乌兰浩特地区玛尼吐组火山岩LA-ICP-MS锆石U-Pb定年及地球化学特征

大兴安岭南段乌兰浩特地区玛尼吐组火山岩主要为一套中酸性岩石组合，化学成分显示为玄武安山岩、安山岩、英安岩和粗面英安岩.LA-ICP-MS锆石U-Pb定年结果显示玛尼吐组火山岩为（142.2±1.0）Ma，形成于早白垩世初期.火山岩SiO₂含量为53.93%~68.44%，Al₂O₃含量为15.03%~17.82%，富碱高钾，属高钾钙碱性系列.稀土元素总量较低（∑REE为103.48×10^-6~147.09×10^-6），轻重稀土分馏较明显，（La/Yb）_N=6.68~9.12，具有弱的正Eu异常（δEu=1.04~1.25）.富集大离子亲石元素Rb、Ba、Th、U、K和LREE，而亏损高场强元素Nb、P、Ti，表明研究区玛尼吐组火山岩形成于蒙古-鄂霍次克洋闭合造山阶段碰撞构造背景，可能为加厚下地壳不同残留矿物相部分熔融的产物.

LA-ICP-MS ZIRCON U-Pb DATING AND GEOCHEMISTRY OF THE VOLCANIC ROCKS FROM MANITU FORMATION IN ULANHOT REGION OF SOUTHERN DAXINGANLING

The Manitu Formation volcanic rocks in Ulanhot region of southern Daxinganling belong to an acid, acid intermediate and intermediate rock assemblage of basaltic andesite, andesite, dacite and trachydacite. The LA-ICP-MS zircon U-Pb dating results show that the volcanic rocks are (142.2±1.0) Ma in age, formed at the beginning of Early Cretaceous, belonging to high-K calc-alkaline series with 53.93%-68.44% of SiO₂ and 15.03%-17.82% of Al₂O₃, low total rare earth elements(ΣREE=103.48×10^-6-147.09×10^-6), distinct LREE and HREE fractionations with (La/Yb)_N=6.68-9.12 and weak positive Eu anomalies(δEu=1.04-1.25). They are enriched in large ion lithophile elements(LILEs, such as Rb, Ba, Th, U and K) and light rare earth elements(LREE), whereas depleted in high field strength elements (HFSEs, such as Nb, P and Ti). The study shows that the volcanic rocks of Manitu Formation were formed in the closing stage of MongoliaOkhotsk Ocean under orogenic collisional tectonic setting, and might be the partial melting product of different residual mineral phases in thickened lower crust.