Early Miocene thin‐skinned tectonics and wrench faulting in the Pongaroa district, Hikurangi margin, North Island, New Zealand

Abstract

The Pongaroa‐Akitio area, Northern Wairarapa, North Island, New Zealand, is part of the exposed East Coast Deformed Belt at the obliquely convergent plate boundary of the Hikurangi margin. The sedimentary succession includes an allochthonous unit of Early Cretaceous greywacke basement resting on latest Cretaceous rocks. Since the unit's basal contact is subparallel to the bedding of the strata it overlies, the allochthon is inferred to be an unrooted gliding nappe similar to allochthonous outliers described in Northland and the Raukumara Peninsula. The southward emplacement of this “Greywacke Nappe” is supported by structural markers in the body of the nappe and is well dated as earliest Miocene by the youngest rocks involved, which are earliest Miocene (Waitakian; c. Aquitanian), and because Otaian‐Altonian (c. Burdigalian) faults postdate nappe emplacement. This thin‐skinned tectonic phase immediately preceded inception of dextral strike‐slip faulting along northeast‐trending Otaian‐Altonian (Burdigalian) faults. The present 300 km offset of similar allochthonous outliers on both sides of the faults of the western coastal ranges results from cumulative dextral strike‐slip movement on these faults through the Miocene.

Keywords:

• New Zealand
• Hikurangi margin
• coastal ranges
• Wairarapa
• tectonics
• faults
• allochthon
• nappes
• olistostrome
• strike‐slip movement
• basement
• Cretaceous
• Whangai Formation
• Miocene
• Akitio Fault Zone
• Adams‐Tinui Fault
• Mara melange
• melange