关键词: 华北板块北缘, 固阳, 达茂旗, 新太古代, 强过铝, S型花岗岩

Abstract: The study of Neoarchean S-type granite, with obvious tectonic significance, which lies in Hejiao area, Darhan Muminggan Lianheqi, Inner Mongolia, in major elements, trace elements and SHRIMP zircon U-Pb geochronology provided further evidence for understanding the nature of tectonic setting of the northern margin of North China plate at the end of Neoarchean. The major elements features of Hejiao granite indicate that it belongs to cal-alkaline series with strongly peraluminous characteristics and Rittman index σis between 0. 54 and 0. 57. The granite has high total rare earth elements (REE) values(243.8- 427. 1 μg/g), and enriches light REE relative to the heavy ones, and has negative anomalies characteristics in Eu ( ( La/ Yb)_N = 14. 88-18. 18, Eu^* / Eu = 0. 31- 0. 65) . In addition, it depletes high field strength elements( HFSE) , such as Nb, Ta, Zr, Hf and Ti. The trace elements characteristics of Hejiao granite reflect that it is formed under post-collisional tectonic setting and it is from normal thick continental crust in low pressure-high temperature conditions, which are similar to the formation conditions of Lachlan fold belt in Australia. The SHRIMP U-Pb zircon age of Hejiao granite is 2556 ±8 Ma. Strongly peraluminous S-type granite of Hej iao indicates that, in the end of Neoarchean, a continent-continent collision event probably occurred at the middle segment of north margin of North China plate, and that the sanukite with the same age in Guyang area, was possibly formed at post-collisional tectonic setting rather than subduction zone.

Key words: the north margin of North China plate, Guyang, Darhan Muminggan Lianheqi, Neorchean, strongly peraluminous, S-type granite