Abstract:
BACKGROUNDThe Changjiang uranium ore field in the southern margin of the Zhuguangshan complex pluton is a typical granite-type uranium ore field in China. Zircon U-Pb dating has been used to date ore-bearing granites. However, due to the high content of uranium in the whole rock and zircon mineral, some zircons tend to be decrystallized, which may lead to scattered zircon U-Pb data and may affect the reliability of zircon U-Pb dating. Monazite is a widespread accessory mineral in granite, and it is an ideal mineral for U-Pb dating due to its high U and Th contents (up to 10000×10-6), and low common Pb content of about 100×10-6-1000×10-6.
OBJECTIVESIn order to constrain the age of the ore-bearing granite and discuss the tectonic setting.
METHODSLA-ICP-MS U-Pb dating method was used to constrain the formation age of monazite from the Youdong and Changjiang plutons. The monazite standard materials USGS44069 and Trebilcock were selected as external standard samples and monitoring standard samples, respectively.
RESULTSThe 206Pb/238U age of monazite in the Youdong pluton is 228.0±1.5Ma (MSWD=0.82, n=23), and that of monazite in the Changjiang pluton is 156.8±1.7Ma (MSWD=0.76, n=14). These ages are consistent with the SHRIMP zircon ages of 232±4Ma and 160±2Ma, respectively, which further confirms that the Youdong pluton is the product of Late Indosinian magmatism, and the Yangtze River pluton is the product of early Yanshanian magmatism.
CONCLUSIONSThis study demonstrates that the U-Pb age of monazite in high-uranium granites can effectively constrain their formation age.
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