大兴安岭北部绣峰组下部砾岩的形成时代及其大地构造意义  

The age of conglomerates in the lower part of the XiufengFormation in the northern Da Hinggan Mountains,NE China, and their tectonic implications

作　　者：李锦轶[1] 和政军[1] 莫申国[1] AndreyA.Sorokin 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]俄罗斯科学院远东分院布拉格维申斯克区域地质水文地质研究所

出　　处：《地质通报》2004年第2期120-129,共10页Geological Bulletin of China

基　　金：国家自然科学基金项目(编号:49872066;4000121475);国土资源部国际合作与科技司项目(编号:992023)资助

摘　　要：对漠河盆地南缘绣峰组下部砾岩的野外观察,发现其碎屑物除了主要来源于被前人置于新元古代的花岗岩外,还含有火山岩砾石;与上部砂岩之间被断层分隔而不是连续沉积。作为该砾岩主要源岩的花岗岩中的锆石蒸发法年龄为354～164Ma,锆石SHRIMP定年揭示其最后一次岩浆活动可能发生在早侏罗世(180～190Ma);全岩-长石-黑云母内部Rb-Sr等时线年龄为177～191Ma,黑云母Ar-Ar年龄为171～175Ma,表明该岩基在中侏罗世还深埋地下没有出露地表。其中的火山岩砾石的岩石学和岩石化学特征与区域上晚侏罗世塔木兰沟组火山岩类似。结合区域地质资料,推测该砾岩的形成时代不是中侏罗世,而可能是早白垩世;漠河盆地是与蒙古-鄂霍茨克造山带有关的前陆盆地,而不是侏罗纪陆内断陷盆地。Field investigations into conglomerate in the lower part of the Xiufeng Formation on the southern margin of the Mohe basin have revealed that clastic materials in conglomerate also include volcanic pebbles in addition to granitic pebbles reported previously from the supposed Neoproterozoic granite batholith, and that the conglomerate and the Middle Jurassic clastic sedimentary strata are in fault contact rather than are continuously deposited. Granite as the principal source rocks of the conglomerate has zircons evaporation 207Pb/206Pb ages of 354-164 Ma, SHRIMP ages of 180-190 Ma, whole rock-feldspar-biotite internal Rb-Sr isochron ages of 177-191Ma and biotite 40Ar/39Ar plateau ages of 171-175 Ma, indicating that the batholith was intruded in the Early Jurassic and had not been exposed on the surface in the Middle Jurassic. The volcanic pebbles display similarities to volcanic rocks in the Late Jurassic Tamulangou Formation in respect to the petrological and petrochemical features. These data, coupled with the regional geological data, imply that the age of the conglomerate is not Middle Jurassic but possibly Early Cretaceous, and that the Mohe basin was a foreland basin related to the Mongolian-Okhotsk orogenic belt, rather than a Jurassic intracontinental down-faulted basin.

关 键 词：大兴安岭 漠河盆地 绣峰组下部砾岩 早白垩世 侏罗纪前陆盆地 蒙古-鄂霍茨克造山带 

分 类 号：P534.53[天文地球—古生物学与地层学] P588.212.5[天文地球—地质学]