| Summary: | Paleomagnetism can reveal ancient tectonic motions and identify the processes that regionally overprint magnetizations. We present paleomagnetic data from greenstones in the 2.72-2.69 Ga Vermillion Belt, Superior Craton, Minnesota. The Vermillion Belt has experienced lower greenschist facies alteration associated with volcanic-hosted massive sulfide (VHMS) deposits on the Archean paleoseafloor, as well as weak metamorphism from later reworking events.
We isolate four magnetization components: a low-temperature viscous remanent magnetization (VRM) recording the present geomagnetic field, a mid-temperature direction consistent with a ~1.11 Ga Midcontinent Rift overprint, a higher temperature component interpreted to be a 1.78 Ga Penokean overprint, and a high-temperature component that exhibits two clusters in in situ coordinates depending on locality: samples from the southern limb of an anticline host a direction D, I = 165.82°, -70.23° (α₉₅ = 14.4°; n= 2 VGPs), while those from the northern limb host D, I = 198.5°, 78.85° (α₉₅ = 14.0°; n = 5 VGPs). To understand the relative timing of these magnetization directions, we also report results for a 2.69 Ga fold test and baked contact test, a 1.78-1.11 Ga baked contact test, and a conglomerate test.
Based on these field tests, we constrain our high temperature component magnetization to either a VMS-related primary thermochemical remanent magnetization at 2.69 Ga, or a 1.78 Ga thermochemical post-orogenic overprint associated with the collapse of the Penokean Orogeny. If primary, our data define a paleopole at 46.85°N/ 84.12°E (α₉₅ = 14.95°; n = 7 VGPs). This would suggest rapid plate motion during the accretion of the Wawa-Abitibi Terrane onto the Superior Craton, suggesting that subduction leading to ribbon continent accretion occurred at a higher velocity than observed in Phanerozoic time. However, more data is required before this motion can be fully confirmed.
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