GEOL 2312
IGNEOUS AND METAMORPHIC
PETROLOGY
Lecture 11B
Continental Flood Basalts
with special emphasis on the
Midcontinent Rift
February 24, 2016
LARGE IGNEOUS PROVINCES
IMPACT SITES OF STARTING MANTLE PLUMES
http://www.largeigneousprovinces.org
MANTLE PLUMES
TRUTH OR FICTION?
2001
2005
2007
2010
CONTINENTAL FLOOD BASALTS
LARGE IGNEOUS PROVINCES IN CONTINENTAL SETTINGS
Table 15-1. Major Flood Basalt Provinces
Name
Volume
Age
Locality
CRB
(1.7x105 km3 )
Miocene
NW US
Keeweenawan
(4x105 km3)
Precambrian
Superior area
Cret.-Eocene
India
Deccan
Parana
Karroo
6
3
(10 km )
6
2
(area > 10 km ) early Cret.
6
3
(2x10 km ?)
Brazil
early Jurassic S. Africa
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.
THE BREAK-UP OF GONDWANALAND
PARANA/KAROO/FERRAR/DECCAN
Ferrar
COLUMBIA RIVER BASALTS, SNAKE RIVER PLAIN
BASALTS AND THE YELLOWSTONE PLUME
VOLUMINOUS RATES OF ERUPTION OF THE
COLUMBIA RIVER BASALTS
Figure 15.6. Time-averaged extrusion rate of CRBG basalts as a function of time, showing cumulative volume. After
Hooper (1988a) The Columbia River Basalt. In J. D. Macdougall (ed.), Continental Flood Basalts. Kluwer. 1-34.
Tectonic Setting of the
Colombia River Basalts
Plume Impact into a Complex
Continental Subduction Zone
MAFIC DIKE SWARMS
VESTIGES OF ANCIENT CONTINENTAL FLOOD BASALTS
The Midcontinent Rift
A Well-preserved Precambrian Large Igneous Province
An Aborted, Mantle
Plume-influenced,
Intracontinental Rift
(1110-1086 Ma)
Rifting
Plume-influenced Magmatism
A. Riftand
Magmatism
Main Evolutionary
Stages of the
Midcontinent Rift
Basalt
Flows
Gabbro
Crust
Mantle
1,115-1,086 Ma
Mantle
Plume
B.
Sedimentand
Infilling
Subsidence
Sedimentation
Sandstone
1,090-1,080Ma
C.
Compression
Compression
and Rift Inversion
1,080-1,040 Ma
EVIDENCE FOR A STARTING MANTLE
PLUME








Large Volume of Volcanic Fill (>1,500,000 km3; Cannon,
1992)
Extensive Intrusive Underplating (gravity modelling)
Potential Temperature of Source ~250oC > 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
Role of the
Grenville
Rivers, 2008 (Fig. 3)
Midcontinent Rift Inversion
~1080-1040 Ma*
Midcontinent Rift Magmatism
1115-1086 Ma
Rivers, 2008 (Fig. 1)
*Cannon, 1994
Exposed Geology
of the
R
Midcontinent
Rift in the Lake
Superior Region
Geochronology
of the
Midcontinent
Rift
Late
Magmatic Stages
Miller and Vervoort (1996),
Nicholson et al. (1997)
Main
Latent
Early
Uplift?
Compilation by Green (2005)
?
-?
Chemostratigraphic data mostly from Green (1986), Klewin & Berg (1991), Lightfoot et al. (1991), Shirey et al. (1994), Nicholson et al.(1997), Vervoort & Green (1997).
Evidence for
Crustal Underplating
Halls (1982)
GLIMPCE Line A
Modified from Thomas & Teskey (1994), Fig. 14; Includes interpretations of Trehu et al., (1991)
Origin of
Felsic Magmas
Partial Melting of the Lower
Crust
Origin of
Anorthositic Rocks
Plagioclase Flotation in the
Lower Crust
Based on
Kushiro
(1980)
Tectonomagmatic
Evolution of the
Midcontinent Rift
GEOLOGIC AND GEOCHEMICAL ATTRIBUTES
OF THE BEAVER RIVER DIABASE AND
GREENSTONE FLOW: TESTING A POSSIBLE
INTRUSIVE-VOLCANIC CORRELATION IN THE
1.1 GA MIDCONTINENT RIFT
Carlton Peak, MN
Blake Pt, Isle Royale
Greenstone Ridge, MI
Michael Doyle and Jim Miller
University of Minnesota Duluth
2014 Geological Society of America
Vancouver, BC CANADA
MCR GEOLOGY OF THE LAKE SUPERIOR REGION
D
U
Portage Lake
Volcanics
U
DBeaver Bay
Complex
U
D
U
D
From Miller and Nicholson (2013
3D STRUCTURE OF THE MCR
Thomas and Teskey (1994)
BEAVER RIVER DIABASE
OF THE BEAVER BAY COMPLEX
U-Pb age = 1095.8±1.2 Ma
Paces and Miller (1993)
FTMD
Silver Bay Intr
Beaver River Db
DIABASE
A
D
AC
A) Ophitic Olivine Diabase
B
C
D
A B C
D
C
A
A
B) Intergranular Ol Gabbro C) Crs Prismatic Fe-monzodiorite
D) Foliated Fe-diorite
10 km
ANORTHOSITE XENOLITHS
IN BRD
Carlton Peak
400 m
Split Rock Lighthouse
ORIGIN OF MCR ANORTHOSITE XENOLITHS
GREENSTONE FLOW OF THE PORTAGE LAKE VOLCANICS
GSF
GSF
From Cannon and Nicholson, 2001
U-Pb age =1094.0±1.5 Ma
Davis and Paces (1990)
From Huber, 1973
Huber (1973)
Thickness of
GSF on IR
30-250 m
Avg. 120 m
From White, 1968
Thickness of
GSF on KP
10-500 m
LITHOLOGIES OF THE GREENSTONE FLOW
A) Upper Collanade
Idealized X-section of GSF
on Keweenaw Peninsula
(from Huber, 1973, after Cornwall, 1951)
From B. Rose (MTU)
B) Upper Ophite (ol diabase)
C) Pegmatite (oxide gabbro- Fe-monzodiorite)
D) Lower Ophite
COMMON ATTRIBUTES OF THE GSF AND BRD
Enormous Volumes of Mafic Magma
• GSF –Thickness – up to 500m; Areal Extent - 5,000 km2 (White, 1960);
Volume - 1,650 km3 (Longo, 1984)
• BRD - exposed over a roughly 600 km2 area; feeder dikes
accommodated anorthosite inclusions up to 400m diameter
Overlapping U-Pb Ages
• GSF – 1094.0 ± 1.5 Ma (Davis and Paces, 1990)
• BRD composite intrusions (Silver Bay Gabbro) – 1095.8 ± 1.2 Ma (Paces
and Miller, 1993)
Similar Range of Rock Types
• GSF - Ophitic Olivine Basalt, Intergranular Oxide Gabbro, Vari-textured
Ferrodiorite – Ferromonzonite/Granophyre
• BRD – Ophitic Olivine Diabase, Intergranular Oxide Gabbro, Crs Prismatic
Ferromonzodiorite, Foliated Ferrodiorite, Ferromonzonite/Granophyre
Composite Emplacement History
• Abrupt contacts between major rock types
• Inclusion/mixing relationships
MAPPING AND SAMPLING
Crosby-Manitou
Central
Phoenix
2 km
Blake Pt.
Lookout
Louise
Duncan Bay
Portage
Silver Bay
Beaver Bay
2 km
ABRUPT CONTACTS BETWEEN COMPOSITE
LITHOLOGIES IN GSF
Prismatic Ferromonzodiorite
NOT IN SITU FRACTIONAL CRYSTALLIZATION
“Pegmatoid”
GSF on Isle Royale
ctc
Intergranular Ox Gabbro
Lower Ophite
Exposure of Lower Ophite/Pegmatite
contact on Duncan Bay Portage
Ophitic Ol Gabbro
PETROGRAPHIC ATTRIBUTES OF THE BRD AND GSF
OPHITIC DIABASE/ BASALT
BRD
5mm
GSF-KP
5mm
2mm
PETROGRAPHIC ATTRIBUTES OF THE BRD AND GSF
INTERGRANULAR OXIDE GABBRO
BRD
5mm
GSF-KP
5mm
PETROGRAPHIC ATTRIBUTES OF THE BRD AND GSF
ALTERED QUARTZ FERROMONZODIORITE
BRD
5mm
GSF-KP
5mm
PETROGRAPHIC ATTRIBUTES OF THE BRD AND GSF
FOLIATED FERRODIORITE
BRD
5mm
GSF-KP
5mm
LITHOGEOCHEMISTRY OF THE GSF OPHITIC ZONES AND BRD
Lithogeochemistry of the GSF-HZ and BRD-SBI
Lithogeochemistry of the GSF-HZ and BRD-SBI
Mineral Chemistry of GSF and BRD-SBI
PLAGIOCLASE PHENOCRYSTS OR
XENOLITHS?
5mm
Plagioclase megacryst in lower ophite of GSF, Phoenix Tra
Anomalously High An Content of Plagioclase
Megacrysts in GSF Lower Ophite Samples
IMPLICATIONS OF BRD-GSF LINKAGE
GSF Volume Estimate
Longo (1984) – 1, 650 km3
20,000 km2 x 100m = 2,000 km3
20,000 km2 x 300m = 6,000 km3
Canyon flow of the Sentinel Bluffs Member
of the CRB’s Grand Ronde Basalt = 4,278 km3