Formation epoch and ts geological mplications of Paleoprotozoic A-ype granite n Shizuizi of Jingyuan County, Ningxia Province

The Shizuizi A-type granite s found n he southern part of Helan aulacogen, western margin of the North China Craton and mainly consist of K-feldspar granite porphyry. The granite s characterized by high silicon and rich potassium, including Na2O + K2O average 7. 61%,K 2O/Na2O = 2. 17 ∼7. 39, A12O3 = 10. 59% ∼11. 84%,and its A/CNK =0. 86 7sim;1. 11 (1. 01 on average), and hus is belong o subalkaline metaluminous o weakly prealuminous series, identified as A-type granite. The abundance of σ REE s high, ranging from 340. 4 X 10-6 to 468. 9 X 10-6 The granite show a LREE enrichment pattern and obviously ntermediate negative Eu anomalies. The race element geochemistry s characterized evidently by negative anomaly of high strength field elements Ta, Nb, Ti, etc. and positively Rb, Ba, Th, etc., and shows the characteristics of post-orogenic granite. The LA-ICP-MS zircon U-Pb age s 1803 ±15Ma, which ndicates that the Helan aulaco gen s formed during Late Paleoprotozoic, and s rela ted o he break-up of the North China Craton from he Columbia supercontinent during he end of Late Paleoprotozoic period.