Proceedings of the 6th New Zealand Geothermal Workshop 1985. Petrochemical grouping of quaternary basalts, Northland, New Zealand : a reassessment and relation to Ngawha geothermal system. New Zealand Geothermal Workshop [7-9 Nov. 1984, New Zealand].

Cox, Malcolm E.

[1984]

171
CIENA

0-86869-056-2

The petrochemistry of basaltic rocks in the Kaikohe-Kaeo areas around Ngawha is reassessed to determined if chemical variations would confirm the apparent association of age and location of the youngest volcanism with the identified Kaikohe structural block, within which the Ngawha geothermal system is located. The outcome of this reassessment is the indication of an apparent change in chemical composition of the Kaikohe lavas from early (Horeke) high-Al to later (Taheke) alkali, the reverse of that previously reported. Comparison of basalts from the Kaeo area to the north of Kaikohe indicates volcanism forming the majority of the basalts there was alkalic and, at least, partly contemporaneous with the older high-Al volcanism in the Kaikohe block. A similar approach to basalts in the Whangarei and Puhipuhi areas to the south of the Kaikohe suggests a compositional change from earlier tholeiites to younger high-Al and Alkali basalts. The age relations in those areas are, however, less clear. Petrochemistry of these Northland basalts indicates an increasing depth of formation northward for the initial magma type in each area.

Presenta gráfs., maps. y tbls.

NUEVA ZELANDIA; ENERGIA GEOTERMICA; PETROQUIMICA; INVESTIGACION; ANALISIS QUIMICO;