Experimental constraints on the partitioning of Cl between topaz rhyolite melt and H sub 2 O and H sub 2 O + CO sub 2 fluids: New implications for granitic differentiation and ore deposition

Journal Article · Mon Aug 01 04:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90189-5· OSTI ID:7164140

Webster, J D; Holloway, J R ^[1]

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1. Arizona State Univ., Tempe (USA)

The partitioning of Cl between superliquidus melts of topaz rhyolite and fluids consisting of H{sub 2}O and H{sub 2}O + CO{sub 2} has been determined experimentally at pressures of 0.5 to 5 kbar and temperatures of 725{degree} to 950{degree}C with f{sub O{sub 2}} controlled near NNO. The major element and Cl contents of a starting material glass and the run product glasses were determined by electron microprobe. The concentration of Cl and the major elements in the fluid are calculated by mass balance. Cl partitions in favor of the fluid for all experimental run conditions. For natural abundances of Cl in a magmatic system, D{sub Cl} ranges from 2 to 20. These values are much lower than those previously reported in the literature. D{sub Cl} increases as the Cl content of the melt and fluid increases, as the F content of the system decreases, as T and P increases, as the melt becomes more peraluminous, and as (H{sub 2}O/H{sub 2}O + CO{sub 2}) of the fluid increases. Peraluminous granitic melts that are in equilibrium with aqueous fluids at 800{degree}C and 2 kbar achieve a maximum concentration of Cl in the melt at 2500 {plus minus} 100 ppm Cl. In experiments with Cl ranging from 40 to 300 g Cl/kg fluid the D{sub Cl} ranges from 20 to 130 and is consistent with literature values. For fluid-saturated, silicic melts of granite composition with H{sub 2}O activities near 1, the strong partitioning of Cl into the fluid also causes partitioning of some ore metals, trace elements and the major elements Na, K and Fe ({plus minus}Ca) into the fluid: this is maximized for granitic melts that are strongly peraluminous, low in F and highly enriched in Cl; partitioning of Cl into aqueous fluids is maximized at high P and T. If the H{sub 2}O-rich fluid is diluted with CO{sub 2} (X{sub H{sub 2}O}{sup fl} {>=} 0.45) the concentration of Cl in the fluid decreases strongly.

• OSTI ID: 7164140
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:8; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AMORPHOUS STATE
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHEMISTRY
CHLORINE COMPOUNDS
EQUILIBRIUM
FLUIDS
GEOCHEMISTRY
GEOTHERMAL FLUIDS
HALOGEN COMPOUNDS
IGNEOUS ROCKS
ION EXCHANGE
KINETICS
MAGMATISM
MASS BALANCE
MINERALOGY
PARTITION
PETROGENESIS
PRESSURE EFFECTS
REACTION KINETICS
RHYOLITES
ROCKS
SOLUBILITY
TEMPERATURE EFFECTS
VOLCANIC ROCKS