冀北单塔子变质杂岩新太古代TTG片麻岩的成因和地壳演化研究

Neoarchean (2.8-2.5 Ga) is globally crustal growth duration and TTG magmatism was widely developed. These magmatic lithological assemblages may provide valuable insights into the mechanism of the Archean crustal growth and evolution, crust-mantle interaction, and geodynamic processes. This proposal is going to carry out systematic investigations for lithological assemblages, petrology, whole-rock geochemical and Sr-Nd isotopic data, zircon U-Pb-Lu-Hf and whole-rock Sm-Nd isotopic characteristics for the representative Neoarchean TTG gneisses in the Dantazi Complex of Northern Hebei Province, NCC. These data are aimed to (1) decipher the lithological assemblages, temporal-spatial distributions, magmatic evolution stages as well as the magma sources, petrogenesis, crustal evolution, and geodynamic regime for each magmatic stage; (2) discuss related crustal growth and recycling processes, and crust-mantle interaction mechanism; and (2) clarify the relationship of evolutionary history between the research terrane and the adjacent Archean metamorphic basement terranes in the NCC. This study is not only critical for unraveling the Neoarchean magmatic evolutionary history for the Dantazi complex of Northern Hebei province, but also important for exploring the crustal growth and crust-mantle interaction modes and evolutionary dynamic processes for the NCC.

新太古代（2.8-2.5 Ga）是地球早期重要的岩浆作用和地壳生长阶段，大规模分布的TTG片麻岩是新太古代大陆地壳形成与演化的关键记录，是这一时期壳幔作用和动力学过程的信息载体。本项目拟对华北克拉通北缘冀北地区单塔子变质杂岩新太古代TTG片麻岩进行岩石组合、岩石学和全岩地球化学、锆石U-Pb年代学以及Lu-Hf同位素和全岩Sm-Nd同位同位素进行系统研究，确定TTG片麻岩的岩石组合、地质特征、时空分布、岩浆演化期次、不同期次岩浆作用的源区性质和岩浆演化过程及其反映的壳幔动力学机制，确定其地壳生长和再循环过程。并通过与相邻太古宙地块地质事件对比，探索华北克拉通北缘新太古代地壳形成演化机制。这对解决华北克拉通东部地块新太古代构造格局、地壳生长方式及其动力学过程具有重要的意义。

本项目对冀北原单塔子杂岩区域的新太古代花岗质片麻岩进行了系统的野外地质、岩相学、全岩主量元素、稀土和微量元素、锆石U-Pb定年和Lu-Hf同位素分析测试。研究发现承德地区的花岗质片麻岩以英云闪长质-奥长花岗质-花岗闪长质（TTG）片麻岩为主，其中英云闪长质-奥长花岗质片麻岩的岩浆结晶年龄为2611-2505 Ma，原始岩浆来自俯冲版块物质的部分熔融，经历了明显的分离结晶过程；花岗闪长质片麻岩的岩浆结晶年龄为2523-2510 Ma，源自下地壳高钾玄武质岩石的部分熔融。张家口地区的花岗质片麻岩则为英云闪长质-奥长花岗质-花岗闪长质-二长花岗质（TTGM）片麻岩，其中英云闪长质-奥长花岗质片麻岩岩浆结晶年龄为2513 ± 24 Ma，与承德地区类似，也来自于俯冲板块的部分熔融；花岗闪长质-二长花岗质片麻岩的岩浆结晶年龄为2521-2516 Ma，是下地壳高钾玄武质岩石熔融产生的岩浆和古老变质沉积岩熔融产生的岩浆，经过岩浆混合作用形成的。结合前人研究工作，项目组认为冀北承德-张家口地区在太古宙末期经历了从洋内俯冲作用（2611-2523 Ma）到碰撞拼合（2523-2505 Ma）的动力学演化历史，进一步证明华北克拉通东部陆块北缘在太古宙末期受控于板块构造作用为主的动力学环境。