Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6442162 | Precambrian Research | 2016 | 61 Pages |
Abstract
U-Pb zircon dating for 10 rock samples collected from the Archean Jiaobei terrain of the eastern block of the North China craton (NCC) yield three groups of ages: â¼2.9 Ga, â¼2.7 Ga and â¼2.5 Ga. Thirteen rock samples studied can be classified into a low Mg# (molecular Mg/(Mg + Fe)) (Mg# = 34-52) and a high Mg# group (Mg# = 52-61), respectively. The low Mg# rocks are typical Archean TTGs with emplacement ages of â¼2.9 Ga, â¼2.7 Ga and â¼2.5 Ga whereas the high Mg# rocks are Archean sanukitoids with age of â¼2.5 Ga. Despite having different ages, all the Jiaobei TTGs have zircon δ18O values between 5.6â° and 6.3â°, essentially identical to those of the â¼2.7 Ga TTGs from adjourning Taishan area and Archean TTGs from other parts of the world. Magmatic zircons from the Jiaobei sanukitoids have δ18O values between 6.4â° and 7.5â°, significantly higher than the Archean TTGs. The whole-rock Nd and the zircon Hf isotopic compositions indicate that the â¼2.9 Ga and â¼2.5 Ga TTGs and â¼2.5 Ga sanukitoids represent crustal growth at â¼2.9 Ga and â¼2.5 Ga in the Jiaobei terrain. Unlike the â¼2.7 Ga TTGs in the adjourning Taishan area that are considered to reflect juvenile crust, the Jiaobei â¼2.7 Ga TTGs, however, are most likely resulted from the reworking of the pre-existing â¼3.0 Ga crust. This is in contrast to the previous suggestion that â¼2.7 Ga is the most significant crust-forming episode and â¼2.5 Ga a period of crustal reworking in the Jiaobei terrain. The high Mg# and high contents of Cr, Ni, LREE and LILE of the â¼2.5 Ga Jiaobei sanukitoids, require a metasomatized peridotitic mantle source for their origin. The significant negative Zr and Hf anomalies and the elevated δ18O values of the â¼2.5 Ga sanukitoids, are inconsistent with a mantle source metasomatized solely by the TTG melts. Instead, we suggest that the Jiaobei sanukitoids could have originated from a mantle wedge metasomatized by a high δ18O component, most likely the slab-derived fluids. The similarity of multi-element patterns and the zircon δ18O values between the Jiaobei and Superior Province sanukitoids may imply similar processes involved to form sanukitoids in both Jiaobei and Superior Province terrains.
Related Topics
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Authors
Neng Jiang, Jinghui Guo, Wenbo Fan, Jun Hu, Keqing Zong, Shuangquan Zhang,