samfrau * flood basalts backarc basins du toit cox

SAMFRAU * flood basaltsBackarc basinsDu ToitCox

LIPS & hotspots associated with continental breakup

DUPAL hotspots are shallow & ridge related

DUPAL

DUPAL is related to continental breakup, delamination and ridges.

LIPS & hotspots associated with continental breakup

DUPAL hotspots are shallow & ridge related

DUPAL

D U P A L D U P A L

LIPS & hotspots associated with continental breakup

DUPAL hotspots are shallow & ridge related

DUPAL

D U P A L D U P A L

Ancient break-up rifts, hotspots & LIPs are related to currrent ridges and upper mantle LVZs

210 km depth

Ridges, triple junctions, continental debris recently covered by Gondwana

DUPAL

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.

Orogenies, subduction, delamination, DUPAL & flood basalts

Keith Cox

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 100-200 km depth), triple junctions, backarc environments …and do so with a higher probablity than Burke et al show for the lower mantle correlations.