CAJ | 학술논문

柴北缘西端青海冷湖盐场北山地区发育黑云母二长花岗岩,岩体高硅(SiO2=73.92%~75.98%)、富钾(K2O=3.71%~4.78%)、贫镁钙,铝饱和指数A/CNK介于1.03~1.11,属强过铝质花岗岩。稀土元素球粒陨石标准化曲线呈右倾型, Eu异常不明显；岩体含有富铝矿物石榴子石,刚玉标准分子约为1%, Th、Y含量低,且与Rb呈负相关性,源岩为沉积岩,具 S 型花岗岩特征,是幔源岩浆底侵作用引发地壳物质部分熔融的产物。LA-ICP-MS 锆石 U-Pb 测年结果表明岩体形成于254±4 Ma。结合区域地质背景及岩石地球化学特征认为盐场北山黑云母二长花岗岩形成与俯冲作用有关,类似于岛弧环境产物,从而揭示柴北缘晚二叠世具有活动大陆边缘性质。
시북연서단청해랭호염장북산지구발육흑운모이장화강암,암체고규(SiO2=73.92%~75.98%)、부갑(K2O=3.71%~4.78%)、빈미개,려포화지수A/CNK개우1.03~1.11,속강과려질화강암。희토원소구립운석표준화곡선정우경형, Eu이상불명현；암체함유부려광물석류자석,강옥표준분자약위1%, Th、Y함량저,차여Rb정부상관성,원암위침적암,구 S 형화강암특정,시만원암장저침작용인발지각물질부분용융적산물。LA-ICP-MS 고석 U-Pb 측년결과표명암체형성우254±4 Ma。결합구역지질배경급암석지구화학특정인위염장북산흑운모이장화강암형성여부충작용유관,유사우도호배경산물,종이게시시북연만이첩세구유활동대륙변연성질。
The Yanchangbeishan biotite adamellite in the Lenghu area of Qinghai is located in the west segment of the north margin of Qaidam. The rocks have high SiO2 (73.92%–75.98%) and K2O contents (3.71%–4.78%), but low MgO and CaO contents. The alumina saturation index (A/CNK) varies from 1.03 to 1.11, indicating the biotite adamellite is peraluminous. The chondrite-normalized REE patterns of the rocks are right dipping and display weak Eu anomalies. The rock contains the Al-rich mineral like garnet and possesses normative corundum contents of 1%. It has low Th and Y contents which are negatively correlated with Rb, suggesting the source rock was sedimentary rock. Thus, the biotite adamellite belongs to S-type granite. The granite was produced by partial melting of the crust material due to the underplating of mantle-derived magma. LA-ICP-MS zircon U-Pb dating shows that the formation age of the rock is 254±4 Ma. Based on the regional geological background and the geochemical characteristics of the rocks, we consider that the formation of the Yanchangbeishan biotite adamellite was related to subduction, which is illustrated by the characteristics similar to those of the island-arc igneous rocks. Therefore, the results reveal that the north margin of Qaidam was in active continental margin tectonic environment during Late Permian epoch.