Alkaline volcanic rocks from the Columbia Hills, Gusev crater, Mars

摘要: [1] Irvine, Backstay, and Wishstone are the type specimens for three classes of fine-grained or fragmental, relatively unaltered rocks with distinctive thermal emission spectra, found as float on flanks Columbia Hills. Chemical analyses indicate that these mildly alkaline basalt, trachybasalt, tephrite, respectively. Their mineralogy consists Na- K-rich feldspar(s), low- high-Ca pyroxenes, ferroan olivine, Fe-Ti (and possibly Cr) oxides, phosphate, glass. The texture is consistent a pyroclastic origin, whereas Irvine Backstay lavas dike rocks. compositions plot near liquid lines descent most elements calculated Adirondack class (olivine-rich basalts from Gusev plains) at various pressures 0.1 to 1.0 GPa. We infer Wishstone-, Backstay-, Irvine-class magmas may have formed by fractionation primitive, oxidized basaltic magma similar Adirondack-class all reveal magmatic province alkaline, distinct subalkaline volcanic thought dominate planet's surface. fact differentiated were not encountered plains prior ascending Husband Hill suggest local source volcanism beneath crater.