Evolution of Cratonic Lithosphere in Eastern China

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9903159RudnickThe Sino-Korean craton is a rare example of an Archean craton that showsevidence for loss of its refractory mantle root. In the Paleozoic,diamondiferous kimberlites erupted through the craton carrying minerals andxenoliths indicative of the presence of a 200 km thick refractorylithosphere, equilibrated to a cool geotherm. In the Triassic, refractorygarnet peridotite was uplifted in the Sulu region during the collision ofthe Yangtze and Sino-Korean cratons. These peridotites may indicate thepresence of the cratonic root at this time. In contrast, Cenozoicrift-related basalts carry fertile mantle xenoliths that record highequilibration temperatures and sample to depths of only 80 km. Theseobservations have been interpreted to reflect the loss of the cratonic rootbeneath the Sino-Korean craton, sometime after the Ordovician and it'sreplacement with more fertile peridotite, typical of off-craton regions.Outstanding questions include: 1) whether all of the cratonic mantle wasremoved, 2) when it was removed and 3) the mechanism by which it wasremoved. We seek to address these questions through a systematicpetrographic, geochemical and Re-Os isotopic study of the three types ofmantle samples described above. Re-Os analyses of chromites from the Suluperidotites and whole rocks from the basalt-borne peridotites will be madein order to determine 1) the origin and age of the tectonic slivers and 2)when the present lithosphere (as sampled by the Cenozoic basalts) formed.These dates will allow us to estimate the timing of lithosphere removal,assuming that it must have occurred shortly before the present lithosphereformed. Given this, it may be possible to infer the mechanism of removalof the cratonic lithosphere.