Geochemical constraints on the tectonic setting of Paleoproterozoic A-type granites in the southern margin of the North China Craton

详细信息    查看全文

• 作者：Tai-Ping Zhao ; Mei-Fu Zhou
• 关键词：Paleoproterozoic ; A-type granite ; SHRIMP zircon dating ; Sr– ; Nd– ; Pb– ; Hf isotopes ; Post-orogenic extension ; North China Craton
• 刊名：Journal of Asian Earth Sciences
• 出版年：2009
• 出版时间：20 September 2009
• 年：2009
• 卷：36
• 期：2-3
• 页码：183-195
• 全文大小：1426 K

文摘

The amalgamation of the Eastern and Western Blocks of the North China Craton (NCC) at 1.85 Ga resulted in the formation of the Central Zone between the two. Post-orogenic A-type granites in the NCC provide constraints on the timing of this collisional event. The Shicheng and Motianzhai granitic plutons in the Songshan district of the southern NCC have SHRIMP zircon U–Pb ages of 1743 ± 14 Ma and 1797 ± 14 Ma, respectively. Both plutons consist of biotite granite and granodiorite with total alkalis (K₂O + Na₂O) ranging from 7.65 to 9.12 wt. % . High Fe^*(FeO^t/FeO^t + MgO) (0.79–0.90) and 10,000×Ga/Al ratios (2.19–3.26), indicate that these are A-type granites formed in a post-collisional environment. Whole-rock ε_Nd(t) values range from −5.7 to −7.8 and T_DM model ages from 2.60 to 2.93 Ga. Zircons from these granites have ε_Hf(t) values ranging from −5.3 to −13.5, corresponding to two stage model ages () of 2.85–3.29 Ga. These isotopic features suggest that the rocks were derived from the late Archean basement complexes. The A-type granites in Songshan are different from typical granitic rocks formed in anorogenic intra-continental rifts, but resemble those emplaced in post-orogenic extensional tectonic settings. Based on the criteria of Eby (1992), the Songshan A-type granites belong to the A₂ (post-orogenic) type. This post-orogenic extensional event occurred after a major orogeny that formed the Central Zone at ca. 1.85 Ga and lasted for more than 50 myr.