Sm-Nd, Rb-Sr, and /sup 18/O//sup 16/O isotopic systematics in an oceanic crustal section: Evidence from the Samial ophiolite
The Sm-Nd, Rb-Sr, and /sup 18/O//sup 16/O isotopic systems have been used to distinguish between the effects of seafloor hydrothermal alteration and primary magmatic isotopic variations. The Sm-Nd isotopic system is essentially unaffected by seawater alteration, while the Rb-Sr and /sup 18/O//sup 16/O systems are sensitive to hydrothermal interactions with seawater. Sm-Nd mineral isochrons from the cumulate gabbros of the Samail ophiolite have an initial /sup 143/Nd//sup 144/Nd ratio of e/sub Nd/ = 7.8 +- 0.3, which clearly substantiates the oceanic affinity of this complex. The initial /sup 143/Nd//sup 144/Nd ratios for the harzburgite, plagiogranite, sheeted diabase dikes, and basalt units have a limited range in e/sub Nd/ of from 7.5 to 8.6, indicating that all the lithologies have distinctive oceanic affinities, although there is also some evidence for small isotopic heterogeneities in the magma reservoirs. The Sm-Nd mineral isochrons give crystallization ages of 128 +- 20 m.y. and 150 +- 40 m.y. from Ibra and 100 +- 20 m.y. from Wadi Fizh, which is approximately 300 km NW of Ibra. These crystallization ages are interpreted as the time of formation of the oceanic crust. The /sup 87/Sr//sup 86/Sr initial ratios on the same rocks have an extremely large range of from 0.7030 to 0.7065 and the d/sup 18/O values vary from 2.6 to 12.7. These large variations clearly demonstrate hydrothermal interaction of oceanic crust with seawater.
- Research Organization:
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125
- OSTI ID:
- 6537689
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 86:B4
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
OCEANIC CRUST
ISOTOPE RATIO
OMAN
GEOCHEMISTRY
ARABIAN SEA
EARTH MANTLE
HYDROTHERMAL ALTERATION
IGNEOUS ROCKS
NEODYMIUM 143
NEODYMIUM 144
OXYGEN 16
OXYGEN 18
SEA-FLOOR SPREADING
STRONTIUM 86
STRONTIUM 87
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
ASIA
BETA DECAY RADIOISOTOPES
CHEMISTRY
EARTH CRUST
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HOURS LIVING RADIOISOTOPES
INDIAN OCEAN
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGHT NUCLEI
MIDDLE EAST
NEODYMIUM ISOTOPES
NUCLEI
OXYGEN ISOTOPES
RADIOISOTOPES
RARE EARTH NUCLEI
ROCKS
SEAS
STABLE ISOTOPES
STRONTIUM ISOTOPES
SURFACE WATERS
YEARS LIVING RADIOISOTOPES
580100* - Geology & Hydrology- (-1989)