Influence of Melt-Peridotite Interaction on Deformation and Seismic Properties of the Upper Mantle beneath the North China Craton

Melt-peridotite interaction can influence significantly the crystallographic preferred orientation (CPO) of olivine and thus seismic anisotropy in the upper mantle. Extensive melt-peridotite interaction had been documented in the lithospheric mantle beneath the North China Craton (NCC), a prime example of craton destruction. Yet the relationship between melt-peridotite interaction and the upper-mantle deformation and seismic anisotropy beneath the NCC remains unclear. Here we carried out a detailed study of microstructure, mineral CPO, and seismic properties on 27 peridotite xenoliths entrained by the Cenozoic basalts erupted in the Damaping area from the NCC, aiming to elucidate the influence of melt-peridotite interaction on olivine CPO and seismic properties in the upper mantle beneath the NCC. The studied samples are dominantly lherzolites (except for one harzburgite) and can be classified into two groups based on the intensity of foliation: strongly foliated and weakly foliated. Microstructural observations suggest that reactive melt percolation followed by annealing occurred in both groups of samples. However, compared with the weakly foliated samples, the strongly foliated ones recorded higher degrees of reactive melt percolation and stronger annealing, as indicated by the presence of more fine-grained undeformed grains and lower average intragranular misorientation and slightly curved to straight grain boundaries in olivine. In addition, irrespective of the CPO patterns, the strongly foliated samples display weaker olivine CPOs relative to the weakly foliated ones (J-index of 1.5-5.3 vs. 4.0-8.6). This is attributed to stronger annealing and probably higher contribution of grain-size-sensitive creep mechanism due to finer grain size as a result of melt reactive percolation in the former. Based on the calculated seismic properties, the strongly foliated samples have nearly the same seismic anisotropy patterns as the weakly foliated ones. But the maximum P-wave and S-wave polarization anisotropy for the strongly foliated samples are much weaker than those for the weakly foliated ones (4.7% vs. 9.1% and 4.6% vs. 9.6%, respectively). These data point to a strong control of intensity of melt-peridotite interaction on deformation and seismic properties of the upper mantle beneath the NCC.