Reconstructing a dismembered Neogene basin along the active Hikurangi subduction margin, New Zealand

Abstract

Abstract The East Coast Basin (ECB), New Zealand, preserves the most complete onshore stratigraphic record of the Cretaceous–Neogene development of Zealandia from Gondwana breakup, through rift-drift, to evolution of the modern Hikurangi subduction margin and Pacific-Australia plate boundary. As such, it provides important constraints for southwest Pacific plate tectonic reconstructions. The basin is, however, deformed and variably dismembered, and in previous tectonic models it has been treated as a zone of poorly constrained deformation. Here, multiple geological and geophysical data sets are integrated with a tectonic reconstruction to provide a synthesis of regional and intrabasin-scale structural evolution of the ECB during the Neogene, producing a new geologically constrained approach toward qualitative and quantitative assessment of deformation across the New Zealand plate boundary zone. We produce the first palinspastic reconstructions for the entire basin during key times in plate boundary development, within a well-constrained plate-tectonic framework, supported by independent deformation estimates. These reconstructions account for contraction, strike-slip, and vertical-axis rotation of crustal blocks. In the context of the reconstruction model, the ECB has dominantly experienced upper-plate shortening and vertical-axis rotations; strike-slip processes are considered comparatively minor. Comparison of the reconstruction model with independent data highlight several pronounced deformation intervals (26–23 Ma, 20–15 Ma, 11 Ma, and 7–4 Ma) in the structural and sedimentary evolution of the ECB, Hikurangi subduction margin, and New Zealand plate boundary zone, demonstrating that it is possible to integrate a wide range of geological data sets to develop meaningful reconstructions in highly tectonised regions.