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Trace Element Geochemistry and Tectonic Setting for Proterozoic Metavolcanics of the Mamianshan Group in the Central Part of Fujian Province

ZHOU Li-ya, WANG He-nian, SUN Cheng-yuan   

  1. Department of Earth Sciences and State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China
  • Received:2001-06-20 Revised:2001-06-20 Online:2001-06-20 Published:2001-06-20

Abstract: The Proterceoic metavolcanies of th Mamianshan Group in the central part of Fujian province are distributed along the Zhenghe--Dapu fault belt. Based on major element geochemical signatures, the volcanic rocks in this area are “bi-modal”. The chondrite-normalized REE pattern s of greenschists and leptynite are enriched in LREE with no or small Eu anomaly. Their MORB normalized spiderdiagrams and trace element tectonic discrimination diagrams have the WPB (within-plate basalt) features, showing continental rifting character Plagioclastic amphibolites have no obvious Eu negative anomaly. Their MORB normalized spiderdiagrams have a Rh-Ba enrichment and a Nb-Ta depletion These are typical of transitional calc-alkaline basalts and T-type MORB. Their primary mantle normalized and Nb-normalized spiderdiagrams indicate their derivation from a depleted mantle or contamination by the continental crusts. It is considered that this area was a failed rift There was an evolution from a continental rifting background to an initial oceanic basin environment, Soon after,convergence and subduction took place