Delineation of the ca. 2.7Ga TTG gneisses in the Fuping Complex, North China Craton and its geological significance

作者：Lu ZengLong^*; Song HuiXia; Du LiLin; Ren LiuDong; Geng YuanSheng; Yang ChongHui

来源：Acta Petrologica Sinica, 2014, 30(10): 2872-2884.

• TTG gneisses
• 2.7Ga
• Greenstone belt
• Fuping Complex
• North China Craton

Through detailed field geological survey and indoor analysis we have delineated a suite of banded TTG gneisses from the Fuping Complex, North China Craton (NCC). The protolith of the gneisses was predominantly tonalite that has undergone intensive metamorphism, deformation and anatexis. The gneiss can be divided into the main rock body and strips. It extents three kinds of stripes: Tiny dark stripes, light stripes, late poured felsic stripes. The zircon LA-MC-ICPMS U-Pb data shows that the tonalite was formed ca. 2669. 2 +/- 9. 7Ma ago. The tonalite is featured with high silicon (SiO2 = 64. 32% similar to 70. 02%), high alumina (Al2O3 = 14.00% similar to 15. 87%), rich in sodic (Na2O = 3. 85% similar to 4. 22%), poor in potassium (K2O = 1. 13% similar to 2. 42%) with a low K/Na ratio. The Mg index is relatively high (Mg-# approximate to 39.5 similar to 49. 6). The gneiss is moderately-strongly fractioned in REE [(La/Yb)(N) = 3. 67 similar to 51.38]. Eu abnormality is not evident. It is enriched in LILE such as Sr (303 x 10 (-6) similar to 431 x 10(-6)), Ba (191 x 10(-6) similar to 696 x 10(-6)) and depleted in HFSE like Nb (4. 70 x 10(-6) similar to 9. 78 x 10(-6) Ta (0.19 x 10(-6) similar to 0.75 x 10(-6)), Ti (1378 x 10(-6) similar to 3295 x 10(-6)), P (174.6 x 10(-6) similar to 960.6 x 10(-6)), low contents of Yb (0.31 x 10(-6) similar to 1.75 x 10(-6)) and Y (3.61 x 10(-6) similar to 8.9 x 10(-6)) with high Sr/Y ratio (16. 0 similar to 119. 1). The contents of compatible elements [Cr (5. 9 x 10(-6) similar to 119 x 10(-6)) and Ni (6. 72 x 10(-6) similar to 45. 8 x 10(-6)) are relatively low. From the above, the gneiss is classified into high-Al TTG series, and has the similar characteristics with high-Si adakite. It is considered to be generated from the partial melting of hot Archean juvenile subducted oceanic crust. The delineation of this ca. 2. 7Ga TTG gneiss in the Fuping Complex further proves that the North China Craton experienced large-scale continental crustal accretion in Early Neoarchean, and gives new constraints on the contrast of time and scale of the magmatic events between the worldwide ones and the NCC. It also provides the subdivision of the early blocks and greenstone belts of the NCC.

• 出版日期2014-10
• 单位中国地质科学院