| 上黑龙江盆地前哨林场黑云母二长花岗岩锆石U-Pb年龄、地球化学特征及地质意义 |
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| 引用本文：巩鑫,张志博,杜蔺,蔡国盛,宋小军,曾凡祥,李光春,苏永虎,但仕生,赵元艺.2023.上黑龙江盆地前哨林场黑云母二长花岗岩锆石U-Pb年龄、地球化学特征及地质意义[J].地球学报,44(6):1017-1035. |
| DOI：10.3975/cagsb.2022.122103 |
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| 基金项目:国家重点研发计划“蒙古-鄂霍茨克洋构造体制成矿系统物质组成与过程”(编号: 2017YFC0601303);贵州省找矿突破战略行动重大协同创新项目“贵州稀土;钡;氟等特色资源成矿规律与找矿预测研究”(编号: [2022]ZD004);贵州省有色金属;核工业地质勘查局科研项目“黔北铝土矿含铝岩系关键金属锂迁移富集机制研究”(编号: GZYSKY2023-1) |
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| 中文摘要:上黑龙江盆地前哨林场位于兴蒙造山带东段额尔古纳微地块北缘, 北与西伯利亚古陆以蒙古—鄂霍次克缝合带相隔, 东以塔源—喜桂图断裂与兴安地块相邻。本文通过对上黑龙江盆地前哨林场黑云母二长花岗岩进行锆石U-Pb年龄、主微量及同位素地球化学系统研究, 为探讨早古生代额尔古纳微地块与相邻地块的碰撞机制提供理论依据。利用LA-ICP-MS锆石U-Pb同位素测定技术, 获得研究区黑云母二长花岗岩结晶年龄为(458.4±2.4) Ma(MSWD=0.022), 确定了岩体形成时代为早古生代中—晚奥陶纪。岩石中锆石Hf同位素?Hf(t)值介于–4.64 ~ 1.84, 其测点大部分位于球粒陨石演化线之下, 两阶段模式年龄(tDM2)介于 715 ~ 1 126 Ma。地球化学显示岩石具有富硅、富铝、富碱等特征; 稀土配分曲线表现出轻稀土(LREE)相对富集, 重稀土(HREE)相对亏损的右倾特征, 且岩石相对富集大离子亲石元素Rb、K及高场强元素Th、U、Zr、Hf, 相对亏损大离子亲石元素Ba、Sr及高场强元素Nb、Ta、P、Ti。岩石成因类型判别图显示前哨林场黑云母二长花岗岩具A型花岗岩特征, 岩石Hf同位素及微量元素特征显示岩体岩浆来源于中—新元古代古老地壳的熔融, 且存在少许幔源物质及新增生地壳物质熔融的参与, 元素特征暗示岩石形成于额尔古纳地块与西伯利亚古陆碰撞后的伸展构造环境背景下。结合前人对额尔古纳地块早古生代花岗岩形成背景的研究, 认为额尔古纳地块北缘及东北缘早古生代花岗岩形成机制不同, 前者形成于额尔古纳地块与西伯利亚古陆及蒙古—图瓦地块碰撞、拼接后伸展背景下; 后者主要形成于额尔古纳与兴安地块碰撞伸展背景下。 |
| 中文关键词:LA-ICP-MS 锆石U-Pb年龄 Hf同位素 地球化学 黑云母二长花岗岩 前哨林场 上黑龙江盆地 |
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| Zircon U-Pb Age, Geochemical Characteristics, and Geological Significance of Biotite Monzogranites from Qianshao Forest Farm,Upper Heilongjiang Basin |
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| Abstract:Qianshao forest farm in the Upper Heilongjiang Basin is located on the northern margin of the Erguna micro-block in the eastern part of the Xingmeng orogenic belt. It is separated from the Siberia ancient land by the Mongolia–Okhotsk suture zone in the north. To the east, the Tayuan–Xiguitu fault is adjacent to the Xing’an block. A systematic study of zircon chronology, major and trace elements, and isotopic geochemistry of biotite monzogranites was undertaken on Qianshao forest farm. This provides a theoretical basis for exploring the collision mechanisms between the Erguna micro-block and its adjacent blocks in the Early Paleozoic. Using LA-ICP-MS zircon U-Pb isotope measurement, the crystallization age of the biotite monzogranite in the study area was found to be (458.4±2.4) Ma (MSWD=0.022). The formation age of the rock mass was determined to be the Early Paleozoic and the Middle–Late Ordovician. The zircon Hf isotope ?Hf(t) values range from ?4.64 to 1.84. Most of the zircons are under the chondrite evolution line, and the two-stage model ages (tDM2) range from 715 to 1 126 Ma. Rock mass geochemistry shows that the rock is rich in silicon, aluminum, and alkali. The rare earth partition curve shows a right-sloping characteristic of relative enrichment of light rare earth elements (LREE) and relative depletion of heavy rare earth elements (HREE). The rocks were found to be relatively enriched in large ion lithophile elements, Rb and K, and high field strength elements, Th, U, Zr, and Hf, and relatively depleted in the large ion lithophile elements, Ba, and Sr, and high field strength elements, Nb, Ta, P, and Ti. The identification map of petrogenetic types shows that the biotite monzogranite on Qianshao forest farm has the characteristics of A-type granite. The characteristics of the rock Hf isotope and trace elements have shown that the magma originates from the melting of the ancient crust in the Meso-Neoproterozoic. A few mantle-derived materials are present and melting of newly formed crustal materials has also occurred. The elemental characteristics suggest that the rocks were formed in the extensional tectonic setting after the collision between the Erguna massif and Siberia. Combined with previous studies on the formation background of Early Paleozoic granites in the Erguna Block, the formation mechanisms of Early Paleozoic granites in the northern and northeastern margins of the Erguna Block are believed to be different. The granites from the northern margins were formed under the background of the collision and splicing of the Erguna block with the ancient Siberia and Mongolia–Tuva blocks, whereas the granites from the northeastern margins were predominantly formed under the background of collision and extension of the Erguna and Xing'an blocks. |
| keywords:LA-ICP-MS zircon U-Pb age Hf isotope geochemistry biotite monzonite granite Qianshao forest farm Upper Heilongjiang Basin |
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