Crustal growth at ∼2.5 Ga in the North China Craton: evidence from whole-rock Nd and zircon Hf isotopes in the Huai’an gneiss terrane

• Published in: Chinese science bulletin Vol. 54; no. 24; pp. 4704 - 4713
• Main Authors: Liu, Fu, Guo, JingHui, Lu, XiaoPing, Diwu, ChunRong
• Format: Journal Article
• Language: English
• Published: Heidelberg SP Science in China Press 01.12.2009
• Subjects: Articles/Geology; Chemistry/Food Science; China; Earth Sciences; Engineering; gneiss; Humanities and Social Sciences; isotopes; Life Sciences; multidisciplinary; Physics; Science; Science (multidisciplinary); zircon; China; crustal growth; Nd-Hf isotope; North China Craton; zircon; TTG gneisses; Archean
• ISSN: 1001-6538; 2095-9273; 1861-9541; 2095-9281
• DOI: 10.1007/s11434-009-0288-y

The Huai’an gneiss terrane mainly consists of TTG gneisses and dioritic gneisses. Laser in situ U-Pb dating of magmatic zircon cores indicates that protolith of these gneisses was formed at ∼2.5 Ga. The TTG gneisses have positive ε Nd ( t ) values of 2.7 to 4.3, and most of the magmatic zircons have positive ε Hf ( t ) values of 2.0 to 8.3. These positive ε Nd ( t ) and ε Hf ( t ) values are both similar to those of the contemporaneous depleted mantle at 2.5 Ga. Moreover, the young Hf model ages of 2.44 to 2.73 Ga for the magmatic zircons are close to the timing of the zircons growth. The whole-rock ε Nd ( t ) values are lower in the dioritic gneisses (0.8 to 1.7) than in the TTG gneisses due to the involvement of ancient crust in its source. However, many magmatic zircons from the dioritic gneisses have similar ε Hf ( t ) values (2.0 to 7.9) to that of the coeval depleted mantle; their Hf model ages of 2.49 to 2.75 Ga are close to the U-Pb ages of zircons. The highest ε Hf ( t ) values are close to the value of the depleted mantle, and the relatively high ε Hf ( t ) values corresponds to the relatively young Hf model age. These Nd and Hf isotope features suggest that these two types of gneisses of the Huai’an gneiss terrane originated from the juvenile crust at ca. 2.5 Ga.