Geochemical Characteristics and Tectonic Significances of the Rocks from Northeastern Jiangxi Ophiolite

Zhou Wenting; Guo Guolin; Liu Xiaodong; Wu Junjie; Fu Feng; Lin Jie

doi:10.3799/dqkx.2016.006

Abstract：The harzburgites and basalts from northeastern Jiangxi ophiolite belt have been investigated in the present study, with the aim to review Neoproterozoic tectonic environment.The results show that harzburgites are characterized by low TiO 2 (0.02%-0.37%),K2 O (0 -0.02%)and Na2 O (0.02%-0.10%),along with high MgO (40.81%-44.58%)and ignition loss (10.09%- 13.47%),suggesting that the harzburgites suffered intensive alteration.The Chondrite-normalized REE pat-terns and primitive-normalized spider diagrams indicate that the harzburgites are sourced from a depleted mantle source suffered metasomatism in subduction zones.The data suggest that the meta-basalts are mostly characterized by high SiO 2 (52.63% -52.63%),Al2 O 3 (13.07% - 1 5.27%),Na2 O (3.42% - 5.03%)and low MgO (3.66% - 6.46%),with medium TiO 2 (1.14%-2.66%)contents,indicating that they are of andesitic basalt rocks.In a Chondrite-normalized REE plots,andesitic basalt rocks are rich in LREE((La/Yb)N =1.84-2.61)with smoothly right declined trend.The trace elements are character-ized by enrichment in LILE such as Th,Ba,U and Pb and depletion in HFSE like Nb and Ti,indicating that andesitic basalts are derived from partial melting of enriched mantle wedge metasomatized by slab fluid in subduction belt,and the TNT (Ta, Nb,Ti)negative anomalies also imply those rocks may be contaminated by crustal materials.These geochemical characteristics indicate that the northeastern Jiangxi ophiolitic may have experienced multi-stage tectonic evolution.Harzburgites with LREE enrichments result from fluid metasomatism under intraoceanic subduction process in ancient Huanan ocean.Subsequently,is-land-arc tholeiite basalts and MORB-like basalts formed in the stage of back-arc basin evolution and those andesitic basalts con-taminated with crustal materials,show strong enrichment of LREE,and with high Pb and low Ti.