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

Expansion in this area 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 when you look at the subsiding Mesilla Basin. These fill that is basin, referred to as Santa Fe Group, are 1500 to 2000 legs dense beneath Kilbourne Hole (Hawley, 1984; Hawley and Lozinsky, 1993). The uppermost sand, silt, and clay associated with the Pliocene to very very very early Pleistocene Camp Rice development, the youngest product associated with the Santa Fe Group in this area of the basin, are exposed into the base of Kilbourne Hole. The Camp Rice development ended up being deposited with a south-flowing braided river that emptied right into a playa pond into the vicinity of El Paso.

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

The Rio Grande began to reduce through the older Santa Fe Group deposits after 700,000 years back in reaction to both climatic modifications and integration regarding the river system with all the gulf. This downcutting had not been a constant procedure; there have been a few episodes of downcutting, back-filling, and renewed incision. This episodic growth of the river system resulted in 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 couple 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 for the Afton basalt moves, showing that the crater is younger than 70,000 to 81,000 years old. Pyroclastic rise beds and vent breccia blown through the crater overlie the Afton basalt movement. The crater formed druing the ultimate phases for the eruption (Seager, 1987).

Volcanic Features

Bombs and bomb sags

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

Bomb sags are normal features within the pyroclastic beds that are suge. The sags form whenever 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 highlights a bomb that is volcanic has deformed the root deposits. Photograph by Richard Kelley.


Lots of the bombs that are volcanic Kilbourne Hole have xenoliths. Granulite, charnokite, and anorthosite are normal xenoliths in bombs at Kilbourne Hole; these xenoliths are interpreted to express pieces of the low to center crust (Figure 7; Hamblock et al., 2007). The granulite may include garnet and sillimantite, indicative of a metasedimentary origin, or the granulite may include pyroxene, suggestive of an igneous beginning (Padovani and Reid, 1989; Hamblock et al., 2007). Other upper crustal 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. Research of these xenoliths has supplied data that are important the structure and temperature of this mantle at depths of 40 kilometers underneath the planet's area ( ag e.g., Parovani and Reid, 1989; Hamblock et al., 2007). Some olivine into the mantle xenoliths is of enough 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 surge that is pyroclastic hot cloud that contains more gasoline or vapor than ash or stone fragments. The turbulent cloud moves close into the ground area, frequently leaving a delicately layered and cross-stratified deposit (Figures 3 and 6). The layering types by unsteady and pulsating turbulence in the cloud.

Hunt’s Hole and Potrillo Maar

Most of the features described above will also be current at Hunt’s Hole and Potrillo maar (Figure 9), that are positioned towards the south of Kilbourne Hole. Xenoliths are uncommon to absent at Hunt’s Hole (Padovani and Reid, 1989), but otherwise the maars are comparable. As opposed to Kilbourne Hole, Potrillo maar is certainly not rimmed with a basalt flow, and cinder cones and a more youthful basalt movement occupy a floor of Potrillo maar (Hoffer, 1976b).

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

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