Ultra-high pressure inclusion in Archean ophiolitic podiform chromitite in melange block suggests deep subduction on early Earth
Ultra-high pressure inclusion in Archean ophiolitic podiform chromitite in melange block suggests deep subduction on early Earth
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混杂岩块中太古宙蛇绿豆状铬铁矿中的超高压包裹体表明早期地球的深俯冲作用
DOI：
10.1016/j.precamres.2021.106318
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发表时间：
2021-07-22
影响因子：
3.8
通讯作者：
Polat, Ali
中科院分区：
文献类型：
--
作者：
Kusky, Timothy;Wang, Lu;Polat, Ali
造山带中超高压（UHP）矿物的发现彻底改变了我们对俯冲和先前深度俯冲物质返回地球表面的理解，作为地壳和地幔系统循环和相互作用的一部分。超高压矿物的一类被发现作为包体在造山橄榄岩托管豆荚状铬铁矿系统，在中生代蛇绿混杂岩和蛇绿混杂岩。这些包裹体为研究古生代造山带中地壳物质通过俯冲和地幔对流向深部地幔再循环的过程打开了一扇窗。本文报道了中国北方中部（太行山）新太古代成对变质带蛇绿岩豆荚状铬铁矿混杂岩中首次发现的超高压矿物。大量的金红石，磷灰石，白云石和角闪石的包裹体被解释为地壳衍生的，他们出现在豆荚状铬铁矿颗粒托管在2.6-2.5 Ga蛇绿混杂岩，现在的一部分，中国北方大陆板块和形成的俯冲洋和大陆的材料。TiO 2（II）、金红石、磷灰石和透闪石多相包裹体的显微结构和相关系在1000 ℃时产生最小P-T条件为7.5 GPa，表明地壳主体（包括碳酸盐）俯冲至深度> 270 km，转移至覆盖板块的地幔，并在2.5 Ga时返回地表。我们认为，板块回滚迫使地幔向上流动，结合实体从下板，也许在蛇纹岩底辟，绝热熔融，使地壳物质被困在铬铁矿颗粒结晶在高镁熔体。对比体积模量和热收缩的包裹体和主机铬铁矿保护包裹体从P诱导的反反应过程中折返。总之，这些特征表明，1600公里长的中央（太行）造山带正在成为世界上第一个有充分记载的中生代风格的造山带，与经典的构造分带，蛇绿混杂岩，成对变质作用，超高压条件，前陆盆地，晚至后造山岩浆活动的地方证据。应用零假设，我们解释了这种高度的相似性，调用操作的中生代风格的板块构造，至少在整个1600公里的长度的COB，并通过地质比较，在其他类似的年龄地质地形全球。由此我们推断现代风格的板块构造作用于新太古代。
The discovery of ultrahigh pressure (UHP) minerals in orogenic belts has revolutionized our understanding of subduction and the return flow of previously deeply subducted material to Earth's surface as part of the cycling and interaction of crustal and mantle systems. One class of UHP minerals is found as inclusions in orogenic peridotite-hosted podiform-chromite systems, within Phanerozoic ophiolites and ophiolitic melanges. Such inclusions have opened a window into processes of recycling of crustal materials to the deep mantle and back through subduction and mantle convection in Phanerozoic orogens. Here, we document the first occurrence of an UHP mineral hosted in an ophiolitic podiform chromitite melange from the Neoarchean paired metamorphic belt of the Central (Taihang) Orogenic Belt, Northern China. Numerous inclusions of rutile, apatite, dolomite, and amphibole are interpreted to be crustal-derived; they occur in podiform chromite grains hosted in a 2.6-2.5 Ga ophiolitic melange now part of the North China Craton and formed by subduction of oceanic and continental material. Microstructures and phase relationships in a multi-phase inclusion of TiO2(II), rutile, apatite, and tremolite yield minimum P-T conditions of 7.5 GPa at 1000 degrees C, indicating that the crustal host, including carbonates, were subducted to depths > 270 km, transferred to the mantle of the overriding plate, and returned to the surface by 2.5 Ga. We suggest that slab rollback forced upward mantle flow, incorporating entities from the lower plate, perhaps in serpentinite diapirs, resulting in adiabatic melting that allowed crustal material to be trapped in chromite grains crystallizing in high-Mg melts. Contrasting bulk moduli and thermal contraction of the inclusions and host chromite protected the inclusions from P-induced back-reaction during exhumation. Together, these features show that the 1600 km long Central (Taihang) Orogenic Belt is emerging as the world's first well-documented Phanerozoic style orogen, with classic tectonic zonation, ophiolitic melanges, paired metamorphism, local evidence for UHP conditions, foreland basins, and late to post orogenic magmatism. Applying the null hypothesis, we explain this high degree of similarity by invoking the operation of Phanerozoic style plate tectonics, at least throughout the 1600 km length of the COB, and by geological comparison, in other similar aged geological terrains globally. From this we infer modern-style plate tectonics was operating in the Neoarchean.