Geotectonic subdivision and areal extent of the Sangun belt, Inner Zone of Southwest Japan
Geotectonic subdivision and areal extent of the Sangun belt, Inner Zone of Southwest Japan
复制标题
日本西南部内区三郡带的大地构造细分和面积范围
DOI：
10.1111/j.1525-1314.1998.00059.x
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发表时间：
1998
影响因子：
3.4
通讯作者：
Y. Nishimura
中科院分区：
文献类型：
--
作者：
Y. Nishimura
长期以来，Sangun 带一直被认为是二叠纪至三叠纪时期的一个主要的连贯青闪岩地体，并与北部的低 P/T Hida 带配对。然而，地质年代学、变质地质学和构造学的最新进展表明，该带实际上是由两个不同年龄和形成条件不同的地质单元组成。较旧的单位称为仁格带，较年轻的单位称为索带。莲华带是日本列岛最古老的高P/T 变质带，从九州北部延伸，穿过山阴沿海地区，到达飞驒边缘带。它的特征是年龄为 330–280 Ma 以及蓝闪石片岩与绿帘角闪岩相片岩的组合。 Renge 带通常还与包括蛇纹岩在内的变蛇绿岩序列（470-340 Ma）有关。 Suo带的特征是230-160 Ma高P/T 片岩，与Akiyoshi带的弱变质二叠纪增生岩密切相关。变质相系列包括葡萄石-半辉石相、半辉石-阳起石相、蓝闪石-片岩相、绿帘石-角闪岩相。该带广泛分布于近畿西部，经中国到九州北部和中部，但也进一步向西南延伸，存在于琉球弧南部的石垣岛西表群岛。整个带内散布着小块变蛇绿岩或透镜体，其残余角闪石的 K-Ar 年龄为 590 至 220Ma。两条带均以低角度断层和逆冲断层为界，形成了缓慢向北倾斜的近水平推覆体。日本西南部内带的大地构造格架从北向南由飞騨冲带、莲华带、秋吉带、周带、舞鹤带以及超丹波带、美浓丹波带和良克带组成，构造极性呈向下年轻化。这是古生代到中生代期间逐步增生的结果。
The Sangun belt has long been considered to be a major coherent glaucophanitic terrane of Permian to Triassic age, and to be paired with the low‐P/T Hida belt to the north. However, recent progress in geochronology, metamorphic geology, and tectonics has revealed that the belt is in fact comprised of two geologic units of different ages and with contrasting conditions of formation. The older unit is named the Renge belt and the younger the Suo belt. The Renge belt is the oldest of the high‐P/T metamorphic belts in the Japanese Islands and extends from northern Kyushu, through the San‐in coastal regions, to the Hida marginal belt. It is characterized by 330–280 Ma ages and the association of glaucophane–schist to epidote–amphibolite facies schists. The Renge belt is also typically associated with meta–ophiolite sequences (470–340 Ma) including serpentinite. The Suo belt is characterized by 230–160 Ma high‐P/T schists closely related to weakly metamorphosed Permian accretionary rocks of the Akiyoshi belt. Metamorphic facies series is from the prehnite–pumpellyite facies through the pumpellyite–actinolite and glaucophane–schist facies to the epidote–amphibolite facies. The belt is widespread in west Kinki to north and central Kyushu via Chugoku, but also stretches further to the southwest and is present in the Ishigaki‐Iriomote Islands of the southern Ryukyu Arc. Throughout this belt, there are scattered small blocks or lenses of meta–ophiolite, whose K–Ar ages of relict hornblendes are 590 to 220 Ma. Bounded by low‐angle faults and thrusts, both belts define subhorizontal nappes dipping gently north. The geotectonic framework in the Inner Zone of Southwest Japan is made up of, from north to south, the Hida‐Oki, Renge, Akiyoshi, Suo, Maizuru plus ultra‐Tamba, Mino‐Tamba, and Ryoke belts, with a tectonically downward‐younging polarity. This has resulted from stepwise accretions during Palaeozoic to Mesozoic time.