Preliminary study of micro- scale zircon oxygen isotopes for Dabie-Sulu metamorphic rocks: Ion probe in situ analyses
CHEN Daogong1, Deloule Etienne2, CHENG Hao1, XIA Qunke1 & WU Yuanbao1 1. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China; 2. CRPG-CNRS, Nancy 54501, France Correspondence should be addressed to Chen Daogong (e-mail: email@example.com)
in situ analyses of oxygen isotopes were carried out by ion micro-probe for zircons from 8 localities of HP-UHP metamorphic rocks including eclogites in the Dabie-Sulu terrane. The results show significant heterogene-ity in d 18O values, with variation in different rocks from 8.5 to +9.7 and within one sample from 2 to 12. No measurable difference in d 18O was observed between proto-lith magmatic (detrital) zircons and metamorphic recrystal-lized zircons within analytical uncertainties from the ion micro-probe measurements. This indicates that the meta-morphic zircons have inherited the oxygen isotopic composi-tions of protolith zircons despite the HP to UHP metamor-phism. According to their protolith ages from zircon U-Pb in situ dating by the same ion micro-probe, two groups of oxy-gen isotope composition are recognized, with one having d 18O values of 6—7 for old protolith of 1.9—2.5 Ga ages and the other 0—2 for young protolith of 0.7—0.8 Ga ages. The latter anomalously low d 18O values of zircons in-dicate that the magma has had the obvious involvement of meteoric water when forming the young protolith of high-grade metamorphic rocks. This may be correlated with the snowball Earth event occurring in South China and the world elsewhere during the Neoproterozoic.
【CateGory Index】： P597