Roberts Victor eclogites: ancient oceanic crust
New data on the oxygen isotopic chemistry of the oceanic crust and ophiolites illustrate the role of circulating seawater in changing the chemistry of aging oceanic crust. A similar range of oxygen isotope ratios in the eclogites suggests a comparable origin. The interpretation is consistent with the following observations: Whole rocks values of S /sup 18/O are negatively correlated with both the /sup 87///sup 86/Sr and K content. The internal whole rock correlations may be explained as a series of rocks that have undergone varying degrees of alteration on an ancient sea floor. Whole rock chemistry when recalculated to 1 atm. norms and compared with 1 atm. liquidus diagrams indicate two different groups of eclogites. One group has trends that are comparable to a series of liquids formed by the fractional crystallization of olivine followed by plagioclase and clinopyroxene while the other group correlate with cumulate assemblages of gabbroic composition. The REE chemistry of separated garnets and clinopyroxenes and whole rocks allow recalculation of the chemistry of the intergranular material which is significantly LREE enriched. K, Rb, Li and Ti are similarly enriched. The intergranular chemistry compares favorably with that of hypothesized mantle metasomatising fluids and is interpreted to evolve during the metamorphic transition to eclogite assemblages during subduction. The data allow for the interpretation that the Roberts Victor eclogite are relicts of at least 3.2 b.y. old oceanic crust and that the two different groups separately represent the volcanic and gabbroic rocks of the upper part of the ancient oceanic lithosphere.
- Research Organization:
- National Science Foundation, Washington, DC (USA)
- OSTI ID:
- 6454220
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GABBROS
CHEMICAL COMPOSITION
PETROGENESIS
OCEANIC CRUST
VOLCANIC ROCKS
ISOTOPE RATIO
LITHIUM COMPOUNDS
OXYGEN ISOTOPES
PETROCHEMISTRY
POTASSIUM COMPOUNDS
RUBIDIUM COMPOUNDS
TITANIUM COMPOUNDS
ALKALI METAL COMPOUNDS
EARTH CRUST
IGNEOUS ROCKS
ISOTOPES
PLUTONIC ROCKS
ROCKS
TRANSITION ELEMENT COMPOUNDS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)