What does Protolith mean?

What is the meaning of protolith?

« Back to Glossary Index. The rocks that existed before the changes that lead to a metamorphic rock, i.e. what rock would exist if the metamorphism was reversed. parent rock, parent rocks.

Does protolith mean parent rock?

In the context of metamorphic rocks, the parent rock (or protolith) is the original rock before metamorphism occurred.

What is a protolith in geography?

A protolith is the original, unmetamorphosed rock from which a given metamorphic rock is formed, e.g. the protolith of a slate is a shale or mudstone. Click here to see list of references, authorities, sources and geographical terms as used in this glossary.

How do you identify protolith?

In low grade metamorphic rocks, original textures are often preserved allowing one to determine the likely protolith. As the grade of metamorphism increases, original textures are replaced with metamorphic textures and other clues, such as bulk chemical composition of the rock, are used to determine the protolith.

Why is protolith important?

Chemical Composition of the Protolith



Therefore, not only does the protolith determine the initial chemistry of the metamorphic rock, most metamorphic rocks do not change their bulk (overall) chemical compositions very much during metamorphism.

What causes Metasomatism?

In the metamorphic environment, metasomatism is created by mass transfer from a volume of metamorphic rock at higher stress and temperature into a zone with lower stress and temperature, with metamorphic hydrothermal solutions acting as a solvent.

What is metasomatic metamorphism?

Metasomatism refers to the process whereby a preexisting igneous, sedimentary, or metamorphic rock undergoes compositional and mineralogical transformations associated with chemical reactions triggered by the reaction of fluids (so-called metasomatic agents), which invade the protolith.

What is cryptic metasomatism?

Two main types of metasomatism were defined: modal (or patent) metasomatism describes the introduction of new minerals; cryptic metasomatism describes changes in composition of pre-existing minerals without formation of new phases.

What are hydrothermally altered rocks?

Hydrothermal alteration is defined as any alteration of rocks or minerals by the reaction of hydrothermal fluid with preexisting solid phases.

What is chlorite alteration?

Chlorite forms by the alteration of mafic minerals such as pyroxenes, amphiboles, biotite, staurolite, cordierite, garnet, and chloritoid. Chlorite can also occur as a result of hydrothermal alteration of any rock type, where recrystallization of clay minerals or alteration of mafic minerals produce chlorite.

What is silicification in geology?

—Silicification is the replacement of original skeletal material accomplished through the concurrent dissolution of calcium carbonate and precipitation of silica. The processes is aided by the nucleation of silica to organic matter which surrounds the mineral crystallites within the shell.

Where is greenschist formed?

These ancient rocks are noted as host rocks for a variety of ore deposits in Australia, Namibia and Canada. Greenschist-like rocks can also be formed under blueschist facies conditions if the original rock (protolith) contains enough magnesium.

What is marble’s parent rock?

Parent Rock. Limestone or Dolostone. Metamorphic Environment. Variable grade regional or contact metamorphism along a convergent plate boundary.

What is greenstone parent rock?

Parent Rock. Basalt; Mafic igneous rocks.

How is greenschist formed?

Greenschists form by regional metamorphism of mafic igneous rocks, usually basaltic rocks, under greenschist facies metamorphism (usually produced by regional metamorphism, typically 300–450 °C and 1–4 kilobars).

What is the parent rock of Granulite?

In continental crustal rocks, biotite may break down at high temperatures to form orthopyroxene + potassium feldspar + water, producing a granulite.

Is greenschist high grade?

The greenschist facies represents lower P-T conditions than the amphibolite facies, i.e., a lower metamorphic grade. Greenschist and amphibolite facies rocks form in typical regional metamorphism related to a geodynamic setting of continental collision tectonics (Figure 2).

What is the parent rock of quartzite?

The parent rock to quartzite is sandstone. Quartzite forms from the recrystallization of quartz grains in the sandstone and often the resulting metamorphic rock will preserve vestiges of the original bedding patterns .

What is anthracite parent rock?

Anthracite Coal – Low grade (if T is too high, the coal turns to graphite), Parent Rock = bituminous coal.

What is phyllite parent rock?

phyllite, fine-grained metamorphic rock formed by the reconstitution of fine-grained, parent sedimentary rocks, such as mudstones or shales.

What is protolith marble?

Limestone is a protolith for marble.

What is Metaconglomerate used for?

A metamorphic rock formed by recrystallization of a conglomerate. This category is also used for meta-conglomerate.

What is the protolith of a quartzite?

quartzite—quartzite is a metamorphic rock made almost entirely of quartz, for which the protolith was quartz arenite. Because quartz is stable over a wide range of pressure and temperature, little or no new minerals form in quartzite during metamorphism.