scholarly journals Origin and occurrence of gem-quality, skarn-hosted barite from Jebel Ouichane near Nador in Morocco

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Magdalena Dumańska-Słowik ◽  
Beata Naglik ◽  
Tomasz Toboła ◽  
Tomasz Powolny ◽  
Miłosz Huber ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Iron Ore ◽  
Surface Reaction ◽  
Spatial Association ◽  
Near Surface ◽  
Precipitation Mechanism ◽  
Surface Conditions ◽  
Fluid Inclusion Data ◽  
Low Salinity ◽  
Fast Growth Rate

AbstractLight-blue barite from Jebel Ouichane in Morocco forms blade-like tabular crystals (up to ca. 10 cm) with superb transparency and lustre and represents one of the most spectacular gem-quality worldwide. The barite is hosted by iron-ore-bearing skarns, developed within Jurassic-Cretaceous limestones, and occurs in close spatial association with calcite. The crystals have their cores enriched in Sr and contain abundant monophase (liquid) fluid inclusions of primary and pseudosecondary origin. The barite probably precipitated slowly at a relatively low supersaturation and under the control of a surface reaction precipitation mechanism. However, there were some episodes during its formation with a fast growth rate and the coupled dissolution and recrystallization processes. A combination of fluid inclusion data and stable δ18O value for barite (+ 6.71‰ VSMOW) suggests that low-salinity barite-forming solutions resulted from the mixing of strongly-diluted meteoric waters (enriched in light oxygen isotope) with magmatic-hydrothermal fluids under low-temperature conditions (< 100 °C). Meanwhile, the mineralizing fluids must have been enriched in Ba, Sr, Ca, Mg, and other elements derived from the alteration of carbonate and silicate minerals in sedimentary and igneous rocks. The coupling between sulphur and oxygen isotope data (+ 16.39‰ VCDT and + 6.71‰ VSMOW, respectively) further suggests that barite crystallized in steam-heated environment, where SO42- derived from magmatic-hydrothermal SO2 reacted with sulphates that originate from the oxidation of H2S under near-surface conditions.

scholarly journals Ground ice in the Northern Foothills, northern Victoria Land, Antarctica

2004 ◽  
Vol 39 ◽  
pp. 495-500 ◽  
Author(s):  
Mauro Guglielmin ◽  
Hugh M. French
Keyword(s):  
Oxygen Isotope ◽  
Ross Sea ◽  
Progress Report ◽  
Ground Ice ◽  
Lake Ice ◽  
Near Surface ◽  
Victoria Land ◽  
Different Types ◽  
Glacier Ice ◽  
Surface Ice

AbstractThis progress report classifies the different types of ground-ice bodies that occur in the Northern Foothills, northern Victoria Land, Antarctica. Oxygen isotope variations are presented, but interpretation is kept to a minimum pending further investigations. Surface ice, as distinct from moving glacier ice, occurs in the form of widespread buried (‘dead’) glacier ice lying beneath ablation (sublimation) till, together with perennial lake ice, snow banks and icing-blister ice.’Dry’ permafrost is uncommon, and interstitial ice is usually present at the base of the active layer and in the near-surface permafrost. This probably reflects the supply of moisture from the Ross Sea and limited sublimation under today’s climate. Intrusive ice occurs as layers within perennial lake-ice covers and gives rise to small icing blisters. Small ice wedges found beneath the furrows of high-centered polygons appear to agree with the model of sublimation-till development proposed by Marchant and others (2002).

scholarly journals A nanocrystalline monoclinic CaCO3precursor of metastable aragonite

2018 ◽  
Vol 4 (12) ◽  
pp. eaau6178 ◽  
Author(s):  
Péter Németh ◽  
Enrico Mugnaioli ◽  
Mauro Gemmi ◽  
György Czuppon ◽  
Attila Demény ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Structure Determination ◽  
Diffuse Scattering ◽  
Diffraction Tomography ◽  
Synthetic Material ◽  
Near Surface ◽  
Surface Conditions ◽  
Terrestrial Sediments ◽  
Living Organisms ◽  
New Phase

Despite its thermodynamical metastability at near-surface conditions, aragonite is widespread in marine and terrestrial sediments. It abundantly forms in living organisms, and its abiotic formation is favored in waters of a Mg2+/Ca2+ratio > 1.5. Here, we provide crystallographic evidence of a nanocrystalline CaCO3polymorph, which precipitates before aragonite in a cave. The new phase, which we term monoclinic aragonite (mAra), is crystallographically related to ordinary, orthorhombic aragonite. Electron diffraction tomography combined with structure determination demonstrates that mAra has a layered aragonite structure, in which some carbonates can be replaced by hydroxyls and up to 10 atomic % of Mg can be incorporated. The diagnostic electron diffraction features of mAra are diffuse scattering and satellite reflections along aragonite {110}. Similar features have previously been reported—although unrecognized—from biogenic aragonite formed in stromatolites, mollusks, and cyanobacteria as well as from synthetic material. We propose that mAra is a widespread crystalline CaCO3that plays a hitherto unrecognized key role in metastable aragonite formation.

A generic soil velocity model that accounts for near-surface conditions and deeper geologic structure

2021 ◽  
Vol 140 ◽  
pp. 106461
Author(s):  
Nasser A. Marafi ◽  
Alex Grant ◽  
Brett W. Maurer ◽  
Gunjan Rateria ◽  
Marc O. Eberhard ◽  
...  
Keyword(s):  
Velocity Model ◽  
Geologic Structure ◽  
Near Surface ◽  
Surface Conditions

CFD Study of an Autonomous Submarine in Extraterrestrial Seas

2017 ◽  
Author(s):  
S. Carberry Mogan ◽  
P. Sawicki ◽  
C. J. Bernardo ◽  
D. Chen ◽  
I. Sahin ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Computational Study ◽  
Liquid Hydrocarbon ◽  
Quantitative Agreement ◽  
Near Surface ◽  
Surface Conditions ◽  
Qualitative And Quantitative

A computational study is conducted to evaluate the performance of an extraterrestrial submarine operating in the liquid hydrocarbon seas of Saturn’s largest moon, Titan. To simulate the flow around the submarine and offer a prediction for thrust and power requirements, Computational Fluid Dynamics tools, ANSYS© FLUENT© and DualSPHysics, are utilized for the deeply submerged and near-surface conditions, respectively. Several operational scenarios are investigated and comparisons are made with other available results with a good qualitative and quantitative agreement.

Photosynthesis below the surface in a cryptic microbial mat

2002 ◽  
Vol 1 (4) ◽  
pp. 295-304 ◽  
Author(s):  
Lynn J. Rothschild ◽  
Lorraine J. Giver
Keyword(s):  
Carbon Fixation ◽  
Early Earth ◽  
Cyanobacterial Mat ◽  
Fixed Carbon ◽  
Daily Production ◽  
Near Surface ◽  
Surface Conditions ◽  
A Value ◽  
Subsurface Environments

The discovery of subsurface communities has encouraged speculation that such communities might be present on planetary bodies exposed to harsh surface conditions, including the early Earth. While the astrobiology community has focused on the deep subsurface, near-subsurface environments are unique in that they provide some protection while allowing partial access to photosynthetically active radiation. Previously we identified near-surface microbial communities based on photosynthesis. Here we assess the productivity of such an ecosystem by measuring in situ carbon fixation rates in an intertidal marine beach through a diurnal cycle, and find them surprisingly productive. Gross fixation along a transect (99×1 m) perpendicular to the shore was highly variable and depended on factors such as moisture and mat type, with a mean of ~41 mg C fixed m−2 day−1. In contrast, an adjacent well-established cyanobacterial mat dominated by Lyngbya aestuarii was ~12 times as productive (~500 mg C fixed m−2 day−1). Measurements made of the Lyngbya mat at several times per year revealed a correlation between total hours of daylight and gross daily production. From these data, annual gross fixation was estimated for the Lyngbya mat and yielded a value of ~1.3×105 g m−2 yr−1. An analysis of pulse-chase data obtained in the study in conjunction with published literature on similar ecosystems suggests that subsurface interstitial mats may be an overlooked endogenous source of organic carbon, mostly in the form of excreted fixed carbon.

scholarly journals Water budget and partial melting in an Archean crustal column: example from the Dharwar Craton, India

2019 ◽  
Vol 489 (1) ◽  
pp. 115-133 ◽  
Author(s):  
Gautier Nicoli
Keyword(s):  
Partial Melting ◽  
Water Budget ◽  
Critical Parameter ◽  
Bound Water ◽  
Dharwar Craton ◽  
Bulk Rock ◽  
Near Surface ◽  
Surface Conditions ◽  
Magma Compositions ◽  
Water Saturated

AbstractThe fluid budget of a composite crustal column is a critical parameter that influences many lithospheric processes. The amount of water introduced into the middle and lower crust can be quantified using phase equilibrium modelling. The Dharwar Craton, India, displays a now-exposed continuous crustal section from near-surface conditions to c. 30 km depth. This section records the different steps of a c. 15 myr-long high-temperature metamorphic event (60°C kbar−1) responsible for the formation of syn- to post-tectonic anatectic intrusions. The global water budget is assessed using thermodynamic modelling on bulk-rock compositions of an average early Proterozoic supracrustal unit and c. 3.0 Ga felsic basement, the Peninsular gneisses. Results show the fast burial of a water-saturated supracrustal package (1.6 wt%) will release c. 50% of its mineral-bound water, triggering water-fluxed partial melting of the basement. Modelled anatectic magma compositions match the observed granitoid chemistries, and distinction can be made between water-fluxed melting and water-absent melting in the origin of syn- to post-tectonic anatectic granites. Findings from this study show the importance of crustal pile heterogeneity in controlling the nature of partial melting reactions, the composition of the magmas and the rheology of the crust.

Crystallization history of a zoned plagioclase

1974 ◽  
Vol 39 (308) ◽  
pp. 867-877 ◽  
Author(s):  
G. J. Pringle ◽  
L. T. Trembath ◽  
G. E. Pajari
Keyword(s):  
Electron Microprobe ◽  
Near Surface ◽  
Surface Conditions ◽  
History Of ◽  
Textural Data ◽  
Zoned Plagioclase

SummaryElectron microprobe and textural data are used to deduce a crystallization history for plagioclase in the Grand Manan Island (Canada) diabase sheet. The plagioclase crystals consist of a prominent core (An79-67) surrounded by a distinctly more calcic zone (An82-76), which grades into a normally zoned mantle (An73-40). This zoning pattern is interpreted as reflecting the elevation of a dry diabase magma from at least 10 to 20 km to near surface conditions.

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