Pyroxenes from the Gabbros of the Marangudzi Ring Complex, Rhodesia

M. T. Hossain
Department of Geology, University of Nigeria, Nsukka, Nigeria

Summary: Chemical, X-ray, and optical analyses of eight Ca-rich pyroxenes and three coexisting Ca-poor pyroxenes from the gabbros of the Marangudzi ring complex, Rhodesia, are presented. Both the series show limited Fe-enrichment. High Ca-content of the clinopyroxenes together with their restricted Fe-enrichment, having a trend from Ca44·8Mg42·6Fe12·6to Ca42·7Mg37·7Fe19·6, could be indicative of an alkaline nature. But the presence of a Ca-poor pyroxene phase with a compositional trend between Ca2·9Mg71·2Fe25·9 and Ca3·1Mg63·0 Fe34·9 onwards in small amounts suggests tholeiitic to calc-alkaline nature. Certain characteristics in the variation in composition of the pyroxenes confirm a transitional nature of the Marangudzi parent magma, originating at a depth comparatively greater than the normal tholeiitic magma, but less deep than alkaline magma, at a fairly high pressure. The Marangudzi pyroxenes are compared with the pyroxenes of the similar world-wide igneous complexes.

Mineralogical Magazine; March 1977 v. 41; no. 317; p. 111-119; DOI: 10.1180/minmag.1977.041.317.16
© 1977, The Mineralogical Society
Mineralogical Society (