The Papua New Guinea (PNG) Mobile Belt adjacent to the Finisterre Arc was formerly the leading NE corner of the Australian plate that converged obliquely with the Pacific plate. Forty new apatite and zircon fission track analyses of Mobile Belt rocks previously dated by K-Ar and Rb-Sr analyses constrain Neogene time-temperature paths and tectonic models. The Paleogene arc along the southern margin of the Caroline plate was juxtaposed against PNG in the early Miocene, coeval with locking up of the west dipping Solomon subduction zone by the Ontong Java Plateau. These events initiated wrenching along the northern PNG margin and increased westward subduction of the Solomon Sea plate beneath the eastern margin. The Mobile Belt underwent extension above the downgoing slab with rapid cooling of metamorphic rocks at ~17 Ma, immediately prior to emplacement of the Maramuni Arc from 17 to 12 Ma. A change in plate motion at ~12--10 Ma terminated the arc and caused PNG-Caroline plate convergence, creating the orogenic belt in New Guinea from 12 to 4 Ma. This resulted in ~4.5 km of uplift and ~3 km of denudation and cooling of the entire Mobile Belt in the late Miocene, propagating westward along the Mobile Belt at 8--5 Ma and southward into the Fold Belt at 5--4 Ma. The compression caused thrusting of Miocene strata within the Mesozoic type section. A further change in plate motion at 4--3 Ma returned the margin to transpression with local compression along strike-slip faults and ongoing collision of the Finisterre Arc terrane. ¿ 1999 American Geophysical Union