Wakamarina Quartzite and associated mafic rocks of Pelorus Group, Marlborough: Geochemistry and origins

Abstract

Wakamarina Quartzite is a formation of the late Paleozoic to early Mesozoic Pelorus Group within the Jurassic metamorphosed Marlborough Schist of South Island, New Zealand. Pelorus Group is geochemically analogous to the type Caples Terrane of Otago, with a predominantly oceanic evolved arc‐derived detrital geochemistry and a possible component derived from a continental margin arc. Wakamarina Quartzite is interlayered with metabasites and has a detrital input similar to the enclosing Pelorus Group semischists.

Previously described as a “meta‐chert”, Wakamarina Quartzite has an oxygen isotope range and trace, major and light REE element ratios that indicate that it is more likely to have been a continental margin, clastic quartzose sediment, and that it had no detrital input from the associated metabasites. These have predominantly N‐MORB geo‐chemical abundances with a suggestion of an arc influence. Although the geochemistry of Wakamarina Quartzite indicates a predominantly terrigenous, mixed basalt‐andesite and more evolved calc‐alkaline arc source for the detrital input, some components may have been derived from spreading ridge hydrothermal activity and from direct hydrogenous precipitation. Some enhanced metallic elements (Ni, Cu, Zn) appear related to the scavenging influence of hydrothermal Fe, whereas Mn and Ba are predominantly of hydrogenous/authigenic origin.

Keywords:

• Pelorus Group
• Caples Terrane
• Marlborough Schist
• Wakamarina Quartzite
• metabasite
• metabasalt
• metagabbro
• geochemistry
• tectonic setting
• sediment sources