Xenoliths from the sub-volcanic lithosphere of Mt Taranaki, New Zealand

Mount Taranaki is located 140km west of the Taupo Volcanic Zone and represents the most westerly expression of subduction-related volcanism on the North Island of New Zealand. Taranaki is a predominantly high-K arc volcano but compositions range from basaltic andesite to andesite with minor dacite and basalt. The sub-volcanic basement under Taranaki is thought to comprise calc–alkaline plutonic and metamorphic rocks of the Median Batholith, overlain by a sequence of Cretaceous and Tertiary sediments. Taranaki lavas contain abundant xenoliths that represent samples of the upper to lower crust beneath the volcano. The xenolith suite has been initially organised into six groups based on petrography, geochemistry and inferred genetic relationships: supracrustal sedimentary rocks (1), mafic hornfels (2), garnet gneiss (3), granite and granodiorite (4), finely banded amphibolitic gneiss (5) and gabbros and ultramafic rocks (6). Groups 1, 3 and 4 are derived from the Median Batholith basement and Cretaceous–Tertiary sediments of the Taranaki Basin while Groups 2, 5 and some fine grained gabbros from Group 6 could either be derived from the Median Batholith or be cognate xenoliths. Group 6 gabbros and ultramafic rocks are dominated by clinopyroxene, amphibole and plagioclase and are predominantly cumulate in origin.