Peperite
Encyclopedia
A Peperite is a sedimentary rock
that contains fragments of igneous material and is formed when magma
comes into contact with wet sediments. The term was originally used to describe rocks from the Limagne
region of France
, from the similarity in appearance of the granules of dark basalt in the light-coloured limestone
to black pepper
. Typically the igneous fragments are glassy and show chilled-margins to the sedimentary matrix, distinguishing them from clasts with a sedimentary origin.
. In the most recent edition of 'Igneous rocks' by Le Maître et al. the definition is given as "A local term for a tuff or breccia, formed by the intrusion of magma into wet sediments. Usually consists of glassy fragments of igneous rock and some sedimentary rock", while White (2000) defines peperite as "a genetic term applied to a rock formed essentially in situ by disintegration of magma intruding and mingling with unconsolidated or poorly consolidated, typically wet sediments. The term also refers to similar mixtures generated by the same processes operating at the contacts of lavas and other hot volcaniclastic deposits with such sediments".
to rhyolite
.
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
that contains fragments of igneous material and is formed when magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
comes into contact with wet sediments. The term was originally used to describe rocks from the Limagne
Limagne
The Limagne is large plain in the Auvergne region of France in the valley of the Allier river, on the edge of the Massif Central. It lies entirely within the département of Puy de Dôme...
region of France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, from the similarity in appearance of the granules of dark basalt in the light-coloured limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
to black pepper
Black pepper
Black pepper is a flowering vine in the family Piperaceae, cultivated for its fruit, which is usually dried and used as a spice and seasoning. The fruit, known as a peppercorn when dried, is approximately in diameter, dark red when fully mature, and, like all drupes, contains a single seed...
. Typically the igneous fragments are glassy and show chilled-margins to the sedimentary matrix, distinguishing them from clasts with a sedimentary origin.
Terminology
The term has been used to describe a wide variety of rocks that are interpreted to have formed by the interaction between magma and sediments. This usage has led to overlap with other terms such as hyaloclastiteHyaloclastite
Hyaloclastite is a hydrated tuff-like breccia rich in black volcanic glass, formed during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It has the appearance of angular flat fragments sized between a millimeter to few centimeters...
. In the most recent edition of 'Igneous rocks' by Le Maître et al. the definition is given as "A local term for a tuff or breccia, formed by the intrusion of magma into wet sediments. Usually consists of glassy fragments of igneous rock and some sedimentary rock", while White (2000) defines peperite as "a genetic term applied to a rock formed essentially in situ by disintegration of magma intruding and mingling with unconsolidated or poorly consolidated, typically wet sediments. The term also refers to similar mixtures generated by the same processes operating at the contacts of lavas and other hot volcaniclastic deposits with such sediments".
Formation
When magma comes into contact with wet sediment several processes combine to produce the mixture of sedimentary and igneous clasts which is characteristic of a peperite. These processes are required to produce both the disintegration or fragmentation of magma to form juvenile clasts and the mingling of these clasts within the sediment. Mechanisms proposed for the fragmentation of the magma include; fracturing due to the stresses associated with quenching, autobrecciation due to continuing flow in the cooling magma, pore-water steam explosions and magma-sediment density contrasts. The main mechanism suggested for mingling of the igneous clasts with the sediment is fluidisation, in the sense of particle support and transport by a fluid.Occurrence
Peperites are found world-wide in sediments with a significant water content at the time of formation associated with igneous rocks covering the compositional range from basaltBasalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
to rhyolite
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
.