滇西保山地块中-新生代岩浆作用及其构造意义  

The Mesozoic-Cenozoic magmatism in Baoshan Block,western Yunnan and its tectonic significance

作　　者：董美玲[1,2] 董国臣[1] 莫宣学[1] 朱弟成[1] 聂飞[1] 于峻川[1] 王鹏[1] 罗微[1] 

机构地区：[1]地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083 [2]国土资源实物地质资料中心,燕郊101149

出　　处：《岩石学报》2013年第11期3901-3913,共13页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2009CB421002;2011CB403102);111计划项目(B07011);长江学者和创新团队发展计划(IRT1083);中国地质调查局研究项目(1212011220920)联合资助

摘　　要：保山地块上的中-新生代岩浆活动以蚌渺岩体和桦桃林岩体为代表,蚌渺岩体岩石类型为石英二长岩、二长花岗岩,锆石U-Pb年龄为83~85Ma,桦桃林岩体为二云母花岗岩,锆石U-Pb年龄为60~66 Ma,表明该地区在晚白垩世和古新世发生了两次不同的岩浆作用。蚌渺岩体和桦桃林岩体都以全碱含量高为特征,K2O/Na2O>1,桦桃林岩体属于高钾钙碱性系列,蚌渺岩体更加倾向于钾玄岩系列。它们的铝饱和指数A/CNK的值均大于1.1,属铝过饱和系列。这两个岩体岩石总体上富集大离子亲石元素和Pb,亏损高场强元素。蚌渺岩体较桦桃林岩体明显富集轻稀土元素[(La/Yb)N=65.2~67.2],而桦桃林岩体较蚌渺岩体显示明显的负Eu异常(δEu=0.17~0.35)。2个岩体中3件样品41个测点的锆石εHf(t)值变化范围较大(-15.8^-1.1),蚌渺岩体和桦桃林岩体的Hf同位素地壳模式年龄分别集中于2.0~1.2Ga和2.0~1.5Ga。全岩锆饱和温度蚌渺高于桦桃林,说明这两个岩体源区岩石的熔融程度不同。这些地球化学特征指示中-新生代花岗岩类为S型花岗岩,主要来源于古元古代-中元古代地壳物质的重熔,并不同程度地混入了幔源物质。保山地块、腾冲地块和拉萨地体在中-新生代存在几乎同期的岩浆活动,但保山地块与拉萨地体由于岩石地球化学特征不同,不存在对比性,而与腾冲地块存在共同点。保山地块与腾冲地块上的中-新生代岩浆作用与新特提斯洋的闭合和印欧大陆的碰撞息息相关。The Bangmiao and Huataolin plutons, located in Baoshan Block of the Tethyan belt, western Yunnan, are representative of the Mesozoic-Cenozoic magmation. The Bangmiao pluton consists mainly of quartz monzonite and monzogranite with zircon U-Pb ages of 83 - 85Ma. The Huataolin two-mica granite pluton was dated at 60 - 66Ma by zircon U-Pb method. These ages indicate that there were two magmatic events during the Late Cretaceous and Paleocene. The two plntons are high-K calc-alkaline and peraluminous, with K20/Na20 〉 1 and A/CNK 〉 1.1, but the Bangmiao pluton is apt to shoshonitic. These rocks are enriched in large-ion lithophile elements （LILEs） and lead, and depleted in high field-strength elements （HFSEs）. The Bangmiao pluton is obviously enriched in light rare-earth elements （LREEs） [ （La/Yb）N = 65.2 - 67. 2 ] in comparison with the Huataolin pluton. However, the Huataolin shows evident negative Eu anomalies （SEu = 0. 17 - 0. 35）. 41 analyses from three samples of the two plutons give a wide range zircon εHf（t） values （ - 15.8 - - 1.1 ） and varying Hf-isotope crustal model ages （2.0 - 1.2Ga and 2. 0 - 1.5Ga）. The Bangnfiao pluton has higher zircon saturation temperatures of the whole rock than the Haotaolin pluton, which indicate that the molten degree of anatexis in the magma source is different. Such geochemical signatures indicate that the Mesozoic-Cenozoic granitoids are S-type granite in character and were derived mainly from anatexis of Paleoproterozoic to Mesoproterozoic crustal materials with varying contributions from mantle-derived components. The Mesozoic-Cenozoic granitoids in Baoshan Block are geochemically comparable to that in Tengchong Block, which can be related to the closure of the Neotethys ocean and the collision between the India and Eurasia, however, are incomparable to the nearly coeval rocks reported in Lhasa Terrane.

关 键 词：中-新生代花岗岩类 地球化学 锆石HF同位素 保山地块 滇西 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]