THERMOMETRY AND TEXTURES OF KILBOURNE HOLE MANTLE XENOLITHS, NEW MEXICO

This study looks at textures through microscope analysis and uses microprobe data to solve for temperatures of mantle xenoliths from Kilbourne Hole, New Mexico. Three types of rocks are defined according to their texture, mineralogy, and fertilization. The first group of mantle zenoliths is identified by its fine –grained texture and by its mineral composition identifying it as an lherzolite. The second group is the porphyroclastic lherzolite. The second group and the first group are both fertile with a fair amount of clinopyroxene, the difference between the two groups are the fabric of the xenoliths. The second group’s rock fabric is different indicating that the porphyroclastic lherzolite occurred at a lower strain. The third group of xenoliths is olivine-rich peridotite. This group’s modal analysis indicates that there is lherzolite, harzburgite and some dunite. This group is less fertile than group one and two and has less clinopyroxene. Microprobe analysis of the three groups indicated that the forsterite content varied systematically such that the both group one and two had forsterite numbers between eighty-eight and ninety. The third group had forsterite numbers at ninety-two. Temperature values for the three groups vary systematically as well. The first group reported low temperatures while the second group reported moderate temperatures and the third group reported high temperatures. These calculations were based on a Al-Cr in orthopyroxene geothermometer of Witt-Eickschen and H.A. Seck (Contrib.Mineral.Petrol.,1991,106:431-439). Comparing the results of this thermometer to results from previous thermometers show that the same range of temperature variations. In conclusion, systematic differences in the forsterite contents correlate to the temperatures that were compared to temperatures of other thermometers.