Keywords:U-Pb dating, K-Ar dating, Xinon isotope dating, Sedimentary rock, Labrador, Canada
The vestiges of life in Eoarchean rocks have the potential to elucidate the origin of life. We have reported carbon isotopes of graphite and carbonate in the oldest metasedimentary rocks from northern Labrador . Based on the difference of δ13C values up to 25 permil, we claimed the oldest evidence of organisms greater than 3.95 Ga in the pelitic rock. The oldest age was estimated by geological field observation in the region . The absolute age of the sample which contained biogenic graphite has not yet been determined. We present here results of conventional age determination of the pelitic rock using ion microprobe U-Pb dating of apatite and K-Ar dating of whole rock. In addition, we carry out xenon isotope dating of whole rock by a method recently developed by research group in CRPG, Nancy . These ages are not concordant each other because their closure temperatures are different, which may give a constraint on thermal and metamorphic history of the sample .
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