The geology of New Mexico's Kilbourne Hole Crater is similar to Arizona’s Peridot Mesa.  They both have lava flows bearing xenoliths (“foreign rocks”) of speckled greenish-blackish material.  The rock shown below is a sample of the Afton Basalt Flow from Kilbourne Hole.  The brown matrix is basalt.  The greenish mass with black specks is a xenolith of lherzolite, a variety of peridotite (green = forsterite olivine; black = pyroxene).


Kilbourne Hole Crater is about 1.25 miles across and about 300 feet deep.  It is a maar volcano, produced by a steam explosion from superheating of water-saturated material under the Afton Lava Flow.


The lherzolite masses in the Afton Basalt Flow come from the upper mantle (lower continental lithosphere).  Isotopic dating has indicated that the lherzolite is late Paleoproterozoic in age.  This strongly constrasts with the age of surrounding basalt matrix, at 15,000 to 20,000 years old (Late Pleistocene).


Locality: Kilbourne Hole, Aden-Afton Basalt Field, ~26 miles southwest of Las Cruces, Potrillo Volcanic Field, Rio Grande Rift, southwestern Dona Ana County, southwestern New Mexico, USA (31º 58’ 18” North, 106º 57’ 49” West).



Lherzolite in basalt (7.4 cm across at its widest) from the Afton Basalt Flow at Kilbourne Hole Crater, New Mexico, USA.



Home page