Geology of the Parnassus area

Warren, G. 1995 Geology of the Parnassus area. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences geological map 18 36 p.

Abstract: The oldest rocks in the Parnassus map area are grey indurated sandstones and mudstones of the early Cretaceous Pahau terrane of the Torlesse Supergroup, now altered to zeolite facies, or locally to prehnite-pumpellyite facies, and highly deformed. Unconformably overlying the Torlesse basement is a relatively thin Late Cretaceous to mid Tertiary succession. The Parnassus area includes Haumuri Bluff, where spectacular outcrops contain the type sections for two of the New Zealand standard Late Cretaceous time-stratigraphic units and for the Amuri Limestone. Motunau Group sediments overlie the Amuri Limestone; they include both terrestrial and marine Miocene to early Pleistocene sediments, some of them deposited in a canyon system similar to that still present close offshore in the Kaikoura Canyon. Some of these sediments have been uplifted during the Pleistocene from bathyal depths. Several different rhyolitic tuffs of North Island origin have been found within the Miocene and younger marine sediments, including a tephra just above the youngest (Castlecliffian) marine beds that is confidently correlated with the Potaka Tephra (1.0 Ma). Coastal marine platforms cut during episodes of relative sea-level stability in the Late Quaternary have been uplifted by up to 300 m, and remnants of the benches and their thin cover of marine and terrestrial sediments (Medina Group) are preserved along the coastal strip south of Haumuri Bluff. Late Quaternary fluvial terraces are common in the middle to upper reaches of the major rivers. The Parnassus area is part of the active convergent plate margin at the onshore extension of the Hikurangi trench. Pliocene and later movement on the subparallel Hundalee and Kaiwara Faults has resulted in the development of a small but well-delineated transform basin where displacement has been transferred between these faults; both faults remain active. Lying immediately southeast of the Hope Fault, a major transcurrent fault, the region has experienced three major earthquakes of intensity MM VI or greater in this century, and is frequently subject to small earthquakes. The principal mineral resources of the Parnassus area are limestone and aggregate. (auth)