Kaapvaal lamproite melts(aka orangeites):A new type of alkalicarbonate liquid?insights from olivine-hosted multiphase inclusions(Silvery Home,South Africa)  

作　　者：Adam Abersteiner Alexey Tarasov Alexander Golovin Geoffrey H.Howarth Vadim S.Kamenetsky 

机构地区：[1]Department of Geosciences and Geography,Research Programme of Geology and Geophysics(GeoHel),University of Helsinki,Finland [2]Institute for Sustainability,Energy and Resources,The University of Adelaide,Adelaide SA-5005,Australia [3]Department of Earth Sciences,School of Physical Sciences,The University of Adelaide,Adelaide SA-5005,Australia [4]V.S.Sobolev Institute of Geology and Mineralogy Siberian Branch,Russian Academy of Sciences,Russia [5]Department of Geological Sciences,University of Cape Town,Rondebosch 7701,South Africa [6]Center of Deep Sea Research,Institute of Oceanology,Chinese Academy of Sciences,266071 Qingdao,China

出　　处：《Geoscience Frontiers》2024年第5期308-322,共15页地学前缘（英文版）

基　　金：funded by the K.H.Renlund Foundation(Finland)and Future Making Fellowship(University of Adelaide);AVG and AAT were supported by the state assignment of IGM SB RAS(No.122041400157-9).

摘　　要：Kaapvaal lamproites(aka orangeites)are a group of volatile-rich(H_(2)O,CO_(2)),micaceous,ultrapotassic igneous rocks that are unique to the Kaapvaal craton in southern Africa.However,the composition of the melts that give rise to these rocks remains poorly understood due to overprinting effects of contamination by mantle and crustal material,volatile exsolution,fractional crystallisation and post-magmatic alteration.Consequently,this lack of reliable data on the initial composition of the Kaapvaal lamproite melts hampers our understanding of their source,petrogenesis and ascent mechanisms.Olivine is a common mineral comprising the Kaapvaal lamproites that has both xenocrystic(i.e.,mantle)and magmatic origins.Multiphase inclusions(melt/fluid)entrapped within olivine have been consistently demonstrated as an effective tool for gaining fundamental insights into the composition and evolution of melts that produce both kimberlites and lamproites,prior to processes,such as eruption,devolatization and syn-/post-magmatic alteration.In this study,multiphase inclusions of both secondary and pseudosecondary origin hosted in olivine from a Kaapvaal lamproite(Silvery Home,South Africa)provide novel insights into the composition of the melt(s)that initially transported olivine to the surface and then crystallised after emplacement to form the lamproite groundmass.The inclusions in our study contain daughter mineral assemblages consisting of diverse Ca-Mg carbonates,including K-,Na-,Ba-,and Sr-bearing varieties,moderate K-rich silicates(phlogopite,tetraferriphlogopite),and subordinate oxides,phosphates,sulphides,sulphates,and halides.Based on these daughter mineral assemblages,we suggest that the composition of the melt entrapped by olivine was SiO_(2)-poor,Ca-Mg carbonate-rich and contained elevated concentrations of K,Na,Ba,Sr,P and Cl.The mineral and reconstructed melt compositions are in stark contrast to the mineral association of the groundmass and the bulk-rock composition of the Silvery Home lamproite,respectively.We su

关 键 词：LAMPROITE KAAPVAAL Multiphase inclusions OLIVINE Orangeite 

分 类 号：P748[天文地球—海洋科学] P931P597