Aarons Sarah M, Reimink Jesse R, Greber Nicolas D, Heard Andy W, Zhang Zhe, Dauphas Nicolas
Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.
Scripps Institution of Oceanography, University of California, San Diego, San Diego, CA 92037, USA.
Sci Adv. 2020 Dec 9;6(50). doi: 10.1126/sciadv.abc9959. Print 2020 Dec.
Plate subduction greatly influences the physical and chemical characteristics of Earth's surface and deep interior, yet the timing of its initiation is debated because of the paucity of exposed rocks from Earth's early history. We show that the titanium isotopic composition of orthogneisses from the Acasta Gneiss Complex spanning the Hadean to Eoarchean transition falls on two distinct magmatic differentiation trends. Hadean tonalitic gneisses show titanium isotopic compositions comparable to modern evolved tholeiitic magmas, formed by differentiation of dry parental magmas in plume settings. Younger Eoarchean granitoid gneisses have titanium isotopic compositions comparable to modern calc-alkaline magmas produced in convergent arcs. Our data therefore document a shift from tholeiitic- to calc-alkaline-style magmatism between 4.02 and 3.75 billion years (Ga) in the Slave craton.
板块俯冲对地球表面和深部地幔的物理和化学特征有着重大影响，然而由于早期地球历史中暴露岩石的匮乏，其开始的时间仍存在争议。我们发现，横跨冥古宙到始太古代转变期的阿卡斯塔片麻岩杂岩中的正片麻岩的钛同位素组成呈现出两种不同的岩浆分异趋势。冥古宙英云闪长质片麻岩的钛同位素组成与现代演化拉斑玄武质岩浆相当，由干母岩浆在热点环境中的分异作用形成。更年轻的始太古代花岗质片麻岩的钛同位素组成与现代汇聚弧中产生的钙碱性岩浆相当。因此，我们的数据记录了在40.2亿年至37.5亿年之间，斯勒夫克拉通地区从拉斑玄武质岩浆作用向钙碱性岩浆作用的转变。
