摘要
Huai'an 片麻岩岩层主要由 TTG 片麻岩和 dioritic 片麻岩组成。在 magmatic 锆石核心标明日期的 situ U-Pb 的激光显示这些片麻岩的 protolith 在 ∼2.5 Ga 被形成。TTG 片麻岩有积极 ε<sub > 2.7 ～ 4.3 的 Nd </sub>(t) 价值，和大多数 magmatic 锆石有积极 ε<sub > 2.0 ～ 8.3 的 Hf </sub>(t) 价值。这些积极 ε<sub > Nd </sub>(t) 和 ε<sub > Hf </sub>(t) 价值两个都类似于在 2.5 Ga 的同时期的弄空的披风的那些。而且，为 magmatic 锆石的 2.44 ～ 2.73 Ga 的年轻 Hf 模型年龄接近预定锆石生长。整个岩石的 ε<sub > Nd </sub>(t) 价值由于在它的来源的古老的外壳的参与比在 TTG 片麻岩在 dioritic 片麻岩(0.8 ～ 1.7 ) 是更低的。然而，从 dioritic 片麻岩的许多 magmatic 锆石有类似的 ε<sub > Hf </sub>(t) 价值(2.0 ～ 7.9 ) 到同时代的弄空的披风的；他们 2.49 ～ 2.75 Ga 的 Hf 模型年龄接近锆石的 U-Pb 年龄。最高的 ε<sub > Hf </sub>(t) 价值接近弄空的披风，和相对高的 ε<sub 的价值 > Hf </sub>(t) 价值对应于相对年轻的 Hf 模型年龄。这些 Nd 和 Hf 同位素特征建议 Huai'an 片麻岩岩层的片麻岩的这二种类型在 ca 从少年外壳发源。2.5 Ga。
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 εNd（t） values of 2.7 to 4.3, and most of the magmatic zircons have positive εHf（t） values of 2.0 to 8.3. These positive εNd（t） and εHf（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 εNd（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 εHf（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 εHf（t） values are close to the value of the depleted mantle, and the relatively high εHf（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.
基金
Supported by National Natural Science Foundation of China (Grant Nos. 40730315, 40721062 and 40372089)
