scholarly journals Dissolution precipitation creep as a process for the strain localisation in gabbro

2020 ◽  
Author(s):  
Amicia Lee ◽  
Holger Stunitz ◽  
Matheus Ariel Battisti ◽  
Jiri Konopasek
Keyword(s):  
Creep Deformation ◽  
Driving Forces ◽  
Transformation Process ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Strain Localisation ◽  
General Transformation ◽  
Active Deformation ◽  
The North ◽  
Extension Direction

<p>Strain localisation and fabric development in the lower crust is controlled by the active deformation mechanisms. Understanding the driving forces of such deformation aids in quantifying the stresses and rates of the deformation processes. Here we show that diffusion creep plays a major role in deformation of gabbro lenses at upper amphibolite facies conditions. The Kågen gabbro in the North Norwegian Caledonides intruded the Vaddas Nappe at 439 Ma at pressures of 7-9 kbar, temperatures of 650-900°C (depths of ∼26-34 km). The Kågen gabbro on south Arnøya is made up of undeformed gabbro lenses with sheared margins wrapping around them. This contribution analyses the evolution of the microstructures and fabric of the low strain gabbro to high strain margins. Microstructural and textural data indicate that preferential crystal growth of amphibole grains in the extension direction has produced the deformation microstructure and the CPO. Dissolution precipitation creep is inferred to be the dominant deformation mechanism, where dissolution of the gabbro took place in reacting phases of clinopyroxene and plagioclase, and precipitation took place in the form of new minerals: amphibole, garnet and zoisite. Synchronous deformation and mineral reactions of clinopyroxene suggests mafic rocks can become mechanically weak during the general transformation weakening process, i.e. the interaction of mineral reaction and deformation by diffusion creep. Deformation and metamorphic reaction were both important transformation processes during diffusion creep deformation of the margins of the gabbro lenses. The weakening is directly connected to a transformation process that facilitates diffusion creep deformation of strong minerals (pyroxene, garnet, zoisite) at far lower stresses than dislocation creep. Initially strong lithologies can become weak, provided that reactions can proceed during deformation, the transformation process itself is an important weakening mechanism in mafic (and other) rocks, facilitating deformation at low differential stresses.</p>

scholarly journals Creeping gabbro: dissolution-precipitation creep facilitating deformation in mafic rocks

2021 ◽  
Author(s):  
Amicia Lee ◽  
Holger Stünitz ◽  
Mathieu Soret ◽  
Matheus Ariel Battisti ◽  
Jiří Konopásek
Keyword(s):  
Transformation Process ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
General Transformation ◽  
Preferential Growth ◽  
Mafic Rocks ◽  
The North ◽  
Dominant Deformation Mechanism ◽  
Textural Data ◽  
Extension Direction

<p>Mafic rocks consist of strong minerals (e.g. clinopyroxene, plagioclase) that can only be deformed by crystal plastic mechanisms at high temperatures (>800°C). Yet, mafic rocks do show extensive deformation by non-brittle mechanisms when they have only reached lower temperatures (~650°C). In many of such cases, the deformation is accommodated by an interaction of deformation with simultaneous mineral reactions. Here we show that dissolution-precipitation creep plays a major role in deformation of gabbro lenses at mid and upper amphibolite facies conditions.</p><p>The Kågen gabbro in the North Norwegian Caledonides intruded the Vaddas Nappe at 439 Ma at pressures of 7-9 kbar, temperatures of 650-900°C, and depths of ∼26-34 km. The Kågen gabbro on south Arnøya is comprised of undeformed gabbro lenses with sheared margins wrapping around them. This contribution analyses the evolution of the microstructures and metamorphism from the low strain gabbro lenses to high strain mylonites at margins of the lenses. Microstructural and textural data indicate that dissolution-precipitation creep is the dominant deformation mechanism, where dissolution of the gabbro took place in reacting phases of clinopyroxene and plagioclase, and precipitation took place in the form of new minerals: new plagioclase and clinopyroxene, amphibole, and garnet. Amphibole shows a strong CPO that is primarily controlled by its preferential growth in the extension direction. Synchronous deformation and mineral reactions of clinopyroxene suggests mafic rocks can become mechanically weak during the general transformation weakening process, i.e. the interaction of mineral reaction and deformation by diffusion creep. The weakening is directly connected to a fluid-assisted transformation process that facilitates diffusion creep deformation of strong minerals at far lower stresses and temperatures than dislocation creep. Initially strong lithologies can become weak, provided that reactions can proceed during deformation, the transformation process itself is an important weakening mechanism in mafic (and other) rocks, facilitating deformation at low differential stresses.</p>

scholarly journals Dissolution precipitation creep as a process for the strain localisation in mafic rocks

2021 ◽  
Author(s):  
Amicia Lee ◽  
Holger Stünitz ◽  
Mathieu Soret ◽  
Matheus Battisti
Keyword(s):  
Transformation Process ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
General Transformation ◽  
Preferential Growth ◽  
Crystallographic Preferred Orientation ◽  
Mafic Rocks ◽  
Dominant Deformation Mechanism ◽  
Lower Temperature ◽  
Extensive Deformation

Unaltered mafic rocks consist of mechanically strong minerals (e.g. pyroxene, plagioclase and garnet) that can be deformed by crystal plastic mechanisms only at high temperatures (>800°C). Yet, many mafic rocks do show extensive deformation by non-brittle mechanisms when they have been subjected to lower temperature conditions. In such cases, the deformation typically is assisted by mineral reactions. Here we show that dissolution-precipitation creep (as a type of diffusion creep) plays a major role in deformation of gabbro lenses at upper amphibolite facies conditions. The Kågen gabbro exposed on south Arnøya is comprised of almost undeformed gabbro lenses with sheared margins wrapping around them. The shearing has taken place at temperatures of 690 ± 25 °C and pressures of 1.0 to 1.1 GPa. This contribution analyses the evolution of the microstructures and fabric of the low strain gabbro to high strain margins. Microstructural and crystallographic preferred orientation (CPO) data indicate that dissolution-precipitation creep is the dominant deformation mechanism, where dissolution of the gabbro took place in reacting phases of clinopyroxene and plagioclase, and precipitation took place in the form of new minerals: new plagioclase and clinopyroxene (with different composition), amphibole, and garnet. Amphibole shows a strong CPO that is primarily controlled by its preferential growth in the stretching direction. Synchronous deformation and mineral reactions of clinopyroxene suggest that mafic rocks can become mechanically weak during a general transformation weakening process, i.e. the interaction of mineral reaction and deformation by diffusion creep. The weakening is directly connected to a fluid-assisted transformation process that facilitates diffusion creep deformation of strong minerals at far lower stresses and temperatures than dislocation creep. Initially strong lithologies can become weak, provided that reactions can proceed during deformation; the transformation process itself is an important weakening mechanism in mafic (and other) rocks, facilitating deformation at low differential stresses and low stress exponents.

Macro- and microstructural analysis of the North Tea Lake Mylonite Zone: an extensional shear zone in the Central Gneiss Belt, Grenville Province, Ontario

2015 ◽  
Vol 52 (11) ◽  
pp. 1027-1044 ◽  
Author(s):  
Nicholas Culshaw ◽  
Christopher Gerbi ◽  
Laura Ratcliffe
Keyword(s):  
Shear Zone ◽  
Microstructural Analysis ◽  
High Stress ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
The North ◽  
Mylonite Zone ◽  
Central Gneiss Belt

The North Tea Lake Mylonite Zone is a late extensional ductile fault that is concordant with and has reworked fabrics of the North Tea Lake Shear Zone, the frontal thrust shear zone of the upper amphibolite–granulite facies Kiosk domain within the interior of the Central Gneiss Belt. North Tea Lake Mylonite Zone fabric is an anomalously fine-grained mylonite compared to Central Gneiss Belt gneisses, and consists of three microstructural domains that display progressive recrystallization and grain size refinement of the protolith granitoid. On the basis of petrography and electron backscatter diffraction, these microdomains are inferred to represent a transition from dominantly dislocation creep to diffusion creep and diffusion-accommodated grain boundary sliding at elevated stress (>100 MPa), low fluid activity, and temperatures ∼500 °C. The North Tea Lake Mylonite Zone is interpreted to mark a step in the progressive transition in deformation mode during late- to post-Ottawan extension and cooling of the Grenville orogen from weak, wide, wet, and warm shear zones to Rigolet-phase cooler, narrow, ultrafine, high-stress shear zones reworking dry protoliths.

Late Miocene to present-day tectonostratigraphy of the northern central Algerian Basin: Evidence of a contractional salt system from reprocessed seismic data

2021 ◽  
Author(s):  
Simon Blondel ◽  
Angelo Camerlenghi ◽  
Anna Del Ben ◽  
Massimo Bellucci
Keyword(s):  
Seismic Data ◽  
Driving Forces ◽  
Salt System ◽  
Good Resolution ◽  
Deep Basin ◽  
The North ◽  
Depth Processing ◽  
Deformation Intensity ◽  
First Time ◽  
Seismic Lines

<p>This study presents the interpretation of reprocessed seismic data covering the southwestern Balearic promontory and the central Algerian basin. The new depth processing of 2D seismic lines dataset allows for the first time a good resolution on salt structures in the deep basin. Most of the salt structures result from active diapirism. In the deep basin, sedimentary loads and regional shortening are proposed to be the dominant driving forces, showing an overall contractional salt system. The north Algerian margin tectonic reactivation could have provoked a regional shortening of the salt structures and overburden. Identified unconformities suggest that this process probably started shortly after salt deposition and is still active nowadays. It is expressed by salt sheets, pinched diapirs and a décollement level. The African convergence and the narrowness of the western Algerian basin could be the explanation of an overall greater salt deformation intensity compared to the eastern Algerian basin. This demonstrates how in tectonic and sedimentary components appear to be dominant in salt deformation in the central Algerian basin compared to gravitational gliding, only localized in the proximal parts of the margin.</p>

Geodynamics of the France Southeast Basin

2010 ◽  
Vol 181 (6) ◽  
pp. 477-501 ◽  
Author(s):  
Xavier Le Pichon ◽  
Claude Rangin ◽  
Youri Hamon ◽  
Nicolas Loget ◽  
Jin Ying Lin ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Sedimentary Cover ◽  
Central Basin ◽  
The South ◽  
Western Basin ◽  
Active Deformation ◽  
The North ◽  
The Alps ◽  
Sediment Cover ◽  
Surrounding Areas

AbstractWe investigate the geodynamics of the Southeast Basin with the help of maps of the basement and of major sedimentary horizons based on available seismic reflection profiles and drill holes. We also present a study of the seismicity along the Middle Durance fault. The present seismic activity of the SE Basin cannot be attributed to the Africa/Eurasia shortening since spatial geodesy demonstrates that there is no significant motion of Corsica-Sardinia with respect to Eurasia and since gravitational collapse of the Alps has characterized the last few millions years. Our study demonstrates that the basement of this 140 by 200 km Triassic basin has been essentially undeformed since its formation, most probably because of the hardening of the cooling lithosphere after its 50% thinning during the Triassic distension. The regional geodynamics are thus dominated by the interaction of this rigid unit with the surrounding zones of active deformation. The 12 km thick Mesozoic sediment cover includes at its base an up to 4 km thick mostly evaporitic Triassic layer that is hot and consequently highly fluid. The sedimentary cover is thus decoupled from the basement. As a result, the sedimentary cover does not have enough strength to produce reliefs exceeding about 500 to 750 m. That the deformation and seismicity affecting the basin are the results of cover tectonics is confirmed by the fact that seismic activity in the basin only affects the sedimentary cover. Based on our mapping of the structure of the basin, we propose a simple mechanism accounting for the Neogene deformation of the sedimentary cover. The formation of the higher Alps has first resulted to the north in the shortening of the Diois-Baronnies sedimentary cover that elevated the top of Jurassic horizons by about 4 km with respect to surrounding areas to the south and west. There was thus passage from a brittle-ductile basement decollement within the higher Alps to an evaporitic decollement within the Diois-Baronnies. This shortening and consequent elevation finally induced the southward motion of the basin cover south of the Lure mountain during and after the Middle Miocene. This southward motion was absorbed by the formation of the Luberon and Trévaresse mountains to the south. To the east of the Durance fault, there is no large sediment cover. The seismicity there, is related to the absorption of the Alps collapse within the basement itself. To the west of the Salon-Cavaillon fault, on the other hand, gravity induces a NNE motion of the sedimentary cover with extension to the south and shortening to the north near Mont Ventoux. When considering the seismicity of this area, it is thus important to distinguish between the western Basin panel, west of the Salon-Cavaillon fault affected by very slow NNE gliding of the sedimentary cover, with extension to the south and shortening to the north; the central Basin panel west of the Durance fault with S gliding of the sedimentary cover and increasing shortening to the south; and finally the basement panel east of the Durance fault with intrabasement absorption of the Alps collapse through strike-slip and thrust faults.

Grain growth and the lifetime of diffusion creep deformation

2011 ◽  
Vol 360 (1) ◽  
pp. 257-272 ◽  
Author(s):  
Mark A. Pearce ◽  
John Wheeler
Keyword(s):  
Grain Growth ◽  
Creep Deformation ◽  
Diffusion Creep

Increased frequency of Eurasian double jets linked to summer heat extremes in Europe

2021 ◽  
Author(s):  
Efi Rousi ◽  
Kai Kornhuber ◽  
Goratz Beobide Arsuaga ◽  
Fei Luo ◽  
Dim Coumou
Keyword(s):  
Zonal Wind ◽  
Large Scale ◽  
Driving Forces ◽  
Linear Regression Analysis ◽  
Reanalysis Data ◽  
Self Organizing Maps ◽  
Upper Troposphere ◽  
The North ◽  
Heat Extremes ◽  
Different Levels

<p>Persistent summer extremes, such as heatwaves and droughts, can have considerable impacts on nature and societies. There is evidence that weather persistence has increased in Europe over the past decades, in association to changes in atmosphere dynamics, but uncertainties remain and the driving forces are not yet well understood. </p><p>Particularly for Europe, the jet stream may affect surface weather significantly by modulating the North Atlantic storm tracks. Here, we examine the hypothesis that high-latitude warming and decreased westerlies in summer result in more double jets, consisting of two distinct maxima of the zonal wind in the upper troposphere, over the Eurasian sector. Previous work has shown that such double jet states are related to persistent blocking-like circulation in the mid-latitudes. </p><p>We adapt a dynamical perspective of heat extreme trends by looking at large scale circulation and in particular, changes in the zonal mean zonal wind in different levels of the upper troposphere. We define clusters of jet states with the use of Self-Organizing Maps and analyze their characteristics. We find an increase in frequency and persistence of a cluster of double jet states for the period 1979-2019 during July-August (in ERA5 reanalysis data). Those states are linked to increased surface temperature and more frequent heatwaves compared to climatology over western, central, and northern Europe. Significant positive double jet anomalies are found to be dominant in the days preceding and/or coinciding with some of the most intense historical heatwaves in Europe, such as those of 2003 and 2018. A linear regression analysis shows that the increase in frequency and persistence of double jet states may explain part of the strong upward trend in heat extremes over these European regions.</p>

Indicators of Possible Driving Forces for the Spread of Quechua and Aymara Reflected in the Archaeology of Cuzco

2012 ◽  
Author(s):  
GORDON F. McEWAN
Keyword(s):  
Cultural History ◽  
Driving Force ◽  
Driving Forces ◽  
Alternative Possibilities ◽  
The Past ◽  
The North ◽  
The Andes ◽  
Inca Empire ◽  
Culture History ◽  
History Of

Linguistic studies have shown that the traditional idea that the expansion of the Inca Empire was the driving force behind the spread of all Quechua cannot be correct. Across much of its distribution, Quechua has far greater time-depth than can be accounted for by the short-lived Inca Empire. Linguistics likewise suggests that Aymara spread not from the south into Cuzco in the late Pre-Inca period, but also from an origin to the north. Alternative explanations must be sought for the expansion of these language families in the culture history of the Andes. Archaeological studies over the past two decades now provide a broad, generally agreed-upon outline of the cultural history of the Cuzco region. This chapter applies those findings to examine alternative possibilities for the driving forces that spread Quechua and Aymara, offering a clearer cross-disciplinary view of Andean prehistory.

Geographies of Agri-food

2006 ◽  
Author(s):  
Kevin Morgan ◽  
Terry Marsden ◽  
Jonathan Murdoch
Keyword(s):  
Driving Force ◽  
Driving Forces ◽  
Transformation Process ◽  
Specific Reference ◽  
Industrial System ◽  
Corporate Capital ◽  
Agricultural Transformation ◽  
Agrarian Question ◽  
General Terms ◽  
Production And Consumption

Chapters 1 and 2 have reviewed the contemporary theoretical and policy context of agri-food with specific reference to Europe and North America. In this chapter we turn our attention to the nature of the new agri-food geographies. What are the driving forces behind these geographies, and how do they play themselves out across time and space? This theme is central to the more detailed treatment of three different regions (Tuscany, California, and Wales) in succeeding chapters. Here, we introduce a conceptual framework that helps us to understand the new agri-food geographies. The chapter starts by outlining the nature of the conventional agri-industrial system. In general terms, we see this as a system that leads to a process of deterritorialization of foods. That is not to say that it comes without any actual geography; rather, its geographies are the result of corporate capitals’ attempts to continue to intensify and to appropriate some of the functions of agriculture in ways that stretch the links, networks, and chains between production and consumption spheres. We then place this trend in conceptual juxtaposition with the more recent forces of reterritorialization (or what some scholars term ‘relocalization’), a process whereby local and regional geographies come back again to play a central role in reshaping food production and consumption systems. We argue here that it is important to see these conflicting geographical forces as distinctive, even though both processes may indeed be operating—to varying degrees and in different ways—in the same region or locality at the same time. This is at the heart of our contingent notion of ‘worlds of food’. Throughout the twentieth century, agri-industrialism struggled with resolving Kautsky’s formulation of the agrarian question, that is, how to continue to intensify production and appropriate some farming functions in processing and agri-industry while at the same time maintaining some sort of ecological or natural balance in the agricultural transformation process (Kautsky, 1988; Goodman and Watts, 1997). In the agri-industrial model, the driving force was corporate capital.

scholarly journals Convergence of the Pamir and the South Tian Shan in the late Cenozoic: Insights from provenance analysis in the Wuheshalu section at the convergence area

Lithosphere ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 507-523 ◽  
Author(s):  
Xinwei Chen ◽  
Hanlin Chen ◽  
Edward R. Sobel ◽  
Xiubin Lin ◽  
Xiaogan Cheng ◽  
...  
Keyword(s):  
Source Area ◽  
Limited Area ◽  
Late Cenozoic ◽  
Provenance Analysis ◽  
The South ◽  
Active Deformation ◽  
The North ◽  
Large Populations ◽  
A Minor ◽  
Tian Shan

Abstract In response to collision and convergence between India and Asia during the Cenozoic, convergence took place between the Pamir and South Tian Shan. Here we present new detrital zircon U-Pb ages coupled with conglomerate clast counting and sedimentary data from the late Cenozoic Wuheshalu section in the convergence zone, to shed light on the convergence process of the Pamir and South Tian Shan. Large Triassic zircon U-Pb age populations in all seven samples suggest that Triassic igneous rocks from the North Pamir were the major source area for the late Cenozoic Wuheshalu section. In the Miocene, large populations of the North Pamir component supports rapid exhumation in the North Pamir and suggest that topography already existed there since the early Miocene. Exhumation of the South Tian Shan was relatively less important in the Miocene and its detritus could only reach a limited area in the foreland area. Gradually increasing sediment loading and convergence of the Pamir and South Tian Shan caused rapid subsidence in the convergence area. Since ca. 6–5.3 Ma, the combination of a major North Pamir component and a minor South Tian Shan component at the Wuheshalu section is consistent with active deformation of the South Tian Shan and the North Pamir. During deposition of the upper Atushi Formation, a larger proportion of North Pamir–derived sediments was deposited in the Wuheshalu section, maybe because faulting and northward propagation of the North Pamir caused northward displacement of the depocenter to north of the Wuheshalu section.

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