Abstract The southern Yangtze is underlain by Mesoarchean igneous rocks that were emplaced in two pulses, including trondhjemites at ca. 3092–3071 Ma followed by potassic granites at 2920 Ma. These represent the oldest TTG suites identified in the southern Yangtze and the oldest potassic granites in the entire Yangtze Block. Hf isotopic analysis reveals eHf(t) values of −2.49–7.49 and Hf crustal model ages (TDMC) of 3601–3000 Ma for zircons from the trondhjemites, whereas those from the potassic granites show eHf(t) values of −1.79–4.18 and TDMC ages of 3453–3043 Ma. The trondhjemites have high SiO2, Mg# and low Al2O3 and K2O/Na2O, and are highly evolved with low Ni, Cr and Co. The trondhjemites are characterized by low Sr/Y, Eu/Gd and (La/Yb)N, and high Y and HREE, typical of high-HREE and low-pressure TTGs. Their geochemical and isotopic compositions indicate that they are derived from melting of juvenile mafic crust with little contribution from older crustal materials, consistent with a plagioclase-bearing basaltic source. The multielement patterns of potassic granites are similar to that of the trondhjemites, albeit with lower HREE and Y contents. Their high K2O values, strongly fractionated REE patterns and low Y contents indicate the presence of garnet and/or amphibole as residual phases in the source region, which indicates they formed at higher pressure than the trondhjemites. The isotopic and geochemical data imply that the formation of the potassic granites could be related to reworking of older TTGs. The increasing K2O/Na2O of the 3092–3071 Ma trondhjemites to potassic 2920 Ma granites corresponds with stabilization, maturation and thickening of the Archean continental crust in the southern Yangtze. The geochemical data of the TTGs in the Kunming region show important differences from that of contemporaneous TTGs from the Kongling Complex, suggesting that southern Yangtze is composed by an independent old nucleus, which is exotic to the northern Yangtze. A synthesis of petrogenesis, geochronology, geochemistry and isotope data of Archean granites of the Yangtze Block provides important insights into the architecture of its Archean crust. We propose that the Yangtze Block can be subdivided into discrete northwestern, northeastern and southern domains, but which are all affected by late Paleoproterozoic tectonothermal events, suggesting that they had been assembled together by then to form the united Yangtze Block.

中文翻译：

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扬子地块南部太古代TTGs和钾质花岗岩的成因：扬子地块早期形成的制约因素

摘要 扬子南部的下方是中太古代火成岩，这些火成岩以两个脉冲的形式出现，包括大约在 10 年前的 trondhjemites。3092-3071 Ma，然后是 2920 Ma 的钾质花岗岩。这些代表了在扬子南地区发现的最古老的 TTG 岩层和整个扬子地块中最古老的钾质花岗岩。Hf 同位素分析显示，长长花岗岩中锆石的 eHf(t) 值为 -2.49-7.49，Hf 地壳模型年龄 (TDMC) 为 3601-3000 Ma，而钾质花岗岩中的锆石的 eHf(t) 值为 -1.79-4.18和 TDMC 年龄为 3453-3043 Ma。长闪长岩具有高 SiO2、Mg# 和低 Al2O3 和 K2O/Na2O，并且高度演化，Ni、Cr 和 Co 含量低。 长闪长岩的特征是低 Sr/Y、Eu/Gd 和 (La/Yb)N，和高 Y 和 HREE，典型的高 HREE 和低压 TTG。它们的地球化学和同位素组成表明它们来源于新生基性地壳的熔融，而较旧的地壳材料贡献很小，与含斜长石的玄武岩源一致。钾质花岗岩的多元素分布与长闪长岩相似，但 HREE 和 Y 含量较低。它们的高 K2O 值、强烈分馏的 REE 模式和低 Y 含量表明在源区存在石榴石和/或角闪石作为残余相，这表明它们形成的压力高于长闪长岩。同位素和地球化学数据表明，钾质花岗岩的形成可能与旧 TTG 的再加工有关。从 3092-3071 Ma 长闪长岩到钾质 2920 Ma 花岗岩的 K2O/Na2O 增加与稳定相一致，长江以南太古代大陆地壳的成熟和增厚. 昆明地区TTGs的地球化学数据与孔岭杂岩体同期TTGs的地球化学数据显示出重要差异，表明扬子南由一个独立的旧核组成，这是扬子北部特有的。扬子地块太古代花岗岩的岩石成因、年代学、地球化学和同位素数据的综合为了解其太古代地壳的结构提供了重要的见解。我们认为扬子地块可以细分为离散的西北、东北和南部域，但都受到晚古元古代构造热事件的影响，表明它们在那时已经聚集在一起形成了统一的扬子地块。