摘要
大兴安岭北部韩家园镇一带的古元古界兴华渡口群中分布有眼球状花岗片麻岩和条带状片麻岩,以往将其作为兴华渡口群的下部地层兴华组,本次研究表明它们是受变质和变形改造的正片麻岩。采用SHRIMP和LA-ICP-MS技术对其中的2件花岗质片麻岩进行了锆石U-Pb年龄测定,其中21TW29-1样品用SHRIMP测得的207Pb/206Pb年龄为1837Ma±5Ma,该年龄被解释为花岗质岩浆的结晶年龄。21TW29-2样品用LA-ICP-MS测得的207Pb/206Pb年龄有1741Ma±30Ma和1854Ma±20Ma2组,其中1741Ma被解释为花岗质岩浆的结晶年龄。21TW29-2样品的锆石微区Hf同位素测定结果显示其εHf(t)值为-3.9--8.5,地壳模式年龄为2.78-3.01Ga,低的锆石εHf(t)值表明其岩浆主要来自古老太古宙地壳物质的部分熔融。1.8Ga左右花岗质片麻岩的发现证实,额尔古纳地块存在早前寒武纪变质基底,为该地块的构造属性提供了明确的证据,对认识区域构造演化及构建区域构造格架具有重要的地质意义。
Augen and banded gneisses of the Xinhuadukou Group occur in the Hanjiayuanzi area of northern Daxinganling, NE China, which were previously attributed to be the lower meta-strata of Xinghua Formation, Xinhuadukou Group. However, our studies indicate that these augen and banded gneisses are actually deformed granites （orthogneisses）. SHRIMP zircon U-Pb dating yields an ^207Pb/^206Pb age of 1837Ma±5Ma, interpreted to be the crystallization age of the granitic gneisses. LA-ICP-MS zircon U-Pb dating yields an ^20 Pb/^206Ppb age of 1741Ma±30Ma and 1854Ma±20Ma, interpreted to be the crystallization age of the granitic gneisses. Zircon Hfanalyses from 21TW29-2 show that the granitic gneisse have negative and variable εHf（t） values between -3.9 and - 8.5, with Mesoarchean （2.78-3.01Ga） crustal model ages which suggests that the magma of the granitic gneisses were mainly derived from an old Mesoarchean crustal source. The discovery of the Paleoproterozoic granites in the studied area suggests that an early Precambrian metamorphic basement exists in the Eerguna massif.
出处
《地质通报》
CAS
CSCD
北大核心
2013年第2期341-352,共12页
Geological Bulletin of China
基金
中国地质调查局项目<兴蒙造山带中古老陆块性质与成矿背景研究>(编号:1212011085478)
<兴蒙造山带基本构造格局综合调查和研究>(编号:1212011085476)
