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dikes (Ernst and Buchan, 2001b) and the 1.24 Ga Sudbury mafic dikes (Dudás et al., 1994)
that are associated with the Nuna supercontinent breakup (Rogers and Santos, 2002).
The breccia-type U 4 and metasomatic-type U 3 uraninites record 400 Myr of alteration
extending from 1.3 to 0.9 Ga (Fig. 2.15), which likely corresponds to the protracted period
of Rodinia supercontinent assembly (Piper, 2000, 2004, Li et al., 2008) through the
Grenville Orogen (Rivers, 1997; Carr et al., 2004). This orogenic activity along the
southern margin of Laurentia (Fig. 2.14) culminated into continent-continent collision that
led to the final Rodinia assembly (Moores, 1991; Bogdanova et al., 2009).
The metasomatic-type U 3 and breccia-type U 4 uraninites show intense alteration at
800-780 Ma and 550-500 Ma (Fig. 2.15). These ages are consistent with diachronous
breakup models of Rodinia (Dalziel, 1991; Moores, 1991; Li et al., 2008), comprised of an
early rifting stage along the western margin of Laurentia at ca. 780-755 Ma (Harlan,
2003b) followed by the main pulse of rifting along the eastern margin at ca. 600-550 Ma
(Ernst and Buchan, 2001b). Mafic intrusions associated with this major extensional event
occur along the western margin of Laurentia (Fig. 2.14) and include the ca. 780-770 Ma
Gunbarrel mafic event (Harlan et al., 2003b). The ca. 570-550 Ma central-Iapetus mafic
intrusion along the eastern margin of Laurentia occurred during Rodinia eastern breakup
(Kamo et al., 1989; Li et al., 2008).
All uraninite types have been affected by alteration between 460 Ma and 280 Ma,
with peaks at ca. 350 Ma (Fig. 2.15) recording the thermotectonic event of the protracted
Appalachian Orogen that affected the eastern margin of Laurentia (Fig. 2.14) during
Pangea assembly (Cocks and Torsvik, 2002; Hatcher, 2002).
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