Steep Head, Greenhills, Invercargill City, Southland Region, New Zealandi

Regional Level Types
Steep Head	Headland
Greenhills	- not defined -
Invercargill City	City
Southland Region	Region
New Zealand	Country

A more general geology of the Steep Head area is under Dunite Quarry Mindat heading, which is part of the area.

Pumpellyite and diopside in the photographs is noted as part of the Greenhills Complex, part of which is at Steep Head.

Over a dozen late ankaramitic dykes are found in the Steep Head area, ranging from a few centimetres to one metre wide, emplaced in wehrlite country rock. The wehrlite contains diopside crystals to 2cms in diameter, with olivine, and amphibolite commonly included within the crystals.

1) The first dyke examined by Mossman et. al. (2000) is a hornblende ankaramite dyke of olivine phenocrysts, some skeletal, scattered diopside phenocrysts, set in a groundmass of magnesiohornblende. The margin of the dyke contains amphibolite, and minor anorthite. Diopsides contain orientated blebs of magnesiohornblende and edenite. In the host pyroxene, spinels are noted ranging from chromian to Al rich, chromian magnetite, and Cr free magnetite. Amphiboles range from magnesiohornblende, edenite, pargasite and tschermakite, with minor late stage high Si magnesiohornblende. Dykes centres tend to be more Mg rich than margins.

2) The next dyke dips 70 degrees north-east, cross-cutting coarse grained feldspathic wehrlite, earlier dykes and veinlets, and medium grained gabbronorite. It has amphibolite margins grading into a phenocryst rich core.

3) A dyke on the north side of Steep Head as a hornblende ankaramite dyke, 30 cms thick, consisting of a monomineralic veneer margin of pale green hornblende crystals, with trace clinochlore. At 4 cms into the dyke are olivine and sub-ordinate diopside phenocrysts, increasing in number towards the dyke centre. The diopside crystals are studded with greenish brown hornblende crystals, with inclusions of clinochlore. Also noted in the dyke is montmorillonite, fine grained white mica, unfortunately un-named zeolites, prehnite, and microscopic Mg rich chlorite. There is veining of olivine with serpentine.

4) Dykes examined in the south-east corner of the Steep Head area, 3 kilometres east of Barracouta Point. A hornblende ankaramite dyke, 30 cms thick of olivine phenocrysts, minor diopside phenocrysts to 6 mms in diameter, set in a groundmass of clinopyroxene, orthopyroxene, abundant pale brown hornblende, and sub-ordinate plagioclase. Chromian spinel is enclosed within olivine phenocrysts.

5) Ankaramitic hornblende microgabbronorite dykes, 200 metres south of Steep Head, low Mg, low hornblende, 15 cms thick. There are abundant clinopyroxene and olivine phenocrysts up to 8 mms in diameter, with the number of them increasing towards the centre of the dyke. The groundmass is orthopyroxene, clinopyroxene, plagioclase, brown hornblende, and titaniferous magnetite granules.

Other Regions, Features and Areas containing this locality

References