Composite metamorphic history recorded in garnet porphyroblasts of Sambagawa metasediments in the Besshi region, central Shikoku, Southwest Japan.
Composite metamorphic history recorded in garnet porphyroblasts of Sambagawa metasediments in the Besshi region, central Shikoku, Southwest Japan.
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日本西南部四国中部别子地区三波川变质沉积物石榴石斑岩记录的复合变质历史。
DOI：
10.1111/iar.12075
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发表时间：
2014
期刊：
影响因子：
1.5
通讯作者：
Okamura M. & Sakurai T
中科院分区：
文献类型：
--
作者：
Kouketsu Y.;Enami M.;Mouri T.;Okamura M. & Sakurai T
本文介绍了在三钵川变质沉积物的石榴石变斑晶记录的复合变质历史的调查，并提出了榴辉岩相岩性的可能分布在百志地区，四国中部，日本西南部的讨论。石榴石晶粒通常表现出化学复合分区，分别与解决内部和过度生长的外部部分。内段通常含有钠长石作为钠质相包裹体，很少含有绿辉石或蓝闪石，而外段很少含有钠长石，但不含钠长石。内段通常包括保持对应于榴辉岩相条件的高残余压力的石英颗粒，而外段包括保持对应于绿帘石-角闪岩相条件的较低残余压力的石英颗粒。钠质相包裹体组合和石英包裹体残余压力值表明，该复合环带石榴子石经历了榴辉岩相→减压水化反应→绿帘石-角闪岩相的连续变质过程。含有这种复合带石榴石的变质沉积物具有榴辉岩相条件的证据，其分布范围比含有绿辉石+石榴石组合的榴辉岩岩性更广。这些结果表明，（i）石榴石的化学复合分带，（ii）钠相包裹体的性质，和（iii）石英包裹体的残余压力的组合是有用的标准，以确定真正的分布的岩石经历了榴辉岩相变质的Sambagawa变质沉积物，这是很难认识到在早期的研究。
This report describes an investigation of the composite metamorphic history recorded in garnet porphyroblasts of Sambagawa metasediments, and presents discussions of the possible distribution of eclogite facies lithologies in the Besshi region, central Shikoku, southwest Japan. Garnet grains usually show chemically composite zoning with resolved inner and overgrown outer segments, respectively. The inner segment usually contains paragonite as a sodic phase inclusion and rarely contains omphacite or glaucophane, whereas the outer segment rarely includes albite but no paragonite. The inner segment often includes quartz grains that preserve high residual pressures corresponding to the eclogite facies conditions, whereas the outer segment includes quartz grains that preserve lower residual pressures corresponding to the epidote–amphibolite facies conditions. For this composite‐zoned garnet, the assemblage of sodic phase inclusions and the values of the residual pressure of quartz inclusions imply the following successive metamorphic path: prograde eclogite facies stage → decompression and hydration reaction stage → prograde epidote–amphibolite facies stage. Metasediments containing this composite‐zoned garnet with such evidence for eclogite facies conditions are more widely distributed than the eclogitic lithologies that contain the assemblage of omphacite + garnet. These results imply that the combination of (i) the chemical composite zoning of garnet, (ii) the nature of sodic phase inclusions, and (iii) the residual pressure of quartz inclusions is useful as criteria to ascertain the true distribution of the lithologies that have experienced eclogite facies metamorphism for the Sambagawa metasediments, which was difficult to recognize in earlier studies.