Ultrabasic Rock

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 It might be outdated or ideologically biased.

Ultrabasic Rock

 

a rock composed chiefly of iron-magnesium silicates—olivine and pyroxene—with small admixtures of secondary minerals, such as chromite and magnesite. Chemically, ultrabasic rocks are relatively poor in Si02 (less than 45 percent) and rich in magnesium (more than 42 percent MgO). There are many different types of ultrabasic rocks. The most important types are the dunites, the olivinites (in which magnetite is present instead of chlorite), the peridotites, and the pyroxenites. Characteristic of ultrabasic rocks is the full or partial conversion of olivine and pyroxene into the serpentine minerals, such as chryso-tile, antigorite, and lizardite, with the formation of serpentinites. Ultrabasic rocks are widely distributed as massifs or tectonic detached masses in all regions of development of magmatic rocks and are also found in the region of the midoceanic ridges. They are often associated with gabbros, alkaline rocks, and carbona-tites. Lava flows of ultrabasic rocks were studied in Australia in the early 1970’s. Effusive ultrabasic rocks have been found in Siberia (maimechites) and on Kamchatka.

The conditions of the formation of ultrabasic rocks have not been fully established. Most tectonic geologists, for example, A. V. Peive, A. L. Knipper, and V. G. Kaz’min, believe that ultrabasic rocks are tectonic, detached masses of rock from the upper mantle, whereas many petrographers, in particular, V. N. Lodochnikov and the Americans H. Taylor and P. Wyllie, continue to develop the idea of the magmatic genesis of ultrabasic rocks.

Many types of mineral deposits are associated with ultrabasic rocks: asbestos and nephrite deposits, silicate deposits, and deposits of the ores of platinum, chromium, nickel, and alloyed iron.

REFERENCES

Peive, A. V. “Okeanicheskaia kora geologicheskogo proshlogo.” Geotektonika, 1969, no. 4.
Wyllie, P. J. “The Origin of the Ultramafic and Ultrabasic Rocks.” Tectonophysics, 1969, vol. 7, nos. 5-6.

V. P. PETROV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
[USPRwire, Tue Oct 09 2018] Pyroxenite is an ultrabasic rock that consists of minerals that belong to the pyroxenes group-- predominantly, ferromagnesian minerals other than olivine.
Within and adjacent to the Olive Highlands, ultrabasic bedrock (harzburgite) is found only just outside the periphery in the north-east, in upper Wadi Hayl and Wadi Saham, at elevations well below the main ridges, but some ultrabasic rock types can be found within what is mapped as a mixed unit, along the short ridge west of the Jebel Qitab summit ridge (separating uppermost Wadi Hiluw from Wadi Hayl) and continuing north along the lower slopes of the Olive Highlands, east of Jebel Sfai and Jebel Samah (British Geological Survey 2006a, Thomas et al.
The parent material of the very deep red, clayey soil is highly fractured and serpentinised ultrabasic rock (peridotite) of Upper Cretaceous origin.
Jebel Rais, in Oman, is an isolated promontory of carbonate sediments within that intervening area of ultrabasic rock (rising to 1800+ metres above uppermost Wadi Hawasina) and for that reason was the subject of a botanical reconnaissance in by the senior author (GRF) in December 2005.
Two opportunities exist to increase resources; a careful assessment of platinum occurrence in ultrabasic rock masses (western Tuva, eastern Sayan, Koryakia) and a detailed study of platinum in black shale sequences, particularly in those locations where the association of platinum with gold mineralisation has already been revealed.
Elsewhere they are notorious for endemism: in California, some 12.5% of the state's 2,000 endemic species are said to be restricted to ultrabasic rock; within the tropics, both Cuba and New Caledonia, each of which has substantial areas of ultrabasic rock, have more than 900 ultrabasic endemics, a number of which are distinctive for having evolved the ability to concentrate heavy metals (Harrison & Kruckeberg 2008).
The measurement was conducted on a weathered block of ultrabasic rock. The dominant frequency of the signal in the first onset is approximately 25 kHz.
Throughout the complex there are sills of gabbro, ultrabasic rocks and dacite porphyrite.
Quite common in basic and ultrabasic rocks, Co is a rare metal existing in porphyritic igneous rocks in small quantities (Dixon, 2012).
The Fischer-Tropsch reaction, considered to be a common inorganic chemical reaction in geothermal systems and ultrabasic rocks [10,11], can produce the precursors of the critical organic molecules required for hydrocarbon generation.