Geology and geochemistry of syenites and adjacent Proterozoic granitic and metamorphic rocks in the Zuni Mountains, Cibola County, New Mexico
Virginia T. McLemore and Christopher McKee
Lenticular to elongate bodies of brick-red syenite occur in Proterozoic granites and metarhyolites in the Zuni Mountains, northwestern New Mexico. The syenites consist of microcline and perthite with subordinate amounts of plagioclase, sericite, hematite and quartz. Accessory minerals include apatite, calcite, zircon and magnetite. Pervasive hematitization has obscured the texture and mineralogy of some syenites; however, other syenites exhibit relict hypidiomorphic-granular texture similar to the granitic rocks. Porphyritic texture similar to the texture of the metarhyolite has been replaced in the syenites by growth of K-feldspar and plagioclase crystals. Geochemically, the syenites are similar to other high-K syenites found in New Mexico and consist of 11-16% K2O, 0.9-1.0% Na20, 17-20% Al2O, and 53-65% SiO2. Outcrop relationships, textures, trace element distributions and high K20/Na20 ratios suggest the syenites may be a result of potassium metasomatism. The syenites may be associated with a widespread alkalic magmatic event characterized by carbonatites, syenites and metasomatism that affected New Mexico and southern Colorado during the Cambrian to Ordovician.
- McLemore, Virginia T.; McKee, Christopher, 1989, Geology and geochemistry of syenites and adjacent Proterozoic granitic and metamorphic rocks in the Zuni Mountains, Cibola County, New Mexico, in: Southeastern Colorado Plateau, Anderson, Orin J.; Lucas, Spencer G.; Love, David W.; Cather, Steven M., New Mexico Geological Society, Guidebook, 40th Field Conference, pp. 149-155.