Am Mam Intrusion Breccia help

Hi, I am carrying out a mapping project on the Isle of Rum and have mapped the Am Mam Intrusion Breccia. I am struggling to work out how it formed, a current theory is that the main ring fault formed fault breccia of the existing rocks which was then picked up by the diorite matrix as it was forced through the fault breccia by the pressure created by the collapse of the caldera. This seems to make sense but I am not sure that this is the whole truth, any help would be appreciated.