Transitional basalts in the Keweenawan Rift

Transitional basalt suites have been recognised in Keweenawan lava sequences at Mamainse Point and Shesheeb Bay, Ontario. These are similar to their accompanying tholeiites in major element chemistry, but have higher, more alkalic contents of incompatible elements. They are believed to be derived from primary mantle melting and illustrate the complexity of magmatic processes within an immature proto-oceanic rift.