Certified GKH Gardening Expert
Did you have a cold snap in your area? An unexpected frost can kill off new growth, but it will regrow shortly, if this is the case. But, you did describe lots of dead wood and new shoots from the base. This would indicate that maybe you had more than a light frost. If you had a hard freeze, it may have caused this damage.
It may also be caused by a fungus. Typically fungus that attack the leaves are not lethal to the plant, but can weaken it and is unsightly. You can treat the tree with a fungicide to help with this.