Tectonite

L-S tectonite viewed in the plane of the S fabric

L-S tectonite viewed perpendicular to the plane of the S fabric

Deformed conglomerate showing no strain in one plane (at left) and strong stretching in the other (at right) – an L-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 formation. Planar foliation results from a parallel orientation of platey mineral phases such as the phyllosilicates or graphite. Slender prismatic crystals such as amphibole produce a lineation in which these prisms or columnar crystals become aligned. Tectonites are rocks with minerals that have been affected by natural forces of the earth, which allowed their orientations to change. This usually includes recrystallization of minerals, and the foliation formation. Tectonites are studied through structural analysis and allows for the determination of two things:

The orientation of shearing and compressive stresses during (dynamic) metamorphism
The later (or final) stages of metamorphism

According to the nature of mineral orientation, there are three main groups of tectonites, L-Tectonites, S-Tectonites, and LS-Tectonites. The different types reflect on the different ways that matter moves.

L-Tectonites are aligned in a linear fabric, which allows the rock to split into rod-like shapes due to the two intersecting planes. The foliation of this type is not strong.
S-Tectonites are the fabric that is dominantly a foliation fabric which allows the rock to split into plate-like sheets that are parallel to foliation. There are little to no linear fabrics within the foliation fabrics.
LS-Tectonites is the perfect mix of the two, with both strong lineations and strong foliations. This is caused by the rotation of the grains around axes that are oriented along the trends of the folds.

Classification

S-tectonites (from the German, Schiefer for schist) have a dominant planar fabric and may indicate a flattening type of strain. This may also be due to a lack of minerals capable of giving a lineation e.g. in a phyllonite.
L-tectonites have a dominant linear fabric and generally indicate a constrictional type of strain. This may be due to a lack of platey phases.
L-S tectonites have equally developed linear and planar fabric elements and may indicate a plane strain deformation. Many mylonites are L-S tectonites consistent with a simple shear deformation.
L-Tectonites (Lineations) indicate Constrictional Strain
S-Tectonites (Foliations) indicate Flattening Strain
L-S Tectonites (Plain strain) indicate both elongation and flattening strain

References

^ a b c Best, Myron G., Igneous and Metamorphic Petrology, Wiley-Blackwell, 2nd ed. 2002, p. 448
^ a b c "Tectonite". The Free Dictionary. Retrieved 2023-07-19.
^ "TECTONITES, S, LS AND L TYPE". structuralgeology.50webs.com. Archived from the original on 2020-02-18.

v t e Structural geology
Underlying theory	Deformation mechanism Lamé's stress ellipsoid Mohr–Coulomb theory Mohr's circle Overburden pressure Rock mechanics Strain Strain partitioning Stress Stress field Tension
Measurement conventions	Brunton compass Inclinometer Orthographic projection Rake Stereographic projection Strike and dip
Large-scale tectonics	Accretionary wedge Allochthon Autochthon Back-arc basin Continental collision Convergent boundary Décollement Divergent boundary Extensional tectonics Fault block Fenster Fold and thrust belt Fold mountains Foreland basin Graben Half-graben Horse Horst Horst and graben Intra-arc basin Inversion Klippe List of tectonic plate interactions Mélange Mountain formation Nappe Obduction Orogeny Passive margin Plate tectonics Pull-apart basin Rift valley Rift Saddle Strike-slip tectonics Structural basin Suture Syneclise Terrane Thick-skinned deformation Thin-skinned deformation Thrust tectonics
Fracturing	Columnar jointing Dike Exfoliation joint Fissure Joint Vein
Faulting	Cataclasite Cataclastic rock Detachment fault Disturbance Fault mechanics Fault scarp Fault trace Thrust fault Transfer zone Transform fault
Foliation and lineation	Cleavage Compaction Crenulation Fissility Oblique foliation Pressure solution Rock microstructure Slickenside Stylolite Tectonic phase Tectonite
Folding	Anticline Chevron Detachment fold Dome Homocline Monocline Syncline Vergence
Boudinage	Competence
Kinematic analysis	3D fold evolution Paleostress inversion Paleostress Section restoration
Shear zone	Mylonite Pure shear Shear
Category

v t e Types of rocks
Igneous rock	Adakite Andesite Alkali feldspar granite Anorthosite Aplite Basalt Basaltic trachyandesite Mugearite Shoshonite Basanite Blairmorite Boninite Carbonatite Charnockite Enderbite Dacite Diabase Diorite Napoleonite Dunite Essexite Foidolite Gabbro Granite Granodiorite Granophyre Harzburgite Hornblendite Hyaloclastite Icelandite Ignimbrite Ijolite Kimberlite Komatiite Lamproite Lamprophyre Latite Lherzolite Monzogranite Monzonite Nepheline syenite Nephelinite Norite Obsidian Pegmatite Peridotite Phonolite Phonotephrite Picrite Porphyry Pumice Pyroxenite Quartz diorite Quartz monzonite Quartzolite Rhyodacite Rhyolite Comendite Pantellerite Scoria Shonkinite Sovite Syenite Tachylyte Tephriphonolite Tephrite Tonalite Trachyandesite Benmoreite Trachybasalt Hawaiite Trachyte Troctolite Trondhjemite Tuff Websterite Wehrlite
Sedimentary rock	Argillite Arkose Banded iron formation Breccia Calcarenite Chalk Chert Claystone Coal Conglomerate Coquina Diamictite Diatomite Dolomite Evaporite Flint Geyserite Greywacke Gritstone Itacolumite Jaspillite Laterite Lignite Limestone Lumachelle Marl Mudstone Oil shale Oolite Phosphorite Sandstone Shale Siltstone Sylvinite Tillite Travertine Tufa Turbidite Varve Wackestone
Metamorphic rock	Anthracite Amphibolite Blueschist Cataclasite Eclogite Gneiss Granulite Greenschist Hornfels Calcflinta Itabirite Litchfieldite Marble Migmatite Mylonite Metapelite Metapsammite Phyllite Pseudotachylite Quartzite Schist Serpentinite Skarn Slate Suevite Talc carbonate Soapstone Tectonite Whiteschist
Specific varieties	Adamellite Appinite Aphanite Borolanite Blue Granite Epidosite Felsite Flint Ganister Gossan Hyaloclastite Ijolite Jadeitite Jasperoid Kenyte Lapis lazuli Larvikite Litchfieldite Llanite Luxullianite Mangerite Novaculite Pietersite Pyrolite Rapakivi granite Rhomb porphyry Rodingite Shonkinite Taconite Tachylite Teschenite Theralite Unakite Variolite Wad

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