A propos d'un schiste a sillimanite pres de Jerdeux (Hague)

1942 ◽  
Vol S5-XII (1-3) ◽  
pp. 21-24
Author(s):  
Elisabeth Jeremine
Keyword(s):  
Crystalline Rocks ◽  
Metamorphic Rocks ◽  
The Hague

Abstract The pre-Cambrian crystalline rocks of the Hague cape region, northwestern France, although exhibiting only slight variations in character, belong to different metamorphic zones. The sillimanite-bearing schist near Jerdeux, intercalated in an amphibole gneiss which is intruded by granitic injections, belongs to a deeper-seated zone than the metamorphic rocks east of Omonville-la-Rogue.

Abundance of halloysite neoformation in soils developed from crystalline rocks. Contribution of transmission electron microscopy

Clay Minerals ◽  
1992 ◽  
Vol 27 (1) ◽  
pp. 35-46 ◽  
Author(s):  
R. Romero ◽  
M. Robert ◽  
F. Elsass ◽  
C. Garcia
Keyword(s):  
Thermal Analyses ◽  
Crystalline Rocks ◽  
Metamorphic Rocks ◽  
X Ray Diffraction ◽  
Nw Spain ◽  
X Ray ◽  
Transmission Electron ◽  
High Concentrations ◽  
Bioclimatic Conditions ◽  
Mineralogical Phases

AbstractThe soils developed from crystalline and metamorphic rocks in Galicia (NW Spain), are characterized by high concentrations of 1 : 1 phyllosilicates and gels. Thermal analyses, X-ray diffraction after formamide treatment, and IR spectroscopy in the OH vibration range have been performed on the clay fractions, but do not discriminate clearly between the different associated mineralogical phases. HRTEM studies linked with microdiffraction and microanalyses have led to the identification of several types of gel which transform into goethite, gibbsite, clay precursors, and/ or halloysite according to their composition (Fe, Al or Si-Al). Halloysite-like minerals are the main constituents and they have a great variety of morphologies: lamellar, spheroidal, tubular, platy or poikilitic. In general, halloysite and gel formation on crystalline rocks is related to the bioclimatic conditions, involving high hydrolysis in the presence of organic matter. This halloysite seems to be a metastable mineral which would evolve into kaolinite with increasing weathering time.

PERMEABILITY OF COVER DEPOSITS OF CRYSTALLINE ROCKS IN THE SUDETY MOUNTAINS (SW POLAND) BASED ON A FIELD STUDY

2021 ◽  
Vol 16 (1) ◽  
pp. 5-15
Author(s):  
Tomasz OLICHWER ◽  
◽  
Katarzyna PIOTROWSKA ◽  
Estera TEREŚKIEWICZ
Keyword(s):  
Hydraulic Conductivity ◽  
Field Measurements ◽  
Crystalline Rocks ◽  
Igneous Rocks ◽  
Metamorphic Rocks ◽  
Infiltration Capacity ◽  
Field Investigations ◽  
Vertical Hydraulic Conductivity ◽  
Sudety Mountains ◽  
Constant Head

Article presents a study on the permeability of weathering covers formed on crystalline rocks, which was conducted in south-western Poland (Sudety Mountains). Evaluation of the infiltration capacity was performed based on field measurements of the vertical hydraulic conductivity carried out by using the Porschet method and the ETC Pask Constant Head Permeameter. During the field investigations conducted in sixteen sites, 28 determinations of the hydraulic conductivity k were made, 16 by the Porschet method and 12 using the ETC Pask Permeameter. Ten sites represent weathering covers of metamorphic rocks (amphibolites, eclogites, mica-schists, crystalline limestones, gneisses) and the next six sites represent covers of igneous rocks (granites). The values of the vertical hydraulic conductivity k determined by the Porschet method ranged between 0.053 and 2.19 m/d, while those obtained using the ETC Pask Permeamet erranged between 0.012 and 0.76 m/d. In the first place, it should be noticed that the results determined during the field investigations conducted according to the Porschet method are generally 3-4 times higher than those obtained using the ETC Pask Permeameter. The results for the vertical hydraulic conductivity allow us to classify weathering sediments of metamorphic and igneous rocks, as semi-permeable to medium permeable rocks. Weathered gneisses were distinctly characterized by the worst capacity to conduct water (semi-permeable) among all types of weathering covers of crystalline rocks. Higher values (0,08-0,8 m/d) of the vertical hydraulic conductivity were found for the weathering covers of the other metamorphic rocks (low permeable). The best conditions to conduct water were found in the weathering covers of granite rocks, which in most cases are classified as medium permeable rocks (more than 0.8 m/d) and exhibit distinctly better permeability coefficients.

An Upper Cretaceous paleodrainage system on the Coastal Plain unconformity of Alabama-Georgia

2021 ◽  
pp. 35-60
Author(s):  
Clinton Barineau* ◽  
Diana Ortega-Ariza*
Keyword(s):  
Coastal Plain ◽  
Upper Cretaceous ◽  
Crystalline Rocks ◽  
Estuarine Environment ◽  
Metamorphic Rocks ◽  
Braided Stream ◽  
Fall Line ◽  
Eutaw Formation ◽  
Appalachian Piedmont ◽  
Chattahoochee River

ABSTRACT Rocks of the Upper Cretaceous Tuscaloosa Formation (Cenomanian) and Eutaw Formation (Santonian) in southwestern Georgia and southeastern Alabama record an interval of fluvial and nearshore marine deposition. In the vicinity of Columbus, Georgia, basal units of the Tuscaloosa Formation consist of a residual paleosol built on crystalline rocks of the Appalachian Piedmont covered by conglomeratic sandstones deposited in braided stream systems flowing across the mid-Cenomanian Coastal Plain unconformity. The unconformity, which separates Cretaceous detrital rocks from underlying metamorphic rocks and residual paleosols built on those metamorphic rocks, lies primarily within the Tuscaloosa Formation in this region and is marked at the modern surface by the geomorphic Fall Line. Mapping of the unconformity across the region reveals areas of significant paleorelief associated with a number of distinct paleovalleys incised into the mid-Cenomanian surface. The most distinct of these lie immediately east of the Alabama-Georgia state line, within 15 km of the modern Lower Chattahoochee River Valley. Spatially, these distinct paleovalleys lie immediately north of a Santonian estuarine environment recorded in the Eutaw Formation, disconformably above the Tuscaloosa Formation. Collectively, paleo-valleys in the mid-Cenomanian surface, the fluvial nature of the Tuscaloosa Formation in southwestern Georgia and southeastern Alabama, and the estuarine environment in the younger Eutaw Formation suggest a persistent (~10 m.y.) paleodrainage system that may be a forerunner to the modern Chattahoochee River.

Evidence by transmission electron microscopy of weathering microsystems in soils developed from crystalline rocks

Clay Minerals ◽  
1992 ◽  
Vol 27 (1) ◽  
pp. 21-33 ◽  
Author(s):  
R. Romero ◽  
M. Robert ◽  
F. Elsass ◽  
C. Garcia
Keyword(s):  
Electron Microscopy ◽  
Solid Phase ◽  
High Resolution Electron Microscopy ◽  
Climatic Conditions ◽  
Crystalline Rocks ◽  
Metamorphic Rocks ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Tropical Areas ◽  
The Continuum

AbstractHigh-resolution electron microscopy and microanalytical studies were performed on clay and bulk soil samples developed on various igneous and metamorphic rocks from Galicia in the Coruna province in NW Spain. Two mineralogical microsystems can be distinguished showing different stages of weathering. For feldspars, exsolution and mass transformation lead to the delineation of parallel domains, and to formation of gel or paracrystalline minerals. For micas, alteration starts with a physical breakdown, i.e. exfoliation and crystal microdivision; individualization of monolayers is followed by gel formation. A solid phase diffusion phenomenon can explain the formation of 1 : 1 phyllosilicates inside 2 : 1 phyllosilicates or within the continuum of the original crystals. Evidence of such weathering stages in crystalline rocks can be related to the occurrence of specific climatic conditions between temperate and tropical areas.

Significance of lineation and minor folds near major thrust faults in the southern Appalachians and the British and Norwegian Caledonides

1969 ◽  
Vol 106 (5) ◽  
pp. 412-429 ◽  
Author(s):  
Bruce Bryant ◽  
John C. Reed
Keyword(s):  
Crystalline Rocks ◽  
Orogenic Belt ◽  
Metamorphic Rocks ◽  
Southern Appalachians ◽  
Thrust Faults ◽  
Blue Ridge ◽  
Thrust Sheet ◽  
Passive Rotation ◽  
Window Displays ◽  
Norwegian Caledonides

SUMMARYThe Blue Ridge thrust sheet is one of the principal thrust masses of metamorphic rocks in the southern Appalachians. A broad zone of sheared and retrogressively metamorphosed rocks near the sole of the thrust sheet around the Grandfather Mountain window displays numerous small tight or isoclinal folds having axes subparallel to an intense penetrative cataclasticalineation and axial planes parallel to foliation in the thrust sheet. These folds seem to have formed by tightening, flattening, and passive rotation of earlier more open folds originally formed perpendicular to the direction of transport. The style and orientation of these folds closely resemble those of analogous structures in thrust masses of crystalline rocks in the Caledonian orogenic belt in Scotland and Norway, suggesting that the structures of both regions may have similar origins.

The volume conjugate in progressive metamorphism

2021 ◽  
Author(s):  
Timothy Chapman ◽  
Geoffrey Clarke ◽  
Luke Milan ◽  
Julie Vry
Keyword(s):  
New Caledonia ◽  
Fluid Pressure ◽  
Crystalline Rocks ◽  
Metamorphic Rocks ◽  
Fluid Consumption ◽  
Volume Changes ◽  
Mineral Equilibria ◽  
Mineral Assemblages ◽  
Physical Changes ◽  
Distribution Of Stresses

<p>Volume changes during metamorphic reactions are key contributors to the physical changes of crystalline rocks. Assessing dehydration or hydration reactions in terms of conjugate <em>V–T</em> pseudosections provides indicators of transient departures in hydrostatic pressure and their impact on observed mineral equilibria. The expansion in volume of major dehydration events such as the breakdown of lawsonite or chlorite delineate zones of fluid overpressure that generate connectivity via fracturing. Net compressional reactions represent sinks for fluid consumption and the focussing of strain. The capacity of metamorphic rocks to generate or consume fluid along portions of the <em>P–T–V</em> path exerts a fundamental control on the distribution of stresses in the crust and the observed mineral assemblages. Coupling a phase equilibria approach to mechanical modelling provides a quantitative framework to assess these changes in fluid pressure that can be compared to prominent case studies in rocks from New Caledonia and New Zealand.</p>

U-Pb dating of carbonate-fluorapatite: a potential chronological tool for ancient marine sediments

2020 ◽  
Author(s):  
Gary O'Sullivan ◽  
Rory Mortimore ◽  
David Chew ◽  
Stephen Daly
Keyword(s):  
Marine Sediments ◽  
Host Rock ◽  
Early Diagenesis ◽  
Crystalline Rocks ◽  
Metamorphic Rocks ◽  
Common Features ◽  
Sedimentary Sequences ◽  
Tectonic Events ◽  
Carbonate Fluorapatite ◽  
Western Ireland

<p>Carbonate-fluorapatite (CFA) is a common early diagenetic component of marine sedimentary sequences. Nodules, laminae and shell overgrowths or infills composed of CFA are relatively common features in phosphorites, carbonates and other marine sediments (e.g., Datillo et al., 2016). CFA U-Pb dating thus has potential application as a chronometer in a wide variety of ancient marine sediments, particularly in those marine sections lacking diagnostic faunal and/or floral assemblages, or well-dated volcanogenic horizons.</p><p>In order to test empirically whether accurate and precise U-Pb ages can be obtained from CFA using LA-ICPMS we have analysed CFA from a several marine sediment samples. These include samples of Cretaceous phosphatic chalk from southern England, phosphatic nodules from the Cretaceous of northern Ireland and western Scotland, and a sample from a laterally extensive Carboniferous phosphorite in western Ireland. Ages obtained from CFA in these rocks can be precise (as low as c. 0.55% 2SE error in one sample), and are all unimodal. U-Pb ages of CFA, however, range from stratigraphically-consistent ages to ages that record much younger events than their host rock stratigraphic ages.</p><p>While ‘ages’ obtained from CFA may be precise, what each of these ages represents geologically requires further study. The genetic relationship between phosphate and its host rock must be petrographically studied to understand the correspondence between the phosphatic and other components of these rocks in terms of their depositional and diagenetic histories. It is apparent that in some cases CFA will record deposition or early diagenesis, but that the U-Pb system in CFA can be overprinted by later tectonic events in other cases. In addition, whilst LA-ICPMS U-Pb dating of apatite (i.e. fluorapatite and chlorapatite) in crystalline rocks is now routine, the crystal structure and composition of CFA differs from apatite derived from igneous and metamorphic rocks, including the established fluorapatite U-Pb standards (e.g. Madagascar apatite, Thomson et al., 2012). Thus, assessment of matrix-matching effects will have to be undertaken to fully establish the CFA U-Pb chronometer.</p><p>Dattilo, B.F., Freeman, R.L., Peters, W.S., Heimbrock, W.P., Deline, B., Martin, A.J., Kallmeyer, J.W., Reeder, J. and Argast, A., 2016. Giants among micromorphs: were Cincinnatian (Ordovician, Katian) small shelly phosphatic faunas dwarfed?. Palaios, 31(3), pp.55-70.</p><p>Thomson, S.N., Gehrels, G.E., Ruiz, J., Buchwaldt, R., 2012. Routine low-damage apatite U-Pb dating using laser ablation-multicollector- ICPMS. Geochemistry, Geophys. Geosystems 13, 1–23. doi:10.1029/2011GC003928</p>

scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2011 ◽  
Vol 1(10)2011 (1(10)) ◽  
pp. 71-74
Author(s):  
Yu. Z. Krupskyi ◽  
◽  
V.P. Marusjak ◽  
Keyword(s):  
Cross Section ◽  
Plate Tectonics ◽  
Tectonic Setting ◽  
Gravity Anomalies ◽  
Crystalline Rocks ◽  
Passive Margin ◽  
Metamorphic Rocks ◽  
Theory Analysis ◽  
Eastern Carpathians ◽  
Local Gravity

Crystalline rocks of the Marmarosh massif of the Eastern Carpathians, taking into account based on the plate tectonics theory analysis of their characteristics and tectonic setting and the constructed cross-section of the local gravity anomalies, have been formed by the metamorphic rocks of Ryphean, Vendian, Cambrian and late Paleozoic as well as by the Meso-Cainozoic rocks in the south-eastern passive margin of the European plate. But later in conditions of collision and gently sloping subduction of substrate during the Cretaceous-Paleogene these rocks have been shifted from their substrate and became a part of Marmarosh nappes of the Eastern Carpathians.

TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

1996 ◽  
Vol 54 ◽  
pp. 694-695
Author(s):  
Gejing Li ◽  
D. R. Peacor ◽  
D. S. Coombs ◽  
Y. Kawachi
Keyword(s):  
Electron Microscopy ◽  
Volcanic Rocks ◽  
Analytical Electron Microscopy ◽  
Metamorphic Rocks ◽  
New Mineral ◽  
Chemical Compositions ◽  
Low Grade ◽  
Fine Grained ◽  
Depth Analysis ◽  
Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

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