Chapter 15 Continental Flood Basalts Large Igneous Provinces

Chapter 15: Continental Flood Basalts Large Igneous Provinces (LIPs) l Oceanic plateaus l Some rifts l Continental flood basalts (CFBs) 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 l l Continental hot spots Continental rifting may be associated with hot spots F Successful rifts F 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.

Figure 15. 6. Time-averaged extrusion rate of CRBG basalts as a function of time, showing cumulative volume. After Hooper (1988 a) 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 (1988 a), 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. 87 Sr/86 Sr vs. 143 Nd/144 Nd for the CRBG. Winter (2001). An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Hooper (1988 a), Carlson et al. (1981), Carlson (1984), Mc. Dougall (1976), Brandon et al. (1993), Hooper and Hawkesworth (1993).

Figure 15. 13. 208 Pb/204 Pb vs. 206 Pb/204 Pb 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 (1988 a), Carlson et al. (1981), Carlson (1984), Mc. Dougall (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. 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)