Peridotite Melting at 1.0 and 1.5 GPa: an Experimental Evaluation of Techniques using Diamond Aggregates and Mineral Mixes for Determination of Near-solidus Melts
Peridotite Melting at 1.0 and 1.5 GPa: an Experimental Evaluation of Techniques using Diamond Aggregates and Mineral Mixes for Determination of Near-solidus Melts
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DOI：
10.1093/petroj/40.9.1343
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发表时间：
1999-09
影响因子：
3.9
通讯作者：
T. Falloon;D. Green;L. Danyushevsky;U. Faul
中科院分区：
文献类型：
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作者：
T. Falloon;D. Green;L. Danyushevsky;U. Faul
热橄榄岩中液体成分随压力和温度变化的实验测定为地幔动力学和岩浆成因提供了约束。在本文中，我们详细评价了使用天然矿物混合物作为起始材料在1.0 GPa下的橄榄岩熔融研究。作为一个例子，我们选择对Baker和Stolper （1994, Geochimica et Cosmochimica Acta 58, 2811-2827）获得的数据进行测试，这些数据来自于一种被认为是洋中脊玄武岩（MORB）潜在来源的橄榄岩成分（MM-3）。这项研究是使用天然矿物混合物的融化研究中记录最完整的。我们从三个方面对Baker和Stolper的数据进行了测试：(1)我们定义了Baker和Stolper得到的部分熔体成分的液相相和条件；(2)将这些部分熔体成分与MM-3组成的细粒合成起始混合物进行反应；(3)利用合成的橄榄岩MM-3进行了1.0和1.5 GPa的熔融实验。我们的研究结果表明，只有Baker和Stolper在1390°C进行的最高温度实验接近于橄榄岩MM-3组成的平衡熔体，而较低温度实验没有达到平衡，保留了残余未反应矿物和亚稳熔体组成。随着温度的降低，不平衡程度逐渐增加。不平衡是由于天然矿物混合物缺乏反应和亚稳的、相对粗粒矿物混合物的不平衡熔化反应。其他影响因素包括使用金刚石集料陷阱造成的不平衡。我们还介绍了使用矿物混合物KLB-1在1.0 GPa下熔融橄榄岩的实验。结果表明，矿物混合物KLB-1在1280 ~ 1300℃的温度下，即使在~340 h后也不能达到平衡。我们提出了Hirose和Kushiro （1993, Earth and Planetary Science Letters, 114, 477-489）的1.0 GPa橄榄岩熔融实验的反转。我们的反转表明，Hirose和Kushiro使用的矿物混合金刚石集合体圈闭技术也未能产生地幔橄榄岩组成的平衡熔体。建议保留使用天然矿物混合物进行橄榄岩熔融研究的数据，天然矿物混合物不是这种研究的合适起始材料。使用金刚石骨料分离和捕获熔融相化合物，而不是解决使用天然矿物混合物所固有的问题。
The experimental determination of liquid compositions in lherzolite as functions of pressure and temperature provides constraints on mantle dynamics and magma genesis. In this paper, we present a detailed evaluation of the use of natural mineral mixes as starting material in peridotite melting studies at 1·0 GPa. As an example we have chosen to test the data obtained by Baker and Stolper (1994, Geochimica et Cosmochimica Acta 58, 2811-2827) on a lherzolite composition (MM-3) presented as a potential source for mid-ocean ridge basalts (MORB). That study is the most fully documented published melting study using natural mineral mixes. We have tested the Baker and Stolper data in three ways: (1) we have defined the liquidus phases and conditions of the partial melt compositions obtained by Baker and Stolper; (2) we have reacted these partial melt compositions with a fine-grained synthetic starting mix of MM-3 composition; (3) we have performed additional melting experiments at 1·0 and 1·5 GPa using the synthetic mix of peridotite MM-3. Our results demonstrate that only the highest temperature experiment of Baker and Stolper, performed at 1390°C, approached an equilibrium melt of peridotite MM-3 composition and that lower temperature experiments have not reached equilibrium, retaining residual unreacted minerals and metastable melt compositions. The degree of disequilibrium increases progressively with lower temperature. Disequilibrium is attributed to the lack of reaction of the natural mineral mix and to disequilibrium melting reactions of the metastable, relatively coarse-grained mineral mix. Other contributing factors include disequilibrium caused by the use of a diamond aggregate trap. We also present peridotite melting experiments using the mineral mix KLB-1 at 1·0 GPa. Our results demonstrate that the mineral mix KLB-1 fails to equilibrate even after ~340 h at temperatures of 1280-1300°C. We present reversals of the 1·0 GPa peridotite melting experiments of Hirose and Kushiro (1993, Earth and Planetary Science Letters 114, 477-489). Our reversals demonstrate that the mineral mix-diamond aggregate trap technique used by Hirose and Kushiro has also failed to produce equilibrium melts of a mantle peridotite composition. It is recommended that data from peridotite melting studies utilizing natural mineral mixes be used with reservation and that natural mineral mixes are not a suitable starting material for such studies. The use of diamond aggregate for separation and trapping of the melt phase compounds rather than solves the problems inherent in the use of natural mineral mixes.