The Yanshanian plutons that occur extensively in Tongling, Anhui Province are essential to the genesis of world-class strata-bound ore deposits. We have sampled plutons ranging from gabbroic diorite to granodiorite in the Shizishan orefield to conduct systematical studies on geochronology with LA ICPMS. The magmatic zircons from the Nanhongchong granodiorite yield an age of 141.2 ± 1.6 Ma. A number of inherited zircons (or inherited cores) have been found in Baimangshan gabbroic diorite as well as Qingshanjiao quartz diorite. In order to reveal geological significance of complicated ages, the age data for these zircons and age data for adjacent quartz diorites are plotted on the 207Pb/235U and 206Pb/238U diagram, from which two groups of age data (one group ranging from Archean to paleo Proterozoic, and the other from middle Paleozoic to Early Cretaceous), do not constitute a straight line, with lower intercepts at 1785-69 +64 and 141.9 ± 8.1 Ma and upper intercepts at 2795- 80+91 Ma, 1290 ± 12 Ma respectively. Of the four ages, the second (141.9±8.1 Ma) is consistent to the times of Yanshanian magma activity and the other three are the old intercept age, close to the three statistical age peaks (2.7Ga, 1.9Ga and 1.2Ga) for juvenile continental crust, implying a possibility of supplement of crustral materials. ZrSiO2 correlation diagram, and the presence of inherited zircons indicate that zirconium reached to saturation in the magma; consequently, the dominant magmatic temperatures were close to the calculated temperatures for saturated zirconium (for gabbroic diorite. 650-700°C, quartz diorite. 750-790°C nd granodiorite: 750-760°C), indicating that the magma temperature in Shizishan was relatively lower.
|Number of pages||7|
|Journal||Acta Geologica Sinica|
|Publication status||Published - 15 Apr 2008|
- Anhui Province
- Inherited zircons
- Shizishan ore field
- U-Pb geochronology