LIPs are some of the most prominent volcanic features on the Earth's surface, forming from collosal upwellings and eruptions of magma (for example the Siberian flood volcanic province is believed to have formed by 4 million cubic kilometres of magma- Czamanske and A. Fedorenko, 2004) Such flood basalts are thought to have formed as a result of large volumes of melt brought up by plume heads which spread out as their reach the lithosphere interface. Detailed mechanisms of formation are still not explicitly understood and much work has been done on LIPs which is not particularly relevant to the subject of this website
An example - the Ontong Java Plateau
The OJ Igneous province is by far the largest ocean flood basalt example and is one of the best studied - ODP Leg 192 on the main or high plateau penetrated 65-217 m of the basalt for studies. Two principle lava types are found called Kwaimbaita and Kroenke, analysis shows that they have formed from high levels of partial melting of between 25 and 31% (Fitton & Godard, 2004; Herzberg, 2004) which may be used to argue the plume head origin hypothesis.
Problems of fitting OJP to the plume hypothesis
OJP has a number of inconsistencies with respect to normal plume hypothesis, most notably the low level of post-eruptive subsidence predicted from the massive upwelling. A few others include
* Reappearance of the Kwaimbaita and Kroenke lava types some 30My after the main event
* Lack of a seamount chain predicted to form from the plume tail left behind after the main 'collision' event
* Lack of a presently active hotspot directly linkable to the OJP
* Excessively deep extrusion depths - the flood basalt should have erupted much nearer the sea sruface in accordance with the large scale uplift predicted by such an upwelling
Other methods of formation ?
OJP has been of particular interest to non-plume hypothesists in suggesting alternative processes for the large scale flood basalt including a bolide impact theory by Garry Rogers (Rogers, 1982) although the argument is not particularly convincing.
Some other ideas include plate tectonic-linked processes similar to plate separation but the significant difference to ridge basalts is not well explained either (See PTP section in Processes)