Crustal and upper mantle structure along a profile from the southern Central Asian Orogenic Belt to the northern Ordos Basin and its tectonic implications
In the regions from the northern Ordos Basin to the Central Asian Orogenic Belt(CAOB),many major geologic events have successively happened,such as the craton formation in the early Pre-Cambrian,the closure of the Paleo-Asian Ocean in the Paleozoic,the intra-continental orogeny in the Mesozoic,and the rifting and sagging since the Cenozoic.There are large scales of energy and mineral resources,and the Hetao Seismic Belt,and thus the characteristics of the crustal and upper mantle structure would be helpful to reveal the geological evolution and mechanisms of resource enrichment and seismogenesis.In this paper,constrained by the P-wave velocity model constructed by a Deep Seismic Sounding(DSS)investigation along the same south-northward profile from Mandula Town in the Inner Mongolia Autonomous Region to Yanchuan County in the northern Shaanxi Province,China,we carried out the joint inversion of multi-frequency P-wave receiver functions(RFs)and surface wave dispersions to obtain the S-wave velocity model beneath the profile.And then,we conducted the Common Conversion Point(CCP)stacking of RFs to construct the geometric structure of the crust and upper mantle constrained by both models derived from the DSS and joint inversion mentioned above.Some characteristics of the crustal and upper mantle structure along this profile are revealed and listed as follows:(1)the Moho topography fluctuates within the range of 35～48 km,and shows a nearly symmetric pattern centered by the Hetao Graben System and featured by step-wise converging and deepening Moho discontinuity;(2)the Moho discontinuity beneath the Hetao Graben System is uplifted with a dome shape,and the domal area coupled with upper mantle low-velocity zone is just beneath the Khondalite Belt;(3)the seismicity in the transition zone of the Daqingshan,Wulashan,and Sertengshan mountains,show two spatially isolated patterns of the flower structure with distinct velocity architectures.These features indicate(1)the crustal pattern beneath the north part of the profile mainly reflects the strong north-south compression and shortening deformations induced by B-episode events of the Yanshanian Movement within a tectonic framework of the amalgamation of the Ordos and Yinshan blocks in the Paleo-Proterozoic and the orogeny of the CAOB in the Paleozoic,and also impose the subsequently extensional deformation since the Cenozoic,especially from the strong rifting and sagging since the Neogene;(2)At the collision zone between the Ordos and Yinshan blocks,was the rifting of the Hetao Graben System initiated in the Oligocene,which implying the junction zone between the continental nuclei of the craton is still tectonically weak up to today;and(3)the Daqingshan and Sertengshan piedmont faults are the major faults with normal and striking senses,while the Wulashan piedmont fault and the northern marginal fault both play the adjusting roles between them.The seismogenic fault of the 1996 Baotou Ms6.4 earthquake is likely the deeply extending part of the eastern part of the south-dipping Sertengshan piedmont fault.
Central Asian Orogenic BeltYinshan Orogenic BeltHetao Graben SystemOrdos BasinJoint inversion of receiver function and surface wave dispersionCrustal and upper mantle structureFlower structure1996 Baotou Ms6.4 earthquake
万方数据
维普
