滇西腾冲地区龙川江河谷上新世火山岩SHRIMP锆石U-Pb年龄及其地球化学特征

报道了应用SHRIMP技术测定云南腾冲地区龙川江河谷附近上新世粗面安山岩和粗面岩的年龄结果。该区粗面安山岩与粗面岩的喷发时代接近,形成时代为2.81Ma±0.11Ma,属上新世。该区火山岩具高钾钙碱性的特点,富集大离子亲石元素、稀土元素和高场强元素（如Zr、Th、Hf）的特征明显不同于典型的岛弧钙碱性火山岩,而与遭受地壳混染的软流圈源大陆玄武岩相类似,是在板内拉张环境下地幔岩浆混染了大量下地壳物质的产物。

SHRIMP zircon U-Pb dating and geochemical analysis of the Pliocene volcanic rocks from Longchuanjiang valley, Tengchong area, western Yunnan Province

In this paper, PLiocene ages （ca. 2.8 Ma） of trachyandesite and trachyte from Longchuanjiang valley in Tengchong area were yielded using SHRIMP Ⅱ in Beijing SHRIMP Laboratory. The ages of trachyandesite and trachyte correspond with each other within uncertainties and are taken to represent the time of eruption （2.81 Ma±0.11 Ma）. The volcanic rocks are rich in alkalis （Na20=3.53- 3.66 wt%, 1（20=3.33-3.64 wt%） and calcium （CAO=4.04-5.05 wt%）. They contain high Ba （1057×10^-6-1145×10^-6）, Sr （502.0×10^-6-650.7×10^-6）, REE （∑REE=315.53×10^-6-365.16×10^-6）, and Zr（308.8×10^-6-382.2×10^-6）. These geochemical features are different from those of typical island arc volcanic rocks but show an affinity with contaminated asthenosphere-generated continental basaltic rocks. The Phocene volcanic rocks from Longchuanjiang valley in Tengchong area were derived from partial melting of an enriched mantle source, contaminated by large crustal materials in an intraplate extensional environment.