Journal
JOURNAL OF ASIAN EARTH SCIENCES
Volume 36, Issue 2-3, Pages 183-195Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jseaes.2009.05.005
Keywords
Paleoproterozoic; A-type granite; SHRIMP zircon dating; Sr-Nd-Pb-Hf isotopes; Post-orogenic extension; North China Craton
Categories
Funding
- National Basic Research Program of China [2006CB403502]
- National Natural Science Foundation of China [40672058]
- State Key Laboratory of Ore Deposit Geochemistry
- Institute of Geochemistry
- Chinese Academy of Sciences [200802]
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The amalgamation of the Eastern and Western Blocks of the North China Craton (NCC) at similar to 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 *(FeOt/FeOt + MgO) (0.79-0.90) and 10,000xGa/Al ratios (2.19-3.26), indicate that these are A-type granites formed in a post-collisional environment. Whole-rock epsilon(Nd)(t) values range from -5.7 to -7.8 and Tom model ages from 2.60 to 2.93 Ga. Zircons from these granites have epsilon(Hf)(t) values ranging from -5.3 to -13.5, corresponding to two stage model ages (T-DM(C)) 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 A(2) (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. (C) 2009 Elsevier Ltd. All rights reserved.
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