摘要
太古宙地壳的构造样式一直是地学界研究的热点问题之一,存在着垂向构造和水平构造两大不同的构造演化认识。位于华北克拉通东缘的辽东鞍山地区广泛出露太古宙TTG岩系、绿片岩相变质的基性-中酸性火山碎屑岩、硅铁质沉积建造构成了典型的太古宙花岗-绿岩带。此外,花岗-绿岩带内丰富的构造变形记录,为探讨早期地壳构造演化提供了重要的线索。详细的野外宏观构造解析表明,鞍山东部白家坟、齐大山地区TTG岩系与(含铁)绿岩接触部位发育了陡倾滑韧性剪切带,代表了新太古宙地壳的垂向"穹脊构造"样式。基于I2VIS有限元差分方法模拟结果表明,鞍山地区花岗-绿岩带垂向构造成因应受控于新太古代末期大规模的岩浆活动造成的TTG上地壳岩石活化,粘度降低,密度变小,(含铁)绿岩建造与TTG岩石的密度差引起的拗沉作用。同时数值模拟结果显示太古代垂向拗沉构造体制很可能是地球演化早期的一种壳-幔物质交换循环的重要机制。
The tectonic pattern of Archean crust is a key issue for the current geology,and rising two classical tectonic models,i. e.horizontal and vertical tectonics. The studied Anshan area,eastern Liaoning Province,located in the northeastern part of North China Craton( NCC),and widely exposed Archean tonalite,trondhjemite and granodiorite( TTGs),greenschist-facies metamorphosed maficmid acid volcanic clastic rocks and BIF-bearing siliceous rocks,composing the typical Archean granite-greenstone belt. Additionally,the abundant deformation developed in the belt provide important evidences to better understanding the tectonic evolution of the early earth crust. In this study,the detailed macro-structural analysis reveals that the steep-dipping-slip ductile shear zones exist around the boundary between the TTGs and greenstones in the Qidashan and Baijiafen districts,respectively,revealing a Neoarchean vertical‘dome and keel structure'tectonic pattern. Moreover,the I2VIS finite difference and mark-in-cell technique,simulates the process of the vertical Archean tectonics in the Anshan area,and suggests the evolutional process: firstly,the large volumes of magmatic activities took place in the Late Neoarchean,resulting in the re-activation of TTG upper crust rocks and the decrease of viscosity and density;subsequently greenstone sagduction happened,caused by the density difference between the greenstone layers and TTGs basement.Meanwhile,the numerical simulation results also show that the Archean vertical tectonic system may be an important mechanism of crust-mantle material exchange cycle in the early earth's evolution.