Oxygen Isotopic Constraints on the Origin of Nodular Silica-Apatite from the Har Peres Pyroclastics, Golan Heights, Israel
Oxygen isotope composition of three types of unique nodules which consist of amorphous silica-apatite, cristobalite-apatite and tridymite-apatite associations interspersed amidst basaltic pyroclastics from the Har Peres volcano, Golan Heights, Israel is reported. Unusual isotopic temperature (75°C estimated from oxygen isotope fractionation between cristobalite (δ18O = +25.5‰)-apatite (δ18O = +12.9‰) pair suggests that the nodule was not formed by present-day pedogenesis as has been previously proposed, but was a xenolith incorporated probably from the underlying siliceous phosphorites at a higher temperature. An observed negative oxygen isotopic fractionation (δ18O = −5.1‰) between tridymite (δ18O = +9.9‰) and associated apatite (δ18O = +15.0‰) is indicative of the nodular formation under disequilibrium conditions. A plausible mechanism of formation of the apatite (and calcite) associated with tridymite is an epitaxial overgrowth on template tridymite of magmatic origin under the current weathering regime. Oxygen isotopic evidence indicates a complicated origin for the nodules.
Key WordsApatite Har Peres pyroclastics Oxygen isotope
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- Friedman, I., and J. R. O’Neil. 1977. Compilation of stable isotope fractionation factors of geochemical interest. In Date of Geochemistry, 6th Edition. I. Friedman and J. R. O’Neil, eds. U.S. Geol. Surv. Prof. Paper. 44. pp.Google Scholar
- Garlick, G. D. 1969. The stable isotopes of oxygen. In Handbook of Geochemistry 2, K. H. Wedepohl, ed. New York: Springer-Verlag, par. 1. chapter 8B.Google Scholar
- Kyser, T. K. 1987. Equilibrium fractionation factors for stable isotopes. In Stable Isotope Geochemistry of Low Temperature Processes. Short Course Handbook, Vol. 13. T. K. Kyser, ed. Mineralogical Association of Canada, 1–84.Google Scholar
- Lang, B., M. Shirav, and R. Bogoch. 1979. Volcanological aspects of the Har Peres composite volcano, Golan Plateau. Isr. J. Earth Sci. 28: 27–32.Google Scholar
- Mizota, C., Y. Domon, and N. Yoshida. 1992. Oxygen isotope composition of natural phosphates from volcanic ash soils of the Great Rift Valley of Africa and east Java, Indonesia. Geoderma Sii: 111–123.Google Scholar
- Shemesh, A., and Y. Kolodny. 1988. Oxygen isotopes variations in phosphates from the southern Tethys. Isr. J. Earth Sci. 37: 1–15.Google Scholar
- Singer, A., A. Silber, and D. Szafranek. 1991. Nodular silica-phosphate minerals of the Har Peres pyroclastics, Golan Heights. TV. Jb. Miner. Mh. 8: 337–354.Google Scholar
- Yamasaki, M. 1937. Occurrence of tridymite from Ishiga-mi-yama, Kumamoto. Warera No Kobutsu 6: 30–31 (in Japanese).Google Scholar