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 Al 2 0 3 relative to this lineage, and are presumed to be the products of preferential fractionation of plagioclase, relative to other crystallising phases.

Relationships between the brook street Terrane and Median Tectonic Zone (Median Batholith): Evidence from Jurassic conglomerates

“…Cipriano (1986) demonstrated significant differences in the petrography and geochemistry of Drumduan and Brook Street basalts. Addition of the datasets of Houghton (1985Houghton ( ,1986) to Cipriano's (1986) data on Fig. 9, still supports these differences.…”

“…Kimbrough et al (1992) suggested that these intrusive complexes represent the roots of ankaramitic volcanic centres. In the Takitimu Mountains, the volcanic pile is intruded by gabbro-quartz diorite of the White Hill Intrusive Suite, and both are cut by hypabyssal dikes with hornblende K-Ar ages of 242-231 Ma (Houghton 1985(Houghton , 1986.…”

“…Recent mapping (Mortimer et al in press a) Graham & Korsch (1990). Age range of Brook Street intrusives from Kimbrough et al (1992;Bluff) and Houghton (1986;Mackinnon Peak Early/Middle Jurassic MTZ magmatism/uplift Early/Middle Jurassic (c. 180-200 Ma) plutonic rocks are a significant component of the conglomerate clasts studied. However, they fall within an apparent "plutonic gap" in Median Suite history (Kimbrough et al 1994).…”

“…The Brook Street Terrane is dominated by basaltic-andesitic volcanic and volcaniclastic rocks, but plutonic rocks locally intrude them (Wood 1966;Mossman 1973;Houghton 1986; in press a; Landis et al 1999). The thick volcanogenic sequences of the Murihiku Terrane represent near-arc basin deposits (Blake et al 1974;Ballance & Campbell 1993), possibly associated with igneous activity represented by the rocks which dominate the MTZ (Kimbrough et al 1994;Coombs et al 1976Coombs et al , 1996.…”

Igneous rocks of the Brook Street Terrane, New Zealand: Implications for Permian tectonics of eastern Gondwana and magma genesis in modern intra‐oceanic volcanic arcs

“…The Brook Street Terrane (BST) is exposed throughout South Island, New Zealand, and represents a remnant of a Permian island-arc system. Comprehensive descriptions of the stratigraphy, paleontology, and sedimentology of the terrane have been published (Houghton 1981;Johnston & Stevens 1985;Houghton & Landis 1989;Landis et al 1999;Campbell 2000). In contrast, with the exception of early work by Sivell & Rankin (1983) and Houghton (1985), detailed petrological and geochemical analysis of the igneous rocks of the BST is limited.…”