Development of the Median Tectonic Line-related shear zone, southwest Japan: An analysis of strain localization processes
Development of the Median Tectonic Line-related shear zone, southwest Japan: An analysis of strain localization processes
复制标题
日本西南部中位构造线相关剪切带的发展：应变局部化过程分析
DOI：
10.1016/j.tecto.2023.229751
复制
发表时间：
2023
期刊：
影响因子：
2.9
通讯作者：
Czertowicz Thomas A.
中科院分区：
文献类型：
--
作者：
Bui Dong Van;Takeshita Toru;Ando Jun-ichi;Yamamoto Takafumi;Huang Wencheng;Yeo Thomas;Czertowicz Thomas A.
研究了日本西南部沿中央构造线（MTL）沿着发育于白垩纪花岗岩中的糜棱岩带，以了解冷却过程中的应变局部化。糜棱岩呈东西走向，北倾，代表MTL的上盘。糜棱岩带包括原糜棱岩和糜棱岩，它们分别来自两种不同的原岩：英云闪长岩（原糜棱岩）和花岗岩（糜棱岩），分别出现在距MTL 0 -300 m和300-700 m处。我们使用石英显微结构和晶体学择优取向（CPOs）和双长石测温推断变形条件的时空发展在MTL糜棱岩带。糜棱岩花岗岩可分为南糜棱岩带和北方糜棱岩带，分别具有亚晶旋转和晶界迁移重结晶形成的A型和B型石英显微结构。在糜棱岩花岗岩和原糜棱岩英云闪长岩中，石英c轴CPO主要显示中等温度Y最大图案，以及不太常见的低温I型交叉环带图案。在北方带，石英变形最初发生在435 °C-490 °C的中等温度下，形成具有B型石英显微结构的糜棱岩花岗岩。当温度降低到355 °C-435 °C时，应变局部化到南部区域，形成A型石英显微结构。在相似的温度条件下形成的原糜棱岩英云闪长岩。在低于355 °C的温度下，大部分花岗岩和英云闪长岩的韧性变形停止，只有一个狭窄的超糜棱岩区宽达50米，在接近石英脆韧性转变的条件下（约300 °C）在MTL附近变形。应变局部化没有发生在一个单一的剪切带，但在几个变形股，形成在不同的原岩，其中一个发展成狭窄的超糜棱岩区改造为脆性MTL，可能控制冷却。
The development of a mylonite zone along the Median Tectonic Line (MTL), southwest Japan, which developed in the Cretaceous granitic rocks, was examined to understand strain localization during cooling. The mylonites are E-W trending, north-dipping, and represent the hanging wall of the MTL. The mylonite zone includes both protomylonite and mylonite, which were derived from two distinct protoliths: tonalite (protomylonite) and granite (mylonite) and occur at distances ofc.0–300 m and 300–700 m from the MTL, respectively. We used quartz microstructures and crystallographic preferred orientations (CPOs) and two-feldspar thermometry to infer the spatiotemporal development of deformation conditions in the MTL mylonite zone. The mylonitic granite is sub-divided into southern and northern mylonite zones, which exhibit A- and B-type quartz microstructure formed by subgrain rotation and grain boundary migration recrystallization, respectively. In both the mylonitic granite and protomylonitic tonalite, quartzc-axis CPOs primarily display a moderate-temperatureY-maximum pattern, as well as a less common low-temperature type-I crossed-girdle pattern. In the northern zone, quartz deformation initially occurred at moderate temperatures of 435 °C–490 °C, forming mylonitic granite with B-type quartz microstructure. As temperature decreased to 355 °C–435 °C, the strain localized into the southern zone to form A-type quartz microstructure. The protomylonitic tonalite formed under similar temperature conditions. At temperatures below 355 °C, ductile deformation ceased in the majority of the granite and tonalite, with only a narrow zone of ultramylonite up to 50 m wide, deforming adjacent to the MTL at conditions approximating the brittle–ductile transition in quartz (c.300 °C). Strain localization did not occur within a single shear zone, but in several deforming strands that formed in distinct protoliths, one of which developed into the narrow ultramylonite zone reworked as the brittle MTL, likely controlled by cooling.