9:30 AM - 9:45 AM
[SMP40-02] Oxygen isotope evidence for growth of zircon in metacarbonate rocks from Sør Rondane Mountains, East Antarctica
Keywords:zircon, oxygen isotope, Antarctica
In contrast to the typical sedimentary O and C isotopic composition, low concentrations for mobile trace elements and flat REE patterns for pure metacarbonates, the impure metacarbonates have heterogeneous O and C isotopic compositions, high concentrations of mobile elements and LREE enriched patterns. These together with the presence of hydrous minerals in impure metacarbonates suggest that they have been affected extensively by fluid infiltration events. Petrographic observations revealed that zircon is abundant. Superficially the grains appear detrital, but CL imaging revealed textures consistent with metamorphic growth. SHRIMP analyses of zircons in three impure metacarbonate rocks gave well defined tight concordia U-Pb zircon ages of 545 +/- 1 Ma (n=55), 546+/- 2 Ma (n=33) and 549 +/- 2 Ma (n=58), younger than the peak metamorphism of the SRMs.
Oxygen analyses of dolomite/calcite and zircon in these rocks yielded interesting results—high d18O(SMOW) for zircon of about 23.4‰, and 24‰ in the surrounding dolomite. Similar to the previous reports on high oxygen isotope ratios for zircons in metacarbonate rocks from Sri Lanka and Myanmar , the zircons in the Sør Rondane impure metacarbonate rocks have not only re-equilibrated with the U-Pb system at c.550 Ma, but also for the oxygen isotopes with the surrounding carbonate minerals. Based on the evidence from oxygen isotopes, we suggest the possibility of oxygen isotope equilibration between zircon and carbonate and total dissolution-reprecipitation of zircons in metacarbonate rocks during the last stage of fluid infiltration coeval with the granitic activity. We also discuss the possible role of alkaline Ca-bearing fluids that might have been instrumental for the recrystallization process of zircon in metacarbonate rocks.
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