We investigated the applicability of micro-Raman spectroscopy for determining carbon isotopic compositions (<sup>13</sup>C/<sup>12</sup>C) of minute CO<sub>2</sub> fluid inclusions in minerals. This method is nondestructive and has sufficiently high spatial resolution (1 μm) to measure each fluid inclusion independently. Raman spectra of CO<sub>2</sub> fluid have <sup>12</sup>CO<sub>2</sub>-origin peaks at about 1285 cm<sup>−1</sup> and 1389 cm<sup>−1</sup> (V<sub>−</sub><sup>[12]</sup> and V<sub>+</sub><sup>[12]</sup>) and a <sup>13</sup>CO<sub>2</sub>-origin peak at about 1370 cm<sup>−1</sup> (V<sub>+</sub><sup>[13]</sup>). The relationship between carbon isotopic compositions and peak intensity ratios of V<sub>+</sub><sup>[12]</sup> and V<sub>+</sub><sup>[13]</sup> was calibrated. Considering several factors affecting the peak intensity ratio, the error in obtained carbon isotopic composition was 2% (20%). The reproducibility of the intensity ratio under the same experimental environment was 0.5% (5%). Within these error values, we can distinguish biogenic CO<sub>2</sub> from abiogenic CO<sub>2</sub>.

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