Petrology of sediments from Sheet N29 - Lake Rotoiti - Tophouse

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Smale, D. 1984 Petrology of sediments from Sheet N29 - Lake Rotoiti - Tophouse. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report SL 7 16 p.

Abstract: The petrology of 22 sedimentary rocks from the Tophouse sheet is described. North of the Alpine Fault the older rocks are feldspathic volcarenites of the Maitai Group. They contain very few quartz or feldspar clasts, and the dominant rock fragments are basic volcanics (some still with pyroxene and olivine). The rocks in the provenance area were probably fairly restricted an similar to the older rocks still outcropping nearby. The two Tertiary limestones examined contain a more varied suite of intermediate to acid igneous fragments in addition ot the basic volcanic debris of the Maitai Group. The Torlesse rocks, south of the Alpine Fault, contain a higher ratio of feldspar to rock fragments that the Maitai Group, and contain an almost entirely different suite of rock fragments; most are porphyritic acid volcanics with plagioclase phenocrysts. The Torlesse provenance was mostly sandstone, mudstone, and acid to intermediate volcanics, with very rare altered basalts; however, a variable proportion of recognizably granitic debris suggests that an area around the present Lake Rotoiti was more influenced by a granitic source (particularly in some of the Rakaia subterrane) either geographically or in time.