| 大陆板片-地幔相互作用:来自大别造山带碰撞后安山质火山岩的地球化学证据 |
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| 引用本文： | 赵子福,代富强,陈启.大陆板片-地幔相互作用:来自大别造山带碰撞后安山质火山岩的地球化学证据[J].地球科学,2019,44(12):4119-4127. |
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| 作者姓名： | 赵子福 代富强 陈启 |
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| 作者单位： | 1.中国科学院壳幔物质与环境重点实验室, 中国科学技术大学地球和空间科学学院, 安徽合肥 230026 |
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| 基金项目： | 国家“973”计划项目2015CB856102 |
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| 摘 要： | 俯冲到地幔深度的地壳物质不可避免地在板片-地幔界面与地幔楔发生相互作用，由此形成的超镁铁质交代岩就是造山带镁铁质火成岩的地幔源区.因此，造山带镁铁质火成岩为研究俯冲地壳物质再循环和壳-幔相互作用提供了重要研究对象.为了揭示俯冲陆壳物质再循环的机制和过程，对大别造山带碰撞后安山质火山岩开展了元素和同位素地球化学研究.这些安山质火山岩的SIMS锆石U-Pb年龄为124±3~130±2 Ma，表明其形成于早白垩世.此外，残留锆石的U-Pb年龄为中新元古代和三叠纪，分别对应于大别-苏鲁造山带超高压变火成岩的原岩年龄和变质年龄.它们具有岛弧型微量元素特征、富集的Sr-Nd-Hf同位素组成，以及变化的且大多不同于正常地幔的锆石δ18O值.这些元素和同位素特征指示，这些安山质火山岩是交代富集的造山带岩石圈地幔部分熔融的产物.在三叠纪华南陆块俯冲于华北陆块之下的过程中，俯冲华南陆壳来源的长英质熔体交代了上覆华北岩石圈地幔楔橄榄岩，大陆俯冲隧道内的熔体-橄榄岩反应产生了富沃、富集的镁铁质地幔交代岩.这种地幔交代岩在早白垩世发生部分熔融，就形成了所观察到的安山质火山岩.因此，碰撞造山带镁铁质岩浆岩的地幔源区是通过大陆俯冲隧道内板片-地幔相互作用形成的，而加入地幔楔中长英质熔体的比例决定了这些镁铁质岩浆岩的岩石化学和地球化学成分.
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| 关 键 词： | 安山岩 碰撞造山带 板片-地幔相互作用 熔体-橄榄岩反应 俯冲隧道 地球化学 |
| 收稿时间： | 2019-09-02 |
Continental Slab-Mantle Interaction: Geochemical Evidence from Post-Collisional Andesitic Rocks in the Dabie Orogen |
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| Abstract: | Crustal material subducted to mantle depths inevitably interacted with the mantle wedge at the slab-mantle interface. This may generate a variety of ultramafic metasomatites that served as the mantle source of mafic igneous rocks in collisional orogens. Therefore, mafic igneous rocks in collisional orogens are the important target to study the recycling of subdcuted crustal materials and its associated crust-mantle interaction. In order to decipher the mechanism and processes of the recycling of subducted continental crustal materials, a combined study of element and isotope geochemistry was performed for post-collisional andesitic volcanics from the Dabie orogen, China. SIMS zircon U-Pb ages for these volcanic rocks are 124±3 to 130±2 Ma, indicating that they formed at Early Cretaceous. In addition, the relict zircons have Middle Neoproterozoic and Triassic U-Pb ages, respectively, corresponding to the ages of protolith formation and ultrahigh-pressure metamorphism (UHP) for UHP metaigenous rocks in the Dabie-Sulu orogenic belt. They have island-arc basalts (IAB)-like trace-element patterns, enriched Sr-Nd-Hf isotope compositions, and variable zircon δ18O values mostly different from the normal mantle. These element and isotope features indicate that the post-collisional andesitic volcanics are the products of partial melting of metasomatically enriched orogenic lithospheric mantle. During the Triassic subduction of the South China block (SCB) beneath the North China block (NCB), the overlying NCB lithospheric mantle wedge peridotite was metasomatized by felsic melts originated from the subdcuted SCB continental crust, the melt-peridotite reaction in the continental subduction channel generated fertile and enriched metasomatites of mafic composition. Partial melting of such metasomatites in the Early Cretaceous gave rise to these andesitic volcanics. Therefore, the mantle sources for post-collisional mafic igneous rocks in collisional orogens would be generated by the slab-mantle interaction in continental subduction channel, and the lithochemical and geochemical composition of these mafic rocks is dictated by the proportion of felsic melts incorporating into the mantle wedge. |
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