Petrogenesis and Tectonic Implications of the Paleoproterozoic A-Type Granites in the Xiong'ershan Area along the Southern Margin of the North China Craton

Paleoproterozoic A-type granites are widely distributed in the southern margin of the North China Craton (SNCC), providing important information for understanding the Paleoproterozoic tectonic regimes in this area. This paper reports newly obtained whole-rock compositions and zircon U-Pb ages for the Tieluping syenogranite porphyry (TLP) and Huoshenmiao alkali granite porphyry (HSM) in the SNCC. Zircons from the TLP and HSM have U-Pb ages of 1 805 +/- 12 and 1 792 +/- 14 Ma, respectively. These ages are taken to date the emplacement of these intrusions. They had high total alkali contents (K2O + Na2O > 7.13 wt.%), with high 10 000 x Ga/Al ratios (3.06-3.41) and Zr + Y + Nb + Ce values (709 ppm-910 ppm) as well as high zircon saturation temperatures (864-970 degree celsius), indicative of A-type granite affinities. High Y/Nb (1.75-3.32), Ce/Nb (7.72-9.72), and Yb/Ta (2.89-5.60) ratios suggested that TLP and HSM belonged to the A2-type granite. The negative whole rock epsilon(Nd)(t) values (-8.4 to -6.6) and negative zircon epsilon(Hf)(t) values (-15.9 to -6.3) confirmed that TLP and HSM were likely generated by the partial melting of an ancient continental crust. The epsilon(Hf)(t) (-7.4 to +4.0) values of inherited zircons in the TLP suggested that they were derived from the partial melting of Archean basement rocks. Considering the geochemical similarity of the 1.80 Ga A-type granitoids in the SNCC, we propose that the TLP and HSM were formed in a post-collisional regime that was likely associated with the break-off of the Paleoproterozoic subducted slab. Upwelling of the asthenosphere provided huge heat to generate the regional 1.80 Ga A-type granite in the SNCC.