scholarly journals Progressive veining during peridotite carbonation: insights from listvenites in Hole BT1B, Samail ophiolite (Oman)

2022 ◽  
Author(s):  
Manuel D. Menzel ◽  
Janos L. Urai ◽  
Estibalitz Ukar ◽  
Thierry Decrausaz ◽  
Marguerite Godard
Keyword(s):  
Wall Rock ◽  
Tectonic Stress ◽  
Vein Wall ◽  
Chemical Zoning ◽  
Reaction Fronts ◽  
Vein Formation ◽  
Median Zone ◽  
Massive Fluid ◽  
Rock Interface ◽  
Dolomite Precipitation

Abstract. The reaction of serpentinized peridotites with CO2-bearing fluids to listvenite (quartz-carbonate rocks) requires massive fluid flux and significant permeability despite increase in solid volume. Listvenite and serpentinite samples from Hole BT1B of the Oman Drilling Project help to understand mechanisms and feedbacks during vein formation in this process. Samples analyzed in this study contain abundant magnesite veins in closely spaced, parallel sets and younger quartz-rich veins. Cross-cutting relationships suggest that antitaxial, zoned carbonate veins with elongated grains growing from a median zone towards the wall rock are among the earliest structures to form during carbonation of serpentinite. Their bisymmetric chemical zoning of variable Ca and Fe contents, a systematic distribution of SiO2 and Fe-oxide inclusions in these zones, and cross-cutting relations with Fe-oxides and Cr-spinel indicate that they record progress of reaction fronts during replacement of serpentine by carbonate in addition to dilatant vein growth. Euhedral terminations and growth textures of carbonate vein fill together with local dolomite precipitation and voids along the vein – wall rock interface suggest that these antitaxial veins acted as preferred fluid pathways allowing infiltration of CO2-rich fluids necessary for carbonation to progress. Fluid flow was probably further enabled by external tectonic stress, as indicated by closely spaced sets of subparallel carbonate veins. Despite widespread subsequent quartz mineralization in the rock matrix and veins, which most likely caused a reduction in the permeability network, carbonation proceeded to completion in listvenite horizons.

Reactions between uranium veins and their host rocks in Vendée and Limousin (France)

1981 ◽  
Vol 44 (336) ◽  
pp. 417-423 ◽  
Author(s):  
M. Cathelineau ◽  
J. Leroy
Keyword(s):  
Structural Characteristics ◽  
Wall Rock ◽  
Structural Features ◽  
Gangue Mineral ◽  
List Type ◽  
Vein Formation ◽  
Wall Rock Alteration ◽  
Rock Alteration ◽  
Host Rocks ◽  
Basic Rocks

AbstractHydrothermal uranium veins, associated with the Hercynian leucogranites show important variations in their mineralogical, chemical and structural features in relation to the host rock lithology. These are described with particular reference to the Chardon deposit, Vendée where the veins cut granite, basic lithologies, and shales. The following features are described: 1Changes in the thickness of veins near to contact zones, particularly those between granites and basic lithologies, lamprophyres, and shales.2Changes in the gangue mineral assemblage with the preferential development of carbonate in veins cutting basic lithologies, and of silica in veins which cut granite.3Paragenetic zoning in the veins in passing from granites to their metamorphic aureoles.Comparisons between deposits of Vendée, Limousin, and Erzgebirge allow the following generalizations to be made: 1Open faults and subsequent mineralization are concentrated at boundaries between competent and more plastic lithologies.2Mineralizing fluids cause wall-rock alteration characterized by the removal of Si from granite and of Ca, Mg, Fe from metamorphic and basic rocks.3The chemical and structural characteristics of wallrocks are important controls on the mineralization but in acid lithologies the main controls on the pitchblende vein formation are the structural characteristics of the wallrock.

Mechanisms of varicose vein formation: valve dysfunction and wall dilation

2008 ◽  
Vol 23 (2) ◽  
pp. 85-98 ◽  
Author(s):  
J D Raffetto ◽  
R A Khalil
Keyword(s):  
Varicose Vein ◽  
Structural Integrity ◽  
Cell Injury ◽  
Varicose Veins ◽  
Venous Pressure ◽  
Venous Disease ◽  
Vein Wall ◽  
Valve Dysfunction ◽  
Functional Changes ◽  
Vein Formation

Varicose veins are a common venous disease of the lower extremity. Although the mechanisms and determinants in the development of varicosities are not clearly defined, recent clinical studies and basic science research have cast some light on possible mechanisms of the disease. In varicose veins, there are reflux and incompetent valves as well as vein wall dilation. Primary structural changes in the valves may make them ‘leaky’, with progressive reflux causing secondary changes in the vein wall. Alternatively, or concurrently, the valves may become incompetent secondary to structural abnormalities and focal dilation in vein wall segments near the valve junctions, and the reflux ensues as an epiphenomenon. The increase in venous pressure causes structural and functional changes in the vein wall that leads to further venous dilation. Increase in vein wall tension augments the expression/activity of matrix metalloproteinases (MMPs), which induces degradation of the extracellular matrix proteins and affect the structural integrity of the vein wall. Recent evidence also suggests an effect of MMPs on the endothelium and smooth muscle components of the vein wall and thereby causing changes in the venous constriction/relaxation properties. Endothelial cell injury also triggers leukocyte infiltration, activation and inflammation, which lead to further vein wall damage. Thus, vein wall dilation appears to precede valve dysfunction, and the MMP activation and superimposed inflammation and fibrosis would then lead to chronic and progressive venous insufficiency and varicose vein formation.

Vein-wall rock relationships, White Pine Mine

1964 ◽  
Vol 59 (1) ◽  
pp. 160-161
Author(s):  
John R. Rand
Keyword(s):  
Wall Rock ◽  
White Pine ◽  
Vein Wall

Field evidence for fluid facilitated fracturing and Dissolution-Precipitaion creep explains observed off-fault tremor and continuous deformation: Field examples from the Alpine Fault, New Zealand 

2021 ◽  
Author(s):  
Jack McGrath ◽  
Sandra Piazolo ◽  
Rebecca Morgan ◽  
John Elliott
Keyword(s):  
New Zealand ◽  
Host Rock ◽  
Tectonic Stress ◽  
High Signal ◽  
Deformation Region ◽  
Stress Regime ◽  
Continuous Deformation ◽  
Alpine Fault ◽  
Vein Formation ◽  
Field Evidence

<div> <p>Geophysical observations show that the Alpine Fault in New Zealand is characterised by mid-crustal off-fault recurring tremor events and off-fault regions of continuous deformation. While geodesy indicates that deformation is distributed across the South Island, evidence from the rock record shows deformation accommodated in a region within several km from the fault. This zone is characterized by a 100-300 m wide mylonitised central fault zone and an approximately 8--10km, wide deformation region marked by the presence of Alpine foliation. Magnetotelluric surveys of the Southern Alps indicate a mid-crustal, high signal area coinciding with the location of the recurring tremors.  </p> </div><div> <p>While the mylonites and their associated mechanisms have been extensively studied in the field area, the wider off-fault deformation region has not had the same scrutiny. In the latter region, we observe frequent layer parallel, folded and crosscutting quartz veins. Quartz vein orientation and geometries are consistent with fracturing in the presence of fluid within an overall tectonic stress regime. The observed overprinting of older veins by younger vein generations, as well as their successive reorientations, indicate recurring fracturing within a continuously deforming region. Quantitative analysis of vein geometries including their width and displacement shows that vein formation may trigger the observed mid-crustal tremor signal. Microstructural signatures within the host rock are consistent with dissolution-precipitation creep as the main deformation mechanism in the host rock and pre-existing veins.  </p> </div><div> <p>In summary, according to field evidence both geophysically observed transient and continuous deformation take place in the presence of fluid and occur contemporaneously. This implies that strain accommodation in the host rock facilitated by dissolution-precipitation creep is insufficient; consequently, stress is build-up over time triggering intermittent fracturing.  </p> </div>

Enhancing the Solidification Between Mud Cake and Wall Rock for Cementing Applications: Experimental Investigation and Mechanisms

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Xiaodong Bai ◽  
Yuqian Xu ◽  
Xuepeng Zhang ◽  
Xuemei Yong ◽  
Tao Ning
Keyword(s):  
Testing Machine ◽  
Xrd Analysis ◽  
Wall Rock ◽  
Solid Particles ◽  
Hydration Products ◽  
Mud Cake ◽  
Rock Interface ◽  
Energy Disperse Spectroscopy ◽  
Cementing Agent

Abstract In conventional cementing operations, the mud cake on the well wall cannot be completely removed， which can easily lead to annular channeling. In order to reduce the influence of loose and fragile mud cake on cementing, a kind of mud cake curing agent is used to effectively improve the curing quality of mud cake and rock. In this article, the mud cake compressive strength are tested by compression-testing machine. The samples are analyzed using X-ray diffractometer (XRD), scanning electron microscopy (SEM), and energy disperse spectroscopy (EDS). The results showed that the cementing agent can significantly improve the cementation strength between mud cake and wall rock. A variety of hydration products were resulted such as CaAl2Si2O8 · 4H2O, Ca(SiO4)2(OH)2, and Mg4Al2(OH)14 · 3H2O, as revealed from the XRD analysis. In addition, it was found that the formation of hydration products is the main reason for the increase of cementation strength. The flocculent inclusions filled with solid particles are formed on the solid particles of the mud cake, which makes an integrated cementation at the interface between mud cake and wall rock. A large amount of cations including Ca2+, Mg2+, and Al3+ are collected at the cementation interface, which is the basic condition for various hydration reactions and helps to enhance the cementation strength of the mud cake and rock interface.

scholarly journals Varicose Veins: Role of Mechanotransduction of Venous Hypertension

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Hussein M. Atta
Keyword(s):  
Blood Pressure ◽  
Varicose Vein ◽  
Varicose Veins ◽  
Financial Burden ◽  
Adult Population ◽  
Venous Pressure ◽  
Venous Hypertension ◽  
Vein Wall ◽  
Vein Formation

Varicose veins affect approximately one-third of the adult population and result in significant psychological, physical, and financial burden. Nevertheless, the molecular pathogenesis of varicose vein formation remains unidentified. Venous hypertension exerted on veins of the lower extremity is considered the principal factor in varicose vein formation. The role of mechanotransduction of the high venous pressure in the pathogenesis of varicose vein formation has not been adequately investigated despite a good progress in understanding the mechanomolecular mechanisms involved in transduction of high blood pressure in the arterial wall. Understanding the nature of the mechanical forces, the mechanosensors and mechanotransducers in the vein wall, and the downstream signaling pathways will provide new molecular targets for the prevention and treatment of varicose veins. This paper summarized the current understanding of mechano-molecular pathways involved in transduction of hemodynamic forces induced by blood pressure and tries to relate this information to setting of venous hypertension in varicose veins.

Vein-wall rock relationships, White Pine Mine

1963 ◽  
Vol 58 (8) ◽  
pp. 1345-1346
Author(s):  
Ira B. Joralemon
Keyword(s):  
Wall Rock ◽  
White Pine ◽  
Vein Wall

Sulphur-isotope geochemistry of silver–selpnarsenide vein mineralization, Cobalt, Ontario

1986 ◽  
Vol 23 (10) ◽  
pp. 1551-1567 ◽  
Author(s):  
M. D. Goodz ◽  
D. H. Watkinson ◽  
V. Smejkal ◽  
Z. Pertold
Keyword(s):  
Isotopic Composition ◽  
Isotope Fractionation ◽  
Isotope Geochemistry ◽  
Wall Rock ◽  
Sulphur Isotope ◽  
Vein Formation ◽  
Metavolcanic Rocks ◽  
Isotope Study ◽  
Vein Deposits ◽  
Sulphur Isotopic Composition

The silver–sulpharsenide vein deposits of Cobalt, Ontario, crosscut basement Archean metavolcanic rocks, Proterozoic strata, and younger Proterozoic diabase sills. A petrographic and sulphur-isotope study of the metallic minerals was initiated to assess possible genetic models of vein formation. Discrete differences exist between the sulphur-isotope compositions of basement sulphides (δ34S = + 4.0‰), brecciated wall-rock sulphides (+ 3.5‰), and vein sulphides (+ 2.3‰). The δ34S values consistently increase with distance from the vein centres. Sulphur-isotope fractionation trends are similar for all the vein deposits studied. Sulphur-isotope data suggest that sulphides were deposited between 130 and 254 °C. Based on the assumption of equilibrium between chalcopyrite and galena, the initial δ34S of the fluid was between + 5.0 and + 11.0‰. The release of sulphur during the reaction of Archean pyrite with Proterozoic formational brines to form pyrrhotite is proposed to explain the heavy sulphur isotopic composition of the fluid. This process could also have provided the Ni, Co, and As, known to be concentrated in some pyrite, that was deposited in the silver veins. Interpretation of mineral paragenesis and geothermometry indicate that temperature decreased and aS2 increased as deposition proceeded.

The Touquoy Zone deposit: an example of "unusual" orogenic gold mineralisation in the Meguma Terrane, Nova Scotia, Canada

2003 ◽  
Vol 40 (3) ◽  
pp. 447-466 ◽  
Author(s):  
Frank P Bierlein ◽  
Paul K Smith
Keyword(s):  
Close Correlation ◽  
Wall Rock ◽  
Convincing Evidence ◽  
Structural Level ◽  
Vein Formation ◽  
Wall Rock Alteration ◽  
Base Metal Sulphides ◽  
Meguma Terrane ◽  
Rock Alteration ◽  
Host Rocks

The Touquoy Zone deposit is host to disseminated gold mineralisation in metasiltstones of lower Palaeozoic age. From the close correlation between ore grades and the intersection of favourable stratigraphy and bounding faults, it is apparent that mineralisation is controlled by both structural and lithological influences. Within the ore zone, disseminated gold, arsenopyrite, pyrite, and rare base-metal sulphides are associated with a network of widely spaced, millimetre-scale, quartz–carbonate veinlets. Quasi-pervasive fluid flow and prolonged interaction with the host rocks resulted in a diffuse, but pronounced halo of wall-rock alteration that is characterized by the breakdown of detrital feldspar and metamorphic chlorite and the development of hydrothermal carbonate phases, K-mica, and disseminated sulphides. These mineralogical changes are accompanied by enrichment in CO2, K, Au, As, and S and depletion in Na across the ore zone. Vein formation occurred at between 250° and 350°C and pressures of less than 1–2 kbar (1 kbar = 100 MPa), corresponding to an estimated depth of between <2.8 and 6 km. Mineralisation resulted from the unmixing of an overpressured (low-salinity, CO2-rich) fluid in response to decreasing pressure during its ascent and penetration into permeable host rocks. Geological and geochemical features of mineralisation in the Touquoy Zone deposit are seen as convincing evidence for a close genetic association between disseminated-style and lode gold mineralisation in orogenic terrains, with the resulting style of mineralisation largely controlled by the overall structural geometry of the mineralising site, rheological properties, permeability and chemical receptiveness of the host rock, and structural level of emplacement.

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