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Journal of the Geological Society; 1972; v. 128; issue.4; p. 333-336;
DOI: 10.1144/gsjgs.128.4.0333
© 1972 Geological Society of London

DISCUSSION

Mr. F. J. FITCH asked the author if he could relate the volume of lava being erupted at any particular time and place to the stage in the volcanic cycle attained at that locality. He confirmed that the great bulk of Karroo Volcanism was confined to a short period of about 20 m.y. in duration at the beginning of Mesozoic time, but agreed that the total time span of Karroo and apparently related magmatic activity might be 10 m.y. or more. In collaboration with Dr. J. A. Miller he had recently suggested that the time sequence of Karroo activity viewed on the K-Ar time scale is as follows: Stages of cycle

The AUTHOR thanked Mr. Fitch for his contribution to the time relations of Karroo igneous rocks. When referring to stages in the volcanic cycle it is necessary to be clear about the definitions employed. In terms of the thermal


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