Brine-assisted anatexis: Experimental melting in the system haplogranite–H2O–NaCl–KCl at deep-crustal conditions

Aranovich, L. Ya.; Newton, Robert C.; Manning, Craig E.

doi:10.1016/j.epsl.2013.05.027

Cited by 106 publications

(68 citation statements)

References 63 publications

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“…The second petrologic consequence of the mixing thermodynamics of water-alkali chloride systems is that contours of constant X H 2 O in the fluid at granite minimum melting have strongly positive dP/dT slopes above 2-3 kbar ( Fig. 4; Aranovich et al, 2013a). At even modest X salt , the slopes are shallower than model adiabatic (Johannes and Holtz, 1991) or isothermal ascent paths for haplogranite.…”

Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 98%

“…In the above example, the granulite-facies assemblage orthopyroxene + K feldspar (±quartz) could form at the expense of phlogopite + quartz due to interaction with a brine of X H 2 O = 0.5 without producing any melt over a 40 • temperature range. This temperature range becomes even greater at higher pressure (Aranovich et al, 2013a). In addition, brine metasomatism may increase alkalis, CaO and SiO 2 in the mid-crust and thus condition it for anatexis .…”

Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 99%

“…Brine-assisted anatexis differs greatly from rock melting in pure H 2 O or in H 2 O-CO 2 fluids. Large changes in feldspar composition in equilibrium with melts can result from small shifts in fluid compositions (Aranovich et al, 2013a). The presence of brines during high-grade metamorphism may help resolve the "granulite paradox": extensive dehydration without wholesale melting in numerous examples of these rocks .…”

Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 99%

“…A similar effect was discovered some 40 years ago in the experiments on granite melting in presence of relatively dilute NaCl-bearing fluids (Holland, 1972;Ryabchikov, 1975) and was attributed to accumulation of Na(OH) in the melt and HCl in the fluid phase. As Cl solubility in felsic melts is restricted to a few tenths of a weight per cent (e.g., Webster, 2004;Aranovich et al, 2013a) and partitioning of Cl between melt and fluid favors the fluid phase, relative Cl enrichment may be expected in the fluid that separates from a felsic magma at the early stages of crystallization.…”

Section: Hydrolysismentioning

confidence: 99%

“…The especially low solubility of Cl (and CO 2 and S) in silicic magmas (Stolper et al, 1987;Webster and Holloway, 1988;Papale, 1999;Newman and Lowenstern, 2002;Webster et al, 2002;Webster, 2004;Aranovich et al, 2013a) also means that, where fluid-saturated melting occurs in the middle and lower crust, the melt will strongly partition H 2 O relative to chloride and promote formation of a residual saline fluid. Most conceptual models of fluid-saturated melting focus solely on the role of H 2 O.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 98%

Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 99%

Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 99%

Section: Hydrolysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Manning

Aranovich

2014

Precambrian Research

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Minerals-Indicators of Fluids Compositions in the Metabasites (by Experimental Data)

Khodorevskaya

2023

Springer Proceedings in Earth and Environmental Sciences

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The Role of Halogens in Terrestrial and Extraterrestrial Geochemical Processes: Surface, Crust, and Mantle

Harlov

Aranovich

2018

Springer Geochemistry

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Brine-assisted anatexis: Experimental melting in the system haplogranite–H2O–NaCl–KCl at deep-crustal conditions

Cited by 106 publications

References 63 publications

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

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

Minerals-Indicators of Fluids Compositions in the Metabasites (by Experimental Data)

The Role of Halogens in Terrestrial and Extraterrestrial Geochemical Processes: Surface, Crust, and Mantle

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