Differentiation and emplacement of the Worthington Offset Dike of the Sudbury impact structure, Ontario
Differentiation and emplacement of the Worthington Offset Dike of the Sudbury impact structure, Ontario
复制标题
安大略省萨德伯里冲击结构沃辛顿偏置堤坝的区分和就位
DOI：
10.1111/j.1945-5100.2008.tb00635.x
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发表时间：
2008
影响因子：
2.2
通讯作者：
R. Grieve
中科院分区：
文献类型：
--
作者：
L. Hecht;A. Wittek;U. Riller;Thomas Mohr;R. Schmitt;R. Grieve
摘要：1.85 Ga萨德伯里火成杂岩（SIC）的偏移岩脉构成了理解撞击熔体的化学演化、成矿作用以及熔体迁移和撞击诱导变形之间相互作用的关键主题。错距岩脉中熔融岩的成因及其侵位方式和时间至今仍有争议。与许多其他错断岩脉一样，沃辛顿岩脉由岩脉边缘的早期侵位结构相当均匀的石英二辉岩（QD）相和后期侵位且主要位于岩脉中心的富含包裹体和硫化物的石英二辉岩（IQD）相组成。QD和IQD内部和之间的化学不均匀性主要是由于变量同化的主机岩石的基础上的SIC，在侵位的熔体到岩墙。岩石学数据表明，沃辛顿岩脉的母岩浆主要是在冲击熔体片热演化的前液相线温度区间（>1200 °C）形成的。根据SIC冷却历史的热模型，沃辛顿堤坝的两阶段就位可能发生在撞击后数千年至约一万年。结构分析表明，沃辛顿岩脉内矿物和寄主岩石碎片的排列是由绿片岩相变质条件下的韧性变形引起的，而不是熔体侵位过程中的流动。得出的结论是，沃辛顿偏置岩墙是由火山口底部断裂造成的，可能是由撞击结构下的地壳后期均衡重新调整驱动的。
Abstract— The Offset Dikes of the 1.85 Ga Sudbury Igneous Complex (SIC) constitute a key topic in understanding the chemical evolution of the impact melt, its mineralization, and the interplay between melt migration and impact‐induced deformation. The origin of the melt rocks in Offset Dikes as well as mode and timing of their emplacement are still a matter of debate. Like many other offset dikes, the Worthington is composed of an early emplaced texturally rather homogeneous quartz‐diorite (QD) phase at the dike margin, and an inclusion‐ and sulfide‐rich quartz‐diorite (IQD) phase emplaced later and mostly in the centre of the dike. The chemical heterogeneity within and between QD and IQD is mainly attributed to variable assimilation of host rocks at the base of the SIC, prior to emplacement of the melt into the dike. Petrological data suggest that the parental magma of the Worthington Dike mainly developed during the pre‐liquidus temperature interval of the thermal evolution of the impact melt sheet (>1200 °C). Based on thermal models of the cooling history of the SIC, the two‐stage emplacement of the Worthington Dike occurred likely thousands to about ten thousand years after impact. Structural analysis indicates that an alignment of minerals and host rock fragments within the Worthington Dike was caused by ductile deformation under greenschist‐facies metamorphic conditions rather than flow during melt emplacement. It is concluded that the Worthington Offset Dike resulted from crater floor fracturing, possibly driven by late‐stage isostatic readjustment of crust underlying the impact structure.