An overview of the Precambrian geology of the Tusas Range, north-central New Mexico
Reinhard A. Wobus
The Tusas Range is a northwest-trending portion of the Brazos uplift of north-central New Mexico (Fig. I ). It is underlain predominantly by Precambrian crystalline and supracrustal rocks that are flanked and locally mantled by Tertiary and Quaternary volcanic and elastic sedimentary strata. Its subdued and partly forested ridges include some of the highest elevations between the Rio Grande depression to the east and the Chama Basin to the west, including Jawbone Mountain (3,256 m), Burned Mountain (3,106 m), Tusas Mountain (3,092 m), and Kiowa Mountain (2,968 m). The range loses its identity to the southeast at La Jarita Mesa, and to the northwest the Precambrian rocks become more thoroughly buried by volcanic rocks of the San Juan volcanic field in the Brazos Peak 15-min quadrangle.
The Precambrian (Proterozoic) rocks that form the core of the Tusas Range are of three general categories: bimodal metavolcanic and associated volcaniclastic metasedimentary rocks, a thick section of vitreous quartzite and interlayered pebble conglomerate, and several small stocks ranging in composition from quartz diorite to granite (Fig. 2). Except for the youngest of these stocks (the Tusas Mountain Granite), all of the Precambrian rocks have undergone regional metamorphism ranging from upper greenschist to middle amphibolite facies and are weakly to moderately foliated. Folding about northwest-plunging axes was probably concurrent with regional metamorphism, but much of the high-angle faulting in the area is Tertiary and younger.
- Wobus, Reinhard A., 1984, An overview of the Precambrian geology of the Tusas Range, north-central New Mexico, in: Rio Grande rift--northern New Mexico, Baldridge, W. S.; Dickerson, P. W.; Riecker, R. E.; Zidek, J., New Mexico Geological Society, Guidebook, 35th Field Conference, pp. 193-198.