Petrographically, the volcanic rocks in Manitu Formation from southern Manchuria are composed of andesite, trachy-andesite and trachyte, but they are mainly trachyte with minor rhyolite based on chemical composition. Zircon U-Pb dating results show that they formed at Late Jurassic from 146 to 158 Ma. These volcanic rocks are alkaline series in composition and rich in alkali and potassium; they are high in total rare earth elements ( ￡ REE = 328. 2 x 10 ~6 ~ 419. 2 x 10 ~6 ) , highly fractionated LREE from HREE ((La/Yb)N =12. 87-23. 10) and moderately negative Eu anomalies (Seu =0.41 -0.70). They contain high LILE (e.g. , Rb and K) and LREE, high ratios of Rb/Sr (0.34-1.88) and positive values of em(t) (3.68-8.65), but low HFSE (e.g. , Nb, Ta, P and Ti). The initial l76Hf/177Hf ratios for magmatic zircons from these volcanic rocks vary in the range of 0. 282780 -0. 282922, and the two-stage model ages of 652 - 972Ma. The data suggest that the magmas for these volcanic rocks derived from the newly accreted Neoproterozoic basic igneous crusts, and formed during the extensional setting of lithosphere after the closure of Mongol-Okhotsk Ocean.%满洲里南部玛尼吐组火山岩的岩相学鉴定为安山岩、粗安岩和粗面岩,化学成分显示其以粗面岩为主,少量流纹岩.LA-ICPMS锆石U-Pb定年结果显示其形成于146 ～ 158Ma之间的晚侏罗世.火山岩富碱高钾,属碱性系列；稀土总量较高(∑REE=328.2×10-6 ～419.2×10-6),轻重稀土分馏较明显((La/Yb)N=12.87～23.10),中等负铕异常(δEu=0.41 ～0.70)；富集大离子亲石元素Rb、K和轻稀土元素,亏损高场强元素Nb、Ta、P、Ti.具有高Rb/Sr比值(0.34 ～ 1.88)和正的εHf(t)值(3.68 ～8.65),锆石176Hf/177 Hf介于0.282780 ～0.282922之间,两阶段Hf模式年龄为652 ～972Ma的新元古代.岩浆源区物质为新元古代增生的基性火成岩地壳,火山岩形成于蒙古-鄂霍茨克洋闭合造山岩的岩石圈伸展构造环境.
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