【作者】 王乔林；

【导师】 董国臣；

【作者基本信息】 中国地质大学（北京） ， 矿物学、岩石学、矿床学， 2011， 硕士

【摘要】 古近纪林子宗群火山岩广泛出露于青藏高原冈底斯带南部,它是一套由同碰撞向后碰撞转化为特征的岩浆作用产物,被认为代表了新特提斯洋俯冲消减结束过渡到印度-亚洲大陆碰撞过程的产物。研究区位于冈底斯带西段,地处班公湖-怒江结合带与雅鲁藏布江缝合带之间,位于南冈底斯岩浆弧构造单元。本文主要对出露于冈底斯带西段的林子宗群火山岩进行系统的岩石学和地球化学以及锆石U-Pb年代学研究,探讨了其岩石成因、演化源区及其构造意义等特征,并同冈底斯带东段研究程度较高的林周盆地的林子宗群火山岩进行了对比研究。研究表明,冈底斯带西段林子宗群火山岩主要为偏铝质-过铝质的钙碱性-高钾钙碱性的一套中酸性火山岩。稀土元素显示轻稀土富集,具有中等程度的Eu负异常(δEu的平均值0.64),不同程度的亏损高场强元素Nb、Ta、Ti等,相对富集大离子亲石元素Rb、Th、U、K等,早期显示弧火山岩的特征,晚期显示碰撞-后碰撞的特征, Pb同位素( 208Pb/204Pb=36.9801～39.003、207Pb/204Pb=15.328～15.645、206Pb/204Pb=16.664～18.563)特征显示壳幔混合源区产物,受冈底斯地壳基底影响明显。研究区林子宗群典中组火山岩锆石U-Pb年龄为64.25±0.91Ma和64.52±0.48Ma。综合现有的冈底斯带各段的高精度年代学资料,林子宗群火山岩在冈底斯带具有穿时性。更多还原

【Abstract】 The Paleogene volcanic rocks in Linzizong Group is widely developed in the southern Gangdese belt of Tibet plateau, it is deemed to represent the result of Neo-tethys from its subduction to the India-Asia collision as it contains the information from syn-collisioal to post-collisioal affinities in the whole group. The study area saturated in the west of Gangdese belt, it belongs to the southern Gangdese magmatic arc tectonic unit. Herein a systematic, including zircon U-Pb ages, major and trace elements and Pb isotopic geochemistry, has been done to volcanic of Dianzhong Formation from Linzizong Group of western Gangdese belt. The petrogenesis source region evolution of the rocks has been discussed. Based on the previous studies, the results of this thesis were also compared to the Linzizong Group in the Linzhou basin of the east of Gangdese belt, and to distributed in other different regions of southern Gangdese belt,in order to find the spatial and temporal change among these volcanic rocks.In the research, we find that most volcanic rocks of Linzizong Group belong to peraluminous and high-potassim, calc-alkaline and high-K calc-alkaline volcanic. They show LREE enrichment with a significant Eu negative anamaly (the average is 0.6453). The rocks are depleted in Nd、Ta、Ti and other HFSE and enriched in Rb、Th and other LILE, both of which showing the typical arc-related magmatism affinities. The rocks are enriched in Pb ( 208Pb/204Pb=36.9801~39.003、207Pb/204Pb=15.328~15.645、206Pb/204Pb=16.664~18.563), which revealed a mixture source region controlled by the continental basement materials in Gangdese belt. The LA-ICP-MS zircon U-Pb data of the 3th group of Dianzhong Formation volcanic rocks which we obtain showing the following ages: 64.25±0.91Ma and 64.52±0.48Ma. Reviewing the data of different area of southern Gangdese belt, which indicate that the India-Asia collision along Gangdese belt may be diachronous.更多还原