Polyphase deformation of the Fuping Complex, Trans-North China Orogen: Structures, SHRIMP U-Pb zircon ages and tectonic implications

Abstract

The Fuping Complex is located in the central part of the Trans-North China Orogen (TNCO), a Paleoproterozoic collisional belt along which the Eastern and Western Blocks were assembled to form the North China Craton. Three stages of deformation (D1-D3) have been identified in the Fuping Complex. D1 formed tight to isoclinal folds F1, penetrative foliation S1 and mineral lineation L1, which resulted from the early NW-SE-orientated thrusting and shearing. D2 progressively overprinted D1 and was dominated by mostly NW-SE shortening and top-to-the-SE(E) thrusting under a compressive environment. D1 and D2 occurred in association with the peak metamorphism (M1). D3 occurred during the exhumation after the crustal thickening, producing regional-scale NWW-SEE-trending open folds (F3) and associated low-angle detachment faults, and was responsible for the isothermal decompression (M2) metamorphism of the complex. Following the D3 deformation, the complex was exhumed to shallow crustal levels where the rocks underwent the retrogressive cooling (M3) metamorphism. Syn-tectonic leucocratic dykes are widespread in the Fuping Complex. Two leucocratic dykes that did not experience D1 but underwent D2 yield SHRIMP zircon ages of 1843 ± 12 Ma and 1844 ± 18 Ma, which indicate that D1 must have occurred at some time earlier than ∼1844 Ma, whereas D2 must have occurred at some time later than this age. Two weakly deformed post-D2 leucocratic dykes yield SHRIMP zircon ages of 1817 ± 14 Ma and 1815 ± 45 Ma, suggesting that the D2 deformation occurred in the period 1843-1815 Ma. The new SHRIMP data indicate that the collision-related deformation of the Fuping Complex must have occurred in the Paleoproterozoic, not in the late Archean. Structural and geochronological data presented in this study, in association with previous lithological and geochemical data, suggest that the Fuping Complex may have been located in the hinterland of an eastward subduction zone and underwent intensive deformation and metamorphism involved in the final collision between the Western and Eastern Blocks at ∼1.85 Ga. © 2008 Elsevier Ltd. All rights reserved.