.2Fe0.8O24 were obtained out of a sample with nominal composition Ca2Fe1.6V0.4O5 prepared at 1400 °C. The crystals are opaque and stable to humid air. Ca10V5.2Fe0.8O24 crystallizes with a new structure type, space group Pnma with a = 6.803(3), b = 16.015(8), c = 10.418(7)Å , Z = 2, R = 0.041. The crystal structure is characterized by two mononuclear tetrahedral species, MO4, which differ significantly from each other with respect to their M-O bond lengths. One with an average bond distance of 1.709(8)Å represents an orthovanadate ion. The other with a significantly larger value d(M-O) = 1.744(6) Å corresponds to a mixed occupation of its centre according to [V0.8Fe0.2O4]3.5−. In the crystal structure the complex anions are arranged in separate sheets parallel to the (010) plane. They are separated from each other by three crystallographically independent Ca2+ ions which are each coordinated by 7 oxygen atoms in distorted pentagonal bipyramidal and trigonal prismatic configurations, respectively.

Facies de metamorphisme profond et de retromorphose au NW du cap Corse

1954 ◽  
Vol S6-IV (4-6) ◽  
pp. 203-208
Author(s):  
Jean Laporte
Keyword(s):  
The Other ◽  
Metamorphic Rocks ◽  
Northwestern Part

Abstract The metamorphic rocks outcropping around Ersa and Centuri in the northwestern part of Corse cape on Corsica, France, may possibly be the more highly metamorphosed equivalents (including retrograde products) of the other rocks forming the cape.

The Effects of Aggregation and Timing on Budgeting: An Experiment

2010 ◽  
Vol 22 (1) ◽  
pp. 67-83 ◽  
Author(s):  
Anthony D. Nikias ◽  
Steven T. Schwartz ◽  
Eric E. Spires ◽  
Jim R. Wollscheid ◽  
Richard A. Young
Keyword(s):  
A Priori ◽  
Behavioral Effect ◽  
The Other ◽  
Image Management ◽  
A Posteriori ◽  
Project Cost ◽  
Face To Face

ABSTRACT: We conduct an experiment to study the behavioral effect of aggregation and timing on budgetary reports. Subordinates submit budgets to superiors regarding two projects in a face-to-face setting. There are three treatments: (1) AGG, wherein subordinates privately observe each project’s cost and submit one budget regarding the aggregate cost of the two projects, (2) SEQ, wherein subordinates observe and submit individual budgets sequentially, so are uncertain about the second-project cost when they submit their first-project budget, and (3) DEL, wherein budgets are delayed, so that subordinates observe both costs before providing individual budgets. In all treatments superiors must approve the budget and subordinates can create more slack by submitting a larger budget. Based on image management, guilt alleviation, and preferences for honesty, we hypothesize that subordinates will (1) create more slack in AGG than in the other two treatments, (2) create more slack in DEL than in SEQ, and (3) decrease their slack creation from the first project to the second project more in SEQ than in DEL. Our results generally support all three hypotheses. However, analysis of the results does not support our a priori beliefs regarding the nonpecuniary motivations of subordinates. We argue, a posteriori, that a likely explanation for our findings is that increased face-to-face interactions in SEQ and DEL cause subordinates to care more about the welfare of the superior than in AGG. In general, the results indicate that frequent budget interactions may provide control benefits to superiors.

De Sousa On Kripke And Theoretical Identities

1975 ◽  
Vol 5 (1) ◽  
pp. 137-141 ◽  
Author(s):  
R. M. Yoshida
Keyword(s):  
Possible Worlds ◽  
The Other ◽  
Saul Kripke ◽  
A Posteriori ◽  
Rigid Designator ◽  
Rigid Designators ◽  
Necessary A Posteriori ◽  
Other Hand ◽  
Identity Statement ◽  
Naming And Necessity

In the by now well known talks he gave at Princeton, Saul Kripke claimed that “[t]heoretical identities … are generally identities involving two rigid designators and therefore are examples of the necessary a posteriori.” (Published as “Naming and Necessity,” in G. Harmon and D. Davidson, eds., Semantics of Natural Language (Dordrecht, 1972) 253-355; (hereafter referred to as “NN”; this quote p. 331.) A rigid designator is an expression that designates the same object in all possible worlds when it is used. So Kripke is claiming that ‘Water is H20’ and ‘Heat is the motion of molecules’ are generally identities involving expressions like ‘water’ and ‘the motion of molecules’ which designate the same objects in all possible worlds. If the identity statement is true, both sides designate the same object rigidly, i.e., in all possible worlds, and therefore the statement is necessarily true. On the other hand, whether it is true is determined ultimately by appeal to experience. It follows that if true, the identity is necessary a posteriori.

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