Grenvillian massif-type anorthosites in the Sierras Pampeanas

We report the discovery of massif-type anorthosites in the Andean basement of the Western Sierras Pampeanas of Argentina. U–Pb zircon dating (by sensitive high-resolution ion microprobe) of a cogenetic gabbronorite dyke yields ages of 1070 ± 41 Ma for igneous emplacement and 431 ± 40 Ma for metamorphism. These anorthosites are petrologically and geochemically comparable with those of the Grenville province of Laurentia. Palaeogeographical reconstructions of Rodinia at 1.0–1.1 Ga suggest that the Sierras Pampeanas anorthosites were part of a large anorthosite province in the late Mesoproterozoic.

本研究报道了阿根廷西部潘帕斯山系（Western Sierras Pampeanas）基底中块状型斜长岩（massif-type anorthosites）的发现。对一条同成因辉长苏长岩（gabbronorite）岩脉开展的高灵敏度高分辨率离子探针（sensitive high-resolution ion microprobe）铀-铅锆石定年结果显示，其岩浆侵位年龄为1070 ± 41 Ma，变质作用年龄为431 ± 40 Ma。该类斜长岩在岩石学与地球化学特征上，与劳伦大陆（Laurentia）的格伦维尔造山带（Grenville province）产出的斜长岩具有可比性。针对1.0~1.1 Ga时期罗迪尼亚超大陆（Rodinia）的古地理重建结果表明，潘帕斯山系的斜长岩在中元古代晚期曾属于一个大型斜长岩省。