Preheat oven to 375 degrees. In a food processor, pulse flour, brown sugar, butter, and salt until combined. In a large bowl, toss together blackberries, tapioca, granulated sugar, and orange zest and juice. Pour blackberry mixture into a 2-quart baking dish. Sprinkle evenly with flour mixture. Bake until topping is golden and juices are bubbling, 50 minutes. Let cool 20 minutes. Serve warm or at room temperature.