Xia Qunke

Preliminary study of microscale zircon oxygen isotopes for Dabie-Sulu metamorphic rocks: Ion probe in situ analyses

Abstract151 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 heterogeneity in δ18O values, with variation in different rocks from −8.5‰ to +9.7‰ and within one sample from 2‰ to 12‰. No measurable difference in δ18O was observed between protolith magmatic (detrital) zircons and metamorphic recrystallized zircons within analytical uncertainties from the ion micro-probe measurements. This indicates that the metamorphic zircons have inherited the oxygen isotopic compositions of protolith zircons despite the HP to UHP metamorphism. According to their protolith ages from zircon U-Pb in situ dating by the same ion micro-probe, two groups of oxygen isotope composition are recognized, with one having δ18O 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 δ18O values of zircons indicate 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.

Hydrogen diffusion in clinopyroxene: dehydration experiments

Hydrogen diffusivity of one clinopyroxene megacryst from Nüshan, eastern China parallel to [001]* crystallographic direction was measured by high-temperature sequential dehydration experiments at 950üC and 850üC, which was (6.5ü1.5)×10-12(m2/s) and (1.8×0.7)×10-12(m2/s) respectively. From these results and the previous published data, it seems that the correlation between hydrogen diffusivity and Fe content suggested by Dyar et al. (1996) possibly does not exist. Clinopyroxene megacrysts from alkali basalts appear to be possible reliable samples for the study of the water evolution and hydrogen isotope compositions of the upper mantle.

Hydrogen isotope compositions of mantle-derived amphibole megacrysts from Qilin, Guangdong and its tectonic significance

Hydrogen isotope compositions of mantle-derived amphibole megacrysts from Qilin, Guangdong Province have been obtained by ion micro-probe. δD and H contents are constant both among different samples and within single sample, demonstrating that their formation condition is very stable. High δD values suggest the presence of a component recycled from crust which is possibly related to the subcluction of Pacific Plate beneath Eurasian Plate in Mesozoic.

Water in granulites: implications for the nature and evolution of the lower continental crust

Abstract The lower continental crust is one of the most important sphere-layers in the deep earth and is the direct place where the crust-mantle interactions occur. Granulites are the dominated rocks in the lower crust and have critical implications for the knowledge of the composition, nature and evolution of the deep crust fluids are important mediums influencing many geochemical, geophysical and geodynamical characteristics of the lower crust and may also play a fundamental role in the petrogenesis of granulites and the formation of the lower crusts. In this paper we review recent advances involved with the deep continental crust granulites and fluids and some longstanding debates. Combined with the Fourier-transform infrared spectroscopy (FTIR analysis performed on the mineral assemblages (cpx, opx, plag and grt) in lower crustal granulite xenoliths and terrains (exposed section) from east China, it is suggested that structural water dominated by OH in these nominally anhydrous phases may constitute t...