华北克拉通北部长城系底界年龄小于1670Ma:来自北京密云花岗斑岩岩脉锆石LA-MC-ICPMS U-Pb年龄的约束  

The base age of the Changchengian System at the northern North China Craton should be younger than 1670 Ma:Constraints from zircon U-Pb LA-MC-ICPMS dating of a granite-porphyry dike in Miyun County,Beijing

作　　者：李怀坤[1] 苏文博[2] 周红英[1] 耿建珍[1] 相振群[1] 崔玉荣[1] 刘文灿[2] 陆松年[1] 

机构地区：[1]中国地质调查局天津地质矿产研究所,天津300170 [2]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地学前缘》2011年第3期108-120,共13页Earth Science Frontiers

基　　金：国土资源部大调查项目(1212010611802;1212011120130;1212010811057);国家重点基础研究发展计划"973"项目(2011CB808800);国家自然科学基金项目(40772076;40372057)

摘　　要：近期在北京密云沙厂北东的大龙门村附近发现一条花岗斑岩岩脉,该岩脉侵入于新太古代密云群角闪斜长片麻岩当中,其顶部则与片麻岩一起被常州沟组含砾砂岩沉积不整合覆盖。对该岩脉采用LA-MC-ICPMS进行锆石U-Pb同位素年龄测定,获得了（1 673±10）Ma的侵位年龄。这表明华北北部的常州沟组底界（也即长城系的底界）年龄小于1 670 Ma,很可能接近1 650 Ma,比传统的底界年龄1 800 Ma至少年轻150Ma左右。这是迄今为止华北北部长城系底界最为直接而精确的年龄约束。结合上覆大红峪组、高于庄组等测年资料,可进一步将新厘定的长城系（含常州沟组、串岭沟组、团山子组、大红峪组）的形成时代限定在1 650~1 600 Ma,归属于固结纪（Statherian Period,1 800~1 600 Ma）最晚期。这一新进展表明,华北北部中—新元古界的底界与西伯利亚里菲系（Riphean）和印度温地亚（Vindhyan）超群等沉积序列的底界几乎完全一致,可能暗示华北与这些古陆在哥伦比亚超大陆旋回中有着紧密的亲缘关系。Recently a granite-porphyry dike has been recognized near the Dalongmen Village in the north of the Shachang Town,Miyun County,Beijing.The dike emplaced into the Neoarchean Miyun Group amphibole-plagio-gneiss.Both the dike and the wall rock gneiss were unconformably overlain by the conglomerate and sandstone of the Changzhougou Formation.By means of LA-MC-ICPMS zircon U-Pb dating,the emplacement age 1673±10 Ma of the granite-porphyry dike has been obtained.This dating result indicates that the base age of the Changzhougou Formation,i.e.the base age of the Changchengian System at the northern North China Craton（NCC） should be younger than 1670 Ma,probably close to 1650 Ma,at least ~150 Ma younger than the conventionally adopted age 1800 Ma.This is the most direct and precise age constraint for the base of the Changchengian System at the northern NCC to date.Combining with the available age results of the overlying Dahongyu and Gaoyuzhuang formations,the duration of the newly-revised Changchengian System can be limited in the time interval from 1650 Ma to 1600 Ma,comparable with the latest of the Statherian Period（1800-1600 Ma）.Moreover,this new achievement suggests that the base age of the Meso-and Neoproterozoic succession at the northern NCC is almost identical with that of the Riphean at the Siberia and the Vindhyan at the northern India,which probably implies that the NCC and the above-mentioned paleo-continents have close affinity relationships during the assemblage and break-up of the Columbia Supercontinent.

关 键 词：华北克拉通 长城系底界 1670Ma花岗斑岩岩脉 锆石LA-MC-ICPMS测年 固结纪 哥伦比亚超大陆 

分 类 号：P597.3[天文地球—地球化学]