Archean TTGs and sanukitoids from the Jiaobei terrain, North China craton: Insights into crustal growth and mantle metasomatism
Archean TTGs and sanukitoids from the Jiaobei terrain, North China craton: Insights into crustal growth and mantle metasomatism
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DOI：
10.1016/j.precamres.2016.06.019
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发表时间：
2016-08
影响因子：
3.8
通讯作者：
Neng Jiang;Jing-hui Guo;Wenbo Fan;Jun-Cheng Hu;K. Zong;Shuangquan Zhang
中科院分区：
文献类型：
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作者：
Neng Jiang;Jing-hui Guo;Wenbo Fan;Jun-Cheng Hu;K. Zong;Shuangquan Zhang
对采自华北克拉通东块太古宙胶北地体的10个岩石样品进行了锆石U-Pb年龄测定，获得3组年龄：102.9Ga、102.7Ga和102.5Ga。研究的13个岩石样品可分为低Mg#（分子Mg/（Mg + Fe））组（Mg# = 34-52）和高Mg#组（Mg# = 52-61）。低Mg#岩为典型的太古宙TTG岩，侵位年龄分别为3.9Ga、3.7Ga和3.5Ga，而高Mg#岩为太古宙sanukitoids岩，侵位年龄为3.5Ga。胶北TTG的锆石δ 18 O值在5.6‰ ~ 6.3‰之间，与邻近泰山地区的2.7Ga TTG及世界其他地区太古代TTG的锆石δ 18 O值基本一致。胶北山怒基岩类岩浆锆石δ 18 O值为6.4‰ ~ 7.5‰，明显高于太古代TTG。全岩Nd和锆石Hf同位素组成表明，胶北地体中的TTG和sanukitoids分别代表了胶北地体在2.9Ga和2.5Ga的地壳生长。与泰山地区晚更新世2.7 Ga TTG不同，胶北晚更新世2.7 Ga TTG可能是由早更新世3.0 Ga地壳改造而成。这与以往认为胶北地体最重要的成壳期为102.7Ga，地壳改造期为102.5Ga的观点不同。胶北岩类的高Mg#、高Cr、Ni、LREE和LILE特征，要求其来源于交代橄榄岩地幔。2.5Ga sanukitoids的Zr和Hf负异常以及δ 18 O值的升高与TTG熔体交代的地幔源区不一致。相反，我们认为胶北sanukitoids可能起源于地幔楔被高δ 18 O组分交代，最有可能是板片流体。胶北和上级省sanukitoids多元素配分模式和锆石δ 18 O值的相似性可能暗示胶北和上级省sanukitoids的形成过程相似。
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: ∼2.9 Ga, ∼2.7 Ga and ∼2.5 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 ∼2.9 Ga, ∼2.7 Ga and ∼2.5 Ga whereas the high Mg# rocks are Archean sanukitoids with age of ∼2.5 Ga. Despite having different ages, all the Jiaobei TTGs have zircon δ18O values between 5.6‰ and 6.3‰, essentially identical to those of the ∼2.7 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 6.4‰ and 7.5‰, significantly higher than the Archean TTGs. The whole-rock Nd and the zircon Hf isotopic compositions indicate that the ∼2.9 Ga and ∼2.5 Ga TTGs and ∼2.5 Ga sanukitoids represent crustal growth at ∼2.9 Ga and ∼2.5 Ga in the Jiaobei terrain. Unlike the ∼2.7 Ga TTGs in the adjourning Taishan area that are considered to reflect juvenile crust, the Jiaobei ∼2.7 Ga TTGs, however, are most likely resulted from the reworking of the pre-existing ∼3.0 Ga crust. This is in contrast to the previous suggestion that ∼2.7 Ga is the most significant crust-forming episode and ∼2.5 Ga a period of crustal reworking in the Jiaobei terrain. The high Mg# and high contents of Cr, Ni, LREE and LILE of the ∼2.5 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 ∼2.5 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.