Continental arc-island arc fluctuations, growth of crustal carbonates, and long-term climate change

Abstract

The Cretaceous to early Paleogene (ca. 140-50 Ma) was characterized by a greenhouse baseline climate, driven by elevated concentrations of atmospheric CO 2. Hypotheses for the elevated CO 2 concentrations invoke an increase in volcanic CO 2 production due to higher oceanic crust production rates, higher frequency of large igneous provinces, or increases in pelagic carbonate deposition, the last leading to enhanced carbonate subduction into the mantle source regions of arc volcanoes. However, these are not the only volcanic sources of CO 2 during this time interval. We show here that ocean-continent subduction zones, manifested as a global chain of continental arc volcanoes, were as much as 200% longer in the Cretaceous and early Paleogene than in the late Paleogene to present, when a cooler climate prevailed. In particular, many of these continental arcs, unlike island arcs, intersected ancient continental platform carbonates stored on the continental upper plate. We show that the greater length of Cretaceous-Paleogene continental arcs, specifi cally carbonate-intersecting arcs, could have increased global production of CO 2 by at least 3.7-5.5 times that of the present day. This magmatically driven crustal decarbonation fl ux of CO 2 through continental arcs exceeds that delivered by Cretaceous oceanic crust production, and was suffi cient to drive Cretaceous-Paleogene greenhouse conditions. Thus, carbonate-intersecting continental arc volcanoes likely played an important role in driving greenhouse conditions in the Cretaceous-Paleogene. If so, the waning of North American and Eurasian continental arcs in the Late Cretaceous to early Paleogene, followed by a fundamental shift in western Pacifi c subduction zones ca. 52 Ma to an island arc-dominated regime, would have been manifested as a decline in global volcanic CO 2 production, prompting a return to an icehouse baseline in the Neogene. Our analysis leads us to speculate that long-term (>50 m.y.) greenhouse-icehouse oscillations may be linked to fl uctuations between continental-and island arc-dominated states. These tectonic fl uctuations may result from large-scale changes in the nature of subduction zones, changes we speculate may be tied to the assembly and dispersal of continents. Specifi cally, dispersal of continents may drive the leading edge of continents to override subduction zones, resulting in continental arc volcanism, whereas assembly of continents or closing of large ocean basins may be manifested as large-scale slab rollback, resulting in the development of intraoceanic volcanic arcs. We suggest that greenhouse-icehouse oscillations are a natural consequence of plate tectonics operating in the presence of continental masses, serving as a large capacitor of carbonates that can be episodically purged during global fl are-ups in continental arcs. Importantly, if the global crustal carbonate reservoir has grown with time, as might be expected because platform carbonates on continents do not generally subduct, the greenhouse-driving potential of co...

Arc volcanism, carbonate platform evolution and palaeo-atmospheric CO<sub>2</sub>: Components and interactions in the deep carbon cycle

“…Cretaceous and late Palaeogene, due to the greater size of carbonate reservoirs in continents and the increased continental arc lengths (Lee et al, 2013;Carter and Dasgupta, 2015;McKenzie et al, 2016;Cao et al, 2017). Our results agree well with the hypothesis, as a relative increase in CIA lengths has been linked to a peak in atmospheric CO2 from 75-50 Ma, contributing to enhanced CO2 degassing.…”

“…Despite the proposal that silicate weathering has, at some stages, been a dominating control of atmospheric CO2 levels (Kump, 2000;Kent and Muttoni, 2013), arc magmatism at icehousegreenhouse transitions is thought to be the first-order control on climate fluctuations while silicate weathering acts to modulate atmospheric CO2 as a secondary regulative process (Ridgwell and Zeebe,20 2005; Lee and Lackey, 2015;McKenzie et al, 2016). Recent studies have found support for links between global arc activity and icehouse-greenhouse transitions using detrital zircon ages, modelling and experimental techniques, particularly as drivers of greenhouse conditions in the Cambrian (McKenzie et al, 2016;Cao et al, 2017), Jurassic-Cretaceous (McKenzie et al, 2016) and early Paleogene (Lee et al, 2013;Carter and Dasgupta, 2015;Cao et al, 2017). 25 Recently, carbon and helium isotope analysis from modern volcanic arc gas has provided evidence that volcanic arcs that assimilate crustal carbonate in their magmas through decarbonation reactions have a greater atmospheric CO2 contribution than other types of arcs (Mason et al, 2017).…”

“…Modern crustal carbonate reservoirs are a result of global organic and inorganic carbonate production throughout the Phanerozoic, which has contributed to the build-up of expansive, shallow-water carbonate sequences 5 including ramps and rimmed shelves along continental margins, hereafter referred to as 'carbonate platforms' (Kiessling et al, 2003). At different points in Earth's history, emissions from continental, carbonate-intersecting arcs (CIAs) may have dominated global volcanic carbon flux, such as during the Cretaceous (144-65 Ma) where continental arcs are hypothesised to have been longer than modern day lengths and where a greenhouse climate prevailed (Lee et al, 2013;van der Meer et al, 2014;Cao et al, 10 2017). It is plausible that crustally-derived carbon at other points in Earth's history has played a significant role in affecting global climate (Lee and Lackey, 2015), yet it is difficult to test this hypothesis, especially due to preservation bias in the geological record (Berner, 2004).…”

“…the planetary cycling of carbon over million-year timescales) attributes fluctuations in the atmospheric carbon dioxide (CO2) to the realm of tectonic forces, where arc-volcanic emissions (Van Der Meer et al, 2014;Kerrick, 2001) and metamorphic decarbonation 10 (Lee et al, 2013) are major CO2 sources, and the processes of silicate weathering (Sundquist, 1991;Kent and Muttoni, 2008) and marine organic carbon burial (Berner and Caldeira, 1997;Ridgwell and Zeebe, 2005) are major sinks removing CO2 from the atmosphere. Subduction plays a critical role in this cycle.…”

Did high Neo-Tethys subduction rates contribute to early Cenozoic warming?

“…To avoid overestimations of CO 2 production, we assumed that only limited margin sediment decarbonation may have occurred after the onset of continental subduction at low-grade conditions, with a 1 to 10 wt% efficiency. Time necessary for subducted margin material to reach the 300 • C isotherm after the onset of continental subduction at ∼ 55-50 Ma (corresponding to 25 km depth with a normal-subduction geothermal gradient of 15 • C km −1 ) was set to 0.5 Ma, as calculated with parameters of Leech et al (2005). Circulation of CO 2 -rich fluids along large-scale collision-related thrust detachments has been proposed as an efficient way to promote degassing at the surface (e.g., Kerrick and Caldeira, 1993;Becker et al, 2008).…”