Huka Group Geological Characterisation And Interpretation, Wairakei-Tauhara Geothermal Field, Taupo

Abstract

Understanding the stratigraphic architecture and evolution within geothermal fields is important for the interpretation of geological controls on system hydrology. In this study, we sample core and use whole-rock immobile element variations (Ti/Zr) to identify lithofacies from within the Huka Group (HG) in the Wairakei-Tauhara Geothermal Field (Wairakei-Tauhara), Taupo Volcanic Zone (TVZ). Facies associations indicate HG deposition occurred within paleo-Lake Huka. Deposition commenced with a thick ignimbrite deposited in the Lake (Waiora Ignimbrite). Mass ignimbrite emplacement was followed by less than 120 kyr of smaller-scale volcaniclastic and sedimentary deposition in the subsiding basin (Waiora Volcaniclastics). Volcanic quiescence is marked by the dominant deposition of lacustrine siltstone beginning with the lower HFF (LHFF). Siltstone deposition was briefly exceeded by eruption of the middle HFF (MHFF) phreatomagmatic unit. Continued lacustrine deposition (UHFF) becomes increasingly fluvial as rivers transgressed the filling basin.