摘要：

The rhyodactic O'Leary Porphyry which forms the Pleistocene (0.233±0.37 m.y.) volcanic domes of O'Leary Peak and Darton Domein the San Francisco Volcanic Field (northern Arizona, U.S.A.) contains sanidine phenocrysts with oligoclase mantles (rapakivitexture). Rapakivi texture occurs worldwide in silicic rocks of many ages and has been attributed to various igneous and metamorphicprocesses. The O'Leary Porphyry contains both mantled and unmantled sanidine (both are Or_63–69 Ab_30–36An₁), oligoclase and quartz phenocrysts, labradorite (An₅₃Ab₄₅Or₂) and kaersutite xenocrysts and andesite xenoliths. The compositional range of oligoclase is the same (An_11–26Ab_70–80Or_r–10) for the rapakivi mantles, the oligoclase phenocrysts, and the oligoclase crystals poikilitic within sanidines. Most mantlesare discontinuous. The sanidine appe

展开