G EOL 2312 I GNEOUS AND M ETAMORPHIC P ETROLOGY Lecture 14 Continental Flood Basalts with special emphasis on the Midcontinent Rift February 25, 2009

L ARGE I GNEOUS P ROVINCES I MPACT SITES OF S TARTING M ANTLE P LUMES

C ONTINENTAL F LOOD B ASALTS L ARGE I GNEOUS P ROVINCES IN C ONTINENTAL S ETTINGS Winter (2001) Figure Columbia River Basalts at Hat Point, Snake River area. Cover of Geol. Soc. Amer Special Paper 239. Photo courtesy Steve Reidel.

M AFIC D IKE S WARMS V ESTIGES OF A NCIENT C ONTINENTAL F LOOD B ASALTS

T HE B REAK - UP OF G ONDWANALAND P ARANA /K AROO /F ERRAR /D ECCAN Ferrar

C OLUMBIA R IVER B ASALTS, S NAKE R IVER P LAIN B ASALTS AND THE Y ELLOWSTONE P LUME

An Aborted, Mantle Plume-influenced, Intracontinental Rift ( Ma) The Midcontinent Rift

1,115-1,086 Ma 1,090-1,080Ma 1,080-1,040 Ma Main Evolutionary Stages of the Midcontinent Rift Rifting and Plume-influenced Magmatism Subsidence and Sedimentation Compression and Rift Inversion

E VIDENCE FOR A S TARTING M ANTLE P LUME  Large Volume of Volcanic Fill (>1,500,000 km 3 ; Cannon, 1992)  Extensive Intrusive Underplating (gravity modelling)  Potential Temperature of Source ~250 o C > Normal Mantle (Hutchinson et al., 1990)  Isotope Geochemistry Indicative of Enriched Mantle Source (Nicholson & Shirey, 1997)  Evidence of Thermal Doming (subaerial basalts, early volcanic-less intrusions)  Rapid Rates of Effusion (avg. ~0.15 km3/y; Cannon, 1992, Davis and Paces, 1990)  Radial Orientation of Dike Swarms in the Lake Superior Region (Green et al., 1987)  Migration of Magmatism from East to West (eastward plate drift over fixed plume?) Inconsistencies with a Mantle Plume  Prolonged magmatism (>23 Ma)  Peak of volcanic activity at midpoint of magmatic interval? Lutgens and Tarbuck, 2003

Midcontinent Rift Magmatism Ma Role of the Grenville Midcontinent Rift Inversion ~ Ma* Rivers, 2008 (Fig. 3) Rivers, 2008 (Fig. 1) *Cannon, 1994

R Exposed Geology of the Midcontinent Rift in the Lake Superior Region

Compilation by Green (2005) Late Main Latent Early Uplift? ? - ? Geochronology of the Midcontinent Rift Magmatic Stages Miller and Vervoort (1996), Nicholson et al. (1997)

Chemostratigraphic data mostly from Green (1986), Klewin & Berg (1991), Lightfoot et al. (1991), Shirey et al. (1994), Nicholson et al.(1997), Vervoort & Green (1997).

Halls (1982) Evidence for Crustal Underplating

Modified from Thomas & Teskey (1994), Fig. 14; Includes interpretations of Trehu et al., (1991) GLIMPCE Line A

Origin of Felsic Magmas Partial Melting of the Lower Crust

Origin of Anorthositic Rocks Plagioclase Flotation in the Lower Crust Based on Kushiro (1980)

From Miller & Vervoort (1996)