Parapara Group: Permian‐Triassic rocks in the Western Province, New Zealand

Abstract

The Parapara Group of northwest Nelson is a faulted sequence of folded and metamorphosed Permian‐Triassic sedimentary rocks. Stratigraphically, from bottom to top, the sequence consists of: massive black Draco Slate (new term), at least 200 m thick; Flowers Formation, which consists of the Pupu Conglomerate Member (20 m thick), Cross Member (new term; 35 m thick), Tarn Sandstone Member (new term; 35 m thick), and Pariwhakaoho Slate Member (30 m thick); and Walker Formation (>200 m thick). Fossils in the Cross Member indicate a Middle Permian (Ufimian‐Kazanian) age and have long been recognised as having affinities with similar faunas in Tasmania and eastern Australia. Dropstones within the Draco Slate and Flowers Formation indicate glacial influence. The geochemical composition of sandstones suggests a dominant continental arc source for the Parapara Group sediments. Thin (<5 m) porphyry sills (mainly trachyandesite) of the Parapara Peak Intrusives (new term) intrude the Draco Slate and Flowers Formation and are correlated with the Separation Point Suite. The whole sequence has been deformed by Mesozoic regional recumbent folding (D1) with development of a penetrative axial planar cleavage (S1) at low grade greenschist facies (M1) metamorphic conditions. The intrusion of sills during the Early Cretaceous is concomitant with a more regional upper greenschist to amphibolite facies prograde metamorphism with M2 porphyroblasts of garnet, biotite, chloritoid, chlorite, ± green hornblende, ± epidote and ilmenite overgrowing the S1 foliation. Post‐M2 deformation (D2) produced kilometre‐scale synclinal folds. The M2 minerals were deformed within the fold axial planar crenulation cleavage (S2) developed best in the nose of D2 folds. The grade of metamorphism increases progressively down‐section (i.e., eastwards), from high‐grade greenschist facies (Walker Formation) to amphibolite facies (Draco Slate).