Need help recovering files.

So I had installed OS X 10.10 on my 2013 iMac to try it out since my MBP is my main computer anyways. However, my iMac is my media hub with much more files loaded onto its 3TB drive.

I got tired of messing with Yosemite and went about downgrading to Mavericks. My plan was to create a new Mavericks partition, move everything over to it, delete the Yosemite partition and bring that free space back to the Mavericks partition.

I successfully made the 10.9 partition, installed 10.9, and spent quite a while moving everything back over. Then, I rebooted the iMac into the installer via USB and go to Disk Utility. From there I saw an option to merge my existing, working Mavericks install with the 10.10 partition. I clicked that, and it told me that everything on Mavericks partition would be erased to do this.

Since that wasn't what I wanted, I hit cancel...or so I thought. Instead, cancel must have been the highlighted (blue) button and the execute button was the white one (which I assumed was cancel). So since I mistakenly didn't take the time to read the buttons, I hit Erase.

As soon as it said "Preparing to erase drive", I shut the iMac off and rebooted it. My Yosemite partition is still there, albeit with no OS because I cleared it a few moments before this within Disk Utility. But now, of course, my Mavericks partition that had all of my files is now unable to be found.

I know that since I didn't leave it any time to delete anything (or very little if it had), these files are somewhere. But how do I access them now? I do have my MBP and Thunderbolt cable to help. The iMac is currently in target disk mode, but all I can see is the blank Yosemite partition.

Sorry for the long post, just wanted to fully explain the situation. Your help is very much appreciated!

 

Also, is there any chance my Time Capsule will restore Yosemite backups to Mavericks? If so then that will be a feasible (although dreadfully time consuming) solution.

 

Thanks! That worked, and it was pretty easy. My biggest problem was recovering the 500GB of space I lost when I stupidly shut off the computer as it was preparing to erase the working partition. But I finally managed to get my fusion drive back to its full 3.12TB capacity and restored everything back on Mavericks.