辽北新宾?苇子峪地区太古宙花岗质岩石的形成年代、成因及其地质意义

辽北新宾?苇子峪地区的花岗质岩石主要由英云闪长质?奥长花岗质片麻岩和二长花岗岩?正长花岗岩岩体等组成。为确定其形成年代及成因, 对这些花岗质岩石进行锆石U-Pb-Hf同位素和全岩地球化学分析。锆石LA-ICP-MS U-Pb同位素定年结果表明这些花岗质岩石均形成于新太古代, 英云闪长质和奥长花岗质片麻岩的岩浆结晶年龄分别为2588±4 Ma (MSWD=1.3)和2587±6 Ma (MSWD=1.8), 二长花岗岩?正长花岗岩则侵位于2555±4 Ma (MSWD=0.51)。全岩地球化学和锆石Lu-Hf同位素研究表明, 英云闪长质?奥长花岗质片麻岩形成于俯冲板片的部分熔融, 其原始岩浆在上升过程中受到地幔楔岩石的交代; 而二长花岗岩?正长花岗岩中一部分岩浆起源于变质杂砂岩的部分熔融, 其余形成于以变质玄武岩与变质沉积岩为主要成分的混合源区的部分熔融。结合近年的研究成果, 认为新宾?苇子峪地区的新太古代花岗质岩石可能形成于活动大陆边缘的动力学背景。

Formation Ages,Petrogenesis and Geological Implications of the Archean Granitoid Rocks in the Xinbin-Weiziyu Area,Northern Liaoning Province

The granitoid rocks in the Xinbin-Weiziyu area, northern Liaoning Province, comprise tonalitic-trondhjemitic gneisses and monzogranite-syenogranite plutons. To determine their formation ages and petrogenesis, zircon U-Pb-Hf isotopic analyses and whole-rock geochemical analyses are conducted on these granitoid rocks. LA-ICP-MS zircon U-Pb isotopic dating data reveal that the tonalitic and trondhjemitic gneisses emplaced at 2588±4 Ma (MSWD=1.3) and 2587±6 Ma (MSWD=1.8), respectively, and the monzogranite-syenogranite intrusions formed at 2555±4 Ma (MSWD=0.51). Whole-rock geochemistry and zircon Lu-Hf isotopes suggest that magmatic precursors of the tonalitic-trondhjemitic gneisses were derived from partial melting of subducted slabs and the magmas were contaminated by the mantle wedge materials during their ascent. Some of the monzogranite-syenogranite plutons were produced by partial melting of metagreywackes, whereas the others were generated by partial melting of a mixed source composed of metabasalts and metasedimentary rocks. Integrated with recent studies, the Neoarchean granitoid rocks in the Xinbin-Weiziyu area may have been generated under an active continental margin.