Lateral variations of crustal structure beneath the Indochina Peninsula

Abstract

Crustal thickness (H) and Vp/Vs (κ) measurements obtained by stacking P-to-S receiver functions recorded at 32 broadband seismic stations covering the Indochina Peninsula reveal systematic spatial variations in crustal properties. Mafic bulk crustal composition as indicated by high κ (>1.81) observations is found to exist along major strike-slip faults and the southern part of the Peninsula, where pervasive basaltic magmatism is found and is believed to be the results of lithospheric thinning associated with the indentation of the Indian into the Eurasian plates. In contrast, crust beneath the Khorat Plateau, which occupies the core of the Indochina Block, has relatively large H values with a mean of 36.9 ± 3km and small κ measurements with an average of 1.74 ± 0.04, which indicates an overall felsic bulk composition. Those observations for the Khorat Plateau are comparable to the undeformed part of the South China Block. The laterally heterogeneous distribution of crustal properties and its correspondence with indentation-related tectonic features suggest that the Indochina lithosphere is extruded as rigid blocks rather than as a viscous flow.