Density of MORB eclogite in the upper mantle
Density of MORB eclogite in the upper mantle
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DOI：
10.1016/j.pepi.2003.10.007
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发表时间：
2004-06-15
影响因子：
2.3
通讯作者：
Takahashi, E
中科院分区：
文献类型：
--
作者：
Aoki, I;Takahashi, E
为了研究榴辉岩（俯冲洋壳）在地球动力学中的作用，利用多砧装置对天然洋中脊玄武岩（MORB）进行了高压实验。在温度范围为1200 ~ 1700℃，压力范围为5 ~ 14 GPa时，测定了MORB的相关系随压力和温度的变化。目前的结果不同于先前对地球行星的高压研究。科学。Lett. 77 (1986) 245]；在1200°c下进行，结果如下：(1)在整个研究压力范围内均出现硅质岩（Coe）或硅质岩（St）；(2)斜辉石/石榴石（Cpx/Gar）比值较小，特别是在低压范围内（< 12 GPa）。研究结果表明，在9 GPa左右，俯冲洋壳的计算容重呈不连续增加，主要是由于硅辉石-硅辉石相变。在小于12gpa的压力下，密度比先前的实验估计的要高得多。因此，榴辉岩在推动俯冲中的作用应该比以前认为的更为重要。另一方面，上升地幔柱中橄榄岩与榴辉岩的密度差随温度升高而减小，这是由于榴辉岩中斜辉石/（石榴石+ SiO2）比值随温度升高而增大。即使在亚固体条件下，榴辉岩仍比橄榄岩密度大，因此，地幔柱中周围橄榄岩的向上流动必须维持上升柱中携带的再循环海洋地壳。(C) 2004 Elsevier B.V.版权所有
In order to study the role of eclogite (subducted oceanic crust) in geodynamics, we carried out high-pressure experiments on natural mid-oceanic ridge basalt (MORB) using a multi-anvil apparatus. We determined phase relations of MORB as a function of pressure and temperature in the temperature range of 1200-1700 degreesC and pressures from 5 to 14 GPa. The present results differ from a previous high-pressure study of MORB ([Earth Planet. Sci. Lett. 77 (1986) 245]; conducted at 1200 degreesC) as follows: (1) coesite (Coe) or stishovite (St) appears throughout the studied pressure range; and (2) the clinopyroxene/garnet (Cpx/Gar) ratio is smaller, particularly in the low-pressure range (< 12 GPa). Our results show that the calculated bulk density of subducted oceanic crust increases discontinuously at around 9 GPa due to the coesite-stishovite phase transition. The density is considerably higher than estimates based on the previous experiments at pressures less than 12 GPa. Thus, the role of eclogite in driving subduction should be more important than previously thought. On the other hand, the density difference between peridotite and eclogite in ascending mantle plumes becomes smaller as temperature increases, a result of the increase in clinopyroxene/(garnet + SiO2) ratio in eclogite with increasing temperature. As eclogite is still denser than peridotite even under subsolidus conditions, recycled oceanic crust entrained in ascending plumes must be sustained by the upward flow of ambient peridotite in mantle plumes. (C) 2004 Elsevier B.V. All rights reserved.