| Early Cretaceous Adakitic Rocks in the Northern Great Xing’an Range, NE China: Implications for the Final Closure of Mongol-Okhotsk Ocean and Regional Extensional Setting |
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| 作者姓名： | ZHANG Lingyu LI Shichao CHU Xiaolei SHANG Yinmin |
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| 基金项目： | the National Natural Science Foundation of China;Self-determined Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Land and Resources;Graduate Innovation Fund of Jilin University |
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| 摘 要： | A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean effected the lithosphere in NE China. In this paper, we carried out a comprehensive study for andesites from the Keyihe area using LA-ICP-MS zircon UPb dating and geochemical and Hf isotopic analysis to investigate the petrogenesis and tectonic setting of these andesites. The U-Pb dating yields an Early Cretaceous crystallization age of 128.3±0.4 Ma. Geochemically, the andesites contain high Sr(686–930 ppm) and HREE contents, low Y(11.9–19.8 ppm) and Yb(1.08–1.52 ppm) contents, and they therefore have high Sr/Y(42–63) and La/Yb(24–36) ratios, showing the characteristics of adakitic rocks. Moreover, they exhibit high K_2O/Na_2O ratios(0.57–0.81), low Mg O contents(0.77–3.06 wt%), low Mg# value(17–49) and negative εHf(t) values(-1.7 to-8.5) with no negative Eu anomalies, indicating that they are not related to the oceanic plate subduction. Based on the geochemical and isotopic data provided in this paper and regional geological data, it can be concluded that the Keyihe adakitic rocks were affected by the Mongol-Okhotsk tectonic regime, forming in a transition setting from crustal thickening to regional extension thinning. They were derived from the partial melting of the thickened lower crust. The closure of the Mongol-Okhotsk Ocean may finish in early Early Cretaceous, followed by the collisional orogenic process. The southern part region of its suture belt was in a post-orogenic extensional setting in the late Early Cretaceous.
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| 关 键 词： | Mongol-Okhotsk Ocean northern Great Xing’an Range Early Cretaceous adakitic rocks lower crust |
| 收稿时间： | 2019/5/15 0:00:00 |
| 修稿时间： | 2019/8/14 0:00:00 |
Early Cretaceous Adakitic Rocks in the Northern Great Xing'an Range,NE China: Implications for the Final Closure of Mongol‐Okhotsk Ocean and Regional Extensional Setting |
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| Authors: | ZHANG Lingyu LI Shichao CHU Xiaolei and SHANG Yinmin |
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| Institution: | 1 College of Earth Sciences, Jilin University, Changchun 130061, China
2 Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources, Changchun, 130061, China,1 College of Earth Sciences, Jilin University, Changchun 130061, China
2 Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources, Changchun, 130061, China,1 College of Earth Sciences, Jilin University, Changchun 130061, China and 1 College of Earth Sciences, Jilin University, Changchun 130061, China |
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| Abstract: | A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol‐Okhotsk Ocean and the Paleo‐Pacific Ocean effected the lithosphere in NE China. In this paper, we carried out a comprehensive study for andesites from the Keyihe area using LA‐ICP‐MS zircon U‐Pb dating and geochemical and Hf isotopic analysis to investigate the petrogenesis and tectonic setting of these andesites. The U‐Pb dating yields an Early Cretaceous crystallization age of 128.3±0.4 Ma. Geochemically, the andesites contain high Sr (686–930 ppm) and HREE contents, low Y (11.9–19.8 ppm) and Yb (1.08–1.52 ppm) contents, and they therefore have high Sr/Y (42–63) and La/Yb (24–36) ratios, showing the characteristics of adakitic rocks. Moreover, they exhibit high K2O/Na2O ratios (0.57–0.81), low MgO contents (0.77–3.06 wt%), low Mg# value (17–49) and negative εHf(t) values (–1.7 to –8.5) with no negative Eu anomalies, indicating that they are not related to the oceanic plate subduction. Based on the geochemical and isotopic data provided in this paper and regional geological data, it can be concluded that the Keyihe adakitic rocks were affected by the Mongol‐Okhotsk tectonic regime, forming in a transition setting from crustal thickening to regional extension thinning. They were derived from the partial melting of the thickened lower crust. The closure of the Mongol‐Okhotsk Ocean may finish in early Early Cretaceous, followed by the collisional orogenic process. The southern part region of its suture belt was in a post‐orogenic extensional setting in the late Early Cretaceous. |
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| Keywords: | Mongol‐Okhotsk Ocean northern Great Xing'an Range Early Cretaceous adakitic rocks lower crust |
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