Fluid processes during the exhumation of high-P metamorphic belts

2002 ◽  
Vol 66 (1) ◽  
pp. 93-119 ◽  
Author(s):  
J. A. Miller ◽  
I. S. Buick ◽  
I. Cartwright ◽  
A. Barnicoat
Keyword(s):  
Fluid Flow ◽  
Partial Melting ◽  
Significant Role ◽  
Large Scale ◽  
Shear Zones ◽  
Direct Role ◽  
Detachment Faults ◽  
Dehydration Reactions ◽  
Exhumation History

AbstractFluids can play a direct role in exhumation by influencing exhumation mechanisms and the driving processes for these mechanisms. In addition, the process of exhumation leads to the development of fluid-related features that in themselves may not drive exhumation. Fluids involved in exhumation are generally derived from dehydration reactions occurring during decompression, but at shallower crustal levels may also involve the introduction of exotic fluids. The composition of fluids attending exhumation are generally saline – CO2 mixtures, but N2, CH4, H2O mixtures have also been recorded. Studies of fluid features related to exhumation have found that fluids may contribute to density changes and the initiation of partial melting during decompression, as well as the development of extensive vein systems. However, the preservation of geochemical signatures related to fluid processes occurring prior to high-P and ultrahigh-P metamorphism indicates that large-scale pervasive fluid flow systems, in general, do not operate at any stage during the exhumation history. Large-scale channelled fluid flow may have operated in detachment faults and shear zones related to exhumation, and this requires further study. The most significant role of fluids during exhumation appears to be their controlling influence on the preservation of high-P or ultrahigh-P rocks.

Hydrofractures and crustal-scale fluid flow

2021 ◽  
Author(s):  
Paul D. Bons ◽  
Tamara de Riese ◽  
Enrique Gomez-Rivas ◽  
Isaac Naaman ◽  
Till Sachau
Keyword(s):  
Fluid Flow ◽  
Large Scale ◽  
Low Flow ◽  
Fault System ◽  
Tectonic Activity ◽  
Field Evidence ◽  
Dehydration Reactions ◽  
Matrix Flow ◽  
Matrix Porosity ◽  
Fluid Sources

<p>Fluids can circulate in all levels of the crust, as veins, ore deposits and chemical alterations and isotopic shifts indicate. It is furthermore generally accepted that faults and fractures play a central role as preferred fluid conduits. Fluid flow is, however, not only passively reacting to the presence of faults and fractures, but actively play a role in their creation, (re-) activation and sealing by mineral precipitates. This means that the interaction between fluid flow and fracturing is a two-way process, which is further controlled by tectonic activity (stress field), fluid sources and fluxes, as well as the availability of alternative fluid conduits, such as matrix porosity. Here we explore the interaction between matrix permeability and dynamic fracturing on the spatial and temporal distribution of fluid flow for upward fluid fluxes. Envisaged fluid sources can be dehydration reactions, release of igneous fluids, or release of fluids due to decompression or heating.</p><p> </p><p>Our 2D numerical cellular automaton-type simulations span the whole range from steady matrix-flow to highly dynamical flow through hydrofractures. Hydrofractures are initiated when matrix flow is insufficient to maintain fluid pressures below the failure threshold. When required fluid fluxes are high and/or matrix porosity low, flow is dominated by hydrofractures and the system exhibits self-organised critical phenomena. The size of fractures achieves a power-law distribution, as failure events may sometimes trigger avalanche-like amalgamation of hydrofractures. By far most hydrofracture events only lead to local fluid flow pulses within the source area. Conductive fracture networks do not develop if hydrofractures seal relatively quickly, which can be expected in deeper crustal levels. Only the larger events span the whole system and actually drain fluid from the system. We present the 10 square km hydrothermal Hidden Valley Mega-Breccia on the Paralana Fault System in South Australia as a possible example of large-scale fluid expulsion events. Although field evidence suggests that the breccia formed over a period of at least 150 Myrs, actual cumulative fluid duration may rather have been in the order of days only. This example illustrates the extreme dynamics that crustal-scale fluid flow in hydrofractures can achieve.</p>

RACE-BASED CONSIDERATIONS AND THE OBAMA VOTE

2009 ◽  
Vol 6 (1) ◽  
pp. 219-238 ◽  
Author(s):  
S. Karthick Ramakrishnan ◽  
Janelle Wong ◽  
Taeku Lee ◽  
Jane Junn
Keyword(s):  
Asian Americans ◽  
Significant Role ◽  
Asian American ◽  
Large Scale ◽  
Telephone Survey ◽  
Party Identification ◽  
Age And Gender ◽  
And Gender ◽  
Poll Data

AbstractIn the 2008 presidential primaries, Barack Obama seemed to have a problem connecting with Asian American voters, as he lost heavily to Hillary Clinton in states such as California and New Jersey. Many speculated that race-based considerations played a significant role in Asian Americans' overwhelming support for Clinton over Obama, with conjectures built on a limited set of aggregate exit poll data from three states. Race may also have accounted for the high proportion of Asian Americans who in polls said they were undecided heading into the November election. In this article, we analyze the importance of race-based considerations in the Asian American vote, after controlling for other factors such as partisanship, issue preferences, age, and gender. We rely on the National Asian American Survey, a large-scale telephone survey of Asian American voters conducted mostly in the fall of 2008, with interviews in eight languages and with sizable numbers of respondents from the six largest national-origin groups. We find that race-based considerations do indeed help explain the Asian American vote in 2008. Respondents who failed to see political commonality between Asian Americans and Blacks were less likely to vote for Obama in the primary, although other factors, such as age and gender, played a more significant role. Finally, the role of race-based considerations paled in comparison to party identification and issue preferences in the general election, suggesting that election contexts can play an important role in shaping whether or not race is relevant to vote choice.

scholarly journals BACKGROUND TO DEVELOPMENT OF TRANSPORT INFRASTRUCTURE OF KYIV CITY AGGLOMERATION

2019 ◽  
pp. 42-47
Author(s):  
I. Savchuk
Keyword(s):  
Significant Role ◽  
Large Scale ◽  
Urban Agglomeration ◽  
Transport Infrastructure ◽  
Residential Areas ◽  
Development Plans ◽  
Ownership Of Land ◽  
The Cost

The role of prerequisites in the development of the transport infrastructure of the capital of Ukraine is revealed. The author formulated methodological approaches to them. A comprehensive geographical description of the prerequisites for the development of the transport infrastructure of the Kyiv city agglomeration was carried out. It has been established that the main limitations are economic factors, which is caused by the highest cost of land resources in Ukraine precisely within this urban agglomeration. Natural factors continue to play a significant role only when carrying out specific prospecting for laying various types of infrastructure objects within it. There are new factors in the functioning and development of transport infrastructure. These include, first of all, the formation of united territorial communities. Their boundaries should be brought to life and their socio-economic development plans and spatial schemes should be developed. Thus, it is necessary to take into account local needs in the development of transport infrastructure with the general needs of the entire Kyiv city agglomeration. A significant role is played by the ownership of land. The concentration of land ownership in the hands of speculators and large developers leads to a sharp rise in the cost of the robot to acquire the necessary land for the construction of a new infrastructure. As a result, many new large residential areas do not have the necessary access roads and they are not connected to the citywide communications system. This leads to significant new problems for the solution of which it is necessary to coordinate new large-scale housing construction with the laying infrastructure. The main problem remains transport accessibility. Laying of highways to new buildings should be carried out at the expense of local budgets. However, there is often a conflict of interest between developers and local authorities. The latter do not want to invest substantial funds in the construction of roads and other types of infrastructure due to the fact that the cost of new relevant construction is much higher than the cost of housing built at the expense of borrowed funds. Thus, the existing suburban transport infrastructure takes on an ever-increasing stream of new daily commuter migrants. As a result, the quality of services provided drops sharply. This leads to a deterioration in the quality of life throughout the urban agglomeration.

Hydrofractures and crustal-scale fluid flow

2020 ◽  
Author(s):  
Paul D. Bons ◽  
Tamara de Riese ◽  
Enrique Gomez-Rivas ◽  
Isaac Naaman ◽  
Till Sachau
Keyword(s):  
Fluid Flow ◽  
Large Scale ◽  
Low Flow ◽  
Fault System ◽  
Tectonic Activity ◽  
Field Evidence ◽  
Dehydration Reactions ◽  
Matrix Flow ◽  
Matrix Porosity ◽  
Fluid Sources

<p>Fluids can circulate in all levels of the crust, as veins, ore deposits and chemical alterations and isotopic shifts indicate. It is furthermore generally accepted that faults and fractures play a central role as preferred fluid conduits. Fluid flow is, however, not only passively reacting to the presence of faults and fractures, but actively play a role in their creation, (re-) activation and sealing by mineral precipitates. This means that the interaction between fluid flow and fracturing is a two-way process, which is further controlled by tectonic activity (stress field), fluid sources and fluxes, as well as the availability of alternative fluid conduits, such as matrix porosity. Here we explore the interaction between matrix permeability and dynamic fracturing on the spatial and temporal distribution of fluid flow for upward fluid fluxes. Envisaged fluid sources can be dehydration reactions, release of igneous fluids, or release of fluids due to decompression or heating.</p><p> </p><p>Our 2D numerical cellular automaton-type simulations span the whole range from steady matrix-flow to highly dynamical flow through hydrofractures. Hydrofractures are initiated when matrix flow is insufficient to maintain fluid pressures below the failure threshold. When required fluid fluxes are high and/or matrix porosity low, flow is dominated by hydrofractures and the system exhibits self-organised critical phenomena. The size of fractures achieves a power-law distribution, as failure events may sometimes trigger avalanche-like amalgamation of hydrofractures. By far most hydrofracture events only lead to local fluid flow pulses within the source area. Conductive fracture networks do not develop if hydrofractures seal relatively quickly, which can be expected in deeper crustal levels. Only the larger events span the whole system and actually drain fluid from the system. We present the 10 square km hydrothermal Hidden Valley Mega-Breccia on the Paralana Fault System in South Australia as a possible example of large-scale fluid expulsion events. Although field evidence suggests that the breccia formed over a period of at least 150 Myrs, actual cumulative fluid duration may rather have been in the order of days only. This example illustrates the extreme dynamics that crustal-scale fluid flow in hydrofractures can achieve.</p>

Towards coupling fluid flow and rate-and-state friction in compacting visco-poro-elasto-plastic reservoirs

2020 ◽  
Author(s):  
Mohsen Goudarzi ◽  
Ylona van Dinther ◽  
Meng Li ◽  
René de Borst ◽  
Casper Pranger ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Induced Seismicity ◽  
Large Scale ◽  
Bulk Material ◽  
Frictional Heating ◽  
Fluid Pressure ◽  
Gas Production ◽  
Modeling Framework ◽  
Fully Coupled

<p>Induced seismicity as a result of natural gas production is a major challenge from both an industrial and a societal perspective. The compaction caused by gas production leads to changes of the effective pressure fields in the reservoir and stress redistributions occur particularly in the surrounding faults. In addition, the strong coupling between fluid flow and solid rock deformations and the role of fluid flow regarding the frictional properties of the faults necessitate a coupled and comprehensive modeling framework. A general and fully coupled thermo-hydro-mechanical finite difference formulation is developed herein and the results are verified against numerical benchmarks. A visco-elasto-plastic rheological behavior is assumed for the bulk material and a return-mapping algorithm is implemented for accurate simulation of the stress evolution. The geometrical features of the faults are incorporated into a regularized continuum framework, while the response of the fault zone is governed by a rate-and-state-dependent friction model. Numerical simulations are provided for large-scale problems and their efficiency is assured through the evaluation of the consistently linearized systems of equations along with the use of advanced numerical solvers and parallel computing. Although the proposed framework is a step towards the modeling of earthquake sequences for induced seismicity applications, the features of the numerical model are highlighted for other applications, including seismic events in subduction settings where the role of fluid flow inside the faults is considerable. Another application of the present, fully coupled hydro-thermo-mechanical formulation is the prediction of the fluid pressurization phenomena, where the frictional heating increases the magnitude of the pore fluid pressure inside the faults, and the resultant degradation of dynamic frictional strength is naturally captured. </p>

Stable isotope constraints on the role of graphite in the genesis of unconformity-type uranium deposits

1989 ◽  
Vol 26 (3) ◽  
pp. 490-498 ◽  
Author(s):  
T. K. Kyser ◽  
M. R. Wilson ◽  
G. Ruhrmann
Keyword(s):  
Fluid Flow ◽  
Stable Isotope ◽  
Uranium Deposit ◽  
Shear Zones ◽  
Limited Range ◽  
Hydrothermal Fluids ◽  
Uranium Deposits ◽  
Athabasca Basin ◽  
Ore Zones

The Key Lake unconformity-type uranium deposit occurs in a shear zone where it intersects the unconformity between Archean and Aphebian gneisses and the overlying Proterozoic Athabasca Group sandstones. The roots of the Key Lake and many other unconformity-type uranium deposits in the Athabasca basin are close to gneisses rich in graphite and most deposits have small amounts of carbonaceous materials (bitumen and hydrocarbon buttons) within and around altered basement and sandstone ore zones. In many Athabasca uranium deposits, hydrothermal fluids have destroyed graphite disseminated in the strongly altered gneisses in the vicinity of the deposits, prompting some to suggest that graphite was converted to CH4, which reduced and precipitated the uranium and partially condensed to form bitumen. The δ13C values of graphite collected from unaltered and altered gneisses around the Key Lake deposit have a limited range (−25 ± 5) and are not a function of distance from the mineralization or the intensity of alteration or deformation. The uniformity of these δ13C values suggests that the destruction of graphite was due predominantly to oxidation by basinal fluids from the sandstone and that the graphite near the deposits did not react to form substantial amounts of 12C-rich phases such as CH4. Most of the bitumen samples, which have higher H/C ratios than the graphite, have δ13C values identical to those of the graphite (−25 ± 5). The similarity in the isotopic compositions of carbon in the bitumen and in the graphite indicates that the bitumen formed from degradation of graphite as a result of reactions with no significant isotopic fractionations, such as ones involving radiolysis of graphite. The hydrocarbon buttons and a few samples of bitumen have petrographic relations and 13C/12C ratios (δ13C values less than −30) that are indicative of reduction of graphite by H2 produced from water by radiolysis. Graphite in these deposits did not play a central role as a reducing agent for uranium, rather it represents a critical structural factor by providing shear zones along which fluid flow can be focussed.

scholarly journals “Poor” archeological levels not to be forgotten: units of Middle and early Upper Magdalenian age in El Mirón Cave (Ramales de la Victoria, Cantabria, Spain)

2021 ◽  
Author(s):  
undefined Lawrence Guy STRAUS ◽  
undefined Manuel R. GONZÁLEZ MORALES
Keyword(s):  
Coastal Zone ◽  
Significant Role ◽  
Large Scale ◽  
Late Glacial ◽  
Short Term ◽  
Large Numbers ◽  
Portable Art ◽  
Early Upper

This succinct contribution focuses on description and preliminary interpretation of “minor” occupations of the large, strategically located El Mirón Cave on the edge of the Cantabrian Cordillera in eastern Cantabria (Spain) during the Middle and early Upper Magalenian that followed upon the massive, culturally rich, faunally dense, functionally complex deposits of the Initial and Lower Magdalenian. The ten levels analyzed here date to the Late Glacial, c. 15.5-12.5 uncal kya BP. At a time when the classic Middle Magdalenian of the nearby French Pyrenees developed and major residential sites with clear social links to it (via the key site of Isturitz) were occupied in the lowland coastal zone of Cantabria and Asturias (e.g. La Garma, Llonín, La Viña), El Mirón had reverted for the most part to the role of a short-term, special-purpose, perhaps logistical campsite, rather than as a long-term, large-scale hub residential base. It is tempting (and indeed traditional) to focus on levels with large numbers of lithic and osseous artifacts, as well as works of portable art and personal ornaments, which are so characteristic of the most famous Magdalenian occupations. However, in hunter-gatherer subsistence systems, the “minor” locations played a significant role in the human exploitation of territories (especially ones with such complex, high relief as Cantabrian Spain). The levels in question here include some that can be interpreted as hunting camps (suggested by high percentages of worked and unworked bladelets and some antler points within the small assemblages), partially reminiscent of the use to which the cave may have been put during pre-Initial Magdalenian times, notably during the Solutrean, which was relatively rich in stone points.

Role of Large Scale Fluid-Flow in Subsurface Arsenic Enrichment

2005 ◽  
pp. 127-164 ◽  
Author(s):  
M.B. Goldhaber ◽  
R.C. Lee ◽  
J.R. Hatch ◽  
J.C. Pashin ◽  
J. Treworgy
Keyword(s):  
Fluid Flow ◽  
Large Scale

scholarly journals The Morphotectonic units of Ikaria island – Contribution in the natural hazards research

2017 ◽  
Vol 44 ◽  
pp. 79
Author(s):  
H. Efraimiadou ◽  
St. Lozios ◽  
N. Evelpidou
Keyword(s):  
Human Impact ◽  
Natural Hazards ◽  
Large Scale ◽  
Drainage System ◽  
Shear Zones ◽  
Normal Faults ◽  
Additional Parameter ◽  
Detachment Faults ◽  
Slip Transfer ◽  
Definition Of

Present morphological and tectonic image of Ikaria island is the complex result of both the tem-poral evolution of the island, as part of the geodynamical evolution of the Hellenic Arc, especially that of the last stages (from the upper Miocene and after), and the exogenous factors. Also human impact functions as an additional parameter for the formation of Ikaria geoenvironment.According to field data and their analysis, computing and estimation which took part with the use of modern technologies (use of GIS, analysis of geographical and descriptive databases) the mor-photectonic units of Ikaria Island were defined. The definition of the morphotectonic units was based on their special features and more precisely on the lithological differentiation (granite, metamorphic rocks and post alpine formations) as well as the complex ductile and brittle structures (large scale ductile shear-zones and brittle detachment faults, normal faults, strike-slip transfer faults and join sets) and the morphological features (slope distribution, asymmetry of the drainage system, planation surfaces, morphological discontinuities etc).The synthesis of the special features of each morphotectonic unit in combination with the human impact (fires, overgrazing etc), defines the kind, the intensity and the geographical localization of the natural hazards which occur in various sites of the island, such as landslides, erosion, floods, seismic activity, relief changes, coastline changes etc.

Sign in / Sign up

Export Citation Format

Share Document