A note on the layered dunite-peridotite-pyroxenite sill in the komatiitic milieu of J.C.Pura belt, Dharwar craton.


Downloads per month over past year

Prabhakar, B.C. and Namratha, R. (2013) A note on the layered dunite-peridotite-pyroxenite sill in the komatiitic milieu of J.C.Pura belt, Dharwar craton. journal of Geol. Soc, 85. pp. 120-121. ISSN 1943-2674.

PRABHAKAR.pdf - Published Version

Download (3MB) | Preview
Official URL: https://scholar.google.co.in/scholar?q=A+note+on+t...


J.C.Pura belt is a small komatiite – rich Archaean (~3.35 Ga) greenstone terrain in Western Dharwar Craton (Fig. 1). Extrusive signature of the komatiite is evident in the form of flow top joints, pillow structures, flow top breccias and vesicular flows. Dunitic, peridotitic and pyroxenitic(by composition) varieties of komatiites are abundant, but all of them are extensively serpentinised, chloritised and carbonatised. Most part of this belt is surrounded by synkinematically emplaced gneissic rocks, besides being domed-up in the central portion by granitic intrusion. While the extrusive ultramafic activity is more predominant in the belt, a rare, strongly layered body of dunite-peridotite-pyroxenite sill is found within this milieu. This note describes the field and petrographic characteristics of the sill with a view to understand varied emplacement conditions of magma during the development of ultramafic profiles in J.C.Pura belt. The layered dunite-peridotitepyroxenite sill is observed about 4 km north commonly seen gradational layering in peridotite, is formed by progressive increase in the modal content and size of the pyroxene crystals (cumulates) from bottom upwards (Fig. 3). Some times small shreds of pyroxenite project into peridotitic bands with sharp contacts. Serpentinisation of primary minerals namely olivine and pyroxene, has been a ubiquitous feature in the layered body especially in dunitic layers. Rarely, vestiges of olivine are found as fragmented tiny grains. In peridotite layers, pyroxene crystals are relatively better preserved whereas olivine crystals are intensely serpentinised. A very coarse cumulus texture, ought to have developed originally in the layered body, is largely obliterated due to the serpentinisation. The coarse, peanut to grape sized pyroxene cumulates, mentioned earlier, show complex texture under microscope. They contain subcumulus-looking or aggregate-like serpentinised masses surrounded by thick rims of iron oxide. Minor amounts of east of Rampura (Fig.1). It is about a km long, trending in N-S direction with a width of about 20 m, lying close to the eastern limb of the J.C.Pura belt. The outcrops of this layered body occur in a low lying mound juxtaposed to serpentinised massive komatiite. Layering is manifested well with distinct colour bands of olive green coloured dunite, buff coloured peridotite and pinkish brown coloured pyroxenite (Figs. 1 and 2).These layers vary in size from 2 cm to nearly half a meter. The surface expression of the layers of dunite and pyroxenite is homogeneous as their predominantly monomineralic composition, but peridotite layers show heterogeneity in surface expression. Peridotite contains olivine and pyroxene cumulates and since pyroxene cumulates are more resistant (to weathering), they stand out prominently in the out crops as pea nut to grape sized crystals. The contact between layers is normally sharp. The sharp contacts are observed between dunite and pyroxenite and peridotite and pyroxenite. The les

Item Type: Article
Subjects: Faculty of Science > Earth Sciences > Geology
Divisions: Jnana Bharathi / Central College Campus > Department of Geology
Depositing User: Mr . Chandrashekar
Date Deposited: 18 Oct 2016 07:07
Last Modified: 18 Oct 2016 07:07
URI: http://eprints-bangaloreuniversity.in/id/eprint/6545

Actions (login required)

View Item View Item