Complex sentence: Backarc rift zones and spreading centers can only develope in the rheologic weaker oceanic crust in the magmatic (volcanic) islands arcs because the oceanic crust is too rigid to break up like continental crust (east Africa, Breakup of Pangaea).
Split into simpler sentences: Backarc rift zones and spreading centers can only develope in the rheologic weaker oceanic crust in the magmatic (volcanic) islands arcs. Becauese the oceanic crust is too rigid to break up like continental crust (east Africa, Breakup of Pangaea).