THE EARLY JURASSIC ADAKITE IN SUNWU AREA, NORTHERN XIAOXINGANLING MOUNTAINS: Genetic Connection to the Activation of Nenjiang-Heihe Tectonic Belt
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摘要: 对孙吴地区石英二长闪长岩进行了系统的年代学和地球化学研究.LA-ICP-MS锆石U-Pb定年结果显示其形成时代为（174.9±1.2） Ma，为早侏罗世晚期岩浆岩侵入体.岩石学和地球化学研究表明，岩石高SiO2和Al2O3，低MgO，相对富Na （Na2O/K2O为1.51~2.53）；Sr>400×10-6，Y ≤ 18×10-6，Yb ≤ 1.9×10-6，轻重稀土分馏明显，（La/Yb）N为12.32~22.45，无明显的Eu负异常，显示了埃达克岩的地球化学特征，结合其较低的Cr、Ni含量和Rb/Sr比值以及相对较高的Mg#，推测其形成于增厚下地壳的部分熔融，并受地幔物质混染.综合区域地质特征，初步认为研究区埃达克岩的形成是在蒙古-鄂霍次克造山带的构造体制下，受嫩江-黑河构造带活化影响，孙吴地区早侏罗世处于陆内伸展的构造环境.Abstract: The quartz monzodiorite in Sunwu area, Northern Xiaoxinganling Mountains, is systematically studied on chronology and geochemistry. The LA-ICP-MS zircon dating yields the emplacement age of 174.9±1.2 Ma (Early Jurassic). Petrological and geochemical study indicates that the rock contains high SiO2 and Al2O3 but low MgO, plus relatively enrichment of Na (Na2O/K2O in 1.51-2.53). It is high in Sr (>400×10-6), low in Y (≤ 18×10-6) and Yb (≤ 1.9×10-6), with notable fractionation between LREE and HREE, (La/Yb)N varying between 12.32 and 22.45. Besides, there is not significant negative Eu anomaly in the chondrite-normalized REE pattern. All of the geochemical characteristics above suggest that the quartz monzodiorite in Sunwu area belongs to adakite. The rock is originated from the partially melted thickened lower crust, and subject to the contamination of mantle material. Integrating with regional geology, it is concluded that the rock is formed under the tectonic system of Mongol-Okhotsk orogenic belt, affected by the activation of Nenjiang-Heihe tectonic belt. This area was in an intracontinental extension during the Early Jurassic Epoch.
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Key words:
- adakite /
- Early Jurassic /
- geological implication /
- Nenjiang-Heihe tectonic belt /
- Sunwu area /
- Xiaoxinganlin Mountains
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