GEOL 2312 IGNEOUS AND METAMORPHIC PETROLOGY

Lecture 14

Continental Flood Basalts

with special emphasis on the

Midcontinent Rift

February 25, 2009

LARGE IGNEOUS PROVINCESIMPACT SITES OF STARTING MANTLE

PLUMES

http://www.largeigneousprovinces.org

CONTINENTAL FLOOD BASALTSLARGE IGNEOUS PROVINCES IN CONTINENTAL SETTINGS

Winter (2001) Figure 15-1. Columbia River Basalts at Hat Point, Snake River area. Cover of Geol. Soc. Amer Special Paper 239. Photo courtesy Steve Reidel.

Table 15-1. Major Flood Basalt Provinces

Name Volume Age Locality

CRB (1.7x105 km3) Miocene NW US

Keeweenawan (4x105 km3) Precambrian Superior area

Deccan (106 km3) Cret.-Eocene India

Parana (area > 106 km2) early Cret. Brazil

Karroo (2x106 km3?) early Jurassic S. Africa

MAFIC DIKE SWARMSVESTIGES OF ANCIENT CONTINENTAL FLOOD

BASALTS

THE BREAK-UP OF GONDWANALAND

PARANA/KAROO/FERRAR/DECCAN

Ferrar

COLUMBIA RIVER BASALTS, SNAKE RIVER PLAIN BASALTS AND THE YELLOWSTONE PLUME

An Aborted, Mantle Plume-influenced, Intracontinental Rift (1110-1086 Ma)

The Midcontinent Rift

A. Rift Magmatism

Gabbro

MantlePlume

BasaltFlows

CrustMantle

B. Sediment Infilling Sandstone

C. Compression

1,115-1,086 Ma1,115-1,086 Ma

1,090-1,080Ma1,090-1,080Ma

1,080-1,040 Ma1,080-1,040 Ma

Main Evolutionary Stages of the Midcontinent Rift

Rifting and Plume-influenced Magmatism

Subsidence and Sedimentation

Compression and Rift Inversion

EVIDENCE FOR A STARTING MANTLE EVIDENCE FOR A STARTING MANTLE PLUMEPLUME Large Volume of Volcanic Fill (>1,500,000 kmLarge Volume of Volcanic Fill (>1,500,000 km33; Cannon, ; Cannon,

1992)1992) Extensive Intrusive Underplating (gravity modelling) Extensive Intrusive Underplating (gravity modelling) Potential Temperature of Source ~250Potential Temperature of Source ~250ooC > Normal C > Normal

Mantle (Hutchinson et al., 1990)Mantle (Hutchinson et al., 1990) Isotope Geochemistry Indicative of Enriched Mantle Isotope Geochemistry Indicative of Enriched Mantle

Source (Nicholson & Shirey, 1997)Source (Nicholson & Shirey, 1997) Evidence of Thermal Doming (subaerial basalts, early Evidence of Thermal Doming (subaerial basalts, early

volcanic-less intrusions)volcanic-less intrusions) Rapid Rates of Effusion (avg. ~0.15 km3/y; Cannon, Rapid Rates of Effusion (avg. ~0.15 km3/y; Cannon,

1992, Davis and Paces, 1990)1992, Davis and Paces, 1990) Radial Orientation of Dike Swarms in the Lake Superior Radial Orientation of Dike Swarms in the Lake Superior

Region (Green et al., 1987)Region (Green et al., 1987) Migration of Magmatism from East to West (eastward Migration of Magmatism from East to West (eastward

plate drift over fixed plume?)plate drift over fixed plume?)

Inconsistencies with a Mantle PlumeInconsistencies with a Mantle Plume Prolonged magmatism (>23 Ma)Prolonged magmatism (>23 Ma) Peak of volcanic activity at midpoint of magmatic Peak of volcanic activity at midpoint of magmatic

interval?interval?

Lutgens and Tarbuck, 2003

Midcontinent Rift MagmatismMidcontinent Rift Magmatism1115-1086 Ma1115-1086 Ma

Role of the Grenville

Midcontinent Rift InversionMidcontinent Rift Inversion~1080-1040 Ma*~1080-1040 Ma*

Rivers, 2008 (Fig. 3)

Rivers, 2008 (Fig. 1)

*Cannon, 1994

R

Exposed Exposed Geology of the Geology of the Midcontinent Midcontinent Rift in the Lake Rift in the Lake Superior Superior RegionRegion

Compilation by Green (2005)

LateLate

MainMainLatentLatentEarlyEarlyUplift?Uplift?

?

- ?

Geochronology of the Midcontinent Rift

Magmatic StagesMagmatic StagesMiller 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 Origin of Felsic Magmas Felsic Magmas Partial Melting of the Lower Crust

Origin of Origin of Anorthositic RocksAnorthositic RocksPlagioclase Flotation in the Lower Crust

Based on Kushiro (1980)

From Miller & Vervoort (1996)