Kinetic energy metamorphosis (KEM) is a recently discovered

tribological Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. Tribology is highly interdisciplinary, drawing on many academic field ...

process of gradual crystal re-orientation and

foliation In mathematics ( differential geometry), a foliation is an equivalence relation on an ''n''-manifold, the equivalence classes being connected, injectively immersed submanifolds, all of the same dimension ''p'', modeled on the decomposition ...

of component minerals in certain rocks. It is caused by very high, localized application of

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its a ...

. The required energy may be provided by prolonged battery of fluvially propelled

bed load The term bed load or bedload describes particles in a flowing fluid (usually water) that are transported along the stream bed. Bed load is complementary to suspended load and wash load. Bed load moves by rolling, sliding, and/or saltating (ho ...

of cobbles, by glacial abrasion, tectonic deformation, and even by human action. It can result in the formation of laminae on specific metamorphic rocks that, while being chemically similar to the

protolith A protolith () is the original, unmetamorphosed rock from which a given metamorphic rock is formed. For example, the protolith of a slate is a shale or mudstone. Metamorphic rocks can be derived from any other kind of non-metamorphic rock and t ...

, differ significantly in appearance and in their resistance to weathering or deformation. These

tectonite Tectonites are metamorphic or tectonically deformed rocks whose fabric reflects the history of their deformation, or rocks with fabric that clearly displays coordinated geometric features that indicate continuous solid (ductile) flow during f ...

layers are of whitish color and tend to survive granular or mass exfoliation much longer than the surrounding protolith.

KEM in cupules

The products of KEM were first identified in 2015 in cupules, a form of rock art consisting of spherical cap or dome-shaped depressions created by percussion with hammer-stones. KEM laminae, caused by solid state re-metamorphosis of

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, cau ...

, have been observed in cupules on three rock types: # On

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

at Indragarh Hill, Bhanpura, India; Nchwaneng, Korannaberg site complex, South Africa; and Inca Huasi, Mizque, central Bolivia. # On

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

at Jabal al-Raat, Shuwaymis site complex, northern Saudi Arabia; Umm Singid and Jebel as-Suqur, Sudan; Tabrakat, Acacus site complex, Libya; and Inca Huasi, Mizque, central Bolivia. # On

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...

at Condor Mayu 2, Santivañez site complex, Cochabamba, Bolivia. # On

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies und ...

at Wushigou 1, Fangcheng, Henan Province, China. Replication has established that cupules produced on very hard rocks, such as quartzite, require many tens of thousands of blows with hammer-stones to make. Therefore, the cumulative force applied to very small surface areas (<15 cm2) is in the order of tens of kN (kilo Newtons). In one extreme case, the KEM lamina has been developed to a thickness of c. 10 mm, but the most commonly observed thickness is about 1–2 mm. The

layer is always thickest in the central part of the cupule, i.e. where the greatest amount of energy was applied.

Geological KEM phenomena

These phenomena have since also been observed in geological contexts, generally of three types: # On the bedrock of

paleochannels A palaeochannel, also spelt paleochannel and also known as palaeovalley or palaeoriver, is a geological term describing a remnant of an inactive river or stream channel that has been filled or buried by younger sediment. The sediments that the ...

(geologically ancient river courses) that has been heavily impacted by battering with

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluv ...

detrital loads in places of high kinetic energy, such as ancient rapids. It can even occur on the transported

cobbles Cobblestone is a natural building material based on cobble-sized stones, and is used for pavement roads, streets, and buildings. Setts, also called Belgian blocks, are often casually referred to as "cobbles", although a sett is distinct ...

and

boulders In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In ...

found deposited in such palaeochannels. # On glacially abraded pavements of quartzite, caused by the tribological action of the lithic load of ancient glaciers. # In the form of whitish sheets of planar or curvi-planar tectonite contained in sandstone that has been subjected to tectonic foliation. Kinetic energy metamorphosis products are tribological phenomena, caused by very focused, localized cumulative effect of kinetic energy on the syntaxial silica (and the voids it contains) that forms the cement of such rocks as sandstones and quartzites. The conversion to tectonite does not appear to be reversible, and the high resistance of that product to

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movemen ...

processes protects the parent rock it conceals from both granular and mass exfoliation. Its susceptibility to dating techniques needs to be explored.

References

{{Reflist Tribology Kinetic energy