滇西腾冲曲石地区中更新世火山岩年龄及成因:SHRIMP锆石U-Pb定年和Hf同位素约束  

Age and origin of Mid-Pleistocene volcanic rocks from Qushi in Tengchong area,western Yunnan Province: SHRIMP zircon U-Pb dating and constraint from Hf-in-zircon isotopes

作　　者：李琳琳[1] 王书兵[2] 刘建辉[1] 石玉若[1] 

机构地区：[1]北京离子探针中心中国地质科学院地质研究所,北京100037 [2]中国地质科学院地质力学研究所,北京100081

出　　处：《岩石学报》2015年第9期2609-2619,共11页Acta Petrologica Sinica

基　　金：中国地质调查项目(1212011120165);国家自然科学基金项目(41173065);国土资源部公益性行业基金(201311116)联合资助

摘　　要：本文报道了腾冲曲石地区英安岩测年结果和该区火山岩样品的地球化学特征。英安岩(TC7)的SHRIMP锆石UPb年龄为0.41±0.01Ma(MSWD=1.18),属于中更新世,是迄今在国内测得的最年轻的高精度锆石U-Pb年龄。该区的火山岩具有高钾钙碱性的特点,为一套粗面玄武岩-玄武粗安岩-粗安岩-粗面岩以及玄武岩-安山岩-英安岩岩石组合。岩石富集LILE、LREE,相对亏损Nb、Ta、Ti等高场强元素,具有高的原始地幔标准化(Th/Nb)N比值(大于6)、低的Nb/La(小于1)和Nb/U比值(3~13),相对富集Zr,Zr/Y比值较高。这些地球化学特征明显区别于典型岛弧钙碱性火山岩。锆石Hf同位素分析结果显示εHf(t)值为-11.0^-1.5,变化较大;tDM1、tDM2分别为747~1115Ma、951~1437Ma,模式年龄远大于SHRIMP测定的锆石U-Pb年龄。腾冲火山岩喷发时该区属于大陆板内环境,该区火山岩与地壳混染的大陆玄武岩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。This paper reports U-Pb age and the geochemical characteristics of volcanic rocks from Qushi in Tengchong area. MidPleistocene age（ 0. 41 ± 0. 01Ma） of zircons in dacite（ TC7） is yielded using SHRIMP in Beijing SHRIMP Center,which is the youngest high sensitive zircon U-Pb age in China by now. Whole rock analyses of major,trace elements for these rocks indicate they are high-K calc-alkaline series rocks including trachybasalt,basaltic trachyandesite,trachyandensite,trachyte and basalt,andesite,dacite. These rocks are enriched in LILE,LREE and low HFSE relatively,such as Nb,Ta,Ti. They have high Th / Nb values normalized by the primitive mantle and low Nb / La（ 1） and Nb / U（ 3 ~ 13）. They are rich in Zr and have high Zr / Y values relatively,which are different from those of typical island arc volcanic rocks. Hf analyses carried out on zircons in TC7 yield εHf（ t）values ranging from- 11. 0 to- 1. 5 and tDM2 modal age of 951 ~ 1437 Ma,which is much larger than its real age. These geochemical features of the Tengchong volcanic rocks show an affinity with contaminated continental basaltic rocks. The volcanoes in Tengchong area erupted in an intraplate tectonic setting and their magma sources may have been strongly contaminated by large-scale crustal materials.

关 键 词：新生代火山岩 SHRIMP锆石U-PB年龄 HF同位素 中更新世 岩浆成因 腾冲曲石 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]