Mafic intrusions in the footwall of the Sudbury Igneous Complex: Origin of the Sudbury impact melt sheet and its associated ore deposits

摘要

The majority of the mafic intrusions and volcanic rocks in the footwall of the Sudbury Igneous Complex (SIC), which is believed to have formed from a melt sheet produced by the impact of a very large bolide, belong to one of two large mafic igneous suites, viz: the similar to 2450 Ma East Bull Lake (EBL) suite of intrusions or the similar to 2200 Ma Nipissing Diabase suite of intrusions. This has been established by U-Pb LA-ICP-MS dating of zircons from the newly recognized Frood intrusion, which hosts the Frood and Stobie ore bodies, and two of the Sudbury Gabbro intrusions, and comparison of the geochemistry of these intrusions with that of the EBL intrusive suite and the Nipissing Diabase suite. The age of the Frood intrusion (2421 +/- 32 Ma) falls within error of other EBL-type intrusions whereas the ages of the Nairn (2203 +/- 11 Ma) and Totten (2168 +/- 11 Ma) intrusions fall within error of published ages for the Nipissing Diabase. Moreover, the primitive mantle-normalized patterns of the petrogenetic trace elements on extended spidergrams of the Nairn and Totten Sudbury Gabbros are similar to those of the Nipissing Diabase as are those of the Frood intrusion to other members of the EBL intrusive suite.