Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China.
Department of Geology and Pedology, Mendel University, 613 00 Brno, Czech Republic.
Sci Adv. 2017 Apr 7;3(4):e1601589. doi: 10.1126/sciadv.1601589. eCollection 2017 Apr.
Minerals recovered from the deep mantle provide a rare glimpse into deep Earth processes. We report the first discovery of ferric iron-rich majoritic garnet found as inclusions in a host garnet within an eclogite xenolith originating in the deep mantle. The composition of the host garnet indicates an ultrahigh-pressure metamorphic origin, probably at a depth of ~200 km. More importantly, the ferric iron-rich majoritic garnet inclusions show a much deeper origin, at least at a depth of 380 km. The majoritic nature of the inclusions is confirmed by mineral chemistry, x-ray diffraction, and Raman spectroscopy, and their depth of origin is constrained by a new experimental calibration. The unique relationship between the majoritic inclusions and their host garnet has important implications for mantle dynamics within the deep asthenosphere. The high ferric iron content of the inclusions provides insights into the oxidation state of the deep upper mantle.
从深部地幔中回收的矿物质为深入了解地球深部过程提供了难得的线索。我们首次发现了富铁尖晶石镁铝榴石，它是在一种来自深部地幔的榴辉岩包体中的寄主石榴石内发现的包裹体。寄主石榴石的成分表明其具有超高压变质成因，可能形成于约 200 千米的深度。更重要的是，富铁尖晶石镁铝榴石包裹体的起源要深得多，至少在 380 千米的深度。包裹体的尖晶石性质通过矿物化学、X 射线衍射和拉曼光谱得到了证实，其起源深度受到新实验标定的限制。包裹体与寄主石榴石之间的独特关系对深部软流圈地幔动力学具有重要意义。包裹体中高铁含量为深部上地幔的氧化状态提供了新的见解。
