Petrology and Cu-Ni-PGE Mineralization of the Bovine Igneous ...

Thrust, the basin is distinguished by isoclinal or tight folds which are often over turned or
recumbent, and are commonly overprinted by a second generation of folding (Rossell, 2008).
1.1.3 Midcontinent Rift
The 1.1 Ga Midcontinent Rift (MCR) extends 2000 km across the North American
craton in an arcuate path stretching from the Lake Superior region to Kansas to the southeast
and lower Michigan to the southwest (Fig. 4). The MCR marks the failed attempt at
continental rifting of the North American craton (Laurentia) and is thought to have been
triggered by a starting mantle plume (Nicholson et al., 1997). The compressive force of the
Grenville orogeny along the eastern margin of North America is thought to have prevented
complete rifting which commonly leads to continental separation and ocean basin formation
(Cannon, 1992). During the period of active rifting and magmatism, the MCR became a large
igneous province, extruding and intruding massive quantities of mafic and felsic magmas into
its nearly 30 km deep rift basin (Hinze et al, 1997).
Magmatic activity in the MCR lasted for roughly 23 million years from 1109 to 1086
Ma, though recent dating of intrusions in Ontario (Heaman et al., 2007) suggest that MCRrelated
magmatism probably began at 1112, and possibly as early as 1120 Ma. As noted in the
introduction, these 23+ million years of magmatic activity can be broken down into at least
four stages.
The early magmatic stage (1112-1107 Ma) consisted of rapid extrusion and
emplacement of primitive melts derived from high degrees of partial melting of an enriched
mantle plume and at greater depths than later magmas. Early primitive mafic magmas rapidly
gave way to more evolved mafic melts that show signs of contamination by the subcontinental
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