Tectonic-hydrothermal pegmatites

The Kiawa pegmatites, New Mexico, are thought to have formed by the process outlined in part I of this paper, i.e., by the reaction, Quartz + Muscovite + (Na⁺, K⁺) Perthite + H⁺.The pegmatites and country rocks were mapped and sampled in detail and geochemical data were obtained by spectrochemical analysis of separated minerals for 17 major and trace elements.Structural compatibility with the model is demonstrated by the occurrence of the pegmatites in structurally low pressure zones. Geochemical evidence indicates that quartz and muscovite, the raw materials for the reaction, were available before formation of the pegmatites. The distribution of major and trace elements in the minerals of the pegmatites and country rocks supports the model. Elements that were released by major reactions are found in secondary minerals in the country rocks and/or in pegmatite minerals. The distribution of barium in the minerals is that which would be predicted from its known geochemical behavior. Geologic evidence suggests that the pegmatites formed synkinematically during regional metamorphism.Other features of the Kiawa pegmatites, such as albitization, structural control of element distributions, and possibly an older generation of pegmatites, are shown to be in accord with the proposed model. Certain features of the pegmatites are not amenable to a magmatic explanation.