Upper-mantle xenoliths and megacrysts in an alkali basalt from Tallante, south-eastern Spain

This basalt contains peridotite and pyroxenite-hornblendite xenoliths as well as kaersutite megacrysts. Some xenoliths are composite and consist both of mantle and magmatic peridotite. The abundant peridotite xenoliths vary from harzburgites to clinopyroxene-poor lherzolites and occasionally contain accessory pargasite and phlogopite. The granuloblastic portions may contain veinlets and small amounts of glass. The pyroxenite-hornblendite xenoliths contain olivine, clinopyroxene and Ti-pargasite as the early crystallized phases, whereas kaersutite, apatite and rare phlogopite are interstitial. The peridotite xenoliths equilibrated at 915-1030 degrees C and 8-16 kbar at <10 (super -11) bar in a zone with high geothermal gradient. The (super 87) Sr/ (super 86) Sr ratios of an alkali basalt, a kaersutite megacryst and a pyroxenite- hornblendite xenolith are significantly different, suggesting that the parent magmas varied slightly in isotopic composition.