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Diatexite Disaggregation and Shearing, Dom Feliciano Belt, Santa Catarina, Brazil



Roberto Weinberg, Fatima Bitencourt, Edinei Koester and students

Monash University and Universidade Federal do Rio Grande do Sul




This page is divided into sections representing different processes: different styles of source disaggregation, with particular focus on disaggregation of amphibolite layers, syn-magmatic shearing of diatexite, folding of migmatites during magmatic flow, and finally examples of the flow of magma through diatexites.



Disaggregation: different styles
source brecciation
Physical disaggregation of protolith by breaking clasts: brecciation.
viscous disaggregation
Physical disaggregation through viscous flow. Notice gradual changes from source (left) to magma (right).
Flow of magma pulling out individual grains and small blocks from schollen. Contact between Corre Mar and Itapema Granite.



Disaggregation of amphibolite layers in the source
amphibolite breccia within source
The Cambori˙ Complex underwent extensive partial melting and disaggregated to form diatexites known as Itapema Granite. Amphibolite layers disaggregate into a magmatic breccia with rounded to angular blocks of amphibolite inside an otherwise coherent, stromatic gneiss.
Net veined amphibolite
Different melting behaviours between gneiss and amphibolite layers inside Cambori˙ Complex. Example of net veining of an amphibolite layer. Praia das Taquaras.
Amphibolite breccia layer
Layer of amphibolite disaggregated into a diatexite/breccia layer. Outcrop in Interpraias road.
Amphibolite pulled apart
Amphibolite blocks being pulled apart within a mobile felsic diatexite: white leucocratic granite with peritectic Hbl (partial melting of amphibolite) are stretched in between the blocks. Syn-anatectic deformation. Pedreira Cazeca, Cambori˙.


Syn-magmatic shearing of diatexite
Syn-magmatic shearing
Syn-magmatic shearing of amphibolite schollen and schlieren in Itapema granite. Vila do Areal, near Itapema Beach.
Syn-magmatic shearing
In situ, dextral shearing in horizontal plane showing S-C-C' planes in heterogeneous Itapema granite. Vila do Areal, near Itapema Beach.
Amphibolite pulled apart
In situ, thrusting shearing in vertical plane showing S-C planes and asymmetric schollen, Itapema granite. Vila do Areal, near Itapema Beach. Vertical scale: 1.5m.
Disagregation, Pedreira Cazeca
Disaggregation of amphibolite, top-to-left shearing.
Amphibolite sigma
Amphibolite sigma-shaped schollen in heterogeneous granite. Vertical wall, thrust to the left, Itapema granite. Praia do Estaleirinho.
Block of stromatic migmatite
Block of Cambori˙ stromatic migmatite inside Itapema Granite, sheared at the margins.
isoclinal folds
Isoclinal folds in layered migmatite sheared top-to-right, vertical wall. Pedreira Cazeca.
Delta clast
Delta clast of amphibolite inside a sigma-shaped leucosome, top-to-right. Pedreira Cazeca.
Amphibolite flow folding
Flow and folding of narrow amphibolite layers around an angular block of amphibolite in diatexite. Pedreira Cazeca.
sheared diatexite
Sheared migmatite gneisses, top-to-left shear sense. Pedreira Cazeca.
Amphibolite with flow veils
Angular to rounded large blocks of amphibolite with flowing veils of felsic granite around them, top to the right sense, exagerated by cut effect. Pedreira Cazeca.
sheared diatexite
Sheared migmatite gneisses, top-to-right shear sense. Praia das Taquaras.


Folding of migmatites
fold axial planar leucosome
Both dextral and sinistral shear zones on axial plane of fold, these trend 345 and 005 representing a fan around the fold. Praia do Estaleiro.
fold axial planar leucosome
Beautiful fold with converging axial planar cleavage filled with melt. Praia do Estaleiro.
fold axial planar leucosome
Hinge zone of a fold with merging axial planar leucosomes. Praia do Estaleiro.
magma channel axial planar
Magma channel with rounded schollen trending N15E, roughly parallel to the axial plane of folds in previous photo. Praia do Estaleiro.
antithetic shear
Sinistral antithetic shear zones in general dextral shearing associated with folding. Taquara do Sul.
antithetic shear
Antithetic sinistral shear zones breaking up a schollen inside granite undergoing dextral shearing. Ponta do Corre Mar.


Flow of magma through diatexites
intrusion into diatexite
Hbl-bearing, felsic granitoid intruding shear zones defining lithons in between. Lithons are also magmatic and Hbl bearing but more mafic than the intruding magmas. Vila do Areal.
Intense flow foliation
Intense flow foliation and stretching of schlieren in betwen two rigid schollen. Praia do Estaleiro.
Amphibolite block
Large amphibolite block broken up by intrusive diatexite forming a clast in shear flow. Praia das Taquaras.