IOCAS-IR  > 海洋地质与环境重点实验室
玻安岩岩浆源区不同富集组分特征与俯冲物质贡献
黄子航
Subtype硕士
Thesis Advisor肖媛媛
2022-05-20
Degree Grantor中国科学院大学
Place of Conferral中国科学院海洋研究所
Degree Name理学硕士
Keyword玻安岩 俯冲带富水流体 含水熔体 俯冲板块 俯冲带岩浆作用
Abstract

  玻安岩为一类具有特殊地球化学性质的岩石,具有高SiO2>52 wt. %),高MgO>8 wt. %),低TiO2<0.5 wt. %)等特征,前人认为它的形成主要归因于在俯冲起始阶段的大洋板块所释放的流体导致亏损程度较高的难熔地幔楔发生熔融,虽然普遍认为俯冲物质对地幔源区具有重要贡献,但玻安岩中不相容元素的不同富集程度反映了复杂的俯冲板片流体的物理化学性质和对玻安岩形成造成的不同影响,所以研究玻安岩的成因对于深入理解板块俯冲初始的过程等地球动力学问题具有重要意义。本研究除分析测试了塞浦路斯Troodos蛇绿岩和中国祁连造山带大岔大坂地区中的玻安岩外,还在数据库中收集了地球上不同地区代表性玻安岩的化学成分数据。因为ZrSm在溶液中均较难以迁移,并且对于Sm而言,Zr更加不相容,所以本次研究中将使用Zr/Sm比值来理解玻安岩的不同富集组分特征,并确定加入玻安岩源区的俯冲流体的物理化学性质(富水流体或含水熔体)。

  根据(Zr/Sm)PM比值,将本次研究中的玻安岩分为两种情况:1)低(Zr/Sm)PM<1)的低锆玻安岩,来自于塞浦路斯Troodos、祁连大岔大坂、蒙古和阿曼地区;2)具有高(Zr/Sm)PM>1)的高锆玻安岩,即来自伊豆-小笠原-马里亚纳、新喀里多尼亚和巴布亚新几内亚地区。对于高锆玻安岩,其CaO/Al2O3Ti/Zr比值较低,Zr/Sm比值较高,这与俯冲板片的含水熔体向高亏损难熔地幔源区的加入有关。结合玻安质岩浆形成所需的温压条件和不同构造环境,认为高锆玻安岩形成于俯冲起始阶段或由弧后扩张中心转变而成的俯冲带中。低锆玻安岩中CaO/Al2O3Ti/Zr含量较高,流体活动性元素含量较高,反映地幔源区亏损程度较低,加入玻安岩地幔源区的俯冲组分以富水溶液为主,没有高Zr含水熔体的贡献。结合前人提出的潜在构造环境,低锆玻安岩可能形成于成熟弧或弧后环境,俯冲带形成过程中,由于板片后撤等作用,导致地幔楔温度相对较高,提供了玻安质岩浆形成的高温。因此,不同的构造背景可能为玻安岩岩浆的地幔源区提供了不同的俯冲板片流体贡献。这为今后利用玻安岩的地球化学特征示踪俯冲板片流体贡献、推断构造环境提供了依据。

Other Abstract

Boninites are high-Si (> 52 wt.%), high-Mg (> 8 wt.%), and low-Ti (< 0.5 wt.%) rocks, the formation of which is attributed to the melting of highly depleted refractory mantle with the addition of fluids during subduction initiation. Although the commonly accepted significant contribution of subducted materials for the mantle source, various extents of enrichment of incompatible elements in boninite reflect that the physicochemical properties of fluids from the subducting slab and the geochemical processes for the boninite formation are complicated. In addition to our data for boninite from Troodos ophiolite (Cyprus) and Qilian orogenic belt (China), this study compiled chemical compositional data of boninite from different representative suites on the Earth. Because of the similar immobility of Zr and Sm and relatively more incompatibility of Zr than Sm, we use Zr/Sm ratio to understand the characteristics of different enrichment components in boninite and identify the variable physicochemical nature of fluids (i.e., aqueous fluids or hydrous melts) released from the subducting slab for the formation of boninite in this study.

Based on the (Zr/Sm)PM ratio, all the compiled boninite can be classified into two groups: (1) low-Zr boninite with low (Zr/Sm)PM (< 1), i.e., from Troodos, Qilian, Mongolia and Oman; (2) high-Zr boninite with high (Zr/Sm)PM (> 1), i.e., from Izu-Bonin-Mariana, New Caledonia and Papua New Guinea. For high-Zr boninite, it has lower CaO/Al2O3 and Ti/Zr ratios and higher Zr/Sm ratios, which are thus attributed to the addition of hydrous melts from the subducting slab into the highly depleted refractory mantle source. Together with previously proposed potential tectonic settings for different boninites and the temperature/pressure of boninitic magma all indicate that high Zr-boninites are formed in the subduction initiation or the subduction initiation from spreading center. The high content of CaO/Al2O3 and Ti/Zr and the high content of fluid-mobile trace elements in the low Zr boninites indicate that the depletion degree of the mantle source is relatively lower. The subduction components added to the boninite magma source are mainly rich aqueous solution, without the contribution of high Zr hydrous melt. Low-Zr boninite may be formed in a mature arc or back-arc environment. Therefore, different tectonic settings may have provided variable contributions of fluids derived from the subducting slab in the mantle source of boninite magmas, which in turn may help to infer tectonic settings in future.

Language中文
Table of Contents

 

第1章  引言... 1

1.1 选题背景及意义... 1

1.2 国内外研究现状... 2

1.3 拟解决的科学问题与研究方法... 4

1.4 完成工作量... 5

第2章 区域地质背景... 7

2.1 北祁连造山带... 7

2.2 塞浦路斯蛇绿岩带... 8

第3章 样品处理及分析测试方法... 11

3.1 岩石学特征和前处理方法... 11

3.2 全岩主量、微量元素... 12

3.3 Sr同位素... 15

3.4 原位地球化学... 16

第4章 地球化学分析结果... 17

4.1主量元素... 17

4.2 微量元素... 20

4.2 Sr同位素... 23

4.3 矿物化学分析结果... 24

第5章 讨论... 29

5.1 玻安岩的进一步分类... 33

5.2 不同类型流体的贡献... 32

5.2.1高锆玻安岩与含水熔体... 34

5.2.2低锆玻安岩与富水溶液... 36

5.3 玻安岩形成的温压条件与俯冲组分的关系... 37

5.4 玻安岩形成的可能原因... 39

第6章 结论... 45

参考文献... 47

附 录... 57

致 谢... 63

作者简历及攻读硕士期间发表的学术论文与研究成果... 65

Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/178397
Collection海洋地质与环境重点实验室
中国科学院海洋研究所
Recommended Citation
GB/T 7714
黄子航. 玻安岩岩浆源区不同富集组分特征与俯冲物质贡献[D]. 中国科学院海洋研究所. 中国科学院大学,2022.
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