Transcript On alternative models for the origin of time

On alternative models for the
origin of time-progressive
volcanic chains
V. Puchkov,
Institute of Geology,
Ufimian Scientific Centre, Russia,
[email protected]
The time-progressive character of some volcanic chains is well
known for decades and is proven with a different degree of
reliability for many of them. The recent overviews of the primary
data can be found in the papers of O'Neil et al. 2005, Clouard &
Bonneville 2005, enhanced by additional information from many
papers and books (all references are in the poster).
The above data were used by the author to compile a world scheme
of time-progressive chains.
The existence of such chains is a real challenge for anyone who works
at the problem of origin of melting anomalies.
Alternative models
for TPVC (time-progressive
volcanic chains)
1. Plume model.

A standard plume and plate
concept of origin of TPVC at
the example of the EmperorHawaii ridge (Norton,2000)

The model was first suggested by T.Wilson (1963) as
a hypothesis of “hot spots”- surficial manifestations
of immovable deep mantle melting anomalies, the
idea eveloped later by W. Morgan (1971)as a theory of
plumes:convective upwellings of a light hot mantle
substance coming from the core-mantle boundary. It
was a smart explanation, and still is, though the idea
of an absolute horizontal immobility of plumes is
disproved now by paleomagnetic and geodetic data
(Antretter et al., 2002; Norton, 2000; O’Neill et al.,
2005 & oth. ). The above-presented map is in a good
accordance with this concept.
(Mazarovich, 2000)
Galapagos (O’Connor et al.)

Some TPVCs demonstrate more complicated progression of ages compared
to Hawaii (e.g. Galapagos, Canaries), where volcanoes, once lit, are slow to
be extinct. But the model can be the same with an admission that a plume
is not necessarily head-and-tail or pillar-like.

The ITRF (International Terrestrial Reference
Frame), 2005, http://itrf.ensg.ign.fr/, showing
vectors of the modern plate movements, is also in a
good conformity with the above model, though the
direction of plate movements changed in time, as it
is demonstrated in the left cutoff.
Note specially:
i. the normal character of TPVCs at the East Pacific;
ii. the oblique character of the chains relatively to
the MOR in the Southern Atlantic, while they are
subparallel to the vectors;
iii. Cobb, Bowie and Yellostone chains are oriented
the same way as the vectors, notwithstanding the
fact that they are situated at the different sides of
the plate boundary;
iv. Reunion and Kerguelen chains cross the MOR,
because the plates at both sides of the MOR drift in
the same direction.
It also cannot be a
coincidence that the
young (active or
recently extinct
volcanoes at the ends
of the chains sit over
superswells.
Time-progressive volcanic chains of the world
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1
Time-progressive volcanic chain,
the arrow indicates the age growth.
Numbers - ages in Ma.
Letters and bracketed numbers in italics names and references.
Currently or recently ridge-centered melting anomaly
The same,with the active or young (less that 1 Ma) volcano
at the end
Time-progressive volcanic pre-drift cracks
A line connecting a single volcanic trail over an active plate margin
Contours of Pacific (I) and African-North Atlantic (II) superswells (LLVSPs) at CMB
Superswells and LIPS [Burke,Torsvik, 2004]
Based on paleomag data,
these authors have shown
that positions of LIPs (Large
Igneous Provinces)
reconstructed to the time of
their eruptions are situated
within or at the edges of two
superswells at CMB, with
minor exceptions.
The background map shows the SMEAN shear-wave
tomography model [Becker,Boschi 2002], which is based
on an average of three global intermediate wavelength
shear-wave tomography models. Note that δVs color
contours are highlighting the red (slower speed) and
blue (higher speed) regions.
We have shown in the
previous slide, based on a
different approach, that
active or shortly extinct
volcanoes at the ends of
time-progressive chains
follow the same pattern
The later scheme of Burke et al (2008) shows also some hot spots (pink crosses).
It manages better with the “exceptions”, connected with Columbia River anomaly,
but still has difficulties with Afar hotspot. I shall try to explain it later.
2. Model of a Propagating crack of lithosphere
connected with cooling stress


These forces, presumably
connected with cooling
stress, do not exist virtually
(by themselves). They are
added vectorially to much
greater forces driving
lithospheric plates (slab pull,
mantle drag and ridge push).
The resulting forces cannot
produce such effect.
Therefore the model
contradicts the plate
tectonics
(Stuart, Foulger, Barall, 2007)


A generalized world stress map based on the research in the frame of LITHOSPHERE
Program (Zoback et al., 1992)
1- tension, 2 – compression with thrusting, 3 – compression with formation of diagonal
wrench faults, 4 – plate boundaries, 5- trajectories of plate movements


Lithgow-Bertelloni and Guynn,2004
Note a scale (greater by an order) and
stresses parallel to Hawaian TPVC
Another objections.
1. The propagation of time-progressive chains in all oceans is
organized as predicted by plume-and-plate tectonics. If so,
why do we need more explanations? Occam's razor: “entia
non sunt multiplicanda praeter necessitatem", (”one should
not increase, beyond what is necessary, the number of
entities required to explain anything”).
2. Why the crack propagation is not affected by the strongest
anisotropy of oceanic, transitional and continental lithosphere,
crossed by many chains;
3. Why the Reunion, Kerguelen and New England-Great Meteor
TPVCs overrode the active MORs and after that co-existed with
them for some time;
4. Why LIPs and TPVCs are correlated with superswells,
as might be predicted by the plume theory;
5. Why the “cracks” tapped fertile sources, producing OIBs,
while the MORs - depleted ones?
To the left: a succession
of a spreading onset
in the Atlantic (Khain,2003)
However
there are TPVCs
called forth by plate
tectonics


The propagating crack idea
by itself is useful in
explanation of TPVCs
connected with timeprogressive graben
formation. In some cases
they preceded splitting
apart of the supercontiment
and ocean floor spreading,
in some they seem to
precede the future split-up
of a lesser continent.
In the TPVC world map
presented in the next slide
such lineaments are shown
tentatively in blue colour
To the right: stages
of development
of a prograding rift
(Martin, 1983)
Filho et al.
3.The model of a drifting fertile “blob”
Another alternative model is that of easily melting magma sources (pyroxenite
“blobs”), drifting in an asthenosphere in the same direction as the overlying
lithosphere, but quicker (Anderson, 2007).


The model, worked out in detail (Cuffaro, Doglioni, 2007 ), suits ad hoc the
Pacific chains (except Easter and Galapagos where the orientation is opposite
to predicted), but at a global scale it fails because it contradicts also to the
behavior of time-progressive chains in the Eastern Atlantic and Indian oceans.
A comparison of the map of time-progressive volcanic chains,presented here ,
with the schemes explaining the model of Cuffaro and Doglioni (2007) shows
contradictions (the next slide). The idea of a uniformly eastward-flowing
mantle, with asthenosphere and lithosphere uniformly lagging behind,
predicts the time succession directions for the chains of the SE Pacific, Indian
and East Atlantic oceans as contrary to what is observed.
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Puchkov (2008)
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Cuffaro, Doglioni
(2007).
Suggested vectors
of plate movements
Suggested
mantle flow
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
The very idea of a pyroxenite “blob” (basic in
composition) hanging in asthenosphere for many tens
of Ma, conflicts with the nature of asthenosphere, the
latter demonstrating readily the effects of
Archimedes law. When situated deeper than 50 km,
the “blob” exists as an eclogite which is much denser
that the ambient peridotite and must sink, if not
supported by a plume upwelling or heated by it.
When situated higher than the phase transition zone,
it turns into gabbro which is much lighter than the
peridotite and therefore must finally strike the bottom
of lithosphere.
Nevertheless, the idea of pyroxenite as an easily melting
part of the Earth's mantle seems, by itself,
to be very promising. It really can be of a great benefit
for the plate tectonic approach in explanation of shallow,
top-asthenospheric decompression-induced
melting anomalies (Anderson, 2007, Foulger, 2007).
But it can be also extremely useful for the real plume
model as it became evident recently from an example
of the deep-sourced Hawaiian magmas
(Sobolev et al., 2005; Yaxley, Sobolev 2007).
Conclusions.
The plume model fits in the best way the features
of the chosen time-progressive volcanic chains:
coincidence of their orientation and time
successions with directions of plate movements,
independence of the chains on “shallow” structures
and processes in lithosphere and asthenosphere,
connection of the young ends of chains with
superswells at CMB.
On the other hand, the alternative hypotheses lead
to useful ideas of a real role of crack propagation
in time-progressive volcanism, importance
of mantle-hosted eclogite-pyroxenite melting anomalies,
and possibility of passive, purely plate tectonic rifting
mechanism leading to a shallow decompressional
hotspot melting.

Probably
it is a way to a conciliation of competing theories.