| 关于拉斯曼丘陵泛非期高级变质作用时代的新限 |
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| 引用本文： | 任留东,李崇,王彦斌,刘平.关于拉斯曼丘陵泛非期高级变质作用时代的新限[J].极地研究,2016,28(4):451-461. |
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| 作者姓名： | 任留东 李崇 王彦斌 刘平 |
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| 作者单位： | 中国地质科学院地质研究所，北京 100037 |
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| 基金项目： | 国家自然科学基金(41072053?41472172?41530209)?国家海洋局“南北极环境综合考察与评估”专项(CHINARE2016-02-05-05)和中国地质调查项目(121201102000150009-4)资助 |
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| 摘 要： | 就目前认识，拉斯曼丘陵地区的所有基底和盖层岩石都卷入到了格林威尔期和泛非期高级变质和变形作用。泛非期高峰变质的时代大致在550—530 Ma，其造山晚期的花岗质岩浆作用遍及全区。我们观察到，中山站区石榴黑 云斜长片麻岩固相变质作用过程，主要是对早期锆石的重启、改造，例如，对早期岩浆锆石环带的模糊化，对锆石棱、角的溶蚀，甚至同位素体系的重启等，难以形成变质锆石（边），退变或重启年龄平均值为522.7±6.6 Ma。峰期变质 之后侵位的花岗岩结晶年龄为545±9 Ma，意味着峰期变质应不晚于该年龄。泛非期的变形、变质作用及花岗岩可对早期“干”岩石进行某种程度的退变质改造，从而造成高级变质岩变质结构的复杂性。这种变质作用及有关的花岗岩活动似乎缘于陆块内部的活化，而不是不同陆块间的碰撞所致。
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| 关 键 词： | 泛非期 锆石年龄 变质年龄 花岗岩 拉斯曼丘陵 |
| 收稿时间： | 2015-05-12 |
On Constraining the Pan-African High-Grade Metamorphism Time of the Larsemann Hills,East Antarctica |
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| Abstract: | Up to now, both the basement and the cover sequences of the Larsemann Hills in East Antarctica have been considered involved in the high-grade deformation and metamorphism of the Pan-African event, which peaked at 550—530 Ma and was responsible for the widespread granitic magmatism at 525—500 Ma. The late Neoproterozoic-Paleozoic (Pan-African) orogenesis was thus constrained to the period of 550—500 Ma. Our studies demonstrated that the zircons of the garnet-biotite-plagioclase gneiss were severely disturbed and reset in the Pan-African high-grade metamorphism. The Pan-African metamorphism and granites can obliterate and reset the older magmatic or metamorphic zircons, and the zircons produce complex inner textures; thus, the true age of metamorphism is hard to obtain. However, the actual metamorphic rims are seldom present and the reset zircons give an average age of 522.7±6.6 Ma. Granite postdating the peak metamorphism places the crystallizing time at 545 ± 9 Ma, while some younger granites suggest a date of c.500 Ma. Peak metamorphism should be older than the oldest granite of the Pan-African event. The Pan-African metamorphism and associated granites seem to have been derived from a special intracontinental reactivation mechanism of older continental materials, not from intercontinental subduction-collision as conventionally considered. |
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| Keywords: | Pan-African zircon age metamorphism time granite Larsemann Hills |
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