An Experimental Study on the Origin and Dynamics of the Earth's Lower Mantle

我们已经建立了一种技术，可以在2 mm^3的样品体积上以2%的可重复精度产生高达60 Gpa的压力，使用Kawai型多砧设备，配备了边缘长度为14 mm的烧结钻石立方锤和1.5 mm的截角。最高压力达到63 Gpa以上。利用同步辐射X射线原位观测技术，对几种材料在高温高压下的相平衡进行了测定。首先，我们研究了高达44 Gpa和2100K的铁，排除了β-Fe的稳定性，并建立了ε[互变构体]γ转变的相界。我们进一步研究了GaN和Fe_2O_3的相平衡，发现GaN和Fe_2O_3的相平衡分别达到62 Gpa/900K和58 Gpa/1400K，并测量了GaN在300K时的电阻，在54 Gpa/300K和51.5 Gpa/750K观察到了纤锌矿-岩盐相变，表明相界面具有负斜率。经证实，…随着压力的增加，更多的Fe_2O_3赤铁矿(I相)相继转变为Rh_2O_3II类(II)和正交相(III)。I[互变构体]II、II[互变构体]III的两个相界都具有负斜率。GaN的电阻为几十兆欧姆，最高可达62 GPA，在纤锌矿-岩盐转变过程中没有表现出明显的变化。另一方面，Fe_2O_3的电阻从0 GPa时的几百兆欧姆单调下降到58 GPa时的几个欧姆。为了模拟地球早期形成的岩浆海洋中的物质分馏作用，我们对橄榄岩和CI地幔物质进行了熔融实验，实验压力高达35 Gpa。在橄榄岩中，第一液相线由铁钙钛矿(FP)转变为镁钙钛矿(Mg-PV)，在33 Gpa时，相继降温，然后是FP和钙钛矿(Ca-PV)。在CI地幔物质中，Mg-PV也是相继降温后的液相。这些结果表明，在深部岩浆海洋中，Mg-PV和Ca-PV都发生了分馏作用，导致地幔底部形成了钙钛矿层。由于Ca-PV具有较强的容纳碱性、稀土等大阳离子的能力，该层可能是一个地球化学库。我们成功地合成了镁-PV等深地幔材料的毫米级单晶。这些晶体将用于测量弹性和各种传输现象，如元素和热扩散系数以及电导率。较少

We have established a technique to generate pressure up to 60 GPa over a specimen volume 2 mm^3 within a repeatable accuracy of 2% using the Kawai-type multi anvil apparatus equipped with sintered diamond cubic anvils with edge length of 14 mm and a truncated corner of 1.5 mm. The maximum pressure reaches higher than 63 GPa. We carried out determination of phase equilibria of several materials under high-pressure and high-temperature by means of in situ X-ray observation using synchrotron radiation at Spring-8. First we examined iron up to 44 GPa and 2100 K. The stability of β-Fe was excluded, and the phase boundary for the ε【tautomer】γ transition was established. We further studied the phase equilbria of GaN and Fe_2O_3 up to 62GPa/900K and 58GPa/1400K, respectively, together with measurement of electrical resistance at 300 K. In GaN, the wurtzire-rocksalt transition was observed at 54GPa/300K and 51.5GPa/750K, suggesting the phase boundary with a negative slope. It was confirmed that … More Fe_2O_3 hematite (phase I) transforms successively into Rh_2O_3II type (II) and an orthorhombic phase (III) with increasing pressure. Both the phase boundaries for the I【tautomer】II, II【tautomer】III have negative slopes. The electrical resistance of GaN was in several tens of mega ohms up to 62 GPa and did not show any remarkable change on the wurtzite-rocksalt transition. The electrical resistance of Fe_2O_3, on the other hand, decreased monotonically from several hundreds mega ohms at 0 GPa to a few ohms at 58 GPa. However, the decrease over a pressure range 54±1 GPa was characteristically abrupt, ca. four orders of magnitude, which can serve as a new pressure fixed point.In order to simulate material fractionation in a magma ocean formed in the early stage of the Earth, we performed melting experiments on peridotite and CI mantle material up to 35 GPa. In peridotite the first liquidus phase changes from feropericlase (Fp) to Mg-perovskite (Mg-Pv) and at 33 GPa liquidus Mg-Pv is successively followed down temperature by Fp and Ca-perovskite (Ca-Pv) within a small temperature interval. In CI mantle material, Mg-Pv is also the liquidus phase followed down temperature by Ca-Pv. These results suggest fractionation of both Mg-Pv and Ca-Pv in a deep magma ocean resulting in formation of a perovskite layer in bottom of the mantle. The layer may be a geochemical reservoir due to the high capability of Ca-Pv to accommodate large cations such as alkaline and rare earth elements.We have successively synthesized single crystals with mm size of deep mantle materials such as Mg-Pv. These crystals are to be used for measurements of elasticity and various transport phenomena such as element and thermal diffusivilitisand electrical conductivity. Less