Environmental Engineering Reference
In-Depth Information
is short. The Caribbean Colombian LIP (CCLIP) could be the OP that was parent
to the active Galapagos hotspot. The CCLIP was erupted at about 90 Ma and
collided with the Great Arc of the Caribbean at about 80 Ma (Burke,
1988
).
However, because of reconstruction uncertainties we have not included the CCLIP
in our analysis.
3.2.2 LIPs of the continents (CLIPs)
Fourteen CLIPs have erupted into and onto continental crust for the past 300
Myr. Two of those CLIPs also lie partly on oceanic crust and a majority of
the remainder lie at the time of, or soon after, their eruption within no more than
a few hundred kilometres of a continental margin. More generally, locations of
CLIPs have shown a close association with intra-continental rifts (
Table 3.1
);
in trying to apply the ideas of plate tectonics to past continental geology
it was long ago suggested that eruption of intra-continental LIPs and hotspots
above mantle plumes led to the formation of topographic domes crested by
newly formed radial intra-continental rifts. Horizontally linked, dog-legged
patterned sets of those new rifts, thousands of kilometres in total length, with
hotspot locations at nodes, were suggested to evolve into the kinds of continu-
ous rifts that mark the initiation of Atlantic-type continental margins (e.g. Burke
and Whiteman,
1973
; Burke and Dewey,
1973
). More recently, temporally
better resolved isotopic, stratigraphic and magnetic anomaly information about
the relative times of formation of CLIPs, rifts and newly formed Atlantic-type
ocean
floor has become available and those ideas have been shown to have been
wrong (see, e.g., Sengor,
2001
;Burke
et al
.,
2003
). It has now become clear
that CLIPs and hotspots have erupted into already existing intra-continental
rifts. As in the case of the Paraná
-
Etendeka rift (
Table 3.1
) some of those rifts
were no more than about 20 Myr old at the time of CLIP eruption; however, in
other cases, such as the Deccan CLIP, the rift into which the CLIP erupted was
already hundreds of millions of years old. CLIPs that formed above underlying
plumes from the CMB intrude into existing intra-continental rifts; they have
not initiated rifts. Sleep
provides a
good explanation of how CLIPs can come to be erupted into pre-existing rifts.
Sengor and Natalin (
2001
) catalogued and plotted on a world map over 400 such
structures. If the rifts were uniformly distributed within the 170
'
s(
1997
)ideaof
'
upside-down drainage
'
10
6
km
2
10
6
km
2
area.
area of the continents then there would be one rift in every 0.5
The only signi
cance of this estimate is that it shows that the upside-down
drainage of the LIP magma is unlikely to have to travel for more than a few
hundred kilometres along the base of continental lithosphere to
find a rift into
whichtoerupt.
