The Lower Crust and Moho Structure Beneath the Great Xing’an Ranges in Northeast China: Revealed by the Large Dynamite Shots

Abstract:

The eastern segment of the Central Asian Orogenic Belt (CAOB) is in the superimposed area of the three major structural domains, which are the Paleo Asian Ocean, the Mongolian Okhotsk and the Paleo Pacific. The Great Xing’an Ranges, whose tectonic structure mainly formed during the evolution of the Paleo Asian Ocean, is one of the important parts to construct the CAOB. However, whether there is a mountain root beneath the Great Xing’an Ranges is still in controversy.

In order to propose new ideas about this issue, we get one 400-kilometer-long deep seismic reflection profile, which starts from the western Songliao Basin, across the main part of the Great Xing’an Ranges, and ends at eastern Hailar Basin. This profile contains 27 large dynamite shots which were acquired by exploding in the deep well and receiving via far offset, therefore, large dynamite shots specialize in tracking the fine structure and lateral variation of lower crust and Moho structure.

After Data Analysis, Pre-Processing, Statics Correction, Noise Attenuation and NMO, we get 27 dynamite shots profiles. Finally, we rearrange these profiles according to the location of shots and we obtain one large dynamite shots’ single profile of near-vertical reflection, describing the formation and evolution of the Great Xing’an Ranges. Beneath the Great Xing’an Ranges, a relatively flat Moho structure is obtained which is located at around TWT 12s (about 36 kilometers thick). And the Moho beneath the Songliao Basin is shallower. In the lower crust, there are several large-scale arc-shaped reflections, which may be related to the magmatic activity in Mesozoic. The flat Moho is usually related to the post-orogenic extension of the crust.