中国科学院南京地质古生物研究所机构知识库

Acquiring the absolute timing for hydrothermal carbonate is a precondition to probing into the basinal-scale, tectonically-driven fluid circulation processes. This study provides an absolute LA-ICP-MS age of ca. 290 Ma from calcite megacrysts within the early Paleozoic dolostones of the Tarim Basin, which corresponds to the timing of Early Permian Large Igneous Province (LIP), which we suggest is genetically linked. The ca. 290 Ma calcite underwent subsequent partial recrystallization or dissolution-precipitation forming younger calcite ages of ca. 250 Ma, consistent with the timing of the Indosinian orogeny. Th/U ratios are demonstrated to be an effective criterion to differentiate domains of primary (ca. 290 Ma) and alteration (ca. 250 Ma) calcite, with the former displaying lower Th/U ratios (0.005-0.05) in comparison to the latter that shows relatively higher Th/U ratios (>0.15). Such differential Th/U ratios may suggest differential involvement of fluids from both within the host dolostones and from magmatic/hydrothermal fluids. This study also demonstrates that Si and Pb prefer-entially enter into the crystal lattice of calcite to replace Ca via charge balance substitution mechanism. In contrast, U, Sr, Y, La and Ce are mainly concentrated around cleavage planes, cracks and veinlets within calcite.