峨眉山大火成岩省二滩玄武岩地球化学及源区特征

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	峨眉山大火成岩省二滩玄武岩地球化学及源区特征
其他题名	Geochemistry and Signature of Source for the Ertan Basalts in Emeishan Large Igneous Province, China
	严再飞
	2007-05-25
学位授予单位	中国科学院地球化学研究所
学位授予地点	地球化学研究所
学位名称	博士
关键词	高钛玄武岩地球化学源区特征二滩地区
摘要	大陆溢流玄武岩根据TiO2含量可划分为高钛玄武岩和低钛玄武岩，这两种不同类型的玄武岩往往有不同的空间分布特征，也具有不同的成因指示意义。峨眉山玄武岩也有高、低钛之分，且其空间分布存在明显差异。然而，在以往的峨眉山玄武岩的研究中只对高、低钛玄武岩进行对比研究，而单独对同一类型玄武岩的研究甚少，尤其是对物质来源的研究。在本论文中，作者以峨眉山大火成岩省中部二滩地区高钛玄武岩为研究对象，通过主量元素、微量元素和Sr－Nd－Pb同位素对其地球化学、岩浆过程以及物质来源进行了探讨，得出以下初步认识和结论： ⑴ 二滩高钛玄武岩可划分出Group I和Group II两种岩石类型。Group I中Sr和Zr显示明显负异常，而Group II无Sr和Zr异常。此两种类型岩石的Sr－Nd－Pb同位素地球化学特征也较为不同。 ⑵ 二滩高钛玄武岩为板内构造环境，Group I和Group II显示出碱性或钙碱性岩特征。 ⑶ Group I和Group II具有不同的熔体形成熔融程度，Group I相对低(0～3.5％)，Group II相对高(4.0～8.0％)。不同的部分熔融程度导致了控制矿物相的不同。 ⑷ Group I和Group II岩浆分别经历了不同的结晶分异过程。Group I主要显示出斜长石结晶分异趋势，Group II则主要显示出橄榄石结晶分异趋势。 ⑸ 微量不相容元素和Sr－Nd－Pb同位素特征表明，Group I和Group II均源自深部富集地幔，具有不同的物质来源，且与地幔柱有成因上的联系。以上特征表明，二滩玄武岩与深源地幔柱有成因上的联系。这可能是深部地幔柱(来自核－幔边界或下地幔)上升过程中在不同深度携带了不同物质，这些物质发生部分熔融，从而导致了Group I和Group II的明显差异。其充分说明，二滩高钛玄武岩的物源是不均一的，反映了源区的不均一性特征。
其他摘要	Continental flood basalts can be subdivided into high-Ti basalts and low-Ti basalts based on the content of TiO2. High- and low-Ti basalts tend to significantly display different spatial features, which suggests that the rocks have different petrogenesis. Emeishan flood basalts can be also subdivided into high-Ti basalts and low-Ti basalts, and their spatial distributions are different. However, most of the researches of Emeishan flood basalts are only related to the difference of the two type rocks. Studies focused on the same type basalts are few, and the other difference of geochemical features in the same Ti-type rocks is possibly ignored. In the dissertation, author will make some discussions about geochemical characteristics, processes of magmatic evolution and source of materials for the Ertan high-Ti basalts from the centre of Emeishan large igneous provinces, by means of major and trace elements and Sr-Nd-Pb isotopes. According to the discussions, some meaning conclusions are obtained: ⑴ Ertan high-Ti basalts can be subdivided into Group I and Group II. Group I displays strikingly negative Sr and Zr anomalies. Geochemical characteristics of Sr – Nd - Pb isotope for Group I and Group II are also distinct. ⑵ Ertan high-Ti basalts (Group I and Group II) belong to withinplate alkaline basalts. ⑶ Degrees of partial melting of Group I and Group II are different. The former has degrees of partial melting of ﹤3.5%, whereas the latter are higher with degrees of partial melting of 4.0~8.0%. ⑷ Group I and Group II have undergone different processes of fractional crystallization. Group I displays mainly trend of fractional crystallization of plagioclase, whereas the fractional crystallization of olivine play an important role for Group II. ⑸ Geochemical features of trace elements and Sr-Nd-Pb isotopes indicate that both of Group I and Group II were derived from deep enriched mantle and were produced by different materials melting. Their petrogenesis are related to mantle plumes. The author suggests that sources of Ertan high-Ti basalts are heterogeneous. Because when plume rose and carried different materials at different mantle depth, these materials underwent distinct degrees of partial melting, which resulted in the differences between Group I and Group II.
页数	115
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3294
专题	研究生_研究生_学位论文
推荐引用方式 GB/T 7714	严再飞. 峨眉山大火成岩省二滩玄武岩地球化学及源区特征[D]. 地球化学研究所. 中国科学院地球化学研究所,2007.

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