Identification of late quaternary tephras for dating Taranaki lahar deposits

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Abstract
Major and minor elements were analysed from titanomagnetites extracted from 12 Taranaki tephras. The tephras fall into five groups characterised by specific abundances of chromium, vanadium, nickel, cobalt and manganese. The titano-magnetite analyses allow the positive identification of two widespread but thin tephras at distances >25 km from their source. The preservation and identification of these dated tephras between three extensive lahar deposits in western Taranaki allows age limits to be placed on periods of lahar deposition. The oldest lahar is dated (NZ942) at > 16 100 years B.P. The middle lahar deposit is dated (NZ1143 and NZ942) between 12 500 and 16 100 years B.P. The youngest lahar is dated (NZ1144) at < 6970 years B.P. Titanomagnetite analyses from Tongariro eruptives are more basic in composition than those from Taranaki tephras and this regional difference allows source areas to be determined for soil parent materials in areas between the two volcanic centres.