Geochemistry and geochronology of intrusive and volcanic rocks of the Three Rivers stock, Sierra Blanca, New Mexico
Fraser Goff, Robert C. Roback, William McIntosh, Cathy J. Goff, and Emily C. Kluk

Abstract:

Recent geologic mapping of the Three Rivers stock has outlined four relatively large syenite to quartz syenite bodies with distinct textural characteristics emplaced at roughly 29 to 28 Ma. These syenitic rocks were later intruded by a variety of smaller volume alkali granites (27.7 to 27 Ma). Three small rhyolites, which have geochemical affinities to the alkali granites, were identified around the north margin of the stock. The age of the freshest of these rhyolites is 28.2 Ma. A last group of two dikes and a small plug (rhyolite, trachyte and monzonite, respectively) conclude the intrusive activity in the stock, but these units are significantly younger (25.9 to 25.4 Ma), geochemically different, and volumetrically insignificant when compared to the main stock. The west margin of the stock has been unroofed and deeply eroded by uplift along normal faults that separate the west margin of Sierra Blanca from the Tularosa Basin. Two geochemical traverses down the highly eroded scarp of the syenite body show that the syenite is more silicic (evolved) at the top of the intrusion than at the bottom and core. The combined data suggest that the syenite is the crystallized remnant of a zoned magma chamber and that the Three Rivers stock represents an upper level intrusive complex beneath a small, eroded caldera.


Citation:

  1. Goff, Fraser; Roback, Robert C.; McIntosh, William; Goff, Cathy J.; Kluk, Emily C., 2014, Geochemistry and geochronology of intrusive and volcanic rocks of the Three Rivers stock, Sierra Blanca, New Mexico, in: Geology of the Sacramento Mountains region, Rawling, Geoffrey; McLemore, Virginia T.; Timmons, Stacy; Dunbar, Nelia, New Mexico Geological Society, Guidebook, 65th Field Conference, pp. 183-196.

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