"Akaroa Volcanic Group (9.1 – 8 Ma): Activity occurred simultaneously at the Mt Herbert and Akaroa volcanoes. Activity at Akaroa produced a 1200 km³ composite strato-shield cone, predominantly composed of alkali lavas, pyroclastics and shallow intrusives, which reached an estimated 1800m above sea level. Activity was predominantly from a central vent (suggested as Onawe Peninsula), although minor vents on the flanks, and radial dyking did occur.
The Akaroa Volcanic Group has been classified into extrusive and intrusive rocks. Extrusive rocks include the early stage Tikao Trachyte and Lushington Breccia, the main cone forming French Hill Formation (9.0 – 8.3 Ma), the flank eruptives of the Mt Sinclair Formation 8.6 – 8.3 Ma) and the Te Oka Formation (8.3 – 8.1 Ma). Intrusive rocks include the Duvachelles Gabbro (8.92 Ma) and the Onawe Syenite exposed on Onawe Peninsula, representing late stage emplacement."
Hampton, S. J. (2010) https://ir.canterbury.ac.nz/handle/10092/4117
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