Context : The origin of coronal type-II radio bursts and the nature of their band-splitting are still not fully understood , though a number of scenarios were proposed to explain them .
This is largely due to the lack of detailed spatially resolved observations of type-II burst sources and of their relations to magnetoplasma structure dynamics in parental active regions .

Aims : To make progress in solving this problem on the basis of one extremely well observed solar eruptive event .

Methods : The relative dynamics of multi-thermal eruptive plasmas , observed in detail by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and of the harmonic type-II burst sources , observed by the Nançay Radioheliograph at ten frequencies from 445 to 151 MHz , is studied for the 3 November 2010 event arising from an active region behind the east solar limb .
Special attention is given to the band-splitting of the burst .
Analysis is supplemented by investigation of coronal hard X-ray ( HXR ) sources observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager .

Results : It is found that the flare impulsive phase was accompanied by the formation of a double coronal HXR source , whose upper part coincided with the hot ( T \approx 10 MK ) eruptive plasma blob .
The leading edge ( LE ) of the eruptive plasmas ( T \approx 1 - 2 MK ) moved upward from the flare region with the speed of v \approx 900 - 1400 km s ^ { -1 } .
The type II burst source initially appeared just above the LE apex and moved with the same speed and in the same direction .
After \approx 20 s it started to move about twice faster , but still in the same direction .
At any given moment the low frequency component ( LFC ) source of the splitted type-II burst was situated above the high frequency component ( HFC ) source , which in turn was situated above the LE .
It is also found that at a given frequency the HFC source was located slightly closer to the photosphere than the LFC source .

Conclusions : Based on the set of established observational facts it is concluded that the shock wave , which could be responsible for the observed type-II radio burst , was initially driven by the multi-temperature eruptive plasmas , but later transformed to a freely propagating blast shock wave .
The most preferable interpretation of the type-II burst splitting is that its LFC was emitted from the upstream region of the shock , whereas the HFC – from the downstream region .
The shock wave in this case could be subcritical .