Timing of Grenville-age vs. Pan-African medium- to high grade metamorphism in western Dronning Maud Land (East Antarctica) and significance for correlations in Rodinia and Gondwana
Timing of Grenville-age vs. Pan-African medium- to high grade metamorphism in western Dronning Maud Land (East Antarctica) and significance for correlations in Rodinia and Gondwana
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DOI：
10.1016/s0301-9268(03)00048-2
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发表时间：
2003-07
影响因子：
3.8
通讯作者：
J. Jacobs;C. Fanning;W. Bauer
中科院分区：
文献类型：
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作者：
J. Jacobs;C. Fanning;W. Bauer
位于东南极Dronning Maud陆地西部的Heimefrontfjella是1.1GaNamaqua-Natal-Maud带的一部分。它位于Rodinia重建的重要位置，也位于新元古代晚期/早古生代东非/南极造山带的西部造山前缘。六个基底样品帮助确定了大约1090-1060 Ma之间格伦维尔时代的变质作用的准确年龄。这些数据表明，莫德带南部Coats陆块的古地磁数据不能支持Coats陆地/Maud/Grunehogna大陆碎片和卡拉哈里在中元古代晚期的毗连。航磁资料和地壳省的对比表明，Coats陆地基底可能由中元古代以前的基底组成，该基底在500 Ma左右在东非/南极造山带内进行了差异改造。东非/南极造山带的西造山前缘被暴露为海前剪切带。来自该剪切带的锆石显示出一个薄的低U反应带，可能是角闪岩相条件下的糜棱岩化作用所致。轮缘太薄了，无法分析。然而，在剪切带以东仅几公里处，存在约500 Ma泛非锆石的过度生长，清楚地表明新元古代晚期/早古生代格伦维尔时代基底的强烈改造，并允许对这一较年轻的叠置进行直接测年。正如一些约500 Ma的K-Ar和Ar-Ar角闪石和云母年龄所表明的那样，高品位重加工之后一定是快速冷却。东非/南极造山带的西部造山带被暴露为Heimefront剪切带，而东部造山带可能以沙克尔顿山脉的奥特高地逆冲为代表，在这两个构造不连续面之间有不同程度的地壳改造至麻粒岩相。
Heimefrontfjella in western Dronning Maud Land, East Antarctica, is part of the c. 1.1Ga Namaqua–Natal–Maud Belt. It is situated at an important location, both for Rodinia reconstructions and at the western orogenic front of the Late Neoproterozoic/Early Palaeozoic East African/Antarctic Orogen. Six basement samples help to precisely date the Grenville-age metamorphism between c. 1090 and 1060Ma. These dates indicate that palaeomagnetic data from the Coats Land Block to the south of the Maud Belt cannot be taken to support the contiguity of the Coats Land/Maud/Grunehogna continental fragment and Kalahari during Late Mesoproterozoic times. A comparison of aeromagnetic data and crustal provinces indicates that the Coats Land basement is likely to be composed of pre-Mesoproterozoic basement that was differentially reworked at c. 500Ma within the East African/Antarctic Orogen. The western orogenic front of the East African/Antarctic Orogen is exposed as the Heimefront Shear Zone. Zircons from this shear zone show a thin, low-U, reaction zone that probably resulted from mylonitisation at amphibolite facies conditions. The rims were too thin to be analysed. However, only a few kilometres to the E of the shear zone, c. 500Ma Pan-African zircon overgrowth is present, clearly indicating intense Late Neoproterozoic/Early Palaeozoic reworking of the Grenville-age basement and allowing the direct dating of this younger overprint. High grade reworking must have been followed by rapid cooling, as shown by a number of c. 500Ma K–Ar and Ar–Ar hornblende and mica ages. Whereas the western orogenic front of the East African/Antarctic Orogen is exposed as the Heimefront Shear Zone, the eastern orogenic front might be represented by the Otter Highland Thrust in the Shackleton Range, with variably reworked crust up to granulite facies in between these two structural discontinuities.