华北克拉通辽南地块新太古代晚期TTG岩石成因及其构造意义

Petrogenesis of Late Neoarchean TTG Rocks in Liaonan Block,North China Craton and Its Tectonic Significance

为加深对华北克拉通辽南地块太古宙大陆地壳形成与演化历史的认识,以辽南地块十间房地区新太古代TTG(奥长花岗岩—英云闪长岩—花岗闪长岩)片麻岩为研究对象,开展了详细的野外地质调查、锆石U-Pb定年、锆石Lu-Hf同位素分析以及全岩地球化学分析。结果表明:十间房地区TTG片麻岩的结晶年龄为(2499.7±5.4)Ma。TTG片麻岩样品具有高的SiO_(2)含量(质量分数,下同,66.1%~69.1%)和Al_(2)O_(3)含量(14.6%~15.6%),富Na、贫K(K_(2)O/Na_(2)O值为0.41~0.51),具有弱的Eu正异常(1.06~1.59),相对富集大离子亲石元素(Ba、Rb、K等)和高场强元素(Zr、Hf等),具有相对高的Sr/Y值(44.3~69.5)和(La/Yb)_(N)值(11.8~24.0)以及亏损的锆石Hf同位素特征,Hf二阶段模式年龄为2903~2687 Ma;相比源自加厚下地壳部分熔融的TTG岩石,十间房地区TTG片麻岩具有相对高的MgO、Cr、Ni含量。上述地球化学特征揭示十间房地区TTG片麻岩为典型的中压TTG岩石,是中—新太古代玄武质地壳部分熔融的产物,其源区富集石榴子石和角闪石,缺乏金红石和斜长石。综合前人研究认为,十间房地区TTG片麻岩形成于俯冲板片的部分熔融,指示古老大陆边缘的暖俯冲构造体制,且新太古代晚期华北克拉通可能同时受控于板块构造和地幔柱构造体制。

In order to enhance the understanding of Archean continental crust formation and evolution history of Liaonan block in North China Craton,the Neoarchean TTG(tonalite-trondhjemite-granodiorite)gneisses in Shijianfang area of Liaonan block were focused on,and the detailed field investigation,zircon U-Pb dating and Lu-Hf isotope analysis,and whole-rock geochemical analysis were intergrated.The results show that TTG gneiss in Shijianfang area crystallizes at(2499.7±5.4)Ma.The TTG gneiss samples have high contents of SiO_(2)(66.1%-69.1%)and Al 2O 3(14.6%-15.6%),are enriched in Na and depleted in K(K_(2)O/Na_(2)O is 0.41-0.51)with weakly positive Eu anomalies(1.06-1.59);the samples are relatively enriched in large ion lithophile elements(Ba,Rb,K,etc.)and high field strength elements(Zr,Hf,etc.),featured by high Sr/Y(44.3-69.5)and(La/Yb)N(11.8-24.0),and depleted zircon Hf isotopic composition with two-stage model ages of 2903-2687 Ma.Compared with TTG rocks derived from partial melting of the thickened lower crust,TTG gneisses in Shijianfang area have relatively higher contents of MgO,Cr and Ni.The above geochemical characteristics reveal TTG gneisses in Shijianfang area are typical medium-pressure TTG rocks,which is the product of partial melting of Meso-Neoarchean basaltic crust.The source area is rich in garnet and amphibolite,but short of rutile and plagioclase.Combined with previous studies,TTG gneisses in Shijianfang area are likely formed by the partial melting of subduction slabs,indicating the warm subduction tectonic system of the ancient continental margin.The North China Craton might be controlled by both plate tectonics and mantle plume tectonics during Late Neoarchean.