Transcript Karoo & SAMFRAU Flood Basalts

SAMFRAU * flood basalts
Backarc basins
Du Toit
Cox
DUPAL is related to continental breakup,
delamination and ridges.
DUPAL
DUPAL hotspots are shallow & ridge related
LIPS & hotspots associated with continental
breakup
DUPAL
DUPAL
DUPAL
DUPAL hotspots are
shallow & ridge
related
LIPS & hotspots associated with continental
breakup
DUPAL
DUPAL
DUPAL
DUPAL hotspots are shallow & ridge related
LIPS & hotspots associated with continental
breakup
Ancient break-up
rifts, hotspots &
LIPs are related to
currrent ridges
and upper mantle
LVZs
210 km depth
DUPAL
Ridges, triple junctions, continental debris recently
covered by Gondwana
32 out of 38 hotspots lie on near the edges of upper
mantle LVAs at 100 or 200 km depth.
“The probability that 18 or more out of 24 randomly
chosen points lie within the belts (23.5% of the CMB area)
is about 1 in 7 million ( p =1.47 ·10−7 ). “ Kevin Burke
Current ridges & hotspots are in these areas
THE hypothesis of Du Toit1 on a continuous zone of orogeny and sedimentation (the
Samfrau geosyncline) along the Pacific side of Gondwanaland in Palaeozoic and early
Mesozoic times has been supported by subsequent geological work.
Dickinson6 has referred to
the ‘Gondwana–Tasman
orogenic trend’ as a zone
of plate consumption.
Keith Cox
Orogenies, subduction, delamination, DUPAL
& flood basalts
Flood basalts, kimberlites, hotspots, non-MORB geochemistry
(Dupal, Sopita, EM…) originated in continenatl rifts under long-lived
continents that became or eill become midocean ridges
AFRICA
Only 5 out of
27 oceanic
hospots occur
outside of the 3
% slow contour
associated with
ridges
Although the patterns are
completely different in the
uppermost & lowermost
mantles, the hindsight criteria
that Burke used to argue for a
D” source for hotspots works
even better for the
asthenosphere.
All of the hotspots &
backtracked LIPs fall
within the 3% slow
contour interval
associated with the
circum-Africa ridge system
& the same is true for the
LIPs in the south Pacific
Most of the backtracked LIPs fall near present day
spreading ridges and currently active hotspots.
Such long-term stability implies control by flat
slabs or by boundary layer deformation perhaps
linked to stable lower mantle features.
Hotspots and LIPs always form under
or near ridges (<30 Ma crust, >1%
shear wavespeed reduction at 100200 km depth), triple junctions,
backarc environments …and do so
with a higher probablity than Burke et
al show for the lower mantle
correlations.