New Mexico Geological Society Annual Spring Meeting — Abstracts

The Carrizo Mountains are located in the northern part of a folded, faulted, and intruded uplift complex which forms the Sacramento, Sierra Blanca, and Jicarilla mountains in south-central New Mexico.

The core of the Carrizo Mountains is a steep-sided, partly fault-bounded stock, with associated silIs on the north and northwest sides. Small plugs and numerous dikes occur on the east and southeast sides of the stock. It is composed of two steeply-dipping, vertically-oriented rhyolite bodies with an intervening quartz monzonite. Field and microscopic examination indicates that differentiation of a silicic magma body had a key role in the formation of the stock. However, the possibility of multiple intrusive phases cannot be ruled out. Chemical data reveal apparent close affinities between the Carrizo stock and the Three Rivers intrusive phase of the Sierra Blanca Mountains. Three Rivers activity occurred between 24.7 and 28.0 million years ago (Thompson, 1972, p. 2350) which suggests a late Oligocene age for the Carrizo stock.

The stock intrudes the Mesaverde Formation (Upper Cretaceous) which is composed of three members: a lower sandstone, a medial interbedded shale, sandstone and coal, and an upper sandstone. Quaternary units include pediment ravels, alluvial fans, talus, and alluvium.

Dikes in the eastern part of the area are composed of diabase, olivine diabase, and olivine diabase porphyry. Intrusion of these bodies probably occurred in middle Miocene time.