Supplemental material
Analytical methods
The samples collected from fresh outcrops were separated for zircons by heavy-liquid and magnetic methods. Zircon grains were photographed with an optical microscope, and their internal structure was checked by cathodoluminescence (CL). The U-Pb dating was done by (LA-ICP-MS) at the State Key Laboratory of Geological Processes and Mineral Resources (GPMR), China University of Geosciences, Wuhan. Zircon 91500 was used as external standard for U-Pb dating, and was analyzed twice every 5 analyses, the laser beam spot was 32μm. Laser sampling was performed using a GeoLas 2005. An Agilent 7500a ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as carrier gas. Argon was used as the make-up gas and mixed with the carrier gas via a T-connector before entering the ICP. Nitrogen was added into the central gas flow (Ar+He) of the Ar plasma to lower the detection limit and improve precision. Concordia diagrams and weighted mean calculations were made using Isoplot/Ex_ver3 (Ludwig 2003); data were processed by ICPMSDataCal (Liu et al. 2008). Detailed operating conditions for the laser ablation system and the ICP-MS instrument are the same as described by Zong et al. (2010).
Whole rock samples were crushed in a corundum jaw crusher (to 60 mesh). About 60 g was powdered in an agate ring mill to less than 200 mesh for whole rock geochemistry analysis. Whole rock major element analysis were conducted by a Rigaku 3080E1-type spectrometer XRF at the Bureau of Geology and Mineral Resources, Hubei Province, China, with analytical precision better than 5%. Trace elements were analysed with an Agilent 7500a ICP-MS at GPMR laboratory, China University of Geosciences, Wuhan. The samples were digested by HF + HNO3 in Teflon bombs, the detailed sample-digesting procedure for ICP-MS analyses, analytical precision and accuracy for trace elements are the same as described by Liu et al. ( 2008). 
Sr-Nd isotope analyses were also determined at GPMR Laboratory, China University of Geosciences, Wuhan. Sample powders were spiked with mixed isotope tracers, dissolved in Teflon capsules with HF + HNO3 acids and separated by conventional cation-exchange techniques. Isotopic measurements were performed on a Finnigan MAT-261 thermal ionization mass spectrometer (TIMS). Procedural blanks were <200 pg for Sm and Nd and <500 pg for Rb and Sr. The mass fractionation corrections for Sr and Nd isotopic ratios were based on 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219, respectively. Analyses of standards during the period of analysis are as follows: NBS987 gave 87Sr/86Sr = 0.710236 ± 16 (2σ); La Jolla gave 143Nd/144Nd = 0.511862 ± 5 (2σ). The analytical precision and accuracy for Sr-Nd isotopic compositions are the same as described by Gao et al. ( 2004).
In situ zircon Hf isotope analyses were carried out on an excimer (193 nm wavelength) laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) at the Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China. The GeoLas 200M laser-ablation system (MicroLas, Göttingen, Germany) was used for the laser ablation experiments. A 44 μm beam size was adopted in this study with a laser pulse frequency of 10 Hz. The detailed analytical technique for this method was described by Yuan et al. (2008). 

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