Torlesse geology of Kakahu, South Canterbury

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Abstract
The Torlesse rocks of Kakahu, South Canterbury, New Zealand, consist of metasiltstone, metagreywacke, conglomerate, chert, metavolcanics, and marble. These rocks belong to textural zones 1 & 2A and the prehnite-pumpellyite metamorphic facies. Laminated, often graded, bedding occurs, but the rocks are generally devoid of sedimentary structures. Conglomerate is uncommon and was found at only three localities. Thirteen occurrences of chert up to 160 m thick are recorded, and radiolaria are provisionally identified in some chert thin sections. Two adjacent lithologies of intercalated metavolcanics and marble outcrop in the lower Kakahu gorge. The westernmost lithology is a 140–m–thick sequence of sixteen bedded units of metatuff, grey marble, and metasiltstone. The second lithology which lies directly to the east of the former is 90 m of intercalated poorly schistose hematitic metavolcanics and white marble. The Kakahu marble is a 30–m–thick grey marble which has yielded a fauna of upper Carboniferous conodonts. Conodonts of similar age have also been obtained from the grey marble which is interbedded with metatuff and metasiltstone in the lower Kakahu gorge. Three phases of folding are recognised. Tight mesoscopic F1 folds are preserved only in the bedded cherts and interbedded metavolcanic and marble rocks. Macrosconic F2 folding was accompanied by the formation of the regional schistosity (S2). S2 was macroscopically folded during F3 deformation. Resistant marker lithologies are traceable along strike for up to 500 m, their abrupt terminations appear to have been produced by tectonic shearing. There is abundant evidence of transposition and shearing in the metasiltstone and metagreywackes, and the whole comprises a tectonic mélange.