Calcium-rich brines and other hydrothermal fluids in fluid inclusions from plutonic rocks, Oceanographer Transform, Mid-Atlantic Ridge

Conference · Wed Jan 01 00:00:00 EST 1992 · Geochimica et Cosmochimica Acta; (United States)

OSTI ID:5088027

Vanko, D A; Griffith, J D ^[1]; Erickson, C L ^[2]

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1. Georgia State Univ., Atlanta, GA (United States)
2. Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)

Fluid inclusions in metagabbro, plagiogranite, and epidosite from the Oceanographer Transform, Mid-Atlantic Ridge, were investigated using microthermometric measurements and laser Raman spectroscopy. Inclusions in quartz reveal the presence of a high-salinity (average 40 wt% NaCl + CaCl{sub 2}), high-temperature (>340C), calcium-rich (Na:Ca about 1, by weight) fluid in metagabbro and plagiogranite. At room temperature these fluids bear a halite daughter crystal, and may also contain small crystals of calcite, titanite, and hematite. A low-density, vapor-rich fluid bearing a small amount of CO{sub 2} is closely associated with the briny fluids in one sample. All samples contain a population of high-temperature (150 to 400C) aqueous liquid-dominated fluid inclusions, commonly of secondary origin, having seawater-like salinity (3 to 8 wt% NaCl equivalent). The authors conclude that the calcium-rich brines are produced by a combination of two processes: fluid phase separation and segregation of brines from vapor prior to trapping to generate the high salinities, and extensive fluid-mafic rock interaction at low water:rock ratio to promote the calcium enrichment. Later introduction along microfractures of low-salinity, modified seawater at high water:rock ratio is recorded by the secondary fluid inclusions. The chemical complexity and association with CO{sub 2} may indicate that there is a magmatic component to the brines in addition to a seawater source. Differences between the Oceanographer Transform brines and those reported in previous studies of oceanic and ophiolite samples are attributed to variations in the degree of water:rock interaction, the host rock lithology, and the influence of a magmatic fluid component.

• OSTI ID: 5088027
• Report Number(s): CONF-9005425-; CODEN: GCACA
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 56:1; Conference: 3. biennial Pan-American conference on research on fluid inclusion, Toronto (Canada), 20-22 May 1990; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
58 GEOSCIENCES
MID-ATLANTIC RIDGE
GEOCHEMISTRY
RESERVOIR FLUIDS
BRINES
CALCIUM CHLORIDES
CARBON DIOXIDE
EXPERIMENTAL DATA
GABBROS
GEOLOGIC FRACTURES
GEOLOGY
GEOTHERMOMETRY
GRANITES
INCLUSIONS
LASER SPECTROSCOPY
LITHOLOGY
MINERALOGY
ORIGIN
PHASE DIAGRAMS
PLUTONIC ROCKS
QUARTZ
RAMAN SPECTROSCOPY
ROCK-FLUID INTERACTIONS
SALINITY
SODIUM CHLORIDES
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM HALIDES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
DATA
DIAGRAMS
FLUIDS
GEOLOGIC STRUCTURES
HALIDES
HALOGEN COMPOUNDS
IGNEOUS ROCKS
INFORMATION
MINERALS
NUMERICAL DATA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
ROCKS
SODIUM COMPOUNDS
SPECTROSCOPY
152001* - Geothermal Data & Theory- Properties of Aqueous Solutions
580000 - Geosciences