Basement structure of the Wanganui Basin, onshore, interpreted from gravity data

Abstract

Abstract The Wanganui Basin, western North Island, New Zealand, contains a thick (up to 5 km) sequence of Cenozoic sediments unconformably overlying Mesozoic and Paleozoic greywacke basement rocks. Gravity anomalies suggest that along the western edge of the basin, north of Moeroa, a trough in the basement extends northwards as far as Waitaanga where it splits into two branches; one continuing NNE to Aria, the other NE to Waimiha. Between the Te Ahi‐Ohura Fault and the Nukumaru‐Hauhungaroa Fault, the basement forms a broad, gently sloping shelf. On the eastern side of the basin, a smaller trough extends NE from Taihape to Erewhon. Known basement uplifts at Mt Stewart, Marton, and Santoft do not have any significant gravity expression. The anomalies do not support the idea that the basin contains two sub‐basins separated by a basement high. Magnetic measurements indicate that no large amounts of strongly magnetised volcanic rock are likely within the Cenozoic sediments.