鹤岗北部地区黑龙江岩群的构造属性:来自岩石地球化学、锆石U-Pb定年和Hf同位素的制约

产于鹤岗北部地区的黑龙江岩群是由绿帘绿泥钠长片岩、绿帘蓝闪片岩(下部)和二云母片岩、石榴白云钠长片岩、方解白云钠长片岩、石榴白云钠长石英片岩(上部)等岩系组成。本文通过岩石地球化学、锆石U-Pb年代学和Hf同位素组成研究,厘定下岩组原岩为幔源碱性玄武岩(SiO_2=47.44%~48.38%)及岛弧钙碱性玄武岩(SiO_2=46.84%~49.22%),有3组锆石U-Pb年龄(526±44 Ma,n=3;249±11 Ma,n=6;207±4 Ma,n=8);上岩组原岩为海陆交互相碎屑岩(SiO_2=66.70%~93.00%),有4组锆石U-Pb年龄(484±13 Ma,n=3;429±24 Ma,n=3;277±4 Ma,n=11;262±3 Ma,n=6)。结合锆石的内部结构、Hf同位素和区域构造演化特征,幔源火山喷发和沉积作用发生在277±4 Ma,碰撞造山作用发生在262~249 Ma,构造折返发生在207±4 Ma。这项研究对于深入认识黑龙江岩群性质和构造属性具有重要的意义。

Tectonic Attribute of Heilongjiang Metamorphic Rocks in the Northern Part of Hegang Area,NE China：Constrains from Geochemistry,Zircon U-Pb Dating and Hf Isotopic Composition

TheHeilongjiang metamorphic rocks located in the northern part of the Hegang area, NE China, consist of epidote-chlorite-albite schist, epidote-glaucophane schist (the lower group), and two-mica schist, garnet-muscovite -albite schist, calcite-muscovite-albite schist, garnet-muscovite-quartz schist (the upper group), etc. Detailed research on geochemistry, zircon U-Pb dating and Hf isotopic composition showed that the protoliths of the lower group are alkali basalt derived from mantle (SiO2=47.44%? 48.38%), and island arc calc alkali basalt (SiO2=46.84%? 49.22%). The lower group contains three groups of zircon U-Pb age (526±44 Ma,n=3; 249±11 Ma,n=6; 207±4 Ma,n=8), whereas the protolith of the upper group is alternative continent-marine facies clastic rock (SiO2=66.70%? 93.00%), and contains four groups of detrital zircon U-Pb age (484±13 Ma,n=3; 429±24 Ma,n=3; 277±4 Ma,n=11; 262±3 Ma,n=6). Combined with zircon internal texture, Hf isotopic composition and regional tectonic evolution features, we suggest that the volcanic eruption and sedimentation occurred at 277±4 Ma, and collision orogeny was during 262 Ma to 249 Ma. Tectonic exhumation occurred at 207±4 Ma. The research is significant to identify the nature and tectonic affinity of Heilongjiang metamorphic rocks.