The calcalkaline white hill intrusive suite, Central Takitimu Mountains, Western Southland, New Zealand

Abstract

The White Hill Intrusive Suite is a sequence of gabbroic to quartz dioritic subvolcanic intrusions within the Permian calcalkaline Takitimu Group. The suite is possibly the lateral and shallow level equivalent of the Longwood Complex and Mackay Intrusives, to the south and north, respectively. The intrusions are predominantly lensoid and concordant and show marked westward size and grain-size increases with increasing stratigraphic depth. The intrusives are characterised by simple mineralogy, dominated by plagioclase, augite, and magnetite, and widely varying grain size. Most of the sills were emplaced in Late Permian time. The suite is interpreted as penecontemporaneous shallow intrusives which intruded the thick Takitimu volcanic pile and tapped the same magma source as the lavas. Sedimentation, volcanism, plutonism, and low-grade metamorphism were all accomplished within 10 Ma. Magmatic heat from the intrusives probably played a major role in establishing short-lived high-temperature gradients during the metamorphic event. The chemical trends for microcrystalline intrusive rocks mirror the Takitimu basalt-siliceous andesite lineage, and were probably generated by the same crystal fractionation processes involving plagioclase, augite, olivine, hypersthene, and magnetite. More coarsegrained rocks are enriched in CaO and A12O3 relative to this lineage, and are presumed to be the products of preferential fractionation of plagioclase, relative to other crystallising phases. © 1986 Taylor & Francis Group, LLC.