Near-surface hydrothermal activity in the eastern Otago schist (Note)

1987 ◽  
Vol 30 (4) ◽  
pp. 437-443 ◽  
Author(s):  
D. Craw ◽  
S.A. McKeag
Keyword(s):  
Hydrothermal Activity ◽  
Near Surface ◽  
Otago Schist

scholarly journals Volcanic hydrothermal systems as potential analogues of Martian sulphate-rich terrains

2015 ◽  
Vol 95 (2) ◽  
pp. 153-169 ◽  
Author(s):  
A. Rodríguez ◽  
M.J. van Bergen
Keyword(s):  
Hydrothermal Activity ◽  
Hydrothermal Systems ◽  
Geothermal Systems ◽  
Ambient Conditions ◽  
Flow Paths ◽  
Near Surface ◽  
Mineral Associations ◽  
The Status ◽  
History Of ◽  
Active Processes

AbstractRemote sensing observations and rover missions have documented the presence of sulphate-rich mineral associations on Mars. Many of these minerals are paleo-indicators of hydrous, acidic and oxidising environments that must have prevailed in Mars´ distant past, contrary to the present conditions. Furthermore, occurrences of silica together with high Cl and Br concentrations in Martian soils and rocks represent fingerprints of chemically atypical fluids involved in processes operating on the surface or at shallow depth. From field observations at representative active volcanoes in subduction settings, supported by geochemical modelling, we demonstrate that volcanic hydrothermal systems are capable of producing Mars-like secondary mineral assemblages near lakes, springs and fumaroles through the action of acidic fluids. Water–gas-rock interactions, together with localised flow paths of water and fumarolic gas emitted from associated subaerial vents, lead to deposition of a range of sulphates, including gypsum, jarosite, alunite, epsomite and silica. Evaporation, vapour separation and fluid mixing in (near-) surface environments with strong gradients in temperature and fluid chemistry further promote the diversity of secondary minerals. The mineralogical and chemical marks are highly variable in space and time, being subject to fluctuations in ambient conditions as well as to changes in the status of volcanic-hydrothermal activity. It is concluded that active processes in modern volcanic-geothermal systems may be akin to those that created several of the sulphate-rich terrains in the early history of Mars.

Interactions between deformation, magmatism and hydrothermal activity during active crustal thickening: a field example from Nanga Parbat, Pakistan Himalayas

1997 ◽  
Vol 61 (404) ◽  
pp. 37-52 ◽  
Author(s):  
Robert W. H. Butler ◽  
Nigel B. W. Harris ◽  
Alan G. Whittington
Keyword(s):  
Shear Zones ◽  
Hydrothermal Activity ◽  
Feedback Mechanism ◽  
Crustal Thickening ◽  
Strain Localisation ◽  
Near Surface ◽  
Geothermal Gradients ◽  
Active Structures ◽  
Nanga Parbat ◽  
Topographic Relief

AbstractThe Nanga Parbat massif is a rapidly eroding, thrust-related antiform that is distinct from other regions of the Himalayan orogen in being both intruded by Late Miocene-Pliocene anatectic granites and permeated by a vigorous hydrothermal system. Exhumation is achieved by erosion during thrusting along the Liachar thrust in the apparent absence of extensional tectonics. At depths in excess of 20 km, small batches of leucogranitic melt have been generated by fluid-absent breakdown of muscovite from metapelitic lithologies. These melts ascend several kilometres prior to emplacement, aided by low geothermal gradients at depth and by interaction with meteoric water as they reach shallow levels. At intermediate depths (∼15 km) limited fluid infiltration is restricted to shear zones resulting in localised anatexis. Within the upper 8 km of crust, magmatic and meteoric fluid fluxes are channelised by active structures providing a feedback mechanism for focusing deformation. Leucogranite sheets show a range of pre-full crystallization and high-temperature crystal-plastic textures indicative of strain localisation onto these sheets and away from the country rocks. At subsolidus temperatures meteoric fluids promote strain localisation and may trigger cataclastic deformation. Since near-surface geothermal gradients are unusually steep, the macroscopic transition between distributed shearing and substantial, but localised, cataclastic deformation occurred at amphibolite-facies conditions (∼600°C). Even with the greatest topographic relief in the world, the meteoric system of Nanga Parbat is effectively restricted to the upper 8 km of the crust, strongly controlled by active structures.

scholarly journals Impact of volcanic and post volcanic activity on fluvial relief

2019 ◽  
pp. 49-66
Author(s):  
E. V. Lebedeva
Keyword(s):  
Explosive Volcanism ◽  
Hydrothermal Activity ◽  
River Network ◽  
Tectonic Activity ◽  
Lava Tubes ◽  
Near Surface ◽  
Volcanic Material ◽  
Mud Volcanism ◽  
High Erosion Rate ◽  
Characteristic Features

The characteristic features of the river network, the structure and functioning of the valleys affected by effusive and explosive volcanism, volcano-tectonic phenomena, gas hydrothermal activity and mud volcanism are revealed. It has been established that within flows and covers of effusives, the formation of new streams channels can occur not only due to backward erosion, but also as a result of the collapse of the roof of the near-surface lava tubes, which are actively used by underground runoff. A high erosion rate, a large volume of solid runoff, and a significant role of deflation in the transformation of the fluvial relief are characteristic for regions of domination of explosive activity. There valleys become zones of accumulation of volcanic material, which is gradually processed by mudflow, alluvial, aeolian and other processes. Volcanic-tectonic activity changes the rivers position, direction of streams and morphology of the valleys, leading to numerous reorganizations of the river network, as a result of which the valleys of modern watercourses often consist of uneven-age fragments. Valleys of hydrothermal zones are characterized by the active development of slope processes, which leads to the formation in them not only of sinter terraces, but also numerous landslide ones. Mud volcanic processes periodically lead to the filling and blocking of the valleys with mud breccia flows, which affects both the composition of the alluvium of watercourses and the morphology of the valleys.

Vein, manto, and chimney mineralization at the Fresnillo sliver–lead–zinc mine, Mexico

1986 ◽  
Vol 23 (10) ◽  
pp. 1603-1614 ◽  
Author(s):  
A. James Macdonald ◽  
Marek J. Kreczmer ◽  
Stephen E. Kesler
Keyword(s):  
Hydrothermal Activity ◽  
Partial Replacement ◽  
Isotopic Ratios ◽  
Near Surface ◽  
Northern Mexico ◽  
Quartz Monzonite ◽  
Lead Zinc ◽  
Zinc Mine ◽  
Lead Isotopic Ratios ◽  
Ore Zones

Discovered in 1553, the Fresnillo mine in central Mexico has produced approximately 18 t Au, 8830 t Ag, 690 000 t Pb, 925 600 t Zn, and 74 000 t Cu (data for production from 1921 to 1984 inclusive). Ore has been mined from an oxide capping near surface and from unoxidized veins, mantos, and chimneys to a depth of 1 km along a strike length of 4 km. Ore zones at depth, in the northwest portion of the mine, are spatially related to a quartz monzonite porphyry stock, which intrudes a sequence of Mesozoic marine sediments that is overlain by terrestrial rhyolites. Manto and chimney mineralization followed development of skarn around the intrusion and was cut, in turn, by the veins that contain the bulk of the ore. The veins cut the quartz monzonite stock. Manto and chimney mineralization is characterized by partial replacement of the Mesozoic sedimentary rocks with axinite, hedenbergite, quartz, carbonate, sulphides, sulphosalts, sulpharsenides, and sulphantimonides. Brecciation preceded replacement in the chimney bodies. One of the largest replacement orebodies, the Cueva Santa Branch Manto in the central part of the mine, contains an orthogonal fracture set formed during antiformal folding. Trends in grade distribution throughout the manto follow the orthogonal fractures, which are filled by quartz and sulphides. Silver/base-metal ratios show marked peaks where manto mineralization abuts against major veins. Fluid-inclusion filling temperatures and salinities are high in ore zones adjacent to the quartz monzonite stock at a depth of 1 km: mean filling temperature is approximately 320 °C (range 230–370 °C), salinity ranges from 4 to 12 eq. wt.% NaCl. Fluid inclusions from ore near surface exhibit lower filling temperatures (a mean of 235 °C and a range of 210–290 °C) and lower salinity (< 1 eq. wt.% NaCl). The data are consistent with a reduction in temperature and with dilution as the hydrothermal fluids flowed away from the intrusive porphyry.δ34S values for sphalerite, galena, and chalcopyrite from deeper and intermediate levels in the mine range from −6.1 to −3.5‰. Calculated δ34SΣS is approximately 0‰, suggesting a magmatic sulphur source. Lead isotopic ratios obtained from galena-bearing vein, manto, and chimney samples throughout the mine fall on a line defined by 34 deposits in northern Mexico with slope of 0.092 ± 0.017 in the 208Pb/204Pb versus 207Pb/204Pb system. The lead data indicate that felsic igneous processes extracted the metal from a Precambrian basement source; this was followed by concentration within mineralized zones during hydrothermal activity.

40Ar/39Ar age evidence for an impact-generated hydrothermal system in the Devonian Siljan crater, Sweden

2021 ◽  
Author(s):  
Maria Herrmann ◽  
Carl Alwmark ◽  
Michael Storey
Keyword(s):  
Hydrothermal System ◽  
Rapid Heating ◽  
Hydrothermal Activity ◽  
Hydrothermal Systems ◽  
Impact Structure ◽  
Near Surface ◽  
Central Uplift ◽  
Target Rock ◽  
Step Heating ◽  
Pressure Regime

ABSTRACT Crater-forming events are generally followed by the development of hydrothermal systems due to the rapid heating of the target rock. Such hydrothermal systems are a feature of nearly all large terrestrial impact structures. For the Siljan impact structure in Sweden, there is evidence for such a fossil hydrothermal system, possibly triggered by the impact event ca. 380 Ma. To investigate the thermal regime of the near-surface hydrothermal activity of the Siljan crater, biotite and amphibole grains extracted from samples collected in a transect across the high-pressure regime recorded by the central uplift, as well as from distal localities outside the central uplift of the crater, were dated using the 40Ar/39Ar laser step-heating technique. Our results show that biotite from inside the central uplift, which was strongly altered to chlorite by low-temperature (200–340 °C) hydrothermal reactions, yields strongly disturbed age spectra. The first and second (low laser power) step ages range from ca. 1300 to 190 Ma. In contrast, biotite from outside the central uplift and amphibole, irrespective of location inside or outside of the central uplift, are much less altered, which is reflected in less disturbed, near-flat age spectra. This result indicates that the hydrothermal temperatures inside the central uplift were &gt;200 °C, sufficient to disturb the K-Ar system of biotite during its chloritization, but too low to affect the amphibole (closure temperature of 480–580 °C). In contrast, the temperature of the hydrothermal system outside of the central uplift was &lt;200 °C, as no significant reset of the K-Ar system can be observed in either biotite or amphibole. Our results are consistent with estimated trapping temperatures from fluid inclusion studies, which show a decrease from 327–342 °C within the central uplift to 40–225 °C toward outside the central uplift. We conclude that the near-surface hydrothermal system in the Siljan impact structure was an impact-triggered system. This system was strongly active, with its highest temperature inside the central uplift and decreasing rapidly toward the outlying part of the crater.

Benthic foraminiferal zonation in deep-water carbonate platform margin environments, northern Little Bahama Bank

1988 ◽  
Vol 62 (01) ◽  
pp. 1-8 ◽  
Author(s):  
Ronald E. Martin
Keyword(s):  
Deep Water ◽  
Benthic Foraminifera ◽  
Carbonate Platform ◽  
Sedimentary Facies ◽  
Depositional Environments ◽  
Near Surface ◽  
Sediment Gravity Flows ◽  
Gravity Flows ◽  
Platform Margin ◽  
Water Carbonate

The utility of benthic foraminifera in bathymetric interpretation of clastic depositional environments is well established. In contrast, bathymetric distribution of benthic foraminifera in deep-water carbonate environments has been largely neglected. Approximately 260 species and morphotypes of benthic foraminifera were identified from 12 piston core tops and grab samples collected along two traverses 25 km apart across the northern windward margin of Little Bahama Bank at depths of 275-1,135 m. Certain species and operational taxonomic groups of benthic foraminifera correspond to major near-surface sedimentary facies of the windward margin of Little Bahama Bank and serve as reliable depth indicators. Globocassidulina subglobosa, Cibicides rugosus, and Cibicides wuellerstorfi are all reliable depth indicators, being most abundant at depths &gt;1,000 m, and are found in lower slope periplatform aprons, which are primarily comprised of sediment gravity flows. Reef-dwelling peneroplids and soritids (suborder Miliolina) and rotaliines (suborder Rotaliina) are most abundant at depths &lt;300 m, reflecting downslope bottom transport in proximity to bank-margin reefs. Small miliolines, rosalinids, and discorbids are abundant in periplatform ooze at depths &lt;300 m and are winnowed from the carbonate platform. Increased variation in assemblage diversity below 900 m reflects mixing of shallow- and deep-water species by sediment gravity flows.

Analysis of 2D and 3D defects associated with precipitation of Cu in silicon

1991 ◽  
Vol 49 ◽  
pp. 870-871
Author(s):  
P.M. Rice ◽  
MJ. Kim ◽  
R.W. Carpenter
Keyword(s):  
Colony Growth ◽  
Dark Field ◽  
Dark Side ◽  
Silicide Phase ◽  
Strain Fields ◽  
Near Surface ◽  
Unknown Composition ◽  
Secondary Precipitates ◽  
20 Nm ◽  
2D And 3D

Extrinsic gettering of Cu on near-surface dislocations in Si has been the topic of recent investigation. It was shown that the Cu precipitated hetergeneously on dislocations as Cu silicide along with voids, and also with a secondary planar precipitate of unknown composition. Here we report the results of investigations of the sense of the strain fields about the large (~100 nm) silicide precipitates, and further analysis of the small (~10-20 nm) planar precipitates.Numerous dark field images were analyzed in accordance with Ashby and Brown's criteria for determining the sense of the strain fields about precipitates. While the situation is complicated by the presence of dislocations and secondary precipitates, micrographs like those shown in Fig. 1(a) and 1(b) tend to show anomalously wide strain fields with the dark side on the side of negative g, indicating the strain fields about the silicide precipitates are vacancy in nature. This is in conflict with information reported on the η'' phase (the Cu silicide phase presumed to precipitate within the bulk) whose interstitial strain field is considered responsible for the interstitial Si atoms which cause the bounding dislocation to expand during star colony growth.

Shock consolidation of Ni-Ti alloy powder

1986 ◽  
Vol 44 ◽  
pp. 430-431
Author(s):  
Naresh N. Thadhani ◽  
Thad Vreeland ◽  
Thomas J. Ahrens
Keyword(s):  
Alloy Powder ◽  
Amorphous Material ◽  
Ti Alloy ◽  
Two Phase ◽  
Near Surface ◽  
Optical Micrograph ◽  
Shock Compaction ◽  
Powder Particles ◽  
Ti Powder ◽  
Rapidly Solidified

A spherically-shaped, microcrystalline Ni-Ti alloy powder having fairly nonhomogeneous particle size distribution and chemical composition was consolidated with shock input energy of 316 kJ/kg. In the process of consolidation, shock energy is preferentially input at particle surfaces, resulting in melting of near-surface material and interparticle welding. The Ni-Ti powder particles were 2-60 μm in diameter (Fig. 1). About 30-40% of the powder particles were Ni-65wt% and balance were Ni-45wt%Ti (estimated by EMPA).Upon shock compaction, the two phase Ni-Ti powder particles were bonded together by the interparticle melt which rapidly solidified, usually to amorphous material. Fig. 2 is an optical micrograph (in plane of shock) of the consolidated Ni-Ti alloy powder, showing the particles with different etching contrast.

Preparation of cross-sectional samples for near-surface TEM studies

1987 ◽  
Vol 45 ◽  
pp. 380-381
Author(s):  
R.C. Dickenson ◽  
K.R. Lawless
Keyword(s):  
Standard Sample ◽  
Surface Region ◽  
Specimen Preparation ◽  
Thick Sheet ◽  
Drill Bit ◽  
Sample Holder ◽  
Metal Interface ◽  
Cross Sectional ◽  
Near Surface ◽  
Cold Worked

In thermal oxidation studies, the structure of the oxide-metal interface and the near-surface region is of great importance. A technique has been developed for constructing cross-sectional samples of oxidized aluminum alloys, which reveal these regions. The specimen preparation procedure is as follows: An ultra-sonic drill is used to cut a 3mm diameter disc from a 1.0mm thick sheet of the material. The disc is mounted on a brass block with low-melting wax, and a 1.0mm hole is drilled in the disc using a #60 drill bit. The drill is positioned so that the edge of the hole is tangent to the center of the disc (Fig. 1) . The disc is removed from the mount and cleaned with acetone to remove any traces of wax. To remove the cold-worked layer from the surface of the hole, the disc is placed in a standard sample holder for a Tenupol electropolisher so that the hole is in the center of the area to be polished.

Near-Surface Aggregation of Sn In Heavily Sn-Doped GaAs Films Grown By Molecular Beam Epitaxy

1985 ◽  
Vol 43 ◽  
pp. 368-369
Author(s):  
S. H. Chen
Keyword(s):  
Molecular Beam Epitaxy ◽  
Cross Section ◽  
Electron Spectroscopy ◽  
Molecular Beam ◽  
Surface Segregation ◽  
Secondary Ion Mass Spectrometry ◽  
Specimen Preparation ◽  
Near Surface ◽  
Gaas Films ◽  
Secondary Ion

Sn has been used extensively as an n-type dopant in GaAs grown by molecular-beam epitaxy (MBE). The surface accumulation of Sn during the growth of Sn-doped GaAs has been observed by several investigators. It is still not clear whether the accumulation of Sn is a kinetically hindered process, as proposed first by Wood and Joyce, or surface segregation due to thermodynamic factors. The proposed donor-incorporation mechanisms were based on experimental results from such techniques as secondary ion mass spectrometry, Auger electron spectroscopy, and C-V measurements. In the present study, electron microscopy was used in combination with cross-section specimen preparation. The information on the morphology and microstructure of the surface accumulation can be obtained in a fine scale and may confirm several suggestions from indirect experimental evidence in the previous studies.

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