Abstract

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Title:: Discrimination of Ratios of Ta, Hf, Th, La, Zr and Nb for Tectonic Settings in Basalts

Author(s):: LI Yong-jun; LI Gan-yu; TONG Li-li; YANG Gao-xue; WANG Ran; 1. School of Earth Science and Resources, Chang’an University, Xi’an 710054, Shaanxi, China; 2. Key Laboratory of Western Mineral Resources and Geological Engineering of Ministry of Education, Chang’an University, Xi’an 710054, Shaanxi, China

Keywords:: basalt; Ta/Hf; Th/Ta; Th/Hf; Nb/Zr; Th/Nb; La/Nb; ratio discrimination; tectonic setting

Abstract:: Basaltic magma, which is found in whole process of plate tectonic evolution and the critical stages, is a most important tectonogeochemical indicator in all igneous rocks. Therefore, the diagrams and ratios of related elements in basalts become the first choice to investigate the igneous diagenesis and tectonic setting. Ta, Hf, Th, La, Zr and Nb, which are high-field strength elements and stronger incompatible elements, have similar geochemical properties and regular changes in basaltic diagenesis, thus, they are most frequently used in basalt genesis and discrimination diagrams of tectonic setting. Moreover, the ratios of contents between the each one of elements can better distinguish the tectonic settings of formation. Based on the double-log discrimination diagrams of Th/Hf-Ta/Hf, Th/Zr-Nb/Zr and La/Zr-Nb/Zr in basalt yielded by previous research, the ratios of Ta/Hf, Th/Ta, Th/Hf, Nb/Zr, Th/Nb, La/Nb values were proposed to distinguish the basalts in various common tectonic settings, and the ratio discrimination table was put forward. The table extremely distinguishes basalt in most common variety of tectonic environments and is a great supplement for the double-log discrimination diagrams.