Abstract
This paper gives an account of some unusual porphyritic basalts containing very large phenocrysts of plagioclase, averaging from 3 cm to 5 cm in length, and at places as large as 10 to 12 cm in length. These flows have been noticed at more than 20 localities, spread all over Western Maharashtra, occurring between levels of 100 feet below sea level (seen in a drill-core) and an elevation of more than 4000 feet above sea level. They appear to have a considerable lateral extent, some of them having been observed to extend for more than ten miles. In vertical extent, the flows were found to vary from 40 to 150 feet.
The giant phenocrysts commonly show cross-twinning. In some flows due to repeated cross-twinning they give star shaped appearance. At places they also occur in clusters. In portions of some flows the tablets seem to have settled at the bottom and are seen in horizontal positions. In hydrothermally altered portions of some flows the phenocrysts are altered and in some patches seem to have been completely destroyed. As a rule, the plagioclase weathers more quickly than the ground mass producing a very characteristic pitted appearance. Some flows seem to have contained large crystals of olivine which have been altered to iddingsite. Highly vesicular and amygdaloidal giant phenocrvst basalts are also met with.
Similar content being viewed by others
References
Agashe, L. V. andGupte, R. B., 1968,Some significant Features of the Deccan Trap. Seminar on the Cretaceous and Tertiary formations of South India, Bangalore (1966), p. 309–319.
Sowani, P. V. andPesiiwa, V. V., 1964,Porphyritic Basalt Flows at Purandar. J. Univ. of Poona, No. 28, p. 85–88.
West, W. D., 1952,A Note on the pyroxenes of the Deccan Trap. Quart. J. Geol. Min. & Met. Soc. of India, Silver Jubilee Volume, p. 156.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Karmarkar, B.M., Kulkarni, S.R., Marathe, S.S. et al. Giant phenocryst basalts in the deccan trap. Bull Volcanol 35, 965–974 (1971). https://doi.org/10.1007/BF02596858
Issue Date:
DOI: https://doi.org/10.1007/BF02596858