Structural Inheritance and Fault Reactivation in the Nelson Thrust Belt (South Island, New Zealand)

The Nelson Thrust Belt (NTB) is a contractional structure within the Australian crust, northwest of the Pacific-Australian plate boundary in the northern South Island of New Zealand. Its structure and evolution record the influence of faults inherited from Paleozoic–Early Mesozoic terrane assembly and Late Cretaceous to Eocene rifting. We integrate revised regional mapping, LiDAR imagery, trench and borehole observations, and reinterpreted vintage seismic reflection lines to reconstruct how inherited fabric controlled fault localization and reactivation. The NTB comprises three principal fault groups, F1–F3, in decreasing order of structural elevation, and a local frontal splay, F4. Geometry, reverse ​reactivation, and association with syn- to late-rift deposits indicate that F2 and F3 are inverted normal faults. Fault inversion began in the Late Miocene and continued through the Pliocene–Pleistocene, but activity on F3 ceased earlier than on F2. F1 is a low- to moderate-angle thrust fault that truncates the underlying structures out of sequence. Together, these relationships suggest a long-term break-back transfer of deformation, while Late Pleistocene–Holocene seismic rupture of the major faults indicates that multiple structures were reactivated within overlapping earthquake cycles. The NTB provides a test case for recognizing how inherited crustal heterogeneity controlled long-term fault evolution and distributed active deformation in a contractional belt where modern subsurface imaging is limited.