Tectono‐metamorphic evolution of the Okcheon Metamorphic Belt, South Korea: Tectonic implications in East Asia
Tectono‐metamorphic evolution of the Okcheon Metamorphic Belt, South Korea: Tectonic implications in East Asia
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DOI：
10.1111/j.1440-1738.2004.00433.x
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发表时间：
2004-06
期刊：
影响因子：
1.5
通讯作者：
C. Oh;S. Kim;In-Chang Ryu;T. Okada;H. Hyodo;T. Itaya
中科院分区：
文献类型：
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作者：
C. Oh;S. Kim;In-Chang Ryu;T. Okada;H. Hyodo;T. Itaya
越川变质带的构造历史是理解韩中日构造关系的关键。OMB中150个砂质岩石的岩石化学表明，沉积环境向西北方向逐渐加深。这些数据，结合氧化物矿物的分布模式和碳质物质的丰度，支持OMB的半地堑盆地模型。黑云母和白云母K-Ar年龄从中央OMB的变质沉积物范围从102至277马。整个地区广泛存在142-194 Ma的K-Ar年龄，而216-277 Ma的更老年龄仅限于OMB中部的变质沉积物。较年轻的（白垩纪）年龄仅在位于白垩纪花岗岩侵入体附近的变质沉积物中发现。弱变形区的216-277 Ma年龄代表M1中压温变质作用的冷却年龄。年龄分布与变形模式之间的关系表明，侏罗纪白云母和黑云母年龄可解释为完全重置年龄，是由与侏罗纪花岗岩深成作用有关的热变形活动引起的。变质沉积物和花岗质岩石中云母的40 Ar/39 Ar坪年龄为155-169 Ma，可与侏罗纪主要的K-Ar云母年龄（149-194 Ma）进行对比。OMB西南部黑云母花岗岩的锆石U-Pb年龄为167-169 Ma。根据研究区以侏罗系为主的火成岩和变质年龄以及碳质物质d 002值的一致性，认为OMB经历了M1变质作用后的角闪岩相M2变质作用。这种低P/T M2区域热变质作用可能是由侏罗纪花岗岩的区域侵入作用引起的。OMB可能经历了如下的构造变质演化：（1）OMB起源于新元古代Rodinia裂解过程中的板内裂谷，可能代表华南陆块内部华南裂陷槽的延伸;（2）从新元古代到奥陶纪，OMB的沉积作用持续不断，可能存在多个不整合面;（iii）M_1中P/T变质作用发生在晚古生代，是南北陆块碰撞挤压的结果;早中侏罗世，Farallon-Izanagi板块向北向西俯冲至亚洲板块之下，花岗岩广泛侵入，触发了OMB中M2期低P/T区域热变质作用。这一事件还在OMB和前寒武纪Yeongnam Wuff之间的边界形成了右行湖南剪切带。
Abstract The tectonic history of the Okcheon Metamorphic Belt (OMB) is a key to understanding the tectonic relationship between South Korea, China and Japan. The petrochemistry of 150 psammitic rocks in the OMB indicates that the depositional environment progressively deepened towards the northwest. These data, combined with the distribution pattern of oxide minerals and the abundance of carbonaceous material, support a half‐graben basin model for the OMB. Biotite and muscovite K–Ar dates from metasediments in the central OMB range from 102 to 277 Ma. K–Ar ages of 142–194 Ma are widespread throughout the area, whereas the older ages of 216–277 Ma are restricted to the metasediments of the middle part of the central OMB. The younger (Cretaceous) ages are only found in metasediments that are situated near the Cretaceous granite intrusions. The 216–277 Ma dates from weakly deformed areas represent cooling ages of M1 intermediate pressure/temperature (P/T) metamorphism. The relationship between age distribution and deformation pattern indicates that the Jurassic muscovite and biotite dates can be interpreted as complete resetting ages, caused by thermal and deformational activities associated with Jurassic granite plutonism. Well‐defined 40Ar/39Ar plateau ages of 155–169 Ma for micas from both metasediments and granitic rocks can be correlated with the main Jurassic K–Ar mica ages (149–194 Ma). U–Pb zircon dates for biotite granite from the southwest OMB are 167–169 Ma. On the basis of the predominantly Jurassic igneous and metamorphic ages and the uniformity of d002 values for carbonaceous materials in the study area, it is suggested that the OMB has undergone amphibolite facies M2 metamorphism after M1 metamorphism. This low P/T M2 regional thermal metamorphism may have been caused by the regional intrusion of Jurassic granites. The OMB may have undergone tectono‐metamorphic evolution as follows: (i) the OMB was initiated as an intraplate rift in the Neoproterozoic during break‐up of Rodinia, and may represent the extension of Huanan aulacogen within the South China block; (ii) sedimentation continued from the Neoproterozoic to the Ordovician, perhaps with several unconformities; (iii) M1 intermediate P/T metamorphism occurred during the Late Paleozoic due to compression caused by collision between the North and South China blocks in an area peripheral to the collision zone; and (iv) during the Early to Middle Jurassic, north‐westward subduction of the Farallon‐Izanagi Plate under the Asian Plate resulted in widespread intrusion of granites, which triggered M2 low P/T regional thermal metamorphism in the OMB. This event also formed the dextral Honam shear zone at the boundary between the OMB and Precambrian Yeongnam massif.