内蒙古东乌旗地区晶洞碱长花岗岩的成因及其地质意义

发布时间：2018-10-31 15:32

【摘要】：中国东北地区处于中亚造山带的最东段，以广泛分布的显生宙花岗质侵入岩为特征。传统认为这些花岗质岩石形成于晚古生代，主要出露于大兴安岭地区，沿嫩江-贺根山断裂带呈北东向展布。由于缺乏精准的年代学和岩石地球化学资料，严重影响了我们对其成因和形成构造背景的认识。本文对大兴安岭南部东乌旗地区5个具有代表性晶洞碱长花岗岩体进行了锆石LA-ICP-MS U-Pb年代学、岩石地球化学和锆石原位Hf同位素的测试分析，确定了研究区花岗岩的形成时代和岩石成因，进而讨论了大兴安岭地区晚古生代构造演化过程。本文研究的这些碱长花岗岩主要由石英和碱性长石组成，含有少量的斜长石、黑云母，角闪石和副矿物，多数样品具有晶洞构造，暗示其就位深度较浅并经过较强的结晶分异作用。新的锆石U-Pb定年结果显示其结晶于315~300Ma。这些花岗岩富SiO2（73.22%~77.36%）和K2O（3.89%~4.86%），，MgO（0.07%~0.49%）、MnO（0.01%~0.09%）、CaO（0.14%~0.60%）和P2O5（0.01%~0.08%）的含量相对较低，A/CNK和δEu值分别为0.98~1.14和0.03~0.60。稀土元素配分模式图显示轻稀土元素相对富集，具有明显的负铕异常。微量元素原始地幔标准化蛛网图显示Ba、Nb、Ta、Sr和Eu相对亏损，而Zr、Hf、Rb、Th和U较为富集。矿物学、岩石学和地球化学特征表明，它们属于弱过铝质高钾钙碱性高分异I型花岗岩。另外，花岗岩的εHf(t)和二阶段模式年龄分别介于+7.6~+15.1和364Ma~835Ma，表明原始岩浆起源于新增生地壳的部分熔融。根据地球化学资料和先前的区域地质调查研究，我们认为这些晶洞碱长花岗岩形成于活动大陆边缘的背景，其形成可能与兴安地块和松嫩地块之间的古亚洲洋持续向西北俯冲有关。
[Abstract]:Northeast China is located in the easternmost part of the Central Asian orogenic belt, characterized by widely distributed Phanerozoic granitic intrusive rocks. Traditionally, these granitic rocks were formed in the late Paleozoic and mainly appeared in the Daxinganling area, and spread along the Nenjiang-Hegenshan fault zone in a northeasterly direction. The lack of accurate geochronological and petrogeochemical data has seriously affected our understanding of its genesis and tectonic background. In this paper, the zircon LA-ICP-MS U-Pb chronology, geochemistry and in situ Hf isotopes of zircon have been measured and analyzed for five representative crystalline cave alkali feldspar granites in Dongwuqi area, south of Daxing'anling Mountains. The formation age and petrogenesis of granites in the study area are determined, and the late Paleozoic tectonic evolution process in Daxinganling area is discussed. These alkali feldspar granites are mainly composed of quartz and alkaline feldspar, and contain a small amount of plagioclase, biotite, hornblende and accessory minerals. It is suggested that it has a shallow depth and strong crystallization differentiation. The new zircon U-Pb dating results show that the zircon crystallized at 315 Ma. These granites are rich in SiO2 (73.222%) and K2O (3.89%), MgO (0.07%) and 0.49%), MnO (0.01% (0.09%). The contents of CaO (0.14% 0.60%) and P2O5 (0.01%) were relatively low, the values of A/CNK and 未 Eu were 0.981.14 and 0.030.60, respectively. The REE partitioning pattern shows that LREE is relatively enriched and has obvious negative europium anomaly. The trace element primitive mantle-standardized spider webs show the relative depletion of Ba,Nb,Ta,Sr and Eu, but the enrichment of Zr,Hf,Rb,Th and U. Mineralogical, petrological and geochemical characteristics indicate that they belong to weakly peraluminous high-potassium calc-alkaline high-grade iso-I-type granite. In addition, the 蔚 Hf (t) and two-stage model ages of the granites ranged from 7.6 to 15.1 and 364 Ma-835 Ma, respectively, indicating that the primitive magma originated from partial melting of the new accretive crust. Based on geochemical data and previous regional geological surveys, we believe that these granites formed in the background of active continental margin. Its formation may be related to the persistent northwestern subduction of the paleo-Asian ocean between the Xingan and Songnen massif.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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