Shellnutt J Gregory, Yeh Meng-Wan, Suga Kenshi, Lee Tung-Yi, Lee Hao-Yang, Lin Te-Hsien
Department of Earth Sciences, National Taiwan Normal University, 88 Tingzhou Road Section 4, Taipei, 116, Taiwan.
Center for General Education, National Taiwan Normal University, 162 Heping East Road Section 1, Taipei, 106, Taiwan.
Sci Rep. 2017 Mar 14;7(1):179. doi: 10.1038/s41598-017-00248-y.
The Early Palæogene Silhouette/North Island volcano-plutonic complex was emplaced during the rifting of the Seychelles microcontinent from western India. The complex is thought to have been emplaced during magnetochron C28n. However, the magnetic polarities of the rocks are almost entirely reversed and inconsistent with a normal polarity. In this study we present new in situ zircon U/Pb geochronology of the different intrusive facies of the Silhouette/North Island complex in order to address the timing of emplacement and the apparent magnetic polarity dichotomy. The rocks from Silhouette yielded weighted mean Pb/U ages from 62.4 ± 0.9 Ma to 63.1 ± 0.9 Ma whereas the rocks from North Island yielded slightly younger mean ages between 60.6 ± 0.7 Ma to 61.0 ± 0.8 Ma. The secular latitudinal variation from Silhouette to North Island is consistent with the anticlockwise rotation of the Seychelles microcontinent and the measured polarities. The rocks from Silhouette were emplaced across a polarity cycle (C26r-C27n-C27r) and the rocks from North Island were emplaced entirely within a magnetic reversal (C26r). Moreover, the rocks from North Island and those from the conjugate margin of India are contemporaneous and together mark the culmination of rift-related magmatism.
早古近纪塞舌尔群岛/北岛火山-深成杂岩体是在塞舌尔微大陆从印度西部裂离期间就位的。该杂岩体被认为是在磁极性时标C28n期间就位的。然而，这些岩石的磁极性几乎完全反转，与正常极性不一致。在本研究中，我们展示了塞舌尔群岛/北岛杂岩体不同侵入相的新的原位锆石U/Pb年代学，以确定就位时间和明显的磁极性二分法。塞舌尔群岛的岩石加权平均Pb/U年龄为62.4±0.9 Ma至63.1±0.9 Ma，而北岛的岩石平均年龄略小，在60.6±0.7 Ma至61.0±0.8 Ma之间。从塞舌尔群岛到北岛的长期纬度变化与塞舌尔微大陆的逆时针旋转以及测量的极性一致。塞舌尔群岛的岩石是跨越一个极性旋回（C26r-C27n-C27r）就位的，而北岛的岩石完全是在一次磁反转（C26r）期间就位的。此外，北岛的岩石与印度共轭边缘的岩石是同期的，共同标志着裂谷相关岩浆作用的顶峰。
