Encyclopedia

Paragneiss

paragneiss

[′par·ə‚nīs]
(geology)
A gneiss showing a sedimentary parentage.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Paragneiss

 

a metamorphic rock formed in the earth’s crust from sedimentary rocks (sandstones and argillaceous schists) that recrystallized in the deep zones of the earth’s crust in an amphibolite facies of metamorphism. Paragneiss consists of quartz and feldspars with admixtures of other minerals, typically andalusite, sillimanite, disthen, staurolite, cordierite, and tourmaline. The varieties of paragneiss are distinguished according to the admixture content. A certain excess of alumina, caused by the content of clay material in the primary sediments, is typical of paragneiss. In contrast to paragneiss, orthogneiss is formed through transformation of magmatic rocks.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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References in periodicals archive
The host rocks at Patrie are orthogneiss, amphibolites and paragneiss. It is this unique geological setting that attracted Sphinx to the Patrie project.
(1990) the high-grade metamorphic rocks in both the Chuggin Road and Lime Hill units include biotite, bioitite-cordierite, and sillimanite-bearing paragneiss, migmatitic paragneiss, marble, quartzite, amphibolite, and tonalitic orthogneiss.
In the study area lithological units is outcrops the second to fourth periods, which from old to new are as follows: phyllite, ouartzite, paragneiss, marble, shell, sandstone with tufa, volcanic rocks, crystalline limestone locally with fosolina, metamorphic volcanic and tufa, cherty limestone, phyllite, metamorphic quartzarenite, micaschist, metadolomite, amphibolite, limestone, shale and sandstone, schist hornfels, orthogneiss, granodiorite, oput rock, shale and phyllite sandstone, granite, granodiorite, diorite, dolomitic lime, radiolarit breccia, rodist lime, orbitoline, radiolarat, black and blue marl with limestone, alluvium.
The main rocks composing the massif in the profile zone are paragneiss, metabasite and their interbedding, granite and metasedimentary rocks.
This paragneiss has a metamorphic age obtained by U-Pb SHRIMP from zircon rims of ~ 472 Ma (Pankhurst et al., 2006).
On slopes with crystalline shists, gneiss, paragneiss in composition appears geomorphological processes of lateral erosion in Valsan catchment, rill wash on slopes with medium values, creeping on steep slopes; tumble down on rocky slopes and landslides on slopes with medium values with consistent layers of depositions.
3) contains a calcite marble horizon, roughly 2 km long by < 10 m wide, intercalated in a sequence of mafic metavolcanic rocks and paragneiss. The marble has returned highly anomalous values of light rare-earth-elements (La, Ce, Nd), which locally reach 1.59% [(REE).sub.2] [O.sub.3] (Lataille showing; Madore et al.
Cal Graphite holds a 100% interest in mining claims in the township of Butt, near Huntsville, where crystalline flake graphite occurs in mafic gneiss and paragneiss. An open-pit mine and a processing plant with an initial milling capacity of 3,000 t/d ore, which could be expanded to 5,000 t/d, was completed during the year and production started during October.
Copper mineralization at Mythril is hosted in a variably altered, foliated granodiorite intrusion, previously interpreted as a quartz-feldspar paragneiss based on limited outcrop exposures.
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