Depth of formation of super-deep diamonds: Raman barometry of CaSiO3-walstromite inclusions
Depth of formation of super-deep diamonds: Raman barometry of CaSiO3-walstromite inclusions
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超深钻石的形成深度：CaSiO3-维斯特石包裹体的拉曼气压测定
DOI：
10.2138/am-2018-6184
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发表时间：
2018
影响因子：
3.1
通讯作者：
F. Nestola
中科院分区：
文献类型：
--
作者：
Chiara Anzolini;M. Prencipe;M. Alvaro;C. Romano;A. Vona;S. Lorenzon;Evan M. Smith;F. Brenker;F. Nestola
摘要“超深”钻石被认为具有岩石圈下的起源（即，低于~300 km深度），因为包裹在其中的某些矿物相被认为是下地幔或过渡带前体的退变产物。超深金刚石中最丰富的含钙矿物包裹体CaSiO 3-钨硅锰矿被认为是由CaSiO 3-钙钛矿形成的，钙钛矿只有在~600 km深度以下才稳定，但其真实的成因深度存在争议。残余压力（Pinc）保留的夹杂物，结合矿物夹杂物和金刚石主机的热弹性参数，允许计算的包埋压力的金刚石夹杂物对。拉曼光谱法与X射线衍射法一起，是在不损坏金刚石基质的情况下测量Pinc的最常用方法。在本研究中，我们提供了，第一次，校准曲线，以确定Pinc的CaSiO_3-walstromite夹杂物的拉曼光谱的装置，而不打破金刚石。要做到这一点，我们进行了高压显微拉曼调查的CaSiO 3-walstromite晶体在静水压力条件下的金刚石压砧细胞。另外，为了避免由于偏应力的存在而引起的CaSiO_3-钨锰矿拉曼峰的异常位移对计算结果的误解，我们还采用从头计算方法计算了在静水应力和非静水应力条件下CaSiO_3-钨锰矿的拉曼光谱。最后，利用单包裹体弹性压力计估算了天然金刚石中CaSiO_3-钨柱石包裹体的最小包封压力，在1800 K时为~9 GPa（~260 km）。这些结果表明，研究的钻石肯定是亚岩石圈和支持的假设，即存在的CaSiO 3-walstromite是一个强有力的指示超深源。
Abstract “Super-deep” diamonds are thought to have a sub-lithospheric origin (i.e., below ~300 km depth) because some of the mineral phases entrapped within them as inclusions are considered to be the products of retrograde transformation from lower-mantle or transition-zone precursors. CaSiO3-walstromite, the most abundant Ca-bearing mineral inclusion found in super-deep diamonds, is believed to derive from CaSiO3-perovskite, which is stable only below ~600 km depth, although its real depth of origin is controversial. The remnant pressure (Pinc) retained by an inclusion, combined with the thermoelastic parameters of the mineral inclusion and the diamond host, allows calculation of the entrapment pressure of the diamond-inclusion pair. Raman spectroscopy, together with X-ray diffraction, is the most commonly used method for measuring the Pinc without damaging the diamond host. In the present study we provide, for the first time, a calibration curve to determine the Pinc of a CaSiO3-walstromite inclusion by means of Raman spectroscopy without breaking the diamond. To do so, we performed high-pressure micro-Raman investigations on a CaSiO3-walstromite crystal under hydrostatic stress conditions within a diamond-anvil cell. We additionally calculated the Raman spectrum of CaSiO3-walstromite by ab initio methods both under hydrostatic and non-hydrostatic stress conditions to avoid misinterpretation of the results caused by the possible presence of deviatoric stresses causing anomalous shift of CaSiO3-walstromite Raman peaks. Last, we applied single-inclusion elastic barometry to estimate the minimum entrapment pressure of a CaSiO3-walstromite inclusion trapped in a natural diamond, which is ~9 GPa (~260 km) at 1800 K. These results suggest that the diamond investigated is certainly sub-lithospheric and endorse the hypothesis that the presence of CaSiO3-walstromite is a strong indication of super-deep origin.
影响因子：
64.8
作者：
Pearson, D. G.;Brenker, F. E.;Vincze, L.
通讯作者：
Vincze, L.