Search results for "rock"
showing 10 items of 1160 documents
Phase equilibrium constraints on a deep crustal metamorphic field gradient: metapelitic rocks from the Ivrea Zone (NW Italy)
2011
The metamorphic rocks of the Ivrea Zone in NW Italy preserve a deep crustal metamorphic field gradient. Application of quantitative phase equilibria methods to metapelitic rocks provides new constraints on the P–T conditions recorded in Val Strona di Omegna, Val Sesia and Val Strona di Postua. In Val Strona di Omegna, the metapelitic rocks show a structural and mineralogical change from mica‐schists with the common assemblage bi–mu–sill–pl–q–ilm ± liq at the lowest grades, through metatexitic migmatites (g–sill–bi–ksp–pl–q–ilm–liq) at intermediate grades, to complex diatexitic migmatites (g–sill–ru–bi–ksp–pl–q–ilm–liq) at the highest grades. Partial melting in the metapelitic rocks is consi…
Rare earth elements and hydrothermal ore formation processes
1992
Abstract The geochemical behaviour of REE is influenced by nearly all important hydrothermal ore formation processes including fluid-rock interactions, fluid precipitations, adsorption and scavenging onto particles, and changes in fluid temperature, pressure, pH, Eh, alkalinity and ligand concentration. Destabilization of REE complexes in response to these physicochemical changes and possible chemical-crystallographic controls determine the concentration and distribution of REE within hydrothermal minerals, mineraloids and amorphous phases. Alteration assemblages of intrusive related mineralisations may exhibit a wide range of REE distributions and REE fractionation trends. The REE distribu…
SHRIMP zircon U–Pb ages and REE partition for high-grade metamorphic rocks in the North Dabie complex: Insight into crustal evolution with respect to…
2012
Abstract We present SHRIMP U–Pb ages and REE data for zircon of two granulites, a garnet pyroxenite and a clinopyroxene amphibolite from the North Dabie complex. The North Dabie complex is a major fault-bounded petrotectonic unit in the Dabie continental collisional orogen between the South and North China Blocks. Zircon REE data are applied to link ages to specific petrological processes. In addition to SHRIMP zircon U–Pb dating, measurements were made on monazites from a HP–UHT metapsammitic granulite. Metamorphic zircon grains and coeval overgrowths on detrital cores from one granulite yielded a weighted mean 207Pb/206Pb age of 2042 ± 7 Ma, corresponding to peak HP/UHT metamorphism. The …
Rare earth elements in apatite as a monitor of magmatic and metasomatic processes: The Ilímaussaq complex, South Greenland
2015
Abstract Textural and compositional variations of apatite from the plutonic Ilimaussaq complex in South Greenland and its surrounding country rocks track magmatic and metasomatic processes. Detailed back-scattered electron (BSE) imaging reveals various types of apatite textures including (i) growth zonation (concentric, oscillatory as well as sector zonation) formed during magmatic differentiation, (ii) resorption and overgrowth textures due to fluid/melt induced metasomatic overprint of precursor apatite and (iii) replacement textures indicating the destabilization of apatite in favor of monazite. In the least evolved rocks of the Ilimaussaq complex, apatite incorporates rare earth element…
The contribution of ultramafic veins in alkaline and non-alkaline mafic magmatism
2006
Occurrence and Genesis of Palygorskite and Associated Clay Minerals in a Pleistocene Calcrete Complex, Sde Boqer, Negev Desert, Israel
1996
AbstractPalygorskite and associated clay minerals have been studied in a Pleistocene calcrete complex from the Negev desert (Sde Boqer, Israel). This complex is divided into five main parts: the chalky and marly bedrock overlain by its weathered product, a brecciated calcrete hardpan; the laminar crust; loess pockets trapped in the calcrete; and the overlying soft surficial soil. The distribution of clay minerals is directly dependent on the position of the sample in the calcrete complex. Smectite is inherited from the bedrock in the calcrete with an aeolian enrichment in loess pockets and upper soft soil. The source of kaolinite is mainly detrital, related to desert dust. Illite is partly …
Weathering Products of a Dismantled Variscan Basement. Minero-Chemical Proxies to Insight on Cretaceous Palaeogeography and Late Neogene Palaeoclimat…
2020
This study compares, for the first time, the mineralogy and geochemistry of two residual-clay deposits in NW Sardinia (Nurra district) that formed at different times in tropical and sub-tropical climates. Both deposits represent palaeosols with deep-weathered residual profiles and overlie Mesozoic carbonate rocks that were deposited on the south European palaeomargin. The older alterite is Cenomanian–Turonian in age and grades upward into a horizon of karstic bauxite, whereas the younger unit occurs within alluvial deposits of Late Neogene age. The Cretaceous palaeosol represents the precursor of the overlying bauxite and formed from unknown sedimentary parent rocks. In contrast, the Messin…
Estudio sedimentológico de los depósitos de inundación en la Ribera del Xúqer (Valencia), en octubre de1982
2013
As a result of the sedimentological study of a series of deposits corresponding to the exceptional flood in the Xuquer River in October 1982, we analyze the behaviour of fluvial dynamics. The sedimentary response enables us lo perceive certain differences between the deposits analyzed, bUI these do not completely adjust to the genetic patterns considered in the classic Geomorphology as the producers ofthe traits ofvertical growth generated during floods.
Model to Assess the Quality of Magmatic Rocks for Reliable and Sustainable Constructions
2017
Geomechanical assessment of rocks requires knowledge of phenomena that occur under the influence of internal and external factors at a macroscopic or microscopic scale, when rocks are submitted to different actions. To elucidate the quantitative and qualitative geomechanical behavior of rocks, knowing their geological and physical–mechanical characteristics becomes an imperative. Mineralogical, petrographical and chemical analyses provided an opportunity to identify 15 types of igneous rocks (gabbro, diabases, granites, diorites, rhyolites, andesites, and basalts), divided into plutonic and volcanic rocks. In turn, these have been grouped into acidic, neutral (intermediate) and basic magmat…
New national and regional bryophyte records, 39
2014
1. Andreaea alpestris (Thed.) Schimp.Contributor: L. ThouvenotAndorra: Encamp, Ensagents, 42°31′07″N, 1°38′41″E, 2520 m a.s.l., on the top of granitic rock in alpine meadow, 17 July 2006, leg. L. T...