Petrology of alkaline volcanic rocks in the Karitane Area, East Otago.

McLeod, Oliver Emerson, 1993 (Oliver)

A study of Miocene alkaline volcanic rocks at Karitane, East Otago was undertaken to characterise the distribution and composition of the ‘Karitane Suite’. The suite is located on the northern periphery of Dunedin Volcano and contains basanites, hawaiites, benmoreites, tephri-phonolites and phonolites that were formed by magmatic differentiation of a basanitic parent magma at upper mantle to crustal levels. Major element trends show strong depletions of Fe, Ca, Mg, Ti, and enrichments of Na, K, Al and P that are consistent with fractional crystallisation involving clinopyroxene, kaersutite and Ti-magnetite for the series basanite to benmoreite, and kaersutite and alkali feldspar for the series benmoreite to phonolite. Kaersutite bearing mafic inclusions in tephri-phonolite and benmoreite also record a history of repeated injections of basanitic melt into crustal magma chambers that may have influenced the style and extent of volcanism in the Karitane area.
Large, columnar jointed blocks at Karitane Beach and rare in situ outcrops further inland are the only remnants of volcanic rock following post Miocene erosion of the area. Field mapping indicates that much of the present and historical erosion is controlled by slumping and landslides in clay rich marine sedimentary rocks that dominate the local stratigraphy. Such landslides are responsible for erosion of the volcanic cover sequence, and the extent of these landslides was used to locate in situ remnants of the Karitane Suite from the ridges above the coast

176p with A2 map in back pocket

2015McLeod

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