Structural and microstructural constraints on the mechanism of eclogite formation in the Sambagawa belt, SW Japan
Structural and microstructural constraints on the mechanism of eclogite formation in the Sambagawa belt, SW Japan
复制标题
日本西南部三波川带榴辉岩形成机制的构造和微观构造约束
DOI：
10.1016/s0191-8141(99)00114-5
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发表时间：
1999
影响因子：
3.1
通讯作者：
S. Wallis
中科院分区：
文献类型：
--
作者：
M. Aoya;S. Wallis
Sambagawa带的Seba基性片岩中的榴辉岩显示出对比鲜明的结构。在一种类型的榴辉岩中，粗粒绿辉石是随机定向的，并横切岩石，表明是后构造生长的。与此相反，在第二种类型中，细粒绿辉石优先平行排列，表明前同构造生长的透明度。前一类榴辉岩被认为是榴辉岩形成后固态接触变质作用的产物，后一类榴辉岩则与桑巴川区域变质作用有关。榴辉岩可以通过接触变质作用形成的想法是非常规的，如果是真的，可能对榴辉岩的一般解释有重大影响。在Seba基性片岩中，一般认为主要的半晶质是在单一变形阶段形成的。然而，野外和显微构造研究表明：（i）有两个不同的透明度，一个形成之前，另一个在榴辉岩形成过程中;（ii）榴辉岩结构的差异反映了第二阶段变形的强度。因此，色坝基性片岩中各种结构类型的榴辉岩均形成于单一阶段的区域变质作用中，不需要援引接触变质作用。
Eclogites in the Seba basic schist of the Sambagawa belt show contrasting textures. In one type of eclogite, coarse-grained omphacite is randomly oriented and cross-cuts the schistosity suggesting post-tectonic growth. In contrast, in the second type, fine-grained omphacite is preferentially aligned parallel to the schistosity suggesting pre- to syn-tectonic growth. The former type of eclogite has been regarded as a product of solid-state contact metamorphism after the formation of the schistosity while the latter type has been related to the Sambagawa regional metamorphism. The idea that eclogite can form by contact metamorphism is unconventional and, if true, could have major implications for the interpretation of eclogitic rocks in general. In the Seba basic schist, it has generally been assumed that the dominant schistosity formed during a single phase of deformation. However, field and microstructural studies show: (i) there are two different schistosities, one formed before and the other during eclogite formation; and (ii) the differences in eclogite texture reflect the strength of deformation during the second stage. Therefore, the various textural types of eclogite in the Seba basic schist all formed during a single phase of regional metamorphism and there is no need to invoke contact metamorphism.