Waiareka-Deborah volcanic field

Waiareka-Deborah volcanic field
Stratigraphic range: Oligocene (39.5–27.6 Ma)[1] PreꞒ Ꞓ O S D C P T J K Pg N
Type	Igneous
Overlies	Rakaia Terrane
Area	890 square kilometres (340 sq mi)[1]
Lithology
Primary	Sub-alkaline basalt and basaltic andesite
Location
Coordinates	45°00′S 170°18′E / 45.0°S 170.3°E / -45.0; 170.3
Region	Otago
Country	New Zealand
Type section
Named for	Waiareka Valley, inland from Oamaru
Map of surface volcanic features of the South Island centred near Oamaru. The basalts of the Waiareka-Deborah volcanic field are more red tinted than those of the Dunedin volcanic group. Clicking on the map enlarges it, and enables panning and mouseover of volcano name/wikilink and ages before present. Key for the volcanics that are shown with panning is:   basalt (shades of brown/orange),   monogenetic basalts,   undifferentiated basalts,   arc basalts,   arc ring basalts,   olivine (basalts shades of olive),   phonolite (pale salmon),   dacite,   andesite (shades of red),   basaltic andesite,   rhyolite, (ignimbrite is lighter shades of violet), and   plutonic or intusive (gray) - so dolerite/diabase/microgabbro will have shadings towards gray compared to erupted basalt.

The Waiareka-Deborah volcanic field is a group of sub-alkaline basalt to basaltic andesite composition volcanics, most of which erupted about 34 million years ago. There is a range of determined ages by various methods and sites although most have very similar timings. At Bridge Point one deposit has an age of 39.5 ± 1.8 and another 34.3 ± 0.5 million years ago.^[1] They are found near Oamaru, South Island New Zealand,^[1] and are small Surtseyan volcanoes that erupted originally on a submerged continental shelf.^[2][3]

The former term, the Waiareka-Deborah volcanic group should not be used as any alkali basalt volcanoes in this group and all of those in the former Waiareka volcanic field are now assigned to the Dunedin volcanic group and its monogenetic volcanic field.^[4]