Phantom plumes in Phantom plumes in Europe and neighbouring Europe and neighbouring

areasareas

Michele LustrinoMichele Lustrinoandand

Eugenio “break-off” CarminatiEugenio “break-off” Carminati

Dipartimento di Scienze della Terra, Università degli Dipartimento di Scienze della Terra, Università degli Studi di Roma La Sapienza, P.le A. Moro, 5, 00185 RomaStudi di Roma La Sapienza, P.le A. Moro, 5, 00185 Roma

Phantom plumes in Phantom plumes in Europe and neighbouring Europe and neighbouring

areasareas

Michele LustrinoMichele Lustrinoandand

Eugenio “break-off” CarminatiEugenio “break-off” Carminati

Dipartimento di Scienze della Terra, Università degli Dipartimento di Scienze della Terra, Università degli Studi di Roma La Sapienza, P.le A. Moro, 5, 00185 RomaStudi di Roma La Sapienza, P.le A. Moro, 5, 00185 Roma

The “anorogenic” magmatism of the The “anorogenic” magmatism of the circum-Mediterranean areacircum-Mediterranean area

(Tyrrhenian Sea, Sardinia, Sicily Channel (Tyrrhenian Sea, Sardinia, Sicily Channel and Middle East)and Middle East)

and of continental Europeand of continental Europe

(French Massif Central, Eifel, Bohemian (French Massif Central, Eifel, Bohemian Massif and Pannonian Basin)Massif and Pannonian Basin)

has been proposed to be related to the has been proposed to be related to the presence of presence of one or more mantle plumesone or more mantle plumes..

1)1) a given chemical and isotopic composition of a a given chemical and isotopic composition of a magma can be explained by different petrogenetic magma can be explained by different petrogenetic models;models;

2)2) a given petrogenetic process can produce a given petrogenetic process can produce magmas with different chemical and isotopic magmas with different chemical and isotopic composition;composition;

3)3) tomographic studies do not furnish unique results tomographic studies do not furnish unique results (i.e., different models can give contrasting (i.e., different models can give contrasting conclusions);conclusions);

4)4) seismic wave velocity anomalies interpreted seismic wave velocity anomalies interpreted exclusively in terms of temperature anomalies is exclusively in terms of temperature anomalies is not granted, since velocities are dependent also on not granted, since velocities are dependent also on other parameters (pressure, rock composition, other parameters (pressure, rock composition, melting, anisotropy and anelasticity).melting, anisotropy and anelasticity).

We emphasize that such conclusions based on We emphasize that such conclusions based on geochemical data and tomographic results are geochemical data and tomographic results are

not fully justified because:not fully justified because:

Tomography and geochemistry are Tomography and geochemistry are powerful tools but must be used in powerful tools but must be used in an interdisciplinary approach, in an interdisciplinary approach, in

combination with geodynamics and combination with geodynamics and structural geology. Alone they structural geology. Alone they

cannot provide compelling evidence cannot provide compelling evidence forfor or or againstagainst the existence of the existence of

mantle plumes.mantle plumes.

Why plumes?Why plumes? Geochemistry says: composition Geochemistry says: composition similar to oceanic intraplate basalts emplaced similar to oceanic intraplate basalts emplaced far away from subduction margins (i.e., OIB, far away from subduction margins (i.e., OIB, Ocean Islands Basalts: Hawaiian-Emperor Ocean Islands Basalts: Hawaiian-Emperor Chain, St. Helena, French Polynesia, and so on).Chain, St. Helena, French Polynesia, and so on).

Geochemists propose a Geochemists propose a contrasting modelcontrasting model: : from one side, they invoke from one side, they invoke isolated sourcesisolated sources (considered to be primordial, never tapped by (considered to be primordial, never tapped by partial melts, undegassed with high partial melts, undegassed with high 33He/He/44He He ratios) but, at the same time, these must be ratios) but, at the same time, these must be open sourcesopen sources because they must allow because they must allow entrance of subducted oceanic crust stored for entrance of subducted oceanic crust stored for at least 2 Ga (necessary to explain the high at least 2 Ga (necessary to explain the high 206206Pb/Pb/204204Pb >21).Pb >21).

Upwelling of hot mantle (in solid state) is Upwelling of hot mantle (in solid state) is commonly called mantle plumecommonly called mantle plume

The difference between the potential The difference between the potential temperature of “normal” asthenosphere (with temperature of “normal” asthenosphere (with Tp ~1280 °C) and mantle plume material can Tp ~1280 °C) and mantle plume material can range between 100 and 300 °C.range between 100 and 300 °C.

Why invoke such a temperature excess?Why invoke such a temperature excess?

To explain huge volumes (millions of kmTo explain huge volumes (millions of km33) of ) of CFB and LIP in a short time (generally 1-2 CFB and LIP in a short time (generally 1-2 Myr).Myr).

The “plume” models are based on the assumption The “plume” models are based on the assumption that the source regions of large igneous provinces that the source regions of large igneous provinces

are are entirely peridotiticentirely peridotitic..

However, during the last decade, new models have However, during the last decade, new models have suggested the presence of lithologies (suggested the presence of lithologies (eclogites, eclogites, pyroxenites, garnet granulitespyroxenites, garnet granulites and so on) with and so on) with solidus temperature several hundred degrees solidus temperature several hundred degrees lower than peridotitic mantle.lower than peridotitic mantle.

At least in some cases, enhanced melt productivity At least in some cases, enhanced melt productivity can be consequence of can be consequence of chemical anomalieschemical anomalies (e.g., (e.g., presence of low temperature melting point presence of low temperature melting point assemblages) rather than assemblages) rather than thermal anomaliesthermal anomalies (as (as requested in the original mantle plume models).requested in the original mantle plume models).

Widespread volcanic activity accompanied the Widespread volcanic activity accompanied the CiMACI (Circum Mediterranean Anorogenic CiMACI (Circum Mediterranean Anorogenic

Cenozoic Igneous) Province.Cenozoic Igneous) Province.

1)1) sodic mildly alkaline and tholeiitic rocks OIB-like;sodic mildly alkaline and tholeiitic rocks OIB-like;

2)2) oceanic floor rocks (from N- to E-MORB and low-oceanic floor rocks (from N- to E-MORB and low-K calcalkaline basalts and andesites);K calcalkaline basalts and andesites);

3)3) calcalkaline rocks (resembling magmas calcalkaline rocks (resembling magmas emplaced in subduction-related settings);emplaced in subduction-related settings);

4)4) potassic to ultrapotassic alkaline rocks with potassic to ultrapotassic alkaline rocks with mildly to strongly SiOmildly to strongly SiO22-undersaturated -undersaturated compositions;compositions;

5)5) rare exotic compositions such as lamproites, rare exotic compositions such as lamproites, lamprophyres and carbonatites.lamprophyres and carbonatites.

The first problem is to try to The first problem is to try to define define what an “anorogenic” what an “anorogenic”

magma ismagma is from a geochemical from a geochemical and geotectonic point of view.and geotectonic point of view.

At the moment there is no consensus At the moment there is no consensus on “anorogenic” (or intra-plate) and on “anorogenic” (or intra-plate) and “orogenic” (or subduction-related) “orogenic” (or subduction-related) terms.terms.

What is important to stress is: What is important to stress is:

Virtually Virtually all the igneous rocksall the igneous rocks reflectreflect in their chemistry the in their chemistry the

effects of effects of interactioninteraction betweenbetween mantlemantle (i.e., peridotitic) (i.e., peridotitic) andand

recycled recycled crustalcrustal (i.e., (i.e., pyroxenitic/eclogitic) pyroxenitic/eclogitic) lithologieslithologies. .

An example?An example?

Hawaiian rocks are really “anorogenic”?

An example?An example?

Hawaiian rocks are really “anorogenic”?

Yaxley and Sobolev (2007) High pressure experimental investigation of interactions between partial melts of gabbro and peridotitic mantle. Contrib. Mineral. Petrol. Sobolev et al. (2007) The amount of recycled crust in sources of mantle-derived melts. Science.

Nielsen et al. (2006) Thallium isotopic evidence for ferromanganese sediments in the mantle source of Hawaiian basalts. Nature

Herzberg (2006) Petrology and thermal structure of the Hawaiian plume from Mauna Kea volcano. Nature

Huang e Frey (2005) Recycled oceanic crust in the Hawaiian plume: evidence from temporal geochemical variations within the Koolau Shield. Contrib. Mineral. Petrol.

Gaffney et al. (2005) Melting in the Hawaiian Plume at 1-2 Ma as recorded at Maui Nui: the role of eclogite, peridotite and source mixing. Geochem. Geophys. Geosyst.

Sobolev et al. (2005) An olivine-free mantle source for Hawaiian shield lavas. Nature.

Lassiter et al. (2000) Generation of Hawaiian post-erosional lavas by melting of a mixed lherzolite/pyroxenite source. Earth Planet. Sci. Lett.

In practice the mantle beneath Hawaii looks like this:

In practice the mantle beneath Hawaii looks like this:

Notwithstanding this, the plume lovers are Notwithstanding this, the plume lovers are numerous.numerous.

Several ad-hoc concepts like:Several ad-hoc concepts like:

fossilfossil plume (Stein and Hofmann, 1992; Rotolo et al., 2006) plume (Stein and Hofmann, 1992; Rotolo et al., 2006)

dyingdying plume (Davaille and Vatteville, 2005) plume (Davaille and Vatteville, 2005)

recycledrecycled plume head (Gasperini et al., 2000) plume head (Gasperini et al., 2000)

tabulartabular plume (Hoernle et al., 1995) plume (Hoernle et al., 1995)

finger-likefinger-like plume (e.g., Granet et al., 1995; Cadoux et al., 2007) plume (e.g., Granet et al., 1995; Cadoux et al., 2007)

babybaby plume (Ritter, 2006) plume (Ritter, 2006)

channelledchannelled plume (Camp and Roobol, 1992; Oyarzun et al, 1997) plume (Camp and Roobol, 1992; Oyarzun et al, 1997)

thoroidalthoroidal plume (Mahoney et al., 1992) plume (Mahoney et al., 1992)

head-freehead-free plume (e.g., Ritter, 2006) plume (e.g., Ritter, 2006)

coldcold plume (Garfunkel, 1989; Hanguita and Hernan, 2000) plume (Garfunkel, 1989; Hanguita and Hernan, 2000)

depleted residualdepleted residual plume (e.g., Danyushevsky et al., 1995) plume (e.g., Danyushevsky et al., 1995)

pulsatingpulsating plume (Krienitz et al., 2007) plume (Krienitz et al., 2007)

subduction fluid-fluxed refractory plume subduction fluid-fluxed refractory plume (Falloon et al., 2007)(Falloon et al., 2007)

CASE STUDIESCASE STUDIESTYRRHENIAN SEATYRRHENIAN SEA

Favouring PlumeFavouring Plume

Bell et al., 2004 (Deep mantle plume. OBell et al., 2004 (Deep mantle plume. Opening of the pening of the Mediterranean region along the SW-ward Mediterranean region along the SW-ward continuation of the Rhine-Rhone rift system)continuation of the Rhine-Rhone rift system). . On On what grounds?what grounds? Sr-Nd-Pb-O-C isotopic ratios. Sr-Nd-Pb-O-C isotopic ratios.

Locardi and Nicolich, 2005 (Locardi and Nicolich, 2005 (E-ward migrating deep-E-ward migrating deep-seated thermal plume). seated thermal plume). Seismic active belt in Seismic active belt in southern Italy?southern Italy? The effect of a convective cell The effect of a convective cell associated with hot asthenolith inducing stress and associated with hot asthenolith inducing stress and seismic activity at the interface with the seismic activity at the interface with the neighbouring cooler mantle.neighbouring cooler mantle.

CASE STUDIESCASE STUDIESTYRRHENIAN SEATYRRHENIAN SEA

Contrasting PlumeContrasting Plume

1) Oligocene-Recent volcanic activity with subduction-like signature 1) Oligocene-Recent volcanic activity with subduction-like signature from NW (Sardinia) to SE (Aeolian Archipelago);from NW (Sardinia) to SE (Aeolian Archipelago);

2) middle Miocene-Quaternary igneous rocks along the W and E 2) middle Miocene-Quaternary igneous rocks along the W and E branch of the Tyrrhenian Sea completely different;branch of the Tyrrhenian Sea completely different;

3) composition of Italian volcanic rocks (mostly potassic to 3) composition of Italian volcanic rocks (mostly potassic to ultrapotassic) never found among OIB;ultrapotassic) never found among OIB;

4) depth of the Tyrrhenian Sea crust very deep compared to the 4) depth of the Tyrrhenian Sea crust very deep compared to the depth of oceanic crust of a similar age;depth of oceanic crust of a similar age;

5) calculated Tp of the Tyrrhenian Sea (~1320 °C vs. 1280 °C);5) calculated Tp of the Tyrrhenian Sea (~1320 °C vs. 1280 °C);

6) numerical modelling requires tectonic forces like those in 6) numerical modelling requires tectonic forces like those in subduction settings (subduction of lithosphere for >200 km in N. subduction settings (subduction of lithosphere for >200 km in N. Apennines, >500 km in S. Apennines, >800 km in Calabria);Apennines, >500 km in S. Apennines, >800 km in Calabria);

7) sub-crustal earthquakes indicate a slab below the Calabrian Arc 7) sub-crustal earthquakes indicate a slab below the Calabrian Arc up to a depth of 500 km;up to a depth of 500 km;

CASE STUDIESCASE STUDIES

SICILY CHANNELSICILY CHANNEL

SICILYSICILY

SARDINIASARDINIA

MEDITERRANEAN SEA AND CENTRAL-WESTERN EUROPEMEDITERRANEAN SEA AND CENTRAL-WESTERN EUROPE

FRENCH MASSIF CENTRALFRENCH MASSIF CENTRAL

EIFEL AND NEIGBOURING AREASEIFEL AND NEIGBOURING AREAS

PANNONIAN BASINPANNONIAN BASIN

MIDDLE EASTMIDDLE EAST

Blah blah blah…Blah blah blah…

(See Lustrino and Carminati, 2007)(See Lustrino and Carminati, 2007)

Many are the models proposed to explain the Many are the models proposed to explain the origin of CiMACI rocks. These can grouped inorigin of CiMACI rocks. These can grouped in::

1)1)Models that require Models that require active upraiseactive upraise of of

asthenospheric mantle (or even deeper asthenospheric mantle (or even deeper sources) (sources) ( mantle plumesmantle plumes););

2) Models that requires lithospheric extension 2) Models that requires lithospheric extension (or detachment and delamination processes) (or detachment and delamination processes) to induce decompression melting and to induce decompression melting and passive upraisepassive upraise of asthenospheric and of asthenospheric and lithospheric melts.lithospheric melts.

Many are the models proposed to explain the Many are the models proposed to explain the origin of CiMACI rocks. These can grouped inorigin of CiMACI rocks. These can grouped in::

1)1)Models that require Models that require active upraiseactive upraise of of

asthenospheric mantle (or even deeper asthenospheric mantle (or even deeper sources) (sources) ( mantle plumesmantle plumes););

2) Models that requires lithospheric extension 2) Models that requires lithospheric extension (or detachment and delamination processes) (or detachment and delamination processes) to induce decompression melting and to induce decompression melting and passive upraisepassive upraise of asthenospheric and of asthenospheric and lithospheric melts.lithospheric melts.

According to According to Plume-loversPlume-lovers, the absence of igneous activity along , the absence of igneous activity along most of the ECRIS (European Cenozoic Rift System) is evidence that most of the ECRIS (European Cenozoic Rift System) is evidence that continental rifting ALONE cannot promote partial melting of the continental rifting ALONE cannot promote partial melting of the mantlemantle. .

E C

R

I S

E C

R

I S

We suggest that if such a crustal thinning is associated to We suggest that if such a crustal thinning is associated to areas where lithosphere thickness is reduced (e.g., French areas where lithosphere thickness is reduced (e.g., French Massif Central and Rhenish Massif) igneous activity may Massif Central and Rhenish Massif) igneous activity may develop without requiring any thermal excess of the develop without requiring any thermal excess of the mantle.mantle.

CONCLUSIONSCONCLUSIONSEvidence supporting Plumes:Evidence supporting Plumes:

Overall geochemical similarities with OIBOverall geochemical similarities with OIB

Geochemical homogeneity of the volcanic rocksGeochemical homogeneity of the volcanic rocks

Tomography sees “hot” areas beneath French Massif Central and EifelTomography sees “hot” areas beneath French Massif Central and Eifel

Geothermometry of mantle minerals indicates excess temperatureGeothermometry of mantle minerals indicates excess temperature

Evidence against Plumes:Evidence against Plumes:

Small volume of volcanic products (with few exceptions); small Small volume of volcanic products (with few exceptions); small ff

Very long magmatic activityVery long magmatic activity

No plume-tracks; No associated CFBNo plume-tracks; No associated CFB

No strong doming before magmatismNo strong doming before magmatism

No definitive and absolute message from geochemistryNo definitive and absolute message from geochemistry

Tomography gives contrasting resultsTomography gives contrasting results

Evidence of subduction and back-arc basin formationEvidence of subduction and back-arc basin formation

All major volcanic areas on thinned lithosphere and/or along plate marginsAll major volcanic areas on thinned lithosphere and/or along plate margins

For further information:For further information:

A. Peccerillo, M. LustrinoA. Peccerillo, M. Lustrino: Compositional variations of Plio-Quaternary magmatism in the : Compositional variations of Plio-Quaternary magmatism in the circum-Tyrrhenian area: deep- versus shallow-mantle processes (2005) In: Foulger et al. circum-Tyrrhenian area: deep- versus shallow-mantle processes (2005) In: Foulger et al. (Eds). Plates, Plumes and Paradigms. Geol. Soc. Am. Spec. Paper, 418, 422-434(Eds). Plates, Plumes and Paradigms. Geol. Soc. Am. Spec. Paper, 418, 422-434

M. Lustrino, M. WilsonM. Lustrino, M. Wilson: The Circum-Mediterranean Cenozoic Igneous Province (2007) Earth-: The Circum-Mediterranean Cenozoic Igneous Province (2007) Earth-Sci. Rev., 81, 1-65Sci. Rev., 81, 1-65

M. Lustrino, E. CarminatiM. Lustrino, E. Carminati: Phantom plumes in Europe and neighbouring areas (2007) In: G. : Phantom plumes in Europe and neighbouring areas (2007) In: G. Foulger and D. Jurdy (Eds.) Plumes, Plates and Planetary Prospetives. Geol. Soc. Am. Spec. Foulger and D. Jurdy (Eds.) Plumes, Plates and Planetary Prospetives. Geol. Soc. Am. Spec. Paper (in press).Paper (in press).