Early Palaeozoic orogenic collapse and voluminous late-tectonic magmatism in Dronning Maud Land and Mozambique: insights into the partially delaminated orogenic root of the East African–Antarctic Orogen?
Early Palaeozoic orogenic collapse and voluminous late-tectonic magmatism in Dronning Maud Land and Mozambique: insights into the partially delaminated orogenic root of the East African–Antarctic Orogen?
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DOI：
10.1144/sp308.3
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
J. Jacobs;B. Bingen;R. Thomas;W. Bauer;M. Wingate;P. Feitio
中科院分区：
文献类型：
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作者：
J. Jacobs;B. Bingen;R. Thomas;W. Bauer;M. Wingate;P. Feitio
摘要晚新元古代—早古生代东非-南极造山带南段晚期构造史以侧向挤压、伸展崩塌和大量高温a2型花岗岩为特征。这个晚构造火成岩省覆盖了位于Dronning Maud地（东南极洲）的EAAO及其向北延伸为莫桑比克东北部的Nampula复合体的面积超过15,000平方公里。岩浆省在北部被卢里奥带所包围。新二次电离质谱（SIMS）分析了来自drning Maud地块两个主要晚构造花岗岩类岩体的锆石的结晶年龄为501±7和499±4 Ma，而一个主要的伸展剪切带的结晶年龄为507±9 Ma。新SIMS锆石U-Pb分析表明，南普拉省晚构造花岗质片和岩体年龄分别为512±4、508±4、508±2和507±3 Ma。因此，晚构造岩浆活动可划分在约530 ~ 485 Ma之间。它始于约530-520 Ma的小辉长岩体，在约510-500 Ma时以主要花岗岩-炭绿岩岩体的侵入达到高潮，在约485 Ma时以小体积片状花岗岩的引入而结束。新的数据表明，伸展剪切与花岗岩类侵入是同步的，造山崩塌与岩浆活动是有联系的。我们认为该岩浆省的分布、构造样式、地球化学组成和年龄是由东侏罗统南三分之一造山带的部分剥离过程引起的。造山崩塌-花岗质岩浆活动是否与鄂西坳陷最南端的南向逃逸构造有关，还有待检验。
Abstract The late tectonic history of the southern part of the Late Neoproterozoic–Early Palaeozoic East African–Antarctic Orogen (EAAO) is characterized by lateral extrusion, extensional collapse and large volumes of high-temperature A2-type granitoids. This late-tectonic igneous province covers an area more than 15 000 km2 of the EAAO in Dronning Maud Land (East Antarctica) and its northerly continuation as the Nampula Complex of NE Mozambique. The magmatic province is bounded in the north by the Lurio Belt. New secondary ionization mass spectrometry (SIMS) U–Pb analyses of zircons from two major late-tectonic granitoid intrusions from Dronning Maud Land indicate crystallization ages of 501±7 and 499±4 Ma, whereas a major extensional shear zone was dated at 507±9 Ma. New SIMS zircon U–Pb analyses of late-tectonic granitoid sheets and plutons from the Nampula Province indicate ages of 512±4, 508±4, 508±2 and 507±3 Ma. Consequently, the late-tectonic magmatism can be bracketed between c. 530 and 485 Ma. It started with small gabbro bodies emplaced at c. 530–520 Ma, culminated with the intrusion of major granite–charnockite plutons at c. 510–500 Ma and terminated with the introduction of small volumes of sheet-like granite at c. 485 Ma. The new dates demonstrate that extensional shearing and granitoid intrusion are synchronous, and that orogenic collapse and the magmatism are related. We ascribe the distribution, structural style, geochemical composition and age of the late magmatic province to a process of partial delamination of the orogenic root in the southern third of the EAAO. It remains to be tested whether there is a relationship between orogenic collapse–granitoid magmatism and south-directed escape tectonics in the southernmost EAAO.