新元古代地幔柱事件在Rodinia超大陆西缘的响应:来自马达加斯加的初步证据
Response to the Neoproterozoic mantle plume(s) on the western margin of Rodinia:Preliminary evidence from the Malagasy Shield
查看参考文献38篇
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文摘
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对于Rodinia超大陆西缘在裂解过程中是否发育巨长安第斯型陆弧存在较大争议。马达加斯加即位于古地理再造Rodinia的西缘位置,其太古宙结晶基底中出露有大量新元古代侵入体,是澄清这一争议的理想研究区。由于基性岩浆岩组分识别不足等原因,前人曾认为这些侵入岩形成于俯冲带陆弧环境。但笔者在中北部Alaotra湖地区野外考察期间发现了大量辉长质岩石,对其中典型岩体的 LA-ICP-MS 锆石 U-Pb 测年表明其结晶于798 ~ 778Ma 之间(最大误差估计)。因此,这些@@B1449103*255*118_179_1131_347@@辉长岩体事实上与岛内其他新元古代侵入体构成了双峰式侵入岩套,暗示了可能的陆内伸展环境。在此基础上,笔者重新审视了前人已发表的地球化学数据,发现该双峰式侵入岩套的基性组分显示富钾特征和拉斑演化趋势,局部甚至发育了强烈地钒钛磁铁矿化; 酸性组分则显示富铁、偏铝-过铝质和碱钙-钙碱性特征,并具有相对较高的 K_2O/Na_2O和Ga/Al比值以及高场强元素含量,属于A型花岗岩(铁质花岗岩)。这些特征进一步表明该双峰式侵入岩套形成于陆内伸展环境而非陆弧环境。结合本文的初步研究结果和区域地质演化历史,笔者认为马达加斯加这一双峰式侵入岩套很可能是新元古代地幔柱事件在Rodinia 超大陆西缘的响应。 |
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其他语种文摘
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It remains open to debate whether there was an extensive Andean-type arc on the western margin of the Rodinia supercontinent. Madagascar is an ideal locality to answer this question because of its western marginal position in Rodinia reconstruction as well as widespread Neoproterozoic intrusions throughout the Archean basement. Partly owing to the rare exposure of mafic component, these intrusive rocks have been previously regarded as subduction-related origin. However, there are lots of gabbroic rocks exposed near the Alaotra Lake area. LA-ICP-MS zircon U-Pb dating reveals that a typical intrusion crystallized from 798Ma to 778Ma (at maximum uncertainty). Together with other intrusive rocks, these gabbros thus constitute a bi-modal intrusive suite in the Malagasy Shield, implying an intra-continental rifting setting. Based on this, we re-examine the previous geochemical data and find that the mafic component indeed exhibits K-enriched feature and tholeiitic trend with local Fe-Ti-V mineralization, while the felsic component shows the ferroan, metaluminous to peraluminous, and alkali-calcic to calc-alkalic compositions of A-type granites, which is further confirmed by their high K_2 O/Na_2O and Ga/Al ratios and high-field-strength-element contents. Both geochemical signatures are consistent with an intra-continental rifting rather than continental arc regime. Our preliminary results, coupled with the knowledge of the regional geological evolution, allow us to speculate that this bi-modal intrusive suite in Madagascar is most likely a response to the Neoproterozoic mantle plume (s) on the western margin of the Rodinia supercontinent. |
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来源
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岩石学报
,2014,30(11):3366-3374 【核心库】
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关键词
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双峰式侵入岩套
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拉斑演化序列
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A型花岗岩
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地幔柱
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新元古代
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马达加斯加
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地址
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1.
(北京)中国地质大学地球科学与资源学院, 北京, 100083
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中国地质调查局沈阳地质调查中心, 沈阳, 110034
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马达加斯加地质矿产部地质司, 马达加斯加, 安塔那那利佛, 101
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语种
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中文 |
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文献类型
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研究性论文 |
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ISSN
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1000-0569 |
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学科
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地质学 |
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基金
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中国地质调查局国外矿产资源风险勘查基金项目
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国土资源部中国地质调查局地质调查项目
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文献收藏号
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CSCD:5299832
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