Geochemical evolution of a 10 m-thick intrusive body: the South Brenterc’h diabase dyke, Western Armorican Massif, France

2004 ◽  
Vol 41 (7) ◽  
pp. 775-784 ◽  
Author(s):  
Martial Caroff ◽  
Joseph Cotten
Keyword(s):  
Transverse Section ◽  
Geochemical Evolution ◽  
The South ◽  
Geochemical Variations ◽  
Flow Differentiation ◽  
Textural Parameters ◽  
Geochemical Analyses ◽  
Armorican Massif ◽  
Dispersive Pressure ◽  
Tholeiitic Magmatism

The South Brenterc’h 9.5 m-thick diabase dyke belongs to the intermediate-Ti quartz-normative tholeiitic magmatism, which has intruded the western end of Britanny (France) near the Trias-Lias boundary. It has been previously identified as a "simple" dyke, resulting from a single magmatic injection. The present study is based on ten samples collected along a half transverse section of this dyke. Geochemical analyses and some textural parameters have been used to point out two flow-related differentiation processes, partially masked by alteration. These late magmatic mechanisms have induced subtle geochemical variations among samples, which sometime counteract each other. The processes pointed out here are (i) expulsion of phenocrysts from the borders during flow differentiation, likely by the way of an hydrodynamic grain dispersive pressure, and (ii) emplacement of a more evolved magma in the central part of the intrusion, probably due to a viscosity segregation mechanism during the flow.

Leaf anatomy of the South African Danthonieae (Poaceae). III. Merxmuellera stricta

Bothalia ◽  
1980 ◽  
Vol 13 (1/2) ◽  
pp. 191-198 ◽  
Author(s):  
R. P. Ellis
Keyword(s):  
Environmental Factors ◽  
South African ◽  
Leaf Anatomy ◽  
Leaf Blade ◽  
Transverse Section ◽  
Anatomical Structure ◽  
The South ◽  
Abaxial Epidermis ◽  
Variable Species ◽  
Morphological Differences

The anatomical structure, of the leaf blade as seen in transverse section, and of the abaxial epidermis, of Merxmuellera stricta (Schrad.) Conert is described and illustrated. In this variable species four distinct anatomical “forms” are recognized viz. the typical  M. stricta form, the Cathedral Peak form, the Drakensberg form and the alpine form. The alpine and Cathedral Peak forms have recently been described as M. guillarmodiae Conert (1975). The degree of anatomical differentiation of these “forms” resembles the situation described in M. disticha (Nees) Conert (Ellis, 1980). Populations of both M. stricta and M. disticha from the Drakensberg mountains display extensive anatomical diversification which appears to be correlated with environmental factors. In addition, morphological differences are exhibited as well and the anatomical “forms” of M. stricta probably warrant taxonomic recognition.

Leaf anatomy of the South African Danthonieae (Poaceae). II. Merxmuellera disticha

Bothalia ◽  
1980 ◽  
Vol 13 (1/2) ◽  
pp. 185-189 ◽  
Author(s):  
R. P. Ellis
Keyword(s):  
South African ◽  
Leaf Anatomy ◽  
Leaf Blade ◽  
Transverse Section ◽  
Taxonomic Status ◽  
Anatomical Structure ◽  
The South ◽  
Abaxial Epidermis ◽  
Environmental Requirements

The anatomical structure, of the leaf blade as seen in transverse section, and of the abaxial epidermis, of Merxmuellera disticha (Nees) Conert is described and illustrated. Three distinct anatomical “forms” are recognized viz. typical M. disticha, the Drakensberg form and the alpine bog form. These three anatomical groups also appear to have differing environmental requirements and probably warrant taxonomic status.

Sur les rhyolites et les granites prevarisques en Normandie et en Vendee

1943 ◽  
Vol S5-XIII (4-6) ◽  
pp. 139-151
Author(s):  
Gilbert Mathieu
Keyword(s):  
Variscan Orogeny ◽  
The South ◽  
The North ◽  
Rigid Mass ◽  
Armorican Massif

Abstract An account of the pre-Carboniferous rhyolites and granites of Normandy and Vendee, France. Precambrian granite masses and Precambrian and Cambrian conglomerates containing ancient granite and rhyolite pebbles occur in both regions, and indicate that the Carboniferous granites of the Armorican massif were emplaced during the Variscan orogeny in a zone of subsidence between the rigid mass of Normandy to the north and Vendee to the south.

The Hercynian orogeny in the South Armorican Massif (Saint-Georges-sur-Loire Unit, Ligerian Domain, France): rifting and welding of continental stripes

Terra Nova ◽  
2001 ◽  
Vol 13 (2) ◽  
pp. 143-149 ◽  
Author(s):  
C. Cartier ◽  
M. Faure ◽  
H. Lardeux
Keyword(s):  
The South ◽  
Hercynian Orogeny ◽  
Armorican Massif

The geochemical evolution of the granitoid rocks in the South Qinling Belt: Insights from the Dongjiangkou and Zhashui intrusions, central China

Lithos ◽  
2017 ◽  
Vol 278-281 ◽  
pp. 195-214 ◽  
Author(s):  
Fangyang Hu ◽  
Shuwen Liu ◽  
Mihai N. Ducea ◽  
Wanyi Zhang ◽  
Zhengbin Deng
Keyword(s):  
Central China ◽  
Geochemical Evolution ◽  
The South ◽  
South Qinling ◽  
Granitoid Rocks

Volcanic degassing along the enigmatic South Sandwich volcanic arc

2020 ◽  
Author(s):  
Emma Liu ◽  
Kieran Wood ◽  
Alessandro Aiuppa ◽  
Gaetano Giudice ◽  
Marcello Bitetto ◽  
...  
Keyword(s):  
Carbon Isotope ◽  
Subduction Zones ◽  
Lava Lake ◽  
Volcanic Eruptions ◽  
Geochemical Evolution ◽  
The South ◽  
Aerosol Composition ◽  
Volcanic Arc ◽  
Volcanic Degassing

<p>The South Sandwich Islands (SSI) are a chain of active volcanoes in the Southern Ocean and remain one of the most remote and enigmatic island arcs on Earth. The relatively recent development of the SSI over the past 20 million years has been closely linked with the formation of the Drake Passage, making this one of the youngest known volcanic arcs and therefore one of the most critical for understanding the early stages of arc geochemical evolution. Recent volcanic eruptions in the SSI have had significant impacts on local terrestrial and marine ecosystems, including some of the largest penguin colonies ever observed, through tephra deposition and from sustained volcanic degassing. Rare cloud-free satellite images over the last two decades have indicated that the summit of Mt Michael (Saunders) hosts a sustained lava lake, but until now these observations have not been ground-truthed by in-situ measurements. Long-term persistent passive outgassing at many of these volcanoes, even between eruptive phases, suggests that the SSI volcanic arc could be a significant source of volatiles to our atmosphere, and yet we lack any constraints on the degassing budgets of this volcanic arc. Here, we present novel measurements of gas chemistry, aerosol composition, and carbon isotope signature from along the South Sandwich Island arc. By combining ground-based measurements of SO<sub>2</sub> flux with in-situ samples of plume composition using Unoccupied Aerial Systems (UAS), we present multi-species volatile fluxes for the major along-arc degassing sources. Further, by evaluating the carbon to sulfur ratio (C/S<sub>T</sub>) and carbon isotope composition in emitted gases together with petrological constraints from erupted tephra, we aim to test the hypothesis that carbon is supplied to the SSI by subduction of oceanic carbonated serpentinite, and thus contribute to our understanding of carbon recycling at subduction zones.</p>

Early Geochemical Evolution of an Oceanic Island Arc and Backarc: Fiji and the South Fiji Basin

1987 ◽  
Vol 95 (5) ◽  
pp. 589-615 ◽  
Author(s):  
James B. Gill
Keyword(s):  
Oceanic Island ◽  
Island Arc ◽  
Geochemical Evolution ◽  
The South

scholarly journals Cyclostratigraphy of the Middle to Upper Ordovician successions of the Armorican Massif (western France) using portable X-ray fluorescence

2022 ◽  
Author(s):  
Matthias Sinnesael ◽  
Alfredo Loi ◽  
Marie-Pierre Dabard ◽  
Thijs R. A. Vandenbroucke ◽  
Philippe Claeys
Keyword(s):  
High Resolution ◽  
Gamma Ray ◽  
Spectral Power ◽  
Upper Ordovician ◽  
Deep Time ◽  
High Resolution Data ◽  
X Ray ◽  
Natural Gamma ◽  
Geochemical Analyses ◽  
Armorican Massif

Abstract. To expand traditional cyclostratigraphic numerical methods beyond their common technical limitations and apply them to truly deep-time archives we need to reflect on the development of new approaches to sedimentary archives that traditionally are not targeted for cyclostratigraphic analysis, but that frequently occur in the impoverished deep-time record. Siliciclastic storm-dominated shelf environments are a good example of such records. Our case study focusses on the Middle to Upper Ordovician siliciclastic successions of the Armorican Massif (western France), which are well-studied in terms of sedimentology and sequence stratigraphy. In addition, these sections are protected geological heritage due to the extraordinary quality of the outcrops. We therefore tested the performance of non-destructive high-resolution (cm-scale) portable X-ray fluorescence and natural gamma-ray analyses on outcrop to obtain major and trace element compositions. Despite the challenging outcrop conditions in the tidal beach zone, our geochemical analyses provide useful information regarding general lithology and several specific sedimentary features such as the detection of paleoplacers, or the discrimination between different types of diagenetic concretions such as nodules. Secondly, these new high-resolution data are used to experiment the application of commonly used numerical cyclostratigraphic techniques on this siliciclastic storm-dominated shelf environment, a non-traditional sedimentological setting for cyclostratigraphic analysis. In the lithological relatively homogenous parts of the section spectral power analyses and bandpass filtering hint towards a potential astronomical imprint of some sedimentary cycles, but this needs further confirmation in the absence of more robust independent age constraints.

Leaf anatomy of the South African Danthonieae (Poaceae). I. The genus Dregeochloa

Bothalia ◽  
1977 ◽  
Vol 12 (2) ◽  
pp. 209-213 ◽  
Author(s):  
R. Ellis
Keyword(s):  
South African ◽  
Leaf Anatomy ◽  
Leaf Blade ◽  
Transverse Section ◽  
Anatomical Structure ◽  
The South ◽  
Abaxial Epidermis ◽  
Generic Description

The anatomical structure, of the leaf blade as seen in transverse section, and the abaxial epidermis, of Dregeochloa pumila and  D. calviniensis is described and illustrated. A generic description is included and the relationships of the genus are briefly discussed.

scholarly journals Timing of magmatic crystallization and Sn–W–Mo greisen vein formation within the Mount Douglas Granite, New Brunswick, Canada

2020 ◽  
Vol 57 (7) ◽  
pp. 814-839 ◽  
Author(s):  
Nadia Mohammadi ◽  
Christopher R.M. McFarlane ◽  
David R. Lentz ◽  
Kathleen G. Thorne
Keyword(s):  
Hydrothermal System ◽  
Parental Magma ◽  
Hydrothermal Activity ◽  
Vein Formation ◽  
Icp Ms ◽  
Mount Pleasant ◽  
Geochemical Variations ◽  
Geochemical Analyses ◽  
Fractional Crystallization Process ◽  
Different Levels

U–Pb geochronology was applied to a combination of magmatic and hydrothermal minerals to help constrain the timing of emplacement of three units in the Mount Douglas Granite (MDG) and reveal their association with a complex mineralized hydrothermal system containing endogranitic Sn–W–Mo–Zn–Bi–U-bearing greisen/sheeted veins within the pluton. Magmatic monazite and zircon U–Pb ages obtained by LA–ICP–MS overlap at 368 Ma, recording a Late Devonian crystallization age for the MDG. Although discrimination, outside analytical error, of sequential pulses of magmatism is beyond the resolution of LA–ICP–MS U–Pb geochronology, geochemical variations of monazite accompanied by previous whole-rock geochemical analyses support a progressive fractional crystallization process starting from a parental magma (Dmd1), leading to the generation of Dmd2, and finally Dmd3 as the most fractionated unit. Hydrothermal uraninite, cassiterite, and monazite, collected from endogranitic greisen/sheeted veins, reveal evidence for syn-magmatic-related mineralization and a longer-lived post-magmatic hydrothermal system. The first stage is recorded by concordant uraninite dates at 367 ± 3 Ma and by an inverse isochron lower intercept of 362 ± 8 Ma for cassiterite. In contrast, hydrothermal monazite crystallized over a wider range of ages from 368 to 344 Ma, demonstrating post-magmatic hydrothermal activity within the MDG. These magmatic and hydrothermal ages combined with the geochemical signature of the MDG are similar to those documented for the nearby Mount Pleasant Sn–W–Mo–Bi–In granite-related deposit, which suggests that the two mineralizing systems occur at different levels of the same magmatic system.

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