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Syenite-diorite intrusion into marble, Matarazzo-Brasileiro quarry, Dom Feliciano Belt, Rio Grande do Sul, Brazil

 

dyke

Roberto Weinberg and Edinei Koester, Nicole Gerhardt, Carla Porcher


Monash University and Universidade Federal do Rio Grande do Sul

 

 

 

This page describes syenite and diorite dyke intrusions into marble. The marble is calcite rich but has diopside, wollastonite and anorthite, as well as isolated quartz grains or quartz grains associated with wollastonite. Mafic dykes have evidence of partial melting forming leucosomes with large peritectic augite in a syenitic matrix. Augite syenite forms their own dykes carrying blocks of source diorite. Both mafic and syenitic dykes interact with marble forming highly irregular margins, mingling features and different kinds of skarn. Early dykes, now amphibolites, several metres wide have been broken up into isolated blocks in the marble with an alteration margin. Most dykes, felsic and mafic intruded into hot marble and their contacts are highly irregular, and marble dykes also intrude and disaggregate the dykes, giving rise to structures similar to back-veining. Blobs of syenite and diorite can also be found inside the marble forming a structure similar to pillows resulting from magma mingling, except for highly irregular, rather than smooth rounded margins. Mafic dykes have different kinds of skarn at the contact with the marble: titanite concentrations, or anorthosites comprising mostly anorthite with diopside rimmed by Ca-amphiboles. Late thin dykes have straight margins and can be boudinaged surrounded by an alteration band of orange grossular, or be planar and lack any evidence of reaction with the marble. Our interpretation is that during peak metamorphism, amphibolite and early diorite dykes underwent partial melting. The resulting augite syenite intruded the marble carrying blocks of the mafic source. In the process of intrusion it interacted with a partially molten marble and reacted with it. Durand et al (2015) have shown that in the presence of water, carbonates melt at temperatures around 650 C. We interpret the structures as resulting from the interaction between the intrusive silicate melts and a partially molten, water-fluxed marble. The syenite is metasomatically altered close to the marble and is rich in up to 1cm long titanite develops, as well as large poikilitic K-feldspar.

 


 

Irregular Dykes
Intrusion of irregular dykes into marble

Amphibolite melt to produce tonalite
Anatectic amphibolite
Amphibolite with coarse-grained patches with large Hbl grains interpreted to represent a result of in situ melting (peritectic Hbl).
Anatectic amphibolite
Same.
Anatectic amphibolite
Patches of leucosome with augite core. In situ melting.
Syenite dyke with angular amphibolite
Syenite dyke with angular blocks of diorite. Upon closer inspection the felsic matrix does not contain any quartz, only Kfs poikilobasts and Pl+Hbl+Ttn. Augite in syenite.
Syenite with amphibolite in marble
Amphibolite plus syenite block in contact with marble.

 


Intrusions of syenite into marble: irregular shapes.
Mafic dyke
Irregular intrusions of syenite into marble with rims of skarn. Notice the fingering of the dyke into marble.
Mafic dyke
Irregular intrusions of syenite into marble.
Irregular dyke into marble
Irregular intrusions of syenite into marble (Cc).
Mafic dyke
Irregular intrusions of syenite into marble with narrow skarn.
Irregular dyke into marble
Irregular intrusions of syenite into marble with rims of skarn. Notice amphibolite inside syenite.
Mafic dyke
Irregular intrusions of syenite with amphibolite into marble with narrow skarn.
Irregular dyke into marble
Irregular intrusions of syenite into marble. Notice syenite fingers.
Mafic dyke
Irregular intrusions of syenite.

 


Feathery contacts between syenite and marble.
Feathery contacts
Irregular intrusion with feathery contacts.
Feathery contacts
Irregular intrusion with feathery contacts.
Feathery contacts
Feathery contacts.

 


Alteration of syenite close to marble contact.
Mafic dyke
Close to the contact, syenite is metasomatized with very coarse poikylitic Kfs, 1cm long and many titanite grains, as well as diopside.
Mafic dyke
Large titanite (e.g. far right of the photo) with coarse green diopside.

 


Angular amphibolite blocks in marble.
Mafic dyke
Angular blocks of amphibolite. The large one at the bottom has a narrow light green alteration rim and is surrounded by syenite. The three blocks above are isolated in the marble and more fully altered by interaction with marble.
Mafic dyke
Amphibolite block inside marble but also cut by an earlier dyke of syenite. How did these blocks end up inside the marble? How did the marble form a dyke through the amphibolite
Mafic dyke
Break-up of amphibolite by marble. Was the marble molten? From Pedreira Matarazzo.
Mafic dyke
Disaggregation of silicate inclusions (amphibolite and syenite with large Hbl) down to small blocks.

 

 


Clean marble clouds in marble surrounding intrusions.
Mafic dyke
Peperite-like contact between mafic and marble. Notice the lighter marble (black arrow) in amongst the corrugated blocks of mafic rock interpreted to be a remobilized carbonate. White arrow points to a block of mafic intrusion inside the marble.
Mafic dyke
Mafic dyke with corrugated margins, there are two light plumes of carbonate magma(?) (black arrows) related to this mafic intrusion. Are they melts produced at the contact or are they hydrothermal alteration?

 

Crack in mafic dyke
Porphyroblasts-rich alteration margin around mafic intrusion (black arrow). Marble intrudes a crack in the mafic intrusion (white arrow).
Crack in mafic dyke
Alteration margins around mafic block. Marble intrudes a crack in the mafic block.
irregular dyke contacts in marble
Angular block of amphibolite (white arrow) surrounded by a strongly irregular granitic margin (possibly without quartz?) (black arrows) and a skarn reaction rim in the marble
irregular dyke contacts in marble
Detail of margin showing small irregular "clasts" of igneous rocks (skarn?) in carbonate (black arrows).
Mafic dyke: corrugated margin
Corrugated contact between silicate reaction front (above) and marble (lower part of photograph).
Mafic dyke: corrugated margin
Corrugated margin of silicate alteration (under the coin and to the left) in marble.
Mafic dyke: grossular
Thin mafic dyke, boudinaged and surrounded by a green rim of dark green calc-silicate and an outer rim of grossular (Ca garnet, black arrows).
late dyke
Thin late dyke, planar boundaries against marble and lacking skarn rims.