ABSTRACT

The petrogenesis and tectonic affinity of late Mesoproterozoic to early Neoproterozoic magmatic records in the Yangtze Block is important to understand its tectonic evolution within the context of the Rodinia supercontinent’s reconstruction. In this paper, our new SHRIMP zircon U-Pb dating results demonstrate that the Luonie granodiorites and Gonghe granites were emplaced at 1019.2 ± 5.3 Ma and 925.0 ± 4.9 Ma, respectively. The Luonie granodiorites show high HFSE and HREE contents and Ga/Al ratios, resembling A-type granites. They exhibit negative εHf(t) values (−1.6 to −3.9) with T_DM2 ages of 1980–2125 Ma, suggesting that they were derived from partial melting of pre-existing continental crust. The Gonghe granites are calc-alkaline, slightly peraluminous and have low P₂O₅ contents, which are typical features of I-type granites. Zircons from Gonghe granites possess positive εHf(t) values (+10.8 to +13.1) with T_DM2 ages of 969–1113 Ma, indicating juvenile mafic lower crust source. In conclusion, Luonie granodiorites were formed in an intra-plate rifting environment, whereas Gonghe arc-related intrusion was emplaced into an arc-setting. On the basis of these results, we propose that the rifting-related igneous rocks and subduction-related magmatism in the southwestern Yangtze Block record a tectonic transition from a continental-rifting basin in the passive plate margin to a collisional setting in an active continental margin in the early Neoproterozoic.

摘要

扬子地块中元古代晚期与新元古代早期岩浆记录的岩石成因和构造亲缘关系，对于了解其在罗迪尼亚超大陆重建背景下的构造演化具有重要意义。在本文中，我们新的 SHRIMP 锆石 U-Pb 测年结果表明，洛涅花岗闪长岩和共和花岗岩分别位于 1019.2±5.3 Ma 和 925.0±4.9 Ma。罗涅花岗闪长岩显示出高 HFSE 和 HREE 含量以及 Ga/Al 比，类似于 A 型花岗岩。它们表现出负的 εHf(t) 值（-1.6 到 -3.9），T _DM2年龄为 1980-2125 Ma，这表明它们源自先前存在的大陆地壳的部分熔融。共和花岗岩为钙碱性、微过铝质、低 P ₂ O₅内容，是I型花岗岩的典型特征。从共和花岗岩锆石具有正εHf（t）值（10.8至13.1）和T _DM2 969-1113马的年龄，表示少年镁铁质下地壳源。综上所述，洛涅花岗闪长岩形成于板内裂谷环境，而共和弧相关侵入体形成于弧圈环境中。在这些结果的基础上，我们提出扬子地块西南部与裂谷相关的火成岩和与俯冲相关的岩浆活动记录了从被动板块边缘的大陆裂谷盆地到活动大陆边缘的碰撞环境的构造转变。在新元古代早期。