U-Pb geochronology of the sublayer environment, Sudbury igneous complex, Ontario
U-Pb geochronology of the sublayer environment, Sudbury igneous complex, Ontario
复制标题
安大略省萨德伯里火成岩杂岩下层环境的 U-Pb 地质年代学
DOI：
10.2113/gsecongeo.91.7.1263
复制
发表时间：
1996
期刊：
影响因子：
5.8
通讯作者：
P. Lightfoot
中科院分区：
文献类型：
--
作者：
F. Corfu;P. Lightfoot
萨德伯里火成杂岩中的铜镍硫化物矿床由富包裹体的亚层、萨德伯里火成杂岩附近的角砾化下盘和向围岩中突出数十公里的偏置岩脉所赋存，富包裹体的亚层不连续地出现在萨德伯里火成杂岩的下盘和主体之间。亚层中镁铁质-超镁铁质包裹体的成因以及亚层、主体和偏置岩脉之间的关系长期以来一直是萨德伯里地质学争论的中心。本文报道了Whistle海湾次层苏长岩基质、黑云母和橄榄石黑云母豆荚、变辉石岩包裹体和闪长岩样品中锆石和斜锆石的U-Pb同位素数据。这些样品的年龄范围为1848.1 ± 1.8 ~ 1849.1 ± 1.1 Ma，与Copper Cliff偏移石英闪长岩中锆石U-Pb年龄1849.8 ± 2.0 Ma相似，与先前公布的萨德伯里火成杂岩体主体平均年龄1850 +或-1Ma的结果没有区别。没有一个样品产生继承锆石成分的证据。同位素数据证明，外来的镁铁-超镁铁夹杂物和豆荚子层不是捕虏体清除旧的层状复合体，但需要存在的原始，适度富镁岩浆结晶的早期阶段的萨德伯里火成杂岩的发展。这种富含镁的堆晶岩不太可能是从熔融的平均上地壳中结晶出来的。
Cu-Ni sulfide deposits of the Sudbury Igneous Complex are hosted by the inclusion-rich sublayer, which occurs discontinuously between the footwall and main mass of the Sudbury Igneous Complex, by brecciated footwall in the vicinity of the Sudbury Igneous Complex, and by offset dikes protruding for tens of kilometers into the country rocks. The genesis of mafic-ultramafic inclusions in the sublayer and the relationships between the sublayer, main mass, and offset dikes have long been at the center of debate on Sudbury geology. This paper reports U-Pb isotope data on zircon and baddeleyite from samples representing norite matrix, melanorite and olivine melanorite pods, a metapyroxenite inclusion, and diabase from the sublayer at the Whistle embayment. These samples yield ages ranging from 1848.1 + or - 1.8 to 1849.1 + or - 1.1 Ma, similar to a U-Pb age of 1849.8 + or - 2.0 Ma obtained for zircons in quartz diorite from the Copper Cliff offset, and indistinguishable from the previously published average age of 1850 + or - 1 Ma for the main mass of the Sudbury Igneous Complex. None of the samples yield evidence for inherited zircon components. The isotopic data prove that the exotic mafic-ultramafic inclusions and pods in the sublayer are not xenoliths scavenged from older layered complexes but require the existence of primitive, moderately Mg-rich magmas that crystallized in the early stages of development of the Sudbury Igneous Complex. Such Mg-rich cumulates are unlikely to have crystallized from melted average upper crust.