Upper-mantle xenoliths and megacrysts in an alkali basalt from Tallante, South-eastern Spain
Capedri, Silvio; Venturelli, Giampiero; Salvioli-Mariani, Emma; Crawford, Antony J.; Barbieri, Mario
European Journal of Mineralogy Volume 1 Number 5 (1989), p. 685 - 700
published: Nov 16, 1989
manuscript accepted: Jun 9, 1989
manuscript received: Jan 30, 1989
ArtNo. ESP147050105008, Price: 29.00 €
Abstract The alkali basalt of Cabezo Negro de Tallante (Murcia Province) contains peridotite and pyroxenitehornblendite (Px-Hb) xenoliths as well as kaersutite megacrysts. Some xenoliths are composite and consist of both magmatic and peridotitic domains. Peridotite xenoliths (Group I nodules), by far the most abundant, vary from harzburgites to clinopyroxene-poor lherzolites and occasionally contain accessory pargasite and phlogopite. The well-equilibrated granuloblastic portions may contain veinlets and small amounts of glass. Px-Hb xenoliths (Group II nodules) are olivine-hornblende pyroxenites/hornblendites in which olivine, clinopyroxene and Ti-pargasite are the early crystallized phases, whereas kaersutite, apatite and rare phlogopite are interstitial. The interstitial spaces may be filled by reddish-brown glass, from which Mg-rich olivine crystallized. Euhedral/subhedral kaersutite megacrysts are unzoned and contain apatite and small inclusions of glass. The peridotite xenoliths equilibrated in the ranges 915-1030 °C and 8-16 kbar, under oxygen fugacities less than about 10-11 bar ( ≤ QFM) in a zone with high geothermal gradient. The 87Sr/86Sr ratios of an alkali basalt (0.70437), a kaersutite megacryst (0.70449) and a Px-Hb xenolith (kaersutite 0.70469, apatite 0.70464) are significantly different suggesting that the parent magmas varied slightly in isotopic composition.