He Deng-Fa, Li Di, Li Chuan-Xin, Li Ying-Qiang, Mei Qing-Hua
The Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Accumulation Mechanism, The Ministry of Education, China University of Geosciences, Beijing, 10083, China.
Sci Rep. 2017 Oct 2;7(1):12542. doi: 10.1038/s41598-017-12764-y.
Well W117 in the Sichuan Basin reveals a suite of ~814 Ma quartz monzonites, unconformably overlain by Sinian clastic and carbonate sediments. The quartz monzonites contain no muscovite and amphibole, and are characterized by high SiO (72.26-77.93%), total alkali, and TFeO/MgO content, and low PO and CaO abundance, with variable A/CNK ratio (0.93-1.19), classified as metaluminous to weakly aluminous highly fractionated I-type granites. They are preserved in the Neoproterozoic rift and exhibit restricted negative ε(t) values (-7.0 to -5.2) and variable zircon ε(t) values (-13.9 to 2.3), suggesting their generation via melting of both ancient and juvenile crustal materials in an extensional setting. Their parent magmas were formed in a low-temperature condition (831-650 °C) and finally emplaced at ca. 9-10 km below the surface, indicating that the intrusion underwent exhumation before the deposition of Sinian sag basin. Such geological processes, together with evidence for Neoproterozoic structures in the surrounding area, support that the Upper Yangtze craton experienced two main phases of rifting from 830-635 Ma. The Well W117 granites and its overlying sediments record a geodynamic evolution from orogenic collapse to continental rifting, and to thermal subsidence, probably related to the Rodinia supercontinent breakup.
四川盆地的W117井揭示了一套约8.14亿年的石英二长岩，被震旦系碎屑岩和碳酸盐沉积物不整合覆盖。这些石英二长岩不含白云母和角闪石，其特征是SiO含量高（72.26 - 77.93%）、总碱含量高、TFeO/MgO含量高，而P₂O₅和CaO含量低，A/CNK比值可变（0.93 - 1.19），被归类为准铝质到弱铝质的高分异I型花岗岩。它们保存在新元古代裂谷中，呈现出有限的负ε(t)值（-7.0至-5.2）和可变的锆石ε(t)值（-13.9至2.3），表明它们是在伸展环境中通过古老和新生地壳物质的熔融形成的。它们的母岩浆在低温条件下（831 - 650℃）形成，最终在地表以下约9 - 10千米处侵位，这表明该侵入体在震旦纪坳陷盆地沉积之前经历了隆升剥蚀。这些地质过程，连同周边地区新元古代构造的证据，支持上扬子克拉通在8.3 - 6.35亿年经历了两个主要的裂谷阶段。W117井花岗岩及其上覆沉积物记录了从造山垮塌到大陆裂谷再到热沉降的地球动力学演化过程，这可能与罗迪尼亚超大陆的解体有关。
