Syenite-diorite intrusion into marble, Matarazzo-Brasileiro quarry, Dom Feliciano Belt, Rio Grande do Sul, Brazil
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| 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. |
Intrusion of irregular dykes into marble |
Amphibolite melt to produce tonalite
Amphibolite with coarse-grained patches with large Hbl grains interpreted to represent a result of in situ melting (peritectic Hbl). |
Same. |
Patches of leucosome with augite core. In situ melting. |
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. |
Amphibolite plus syenite block in contact with marble. |
Intrusions of syenite into marble: irregular shapes.
Irregular intrusions of syenite into marble with rims of skarn. Notice the fingering of the dyke into marble. |
Irregular intrusions of syenite into marble. |
Irregular intrusions of syenite into marble (Cc). |
Irregular intrusions of syenite into marble with narrow skarn. |
Irregular intrusions of syenite into marble with rims of skarn. Notice amphibolite inside syenite. |
Irregular intrusions of syenite with amphibolite into marble with narrow skarn. |
Irregular intrusions of syenite into marble. Notice syenite fingers. |
Irregular intrusions of syenite. |
Feathery contacts between syenite and marble.
Irregular intrusion with feathery contacts. |
Irregular intrusion with feathery contacts. |
Feathery contacts. |
Alteration of syenite close to marble contact.
Close to the contact, syenite is metasomatized with very coarse poikylitic Kfs, 1cm long and many titanite grains, as well as diopside. |
Large titanite (e.g. far right of the photo) with coarse green diopside. |
Angular amphibolite blocks in marble.
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. |
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 |
Break-up of amphibolite by marble. Was the marble molten? From Pedreira Matarazzo. |
Disaggregation of silicate inclusions (amphibolite and syenite with large Hbl) down to small blocks. |
Clean marble clouds in marble surrounding intrusions.
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 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? |
Porphyroblasts-rich alteration margin around mafic intrusion (black arrow). Marble intrudes a crack in the mafic intrusion (white arrow). |
Alteration margins around mafic block. Marble intrudes a crack in the mafic block. |
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 |
Detail of margin showing small irregular "clasts" of igneous rocks (skarn?) in carbonate (black arrows). |
Corrugated contact between silicate reaction front (above) and marble (lower part of photograph). |
Corrugated margin of silicate alteration (under the coin and to the left) in marble. |
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). |
Thin late dyke, planar boundaries against marble and lacking skarn rims. |