Identifying a source assemblage for Buckland volcanic province
thesisposted on 2022-03-28, 16:19 authored by Joshua Shea
Buckland volcanic province lies on lithosphere transitioning from thick > 160 km in the west to< 110 km thick to the east. Similar intraplate volcanic provinces to the north and south show signs of a metasomatised lithospheric mantle source assemblage that produced non-four phase peridotitephases such as amphibole and apatite. This study investigates the role of metasomatism on thelithospheric mantle source assemblage for Buckland volcanic province. Here both whole rock andolivine minor and trace element chemistry is used to better indicate the mineralogy and metasomaticagent of the source assemblage. High whole rock Zr/Hf (range = 50 - 58) and low Ti/Eu (range= 3071 - 8059) trend towards values for natural carbonatite melts. These carbonatite-like valuesare interpreted as being adopted by the subsequent silicate melts generated in regions affected bycarbonatite metasomatism. Three groups of olivines are characterised, peridotitic xenocrysts, alkalibasalt olivines, and basanite olivines. Olivine xenocrysts Sc/Zr and Al/Mn are characteristic of aspinel lherzolite peridotite assemblage. Olivine phenocrysts Fo73-87.5 from both the alkali basalts,and basanites have concentrations of Li, Zn, Ti and Mn/Fe indicating the presence of mica in the source assemblage. While elevated Ni is characteristic of high modal pyroxene, and Ni/Mg and Mn/Fe suggest both mica and pyroxene in the source assemblage are mixed with peridotite wall rock components to produce the Buckland primary melt. It is suggested here that the source assemblagefrom the Buckland Volcanic Province is spinel lherzolite veined by a varying amounts of pyroxene-glimmerite ± apatite, for both the alkali basalts and basanites. This suggests mica has a larger role in intraplate basalt source assemblages, and agrees with literature that metasomatism plays a large role in the generation of intraplate basalts in eastern Australia.