Detrital zircon age constraints on depositional history and provenance of the Murihiku Supergroup, Murihiku Terrane, North Island, New Zealand

Abstract

In the Murihiku Terrane of New Zealand, U-Pb detrital zircon ages in Murihiku Supergroup sandstones of Late Triassic, Jurassic and possibly earliest Cretaceous age have a marked youngest age component that is close to, and sometimes coincident with, established biostratigraphic ages, thus reflecting contemporary volcanism. However, youngest Huriwai Group samples yield 137–142 Ma zircon age components (earliest Early Cretaceous) in conflict with palynofloras that suggest only a latest Jurassic age. This is resolved if the age of the Jurassic/Cretaceous boundary is lowered to ca. 140 Ma. Older, reworked zircons are mainly Early Jurassic, Late Triassic and Late Permian reflecting an enduring exhumed magmatic arc source nearby. This might be in the adjacent Median Batholith but as a Murihiku sediment source its Jurassic, Triassic and Permian elements are not well-matched in terms of extent, age and bulk compositions. A connection between the Murihiku (proximal forearc) and Waipapa Composite (distal accretionary wedge) terranes is probable, with a common magmatic arc, speculatively situated in the New England Orogen, eastern Australia.