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How it began
New Zealand oldest rocks are over 500 million years old, and were once part of Gondwanaland. This massive super-continent started to split up about 160 million years ago, and New Zealand separated from it about 85 million years ago.
New Zealand sits on two tectonic plates - the Pacific and the Australian. Fifteen of these gigantic moving chunks of crust make up the Earth& surface. The North Island and some parts of the South Island sit on the Australian Plate, while the rest of the South Island sits on the Pacific. Because these plates are constantly shifting and grinding into each other, New Zealand gets a lot of geological action.
Lying in the south-west Pacific, New Zealand consists of two main islands - the North Island and the South Island. Stewart Island and many smaller islands lie offshore.
The North Island of New Zealand has a spine of mountain ranges running through the middle, with gentle rolling farmland on both sides. The central North Island is dominated by the Volcanic Plateau, an active volcanic and thermal area. The massive Southern Alps form the backbone of the South Island. To the east of the Southern Alps is the rolling farmland of Otago and Southland, and the vast, flat Canterbury Plains.
Rock Types
The three major rock classes are based on how they were formed.
Sedimentary rocks
Igneous rocks
Metamorphic rocks
Sedimentary rocks
Sedimentary rocks form from deposition and joining together of particles, mostly eroded from the surrounding area. Most of New Zealand’s sedimentary rocks are mudstone and sandstone that were deposited beneath the sea. A sedimentary rock made from ejected volcanic fragments (e.g. ash) is called tuff. Some sedimentary rocks, such as chert and certain limestones, are formed from chemical precipitation – the formation of a solid from a solution. Sedimentary rocks are the best places to find fossils.
Igneous rocks
Igneous rocks form when molten rock (magma) from deep within the Earths crust moves towards or onto the surface and cools.
Plutonic igneous rocks are formed at depth. Because they don't get erupted onto the surface they cool slowly, and are coarse grained (i.e. they are made of of relatively large crystals) New Zealand examples include the granites of Fiordland, Stewart Island and the Abel Tasman National Park.
Volcanic igneous rocks are thrown out onto the land surface or beneath the sea, and cool quickly to form fine grained and sometimes glassy rocks e.g. rhyolite, ignimbrite, pumice, andesite and basalt. Active volcanism is occurring in the North Island, but New Zealand also has ancient volcanic rocks such as Banks Peninsula and around Dunedin.
Igneous rocks are also classified as acid, intermediate, or basic, according to the amount of silica they contain. Acid (silica-rich) igneous rocks are usually light in colour, whereas the basic (silica-poor) igneous rocks are darker. Silica rich magmas (e.g. rhyolitic magma) crystallise at higher temperatures, making stickier lavas and more explosive eruptions, whereas silica poor magmas (e.g. basaltic magma) crystallise at lower temperatures. They are therefore more fluid at a given temperature, and typically erupting with less violence.
Metamorphic rocks
Metamorphic rocks are rocks that began as sedimentary or igneous rocks (or even previously metamorphosed rocks), and that have subsequently been recrystallised under conditions of high temperature and/or pressure.
Characteristic minerals form under certain conditions of temperature and pressure. For example, chlorite tends to crystallise in rocks metamorphosed at low to moderate temperatures and pressures, and biotite and garnet form at higher temperatures and pressures. Many of the rocks found in New Zealand have been metamorphosed by being buried deep in the crust, and then uplifted to the surface as the overlying rock has been eroded away. Examples are the schists that outcrop over much of the South Island.
The rock cycle involves particles being continually eroded, transported, deposited, and cemented to form new rock that may later be uplifted. Then erosion starts the cycle again.
Compressional and tensional forces (squeezing and stretching) cause the earth’s crust to buckle and crack.
When compression forces the crust upward, mountain chains are formed often accompanied by severe folding, fracturing of the rocks and the intrusion of magma. The effect of mountain building (orogeny) varies from place to place, and locally the rocks may be only gently tilted.
Long-continued downward movement (downwarping) may occur to form extensive troughs or basins in which many thousands of metres of sediments can accumulate. The high temperature and pressure deep within the sedimentary pile can cause metamorphism. In contrast, slight downwarping allows the sea to extend over the land, producing shallow shelves close to the land and deeper basins further offshore.
Uplift and erosional episodes make it impossible for any one area to have a rock sequence representing the whole of geological time. Only when an area is submerged beneath the sea can there be continuous sedimentation for a prolonged time period, and even then there may be gaps (unconformities) from the removal of sediments by strong bottom currents or periods of non-deposition. When an area is above sea level, sporadic terrestrial deposits, such as river (fluvial) sediments, coal measures (swamps), and igneous rocks may be the only representatives of that geological time.
The co ords to this cache bring you to a rocky cliff face at the end of Taipa beach .
There is plenty of parking close by but you may need to check tide times before attempting cache .
Take the time to observe the area and then forward answers to questions listed below
There is no need to await my reply to log I will notify you if need be
Q1
At the base of the rocky cliff face is a flat platform ,Is this platform made up of small rocks bonded together or larger boulder type rocks .
Q2
Is there any erosion occurring on the platforms rocks surface or sides ,and if so explain your reason .
Q3
Is this rock from your observations
Sedimentary rocks
Igneous rocks
Metamorphic rocks
Information gathered for this earthcache was obtained from the internet ,NEW ZEALAND GEOGRAPHY &GEOLOGY
We hope you enjoy this simple earthcache
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