Basic Rocks

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Basic Rocks

 

igneous rocks that are comparatively low in silica (45–55 percent) and rich in magnesium and calcium. Basic plagioclases (labradorite, bytownite) are characteristic of the mineral composition of basic rocks; olivine and other minerals that are undersaturated with silica are also present. Basic rocks may be either intrusive (gabbro, norites, anorthosites) or extrusive (basalts). Most of the present-day volcanoes erupt basic lavas, and basic lavas are also characteristic of all fissure eruptions.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Petrology of the Nagar Parkar granites and associated basic rocks, Thar District, Sindh, Pakistan.
These rocks are the product of the reaction between the hydrothermal solutions and the Serpentinized ultramaphic and basic rocks (gabbro to basalt) of the oceanic floor along the fractures; the minerals constituting these rocks therefore include an ensemble of Calcite, quartz, rarely Serpentine and Chlorite and crystals of Chrome Spinel.
Around 1.7 million years ago, our ancestors' tools went from basic rocks banged together to chipped hand axes.
The relative distribution of immobile elements differing in concentration in felsic and basic rocks such as La and Th (felsic rock-enriched) and Sc, Cr and Co (enriched in basic rocks relative to felsic rocks) has been used to infer felsic and basic sources' relative contribution in shales from different tectonic environments (Wronkiewicz and Condie, 1990).
Carbon content (kg m-2, 0-30cm depth) in dominant soil units in PNM C (kg m-2) Umbric Leptosols of granites 18.2 Umbric Cambisols of schists 17 Umbric Cambisols of granites 7.6 Umbric Leptosols of basic rocks 6.9 Umbric Leptosols of schists 5.0 Chromi Luvisols of basic rocks 4.6 Dystric Fluvisols of alluvium 4.6 Dystric Leptosols of migmatites 2.6 Dystric Cambisols of migmatites 2.5 Eutric Leptosols of ulti amafie rocks 2.2 Haplic Alisols of sedimentary deposits 2.2 Eutric Leptosols of ultramafic rocks 2.2 Dystric Cambisols of sedimentary.
Besides intrusive rocks, some veins as well as effusive basic rocks are represented.
The company is also developing the East Boulder deposit, an assemblage of basic and ultra basic rocks some 21 km west of the Stiliwater operation.
(1989) reinterpreted the gravity anomaly data of Farah and Jafree (1965) and suggested that the basic rocks of the basement underlie much of the Nagar Parkar area whereas the granitic intrusions form thin sheet-like masses.
The rocks from four tectonic settings that can be discriminated from these new sets of diagrams are as follows: IAB (island arc basic rocks) numbered as group 1, CRB (continental rift basic rocks) as group 2, OIB (ocean-island basic rocks) as group 3, and MORB (mid-ocean ridge basic rocks) as group 4.
Two different types of basic rocks have been recognized, according to their geological setting.
Petrology of the Nagar Parkar granite and associated basic rocks, Tharparkar, Sindh, Pakistan.

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