Complex sentence: First the Arabian-Nubian Shield collided with eastern Africa (in the Kenya-Tanzania region) in the East African Orogeny, then Australia and East Antarctica were merged with the remaining Gondwana in the Kuunga Orogeny.
Split into simpler sentences: First the Arabian-Nubian Shield collided with eastern Africa (in the Kenya-Tanzania region) in the East African Orogeny. Then Australia and East Antarctica were merged with the remaining Gondwana in the Kuunga Orogeny.