Preliminary study of Tuapeka Group rocks in the lower Clutha Valley

Becker, W. Noel.

The metagreywackes of the Tuapeka Group in the lower Clutha Valley, are described in terms of lithology, sedimentology, metamorphism and structure. The majority of the metagreywackes are in the prehnite-pumpellyite metamorphic facies with some in the northern extent of the area metamorphosed to pumpellyite-actinolite schist facies.
A scheme is proposed to differentiate the sand-grade metagreywackes by the relative proportions of microlitic (intermediate) volcanic rock fragments and felsitic (acid) volcanic rock fragments observed ir1 thin section~ combined with the amount of quartz and ferro-magnesian minerals in the rock.
The metagreywackes are very lithic, and have high volumes of andesitic (± acid volcanic) rock fragments within them, thus showing greater affinity to the Hokonui Facies metagreywackes then the Torlesse Group of the Alpine Facies.
Folding is complex, but a large recumbent, isoclinal fold has a gently plunging south-west fold axis and an axial plane dipping gently to the north-east. There is also evidence of conical folding.

73 leaves : illus., maps (fold.) ; 29 cm.

1973Becker

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