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J4 ›› 2010, Vol. 16 ›› Issue (3): 294-308.

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Zircon U-Pb Dating and Hf Isotopic Compositions of Porphyrites from
the Ningwu Basin and Their Geological Implications

 HU Jin-ping, JIANG Shao-yong   

  1. tate Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China
  • Received:2009-06-23 Revised:2010-03-15 Online:2010-09-20 Published:2010-09-20


Ningwu volcanic basin is one of the most important basins related to mineral deposits in middle-lower reaches of the
Yangtze River belt. Four volcanic units occur in the basin, in an ascending order, the Longwangshan Formation, the Dawangshan
Formation, the Gushan Foramtion and the Niangniangshan Formation, with some high-level sub-volcanic igneous rocks intruding
them. Detailed zircon U-Pb dating and Hf  isotopic composition measurement were performed on  the host  rocks  (gabbro-diorite
porphyrites) of  the Washan  iron deposit. The zircon U-Pb ages of  three samples are  (123±1) Ma,  (127±3) Ma and  (125±2)
Ma, respectively.Together with previously published precise zircon U-Pb dating results for volcanic rocks (127 to 131Ma), these
results have placed a better constraint on  the magmatic and mineralization activity duration of  the Ningwu volcanic basin. The
zircons  from  the Ningwu porphyrites have εHf
( t ) values  from -6.3  to -8.6. Together with other available geochemical data,  the
Hf  isotope data  indicate  that  the Ningwu porphyrites may have derived  from upwelling depleted asthenospheric mantle mixed
with enriched mantle and crust, which was controlled by the extensive lithosphere extension at around 125 Ma. The lower εHf(t)
values and slightly younger ages of  the gabbro-diorite porphyrites  than  their hosting volcanic  rocks may  indicate more crust
material involvement in the porphyrite petrogenesis.

Key words: :Ningwu volcanic basin, grabbro-diorite porphyrite, zircon U-Pb age, Hf isotopes

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