| 青海拉脊山东段白家藏侵入岩锆石U-Pb年代学、地球化学特征及其地质意义 |
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| 引用本文： | 张新远,李五福,王春涛,刘建栋,欧阳光文.青海拉脊山东段白家藏侵入岩锆石U-Pb年代学、地球化学特征及其地质意义[J].吉林大学学报(地球科学版),2020,50(6):1703-1719. |
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| 作者姓名： | 张新远 李五福 王春涛 刘建栋 欧阳光文 |
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| 作者单位： | 1. 青海省青藏高原北部地质过程与矿产资源重点实验室, 西宁 810012;2. 青海省地质调查院, 西宁 810012 |
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| 基金项目： | 国家科技部项目（2019QZKK0702）；中国地质调查局项目（12120114041301，12120114079701，1212011221151） |
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| 摘 要： | 白家藏侵入岩位于青海省民和县，大地构造位置上处于拉脊山蛇绿混杂岩带东段。通过岩石学、同位素年代学和岩石地球化学方法，对白家藏侵入岩进行了研究，以确定其侵位时代并探讨大地构造环境。结果表明，白家藏侵入岩主要由闪长岩和石英闪长岩组成，分别在闪长岩和石英闪长岩中获得锆石U-Pb年龄为（472.5±1.9）Ma和（467.3±2.5）Ma，二者在误差范围内一致，据此判断白家藏侵入岩的侵位年龄约470 Ma，为中奥陶世。地球化学特征显示：岩体w（SiO2）为55.67%~59.04%，Na2O/K2O值为3.35~6.14，且w（Na2O）高于w（K2O），显示富钠、贫钾特征；A/CNK值主体介于0.76~1.01之间，属于准铝质钙碱性系列岩石；稀土配分曲线呈轻稀土元素相对弱富集（（La/Yb）N=2.51~4.57），轻、重稀土元素内部分馏较弱的微右倾型曲线；岩石明显富集大离子亲石元素Rb、Ba和活泼的不相容元素Th、U，相对亏损高场强元素Nb、Ta、P、Ti等；环境判别显示具岛弧花岗岩特征。以上特征表明白家藏侵入岩为拉脊山洋俯冲阶段的产物。
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| 关 键 词： | 地球化学 锆石U-Pb年龄 岩石成因 俯冲环境 中奥陶世 拉脊山 |
| 收稿时间： | 2019-05-20 |
Zircon U-Pb Dating,Geochemistry and Their Geological Significance of Baijiazang Pluton in Eastern Section of Lajishan in Qinghai Province |
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| Zhang Xinyuan,Li Wufu,Wang Chuntao,Liu Jiandong,Ouyang Guangwen.Zircon U-Pb Dating,Geochemistry and Their Geological Significance of Baijiazang Pluton in Eastern Section of Lajishan in Qinghai Province[J].Journal of Jilin Unviersity:Earth Science Edition,2020,50(6):1703-1719. |
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| Authors: | Zhang Xinyuan Li Wufu Wang Chuntao Liu Jiandong Ouyang Guangwen |
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| Institution: | 1. Qinghai Provincial Key Laboratory of Geological Processes and Mineral Resources of Northern Qinghai-Tibetan Plateau, Xining 810012, China;2. Qinghai Geological Survey Institute, Xining 810012, China |
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| Abstract: | The intrusive rocks of Baijiazang is located in Minhe County, Qinghai Province, and the geotectonic position is located in the eastern section of Lajishan ophiolis melange belt. Through petrology, petrogeochemistry and isotopic chronology, the intrusive rocks of Baijiazang have been studied in order to determine their time of emplacement and to explore the tectonic environment. The results show that the intrusive rocks in Baijiazang are mainly composed of diorite and quartz diorite. Zircon U-Pb age obtained from diorite and quartz diorite is (472.5±1.9) Ma and (467.3±2.5) Ma, respectively, and they are consistent within the error range. Therefore, it can be judged that the emplacement age of Baijiazang rock is about 470 Ma, which is Middle Ordovician. The geochemical characteristics show that the SiO2 content of the rock mass is 55.67%-59.04%. The value of Na2O/K2O was 3.35-6.14, and w (Na2O) was higher than of w (K2O), showing the characteristics of rich in sodium and poor in potassium. The main body of A/CNK value is between 0.76 and 1.01, belonging to the quasi-aluminum calc-alkaline series rocks. The rare earth partition curve presented a slightly right-leaning curve, where light rare earth elements were relatively weakly enriched ((La/Yb)N=2.51-4.57), and light and heavy rare earth elements were weakly fractionated internally. The rocks were obviously enriched with large ion lipophilic elements Rb, Ba and active incompatible elements Th and U, while relatively deficient with high-field strength elements Nb, Ta, P, Ti, etc. Environmental discrimination shows that it has the characteristics of island-arc granite. The above characteristics indicate that the intrusive rocks in Baijiazang were produced at the subduction stage of the Lajishan ocean. |
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| Keywords: | geochemistry zircon U-Pb age petrogenesis subduction Middle Ordovician Lajishan |
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