广东三水盆地始新世火山岩地球化学特征

摘要: 广东三水盆地的演化伴随着强烈的火山活动.为研究三水盆地各类岩石之间的演化关系, 对在盆地内的玄武岩、粗面岩和流纹岩样品进行常量、微量元素地球化学分析.对样品的地球化学投图表明: 玄武岩样品表现为轻稀土富集的板内玄武岩稀土配分模式, 而其微量元素也具有Nb、Ti富集、Sr弱亏损的特征, 由部分熔融产生；粗面岩与流纹岩样品稀土与微量元素配分模式相似, 两类岩石均经历以斜长石为主的分离结晶过程.华南陆缘在始新世早期处于与红海相似的大陆裂谷环境, 喷发来源于深部软流圈地幔的岩浆, 但在42 Ma之后, 火山活动因区域挤压作用而停止.其后的南海扩张可能是两种作用的叠加影响的结果.
- 三水盆地 /
- 火山岩 /
- 结晶分离 /
- 部分熔融 /
- 地球化学
Abstract: Guangdong Sanshui basin developed with extreme volcanic activities. Eruptions from Paleocene to Eocene were concentrated on Xinzhuang, Buxin, Baoyue and Huayong formations. For research of the relationship between various kind of rocks, geochemistry analyses such as multi-element and rare-earth element determination were launched on basalt, trachyte and rhyolite samples from the research area. Geochemistry diagrams suggest that: REE distribution of basalt followed as mid-plate alkali basalt mode, while their trace element spider diagrams act as continental alkali basalt with Nb, Ti rich and Sr loss. REE distributions of trachyte and rhyolite are similar, which indicate the same crystallization separation process. S-B diagram and pearce diagram show that: granites were partially melted from source region, while trachyte in ZMY and rhyolite in LBS originated from the same source region, and occurred with the process of crystallization separation with plagioclase adventage. Southeast China performed continental rift environment as Red Sea, and its magma may came from lithospheric mantle source. The magmatic activities suspended after 42 Ma because of regional extrusion, while breaking up of South China Sea (SCS) later may be a mixed effect of two functions.
- Sanshui basin /
- volcanic rocks /
- crystallization separation /
- partial melting /
- geochemistry

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图 1 三水盆地采样点分布

Fig. 1. Sampling locations in Sanshui basin

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图 2 三水盆地火山岩与地层(参考李大明等, 1989；张显球等, 1993；董月霞等, 2006)

Fig. 2. Volcanic rocks and stratigraphy of Sanshui basin

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图 3 WJG玄武岩橄榄石斑晶(a)和ZD玄武岩(b)镜下照片(单偏光)

Fig. 3. Photos of WJG basalt (a) and ZD basalt (b) under microscope

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图 4 ZMY粗面岩(a)和LBS流纹岩(b)镜下照片(单偏光)

Fig. 4. Photos of ZMY trachyte (a) and LBS rhyolite (b) under microscope

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图 5 火山岩样品TAS图解

Fig. 5. TAS diagram for volcanic rock samples

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图 6 三水盆地玄武岩稀土元素配分曲线(a)与微量元素配分模式图(b)(标准化数据来源于Sun and McDonough, 1989)

Fig. 6. REE distribution and trace elements spidergram for basalts in Sanshui basin

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图 7 三水盆地粗面岩稀土元素配分曲线(a)与微量元素配分模式图(b)(标准化数据来源于Sun and McDonough, 1989)

Fig. 7. REE distribution and trace elements spidergram for trachytes in Sanshui basin

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图 8 三水盆地流纹岩稀土元素配分曲线(a)与微量元素配分模式图(b)(标准化数据来源于Sun and McDonough, 1989)

Fig. 8. REE distribution and trace elements spidergram for rhyolites in Sanshui basin

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图 9 三水盆地火山岩La/Sm vs La比值(a)和2(Fe+Mg)/P vs Si/P(b)图解(虚线表示结晶分离线, 实线表示部分熔融线)

Fig. 9. Binary variation diagram of La/Sm vs. La (a) and 2 (Fe+Mg)/P vs. Si/P (b) of volcanic rocks in Sanshui basin

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图 10 三水盆地火山岩La/Yb vs. Nb/La比值(参考Moustafa and Ahmed, 2012；下地壳平均值来源于Chen and Arculus, 1995；区分软流圈地幔和岩石圈地幔的虚线来源于Smith et al., 1999)

Fig. 10. Binary variation of La/Yb vs. Nb/La for volcanic rocks in Sanshui basin

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图 11 三水盆地火山岩Sr-Nd同位素比值(数据来源于朱炳权等, 1991；图中数字表示K-Ar测年得出的年龄)

Fig. 11. ¹⁴³Nd/¹⁴⁴Nd vs. ⁸⁷Sr/⁸⁶Sr for volcanic rocks from Sanshui basin

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