Ignimbrites, trachytes, and sedimentary rocks of the Precambrian Thunderbird Group, Franklin Mountains, El Paso, Texas

摘要

Metamorphosed trachytes, ignimbrites of rhyolitic composition, and volcaniclastic rocks are recognized in the Precambrian Thunderbird Group, Franklin Mountains, near El Paso, Texas. Chemically, both the trachytes and pyroclastic rocks are alkalic. Contact metamorphism due to intrusion of the Red Bluff Granite recrystallized the Thunderbird Group to the albite-epidote hornfels facies. However, primary igneous and sedimentary structures are well preserved, as seen both in outcrops and thin sections, throughout most of the Thunderbird Group.