A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust

Details A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust

Jan 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980e%26psl..46..201m&link_type=abstract

Earth and Planetary Science Letters, Volume 46, Issue 2, p. 201-211.

Mathematics

Logic

19

Scientific paper

In the Samail ophiolite, 147Sm-143Nd, 87Rb-87Sr, and 18O/16O isotopic systems have been used to distinguish between sea-floor hydrothermal alteration and primary magmatic isotopic variations. The Rb-Sr and 18O/16O isotopic systems clearly exhibit sensitivity to hydrothermal interactions with seawater while the Sm-Nd system appears essentially undisturbed. Internal isochrons have been determined by the 147Sm-143Nd method using coexisting plagioclase and pyroxene and give crystallization ages of 130 +/- 12 m.y. from Ibra and 100 +/- 20 m.y. from Wadi Fizh. These ages are interpreted as the time of formation of the Samail oceanic crust and are older than the inferred emplacement age of 65-85 m.y. The initial 143Nd/144Nd ratios for a tectonized harzburgite, cumulate gabbros, plagiogranite, sheeted dikes and a basalt have a limited range in ɛNd of from 7.5 to 8.6 for all lithologies, demonstrating a clear oceanic affinity and supporting earlier interpretations based on geologic observations and geochemistry. The 87Sr/86Sr initial ratios on the same rocks have an extremely large range of from 0.70296 to 0.70650 (ɛSr = -19.7 to +30.5) and the δ 18O values vary from 2.6 to 12.7. These large variations are clearly consistent with hydrothermal interaction of seawater with the oceanic crust. A model is presented for the closed system exchange of Sr and O, that in principle illustrates how the Sr isotopic data may be utilized to estimate the water/rock ratio and subsequently used to evaluate the temperature of equilibration between the water and silicates from the 18O/16O water-rock fractionation.

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