Structural evolution of the active Waimea-Flaxmore Fault System in the Nelson-Richmond urban area, South Island, New Zealand

Abstract

ABSTRACTThe Waimea-Flaxmore Fault System (W-FFS) comprises NE-striking, SE-dipping reverse faults superposing Eastern Province terranes on Cenozoic sedimentary units of the Moutere Depression. We present a revised geological map and cross sections of the W-FFS in the Nelson-Richmond urban area, aimed at reconstructing the structural evolution during multiple phases of reactivation. Our data and structural interpretations depict the inversion of the W-FFS from an inherited system of Late Cretaceous-Eocene normal faults to multiple reverse fault splays that propagated through the cover sequence over the last 10 Ma. Fault tip propagation with folding of the cover sequence persisted during the Quaternary, with breaching of the Waimea and Flaxmore faults to the surface and propagation of a splay thrust (Tahunanui Fault) still concealed beneath Quaternary deposits. Ongoing crustal shortening associated with the Pacific-Australian plate boundary in the northern South Island creates favourable conditions for reactivation of the long-lived W-FFS in the contemporary stress field.