Orthopyroxene from a metabasite of the Ryoke belt in the Ina district, Nagano Prefecture, Central Japan: textural evidence of partial melting.
Orthopyroxene from a metabasite of the Ryoke belt in the Ina district, Nagano Prefecture, Central Japan: textural evidence of partial melting.
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来自日本中部长野县伊那地区 Ryoke 带变碱岩的斜方辉石：部分熔融的结构证据。
DOI：
10.2465/ganko.91.253
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
T. Hokada
中科院分区：
文献类型：
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作者：
T. Hokada
含斜方辉石的基性变质岩在Ryoke带的Ina地区以封闭在泥质-砂质变质岩中的块体形式出现。斜方辉石的形状不规则，包括许多圆形的钙角闪石和斜长石晶体。斜方辉石是麻粒岩相岩石中的一种代表性变质矿物，人们提出了许多生成斜方辉石的变质反应。然而，没有一个变质反应是与观察到的结构关系和矿物共生的岩石。因此，作者认为斜方辉石是由一个独特的过程形成的。解释斜方辉石存在的一个简单假设是斜方辉石在部分熔融过程后结晶，即，部分熔融产生的熔体沿着钙质角闪石和斜长石的晶界分布，并沉淀出斜方辉石。这一假说得到了以下事实的支持：1）斜方辉石的结构是一种不寻常的变质矿物。2）没有简单的过程以外的结晶从部分熔融部分可以一贯解释斜方辉石的产状模式。3)最近的实验结果表明，部分熔融的基性岩可以发生的温度在高品位部分的Ryoke带，而且，斜方辉石是一个可能的产品，这种部分熔融。
Orthopyroxene-bearing basic metamorphic rock occurs as a block enclosed within pelitic-psammitic metamorphic rock in the Ina district of the Ryoke belt. The orthopyroxene is irregular in shape and includes many rounded crystals of calcic amphibole and plagioclase. Orthopyroxene is a representative metamorphic mineral of the granulite facies for rocks of basic composition and a number of metamorphic reactions to produce orthopyroxene have been proposed. However, none of the metamorphic reactions is consistent with the observed textural relationships and the mineral paragenesis of the rock. The author, therefore, suggests that the orthopyroxene was formed by a distinct process. A simple hypothesis to account for the occurrence of the orthopyroxene is that the orthopyroxene was crystallized after a process of partial melting, i.e., melt produced by partial melting was distributed along grain boundaries of calcic amphibole and plagioclase, and this melt precipitated the orthopyroxene. This hypothesis is supported by the following facts: 1) The texture of the orthopyroxene is unusual for a metamorphic mineral. 2) No simple process other than the crystallization from a partial melt fraction can consistently account for the mode of occurrence of orthopyroxene. 3) Recent experimental results suggest that partial melting of basic rock can take place at the temperatures in the high-grade parts of the Ryoke belt, and furthermore that orthopyroxene is a likely product of such partial melting.