Ion probe U-Th-Pb zircon dating of polymetamorphic orthogneisses from northern Labrador, Canada
Ion probe U-Th-Pb zircon dating of polymetamorphic orthogneisses from northern Labrador, Canada
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DOI：
10.1139/e89-131
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发表时间：
1989-08
影响因子：
1.4
通讯作者：
L. Schiøtte;W. Compston;D. Bridgwater
中科院分区：
文献类型：
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作者：
L. Schiøtte;W. Compston;D. Bridgwater
拉布拉多北方Uivak I片麻岩中的火成锆石中的圆形锆石的年龄高达3863 ± 12 Ma（2σ），表明在Uivak片麻岩形成之前就存在100 Ma以上的岩石。火成锆石本身经历了不同数量的早期铅损失，但基于三个独立片麻岩样品的最大207 Pb/206 Pb的年龄估计在3732 ± 6 Ma（2σ）的误差范围内，这被认为是Uivak片麻岩主要成分的火成前体的侵位年龄。新一代的锆石是在约1000年的混合岩化作用中形成的。3620 Ma.体积上不太重要的利斯特片麻岩的侵位时间为3235 ± 8 Ma（2σ）。晚中生代，片麻岩杂岩的不同部位经历了不同程度的变质叠加作用。受麻粒岩相变质作用影响的片麻岩的锆石年代学表明，变质事件的发生具有快速的序列性，老锆石的重结晶和新的贫铀锆石的生长同时进行。
Rounded zircons included within igneous zircons from the Uivak I gneisses, northern Labrador, have ages of up to 3863 ± 12 Ma (2σ), showing the (former) existence of rocks that predate the Uivak gneisses by more than 100 Ma. The igneous zircons themselves have experienced varying amounts of early Pb loss, but age estimates based on maximum 207Pb/206Pb from three separate gneiss samples agree to within error at 3732 ± 6 Ma (2σ), which is taken as the age of emplacement of the igneous precursor to the dominant component of the Uivak gneisses. A new generation of zircons was formed during migmatization at ca. 3620 Ma. The volumetrically less important Lister gneiss was emplaced at 3235 ± 8 Ma (2σ). In the late Archaean, different parts of the gneiss complex were subjected to different grades of metamorphic overprinting. The zircon chronology of gneisses affected by granulite facies metamorphism suggests a rapid sequence of events, with simultaneous recrystallization of old zircons and growth of new U-poor zi...