THE RISE OF NEW GUINEA AND THE FALL OF NEOGENE GLOBAL TEMPERATURES

The Earth’s long-term climate is controlled by the concentration of CO₂ in the ocean-atmosphere system, which is set by sources and sinks of carbon and the silicate weathering feedback. On geological timescales, the main source of CO₂ is volcanism, while the main sink of CO₂ is the chemical weathering of silicate rocks, with ultramafic and mafic lithologies being especially efficient sinks. Thus, a long-term change in either CO₂ outgassing or weatherability has the potential to shift the climate to a warmer or cooler equilibrium. Proxy records suggest that global temperatures were on the order of 10°C warmer than present from ~19-10 Ma, cooling after 10 Ma to modern temperatures by ~6 Ma. It remains unknown if this cooling trend was the result of a decrease in volcanic CO₂ outgassing, an increase in global weatherability, or some combination.

The Central Range of New Guinea hosts the Iran Jaya ophiolite, which is one of the largest ophiolites in the world and is situated in the warm, wet tropics. Here we reconstruct the Central Range orogeny of New Guinea using new zircon U-Pb, new zircon and apatite (U-Th)/He (ZHe and AHe), and existing zircon and apatite fission-track (ZFT and AFT) data. We combine these data with a palinspastic reconstruction of the belt and use the thermokinematic model Pecube to derive a detailed topographic, erosional, and structural history of the arc-continent collision that led to the Central Range orogeny. These data reveal rapid exhumation, erosion, and the generation of steep topography in New Guinea between 10-6 Ma. The coupled climate and weathering model GEOCLIM demonstrates that this paleogeographic change in the tropics would have increased both erosion and global weatherability from the Miocene to present. The timing and scale of the rise of New Guinea suggests that it contributed to Neogene global cooling.