Kelley, Deborah S; Frueh-Green, Gretchen L (2001): Results of analyses of fluid inclusions from ODP Site 735B, Leg 118 and 176 [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.708401, Supplement to: Kelley, DS; Frueh-Green, GL (2001): Volatile lines of descent in submarine plutonic environments; insights from stable isotope and fluid inclusion analyses. Geochimica et Cosmochimica Acta, 65(19), 3325-3346, https://doi.org/10.1016/S0016-7037(01)00667-6
Always quote citation above when using data! You can download the citation in several formats below.
Abstract:
Microthermometric and isotopic analyses of fluid inclusions in primitive olivine gabbros, oxide gabbros, and evolved granitic material recovered from Ocean Drilling Program Hole 735B at the Southwest Indian Ridge provide new insights into the evolution of C-O-H-NaCl fluids in the plutonic foundation of the oceanic crust. The variably altered and deformed plutonic rocks span a crustal section of over 1500 m and record a remarkably complex magma-hydrothermal history. Magmatic fluids within this suite followed two chemically distinct paths during cooling through the subsolidus regime: the first path included formation of CO2+CH4+H2O+C fluids with up to 43 mole% CH4; the second path produced hypersaline brines that contain up to 50% NaCl equivalent salinities.
Subsequent to devolatilization, respeciation of magmatic CO2, attendant graphite precipitation, and cooling from 800°C to 500°C promoted formation of CH4-enriched fluids. These fluids are characterized by average d13C(CH4) values of -27.1+/-4.3 per mil (N=45) with associated d13C(CO2) compositions ranging from -24.9 per mil to -1.9 per mil (N=39), and average dD values of exsolved vapor of -41+/-12 per mil (N=23). In pods, veins, and lenses of highly fractionated residual material, hypersaline brines formed during condensation and by direct exsolution in the absence of a conjugate vapor phase. Entrapped CO2+CH4+H2O-rich fluids within many oxide-bearing rocks and felsic zones are significantly depleted in 13C (with d13C(CO2) values down to about -25 per mil) and contain CO2 concentrations higher than those predicted by equilibrium devolatilization models. We hypothesize that lower effective pressures in high-temperature shear zones promoted infiltration of highly fractionated melts and compositionally evolved volatiles into focused zones of deformation, significantly weakening the rock strength. In felsic-rich zones, volatile build-up may have driven hydraulic fracturing of gabbroic wall rocks resulting in the formation of magmatic breccias. Comparison of isotopic compositions of fluids in plutonic rocks from 735B, the MARK area of the Mid-Atlantic Ridge, and the Mid-Cayman Rise indicate (1) that the carbon isotope composition of the lower oceanic crust may be far more heterogeneous than previously believed and (2) that carbon-bearing species in the oceanic crust and their distribution at depth are highly variable.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: -32.723737 * Median Longitude: 57.266137 * South-bound Latitude: -32.724000 * West-bound Longitude: 57.266010 * North-bound Latitude: -32.723210 * East-bound Longitude: 57.266200
Date/Time Start: 1987-12-06T04:45:00 * Date/Time End: 1997-12-01T19:00:00
Event(s):
118-735B * Latitude: -32.724000 * Longitude: 57.266200 * Date/Time Start: 1987-12-06T04:45:00 * Date/Time End: 1987-12-11T01:00:00 * Elevation: -731.0 m * Penetration: 500.7 m * Recovery: 434.81 m * Location: South Indian Ridge, South Indian Ocean * Campaign: Leg118 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 88 cores; 500.7 m cored; 0 m drilled; 86.8 % recovery
176-735B * Latitude: -32.723210 * Longitude: 57.266010 * Date/Time Start: 1997-10-24T13:45:00 * Date/Time End: 1997-12-01T19:00:00 * Elevation: -720.6 m * Penetration: 1508 m * Recovery: 865.99 m * Location: Indian Ocean * Campaign: Leg176 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 122 cores; 1003.2 m cored; 504.8 m drilled; 86.3 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
3 datasets
Download Data
Datasets listed in this publication series
- Kelley, DS; Frueh-Green, GL (2001): (Table 1) Fluid inclusion analyses of minerals from ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.708396
- Kelley, DS; Frueh-Green, GL (2001): (Table 2) Isotopic analyses and carbon contents of C-O-H fluids in ODP Hole 118-735B extracted by step-heating at temperatures >1000°C. https://doi.org/10.1594/PANGAEA.708398
- Kelley, DS; Frueh-Green, GL (2001): (Table 2) Isotopic analyses and carbon contents of C-O-H fluids in ODP Hole 176-735B extracted by step-heating at temperatures >1000°C. https://doi.org/10.1594/PANGAEA.708400