Athapuscow aulacogen revisited: Geochronology and geochemistry of the 2046 Ma Union Island Group mafic magmatism, East Arm of Great Slave Lake, Northwest Territories, Canada

摘要

The Slave craton underwent widespread extension during the Paleoproterozoic. The East Arm basin of Great Slave Lake formed during this period and preserves a protracted record of sedimentation and volcanism in the southeastern Slave craton. Within the East Arm basin package, the Union Island Group represents voluminous mafic volcanism with subordinate sedimentary strata. We report the first high precision U-Pb zircon and bad-deleyite dates for the Union Island Group; 2045.8 +/- 1.0 Ma for a volcaniclastic unit from the lower basalt formation and 2042.7 +/- 3.0 Ma for a diabase intrusion within volcaniclastic horizons in the lower basalt formation. We fundamentally revise the lower basin stratigraphy and demonstrate that the Union Island Group is the oldest identified supracrustal package in the East Arm basin, similar to 120 Myr older than previously thought. This revised stratigraphy is supported by detrital zircon provenance age distribution in two Union Island Group sedimentary samples, which is dominated by 2.76-2.56 Ga ages, reflecting prominent input from the local Archean Slave basement.