| 华北古元古代碳酸岩起源深度及现代板块构造启动 |
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| 引用本文： | 许成,匡光喜,曾亮,宋文磊,邓淼,韦春婉.华北古元古代碳酸岩起源深度及现代板块构造启动[J].地球科学,2019,44(4):1083-1095. |
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| 作者姓名： | 许成 匡光喜 曾亮 宋文磊 邓淼 韦春婉 |
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| 作者单位： | 北京大学地球与空间科学学院, 造山带与地壳演化教育部重点实验室, 北京 100871 |
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| 基金项目： | 国家自然科学基金项目41773022国家自然科学基金项目41573033国家自然科学基金项目41825008 |
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| 摘 要： | 俯冲作用是改变地球内部物质演化的关键因素之一，而现代板块的启动时间一直存在争论.华北克拉通中部造山带内蒙古丰镇古元古代碳酸岩内超硅石榴石包体和榴辉岩捕虏体的发现，为研究岩浆起源深度和板块构造提供了窗口.矿物学和高温高压实验限定超硅石榴石（Si~3.18 pfu）富集三价铁（Fe3+/∑Fe~0.8），来源于地幔约400 km的深度表明碳酸岩岩浆起源于地幔过渡带.矿物对温压计和P-T视剖面图确定榴辉岩捕虏体变质峰期温压分别为~660 ℃和~2.65 GPa，温压梯度为~250 ℃·GPa-1，与现代板块深俯冲产物相似，说明现代板块构造在古元古代已经启动.统计显示全球古元古代碳酸岩与造山带内高压变质岩石密切共生.全球古元古代的板块俯冲可能与哥伦比亚超大陆的拼合有关.大规模板片俯冲携带地壳沉积物质进入深部地幔，形成碳酸岩岩浆及氧化的富Fe3+超硅石榴石.地壳物质在地幔源区循环约20亿年，导致了地幔源区的不均一性以及长时间的碳循环.
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| 关 键 词： | 碳酸岩 板块构造 岩浆起源 华北克拉通 丰镇 俯冲作用 岩石学 |
| 收稿时间： | 2018-06-28 |
Original Depth of Paleoproterozoic Carbonatites in North China Craton and Onset of Modern-Style Plate Tectonics |
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| Abstract: | Subduction is one of the key factors that change the evolution of the interior of the Earth, and there have been controversies over the starting time of modern-style plate tectonics. The discovery of majorite garnet inclusions and eclogite xenoliths hosted by the Paleoproterozoic carbonatites in the Fengzhen area, Inner Mongolia, provides a rare window into the origin depth of magma and plate tectonics. Mineralogy and high temperature and pressure experiments constrain the ferric iron-rich (Fe3+/∑Fe~0.8) majoritic garnets (Si ~3.18 pfu) originated from about ~400 km in depth, indicating that the carbonatitic magma originated from the mantle transition zone. The mineral-pair thermobarometer and P-T phase diagram determine the peak metamorphic pressure and temperature at ~660 ℃ and ~2.65 GPa, which gives a peak thermal gradient of ~250 ℃·GPa-1, similar to the product of modern plate deep subduction, indicating that the modern plate tectonics has started since the Paleoproterozoic. Statistics show that the global Paleoproterozoic carbonatites are closely associated with high-pressure metamorphic rocks in Paleoproterozoic orogens. Global Paleoproterozoic slab subduction might be linked to the Columbia supercontinent amalgamation. Large-scale slab subduction inputted crustal sediments into the deep mantle, forming carbonatitic magmas and oxidized ferric iron-rich majoritic garnets. Crustal materials recycled for about 2 billion years in the mantle source region, leading to the compositional heterogeneities and carbon cycle in the deep mantle. |
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