中文摘要：

通过对发源于大兴安岭的主要河流河漫滩沉积物地球化学与从其分离出的锆石U—Pb年龄与Hf同位素组成的系统研究，揭示河漫滩沉积物的稀土和微量元素与大陆上地壳组成基本一致。不同地段的河漫滩沉积物微量成矿元素含量存在明显的差别，可能反映了不同地段不同元素成矿的差异。大兴安岭最南部的西拉木伦河无论是从SiOz含量还是Nd同位素组成上，均反映有华北板块北缘物质的明显贡献；最北部的南翁河从Nd同位素组成上表明有西伯利亚板块南缘前寒武纪微陆块物质的贡献。大兴安岭河漫滩沉积物全样Nd亏损地幔模式年龄平均值与锆石Hf同位素亏损地幔模式年龄基本一致，分别为1．03Ga、1．01Ga。锆石U—Pb年龄最大值为2473Ma，对应的Hf亏损地幔模式年龄为3．75Ga，证明大兴安岭中古陆块基底是更老的陆块（3．75Ga）在古元古代的壳内岩浆作用过程中形成的，中元古代开始古陆块从母陆块分离，可能是古亚洲洋打开的前奏。中新元古代一早古生代末是从亏损地幔增生到大兴安岭区域地壳事件的最强烈阶段，形成古亚洲洋的洋壳与底侵于古陆块中的超镁铁质一镁铁质岩类。晚古生代是古亚洲洋洋壳消减俯冲的主要阶段，至晚二叠世大洋消失殆尽进入到陆内造山阶段。中生代受古太平洋构造域的影响，以底侵于古陆块中的幔源物质为主发生部分熔融，同时也有少量基底物质卷入到此期岩浆作用中，形成占现今该区出露地壳近80％的印支一燕山期火山一侵入岩，但此时基本为一个没有亏损地幔来源的物质直接参与的岩浆作用过程。

英文摘要：

Systematic study of geochemistry, zircon U-Pb dating and Hf isotopic compositions on rivers＇ overbank sediments in the Da Hinggan Mountains, southeast segment of Paleozoic Central Asian Orogen, shows that REE and other trace elemental characteristics of the sediments are consistent with those of upper continental crust. There exist distinct differences in contents of mineralized elements between northern and southern segments, which may indicate different mineralization of corresponding elements in different segments. The overbank sediment in the Xar Moron River indicates significant contribution of material from the northern margin of the North China Plate based on either its content of SiO2 or Nd isotopic composition. Nd isotopic composition of the sediment from the northern end of the Nanweng river also shows the contribution of material from the Precambrian micro-continental block attached to the Siberian Plate. The average Nd depleted mantle model age of bulk sediments is almost consistent with that of Hf depleted model ages of zircons, and are 1.03 Ga, 1.01 Ga,respectively. The oldest zircon U-Pb age is 2473 Ma, and corresponding Hf depleted model age is 3.75 Ga. These data support that the basements of micro-continental blocks of the Da Hinggan Mountains formed by intra-continental magmatism of precursor block during the Paleo-proterozoic （3.75 Ga）. The micro-continental blocks began to separate from the parent block during Mid-Proterozoic, which may indicate a prelude of the Paleo-Asian ocean＇s opening. The period of Neo-proterozoic-Mid-proterozoic to Late Early Paleozoic is the transition stage, i. e. the most intensive crustal accretion from the depleted mantle to the regional crust, forming the oceanic crust of Paleo-Asian Ocean and underplating mafic-ultramafic rocks beneath the micro-continental blocks. The Paleo-Asian Oceanic crusts subducted to the Siberian Plate in north and to the North China Plate in south primarily during Late Paleozoic. The ocean disappeared during Late Permian, when i