In situ X-ray diffraction study of post-spinel transformation in a peridotite mantle: Implication for the 660-km discontinuity
In situ X-ray diffraction study of post-spinel transformation in a peridotite mantle: Implication for the 660-km discontinuity
复制标题
DOI：
10.1016/j.epsl.2005.08.001
复制
发表时间：
2004-12
影响因子：
5.3
通讯作者：
K. Litasov;E. Ohtani;A. Sano;A. Suzuki;K. Funakoshi
中科院分区：
文献类型：
--
作者：
K. Litasov;E. Ohtani;A. Sano;A. Suzuki;K. Funakoshi
我们提出了无水 CaO-MgO-FeO-Al2O3-SiO2-黄铁矿中的相关系，以研究黄铁矿和 Mg2SiO4 之间的成分差异对后尖晶石相变的影响。结果表明，在热熔石体系中，该转变发生在比 Mg2SiO4 低约 0.5 GPa 的压力下。我们对尖晶石到镁钙钛矿+铁尖晶石的原位X射线衍射实验以及反向转换进行了多次实验，发现使用Tsuchiya的金状态方程可以将尖晶石转换后边界表示为P(GPa)=−0.0005 T(K)+23.54 Tsuchiya，金的 P-V-T 状态方程和地幔 660 公里不连续性的第一性原理预测，J. Geophys。资源。 108（2003）doi：10.1029/2003JB002446]。发现共存尖晶橄榄石和镁钙钛矿的间隙为 0.1-0.5 GPa。在1850 K时，我们的数据与地震不连续深度（全球平均654 km）之间的差异约为20 km。根据现场测量结果，我们证实了镁铁矿和Mg2SiO4之间化学成分的差异不能改变尖晶石转变后的克拉佩龙斜率。利用实验数据并假设 660 公里处的平均地幔温度为 1850 K，我们只能解释俯冲带和热点处 660 公里不连续面深度变化的一半。需要对 660 公里间断处观测到的地震变化进行补充解释，并且可能反映其他次要成分或挥发物的影响。
We present the phase relations in anhydrous CaO–MgO–FeO–Al2O3–SiO2–pyrolite to examine the influence of compositional difference between pyrolite and Mg2SiO4on the post-spinel phase transformation. It is shown that in the pyrolite system the transformation occurs at about 0.5 GPa lower pressure relative to Mg2SiO4. We have carried out several in situ X-ray diffraction experiments on ringwoodite to Mg–perovskite+ferropericlase and backward transformations and found that post-spinel transformation boundary can be expressed as P (GPa)=−0.0005 T (K)+23.54 using the gold equation of state by Tsuchiya [T. Tsuchiya, First-principles prediction of the P–V–T equation of state of gold and the 660-km discontinuity in Earth's mantle, J. Geophys. Res. 108 (2003) doi: 10.1029/2003JB002446]. The interval for coexisting ringwoodite and Mg–perovskite was found to be 0.1–0.5 GPa. The discrepancy between our data and the depth of the seismic discontinuity (global average 654 km) is about 20 km at 1850 K. Based on the results of in situ measurements we confirmed that the difference in chemical composition between pyrolite and Mg2SiO4cannot modify the Clapeyron slope of the post-spinel transformation. Using experimental data and assuming the average mantle temperature 1850 K at 660 km we can account for only a half of variations in the depth of the 660-km discontinuity in subduction zones and at hot spots. An additional explanation for the observed seismological variations at the 660-km discontinuity is required and may reflect influence of other minor components or volatiles.