Minerogenesis of Shilu iron ores with special reference to Sm-Nd isotope geochemical characteristics of Shilu Group bimodal volcanic rocks in Hainan Island |
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| Authors: | Fang Zhong Xu Shijin Chen Kerong Xia Bangdong Zhao Jianxin M T McCulloch |
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| Institution: | (1) Department of Earth Sciences, Nanjing University, 210008 Nanjing, China;(2) Research School of Earth Sciences, Australian National University, 2601 Canberra, ACT, Australia |
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| Abstract: | Presented in this paper are Sm-Nd isotope and major, trace and rare-earth element analyses of bimodal volcanic rocks of the
Shilu Group and other stratigraphic units in northwestern Hainan Island, South China. It is shown that there are some N-MORB-type
basalts (spilites) in the western part of the bimodal volcanic belt, in addition to some E-MORB-type and initial rift-type
tholeiites (IRT) in the middle and eastern parts. Sm-Nd model ages of these basalts range from 545 Ma to 460 Ma. The other
extremes of the bimodal volcanics are porphyritic quartz rhyolites. which are characteristic of crustal material source. Sm-Nd
model ages of the rhyolites range from 1562 Ma to 1371 Ma. The bimodal volcanic rocks are almost distributed in rifts or faulted
depressions, as well as in the Upper Paleozoic rift of Hainan Island.
Tholeiites of the Shilu Group can be compared with Cenozoic basalts in the middle and southern parts of the Red Sea Rift Belt
in petrology, elemental geochemistry and Sm-Nd isotope geology. Shilu iron ores are closely associated with N-MORB-type basalts
located in the western bimodal volcanic belt. It is very interesting to note that the Shilu Fe-Co-Cu deposit can also be compared
with Atlantis II Deep in the Red Sea Rift Belt. Therefore, the present authors believe that the Shilu deposit is a kind of
hydrothermal deposit related to ocean volcanic belt, where the geotectonic setting belongs to initial extensional rifts in
the oceanic crust. On the other hand, the largest Fe-Co-Cu ore deposit in China used to be influenced by Hercynian granites
after mineralization, as is clearly observed on both ε Nd (T)-1/Nd and ε Nd (T)-147Sm/144Nd diagrams.
This project was jointly funded by the National Natural Science Foundation of China and Research School of Earth Sciences.
Australian National University, Australia. |
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| Keywords: | bimodal volcanic rocks Sm-Nd isotopes Shilu Fe-Co-Cu deposit |
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