Raton-Clayton (Capulin Volcano) Volcanic Field

The Raton-Clayton volcanic field lies at the northeastern end of the "Jemez lineament", a prominent alignment of volcanic fields extending from the Pinacate field of Mexico, through the Springerville field on the southern margin of the Colorado Plateau in eastern Arizona, the Zuni-Bandera field, the Mount Taylor field, the Jemez field, and Cerros del Rio Field, and terminating in the northeastern corner of New Mexico in the Raton-Clayton field (Figure 1A & B). Some studies also include the Taos volcanic field as part of the general trend as well. In fact, the Taos field bears many similarities with the Raton-Clayton field in terms of age, morphology of silicic vents, and compositions. Because the alignment of fields in the Jemez lineament is parallel to the Snake River-Yellowstone hot spot track, the Jemez Lineament also has been considered by some to be a type of hot spot. As such the Raton-Clayton "hot spot" is one of only 49 hot spots identified on Earth (Figure 2).It should be clarified that the status as a true hot spot is not clear-cut largely because there is no strong age progression, for example, from southwest to northeast, as is typical of true hot spot tracks.

There are many volcanic fields of late Cenozoic age throughout the Southwest, each of which is distinctive in terms of the details of petrology, timing of eruptions, size, and morphology of vents, and character of pyroclastic deposits. But overall, they are all characterized by many small centers of eruption (one to a few kilometers across) of fundamentally basaltic, but ranging to more silicic, compositions. Instead of one big volcano, volcanic fields are typically on the order of one hundred kilometers across, and contain from several tens of vents to several hundred volcanic vents erupted over a period of several million years. Volcanic fields also differ from single large volcanoes, like Hawaii or the large volcanoes of the Cascades. They are also characterized by low rates of magma eruption, typically an order of magnitude less than large volcanoes. The Raton-Clayton field is elongated northwest-southeast, the axis extending from near Trinidad, Colorado, 140 km southeastward to Clayton, New Mexico (Dungan, et al, 1989). Including the outlying parts, the field covers nearly 20,000 km2 (Figure 3) (Stormer, 1987; Muehlberger, et al, 1967). The oldest rocks range from about 9 Ma and the youngest erupted less than 60,000 years ago (Sayre et al, 1995; Stroud, 1996). The distinctive characteristic of the Raton-Clayton field is the presence of highly alkalic mafic lavas with SiO2 contents as low as 36%. However, the field also contains centers, such as Sierra Grande, that erupted andesite, dacite or rhyodacite (up to nearly 70% SiO2).

Phases of Volcanic Activity (Stratigraphy) in the Raton-Clayton Volcanic Field

Traditionally the RCVF has been divided into three main phases of volcanic activity (Baldwin and Muehlberger, 1959; Muehlberger, et al, 1967). As a result of recent age radiometric determinations (Stroud, 1996), the ages of these phases are now known to be older than reported in earlier published accounts. Nonetheless, the basic stratigraphy remains adequately defined by three periods. (Note: The following is from Mathis, 1997.)

Raton Phase 9.0 - 3.5 Ma

Clayton Phase 3.0 -2.25 Ma

Capulin Phase1.7 - 0.04 Ma

These are defined in part by a sequence of inverted topography in which the older units are situated on earlier and now higher erosion surfaces, and subsequent eruptions were emplaced on younger and lower surfaces.The earliest lavas of the Raton-Clayton field flowed onto the surface of an alluvial apron of sediment shed eastward from the Sangre de Cristo Mountains (which are to the west of the field) (Baldwin and Muehlberger, 1959; Dungan, et al, 1989). Continuing uplift during eruption resulted in the erosion of this surface where it was not capped by volcanic rocks. During subsequent eruptions, lava flowed down valleys cut into this surface. The result is a series of "inverted topographic valleys" such that the oldest volcanic rocks are generally found at the highest elevations above present erosional levels, with younger lavas at progressively lower levels and in modern drainages. Thus the field is characterized by a kind of inverted stratigraphy.

The rate of down-cutting has been significantly greater in the western part of the field along the head of valleys draining into the Canadian River. The high, lava-capped mesas in the distance to the north are over 700 m above the valley floor. To the east, the elevation of the older basalt-capped mesas decreases, and at Clayton they are only a few meters above the present valley floors.