Microstructural and seismic characteristics of oriented mantle xenoliths
from Damaping area, and their geodynamic implications of North China
Craton destruction
Abstract
The large-volume lithospheric mantle xenoliths around the Damaping area
provides valuable insights into the detailed destruction progression of
the North China Craton (NCC). This paper presents a quantitative
analysis of the microstructural and seismic properties of oriented
mantle xenoliths (with distinct foliation and lineation). The selected
peridotites have either coarse-grained (CG) or coarse-grained and
elongated (CGE) textures. The olivine crystallographic preferred
orientations (CPOs) are predominantly B-type in CG samples and AG-type
in CGE samples, with all xenoliths have girdled olivine [100] and
[001] characteristics. Analysis of crystallographic vorticity axis
(CVA) projections indicates that the majority of Damaping xenoliths have
CVA maxima (sub)parallel to the lineation. These microstructure
characteristics suggest that B-type CPOs were formed before the onset of
pure shear-based transpression, which significantly influenced the
lithospheric mantle evolution. The upwelling asthenosphere beneath
Eastern Block of the NCC not only delaminated its lithospheric mantle
but also experienced rollback and flowed along the NWW-SEE direction.
This progression likely serves as the primary driving force of
transpression. If foliation were vertical and lineation were horizontal,
the valid S-wave anisotropies range is 5-12%. All selected samples are
spinel facies, resulting in a maximum in-situ depth of 90 km, and the
calculated SKS splitting delay times (0.5-1.3 s) align with previous
seismological observations. The SKS direction in the research area is
predominantly oriented perpendicular (NNE-SSW) to the flow direction of
nearby asthenosphere. These characteristics are likely attributed to
transpression. Therefore, the “fossil” anisotropy may have developed
after the cessation of transpression.