Impact melt dikes in the Sudbury multi-ring basin (Canada): Implications from uranium-lead geochronology on the Foy Offset Dike
Impact melt dikes in the Sudbury multi-ring basin (Canada): Implications from uranium-lead geochronology on the Foy Offset Dike
复制标题
萨德伯里多环盆地（加拿大）的冲击熔岩脉：铀铅地质年代学对福伊偏置岩脉的影响
DOI：
10.1111/j.1945-5100.1996.tb02091.x
复制
发表时间：
1996
影响因子：
2.2
通讯作者：
A. Deutsch
中科院分区：
文献类型：
--
作者：
Markus Osterman;U. Schärer;A. Deutsch
摘要为了研究萨德伯里多环撞击构造中错距岩脉的成因及其与主要撞击生成岩性的年龄关系，如萨德伯里“火成”杂岩的主体，用U-Pb计时器测定了锆石和斜锆石的年龄。分析的岩石是来自福伊偏移内的一个闪长岩和两个石英闪长岩，来自接触带的一个石英闪长岩，以及在距离Levack片麻岩杂岩内的接触10和30 m处收集的两个围岩样品。21个分析的锆石和斜锆石组分得出Foy偏移岩脉中副矿物的结晶年龄为1852 + 4/-3（2σ）Ma，受冲击的Levack围岩的年龄为2635 ± 5 Ma，其中锆石显示出明显的冲击效应（多组平面断裂），与偏移岩脉中完全未受冲击的锆石形成对比。在一定误差范围内，1852 Ma的新年龄与Krogh等人（1984）确定的1850 ± 1 Ma的U-Pb年龄相一致，后者是萨德伯里“火成”杂岩不同岩性中副相的结晶年龄，它被解释为萨德伯里构造的相干碰撞熔融岩片。这一极好的年龄一致性证实了偏移岩脉的侵位与冲击熔片的形成是同时发生的。在福伊偏移的中心部分完全没有继承的锆石，表明前体物质在远高于1700 °C的温度下熔化，这强调了岩脉岩性的起源是由冲击熔化造成的。
Abstract To investigate the origin of Offset Dikes and their age relationships to major impact generated lithologies in the Sudbury multi-ring impact structure, such as the Main Mass of the Sudbury “Igneous” Complex, zircon and baddeleyite were dated by the U-Pb chronometer. The rocks analysed are one diorite and two quartz diorites from inside the Foy Offset, one quartz diorite from the contact zone, and two country rock samples collected at 10 and 30 m distances from the contact within the Levack Gneiss Complex. The 21 analysed zircon and baddeleyite fractions yield a crystallization age of 1852 +4/-3 (2σ) Ma for the accessory minerals in the Foy Offset Dike and an age of 2635 ± 5 Ma for the shocked Levack country rock, in which zircons show significant shock effects (multiple sets of planar fractures), in contrast to the totally unshocked zircons of the Offset Dike. Within given errors, the new age of 1852 Ma is identical to the pooled 1850 ± 1 Ma U-Pb age determined by Krogh et al. (1984) as the crystallization age of accessory phases in different lithologies of the Sudbury “Igneous” Complex, which has been interpreted to represent the coherent impact melt sheet of the Sudbury Structure. This excellent agreement of the ages substantiates that emplacement of the Offset Dikes occurred coevally with the formation of the impact melt sheet. Total absence of inherited zircons in the central part of the Foy Offset indicates melting of the precursor material at temperatures well above 1700 °C, which emphasizes the origin of the dike lithologies by impact melting.