The pyroxene-garnet transformation in the earth's mantle
The pyroxene-garnet transformation in the earth's mantle
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DOI：
10.1016/0012-821x(67)90138-0
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发表时间：
1967-05
影响因子：
5.3
通讯作者：
A. .. Ringwood
中科院分区：
文献类型：
--
作者：
A. .. Ringwood
描述了在压力范围 0–250 kb 和约 900°C 下石榴石结构中辉石固溶度的研究。在约 100 kb 时，顽辉石在镁铝榴石中的固溶度突然增加，导致形成成分为 Mg3(AlMg0.5Si0.5)Si3O12 的石榴石。人们发现富钙辉石和石榴石之间也存在类似的关系。结果表明发生了一种辉石-石榴石转变，其中石榴石的特征是硅的部分6重配位。这种转变伴随着约10%的密度增加。各种证据有力地表明这些新石榴石在热力学上是稳定的。这种转变也在典型的榴辉岩中得到证实，在 127 kb 的压力下，它会结晶成 95% 石榴石和 5% 辉石的组合，平均密度为 3.75 g/cm3。辉石-石榴石转变在地幔中可能很重要，它发生在约 350 km 的深度，从而标志着过渡带的开始。还提出了一个推测模型，通过地幔下沉的榴辉岩块中石榴石-辉石转变的发生提供了深源地震的机制。
An investigation of the solid solubility of pyroxenes in garnet structures in the pressure range 0–250 kb and at about 900°C, is described. At about 100 kb, the solid solubility of enstatite in pyrope increases suddenly, resulting in formation of a garnet of composition Mg3(AlMg0.5Si0.5)Si3O12. Analogous relationships are found to exist between calcium-rich pyroxenes and garnets. The results imply the occurrence of a type of pyroxene-garnet transformation, in which the garnets are characterized by partial 6-fold coordination of silicon. The transformation is accompanied by a density increase of about 10%. A variety of evidence strongly indicates that these new garnets are thermodynamically stable. The transformation has also been demonstrated in a typical eclogite, which, at a pressure of 127 kb, crystallizes to an assemblage of 95% garnet and 5% pyroxene, with a mean density of 3.75 g/cm3.The pyroxene-garnet transformation may be important in the earth's mantle where it would occur at a depth of about 350 km, thus marking the beginning of the transition zone. A speculative model is also presented whereby the occurrence of the garnet-pyroxene transformation in blocks of eclogite which are sinking through the mantle provides a mechanism for deep-focus earthquakes.