腾冲新生代火山岩年代学、岩浆源区特征及其成因探讨

The Tengchong area, which is located within the India-Eurasia collision zone, is the section of the Himalayan geothermal belt that contains widespread Cenozoic volcanism and earthquakes. Active magma is nowdays probably present in the magma chamber at shallow crustal level beneath the field. However, ages and origin of the Cenozoic volcanic rocks in Tengchong area are still controversial. .In recent years, our studies focused on petrology, geochemistry and zircon SHRIMP U-Pb dating of the volcanic rocks. Large amount of zircons with different sources and genesis have been separated from these rocks. Geochronology studies on typical volcanic zircons have precisely constrained four volcanic magma crystallization periods, namely ca. 0.48 Ma, 0.80 Ma, 2.82 Ma and 12.28 Ma, and suggested some earlier volcanic activities ca. 16.2 Ma and 21.6 Ma. .This study aims to precisely constrain the temporal-spatial distribution as well as promoting geochronology study on the young geological bodies by conducting systematic petrology, petrography, geochemistry, zircon SHRIMP U-Pb, U-Th dating and U series dating simultaneously. We’ll make further studies of in-situ texture and composition of certain minerals and P-T estimates especially on the Holocene volcanic rocks, trying to understanding the magma chamber process. Detailed O-Hf isotopic analyses on different kinds of zircon from these volcanic rocks will be carried out to investigate their origin. .The study will be significant for both technical methods and geological research of magma chamber process as well as crust-mantle interaction.

滇西腾冲地区广泛分布新生代火山岩，但其形成期次尚缺乏统一认识，同时该区火山岩的岩浆源区特征及其成因也存有争议！我们近年来致力于腾冲火山岩SHRIMP锆石U-Pb定年研究工作，在很多火山岩样品中分选出大量多源区、多成因的锆石，精确限定了4期火山岩形成时代（0.48 Ma、0.80 Ma、2.82 Ma和12.28 Ma）。本项目拟通过对一系列关键剖面开展系统的岩石学、岩相学、地球化学和SHRIMP锆石U-Pb定年、铀系不平衡定年研究，在国内率先建立 SHRIMP锆石U-Th定年方法，精确划分腾冲火山岩的活动期次；并通过对不同时代、不同成因锆石O-Hf同位素组成分析来探讨岩浆源区特征。本立项在国内将是一种技术方法的突破，同时对于进一步探讨岩浆房演化过程及壳幔相互作用有重要的科学意义。

本项目以国家科技基础条件平台北京离子探针中心为基础，以滇西腾冲地区新生代火山岩为主要研究对象，建立了年轻地质体锆石定年方法，优化了年轻地质体年龄校正公式；精确厘定了腾冲火山岩活动期次；探讨了腾冲火山岩的源区特征和成因；并针对中国东部地区以及特提斯造山带内出露的火山岩开展应用示范及对比研究，精确测定了中国东部中生代火山岩、特提斯构造域各中生代火山岩以及代表性月球陨石的形成时代。取得的主要成果及其科学意义如下：1.建立年轻地质体锆石定年方法，精确厘定腾冲地区新生代火山岩至少存在六期岩浆活动：21.6 Ma、16.2 Ma、12.28Ma、2.82 Ma、0.80Ma 和0.48Ma；2.提出腾冲火山岩与地壳混染的软流圈来源的大陆玄武岩的地球化学特征相类似，是幔源物质遭受壳源富集组分强烈混染的产物；3.精确测定中国东部中生代火山岩的形成时代，系统探讨中国东部中生代岩浆源区随时间演化规律以及对华北克拉通破坏的约束；精确测定狮泉河地区林子宗火山岩底部岩层锆石SHRIMP U-Pb年龄，进一步约束新特提斯洋演化历史；精确测定月球陨石NWA 6950的形成时代，推断31.2亿年位于月球KREEP岩体附近存在一次明显的岩浆活动事件。本项目的顺利实施，为解决年轻地质体的定年问题提供了研究方法，同时为解决相关研究领域重大地质科学问题提供了精确的年代学制约。在项目实施过程中，广泛构建国际合作，促进人才培养，并为支撑国家的深空和深地战略提供了坚实科研基础。