Transcript Chapter 15: Continental Flood Basalts

Chapter 15: Continental Flood Basalts
Large Igneous Provinces (LIPs)
 Oceanic plateaus
 Some rifts
 Continental flood basalts
(CFBs)
Table 15.1. Major Flood Basalt Provinces
Name
CRB
Keeweenawan
Deccan
Parana
Karroo
Siberian
Approximate Volume
(1.7x105 km3)
(4x105 km3)
(8.6 x 106 km3)
(area > 106 km2)
(2x106 km3?)
(3-5 x 106 km3)
Age
Miocene
Precambrian
Cret.-Eocene
early Cret.
early Jurassic
l. Permian - e. Triassic
Locality
NW US
Superior area
India
Brazil
S. Africa
Siberia
Figure 15.2. Columbia River Basalts at Hat Point, Snake
River area. Cover of Geol. Soc. Amer Special Paper 239.
Photo courtesy Steve Reidel.
Large Igneous Provinces (LIPs)
Figure 15.1. Map of the major large igneous provinces (LIPs) on Earth, including continental flood basalt
provinces, volcanic passive margins, oceanic plateaus, aseismic submarine ridges, ocean basin flood basalts,
and seamount groups. After Saunders et al. (1992) and Saunders (pers. comm.).
Tectonic Setting of CFBs


Continental hot spots
Continental rifting may be associated with hot
spots
 Successful rifts
 Failed rifts (aulacogens)
Figure 15.3. Flood basalt provinces of Gondwanaland prior to break-up and
separation. After Cox (1978) Nature, 274, 47-49.
Figure 15-4. Relationship of the Etendeka and Paraná plateau provinces to the
Tristan hot spot. After Wilson (1989), Igneous Petrogenesis. Kluwer.
Figure 15.5 Setting of the Columbia River Basalt Group in the Northwestern United States. Pink star is the location proposed by Camp and
Ross (2004) of the 16.6 Ma outbreak of the plume and plume-related basaltic volcanism. Yellow star is the location of the deep plume conduit
proposed by Jordan et al. (2004). Blue areas are Quaternary basalts and pink areas are rhyolite centers. Heavy dashed curves represent the
progressive younging of rhyolitic centers (with ages in Ma). Those on the east represent the proposed Yellowstone hotspot track (heavy arrow).
Those on the west are the opposing westward track leading to Newberry Volcano (N) with ages reported by Jordan et al. (2004). After Camp
and Ross (2004).
Figure 15.5 (continued). The cross-section is diagrammatic, generally across southern Oregon and Idaho (south of the main CRBG) and
illustrates the westward deflection of the plume head by the deep keel of the North American craton to beneath the thinner accreted terranes
and the migration of the hotspot tracks both east and west. After Jordan et al. (2004) © AGU with permission.
Table 15.2. Stratigraphy of the Columbia River Basalt Group.
Sub-
group
Formation
Saddle
Mountains
Basalt
Clarkston
Wanapum
Basalt
Grande
Ronde
Basalt
Imnaha
Basalt
Lower Steens
Magnetic
Polarity*
Lower Monumental
N
Ice Harbor
N,R
Buford
R
Elephant Mountain
R,T
Pomona
R
Esquatzel
N
Weissenfels Ridge
N
Asotin
N
Wilbur Creek
N
Umatilla
N
Priest Rapids
R
Roza
T,R
Frenchman Springs
N
Eckler Mountain
N
See Reidel et al .
N2
Picture
(1989) for
R2
Gorge
Grande
N1
Ronde Units
R1
R1
T
See Hooper et al .
(1984) for Imnaha Units
N0
R0
R0
Member
Data from Reidel et al . (1989); Hooper and Hawkesworth (1993),
Hooper(1997), Hooper et al. (2008).
* N = normal, R = reversed, T = transitional
K/Ar
Dates
6 Ma
8.5
10.5
12
13
14.5
15.0
16.5
!6.6
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.
Figure 15.7 Variation in wt.% of selected major element oxides vs. Mg# for
units of the Columbia River Basalt Group. Winter (2001). An Introduction
to Igneous and Metamorphic Petrology. Prentice Hall. Data from BVTP
(Table 1.2.3.3), Hooper (1988a), Hooper and Hawkesworth (1993).
Figure 15.8. Condrite-normalized rare earth element patterns of some typical CRBG samples. Winter (2001). An
Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Hooper and Hawkesworth (1993) J.
Petrol., 34, 1203-1246.
Figure 15.9. N-MORB-normalized spider diagram for some representative analyses from the CRBG. Winter (2001). An
Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Hooper and Hawkesworth (1993) J. Petrol., 34,
1203-1246. Picture Gorge from Bailey (1989) Geol. Soc. Amer. Special Paper, 239, 67-84.
Figure 15.10 OIB-normalized spider diagram for some representative CRBG analyses. Winter (2001). An
Introduction to Igneous and Metamorphic Petrology. Prentice Hall. (data as in Figure 15-8).
Figure 15.11. Ce/Zr vs. Ce/Nb (un-normalized) for the basalts of the Columbia River Basalt Group. After
Hooper and Hawkesworth (1993) J. Petrol., 34, 1203-1246.
Figure 15.12. 87Sr/86Sr vs. 143Nd/144Nd for the CRBG. Winter (2001). An Introduction to Igneous and Metamorphic
Petrology. Prentice Hall. Data from Hooper (1988a), Carlson et al. (1981), Carlson (1984), McDougall (1976),
Brandon et al. (1993), Hooper and Hawkesworth (1993).
Figure 15.13. 208Pb/204Pb vs. 206Pb/204Pb for the basalts of the CRBG. Included for reference are EMI, EMII, the
DUPAL group, the MORB array, and the NRHL (northern hemisphere reference line) connecting DM and HIMU
mantle reservoirs from Figure 14-6. Winter (2001). An Introduction to Igneous and Metamorphic Petrology.
Prentice Hall. Data from Hooper (1988a), Carlson et al. (1981), Carlson (1984), McDougall (1976), Brandon et al.
(1993), Hooper and Hawkesworth (1993).
Figure 15.14. A model for the origin of the Columbia River Basalt Group From Takahahshi et al. (1998) Earth Planet. Sci. Lett.,
162, 63-80.
Figure 15.15. Diagrammatic cross section illustrating possible models for the development of continental flood basalts. DM is
the depleted mantle (MORB source reservoir), and the area below 660 km depth is the less depleted, or enriched OIB source
reservoir. Winter (20010 An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Figure 15.6 Dewey and Burke model for the evolution of a continental rift by the concatenation of a series of 3-rift triple junctions, each
centered on a hotspot. Two arms of each hotspot link up to adjacent hotspots, although generally not perfectly. The third arm fails and becomes a
rift valley (aulacogen). The hotspots need not be coeval and different segments can form sequentially. From Dewey and Burke (1974)