P-T-D path of eclogite from the Sambagawa belt deduced from combination of petrological and microstructural analyses
P-T-D path of eclogite from the Sambagawa belt deduced from combination of petrological and microstructural analyses
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DOI：
10.1093/petrology/42.7.1225
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发表时间：
2001-07-01
影响因子：
3.9
通讯作者：
Aoya, M
中科院分区：
文献类型：
--
作者：
Aoya, M
结合构造和岩石学资料，可以确定日本西南部三钵川带榴辉岩片岩单元（色场基性片岩）的P-T轨迹。这两组数据之间的关系很好地定义了变斑和其他微结构。派生的P-T路径的Seba基性片岩有一个整体顺时针的减压轨迹，或折返相关的，路径发生在一个较低的P/T梯度比埋藏，或俯冲相关的，path. The顺时针性质的P-T路径的定性，支持的化学分带的角闪石共存榴辉岩矿物。P-T路径的显著特征是存在两个温度极大值，第一个在榴辉岩相中，第二个在绿帘石-角闪岩相中。两个温度最大值的存在给出了一个简单的解释，观察到变质带边界滞后榴辉岩相变质横切的主要榴辉岩体的分布在Sambagawa钟。估计变质压力使用的硬玉含量的单斜辉石在色巴地区表明存在构造不连续性，榴辉岩片岩和周围的非榴辉岩片岩。结构研究表明，虽然这两个单位经历了非常不同的高峰变质条件，他们成为并列在一个单一的韧性变形影响两个单位。这种变形与榴辉岩的折返和非榴辉岩的俯冲有关，表明二者形成于同一俯冲事件。在两个单元之间存在一个主要的构造边界，这两个单元具有相似的俯冲和增生物质，但不同的变质历史，可以用推覆构造来解释，并提出存在一个榴辉岩推覆体，即Sambagawa带的第三个推覆体。
Both structural and petrological data can be wed to constrain the P-T path of an eclogitic schist unit (the Seba basic schist) in the Sambagawa belt of SW Japan. The relationships between these two sets of data are well defined by porphyroblastic and other microstructures. The derived P T path for the Seba basic schist has an overall clockwise trajectory with the decompression, or exhumation-related, path taking place under a lower P/T gradient than the burial, or subduction-related, path. The clockwise nature of the P T path is qualitatively, supported by chemical zoning of amphibole coexisting with eclogitic minerals. The significant feature of the P T path is the presence of two temperature maxima, the first in the eclogite facies, and the second in the epidote-amphibolite facies. The existence of two temperature maxima gives a simple explanation for the observation that metamorphic zonal boundaries postdating the eclogite facies metamorphism cross-cut the distribution of the main eclogite bodies in the Sambagawa bell. Estimates of metamorphic pressure using the jadeite content of clinopyroxene in the Seba area demonstrate the existence of a tectonic discontinuity, between the eclogitic schist and surrounding non-eclogitic schist. Structural studies show, that although these two units have experienced very different peak metamorphic conditions, they became juxtaposed during a single ductile deformation affecting both units. This deformation is related to exhumation of the eclogitic schist and subduction of the non-eclogitic schist, indicating that both were formed during the same subduction event. The presence of a major tectonic boundary between two units with a similar or gain as subducted and accreted material, but contrasting metamorphic histories, can be interpreted in terms of nappe tectonics, and the existence of an 'eclogite nappe the third nappe of the Sambagawa belt, is proposed.