Tusas Introduction

Masters Thesis - Introduction

Structure, Petrology, and Geochronology of Middle Proterozoic Rocks in the Tusas Mountains of Northern New Mexico.

Middle Proterozoic rocks of northern New Mexico are thought to have been produced and accreted to the margin of Laurentia from 1.75 1.65 Ga. These rocks typically contain evidence for at least three deformational events and multiple metamorphic events that have historically thought to have been developed during the 1.68-1.65 Ga Mazatzal orogeny; however few constrains exist for this interpretation.

Most of the exposed proterozoic rocks of northern New Mexico have been overprinted by an intense thermal and plutonic event at 1.4 Ga. Recently, workers have proposed that the last of the thermotectonic events attributed to the Mazatzal orogenic period was actually coeval with the 1.4 Ga thermal and plutonic overprint (Wingsted, et al. 1996; Bishop, et al. 1996). Two factors are important to the interpretation of tectonic events in Northern New Mexico; thermal and plutonic overprinting, and reactivation of previously formed structures. These two factors make it difficult to establish what portion of the earlier deformational events occurred during the Mazatzal orogeny.

The north-central Tusas Mountains contains a transition between what is thought to be a 1.4 Ga thermal and plutonic dominated region of the southern Tusas Mountains, and a region of less overprinted rocks to the north. This location was investigated to separate the affect of thermal overprinting and reactivation of structures from the true contribution of earlier deformation and metamorphic events to the overall Proterozoic tectonic history of northern New Mexico.