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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >U-Pb geochronology of Seychelles granitoids: a Neoproterozoic continental arc fragment
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U-Pb geochronology of Seychelles granitoids: a Neoproterozoic continental arc fragment

机译：塞舌尔花岗岩的U-Pb年代学：新元古代大陆弧片段

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摘要

New high-precision U-Pb zircon ages for 14 granitoid rocks of the Seychelles, including samples from Mahe, 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 hydridization 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.
机译：塞舌尔14个花岗岩岩石的新高精度U-Pb锆石年龄，包括Mahe，Praslin，La Digue和Ste。的样品。安妮（Anne），玛丽安（Marianne），弗雷盖特（Fregate）和雷西夫斯（Recifs）岛的屈服日期介于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。其他工人报告说，U-Pb锆石的年龄小至703 Ma，因此塞舌尔岩浆活动的时间跨度约为100 Myr。然而，绝大多数年龄都在748-755 Ma时期，这表明此时是花岗岩成岩作用的主要时期。至少一些塞舌尔白云石岩脉具有相同的年龄，表明花岗岩和玄武质岩浆同时存在，并为通过水化作用和岩浆混合生产次要石英闪长岩提供了田野和化学证据。塞舌尔新元古代晚期（〜700-800 Ma）花岗岩和白云岩的可能相关性包括马达加斯加和印度西北部的火山岩和深成岩（Malani Igneous Suite，拉贾斯坦邦），它们可能形成于连续的大陆（安第斯型）中弧位于Rodinia超大陆的西边缘。这个想法与岩浆作用的时间跨度，火成岩的岩石学特征以及古磁确定的重建相一致，而不是通常认为的塞舌尔和马拉尼火成岩板块内伸展背景。

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