CENOZOIC FELSIC MAGMATISM IN THE FRANKLIN MOUNTAINS

Abstract

Cenozoic felsic magmatism in the Franklin Mountains, El Paso, Texas, USA

University of Texas El Paso, Department of Geological sciences

Lewis, Joshua., Dr. Elizabeth Anthony

Felsic intrusions throughout the Franklin Mountains are a small component of the geology in the area yet produce beautiful scars that disrupt the stratigraphy and generate mystery in the minds of those who observe their features. The intrusive system is composed of felsic dikes and sills on both the east and west sides of the mountain. It is an extremely fine-grained, white to pink, intrusive rock consisting of potassic feldspar (orthoclase) and quartz.

The age is approximately 28 million years [Kottlowski, 1]. This age combined with the tectonic location of this intrusive system likely means the magmatism is associated with early stage Rio Grande rifting. Felsic magmatism took place in the first stage of rifting between 35 – 15 million years ago [2]. As the subduction of the Farallon slab concluded roughly 40 million years ago, the deformation related to convergent boundaries began to wane and the Farallon’s back arc began to extend [3]. As felsic magmatism slowed, mafic magmatism took its place as the tectonics of the region became completely rift related [4].

This felsic system has been poorly documented . This study is important to completing the geological history of the Franklin Mountains and to further understanding the felsic magmatism related to the early stages of Rio Grande rift extension.

References:

[1] Kottlowski, F.E, LeMone, D.V. and Foster, R.W., (1973) Remnant Mountains in Early Ordovician Seas of the El Paso Region, Texas and New Mexico. Geology (boulder), vol. 1, no. 3, pp. 137-140

[2] Keller, G.R., Morgan, P. and Seager, W.R., 1990, Crustal structure, gravity anomalies and heat flow in the southern Rio Grande rift and their relationship to extensional tectonics. Tectonophysics 174: 21-37

[3] Greer Price, L., (2010), The Geology of Northern New Mexico’s Parks, Monuments, and Public Lands. New Mexico Bureau of Geology and mineral Resources. pp. 6-15

[4] Ensenat, Susan E., (1989), The Geology and Geochemistry of Sierra de Cristo Rey and its Inclusions, Dona Ana County, New Mexico