I can only think of two possible explanations - something's been spilt where that pattern is on the grass, or there's something under the turf, like tree or shrub roots, which are fairly close to the surface. It may just recover on its own over time.

Hmm...Crop Circles!! Seriously, it looks like someone stood right about where that prominent bright yellow leaf is, and waved a watering can without a rose about with something too strong for the grass and some of the plants in the flower bed. Anyone trying to help you garden, Audrey?

I've only just realised the pictures are displaying upside down and its clearer when its rotated. So another solution occurs to me. Do you mow the grass from the middle, pushing the mower out in a pattern like the spokes of a wheel? (Often the easiest way to mow a lawn this shape)If so you might have contaminated the mower with something that has killed the grass - perhaps something a wheel went over on its way to the lawn?

Thanks guy's for your help Xx