锦州-迁安太古宙赞岐岩类片麻岩成因及其动力学意义

详细的野外地质调查和综合研究表明冀东-辽西南部地区太古宙变质基底主要由富钾花岗质岩石组成,由锦州至迁安构成一条NEE向延伸200余千米的富钾花岗质岩石带。这些富钾花岗质岩石主要由似斑状/中粒石英二长闪长质-花岗闪长质-二长花岗质片麻岩和中粒二长花岗岩-正长花岗岩构成。全岩地球化学分析表明这些石英二长闪长质-花岗闪长质-二长花岗质片麻岩具有高FeO~T、MgO、K_2O和Mg~#值的地球化学特征,与全球范围内中-新太古宙赞歧岩类相似。LA-ICP-MS锆石U-Pb同位素定年结果表明这些岩石形成于2546~2543Ma。岩石成因研究表明这些赞歧岩类片麻岩形成于俯冲板片及其拖曳的洋壳沉积物、增生楔物质的熔体和受俯冲流体、熔体交代的地幔楔之间相互作用引发的一系列的岩浆作用。这一多样化的赞岐岩类岩浆作用形成了一条新太古代赞岐岩类带,该赞岐岩类带反映了冀东-辽西南部地区新太古代从NNW向SSE向板片热俯冲的动力学体制。

Petrogenesis and geodynamics of Archean sanukitoid gneisses in the Jinzhou-Qian'an area

Detailed field geological mapping and comprehensive studies reveal that the Archean metamorphic basement terranes in the eastern Hebei-southwestern Liaoning provinces consist primarily of K-rich granitoid rocks, which extend more than 200km from Qian''an to Jinzhou. The K-rich granitoid rocks are chiefly composed of porphyritic or medium-grained quartz monzodioritic-granodioritic-monzogranitic gneisses and medium-grained monzogranites-syenogranites. Whole-rock geochemical analyses indicate that the most of quartz monzodioritic-granodioritic-syenogranitic gneisses are characterized by high K₂O, MgO and FeO^T contents with high Mg^# values, similar to the classic Meso-to Neo-Archean sanukitoid rocks in the global range. LA-ICP-MS zircon U-Pb isotopic dating indicates that their magmatic precursors were emplaced during 2546~2543Ma. Petrogenesis studies reveal that magmatic procursors of these sanukitoid gneisses were generated by interactions between partial melts from subducted slabs, oceanic sediments and accretionary wedge materials, and enriched mantle wedge metasomatized by slab-derived melts or fluids. The magmatism of these sanukitoids gneisses constructs a Neoarchean sanukitoid belt extending from NEE to SWW direction, which suggests that the Neoarchean basement rocks of the eastern Hebei-southwestern Liaoning provinces were formed under a hot subduction setting with a SSE polarity.