Hello:
So sorry about your beautiful tree!

Your tree’s leaves start to change colors, even under normal conditions, due to a lack of chlorophyll. It is breaking down chlorophyll faster than it’s being manufactured. This can happen when the tree starts to prepare itself for winter, or it can happen when the tree or shrub perceives a threat to its health. It is commonly a sign of stress. This is usually due to a problem with the tree's environmental conditions causing decline, usually moisture stress(too much or too little water), root damage, or the presence of insects/disease.We have had excessively hot and dry conditions for much of this summer, so your maple tree might be asking for more water.

 Not all injuries can be corrected, but the impact of the stress can often be reduced by watering heat or drought-stressed plants. It can be minimized through the proper use of mulches to help reduce the loss of water from the soil and also to protect roots from quick changes in soil temperatures. Careful inspection of the plant may show insect damage that if caught early may prevent needless injuries. If your leaves appear healthy, it may be the stress related to moisture.

I’ve included a couple articles to inform.


http://plantclinic.cornell.edu/factsheets/mapledecline.pdf

https://www.canr.msu.edu/news/how_weather_affects_fall_colors