Detrital anisotropic grandite garnet as an indicator of denudation level of Permian volcanic arc in the provenance of the South Kitakami Belt, Northeast Japan.
Detrital anisotropic grandite garnet as an indicator of denudation level of Permian volcanic arc in the provenance of the South Kitakami Belt, Northeast Japan.
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碎屑各向异性花岗岩石榴石作为日本东北部南北上带物源二叠纪火山弧剥蚀程度的指标。
DOI：
10.1111/iar.12043
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
M.
中科院分区：
文献类型：
--
作者：
Takeuchi;M.
本文研究了日本东北北上带南部中二叠世至上三叠统砂岩中二叠世至上三叠统碎屑石榴石的化学和光学特征，以揭示物源的构造运动。砂岩中含有大量的花岗岩石榴石碎屑颗粒，安山岩的含量范围很广。其中，一些花岗岩石榴石颗粒表现出光学各向异性特征，很少出现振荡分带和扇形孪生。碎屑各向异性花岗岩石榴石的比例从二叠纪到中三叠世逐渐增加，到晚三叠世逐渐减少。这类花岗岩石榴石含量不同，产于矽卡岩型矿床中。夕卡岩演化早期各向同性花岗岩石榴石广泛分布于岩体周围，影响周围地层的热变质作用。而各向异性花岗岩石榴石则是在中晚期热液冷却时沿细脉和裂隙形成的，与早期形成的变质晕相比，其分布范围仅限于岩体附近较窄的区域。碎屑石榴石的化学和光学特征的变化表明，源区伴随夕卡岩矿床的深成岩体逐渐剥蚀。碎屑各向异性花岗岩石榴石在所有碎屑花岗岩石榴石中的比例，与传统的砂岩成分数据一起，被认为是与夕卡岩矿床有关的火山弧深部剥蚀程度的敏感指标。这一新方法有助于阐明东亚大陆边缘二叠纪至三叠纪的古地理，与二叠纪火山弧的抬升和剥蚀有关，这似乎是由北中国地块和南中国地块碰撞引起的。
In this study, the chemical and optical features of detrital garnets from the Middle Permian to Upper Triassic sandstones in the South Kitakami Belt, Northeast Japan, were examined to reveal the tectonic movement in the provenance. The sandstones contain a large amount of detrital grandite garnet grains with a wide range of andradite content. Among them, some grandite garnet grains show optically anisotropic features and rarely oscillatory zoning and sector twinning. The proportion of the detrital anisotropic grandite garnet increases from the Permian to the Middle Triassic and decreases in the Late Triassic. Such grandite garnets with various andradite contents occur in skarn deposits. Isotropic grandite garnets in the early stage of skarn evolution are distributed widely around a pluton, which affects the thermal metamorphism of the surrounding strata. However, anisotropic grandite garnets are formed along veinlets and fractures in the middle to late hydrothermal stage as the pluton cools, and their distribution is limited to a narrower area near the pluton compared to the metamorphic aureoles formed in the early stage. Changes in the chemical and optical features of the detrital garnets indicate a progressive denudation of the plutonic body accompanying skarn deposits in the provenance. The proportion of detrital anisotropic grandite garnet grains among all of the detrital grandite garnet is considered to be a sensitive indicator of the denudation level in a deeper part of the volcanic arc in association with skarn deposits, together with traditional sandstone composition datasets. This newly proposed method should be useful for clarifying the paleogeography during the Permian to Triassic in the East Asian continental margin, associated with uplift and denudation of the Permian volcanic arc, which seems to have been induced by the collision of the North China and South China Blocks.