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What is a Lopolith?

A lopolith is a huge igneous intrusion that is saucer-shaped with depressed central regions that lie parallel to the strata of intruded country rock. Lopoliths are usually the concordant emplacements having an intruded stratum with a dike or funnel-shaped feeder bodies beneath the body.


Lopoliths are comparatively small plutons which customarily develop an upper surface that is concave downward. This dangling shape may be a cause of volume reduction when magmas crystallize. The weight of the blanketing strata would cause disintegration into the volume previously acquired by more voluminous liquid magma.


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Intrusive Igneous Rocks

Erosion of volcanoes will instantly reveal shallow intrusive bodies such as volcanic necks and diatremes. A volcanic neck is said to be the “throat” of a volcano and contains a pipelike conduit immersed with hypabyssal rocks. Devil’s Tower in Wyoming and Ship Rock in New Mexico are remnants of volcanic necks that were revealed after the surrounding sedimentary rocks get weathered away. Many craterlike depressions can be filled with angular pieces/particles of country rock and juvenile pyroclastic remainder.

Upon erosion, such a depression reveals a vertical funnel-shaped pipe that depicts a volcanic neck having an exception of the brecciated filling. These pipes are known as the dubbed diatremes.


Pluton

Pluton is a body of intrusive igneous rock the size.  They include laccoliths, batholiths, dikes, sills, and other kinds of intrusions. Most plutons are thought to be a consequence of igneous activity which involves magma.


Formation of Lopolith

Lopolith, lenticular in shape, is igneous intrusion with a depressed central region. This mass of igneous rock developed as an attribute to magma do not find its way to the surface but spread laterally into a lenticular body forcing overlying strata to bulge upwards. They are usually lenticular in shape. They are made up of dense, mafic magma that allows depression by the overlying strata on cooling. 

Bushveld Lopolith

Bushveld complex of South Africa is the world's largest and most important repository of Platinum Group Metals.


Bushveld Igneous Rock Geographics

It extends laterally over 65,000 square kilometres and is up to eight kilometres thick more than 2 billion years ago.


Formation of Bushveld Lopolith Complex

The bushveld complex was formed by volcanic eruptions that repeatedly injected molten basaltic rock known as magma or lava into some volcanic chamber inside the Earth the cooling and solidification of the molten magma resulted in the formation of igneous rock because the molten rock was beneath the surface of the Earth it cooled much more slowly than usual by slow cooling different minerals crystallized at different temperatures and accumulated as layers from the base upwards with time the weight of the cooled magma and the forces of the Earth cause the layers to Sag down in the middle giving them the shape of a pile of very thin sources time and weather combined eroding the landscape moulding the surface of the Earth the central part of the sorcerer was buried under younger rocks by the edges cropped out as two semicircular arcs of rocks.


Fun Facts

  • Lopoliths formed by the same process as laccoliths, but they are made of dense, mafic magma which enables depression by the overlying strata on cooling.

  • Many lopoliths consist of layered gabbroic rocks.

  • Some lopoliths are quite huge, having thicknesses of many kilometres.

  • The Bushveld lopolith in southern Africa is some hundred kilometres across and has the richest platinum deposits known.

FAQs (Frequently Asked Questions)

1. How is Bushveld Lopolith Formed?

Answer: The formation mechanisms of the chromitite seams Bushveld Igneous Complex are extremely controversial: various mechanisms have been proposed. Below are some of the non-exhaustive lists of chromitite formations processed in the Bushveld.

  • Rise in overall pressure of the system, alpha-silica and oxygen fugacity.

  • Alterations in chemical and physical properties owing to magma becoming concentrated in chromite. When this takes place, the liquidus gets liberated from any other phases. Thus, chromite is the only mineral to crystallize in the melt, therefore, gathering in monomineralic layers on the floor of the magma chamber.

  • Mixing of resident magma and granitic melts extracted from fusible country rocks

  • Mixing of ultramafic magma of overlaid intrusions, having a magma parental to anorthosites

  • An increase in oxygen fugacity of the magma within the chamber most likely through the dispersion of gas pressure, loss of gasses by diffusion or differential diffusion of hydrogen.

2. What are Diatremes in Lopolith?

Answer: Many diatremes occur by an explosion resulting from a quick expansion of gas—carbon dioxide and water vapour. These gases are dispersed as an outcome of the rising magma due to the decrease in pressure as it nears the surface. Some diatremes consist of kimberlite, a peridotite that has a hydrous mineral known as phlogopite. Kimberlite may also contain diamonds.

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