U–Pb geochronology of Seychelles granitoids: a Neoproterozoic continental arc fragment
U–Pb geochronology of Seychelles granitoids: a Neoproterozoic continental arc fragment
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DOI：
10.1016/s0012-821x(01)00282-5
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发表时间：
2001-04
影响因子：
5.3
通讯作者：
R. Tucker;L. Ashwal;T. Torsvik
中科院分区：
文献类型：
--
作者：
R. Tucker;L. Ashwal;T. Torsvik
对塞舌尔群岛14个花岗岩类岩石进行了新的高精度锆石U-Pb年龄测定，包括Mahé、Praslin、La Digue、Ste.安妮、玛丽安、弗雷盖特和累西腓群岛的产出年龄介于748.4±1.2 Ma和808.8±1.9 Ma之间，被解释为代表岩浆结晶年龄。其他工作者报道的锆石U-Pb年龄为703 Ma，因此塞舌尔岩浆活动的时间跨度为1亿年。然而，绝大多数的年龄都落在748-755 Ma之间，这表明当时是花岗岩深成作用的主要时期。至少有一些塞舌尔粗玄岩脉具有相同的年龄，表明花岗质和玄武质岩浆的同时代性，并支持通过杂交和岩浆混合产生次要石英闪长岩的现场和化学证据。塞舌尔新元古代晚期（距今700-800 Ma）花岗岩和黑玄岩的可能相关物包括马达加斯加和印度西北部的火山岩和深成岩（拉贾斯坦邦的马拉尼火成岩套），它们可能形成于罗迪尼亚超大陆西缘的一个连续大陆（安第斯型）弧。这一想法是更一致的岩浆作用的时间跨度，火成岩的岩石学特征，和古地磁确定的重建，比普遍认为的塞舌尔和马拉尼火成岩套板内伸展设置。
New high-precision U–Pb zircon ages for 14 granitoid rocks of the Seychelles, including samples from Mahé, Praslin, La Digue, Ste. Anne, Marianne, Fregate and Recifs Islands, yield dates between 748.4±1.2 Ma and 808.8±1.9 Ma, interpreted as representing magmatic crystallization ages. U–Pb zircon ages as young as 703 Ma have been reported by other workers, and the time span of Seychelles magmatic activity, therefore, is ∼100 Myr. The vast majority of ages, however, fall in the period 748–755 Ma, suggesting a major period of granite plutonism at this time. At least some Seychelles dolerite dikes have equivalent ages, indicating the contemporaneity of granitic and basaltic magmas, and supporting field and chemical evidence for the production of minor quartz dioritic rocks by hybridization and magma mingling. Possible correlatives of the late Neoproterozoic (∼700–800 Ma) granitoids and dolerites of the Seychelles include volcanic and plutonic rocks in Madagascar and northwestern India (Malani Igneous Suite, Rajasthan), which may have formed in a continuous continental (Andean-type) arc located at the western margin of the Rodinia supercontinent. This idea is more consistent with the time span of magmatism, petrologic character of the igneous rocks, and paleomagnetically determined reconstructions, than the commonly held view of an intra-plate extensional setting for the Seychelles and Malani Igneous Suite.