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Database expansion. Until recently characterizing LIPs has relied almost exclusively on the Mesozoic and Cenozoic record (e.g. Coffin and Eldholm, 1994, 2001; Courtillot and Renne, 2003). R elatively well preserved, this young record remains an important source of additional information on LIPs and their origin. Progress has recently been made in extending the LIP record back to the Paleozoic, Proterozoic and Archean (Ernst and Buchan, 1997; Condie, 2001; Tomlinson and Condie 2001; Arndt et al. 2001; Ernst and Buchan, 2001, 2002; Isley & Abbott, 1999, 2002). Although older LIPs are less well preserved than younger LIPs, they will be particularly valuable in investigating changes in LIP properties with time (continuous changes, cyclical changes), in understanding the plumbing system of LIPs.
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| LIP
plumbing system, 1270 Ma Mackenzie giant radiating dyke swarm of northern
Canada. Dots indicate areas where flow direction was determined. Arcuate
line indicates boundary between vertical flow (close to swarm centre) and
horizontal flow (at all greater distances). From Baragar WRA, R.E. Ernst, L. Hulbert, T. Peterson, Longitudinal petrochemical variation in the Mackenzie dyke swarm, northwestern Canadian Shield. J. Petrol. 37: 317-359, 1996. |
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| Possible LIP in northern Canada, extending for 2000 km along an Archean continental margin consisting of 2730 -2700 Ma komatiite-bearing greenstone belts: Murmac Bay Group, Woodburn Lake Group, Prince Albert Group, and probable equivalent (Mary River Group) on Baffin Island to the northeast (click here for references). | |||
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Original
size & areal extent. Size is an important parameter
in the study of LIPs. It has been used to draw conclusions about the flux
of mafic magma from the mantle, the relationship between continental and
oceanic LIPs, the origin of LIPs (e.g. plume vs. non-plume), the variation
in plume size and the existence of super-sized plumes, climatic effects
of LIPs, etc. For example, it is critical to establish if LIPs have a
relatively uniform size, or if there are large differences in size which
might reflect different origins. However, there are a number of uncertainties
in estimating LIP size. Estimating the intrusive component of LIPs (especially
underplating) is particularly difficult. In the older record, only remnants
of the extrusive component have escaped erosion, and the LIP may have
been fragmented by plate tectonic processes. Even in the younger record,
where erosion and plate tectonic effects are less pronounced, the estimated
size of a LIP may increase dramatically as additional components are recognized
through better dating, modeling and stratigraphic correlation. A recent
example is a doubling in the recognized size of the 250 Ma Siberian Traps
based on dating of basalts recovered by drill core from beneath the West
Siberian basin (Reichow et al., 2002). It is clear that a more robust
database of LIP sizes is needed.
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| Reconstructed
200 Ma Central Atlantic Magmatic Province LIP. Lines are dykes, s = sills
and v= volcanics. Note the importance of continental reconstruction (i.e.
closing the Atlantic Ocean) in restoring the primary giant radiating dyke
swarm pattern and revealing the extent of the event. After Ernst and Buchan (2001); note different interpretation of dyke swarm pattern in some papers of Hames et al. (2003). |
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Plumbing
system. Mapping
the LIP plumbing system of dykes, sills and layered intrusions is important
in order to identify centres at which melt from sub-lithospheric mantle
source areas is transported through lithospheric mantle and into the crust,
and to determine the pattern of magma distribution from these centres
within the crust and onto the surface as flood basalts. Of particular
interest is the recognition of giant radiating dyke swarms (e.g. Halls,
1982; Fahrig 1987; Ernst & Buchan 1997; 2001; Wilson and Head 2003),
links with feeder chambers marked by layered intrusions (Baragar et al.
1996), and patterns of sublithospheric channelling of plume mantle (Ebinger
and Sleep 1998; Wilson 1997). |
| Some
models for locations of feeder chambers for giant dyke swarms (after Ernst
et al., 2001). a) Centrally located chamber (as implied by ‘novae’ on Venus) b) off axis chambers (e.g. Mackenzie swarm, Earth; Baragar et al. 1996) c) chambers along a linear swarm. For more about giant radiating dyke swarms click here. |
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| Mantle
source region (geochemistry).
LIP geochemistry can be used to characterize mantle sources, provide it
is not overprinted by continental crust contamination, a common problem
with continental LIPs. The involvement of known mantle reservoirs, DMM,
EMI, EMII, HIMU and FOZO, can be assessed using isotopes and trace elements.
Of particularly current interest is the role of eclogite in the source area
(Campbell, 1998; Takahashi et al., 1998; Cordery et al., 1997), which probably
derives from fossil subducted slabs. Using trace elements and isotopes it
should prove possible to model the cycling of components (e.g. Campbell,
2002). references |
| A)Mantle
tetrahedron with components DM, EM1, EM2, HIMU) and FOZO (e.g. Hart et al.
1992; Condie 2001). B) and C) Note patterns in Os and He converging toward FOZO (after van Keken et al. 2002). |
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| Links
with ore deposits. At present the link between LIPs
and ore deposits is poorly understood. The most important link is with PGEs.
Prominent examples are the Noril’sk deposits (of the 250 Ma Siberian
Trap event) which produce most of the world’s palladium and the 2060
Ma Bushveld intrusion which is the largest known mafic-ultramafic intrusion
and is the world’s most important producer of platinum and chrome.
Archean komatiites are also an important source of Ni. references |
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| Model for feeder system of Norilsk deposits associated with the Siberian Traps (Naldrett 1997, 1999; Pirajno 2000, p. 432). |
| Testing
plume & non-plume origins A fundamental question in LIP research involves their origin. Many LIPs have been attributed to deep mantle plumes (e.g. Campbell et al. 1989; Griffiths and Campbell, 1990, 1991; Campbell 1998, 2001; Courtillot et al. 2003). Other models involve decompression melting in a rift setting (White and McKenzie, 1989, 1995), back-arc setting (Rivers and Corrigan 2000), edge-driven convection (Anderson, 1996, 1998; King and Anderson, 1998; Hames et al. 2003), and meteorite impact (Jones et al., 2002). There is a pressing need for the development and application of a set of rigorous tests to distinguish between different origins for LIPs. Several possible tests include: seismic tomography; presence or absence of domal uplift; and relative timing of rifting and magmatism. references |
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| Models for origin of Large Igneous Provinces. After Coffin and Eldholm (1994). |
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| Three distinct types of hotspots in the Earth’s mantle (after Courtillot et al. 2003) |
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Distribution
of LIPs in space and time (Archean to Present)
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| Age correlations between LIP events and major extinction events (after Courtillot and Renne 2003). |
| Time
series analysis of LIP record. A recent wavelet analysis
of the Ernst and Buchan database reveals only weakly developed cycles during
the period 3500-present (Prokoph et al., 2003), broadly similar to the results
of the fourier analysis of Isley and Abbott (2002). These cycles are at
730-550, 330, 170, 100, and 30 Myr. However, given the broadband nature
and weak persistence of most of these cycles, their significance and link
with forcing functions remains uncertain. Possible controls on LIP production that have been previously advanced included: a 800 Myr nutation frequency of the core, a 300-500 Myr supercontinent formation/breakup, and 30 Myr meteorite impact cycle (Isley and Abbott, 2002). As the LIP database improves, appropriate time series analysis (including wavelet analysis) will yield more definitive results. references |
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| Time series analysis of LIPs through time. Upper part is cumulative percentage diagram showing nearly constant rate of 1 LIP per 20 Myr for post-Archean time. The two curves are based on different age uncertainty criteria; details are in Ernst and Buchan (2002). ‘Bar-code’ diagram shows distribution of events (Ernst and Buchan 2001). | |
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| Wavelet analysis revealing weak cycles at 730-550, 230, and 170 Myr (after Prokoph et al. in press). |
| LIP
clusters (“superplume events”), and link with supercontinent breakup
and juvenile crust production. Clusters
of LIPs have been linked with supercontinent breakup (Storey, 1995; Li et
al., 2003) and with bursts of juvenile crustal production (Condie, 2001).
Therefore, an important frontier is the use of the expanded LIP record through
time to assess their importance in the geological record. At about 30 times
since 3.5 Ga, coeval mafic magmatism is recognized on more than one continental
block (Ernst and Buchan, 2001, 2003). However, the absence of reliable Precambrian
continental reconstructions (Buchan et al., 2000, 2001) prevents the assessment
of which of these represent single fragmented LIPs and which represent clusters
of independent LIPs. Determination of reliable Precambrian reconstructions
is therefore an important LIP frontier. references |
| A) Evidence for more than one centre at 1270 Ma. Mackenzie gaint radiating dyke swarm of northern Canada is too distant from Central Scandinavian Dolerite sill Complex of Baltica to be related to the same event. Harp dyke swarm and coeval Gardar magmatism may represent a third node of activity (after Ernst and Buchan 2002). B) Multiple centres of activity at 135 Ma (Ernst and Buchan 2002). |  |
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| Comparison
of LIPs on Earth, Venus and Mars Plate tectonics; coronae. LIPs are present on both Mars and Venus (Head and Coffin, 1997). On Mars they consist of massive individual volcanic edifices of the Tharsis Montes region and individual flows that can be 1800 km long (Fuller and Head, 2003). On Venus, they are associated with large flow fields averaging 0.2 Mkm2, and large volcanic edifices hundreds of km across. In addition, an important class of LIPs on Venus is associated with widespread annular structures (diameter 50-2600 km) termed coronae, which are interpreted to result from mantle diapirs. Does erosion mask identification of their characteristic annular topography or were coronae never present on Earth? Difference between LIPs on Mars and Venus and those on Earth are thought to reflect, at least in part, the absence of plate tectonics on Mars and Venus. Therefore, LIPs on these planets can be studied in the context of non-plate boundary (in traplate) processes. references |
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| 1800 km long and 300 km wide preaureole lave flow emanating from Olympus Mons, Mars (Fuller and Head 2003). |
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| Fatua corona, Venus (image 690 km across). After Squyres et al. (1992). |
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