Post-metamorphic CO2-rich fluid inclusions in granulites

Lamb, William M.; Valley, John W.; Brown, P. E.

doi:10.1007/bf01166693

Cited by 126 publications

(59 citation statements)

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“…Although fluid inclusion studies in the orthopyroxene bearing dry granulite facies rocks (charnockites) in southern India provided support for the CO 2 influx model (e.g., Santosh, 1986;Hansen et al, 1987), later investigations have favoured alternate models which envisage specific magmatic carriers and structural conduits for the transfer of CO 2 (see reviews in Santosh, 1992;. The timing of CO 2 entrapment in granulites was also a topic of debate with examples from some terrains suggesting post metamorphic fluid capture (Lamb et al, 1987) while others attesting to peak metamorphic fluid trapping (Santosh et al, 1991). Although a number of studies have tried to elucidate the origin of fluids and mechanism of fluid transfer, the ultimate source of CO 2 rich fluids in high grade metamorphism still remains elusive.…”

Section: Discussionmentioning

confidence: 99%

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

Santosh

Tsunogae

Yoshikura

2004

Journal of Mineralogical and Petrological Sciences

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Ultrahigh temperature (UHT) granulites in Tonagh Island, Napier Complex, East Antarctica record peak metamorphic pressure temperature (P T) conditions of up to 9 kbar and 1100°C. Sapphirine, garnet, orthopyroxene and quartz in these rocks contain very high density fluid inclusions with melting temperatures close to that of pure CO 2 (−56.6°C) and homogenization temperatures down to −34.9°C translating into high CO 2 densities (up to 1.07 g/cm 3 ). The UHT granulites of Vizianagram in Eastern Ghats Belt, India which were subjected to extreme crustal metamorphism at >1000°C and 8 9 kbar also carry very high density (up to 1.15 g/cm 3 ) pure CO 2 inclusions in quartz adjacent to spinel rimmed by various coronas of sillimanite, orthopyroxene and garnet. Garnets in a granulite facies rock from Salem in southern India that equilibrated at peak P T conditions of 740 800°C and 9 11 kbar carry the highest density (1.17 g/cm 3 ) pure CO 2 yet reported from continental crust. This rock also contains very high density CO 2 inclusions in plagioclase and quartz. High density (0.998 g/cm 3 ) pure CO 2 rich fluid inclusions also occur abundantly within garnets from a mafic granulite in Ampitiya, central Highland Complex, Sri Lanka. The peak P T conditions of metamorphism of the mafic granulite are around 10.6 kbar and 985°C with subsequent rapid isothermal decompression along a clock wise path down to 5.5 kbar. In most of the cases above, the representative isochores for the CO 2 inclusions either penetrate through or pass very close to the P T windows defined from mineral phase equilibria indicating that the fluid inclusions were trapped at the time of peak or near post peak metamorphism. We thus recognize a group of "ultrahigh density" (UHD) CO 2 rich fluids that characterize UHT rocks and other granulites formed under extreme crustal metamorphism. These fluids contrast sharply with the lower density (generally <1.0 g/cm 3 ) CO 2 inclusions commonly reported from normal granulite facies rocks in various terrains. The presence of "synmetamorphic" UHD CO 2 within various minerals is consistent with the low water activities predicted by the mineral assemblages in these rocks. Although the source of the CO 2 is equivocal, mantle derived mafic magmas could have provided the heat and volatiles required for crustal metamorphism at extreme conditions displayed by these rocks.

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Section: Discussionmentioning

confidence: 99%

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

Santosh

Tsunogae

Yoshikura

2004

Journal of Mineralogical and Petrological Sciences

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“…It may explain granulite terranes in which field and petrologic data require presence of a low-a H 2 O fluid phase capable of metasomatizing major and trace elements. The CO 2 -rich fluid inclusions often found in high-grade rocks led Newton et al (1980) to suggest that dilution of H 2 O by CO 2 may explain reduced a H 2 O ; however, this is not consistent with petrologic observations (e.g., Lamb et al, 1987). Brine and vapor immiscibility may offer a better explanation (Touret, 1985;Newton et al, 1998;Newton and Manning, 2010) because the wetting properties of the CO 2 -rich vapor phase lead to preferential entrapment as fluid inclusions relative to the brine phase (Gibert et al, 1998).…”

Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 42%

Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

Manning

Aranovich

2014

Precambrian Research

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a b s t r a c tA number of observations point to the participation of brines in high-grade metamorphic processes. These include findings of alkali and alkaline-earth halides as daughter crystals in fluid inclusions, appreciable concentrations of Cl measured in amphiboles, biotite, scapolite and apatite, and direct observations on high-temperature halides present in the intergranular space in high-grade rocks. This paper reviews some thermodynamic, petrologic and geochemical effects of these brines. Thermodynamic mixing properties of concentrated water-salt fluids at high pressure (P) and temperature (T) differ greatly from those of water-non-polar gas mixtures: the former are characterized by a large negative deviation from ideal solutions, while the latter exhibit positive deviation from ideality. The contrasting behavior has three major petrologic implications. First, compared to mixtures of water and non-polar gases, brines more strongly increase the melting temperature of quartzofeldspathic rocks and more strongly decrease dehydration temperature of water-bearing minerals. This allows a wide P-T window in which subsolidus deep-crustal metasomatism may take place at relatively low H 2 O activity (a H 2 O ) via migrating fluids. In addition, above 2-3 kbar, brine-saturated solidi for simple granite melting show positive dP/dT at constant H 2 O mole fraction (X H 2 O ), favoring ascent of fluid-saturated liquids. Finally, a large miscibility gap exists in H 2 O-CO 2 -salt ternaries at lower crustal conditions, which may concentrate salts in a separate phase and help explain the common observation of CO 2 -rich inclusions in high-grade minerals. We discuss three geochemical consequences of high-grade brines. We report new experimental data on melting of a model granitoid liquid (69 wt% NaAlSi 3 O 8 , 31 wt% SiO 2 ) at 2 kbar in the presence of aqueous NaCl solutions ranging in concentration from a salt mole fraction (X NaCl ) of 0.1-0.3. The results show that Na preferentially partitions into the silicate liquid, enriching the coexisting fluid in HCl. This hydrolysis effect, known previously for granite melts equilibrated with dilute solutions, therefore also extends to more saline brines. Mineral solubilities depend strongly on salt concentration in the coexisting fluid. Below 5 kbar at 700• C, quartz initially salts in with addition of NaCl to H 2 O, reaches a maximum, and then declines; however, it salts out at all X NaCl at higher P. At granulite-facies P-T conditions, the solubilities of other oxide and silicate minerals (corundum, wollastonite, grossular) salt in and then either reach a plateau or salt out slightly at high X NaCl . In contrast, the solubility of Ca-salt minerals increases exponentially with rising X NaCl . The solubility patterns reflect variations in complexing and H 2 O activity in the brine. Partitioning of REE between rock forming minerals and brines, and between felsic melts and brines, differs strongly from that between minerals, melts and water (±non-polar gas). Brines extract REE f...

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“…Entrapment of a COz-rich fluid which percolated through the rock during cooling This mechanism was proposed by Lamb, Brown & Valley (1987) for the C02-rich inclusions in the wollastonite-bearing rocks of the Adirondacks. They argue that C 0 2 + H 2 0 fluids, which flowed along microcracks during cooling after the peak of metamorphism, reacted with host minerals to produce hydrous retrograde minerals.…”

Section: Possible Mechanisms For Forming Pure C02 Inclusionsmentioning

confidence: 96%

On the origin of CO₂‐rich fluid inclusions in migmatites

Hollister

1988

Journal Metamorphic Geology

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Abstract. Nearly pure C 0 2 fluid inclusions are abundant in migmatites although H20-rich fluids are predicted from the phase equilibria. Processes which may play a role in this observation include (1) the effects of decompression on melt, (2) generation of a COz-bearing volatile phase by the reaction graphite t quartz + biotite t plagioclase = melt + orthopyroxene + C02-rich vapour, (3) selective leakage of H 2 0 from C 0 2 + H 2 0 inclusions when the pressure in the inclusion exceeds the confining pressure during decompression, and (4) enrichment of grain-boundary vapour in C 0 2 by subsolidus retrograde hydration reactions.

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Post-metamorphic CO2-rich fluid inclusions in granulites

Cited by 126 publications

References 37 publications

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

On the origin of CO₂‐rich fluid inclusions in migmatites

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Post-metamorphic CO2-rich fluid inclusions in granulites

Cited by 126 publications

References 37 publications

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism

Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

On the origin of CO2‐rich fluid inclusions in migmatites

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On the origin of CO₂‐rich fluid inclusions in migmatites