Phanerozoic tectonic setting of Santa Fe country
— Lee A. Woodward and R. V. Ingersoll

In the area of this field conference, there have been four main periods of Phanerozoic tectonic activity: late Paleozoic, Laramide (Late Cretaceous-early Tertiary), mid-Tertiary and late Cenozoic. Only the latter three have associated structures expressed in the present physiography of the region. Precambrian tectonics are not considered here.

From Cambrian through Devonian time, this region was stable, being located on the south flank of the transcontinental arch, a mildly positive feature (e.g., Lochman-Balk, 1972). There are no lower Paleozoic rocks in this region. The Mississippian was a time of quiescence also, during which a thin sequence of shelf carbonates accumulated (Armstrong, 1967; Armstrong and Mamet, this guidebook). High-angle faulting and epeirogenic uplift resulted in removal of most of the Mississippian strata prior to deposition of Pennsylvanian rocks.

During late Paleozoic time, the San Luis uplift, part of the larger Uncompahgre uplift (Baltz, 1965), developed near the site of the present Brazos uplift, and the smaller Pefiasco axis (Read and Wood, 1947) developed along the present Nacimiento uplift to the west of the Jemez region; these positive areas shed clastic debris into adjacent basins (e.g., Casey and Scott, this guidebook). The area of the southern Sangre de Cristo uplift was a major basin (Rowe-Mora basin of Read and Wood, 1947) that was to the east of the contemporaneous San Luis uplift. DuChene and others (1977) suggested that shelf deposition of Lower Pennsylvanian sediments on the southern and western sides of the San Luis uplift (Uncompahgre high-land) occurred in most of the area southwest of Santa Fe.

Mesozoic strata were deposited throughout the region except for the Brazos area which underwent several episodes of uplift (Muehlberger, 1967). Epeirogenic uplift resulted in regional unconformities between Permian and Triassic strata, and between Jurassic and Cretaceous strata.

The Brazos and Sangre de Cristo uplifts, and the Raton and Chama basins attained their present structural outlines during Laramide time. The Hagan embayment area was low at this time, as indicated by the presence of the Galisteo Formation of Eocene age (Gorham and Ingersoll, this guidebook). Numerous sills, dikes and laccoliths were emplaced in the northerly trending Ortiz porphyry belt during middle Tertiary time. These igneous bodies are mostly porphyritic laccoliths, and from north to south, comprise the Cerrillos, Ortiz, San Pedro and South Mountain igneous centers.

Late Cenozoic epeirogenic rise of the entire region may have been contemporaneous with development of the Rio Grande rift, an event that is Miocene to Holocene in age. During the later stages of rifting (Pliocene and Quaternary), volcanism occurred along the western margin of the rift to form the Jemez volcanic field. Related flows formed the extensive Cerrosdel Rio volcanic field southeast of the Jemez area.

All of these complex tectonic events may be understood more completely when viewed in the regional context of plate tectonic interactions that occurred along both the Pacific and Gulf of Mexico margins through the Phanerozoic. Timing of tectonic events along plate margins closely corresponds with the above-described events although distances to Santa Fe country are large. Thus, tectonic events of global significance can be related to local manifestations.