Thanks for this, I'm only remotely connected to the field, but High Artic gelogy is so fascinating. I did the Boothia work w Okulitch 30 yrs ago. RL Christie explained way back when how hard Zircon geochron was with lines intercepting at low angles giving large uncertainties, apologies for mangling the tech... But this was the best update! Cheers from Cambridge (UK neither MA nor ON lol)