Four potential carbonite reference materials for in situ U-Pb geochronology

Carbonite forms in a wide variety of geological environments as both a primary and secondary mineral phase and may contain sufficient U for U-Pb geochronology. The limited availability of well-characterized calcite reference materials, however, has impeded its broader application in microanalysis, in particular for the low-U (<0.1 mg g^-1) calcite and dolomite. In this study, four potential carbonite reference materials (JCL03, THMT, TL-2, TL10-7) were primary characterized for in situ U-Pb geochronology. JCL03 and THMT are low-Mg calcite with Mg concentrations of ~0.35 wt.%, ~0.39 wt.%, respectively. TL-2, TL10-7 are the dolomite with Mg concentrations of ~21.5 wt.%, ~17.4 wt.%, respectively. JCL03 and THMT were characterized as low-U calcite with U concentrations of ~0.036 mg·g^-1, ~0.021 mg·g^-1, respectively. TL-2 and TL10-7 have U concentrations of ~2.3 mg·g^-1, ~1.5 mg·g^-1, respectively. JCL03 and THMT have homogeneity ages, while TL-2 and TL10-7 shows multiple dolomitization process. Multiple LA-ICP-MS analytical sessions yielded ages of 428.7 ± 5.2 Ma, 286.3 ± 7.1 Ma, 233.8 ± 4.4 Ma and 180.0 ± 6.3 Ma for JCL03, THMT, TL-2 and TL10-7, respectively. These four carbonaite are the useful additions to the widely distributed WC-1 reference material for LA-ICP-MS U-Pb geochronology.