Permian Tectonic Evolution in Southwestern Khanka Massif: Evidence from Zircon U‐Pb Chronology, Hf isotope and Geochemistry of Gabbro and Diorite
Permian Tectonic Evolution in Southwestern Khanka Massif: Evidence from Zircon U‐Pb Chronology, Hf isotope and Geochemistry of Gabbro and Diorite
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DOI：
10.1111/j.1755-6724.2011.00594.x
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发表时间：
2011-12
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影响因子：
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通讯作者：
Huahua Cao;Wenliang Xu;F. Pei;Xingzhou Zhang
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文献类型：
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作者：
Huahua Cao;Wenliang Xu;F. Pei;Xingzhou Zhang
通过对珲春地区二叠纪辉长岩和闪长岩的激光烧蚀-电感耦合等离子体质谱（LA-ICP-MS）锆石U-Pb定年和地球化学数据的分析，对该区区域构造演化进行了研究。辉长岩和闪长岩中的锆石呈自形-半自形，具有精细的振荡分带，Th/U比值较高（0.26-1.22），表明其为岩浆成因。测年结果表明，辉长岩和闪长岩分别形成于早二叠世（282±2 Ma）和晚二叠世（255±3 Ma）。此外，还在闪长岩中发现了捕获锆石，其加权平均年龄为279±4 Ma，与辉长岩的形成年龄在不确定范围内一致。辉长岩属低钾拉斑玄武岩系列，稀土元素丰度低，稀土配分模式平坦，Eu呈弱正异常（δEu），高场强元素（HFSEs、Nb、Ta和Ti）亏损，与岛弧环境下的高铝玄武岩相似。辉长岩中锆石的初始Hf同位素比值为+7.63 ~+14.6，表明其原始岩浆可能主要来自亏损岩石圈地幔的部分熔融。闪长岩属中钾钙碱性系列。与辉长岩相比，闪长岩具有较高的稀土元素丰度，弱的负Eu异常，高场强元素（Nb、Ta、Ti）亏损较多，与活动大陆边缘环境下的火山岩化学成分相似。锆石Hf初始同位素比值和Hf两阶段模式年龄分别为+11.22 ~+14.17和424 ~ 692 Ma，表明其原始岩浆可能主要来自早古生代和新元古代增生下地壳的部分熔融。从早二叠世辉长岩到晚二叠世闪长岩的地球化学变化表明，古亚洲洋板块俯冲到汉卡地块之下，弧陆碰撞（汉卡地块）发生在晚古生代晚期。
Laser ablation‐inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U‐Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral‐subhedral in shape and display fine‐scale oscillatory zoning as well as high Th/U ratios (0.26–1.22), implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian (282±2 Ma) and in the Late Permian (255±3 Ma), respectively. In addition, the captured zircons with the weighted mean age of 279±4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low‐K tholeiitic series, and are characterized by low rare earth element (REE) abundances, flat REE pattern, weak positive Eu anomalies (δEu), and depletion in high field strength elements (HFSEs, Nb, Ta, and Ti), similar to the high‐aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from +7.63 to +14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc‐alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs (Nb, Ta, and Ti), similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two‐stage model ages of zircons from the diorite range from +11.22 to +14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo‐Asian oceanic plate beneath the Khanka Massif and collision between the arc and continent (Khanka Massif) happened in the late stage of the Late Paleozoic.