How old is miocene basalt

On the east coast of the North Island, Miocene rocks include massive blue-grey sandstone and mudstone sometimes known as papa , mudstone with minor sandstone and conglomerate, and alternating sequences of sandstone and mudstone. In Northland and at East Cape, mixtures of Cretaceous to Miocene sedimentary and igneous rocks were emplaced in the Early Miocene, by sliding over the underlying sedimentary rocks.

These are referred to as the Northland and East Coast allochthons, and they consist of sheets of rock separated by faults and transported by tectonic processes some distance from their original sites of deposition. Miocene deposits in southern Wairarapa and northeastern South Island are characterised by large amounts of marine conglomerate, particularly in the Wairau and Awatere valleys. Calcareous mudstone and sandstone are more common nearer the coast.

In inland Canterbury non-marine deposits of sandstone, conglomerate, and mudstone are typical of the Late Miocene whereas marine mudstone and coarse sandstone are representative of earlier Miocene times, as well as being more common nearer the coast and further south into north Otago.

A phosphatic sandstone is the only marine sediment south of Dunedin, with all other Miocene deposits in the southeast being non-marine, including coal measures and oil shale. Marine deposition, however, continued in the Waiau River area of Southland, with a sequence of mudstone, limestone, micaceous sandstone, and coarse sandstone. The northwest of the South Island from Greymouth through to Nelson is an area of extensive Miocene deposition which is characterised by great thicknesses of brown or blue-grey mudstone and sandstone, locally in alternating sequences.

The youngest Miocene rocks here are non-marine conglomerate, sand, and coal measures. Further south near Jackson Bay, a small area of limestone, conglomerate, and alternating sandstone and mudstone is of Miocene age. Volcanic activity levels were high in the Miocene. Andesite, basalt, and dacite with volcanic breccia in Northland are but remnants of huge volcanoes that existed off the present west coast. The Waitakere Ranges, west of Auckland and the hills near Tokatoka, further north, are composed of andesite, volcanic breccia, and volcanic sediments, while basalt is present near Waipoua.

Andesite, dacite, and rhyolite around Whangarei probably represent separate volcanic outlets. In the Coromandel area andesite and volcanic breccia are the most common Miocene rocks, although there are some areas of basaltic andesite as well as areas of rhyolite and dacite.

Many of the offshore islands of Coromandel and Northland are of Miocene volcanic origin. Minor plutonic intrusions were associated with the volcanic activity, including the granite and diorite of Doubtless Bay, and diorite south of Cape Colville and that making up Cuvier Island.

In the South Island, Miocene volcanoes erupted mainly basaltic lavas to build the Otago and Banks peninsulas. The two harbours of Banks Peninsula are both breached volcanic craters. The Otago Peninsula is made up of basalt with a high alkali content, and the harbour here is the result of later downwarping. Miocene basalt and tuff also occur in inland Otago and mid Canterbury. Paleogeographic conditions At the end of the Oligocene the New Zealand area was almost entirely under water. At the beginning of the Miocene, a new round of tectonic activity and mountain building started.

This had the effect of uplifting the central part of the South Island, so that coastal areas were still experiencing marine conditions while the environment inland became progressively non-marine.

The vast quantities of conglomerate in the Marlborough area result from rapidly rising and eroding ground. The tectonic movements, however, were not simply uplift; there were varying degrees of uplift, down warping, and buckling caused by the tectonic stresses. Volume 94, Number 2. Previous Article Next Article. Article Navigation. Research Article February 01, Google Scholar. GSA Bulletin 94 2 : — Article history first online:.

Abstract A dominantly basaltic late Miocene and early Pliocene about 5 to 10 m. This content is PDF only. Please click on the PDF icon to access. First Page Preview. Close Modal. Had there been more or less continuous volcanic activity in Iceland from Miocene times down to the present, we might well be surprised that the later volcanic masses are not much more considerable than they are.

Either they have not been so, or the denuding agents have far surpassed them in energy. You can also search for this author in PubMed Google Scholar. Reprints and Permissions. The Age of the Igneous Rocks of Iceland. Nature 24, — Download citation. Issue Date : 27 October Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative.