Lecture 3. Beyond the Plate Tectonics: Plumes, Large Ign. Provinces and Mass Extinctions

Outline  Plumes and LIPs general features  Siberian Traps  Major open questions  Model  Relation to mass extinction

Plates

Hot Spots

Hot Spot Track Willson, 1963; Morgan, 1971

Hot Spot= Mantle Plume- Classical feature beyond plate tectonics Currently, existence of plumes is under debate: anti- plume site– Main anti-plume argument—no predicted uplift before eruption of Large Igneous Province

Large Igneous Provinces (LIPs) After Saunders et al. (1992)

Large Igneous Provinces (LIPs) After Saunders et al. (1992)

Large Magma Volume Siberian Flood Basalts- over 4 mln. km 3 Deccan Traps- 2 mln. km 3 North Atlantic Province- over 2-4 mln. km 3 Columbia River Province- 0.3 mln. km 3 Plato Onthong-Java- over 40 mln. km 3

Short Time Scales of Major Magmatic Phases The most precise dating gives age ranges for the main magmatic phase within method accuracy ±1 mln.y. The full range of magmatic activity may exceed 10 mln.y.

Ar-Ar age of Siberian Flood Basalts 250±1.1 Ma Reichow et al, 2009

LIPs often predate continental break-up

Continental break-up

LIPS are related to hot spots Deccan Traps—Reunion HS

Parana-Etendeka—Tristan HS

LIPs source has high temperature Herzberg & Gazel, 2009

Torsvik et al., 2007, 2008 LIPs sources are in the Lower Mantle ?

Campbell & Griffiths, 1990 An experimental starting plume (in glucose syrup) Plume Plume head model of LIPs

Surface uplift = km/100°, i.e km for DT= ° White and McKenzie, 1989; Richards et al.,1989, Campbell and Griffiths, 1990 Uplift of >1 km must be common for LIPs but it is not!

White and Saunders (2005) LIPs correlate with mass extinction events Ridgwell, 2005

Payne et al, PNAS, 2010 Ocean acidification as a kill mechanism

Ganino & Arndt, 2009, Svensen et al., 2009 No correlation with LIPs volume

Ganino & Arndt, 2009, Svensen et al., 2009 Elegant explanation

Over 4 mln. km 3 of magmas produced in less than 1 ma The age of province is about 252 ma and coincides with P-T mass extinction No uplift before magmatism Siberian LIP

Siberian Traps Reichow et al, 2009

Siberian Traps

Questions Why no pre-magmatic uplift? Why enormous volume of magmas erupted at thick cratonic lithosphere without extreme extension? How lithosphere was thinned by >50 km during only few 100 thousand years? What was the source of large volumes of CO2 and other gases that triggered P-T mass extinction? Heating of coal?

Sobolev et al, Science, 2007

Crustal recycling Hofmann and White, Kellogg et al., 1999

Eclogite: clinopyroxene ≥ garnet ± SiO 2 phase Photo and sample of I. Aschepkov см 1 см

Sobolev, et al, 2005 Pyroxenite -Sobolev et al, 2007; peridotite- Walter, 1998 T C

Pyroxenite-derived melt compared with peridotite-derived melt High Ni and Si and low Mn/Fe, Ca and Mg: because pyroxene and garnet buffers Ni, Si, Mn, Fe, Ca and Mg instead of olivine (Kelemen et al 1998, Humayun et al, 2004, Sobolev et al, 2005, Herzberg, 2006, Sobolev et al, 2007);

Thermomechanical model of Siberian LIP constrained by petrological data based on 2011 paper

Petrological constraints Plume potential temperature Tp=1600°C Eclogite content in plume 10-20wt% (15wt%) Initial lithospheric thickness >130 km

Melt sources composition

Melting of peridotite (Katz et al, 2003), of eclogite and pyroxenite (based on experiments of Yaxley, and Hirschmann group, Sobolev et al, 2007 Improvements of tne thermomechanical modeling technique Melt transport procedure (fast compaction porous- flow-like in the melting region and intrusion in the lithosphere)

Model setup

Thermal plume(Tp=1650°C) no melting 0 Myr

Thermal plume no melting 0.25 Myr

Thermal plume no melting 0.5 Myr

Thermo-chemical plume (Tp=1650°C,18% eclogite) no melting 0 Myr

Thermo-chemical plume no melting 0.5 Myr

Thermo-chemical plume no melting 1.5 Myr

0.5 Myr Thermal plume Thermo-chemical plume

Elevation

Temperature

0.5 Mln years Composition

Numerical model Sobolev et al. submitted

Effect of lithosphere Different lithospheric depletionDifferent lithospheric thickness

Effect of plume

Different plume composition Effect of plume

Melt production and composition

Plume degassing

Ganino & Arndt, 2009, Svensen et al., 2009 But we lose elegant explanation!

But we have another!

Such a plume is able to thin dramatically cratonic lithosphere without extension and to generate several mln km3 of melt in few 100 thousand years Conclusions Thermochemical plume rich in recycled crust does not generate significant pre-magmatic uplift of the lithosphere Massive CO2 and HCl degassing from the plume could alone trigger the Permian-Triassic mass extinction and before the main volcanic phase

Conclusions Plumes do exist, but they are not purely thermal but thermochemical

Sobolev et al. in prep. Model of the Ontong Java Plateau