Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle:1.Melting relations and major element compositions of melts  

作　　者：Stephen F.Foley Isra S.Ezad Sieger R.van der Laan Maik Pertermann 

机构地区：[1]School of Natural Sciences,Macquarie University,North Ryde,New South Wales 2109,Australia [2]Research School of Earth Sciences,Australian National University,Canberra,ACT 2601,Australia [3]Tata Steel Europe,Research and Development,Ijmuiden,The Netherlands [4]Coos Bay,Oregon,USA

出　　处：《Geoscience Frontiers》2022年第4期48-74,共27页地学前缘（英文版）

基　　金：funded by grants from the Deutsche Forschungsgemeinschaft(Fo 181/3);the Australian Research Council(FL180100134)。

摘　　要：Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite+K-rich terite,some including 5%of accessory phases,have been conducted at 15 and 50 kbar.The assemblages represent probable source components that contribute to melts in cratonic regions,but whose melt compositions are poorly known.A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene(CPX),phlogopite(PHL)and K-richterite(KR)with or without 5%ilmenite,rutile or apatite.Additional experiments were run without KR and with higher proportions of accessory phases.Melt traps were used at near-solidus temperatures to facilitate accurate analysis of wellquenched melts,for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50°C of the solidus,so that melts reflect the composition of the amphibole and its melting reaction.Melts have high SiO_(2) and especially K_(2)O but low CaO and Al_(2)O_(3) relative to basaltic melts produced from peridotites at similar pressures.They have no counterparts amongst natural rocks,but most closely resemble leucite lamproites at 15 kbar.KR and PHL melt incongruently to form olivine(OL)and CPX at 15 kbar,promoting SiO2 contents of the melt,whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures,leading to an increase in Mg O and decrease in SiO_(2) in melts,which resemble olivine lamproites.Melts of mica pyroxenites without KR are richer in CaO and Al_(2)O_(3) and do not resemble lamproites.These experiments show that low CaO and Al_(2)O_(3) in igneous rocks is not necessarily a sign of a depleted peridotite source.Accessory phases produce melts exceptionally rich in P_(2)O_(5) or TiO_(2) depending on the phases present and are unlike any melts seen at the Earth’s surface,but may be important agents of metasomatism seen in xenoliths.The addition of the 5%accessory phases ilmenite,rutile or apatite result in melting temperatures a few ten of degrees lower;at least tw

关 键 词：Hydrous pyroxenite Experimental petrology Mantle melts Phlogopite LAMPROITE Mantle metasomatism 

分 类 号：P589[天文地球—岩石学] P542.5[天文地球—地质学]