Huang, X.L., Niu, Yaoling
, Xu, Y.G., Yang, Q.J. & Zhong, J.W. (2010). Geochemistry of TTG and TTG-like gneisses from Lushan-Taihua complex in the southern North China Craton: Implications for late Archean crustal accretion. Precambrian Research 182
Author(s) from Durham
The late Archean Taihua complex, mainly composed of amphibolite and TTG and TTG-like gneisses, is volumetrically most important metamorphic rock suites scattered along the southern margin of the North China Craton (NCC). Zircon SHRIMP U-Pb dating shows two episodes (2765 +/- 13 and 2723 +/- 9 Ma) of Archean magmatism in the Lushan area with distinct geochemical features. The early (2765 13 Ma) suite (TTG-like gneisses) has low-SiO2 (52.5-66.1 wt%), high-Mg-# (0.47-0.68), low HREE (Yb-N = 3.0-5.4) and Y(8.07-13.9 ppm) with low to moderate (La/Yb)(N) (6.7-37.1) and Sr/Y (25.9-119.3). The younger (2723 9 Ma) suite (TTG gneisses) has high-SiO2 (63.5-74.3 wt%), low-Mg-# (0.13-0.52), very low REE (Yb-N < 1.8) and Y (<4 ppm) with a wide range of (La/Yb)(N) (5.2-86.6), Sr/Y (71.4-949) and showing Eu/Eu* > 1 (1.20-2.43). Both suites show pronounced negative Nb-Ta and Ti anomalies on the primitive mantle-normalized spidergram. The TTG-like gneiss suite has similar bulk-rock Nd and zircon Hf model ages (similar to 3.0 Ga) with epsilon(Nd)(r)> 0 (0.26-1.46), and is interpreted as resulting from melt of mantle interactions with the melts derived from partial melting of subducted ocean crust with a residual assemblage of garnet+ clinopyroxene + rutile +/- amphibole, which favors subducted slab model for the late Archean TTG. The TTG gneiss suite has abundant relic zircons (2.95-2.80 Ga) with epsilon(Nd)(t)< 0 (-1.31 to -0.23), which is best interpreted as derived from partial melting of thickened lower continental crust with a garnet-amphibolite residue (garnet + amphibole rutile). Significant high-pressure fractional crystallization (garnet amphibole) and accumulation (plagioclase) are also required in the petrogenesis. The Lushan amphibolite with nearly flat primitive mantle-normalized trace-element pattern is interpreted to represent early ocean crust metamorphism. These observations suggest a possible model of late Archean crustal accretion from ocean crust to continental terrain in the southern North China Craton. (C) 2010 Elsevier B.V. All rights reserved.