Journal
CHINESE SCIENCE BULLETIN
Volume 57, Issue 31, Pages 4064-4076Publisher
SCIENCE PRESS
DOI: 10.1007/s11434-012-5315-8
Keywords
TTG; 2.5 Ga; Zircon U-Pb dating; Hf isotope; Beidashan; Alxa Block; North China Craton
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Funding
- Ministry of Land and Resources of China [201011058, 201011034]
- National Natural Science Foundation of China [41072151, 41772138]
- Geological Survey Project of China [1212011120157]
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The Alxa Block is considered part of the North China Craton, but the unambiguous Archean basement has not been reported. In this study, we present the first evidence of the Neoarchean rocks in the Beidashan area of the western Alxa Block. The petrographic and geochemical data show that these rocks are granodiorite with TTG (tonalite-trondhjemite-granodiorite) characteristics. Zircon U-Pb dating gave an age of 2522 +/- 30 Ma for the magmatic core and 2496 +/- 11 Ma for the metamorphic recrystallized rim. The near-identical age between the Latest Neoarchean magmatism and the high-grade metamorphism shows that these features were related to the same Latest Neoarchean-Earliest Paleoproterozoic tectonothermal event. The age-corrected E >(Hf)(t) value is mainly between 0.4 and 4.9. The two-stage zircon Hf model age ranges from 2.7 to 3.0 Ga, suggesting that the Mesoarchean-Neoarchean (2.7-3.0 Ga) juvenile crust was reworked at the end of the Neoarchean in the western Alxa Block. These data suggest that the western Alxa Block experienced a Mesoarchean-Neoarchean crust growth and Latest Neoarchean-Earliest Paleoproterozoic tectonothermal event similar to the North China Craton.
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