DEFINITION OF KIMBERLITE

Large volcanic pipes that come from deep in the

Earth and explode their way to the surface with such force

that they may blow holes through the stratosphere. Some kimberlite

pipes carry diamonds from hundreds of kilometers in

the Earth and seem to form in places that were abnormally

rich in fluids. Kimberlites and related diatremes represent rare

types of continental volcanic rock types, produced by generally

explosive volcanism with an origin deep within the mantle.

They form pipe-like bodies extending vertically downward

and are the source of many of the world’s diamonds. Kimberlites

were first discovered in South Africa during diamond

exploration and mining in 1869, when the source of many

alluvial diamonds on the Vaal, Orange, and Riet Rivers was

found to be circular mud “pans,” later appreciated to be kimberlite

pipes. In 1871 two very diamond-rich kimberlite pipes

were discovered on the Vooruitzigt Farm, owned by Nicolas

de Beer. These discoveries led to the establishment of several

large mines and one of the most influential mining companies

in history.

Kimberlites are very complicated volcanic rocks, with

mixtures of material derived from the upper mantle and complex

water-rich magma of several different varieties. A range

of volcanic intrusive styles, including some extremely explosive

events, characterizes kimberlites. True volcanic lavas are

only rarely associated with kimberlites, so volcanic styles of

typical volcanoes are not typical of kimberlites. Most nearsurface

kimberlite rocks are pyroclastic deposits formed by

explosive volcanism filling vertical pipes, and surrounded by

rings of volcanic tuff and related features. The pipes are typically

a couple of hundred yards wide, with the tuff ring

extending another hundred yards or so beyond the pipes. The

top part of many kimberlite pipes includes reworked pyroclastic

rocks, deposited in lakes that filled the kimberlite pipes

after the explosive volcanism blasted much of the kimberlite

material out of the hole. Geologic studies of kimberlites reveal

that they intrude the crust suddenly and behave differently

from typical volcanoes. Kimberlites intrude violently and

catastrophically, with the initial formation of a pipe filled with

brecciated material from the mantle, reflecting the sudden and

explosive character of the eruption. As the eruption wanes, a

series of tuffs falls out of the eruption column and deposits

the tuff ring around the pipes. Unlike most volcanoes, kimberlite

eruptions are not followed by the intrusion of magma into

the pipe. The pipes simply get eroded by near-surface processes,

lakes form in the pipes, and nature tries to hide the very

occurrence of the explosive event.

Below these upward-expanding craters are deep vertical

pipes known as diatremes that extend down into the mantle

source region of the kimberlites. Many diatremes have features

that suggest the brecciated mantle and crustal rocks

were emplaced at low temperature, nonviolently, presenting a

great puzzle to geologists. How can a deep source of broken

mantle rocks passively move up a vertical pipe to the surface,

suddenly explode violently, and then disappear beneath a

newly formed lake?

Early ideas for the intrusion and surface explosion of

kimberlites suggested that they rose explosively and catastrophically

from their origin in the mantle. Subsequent studies

revealed that the early deep parts of their ascent did not seem

to be explosive. It is likely that kimberlite magma rises from

deep in the upper mantle along a series of cracks and fissures

until it gets to shallow levels where it mixes with water and

becomes extremely explosive. Other diatremes may be more

explosive from greater depths and may move as gas-filled

bodies rising from the upper mantle. As the gases move into

lower pressure areas they would expand, resulting in the kimberlite

moving faster until it explodes at the surface. Still other

ideas for the emplacement of kimberlites and diatremes

invoke hydrovolcanism, or the interaction of the deep magma

with near-surface water. Magma may rise slowly from depth

until it encounters groundwater in fractures or other voids

then explodes when the water mixes with the magma. The

resulting explosion could produce the volcanic features and

upward-expanding pipe found in many kimberlites.

It is likely that some or all of these processes play a role

in the intrusion of kimberlites and diatremes, the important

consequence being a sudden, explosive volcanic eruption at

the surface, far from typical locations of volcanism, and the

relatively rapid removal of signs of this volcanism. The initial

explosions are likely to be so explosive that they may blast

material to the stratosphere, though other kimberlite eruptions

may only form small eruptions and ash clouds.

Title Post:
Rating: 100% based on 99998 ratings. 99 user reviews.
Author:

Terimakasih sudah berkunjung di blog SELAPUTS, Jika ada kritik dan saran silahkan tinggalkan komentar