New Mexico Geological Society Annual Spring Meeting — Abstracts

A representative collection of crustal and mantle xenoliths has been obtained from the Kilbourne Hole maar, New Mexico. In spite of the site's international fame, no previous comprehensive study has been done on these xenoliths. This suite of xenoliths will be compared to other xenolith suites from around the world to more fully understand crustal structure and how xenoliths become entrained in basaltic eruptions.

Xenoliths from Kilbourne Hole fall into eight broad categories. In order of decreasing abundance, these are: 1) ultramafic peridotites, 2) mafic granulites, 3) pyroxenites, 4) intermediate and silicic volcanic rocks, 5) clastic sedimentary rocks, 6) basalts and basaltic andesites, 7) limestones, and 8) pelitic granulites. Collectively, these represent samples of the entire lithospheric section. The peridotites were entrained in the upper mantle. Mafic and pelitic granulites represent the lower crust. Pyroxenites represent either the mantle or lower crust. All other lithologies have not been metamorphosed and thus represent the middle to upper crust. The basalts and basaltic andesites are coarser grained than the coatings of juvenile basalt on the xenoliths, and thus could represent upper crustal lava flows through which Kilbourne Hole erupted. Lithologic correlations with exposed formations are in progress.

Most xenolith studies focus on specific lithologies, especially lower crustal granulites and upper mantle peridotites. The Kilbourne Hole data will be compared to other xenolith studies worldwide in which the entire spectrum of lithologies have been collected. For instance, the crustal xenolith suite from Hill 32 in the McBride volcanic province, north Queensland, Australia, is dominated by lower crustal lithologies; upper crustal xenoliths constitute only a few percent of the population, and no sedimentary or volcanic xenoliths are reported (Rudnick and Taylor, 1987, JGR, 92:13981-14005). In contrast, the Kilbourne Hole crustal suite contains a more diverse and abundant selection of upper crustal lithologies.