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Mesozoic shoshonitic intrusives in the Yangchun Basin, western Guangdong, and their tectonic significance:Ⅱ . Trace elements and Sr- Nd isotopes

LI Xian- hua1, ZHOU Han- wen1, LIU Ying1, LEE Chi- yu2, CHEN Cheng- hong2, YU Jin- sheng1, GUI Xun- tang1 ( 1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 2. Department of Geology, National Taiwan Unive  
Trace elements and Sr- Nd isotopic data are presented for the Mesozoic intrusives in the Yangchun Basin, western Guangdong. The Mashan monzo- diorites are characterized by strong enrichment of K, Sr and LREE, and nearly chondritic isotopic compositions with (87Sr/86Sr)i≈ 0.704 6 andε Nd(t)≈ 1. The Gangwei- Lunshui quartz monzonites and granodiorites are moderately enriched in K, Sr, Rb and LREE, but strongly enriched in Th. They have enriched Sr- Nd isotopic compositions with (87Sr/86Sr)i≈ 0.706 3 andε Nd(t)≈- 2. The Shilu granodiorites are enriched in Sr, but less enriched in K, Rb, Th and LREE. They are characterized by more radiogenic Sr- Nd isotopic compositions with (87Sr/86Sr)i = 0.708 4~ 0.708 9 andε Nd(t)≈- 6. It is concluded, in terms of geochemical and Sr- Nd isotopic features, that the Mashan monzo- diorites were generated from a metasomatism mantle source strongly enriched in LILE and LREE, while the Gangwei- Lunshui plutons were derived from a metasomatism mantle source with more radiogenic Sr- Nd isotopic compositions followed by extensive crystal fractionation. The Shilu pluton was formed by re- melting of pre- existing underplating mafic rocks at the lower crustal level. The secular variation of magma compositions was mostly attributed to the upwelling of asthenosphere and extension of overlying lithosphere in the Nanling Region during the early Jurassic to early Cretaceous.
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