Geochemical Characteristics of the Late Paleozoic Diabase Dyke Swarms of Chang maohezi from Western Liaoning, Northeast China
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摘要: 根据全岩K-Ar年龄(287.5~243.6Ma), 辽西朝阳长茂河子辉绿岩墙群形成于晚古生代.这些辉绿岩分为低铁钛辉绿岩和高铁钛辉绿岩2种, 以低铁钛辉绿岩为主.低铁钛辉绿岩以低TiO2(< 2%)、FeOt(12.39%~15.33%)、V(227~335μg/g)、Sc(24~36μg/g) 含量和高的SiO2 (45.61%~47.72%)、Al2O3(12.51%~16.71%)、MgO(6.66%~9.31%)、K2O(0.57%~2.39%)、Cr(107~177μg/g)和Ni(96~235μg/g) 含量, 以及低Ti/Y(327~496)和Ti/Zr (69~114) 比值为特征, 类似于大陆拉斑玄武质岩石; 高铁钛辉绿岩以高的TiO2 (5%~6%)、FeOt(22.13%~22.16%)、V(850~859μg/g)、Sc(51~52μg/g) 含量和低的SiO2 (42.88%~44.90%)、Al2O3(11.53%~11.57%)、MgO (5.15%~5.29%, Mg#=0.32)、K2O (0.48%~0.51%)、Cr(< 2μg/g)和Ni(< 30μg/g) 含量及高的Ti/Y(1046~1106)、Ti/Zr(250~263) 比值为特征, 类似于Skaergaard侵入体.这些辉绿岩相对富集Rb、Th、U、Pb、Ti和轻稀土元素, 而相对亏损Ba、Sr、P和Nb、Ta.εNd(t) (-6.43~-4.12)、εSr(t) (42.94~64.19) 显示Sr-Nd同位素组成较为均匀, 并反映它们源于富集岩石圈地幔.认为长茂河子辉绿岩形成于富集岩石圈地幔的部分熔融, 经历了岩浆结晶分异与地壳混染作用.高铁钛辉绿岩和低高铁钛辉绿岩形成环境不同, 前者形成于相对低氧逸度或相对封闭的结晶环境中.Abstract: Based on K-Ar isotopic ages (287.5-243.6 Ma), diabase dyke swarms of the Changmaohezi from western Liaoning, Northeast China, formed in the Late Paleozoic. These diabases can be divided into low Ti-Fe diabase and high Ti-Fe diabase. The low Ti-Fe diabases are characterized by low TiO2 (< 2%), FeOt (12.39%-15.33%), V (227-335 μg/g), Sc (24-36 μg/g) and high SiO2 (45.61%-47.72%), Al2O3 (12.51%-16.71%), MgO (6.66%-9.31%), K2O (0.57%-2.39%), Cr (107-177 μg/g), Ni (96-235 μg/g), and low Ti/Y (327-496), Ti/Zr (69-114), which are similar to continental flood basalts. The high Ti-Fe diabases are characterized by high TiO2 (5%-6%), FeOt (22.13%-22.16%), V(850-859 μg/g), Sc (51-52 μg/g), and low SiO2 (42.88%-44.90%), Al2O3 (11.53%-11.57%), MgO (5.15%- 5.29%), K2O (0.48%-0.51%), Cr (< 2 μg/g), Ni (< 30 μg/g), and high Ti/Y (1 046-1 106), Ti/Zr (250-263), which are similar to the Skaergaard intrusion. All these rocks are enriched in Rb, Th, U, Pb, Ti, and light REE, and depleted in Ba, Sr, P, Nb and Ta. They have well-evolved Nd and Sr isotope compositions with εNd(t) =-6.43 to -4.12 and εSr(t) =42.94-64.19. The diabases were probably derived from the enriched lithospheric mantle and underwent fractional crystallization and crust assimilation. The high Ti-Fe diabases and the low Ti-Fe diabases are from different crystal conditions, the former in a closed system or a relatively oxidized state.
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Key words:
- low Ti-Fe diabase /
- lithosphere mantle /
- Late Paleozoic /
- Changmaohezi /
- western Liaoning Province
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图 3 稀土元素配分曲线型式和微量元素蛛网图(标准值采用Sun and McDonough, 1989推荐值, 图例同图 2)
Fig. 3. Chondrite-normalized REE distribution patterns and primary mantle-normalized incompatible element patterns
图 4 辉绿岩SiO2与主微量元素相关图(图中符号同图 2)
Fig. 4. SiO2 vs. major and trace element diagrams
图 5 Zr/Y-Zr关系图解(图例同图 2)
Fig. 5. Zr/Y vs. Zr diagram
表 1 辉绿岩K-Ar年龄分析结果
Table 1. K-Ar ages of diabases
表 2 辉绿岩主量和微量元素分析结果
Table 2. Major and trace element analysis of diabases
表 3 辉绿岩Nd、Sr同位素分析结果
Table 3. Nd and Sr isotopic data of diabases
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