Geology of the Neck, northeastern Stewart Island


Cook, N. D. J.


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The Anglem Complex, Tarpaulin Metagranite (new name), Paterson Group, and the Rakeahua Granite crop out on The Neck, northeastern Stewart Island.
Five intrusive suites of the Anglem Complex range in composition from hornblende gabbro, through diorite and tonalite to granite. A heterogeneous suite formed in part by mingling of basaltic and tonalitic magmas intrudes diorite and microdiorite. Later intrusion of granite followed by porphyritic microtroqdhjemite is noted. Coexisting basalt, aplite, and mixed basalt-aplite dikes in the one dike swarm provide compelling evidence for magma mingling.
A deformed granite inferred to be fault bounded to the north and south, and metamorphosed to greenschist facies assemblages, is here named the Tarpaulin Metagranite.
One kilometre of steeply dipping, metamorphosed clastic sediments and volcanics of the Paterson Group are sandwiched between the Tarpaulin Metagranite and the Rakeahua Granite. Extensively recrystallised crystal tuffs, lapilli tuffs, and crystal-lapilli tuffs are interspersed with rhyolitic volcanics, rudites. and thinly bedded ashes. Metamorphism to greenschist facies conditions accompanied a heterogeneous flattening associated with cleavage formation. Some rudites are flattened to plane strain ellipsoids with aspect ratios of 10:1 or greater. Pyroclastic flow is a likely emplacement mechanism for the rudites.
The Rakeahua Granite is extensively altered and contains many xenoliths of volcanic and sedimentary parentage. Unlike the Tarpaulin Metagranite, the Rakeahua Granite is essentially undeformed.

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130 p. : ill. (some col.), maps ; 30 cm.


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Cook, N. D. J., “Geology of the Neck, northeastern Stewart Island,” Otago Geology Theses, accessed May 22, 2024,

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