Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

P. G. Cooray ¹

Affiliations
1 Department of Mineralogy, (Geological Survey of Ceylon), Colombo, LK

Abstract

Basic charnockites several feet thick and completely contained in quartzites of the Khondalite Series are common in the Rangala-Madulkele area of Ceylon. Recently however, extremely Darrow bands of basic charnockites, 1/3 to 1 1/2 inches thick, in quartzite, have been noted. The nature of the field occurrence and the petrographic characteristics of these locks are described. It is concluded that the significant features of these occurrences can be best explained on the assumption that the basic charnockites, at least in this area, are the metamorphosed equivalents of sediments which formed part of the Khondalite Series.

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P. G. Cooray ¹

Affiliations
1 Department of Mineralogy, Geological Survey of Ceylon, Colombo, LK

Abstract

Several dyke-like bodies of uniform width (called "purple dykes" in the field) are found within the Tonigala Granite in north-west Ceylon. These are shown to be true dykes and comparable in some respects to the "relict dykes" of the Cornucopia and the Vancouver regions (Goodspeed, 1955; Roddick and Armstrong, 1959) and to the "early dykes" in the Main Donegal Granite (Pitcher and Read, 1960). The complex relations of the purple dykes to such elements in the Tonigala Granite as pegmatites, granitic veinlets, and biotite-rich foliae indicate that the dykes were intruded early in the history of the granite, after tensional stresses had been set up and during a long period of pegmatisation. Little evidence is however available to show the original composition and the actual mode of emplacement of the dykes. Petrographical and petrochemical similarities between the dyke rock and the surrounding granite suggest that the dykes underwent the same metasomatic changes viz. granitisation, as affected the granite in the later stages of its history.

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N. J. Money ¹, P. G. Cooray ²

Affiliations
1 Department of Geology, University of Oxford, IN
2 Geological Survey of Ceylon, Colombo, LK

Abstract

The Tabbowa Beds of Ceylon, Upper Jurassic in age, constitute a part of the Gondwana System, and consist mainly of arkose, siltstone and mudstone. In a recent study, five detailed sections with a total thickness of 360 feet were examined, and cyclic sedimentation, channelfill, and cross-bedding are described for the first time in these beds. On the basis of lithology and sedimentary features, the Tabbowa Beds are thought to have been deposited in a transitional environment in a semi-arid climate. The sediments were probably derived from the northwest (that is, the South Indian shield), the source area being one of tectonic instability.

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P. G. Cooray

Abstract

No Abstract.

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P. G. Cooray ¹

Affiliations
1 426, Mahakanda Road, Hindagala, Kandy Dist, LK

Abstract

No Abstract.

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