班公湖—怒江缝合带西段纳屋错地区岩浆岩特征及构造意义

发布时间：2018-06-26 03:31

本文选题：班公湖-怒江缝合带西段 + 中酸性侵入岩　；参考：《成都理工大学》2015年硕士论文

【摘要】：在野外地质调查基础上,对班公湖-怒江缝合带西段纳屋错地区的中酸性侵入岩及早白垩世去申拉组中基性火山岩进行了详细的岩石学、岩石地球化学、锆石U-Pb测年等研究工作,查明了主要岩石类型、岩石组合及其时空分布规律;分析并探讨了该区的岩浆活动及构造环境,讨论了该区班-怒特提斯洋的俯冲极性。缝合带内中酸性侵入岩以闪长玢岩为主,石英闪长玢岩、石英二长闪长岩、石英斜长(斑)岩、斜长花岗斑岩、花岗闪长斑岩零星出现,均属钙碱性和高钾钙碱性系列。具有LREE富集而HREE亏损的右倾模式,微弱的Eu负异常,表明岩浆分异程度较低,斜长石分离结晶作用不明显。富集大离子不相容元素(HFSE)Rb、K、Ba,亏损高场强元素(LILE)Nb、Ta、Ti、P,曲线总体呈平坦型,显示出岛弧钙碱性系列岩体特征和演化趋势。在构造环境判别图解上显示既有火山弧花岗岩,也有同碰撞花岗岩的特征,说明其形成于班公湖-怒江特斯洋壳的俯冲阶段。缝合带南侧盐湖复式岩体中酸性侵入岩属于高钾钙碱性和钙碱性系列。稀土元素配分显示轻稀土较富集的右倾型,Eu异常不明显,显示壳幔型物源特点。原始地幔标准化图解呈向右缓倾的模式,具俯冲带岩浆作用岛弧型特征。在构造判别图解上均落入火山弧花岗岩VAG区域,岛弧型特征明显,说明其形成于班公湖-怒江特提斯洋壳南向俯冲阶段的活动大陆边缘。缝合带内和盐湖复式岩体的岩石学、岩石地球化学特征相似,其岩石成因均来自俯冲带地幔锲的部分熔融,并受到来自俯冲板片沉积物熔体的交代。锆石U-Pb定年结果表明缝合带内石英闪长玢岩年龄值为104.5Ma,盐湖复式岩体的钾长花岗岩年龄值为100.7Ma,石英二长闪长岩年龄值为108.3Ma。结合区域地质资料,可知其它们的成岩地质时代主要为早白垩世晚期到晚白垩世,说明其形成于俯冲岩浆弧环境,为岩浆弧花岗岩类岩石。早白垩世去申拉组火山岩主要为一系列的中基性火山岩,其稀土元素分布型式为轻稀土弱富集型的右倾型,Eu呈现弱异常;微量元素整体上富集Rb、Ba、Th、U等大离子亲石元素(LILE),亏损Nb、Ta等高场强元素(HFES),具有明显岛弧火山岩特点。说明其形成于班公湖-怒江特提斯洋壳南向俯冲的消减过程。
[Abstract]:On the basis of field geological investigation, the intermediate-acid intrusive rocks of the Nawuso area in the western section of Bangong Lake-Nujiang suture zone were studied in detail in petrology, petrogeochemistry, and petrochemistry of the Middle and basic volcanic rocks of the early Cretaceous Cretaceous Cretaceous Gesheng-La formation. The main rock types, rock assemblages and their temporal and spatial distribution are identified, magmatic activity and tectonic environment in the area are analyzed and discussed, and the subduction polarity of the Ban-Nutertes Ocean in this area is discussed. The intermediate-acid intrusive rocks in the suture zone are mainly diorite porphyrite, quartz diorite, quartz plagioclase (porphyry), plagioclase porphyry and granodiorite porphyry, all of which belong to calc-alkaline and high-potassium calc-alkaline series. The weak EU negative anomaly with LREE enrichment and hree depletion shows that the magmatic differentiation is low and the crystallization of plagioclase is not obvious. The enrichment of large ion incompatibility element (HFSE) RbSe Kni-Bai, depleted high field strength element (Lile) NbPe Tajiao TiTiP.The curve is flat in general, showing the characteristics and evolution trend of the island arc calc-alkaline series rock mass. Both volcanic arc granite and syncollision granite are shown in the tectonic environment discriminant diagram, which indicates that they were formed in the subduction stage of Bangonghu-Nu Jiangtes oceanic crust. The acidic intrusive rocks in the salt lake complex on the southern side of the suture zone belong to the high potassium calc-alkaline and calc-alkaline series. The REE partition shows that the REE distribution is not obvious in the right dip type EU which is rich in LREE and shows the characteristics of the crust-mantle type provenance. The normalized diagram of the primitive mantle shows a rightward gentle dip pattern, which is characterized by the island arc of magmatism in the subduction zone. All of them fall into the VAG area of volcanic arc granite on the tectonic discriminant diagram, and the island arc type is obvious, which indicates that it was formed in the active continental margin of the southern subduction stage of Bangong Lake-Nu River Tethys oceanic crust. The petrology and geochemistry of the suture zone are similar to those of the salt lake complex. The petrogenesis of the suture zone is derived from the partial melting of the mantle of the subduction zone and from the metasomatism of the subduction plate sediment melt. The results of zircon U-Pb dating show that the age of quartz diorite porphyrite in suture zone is 104.5 Ma. the age of potassium feldspar in salt lake complex is 100.7 Ma, and the age of quartz diorite is 108.3 Ma. In combination with regional geological data, their diagenetic geological ages are mainly from the late early Cretaceous to the late Cretaceous, indicating that they were formed in the subduction magmatic arc environment and are magmatic arc granitic rocks. The volcanic rocks of the early Cretaceous Cretaceous are mainly of a series of meso-basic volcanic rocks, and the REE distribution pattern is the LREE enriched weakly enriched right-dip type EU shows weak anomaly. The trace elements are enriched in large ion lithophile elements (lie), such as RbBX, BaTiThU, etc., and depleted in high field strength elements (HFES), such as NB, Ta, etc., and have obvious characteristics of island arc volcanic rocks. It was formed in the course of subduction of Tethys oceanic crust in Bangong Lake-Nu River.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.1

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