Partial Melting of Deeply-Subducted Eclogite: Implications for Melt Transport, Rheology, and Decratonization (Invited)

We report textural and geochronological data from melts derived from deeply-subducted eclogite in the Sulu orogen, China that are similar in composition and age to melts thought to be responsible for the thermo-chemical erosion of the root of the North China craton. Successive stages of partial melting are preserved from initial grain boundary melting to small pockets of melt accumulation in pressure shadow areas, which then aggregate to form melt channels and dykes that transported large volumes of magma from the melting region to higher in the lithosphere. This is the direct evidence from outcrop scale indicating partial melting from the deeply subducted eclogite. This has important implications for interpreting seismic signals and the rheological structure and mechanical behaviour of the deep crust, the interaction between deformation and magmatic processes, and melt transportation proceses in deeply subducted lithosphere. Partial melting of eclogite from deeply subducted oceanic or lower continental crust may be an important process in determining the mechanical behavior of subducted lithosphere and its rapid exhumation, for flow of deep crustal material, and for destruction of cratonic roots. Field photos and sketches showing the partial melting process: I. Early stage of partial melting, finger shaped melts start to aggregate within the hinge of the isoclinal eclogite fold; II. Medium stage of partial melting, melt channels interlayered and flowing surrounding the sheared folded eclogite; III. Mature stage of partial melting, melt aggregates into larger scale and form the felsic melt as a dyke.