Early Carboniferous HP metamorphism in the Hida Gaien Belt, Japan: Implications for the Palaeozoic tectonic history of proto‐Japan
Early Carboniferous HP metamorphism in the Hida Gaien Belt, Japan: Implications for the Palaeozoic tectonic history of proto‐Japan
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DOI：
10.1111/jmg.12564
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发表时间：
2020-08
影响因子：
3.4
通讯作者：
Takumi Yoshida;Tomoki Taguchi;H. Ueda;K. Horie;M. Satish‐Kumar
中科院分区：
文献类型：
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作者：
Takumi Yoshida;Tomoki Taguchi;H. Ueda;K. Horie;M. Satish‐Kumar
本文报道了日本新泻县最西部地区尾美地区高磷(HP)变质岩中两个新的榴辉岩位置(Kanayamadani和Shinadani)，并确定了变质条件和压力-温度(P-T)轨迹。榴辉岩的变质演化表现为从前进型绿帘石-蓝片岩相到峰期榴辉岩相再到退变蓝片岩相的紧凑的发夹型P-T轨迹。进变质阶段以石榴石中的角闪石包裹体为特征，峰期榴辉岩相组合以绿辉石、石榴石、多硅白云母和金红石为特征。用常规阳离子交换测温法、钛锆石测温法和石英包裹体拉曼压力法估算榴辉岩的峰温条件分别为~600℃和2.0 GPa.而与榴辉岩共生的变质岩的拉曼光谱峰温较低，可能是由于在折返过程中变质作用不同所致。根据基质中蓝闪石的丰度，识别出变质作用高峰期后的蓝片岩相叠加。与榴辉岩相邻的两个地点的蓝片岩相变质沉积样品中的锆石颗粒具有明显的振荡带核和增生边缘。碎屑岩芯的激光消融电感耦合等离子体质谱U-Pb值范围在3200~400 Ma之间，峰值出现在600~400 Ma。早古生代，原日本地处中国克拉通南部大陆边缘，为沟充填沉积中较老的碎屑锆石颗粒(3,200~600 Ma)提供了物质来源。此外，在原日本以下的地壳中还记录到与俯冲有关的大约500-400 Ma的岩浆活动，这可能是较年轻的碎屑状锆石颗粒的来源。峰期变质年龄受SHRIMP年龄限制，Tournaisian年龄为347±4 Ma，表明早石炭世为俯冲作用。我们的研究结果为南中国克拉通活动大陆边缘俯冲、吸积和弧沟系统的形成提供了明确的制约条件，有助于解开古日本古生代构造史。
We report two new eclogite localities (at Kanayamadani and Shinadani) in the high‐P (HP) metamorphic rocks of the Omi area in the western most region of Niigata Prefecture, Japan, which form part of the Hida Gaien Belt, and determine metamorphic conditions and pressure–temperature (P–T) paths. The metamorphic evolution of the eclogites is characterized by a tight hairpin‐shaped P–T path from prograde epidote–blueschist facies to peak eclogite facies and then retrograde blueschist facies. The prograde metamorphic stage is characterized by various amphibole (winchite, barroisite, glaucophane) inclusions in garnet, whereas the peak eclogite facies assemblage is characterized by omphacite, garnet, phengite and rutile. Peak P–T conditions of the eclogites were estimated to be ~600°C and up to 2.0 GPa by conventional cation‐exchange thermobarometry, Ti‐in‐zircon thermometry and quartz inclusion Raman barometry respectively. However, the Raman spectra of carbonaceous material thermometry of metapelites associated with the eclogites gave lower peak temperatures, possibly due to metamorphism at different conditions before being brought together during exhumation. The blueschist facies overprint following the peak of metamorphism is recognized by the abundance of glaucophane in the matrix. Zircon grains in blueschist facies metasedimentary samples from two localities adjacent to the eclogites have distinct oscillatory‐zoned cores and overgrowth rims. Laser ablation inductively coupled plasma mass spectrometry U–Pb ages of the detrital cores yield a wide range between 3,200 and 400 Ma, with a peak at 600–400 Ma. In the early Palaeozoic, proto‐Japan was located along the continental margin of the South China craton, providing the source of the older population of detrital zircon grains (3,200–600 Ma) deposited in the trench‐fill sediments. In addition, subduction‐related magmatism c. 500–400 Ma is recorded in the crust below proto‐Japan, which might have been the source for the younger detrital zircon grains. The peak metamorphic age was constrained by SHRIMP dating of the overgrowth rims, yielding Tournaisian ages of 347 ± 4 Ma, suggesting subduction in the early Carboniferous. Our results provide clear constraints on the initiation of subduction, accretion and the development of an arc‐trench system along the active continental margin of the South China craton and help to unravel the Palaeozoic tectonic history of proto‐Japan.