Evidence for extensive Proterozoic remobilization of the Aldan shield and implications for Proterozoic plate tectonic reconstructions of Siberia and Laurentia
Evidence for extensive Proterozoic remobilization of the Aldan shield and implications for Proterozoic plate tectonic reconstructions of Siberia and Laurentia
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DOI：
10.1016/s0301-9268(97)00074-0
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发表时间：
1998-05
影响因子：
3.8
通讯作者：
B. Frost;O. Avchenko;K. Chamberlain;C. Frost
中科院分区：
文献类型：
--
作者：
B. Frost;O. Avchenko;K. Chamberlain;C. Frost
沿阿尔丹河沿着穿越阿尔丹地盾的地质图表明，该地区的下面有两种不同的岩石组合。中阿尔丹组合由变质沉积岩组成，主要是石英岩，被钾质黑云母花岗岩侵入。下游，中阿尔丹组合以北，是下阿尔丹组合，主要由紫苏花岗岩和筏状较老的麻粒岩片麻岩，其中含有丰富的变质沉积层。中阿尔丹组合花岗岩（1900 Ma）、下阿尔丹组合紫苏花岗岩（最大年龄1918 Ma）和花岗质片麻岩（最大年龄2230 Ma）的锆石U-Pb年龄表明，阿尔丹河沿着出露的岩石大部分为元古代岩石。花岗岩、花岗片麻岩和紫苏花岗岩虽然具有元古界的结晶年龄，但其Nd模式年龄为太古代，表明它们是由太古代早期地壳的再活化（即部分或完全重熔）形成的。相比之下，泥质片麻岩包括在下阿尔丹协会的charronykites给元古代Nd模式年龄，表明大量的元古代岩石被纳入下阿尔丹协会。目前的研究结果表明，沿阿尔丹河，这是阿尔丹块的一部分，显示出显着不同的历史，从那些在奥莱克马块到西部。Olekma地块包含约3.0 Ga的绿岩带，为晚太古代斜长角闪岩级花岗质片麻岩;不存在代表Aldan岩的元古代再活化。奥莱克马块下的阿尔丹块在约1.9 Ga造山同期，或稍晚于阿尔丹的1.9 Ga charickitic事件。在阿尔丹发现的1.9 Ga岩浆和麻粒岩事件与加拿大北方的Thelon岩浆带在时代和性质上相似。这种相关性使得前寒武纪劳伦蒂亚-西伯利亚连接的优选构造得以发展，其中现今西伯利亚地台的南部与劳伦蒂亚的北方边缘相连。
A geological traverse across the Aldan shield along the Aldan River shows that the area is underlain by two distinct rock associations. The Middle Aldan association consists of metasedimentary rocks, mainly quartzite, that have been intruded by a potassic biotite granite. Downstream, north of the Middle Aldan association, lies the Lower Aldan association, which consists mostly of charnockite with rafts of older granulite gneiss that contains abundant metasedimentary layers. UPb dating of zircons from the Middle Aldan association granite (1900 Ma) and Lower Aldan association charnockite (maximum age 1918 Ma) and granitic gneiss (maximum age 2230 Ma) shows that the majority of the rocks exposed along the Aldan River are Proterozoic in age. Although they have Proterozic crystallization ages, the granite, granite gneiss and charnockite yield Archean Nd model ages, suggesting that they formed by remobilization—that is, partial or complete remelting—of earlier Archean crust. In contrast, pelitic gneisses included within the charnockites of the Lower Aldan association give Proterozoic Nd model ages, indicating that a substantial amount of Proterozoic rock is incorporated within the Lower Aldan association. The present results show that the rocks along the Aldan River, which are part of the Aldan block, display a significantly different history from those in the Olekma block to the west. The Olekma block contains ca 3.0 Ga greenstone belts Late Archean amphibolite-grade granitic gneisses; the Proterozoic remobilization that typifies the Aldan terrane is absent. The Olekma block was thrust under the Aldan block during the ca 1.9 Ga orogeny contemporaneous with, or slightly after the 1.9 Ga charnockitic event in the Aldan. The 1.9 Ga magmatic and granulite event seen in the Aldan is similar in age and character to the Thelon magmatic zone of northern Canada. This correlation allows the development of a preferred construction for the Precambrian Laurentia-Siberia connection in which the present day southern portion of the Siberia platform was connected to the northern margin of Laurentia.