Palaeomagnetic and petrological reconstruction of the Seychelles
Palaeomagnetic and petrological reconstruction of the Seychelles
复制标题
塞舌尔群岛的古地磁和岩石学重建
DOI：
10.1016/0301-9268(94)90092-2
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发表时间：
1994
影响因子：
3.8
通讯作者：
M. Hoshino
中科院分区：
文献类型：
--
作者：
K. Suwa;K. Tokieda;M. Hoshino
塞舌尔马埃岛及其邻近岛屿的地质由三种类型的晚前寒武纪花岗质岩石系列组成：（1）片麻状花岗闪长岩-片麻状英云闪长岩和角闪岩-浅色花岗闪长岩系列，（2）斑状花岗岩-粉红色花岗岩系列，（3）灰色花岗岩-片麻状灰色花岗岩系列。所有这些花岗质岩石都被辉长岩组成的岩墙切割，大多具有WNW-ESE走向。片麻状花岗闪长岩为钙碱性I型花岗岩，Ab > Or，斑状花岗岩为亚碱性A型花岗岩，Ab > Or，灰色花岗岩为碱性A型花岗岩，Ab > Or。Rb-Sr放射性同位素分析结果表明，片麻状花岗闪长岩的年龄为713±19 Ma，斑状花岗岩的年龄为683±16 Ma，灰色花岗岩的年龄为570±5 Ma.岩石学、地质学、年代学和地球化学研究表明，塞舌尔晚前寒武纪花岗质岩石与在塞舌尔马埃岛群采集了408个晚前寒武纪花岗岩标本。采用渐进交变场退磁和热退磁方法，成功地分离了花岗岩自然剩磁中具有良好组合方向的稳定剩磁。花岗岩的稳定剩磁分布在平均偏北方向，偏北角为348.5°，倾角为+48.7°。马埃岛群花岗岩的稳定剩磁产生了一个位于54.0°N，38.2°E的古磁极。根据上述数据，结合报道的极移路径和板块旋转极，可以得出结论，塞舌尔最初位于非洲之角东端附近，并在大陆分裂后漂移到现在的位置。
The geology of Mahé-Island and adjoining islets, Seychelles, consists of three types of late Precambrian granitic rock series: (1) a gneissose granodiorite-gneissose tonalite and amphibolite-leucogranodiorite series, (2) a porphyritic granite-pink granite series, and (3) a grey granite-gneissose grey granite series. All these granitic rocks are cut by dykes of doleritic compositions, mostly with a WNW-ESE trend. The gneissose granodiorite is a calcalkaline I-type granite with normative Ab ⪢ Or, the porphyritic granite is a sub-alkaline A-type granite with normative Ab > Or, and the grey granite is an alkaline A-type granite with normative Ab > Or. RbSr radiometric analyses yielded ages of 713±19 Ma for the gneissose granodiorite, 683±16 Ma for the porphyritic granite and 570±5 Ma for the grey granite.Petrological, geological, geochronological and geochemical studies suggest that the late Precambrian granitic rocks of the Seychelles are very similar to, and are well correlated with those of the Arabian-Nubian shield.408 late Precambrian granite specimens were collected from the Mahé island group, Seychelles. Progressive alternating field demagnetization and thermal demagnetization have been successfully performed to isolate stable remanence with well-grouped direction from natural remanent magnetization of the granites. The stable remanences of the granite fall around a northerly mean direction, of which the declination is 348.5° and the inclination +48.7°. The stable remanences of the Mahé island group granite yield a palaeomagnetic pole at 54.0°N, 38.2°E.From the above data, in conjunction with reported polar wander path and plate rotation poles, it is concluded that the Seychelles were originally located near the eastern end of the Horn of Africa and have drifted to the present position since continental break-up.