Geochemical Characteristics and Tectonic Significance of the Neoproterozoic Amphibolites from Datian Area, Panzhihua City
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摘要: 对攀枝花大田地区斜长角闪岩进行了系统的主微量地球化学特征、锆石LA-ICP-MS U-Pb年代学以及Lu-Hf同位素特征研究.结果表明:斜长角闪岩的SiO2含量为47.88%~50.05%,原岩为亚碱性-碱性玄武岩.斜长角闪岩稀土总量(ΣREE)较高,稀土元素配分模式为轻稀土富集的右倾型,与洋岛玄武岩相似.微量元素原始地幔标准化蛛网图为"隆起"型,与板内玄武岩特征类似.Zr/Nb、Hf/Th等比值均表明其与板内玄武岩类似,而与岛弧玄武岩具有明显的差异.锆石U-Pb定年结果表明岩浆结晶年龄为816.0~833.6 Ma,同期岩浆结晶锆石的εHf(t)值在-6.8~+3.8之间,其岩浆源区为与OIB类似的富集地幔源区且受到了地壳物质的混染.综合上述资料,认为其形成于Rodinia超级地幔柱活动导致的大陆裂谷环境.
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关键词:
- 斜长角闪岩 /
- 地球化学 /
- 锆石U-Pb定年和Lu-Hf同位素 /
- 构造意义 /
- 大田地区
Abstract: The amphibolites are widespread in the Kangding complex in Miyi-Panzhihua area,south Sichuan. The petrological,geochemical,zircon U-Pb dating and Lu-Hf isotope characteristics from the amphibolites in the Datian area have been studied in this work. The results show that:(1) The SiO2 contents range from 47.88% to 50.05%,falling into the range of subalkaline-alkaline basalt in the discrimination diagrams of TAS and Zr/TiO2-Nb/Y; (2) The total REE contents (ΣREE) range from 121.59×10-6 to 230.43×10-6,which is characterized by LREE-rich pattern((La/Yb)N=2.73-7.52) and is similar to oceanic island basalt; (3) The primitive mantle-normalized trace elements spider diagram is similar to that of intra-plate basalt. (4) The ratios of Zr/Nb,Hf/Th indicate that they are similar to intraplate basalt,while have obvious differences with arc basalt; (5) Zircon LA-ICP-MS U-Pb dating demonstrates that the crystallization age of amphiboliteis is 816.0-833.6 Ma,which is contemporary to the large-scale Neoproterozoic mafic magmatism in the west margin of Yangtze block (860-750 Ma),the εHf(t) of zircons is -6.8~+3.8,indicating that the basalts were derived from enriched mantle and has been contaminated by crustal materials. Thus,the amphibolites may formed in the continental rift environment caused by the breakup of Rodinia supercontinent.-
Key words:
- amphibolites /
- geochemistry /
- zircon U-Pb data and Lu-Hf isotope /
- tectonic significance /
- Datian area
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图 3 大田地区斜长角闪岩Zr/TiO2-Nb/Y图解
Fig. 3. Zr/TiO2 vs. Nb/Y diagrams of the amphibolites in Datian area
图 4 大田地区斜长角闪岩球粒陨石标准化稀土元素配分模式图(a)和微量元素原始地幔标准化蛛网图(b)
球粒陨石和原始地幔标准化值据Sun and McDonough(1989);俯冲带玄武岩范围据Tatsumi and Eggins(1995)
Fig. 4. Chondrite-normalized REE patterns (a) and primitive mantle-normalized trace elements spider diagram (b) for the amphibolites in Datian are
图 9 大田地区斜长角闪岩(176Hf/177Hf)i与锆石结晶年龄图解(a)和εHf(t)与锆石结晶年龄图解(b)
a. 176Lu/177Hf=0.015据Griffin et al.(2002); b. Hf亏损地幔演化线据Dhuime(2011)
Fig. 9. Composite plot of (176Hf/177Hf)i vs. U-Pb age (a) and εHf(t) values vs. U-Pb age (b) of zircons for the rocks form Datian area
图 10 大田地区斜长角闪岩的Zr/Nb-Ce/Y图解(a)和Nb/Yb-Th/Yb图解(b)
OIB-type.洋岛型; E-MORB-type.富集型洋中脊型; N-MORB-type.正常洋中脊型; SSZ-type.俯冲带型;据Goncuoglu et al.(2010)
Fig. 10. Zr/Nb-Ce/Y diagram (a) and Nb/Yb-Th/Yb diagram (b) for the amphibolites in Datian area
图 11 大田地区斜长角闪岩的Zr/Y-Zr图解(a)和Th-Hf/3-Nb/16图解(b)
WPB.板内玄武岩; MORB.洋脊玄武岩; IAB.火山弧玄武岩; MORB.洋脊玄武岩; OIB.洋岛玄武岩; IAB.火山弧玄武岩; a.据Pearce(1982);b.据第鹏飞等(2017)
Fig. 11. Zr/Y-Zr diagram (a) and Th-Hf/3-Nb/16 diagram (b) for the amphibolites in Datian area
图 12 大田地区斜长角闪岩的La/10-Y/15-Nb/8图解(a)和Ti/V图解(b)
图a中:1.火山弧玄武岩; 2.大陆玄武岩; 3.大洋玄武岩; 1A.钙碱性玄武岩; 1C.火山弧拉斑玄武岩; 1B. 1A区和1B区间的重叠区域; 2A.大陆玄武岩; 2B.弧后盆地大陆玄武岩; 3A.大陆内裂谷区的碱性玄武岩; 3B及3C区为富集型洋脊玄武岩(3B区为富集区, 3C区为弱富集区); 3D.正常洋脊玄武岩; a.据Pearce(1982);b.据Shervais(1982)
Fig. 12. La/10-Y/15-Nb/8 diagram (a) and Ti/V diagram (b) for the amphibolites in Datian area
图 13 大田地区斜长角闪岩Th/Hf-Ta/Hf(a)和Th/Zr-Nb/Zr(b)构造环境判别图解
a.据汪云亮等(2001); b.据孙书勤等(2003)
Fig. 13. Th/Hf vs. Ta/Hf (a) and Th/Zr vs. Nb/Zr (b) tectonic setting discrimination diagrams for the amphibolites in Datian area
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