Geologic History. Expansion in this right area of the Rio Grande rift started about 36 million years back.

Geologic History. Expansion in this right area of the Rio Grande rift started about 36 million years back.

Expansion in this an element of the Rio Grande rift started about 36 million years back. Rock debris that eroded through the developing highlands that are rift-flank in addition to wind-blown and playa pond deposits, accumulated within the subsiding Mesilla Basin. These fill that is basin, referred to as Santa Fe Group, are 1500 to 2000 foot dense beneath Kilbourne Hole (Hawley, 1984; Hawley and Lozinsky, 1993). The uppermost sand, silt, and clay associated with Pliocene to very early Pleistocene Camp Rice development, the youngest product for the Santa Fe Group in this area of the basin, are exposed into the base of Kilbourne Hole. The Camp Rice development had been deposited by way of a south-flowing braided river that emptied right into a playa pond within the vicinity of El Paso.

The Los Angeles Mesa surface, a flat working surface that developed along with the Camp Rice development, represents the utmost basin fill regarding the Mesilla Basin at the conclusion of Santa Fe Group deposition about 700,000 years back (Mack et al., 1994). This area is mostly about 300 ft over the contemporary Rio Grande floodplain. The top formed during a time period of landscape security. Basalt moves through the Portillo volcanic field are intercalated with all the upper Camp Rice development and lie regarding the Los Angeles Mesa area.

The Rio Grande started initially to decrease through the older Santa Fe Group deposits after 700,000 years back as a result to both climatic modifications and integration regarding the river system aided by the gulf. This downcutting wasn’t a constant procedure; there have been a few episodes of downcutting, back-filling, and renewed incision. This episodic growth of the river system generated the synthesis of a few terrace amounts over the Rio Grande between Las Cruces and El Paso.

Basalt that erupted about 70,000 to 81,000 years back from a collection of ports called the Afton cones found north-northeast of Kilbourne Hole flowed southward. The explosion that created Kilbourne Hole erupted through the distal sides regarding the Afton basalt moves, showing that the crater is more youthful than 70,000 to 81,000 years of age. Pyroclastic surge beds and breccia that is vent through the crater overlie the Afton basalt movement. The crater formed druing the last phases regarding the eruption (Seager, 1987).

Volcanic Features

Bombs and bomb sags

Volcanic bombs are blobs of molten lava ejected from a volcanic vent. Bombs are in minimum 2.5 ins in diameter and therefore are usually elongated, with spiral surface markings acquired because the bomb cools because it flies although the fresh air(Figure 5).

Bomb sags are typical features into the pyroclastic suge beds. The sags form when ejected volcanic bombs effect in to the finely surge that is stratified (Figure 6).

Figure 5 – Volcanic bomb from Kilbourne Hole. Figure 6 – Hydromagmatic deposits exposed in cliffs of Kilbourne Hole. The arrow features a volcanic bomb that has deformed the root deposits. Photograph by Richard Kelley.


A number of the volcanic bombs at Kilbourne Hole have xenoliths. Granulite, charnokite, and anorthosite are typical xenoliths in bombs at Kilbourne Hole; these xenoliths are interpreted to express items of the reduced to crust that is middleFigure 7; Hamblock et al., 2007). The granulite may include garnet and sillimantite, indicative of the origin that is metasedimentary or the granulite may include pyroxene, suggestive of an igneous beginning (Padovani and Reid, 1989; Hamblock et al., 2007). Other upper crustal Click Here xenoliths include intermediate and silicic-composition volcanic stones, clastic sedimentary stones, basalt and andesite that is basaltic and limestone (Padovani and Reid, 1989; French and McMillan, 1996).

Mantle xenoliths (Figure 8) consist of spinel lherzolite, harzburgite, dunite, and clinopyroxenite. Study of these xenoliths has furnished data that are important the structure and heat associated with the mantle at depths of 40 kilometers under the planet’s area ( ag e.g., Parovani and Reid, 1989; Hamblock et al., 2007). Some olivine into the xenoliths that are mantle of adequate size and quality to be looked at gem-quality peridot, the August birthstone.

Figure 7 – Crustal xenoliths from Kilbourne Hole. Figure 8 – Mantle xenolith from Kilbourne Hole.

Surge beds

A pyroclastic rise is hot cloud which contains more gasoline or vapor than ash or rock fragments. The cloud that is turbulent close to your ground area, frequently leaving a delicately layered and cross-stratified deposit (Figures 3 and 6). The layering kinds by unsteady and turbulence that is pulsating the cloud.

Hunt’s Hole and Potrillo Maar

A number of the features described above may also be current at Hunt’s Hole and Potrillo maar (Figure 9), that are positioned to the south of Kilbourne Hole. Xenoliths are uncommon to absent at Hunt’s Hole (Padovani and Reid, 1989), but otherwise the maars are comparable. Contrary to Kilbourne Hole, Potrillo maar isn’t rimmed by a basalt movement, and cinder cones and a more youthful basalt flow occupy a floor of Potrillo maar (Hoffer, 1976b).

Figure 9 – View to your western from Potrillo maar looking toward Mt. Riley and Mt. Cox, two Cenocoic that is middle dacite . Photograph by Richard Kelley.