Paper No. 146-12
Presentation Time: 11:45 AM
PLATE TECTONIC DRIVEN CHANGES IN PLANETARY WEATHERABILITY AS THE LONG-TERM CONTROL OF EARTH'S CLIMATE STATE
Long term changes in Earth’s climate resulting in shifts between prolonged non-glacial and glacial intervals are widely considered to result from plate tectonic processes. However, the primary tectonic drivers for long-term climatic variability remain unclear. On geological time-scales, CO2 is emitted primarily by volcanism and consumed primarily by the chemical weathering of silicate rocks. Prolonged imbalances between sources and sinks would catastrophically manifest in either the onset of a Snowball Earth or a runaway greenhouse. The relative clemency of Phanerozoic climate requires that CO2 sinks scale with sources, which can be explained through the silicate weathering feedback where elevated CO2 leads to higher temperatures and invigorated hydrological cycling that enhances chemical weathering and vice versa. Given that CO2 sources and sinks must equal on long timescales, what sets steady-state CO2 levels on Earth at a given time? And what determines whether Earth is in a glacial or non-glacial climate state? The concept of global weatherability is a useful framework to address these questions. On a more weatherable planet, the CO2 concentration needed for the sink to equal the source is lower than on a less weatherable planet where CO2 increases until high enough levels are reached for the chemical weathering flux to be sufficiently large. Global weatherability is the product of variables such as lithology, tectonic uplift rates, and paleolatitude, which are set by evolving plate tectonic boundary conditions. In this contribution, we evaluate long-term changes in paleogeography and mountain-building and their connections to Phanerozoic climate. We seek to test the hypothesis that ocean basin closure, arc-continent collision and ophiolite exhumation exert a major control on Earth's climate state by enhancing global weatherability. Using paleogeographic models, we reconstruct the past position of a new database of ophiolite-bearing sutures. We find that when extensive arc-continent collisions have occurred in the tropics the Earth has experienced a glacial climate, and otherwise, the Earth has been in a non-glacial climate state. We interpret plate tectonic driven changes in rock type and topography in the tropics to be the most significant control on Earth’s long-term climate state.