A Fossil Mantle Plume under the Emeishan Flood Basalts: Integration of Geology, Geophysics and Geochemistry

Details A Fossil Mantle Plume under the Emeishan Flood Basalts: Integration of Geology, Geophysics and Geochemistry A Fossil Mantle Plume under the Emeishan Flood Basalts: Integration of Geology, Geophysics and Geochemistry

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.v53c..03x&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #V53C-03

Mathematics

Logic

8450 Planetary Volcanism (5480), 8121 Dynamics, Convection Currents And Mantle Plumes, 7207 Core And Mantle, 3640 Igneous Petrology, 1025 Composition Of The Mantle

Scientific paper

The plume hypothesis is now challenged because some fundamental aspects predicted by the modeling of plumes are found to be lacking in classic regions like Iceland and Yellowstone. Instead of invoking a ¡°bottom-up¡± process, some researchers favor a ¡°top-down¡± hypothesis for the formation of large igneous provinces (LIPs), in which shallow lithospheric processes may fuel melt production. Seismic investigations and tomographic models help trace mantle plumes in modern, active hotspots, but are of limited benefit in identifying ancient plumes, mainly because geophysics provides us with a snapshot of the present-day Earth¡_s structure. Consequently the geological ¡°footprint¡± associated with thermal anomalies are the clues to tracing ancient plumes. According to some theoretical models, pre-volcanic lithospheric uplift is the most important criteria used to identify the presence of plumes. The lack of such evidence, on the other hand, is an argument against the involvement of plumes in the formation of LIPs. Recent examination of the middle-late Permian sedimentology in southwest China reveals kilometer-scale lithospheric doming prior to the Emeishan flood volcanism (He et al., 2003). This, and correlations between diverse, independent parameters involving crustal doming, paleo-geography, sea level change, mantle melting mechanism and crust-mantle structure, provide evidence for a fossil mantle plume under the Emeishan LIP. Specifically, the consequences of plume-lithosphere interaction include: (a) pre-volcanic uplift including thinning of marine carbonates, a marine to sub-aerial transition, local provenance of clastic sediments, and a marked erosional unconformity, evident as palaeokarstic surfaces on the marine carbonates; (b) a domal structure (700 km radius); (c) variations in the thickness of volcanic rocks across the domal structure; (d) variations in flood basalt geochemistry from the center to the edge of the domal structure that are interpreted as high temperature melts in the center and lower temperature melts at the edge; (e) gradual decrease in crustal thickness from the center to the margin of the dome; and (f) the presence of high velocity lower crust (20-30km) immediately beneath the domal structure which is consistent with significant melt production and possible underplating/intrusion into the lower crust.

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