科研之友
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摘要
Recently published observations of teleseismic wave propagation indicate that wave-speed anisotropy nearly doubles within the Lac de Gras kimberlite field in NW Canada when compared to surrounding parts of the Slave craton. The implied increase in structural fabric in the lithospheric mantle cannot be explained entirely by stronger alignment of minerals or temperature effects beneath the kimberlite field and forward modelling of the observed anisotropy implies the superposition of an additional fabric related to kimberlite eruption. Here the source of this fabric is newly interpreted to be fluid conduits that form a macroscopic stockwork of carbonated, hydrated or otherwise metasomatised peridotite dykes within depleted harzburgite. The superimposed fabric is thus composed of residual rocks that record the passage of kimberlite clan rocks formed from <1% partial melts of carbonated lherzolite. These metasomatised peridotite conduits probably are composed of rocks such as pyroxenites or wehrlites and occupy 10% of the mantle where present. Using teleseismic anisotropy to reliably predict the alignment of these dyke stockworks in the mantle lithosphere beneath known diamondiferous kimberlites has general application for informed target selection in diamond exploration. Reduced bulk shear wave speeds near these stockworks may also be diagnostic of their presence deep in the sub-continental lithospheric mantle.
- 出版日期2009-11
