Igneous Instrusives at Wakapatu and Oraka Peninsula, Coastal Southland.


Spencer, PL


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Between Pahia Peninsula and Kawakaputa Bay to the East, a S.E. trending arm of crystalline rock separates Foveaux Strait from a strip of fossil estuarine clays and sands. To the East, Oraka Peninsula performs the same function. The two topographic features are the result of adamolite and granodiorite masses respectively intruding a previously emplaced gabbroic mass composed mostly of norite. The following phenomena are thought to have occurred.
The formation of an auroole (probably no more than 200' thick) at the contact between the norite and the intruding acid body. Hybrid rocks are formed due to the metasomatic hydrothermal effect on the norite of emanations from the acid body. Mechanical mixing in places causes a very distinctive microscopic lithology which is, however, difficult to distinguish from in hand specimen, those rocks that have undergone 'in-situ' metasomatism.
The contamination of the acid magma by reciprocal reaction between the magma, and the myriad basic inclusions within the magma, that are thought to have been derived from the noritic wall rock.
The acid rocks(at Wakapatu at least) are believed to have been basified from an original adamellite gradationally through to a diorite. (these are so named on the basis of(Or/0r+Ab), because it is thought that orthoclase, in this case, is a most important mineral. Its concentration is indicative of.tho processes at work)
The presence of a large regional batholith (probably equivalent to Anglem Complex rocks), intruding norites(Bluff Complex probably) for the whole Longwood-Wakapatu-Pahia-Bluff-Stewart Island-Ruapuke Island region North of the Median Tectonic Line, and possibly extending much further North than the Longwoods,is postulated.

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98 leaves, photos, map(folded in pocket) 26 cm.


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POLYGON ((167.898165306076663 -46.367765882808179,167.894896613933213 -46.402748908665671,167.719972685713515 -46.395975449319167,167.725867057603693 -46.34385124750699,167.899327273282239 -46.355314202539347,167.898165306076663 -46.367765882808179))





Spencer, PL, “Igneous Instrusives at Wakapatu and Oraka Peninsula, Coastal Southland.,” Otago Geology Theses, accessed May 22, 2024, https://theses.otagogeology.org.nz/items/show/56.

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