Abstract

A paragenetic scheme modified from Brotzen (1959) shows in a diagram the inferred sequence of paragenetic associations and the four main types of zoned pegmatites in the Sierras Pampeanas of Argentina; the scheme is believed to have general application. The four types constitute a continuous time series, the types differing in the extent to which four or more of the following associations (listed in order of formation) are developed: border association; plagioclase association; microcline association; Na, K, and Li replacement; quartz core. The following genesis is proposed: '(a) The pegmatites originated from residual liquids of changing composition successively emitted from cooling magma chambers, (b) the process in all the emission centers was essentially similar, (c) the present distribution of the pegmatites was determined by the depth of the magmatic foci and by the subsequent erosion.'

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