Dating for Jifanggou metamorphic complex in central Jilin and its tectonic implications

Based on the results of four regional geological surveys of 1: 50000 including Shulan County map in Jilin,taking Shulan area as the study area,the authors re-delineated the rock type assemblages,e.g. metamorphic rhyolite,metamorphic tuffaceous breccia lava,sericite-quartz schist and tremolite altered rock,etc.,and the structural contacts between them. With the help of in-situ LA-ICP-MS U-Pb dating for zircons,it is concluded that the zircon crystallization ages of the metamorphic rhyolite,the metamorphic andesitic tuff breccia lava and the tremolite altered rock are 339. 1 ± 1. 3 Ma( n = 27,MSWD = 0. 78),351. 8 ± 1. 7 Ma( n = 21,MSWD = 0.82),and 362.0±1.8 Ma( n = 43,MSWD = 2.2) respectively. The metamorphic complex is actually a set of tectonic melange which comprises the rocks in different types,sources,times,or tectonic settings,and was formed by tectonism.

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

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 2.7 ～ 4.3 的 Nd (t) 价值，和大多数 magmatic 锆石有积极 ε 2.0 ～ 8.3 的 Hf (t) 价值。这些积极 ε Nd (t) 和 ε Hf (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 Nd (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 Hf (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 Hf (t) 价值接近弄空的披风，和相对高的 ε Hf (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。