Charnockite


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charnockite

[′chär·nə‚kīt]
(petrology)
Any of various faintly foliated, nearly massive varieties of quartzofeldspathic rocks containing hypersthene.

Charnockite

 

(named for the founder of Calcutta, J. Charnock), a hypersthene granite typical of Precambrian assemblages that contain migmatites. Charnockite is composed of orthoclase, oligoclase, quartz, and hypersthene; it also often includes the garnets almandine and pyrope, as well as biotite, magnetite, and other minerals. Two types of charnockites are distinguished: ferrohypersthene charnockite and garnet charnockite.

The composition of charnockite varies. It is currently believed that ferrohypersthene charnockites occur in relatively shallow fades, whereas garnet charnockites are typical of more deep-seated metamorphic facies. The formation of garnet charnockites whose outcroppings are observed in the most deeply eroded Precambrian shields (Indian, Sinian, Aldan, Baltic, and Canadian), is distinguished. The origin of charnockites is linked with magmatism and metamorphism; charnockites are associated with anorthosites and other plutonic rocks, forming the charnockite-anorthosite series.

The term “charnockite” was first proposed by the British geologist T. Holland in 1900 for the intrusive rocks of the Madras area, which contain ferruginous hypersthene as the chief mineral.

REFERENCES

Winkler, H. Genezis metamorficheskikh porod. Moscow, 1969.
Charnockites. New Delhi, 1964. (International Geological Congress: Report of the Twenty-second Session. India, 1964, part 13.)

V. P. PETROV and A. A. MARAKUSHEV

References in periodicals archive ?
2008), this region is occupied by the large Kursiai batholith with a few minor plutons made up of a suite of dominantly charnockitic granitoid rocks (mangerite, enderbite, opdalite, charnockite and granite).
Geology Rank Weight Total weight Charnockite Group 6 4 24 Gneiss 6 4 24 Ultrabasic rocks 6 3 18 (a) Geology Weight.
Other secondary rocks used in delineating them are carbonates, calc gneiss and banded iron formation (BIF) and Older granites, which include granite, granodiorite, diorite charnockite, pegmatites and aplites.
The geology of the area is represented by Archaean to Precambrian crystalline formations such as charnockite, granite gneiss and ultrabasic rocks, overlain by Mesozoic and Tertiary sedimentary rocks (Rajmohan & Elango 2005).
The important rock types encountered in this area are Granitic gneiss, Mica Gneiss, Hornblende Gneiss, Charnockite and pink Granite.
The author observed this in the Archean Granite 7-32-89-10 well drilled to a depth 2,368 meters (7,700 feet) into pink, charnockite granite basement in northeastern Alberta, Canada.
The NESP is dominated by foliated plutonic rocks consisting of tonalite-trondhjemite (40%), granite (20%), granodiorite (15%) and enderbite, along with subordinate opdalite, charnockite and mangerite (15%).
This assemblage is similar to the highland/Southwestern Complex of rocks of Sri Lanka (which consist of granulite-facies metamorphic rocks such as garnetiferous biotite gneisses, garnet-sillimanite-biotite gneisses, calc-silicate gneisses, amphibolite and especially calciphye, charnockite and cordierite bearing gneisses), that have produced some of the world's largest alluvial gemstone deposits.
The positive anomalies occurring over or near higher metamorphic formation outcrops appeared to be associated with mafic igneous bodies Shandini et al, (2010) used spectral analysis and 3D gravity modelling to provide evidence that the Bouguer anomaly on the northern edge of the CC could not be modelled without high-density intrusive-like deep bodies and attributed positive anomalies in this region to deep and dense intrusive bodies A positive NW-SE trending anomaly was the dominant feature in the southern part of the area which could be interpreted in terms of TTG group igneous charnockite intrusion
The basement of the study area consists of charnockite, granite gneiss, Leptinite, Leptinite Gneiss, Peninsular Gneiss, Laterite, Warkalai Sandstone, Variegated Clay, River Alluvium etc.