Vestiges of early Earth’s deep subduction and CHONSP cycle recorded in Archean ophiolitic podiform chromitites
Vestiges of early Earth’s deep subduction and CHONSP cycle recorded in Archean ophiolitic podiform chromitites
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太古代蛇绿豆状铬铁矿中记录的早期地球深俯冲和 CHONSP 旋回的遗迹
DOI：
10.1016/j.earscirev.2022.103968
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发表时间：
2022-02
影响因子：
12.1
通讯作者：
Hu Wei
中科院分区：
文献类型：
--
作者：
Timothy Kusky;Yang Huang;Lu Wang;Paul T. Robinson;Richard Wirth;Ali Polat;Hu Wei
蛇绿岩豆荚状铬铁矿从中生代造山带已被证明保存了丰富的结构和包裹体，在某种程度上，跟踪俯冲和壳幔相互作用的早期事件，包括微量的主要元素碳-氢-氧-氮-硫-磷（CHONSP）需要维持一个可居住的星球。在这里，我们报告的第一个全面的文件的纹理和包裹体的太古代中国造山带蛇绿混杂岩中的豆荚状铬铁矿（约2.55Ga），记录了一个古老的CHONSP旋回，为太古宙-古元古代构造的动态联系提供了证据，创造一个可居住的星球。包裹体的成分表明在太古代地壳和地幔源的深度混合，并且结构显示它们被包含在铬铁矿颗粒中，铬铁矿颗粒开始作为球粒生长，这些球粒在1900°C以上的温度下从地幔过渡区附近的不混溶的硅酸盐-氧化物熔体中聚集，在14 GPa或约410 km处形成宿主chenmingite。然后，熔体向上突出的伸展弧前，与主机方辉橄榄岩反应，逐步包括各种各样的以前俯冲的矿物和岩石碎片作为捕虏晶和捕虏体在逐步结晶铬铁矿。包裹体包括在1000 °C下稳定在7.5 GPa（或约270 km）的超高压TiO 2（II），加上碳酸盐，含水和名义上无水的硅酸盐，氧化物，贱金属，铂族矿物，以前未鉴定的OsIrS和纯碳作为石墨聚合物。随着含铬铁矿的熔体进一步上升，它们最终在大约25.5亿年前的弧前蛇绿岩的壳-幔边界附近结晶，很快，到古元古代黎明时，该蛇绿岩就参与了弧/大陆碰撞，将地幔岩石嵌入到古老大陆地壳的碎片上。这一早期记录包含了造山带蛇绿岩豆荚状铬铁矿中以前深俯冲的矿物，表明板块构造和俯冲至少自太古代以来就调节了地球上的壳幔相互作用和维持生命的深部CHONSP循环，这与数值模型一致，该模型显示了与俯冲有关的C-O-H循环如何导致太古代晚期地幔的快速氧化。
Ophiolitic podiform chromitites from Phanerozoic orogens have been shown to preserve a wealth of textures and inclusions that, in some way, trace earlier episodes of subduction and crust mantle interactions, including traces of the major elements Carbon – Hydrogen – Oxygen – Nitrogen – Sulfur - Phosphorous (CHONSP) needed to sustain a habitable planet. Here, we report the first comprehensive documentation of the textures and inclusions of an Archean (circa 2.55 Ga) podiform chromitite from an orogenic ophiolitic mélange in China, recording an ancient CHONSP cycle, during the start of Earth’s transition from a reducing to an oxidized surface environment during the Great Oxidation Event, providing evidence for a dynamic link of Archean-Paleoproterzoic tectonics, and creation of a habitable planet. The composition of the inclusions indicates profound mixing of crustal and mantle sources in the Archean, and the textures show that they were included in chromite grains that began their growth as spherules that aggregated from immiscible silicate-oxide melts near the mantle transition zone at temperatures above 1900°C, forming host chenmingite at 14 GPa, or about 410 km. The melts then protruded upward in an extensional fore-arc, reacting with host harzburgites, progressively including a wide assortment of previously subducted mineral and rock fragments as xenocrysts and xenoliths in the progressively crystallizing chromite. The inclusions include ultra-high pressure TiO2(II) stable at 7.5 GPa (or about 270 km) at 1000 °C, plus carbonates, hydrous and nominally anhydrous silicates, oxides, base metals, platinum group minerals, previously unidentified OsIrS, and pure carbon as graphite polymers. As the chromite-bearing melts rose further, they finally crystallized near the crust-mantle boundary of a circa 2.55-billion-year-old fore-arc ophiolite, that was soon, by the dawn of the Paleoproterozoic, involved in an arc/continent collision that emplaced the mantle rocks onto a fragment of older continental crust. This early record of inclusion of previously deeply subducted minerals in an orogenic ophiolitic podiform chromitite shows that plate tectonics and subduction have regulated crust-mantle interactions and the life-sustaining deep CHONSP cycles on Earth at least since the Archean, consistent with numerical models showing how C-O-H cycling related to subduction led to a rapid oxygenation of the mantle in the late Archean.
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