| Popis: |
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of calcite has been an emerging research direction in recent years that has been widely applied to various disciplines, such as dating of brittle deformation, biological biomineralization, oceanic crust alteration, and hydrocarbon migration. The method has the advantage of quickly locating regions of relatively high uranium content and radiogenic lead that avoids the time-consuming procedures traditionally required for isotope dilution methods. Herein, we show how this method is successfully applied to dating of diagenesis and hydrothermal activity in Precambrian-Phanerozoic sedimentary rocks, but with a note of caution that the susceptibility of the calcite U-Pb isotope system to fluid activities means interpretation of calcite U-Pb data and selection of calcite standard should be cautioned. We demonstrate the following case studies: LA-ICP-MS calcite U-Pb geochronology has aided in defining the Mesoproterozoic-Neoproterozoic boundary (ca. 1010 Ma) in North China Craton. It also constrains the timing of calcite infillings in the Ediacaran cap carbonate to be ca. 636 Ma, indicating an early diagenetic origin and thus confirming a methane seepage hypothesis. Two episodes of hydrothermal activity (ca. 290 Ma and ca. 250 Ma) have been recognized from the Cambrian carbonate in the Tarim region, which was induced by the Permian Tarim Large Igneous Province (LIP) and Indosinian orogeny, respectively. |
