| 阿尔泰南缘泥盆纪变火山岩的地球化学研究 | |
| Alternative Title | Geochemical Study on the Devonian Metavolcanic Rocks in the Southern Altay, Xinjiang, Northwest China |
| 丛峰 | |
| Subtype | 硕士 |
| 2007-05-22 | |
| Degree Grantor | 中国科学院地球化学研究所 |
| Place of Conferral | 地球化学研究所 |
| Degree Name | 硕士 |
| Keyword | 斜长角闪岩 流纹岩 岛弧 弧后盆地 俯冲带 泥盆纪 克朗盆地 麦兹盆地 阿尔泰 新疆 |
| Abstract | 新疆阿尔泰南缘泥盆纪的构造背景一直存在争论。而且，该地区系统的地球化学工作还很薄弱。对阿尔泰南缘克朗和麦兹盆地内的斜长角闪岩和变流纹岩进行的系统的岩石学和地球化学研究，为阿尔泰南缘泥盆纪的构造背景和地壳演化提供了重要证据。获得的主要结论有： （1）斜长角闪岩的原岩为拉斑玄武岩。克朗盆地样品相对于N-MORB表现为“隆起型”曲线形式，而麦兹盆地样品相对于N-MORB表现为富集大离子亲石元素和轻稀土元素，而亏损高场强元素。另外，克朗盆地样品具有较高的εNd(t)值（+6.4～+7.4），而麦兹盆地样品则具有偏低的、较宽泛的εNd(t)值（+1.7～+7.3）。地球化学和Nd同位素组成表明，麦兹盆地部分样品可能受到了不同程度的陆壳物质混染。克朗盆地地幔源区表现为亏损上地幔和富集地幔组分的相互作用，而麦兹盆地的地幔源区为受俯冲板片流体/熔体交代的地幔楔。研究表明斜长角闪岩的原岩可能形成于具有陆壳基底的岛弧/弧后盆地环境。 （2）克朗和麦兹盆地的变流纹岩具有高SiO2、较高（Na2O+K2O）、低TiO2和CaO含量，属于亚碱性系列。稀土元素配分模式表现为富集轻稀土元素、Eu负异常强烈。变流纹岩的微量元素蛛网图曲线形式类似于智利岛弧花岗岩。在相关判别图上，它们落入火山弧花岗岩区。变流纹岩的εNd(t)值为-2.9～+1.3，它们的两阶段Nd模式年龄（TDM2）为1.04～1.38Ga。其成因与中元古地壳熔融有关，同时有一定量年轻地壳物质的参与。这些结果显示，变流纹岩形成于发育俯冲带的陆缘火山弧环境。 （3）根据本次研究结果并综合区域地质资料和前人研究成果，提出了阿尔泰南缘泥盆纪的构造岩浆模式。 |
| Other Abstract | The tectonic setting during the Devonian in southern Altay, Xinjiang, northwest China is still a controversial issue. In particular, systemic geochemical investigation about this region is not well documented until now. Petrological and geochemical results are reported for the amphibolites and metarhyolites from two sedimentary- volcanic basins, Kelang and Maizi, in southern Altay. The data, combined with those in earlier studies, provide important constraints on the tectonic setting and crustal evolution of the region during the Devonian. The main conclusions are as follows. (1) The protoliths for the amphibolites are tholeiitic basalts. The basalts in Kelang basin display a “humped” pattern in which most incompatible elements are enriched compared to N-MORB on the spider diagram, while those in Maizi basin are depleted in HFSE and enriched in LILE and LREE compared to N-MORB on the spider diagram. In addition, the basalts in Kelang basin have relatively high εNd(t) values of +6.4 to +7.4, whereas those in Maizi basin have a large range of εNd(t) values of +1.7 to +7.3. Geochemical and Nd isotopic results imply that some basalts in Maizi basin have been contaminated by the materials from continental crust. Two components, depleted mantle and enriched upwelling mantle, have been involved in the source of the magma to form the basalts in Kelang basin. The basalts in Maizi basin have been originated from partial melting of a depleted mantle wedge variably matasomatised by subducted slab-derived fluid and/or melt. All these features suggest that the basalts studied were formed under tectonic setting of island-arc and back-arc basin with a continental crust basement. (2) The metarhyolites from both Kelang and Maizi basins have high SiO2, moderate (Na2O+K2O), low TiO2 and CaO contents, and belong to the sub-alkaline series. The chondrite-normalized REE patterns for these rocks display LREE enrichment and strongly negative Eu anomaly. Their trace element characteristics are similar to the Chile granite in the spider diagram. In addition, all the samples are plotted in the field defined by volcanic arc granites in the Nb-Y and Rb-(Y+Nb) discrimination diagrams. The rhyolites have moderate εNd(t) values of -2.9 to +1.3, and their TDM2 values are 1.04 to 1.38Ga. Thus, the middle Proterozoic crust in this region, together with a juvenile crust component, might have contributed to the generation of the rhyolites. All these characteristics suggest that the rhyolites were formed in a continental volcanic arc with subduction zone. (3) Combined with a number of earlier geological investigations and previous reports about the studied region, a tectonic-magmatic model for southern Altay during Devonian has been brought in this dissertation. |
| Pages | 50 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/3352 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 丛峰. 阿尔泰南缘泥盆纪变火山岩的地球化学研究[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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