Fluid compositions and local fluid buffering during the retrograde metamorphism of Al-bearing dolomitic calc-silicate granulites in the Limpopo Central Zone, southern Africa

Kaneko, Yasunari; Miyano, Takashi; Tsunogae, Toshiaki

doi:10.1016/j.jafrearsci.2005.02.006

Cited by 3 publications

(2 citation statements)

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“…Similar local fluid buffering during peak metamorphism has been well documented in metacarbonate rocks from many granulite facies terranes (e.g. Kaneko et al., ; Satish‐Kumar et al., , ). These studies also concluded that the

X_{{normalCO}_{2}}

of the metamorphic fluids was probably maintained as high as 0.5–0.8 even during the low‐granulite and amphibolite facies stages of the retrograde stage.…”

Section: Discussionmentioning

confidence: 99%

“…The evolution of metamorphic fluid compositions has been discussed for metacarbonate rocks from many granulite facies regions, e.g. India (Satish‐Kumar, Santosh, Harley, & Yoshida, ; Satish‐Kumar et al., ), Africa (Kaneko, Miyano, & Tsunogae, ), Antarctica (Satish‐Kumar, Hermann, Tsunogae, & Osanai, ) and Australia (Buick et al., ). Most of these studies have considered recrystallizations under extremely high

X_{{normalCO}_{2}}

[=CO 2 /(CO 2 +H 2 O)] fluid conditions at the granulite facies stage as well as the subsequent retrograde stage.…”

Section: Introductionmentioning

confidence: 99%

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Evolution of metamorphic fluid recorded in granulite facies metacarbonate rocks from the middle segment of the Mogok metamorphic belt in central Myanmar

Thu

Enami

2018

Journal Metamorphic Geology

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The Mogok metamorphic belt of Palaeogene age, which records subduction‐ and collision‐related events between the Indian and Eurasian plates, lies along the western margin of the Shan plateau in central Myanmar and continues northwards to the eastern Himalayan syntaxis. Reaction textures of clinohumite‐ and scapolite‐bearing assemblages in Mogok granulite facies metacarbonate rocks provide insights into the drastic change in fluid composition during exhumation of the collision zone. Characteristic high‐grade assemblages of marble and calcsilicate rock are clinohumite+forsterite+spinel+phlogopite+pargasite/edenite+calcite+dolomite, and scapolite+diopside+anorthite+quartz+calcite respectively. Calculated petrogenetic grids in CaO–MgO–Al2O3–SiO2–H2O–CO2 and subsets of this system were employed to deduce the pressure–temperature–fluid evolution of the clinohumite‐ and scapolite‐bearing assemblages. These assemblages suggest higher temperature (>780–810°C) and XnormalCO2 [=CO2/(CO2+H2O) >0.17–0.60] values in the metamorphic fluid for the peak granulite facies stage, assuming a pressure of 0.8 GPa. Calcite grains commonly show exsolution textures with dolomite particles, and their reintegrated compositions yield temperatures of 720–880°C. Retrograde reactions are mainly characterized by a reaction zone consisting of a dolomite layer and a symplectitic aggregate of tremolite and dolomite grown between clinohumite and calcite in marble, and a replacement texture of scapolite by clinozoisite in calcsilicate rock. These textures indicate that the retrograde reactions developed under lower temperature (<620°C) and XnormalCO2 (<0.08–0.16) conditions, assuming a pressure of 0.5 GPa. The metacarbonate rocks share metamorphic temperatures similar to the Mogok paragneiss at the peak granulite facies stage. The XnormalCO2 values of the metacarbonate rock at peak metamorphic stage are, however, distinctly higher than those previously deduced from carbonate mineral‐free paragneiss. Primary clinohumite, phlogopite and pargasite/edenite in marble have F‐rich compositions, and scapolite in calcsilicate rock contains Cl, suggesting a contrast in the halogen compositions of the metamorphic fluids between these two lithologies. The metamorphic fluid compositions were probably buffered within each lithology, and the effective migration of metamorphic fluid, which would have extensively changed the fluid compositions, did not occur during the prograde granulite facies stage throughout the Mogok metamorphic belt. The lower XnormalCO2 conditions of the Mogok metacarbonate rocks during the retrograde stage distinctly contrast with higher XnormalCO2 conditions recorded in metacarbonate rocks from other metamorphic belts of granulite facies. The characteristic low XnormalCO2 conditions were probably due to far‐ranging infiltration of H2O‐dominant fluid throughout the middle segment of the Mogok metamorphic belt under low‐amphibolite facies conditions during the exhumation and hydration stage.

show abstract

X_{{normalCO}_{2}}

of the metamorphic fluids was probably maintained as high as 0.5–0.8 even during the low‐granulite and amphibolite facies stages of the retrograde stage.…”

Section: Discussionmentioning

confidence: 99%

X_{{normalCO}_{2}}

[=CO 2 /(CO 2 +H 2 O)] fluid conditions at the granulite facies stage as well as the subsequent retrograde stage.…”

Section: Introductionmentioning

confidence: 99%

Evolution of metamorphic fluid recorded in granulite facies metacarbonate rocks from the middle segment of the Mogok metamorphic belt in central Myanmar

Thu

Enami

2018

Journal Metamorphic Geology

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Paleoproterozoic hydration of gabbronorite from the Mesoarchean Lechana layered complex, eastern Botswana

Rajesh

Сафонов

Mfa

et al. 2023

Journal of African Earth Sciences

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Primary magmatic amphibole in Archaean meta-pyroxenite from the central zone of the Limpopo Complex, South Africa

KEEDITSE

Rajesh

Belyanin

et al. 2016

South African Journal of Geology

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Fluid compositions and local fluid buffering during the retrograde metamorphism of Al-bearing dolomitic calc-silicate granulites in the Limpopo Central Zone, southern Africa

Cited by 3 publications

References 48 publications

Evolution of metamorphic fluid recorded in granulite facies metacarbonate rocks from the middle segment of the Mogok metamorphic belt in central Myanmar

Evolution of metamorphic fluid recorded in granulite facies metacarbonate rocks from the middle segment of the Mogok metamorphic belt in central Myanmar

Paleoproterozoic hydration of gabbronorite from the Mesoarchean Lechana layered complex, eastern Botswana

Primary magmatic amphibole in Archaean meta-pyroxenite from the central zone of the Limpopo Complex, South Africa

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