**Acknowledgements**

This study was supported by the Science Research from the Northwest Subcompany of SINOPEC (no: KY2013-S-024), the work project of China Geological Survey (no. 12120115002001, DD20160169), a Special Research Grant from Ministry of Land and Resources of the People's Republic of China (no. 201011034), the Major Project of National Natural Science Foundation of China (no. 41630207).
