| Summary |
The study area is located on Rancho Los Filtros approximately 13.5 kilometers northwest of Aldama, Chihuahua, Mexico. In the study area massive cliff-forming Cretaceous limestones are intruded by sills of reddish altered rhyolite. Rhyolite is also found as a hypabyssal plug or small flow. Later intrusion of Paleoceno granodiorite produced fine-to coarse-grained marble, grossularite and wollastonite near the limestone-granodiorite contact. These rocks overlie the Paleozoic Rara Formation. The Rara Formation is divided into two units. One is a highly sheared turbidite sequence consisting of interbedded fine-grained sandstones and phyllitic shales. This unit also contains a meter-thick bed of strongly sheared arkosic, pebbly graywacke. The other unit consists of interbedded fine-grained sandstones and mudstones. These rocks are not so highly deformed as the turbidite unit. This unit forms an angular unconformity with the flat-lying Cretaceous rocks. The Precambrian rocks in the area are restricted to several tectonic blocks which are in the turbidite sequence of the Rara Formation. These Precambrian rocks are primarily metagranites which are cut by abundant dikes of amphibolite. The metagranites exhibit moderately well-developed granoblastic textures, unmixing of alkali feldspar, bulbous myrraekite, and rimming of plagioclase with albite. The amphibolites generally show well developed granoblastic textures. Relict igneous minerals and textures suggest that the amphibolites were metamorphosed under high load pressures and low differential stress conditions. Two K-Ar dates on hornblende (1025 and 1037 m.y.) from the amphibolites indicate that they are Grenvillian in age. These are the first Precambrian outcrops to be described from Chihuahua. The Rara Formation and the Precambrian blocks are cut by numerous diabase dikes. The diabases plot well within the alkaline field of the alkali-silica diagram. Two varieties of lamprophyre (minettes and camptonite) are found as dikes and sills cutting the Precambrian, Paleozoic, and Cretaceous sections. Phlogopite from a camptonite dike was dated at 88.9 m.y. by K-Ar. |
| General note | "The work was done with support from National Science Foundation grant, EAR-7915240." |
| General note | "Presented to the faculty of the Department of Geology ... in partial fulfillment of the requirements for the degree Master of Science in Geology." |
| General note | Advisor: Richard L. Mauger |
| Dissertation note | M.S. East Carolina University 1982 |
| Bibliography note | Includes bibliographical references (leaves 68-70). |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |
