Page 9 - i1052-5173-30-5

TABLE 1. COMPARISON AND SUMMARY OF ESTIMATES OF ENDOGENIC CO FLUXES
2
Flux type Magnitude Method(s) for estimation Reference(s)
(Mt/yr)
Cretaceous continental arcs 1 Area distribution of skarn This study
(Sierra Nevada batholith)
Cretaceous continental arcs 4–58 Analogue decarbonation model with Sierra Nevada batholith stratigraphy This study
(North America)
Cretaceous continental arcs 85–127 Mass balance calculation Lee et al. (2013)
(global)
Contact metamorphism in 0.7–11 Reactive transport model Chu et al. (2019)
continental arcs (global)
Mid-ocean ridges (global) 53–97 a Geochemical analysis of mid-ocean ridge basalt glasses; measurement a Marty and Tolstikhin (1998)
b
c
of noble gas fluxes at mid-ocean ridges; geochemical analyses of emitted b Hilton et al. (2002)
d
volatiles from mid-ocean ridges; petrologic analysis of basaltic magmas c Fischer (2008)
d Dasgupta and Hirschmann (2010)
Continental rifts 4 Gas efflux measurements Lee et al. (2016)
Mountain building 13–440 a Petrologic and geochemical measurements of exhumed metamorphic rocks; a Kerrick and Caldeira (1998)
b geochemical analysis of groundwater draining active mountain belt; geochemical a Skelton (2011)
c
analyses of hydrothermal fluids in active mountain belts; thermodynamic b Chiodini et al. (2000)
d
modeling (P-T-t path calculations) of exhumed metamorphic rocks c Becker et al. (2008)
d Stewart and Ague (2018)
fluxes appear weakly correlated with pCO other endogenic fluxes necessary, such as ACKNOWLEDGMENTS
2
from 200 Ma to present (Wong et al., 2019). organic carbon oxidation or continental rift- J. Muller and J. Ryan-Davis helped with digitizing
From our predictions, we find that the con- ing (e.g., Lee et al., 2016)? Between these maps for area calculations. We thank C.-T.A. Lee for
nection between metamorphic CO fluxes contrasting scenarios, the unifying question comments on an early draft of the paper, two anony-
mous reviewers for thorough suggestions, and M. Ducea
2
from continental arcs and atmospheric concerns the thresholds at which metamor- for careful editorial handling. All MATLAB codes used
pCO is tenuous (Fig. 3D). Beyond the simi- phic CO fluxes can be attributed to the in the analogue model and for figure generation can be
2
2
lar decreases from the Cambrian toward the development of past climates, if at all. found in the GitHub repositories of the first author:
present and the shared relative maxima Of all time periods on Earth, the Cre- https://github.com/ejramos/skarn_model and https://
prior to the Devonian, atmospheric pCO taceous period likely represents a time in github.com/ejramos/Phanerozoic_decarbonation.
National Science Foundation grant NSF-OCE-1338842
2
and metamorphic CO fluxes appear dis- which enhanced continental arc metamor- awarded to Lackey, Barnes, and others as part of the
2
connected and cannot be wholly compared phism promoted a hothouse climate. The Frontiers in Earth Systems Dynamics program sup-
without knowledge of other fluxes. emergence of deep-water calcifiers in the ported this work.
Nonetheless, times where the correlation Triassic (e.g., Ridgwell and Zeebe, 2005),
between metamorphic CO fluxes and atmo- increases in granitoid addition rates, dou- REFERENCES CITED
2
spheric pCO are weakest can be leveraged bling in length of continental arcs that inter- Ague, J.J., 2000, Release of CO from carbonate
2
2
to explore the operation of other Earth sys- sect crustal carbonates (Lee et al., 2013), rocks during regional metamorphism of litho-
tem processes. For example, between 320 and increased evidence of skarn formation logically heterogeneous crust: Geology, v. 28,
no. 12, p. 1123–1126, https://doi.org/10.1130/
and 270 Ma during icehouse conditions in within circum-Pacific batholiths (e.g., Lee 0091-7613(2000)28<1123:ROCFCR>2.0.CO;2.
the Permian, metamorphic CO fluxes and Lackey, 2015) support the plausibility Aiuppa, A., Fischer, T.P., Plank, T., and Bani, P.,
2
remain high while atmospheric pCO is low. of elevated metamorphic CO fluxes con- 2019, CO flux emissions from the Earth’s most
2
2
2
This time interval also coincides with the tributing to hothouse climate conditions in actively degassing volcanoes, 2005–2015: Scien-
waning stages of Pangea formation. Despite the Cretaceous. Our model predicts maxi- tific Reports, v. 9, no. 1, article no. 5442, https://
doi.org/10.1038/s41598-019-41901-y.
elevated metamorphic fluxes, could atmo- mum values for aureole volume fractions Baumgartner, L.P., and Ferry, J.M., 1991, A model
spheric pCO have remained low because during the Mesozoic (Fig. 3B), purporting for coupled fluid-flow and mixed-volatile miner-
2
generation of relief during supercontinent an increased proportion of aureole decar- al reactions with applications to regional meta-
assembly enhanced silicate weathering (e.g., bonation. The average metamorphic CO morphism: Contributions to Mineralogy and Pe-
2
.
West et al., 2005)? Instead, could there have flux from arcs during the Cretaceous ex- trology, v. 106, no. 3, p. 273–285, https://doi org/
10.1007/BF00324557.
been prolonged organic carbon burial as ceeds estimates for mid-ocean ridge CO Becker, J.A., Bickle, M.J., Galy, A., and Holland,
2
equatorial regions remained hot and humid fluxes (60 Mt/yr; Wong et al., 2019). Unless T.J., 2008, Himalayan metamorphic CO fluxes:
2
and forests proliferated (Ronov, 1982)? For a CO fluxes from continental rifts or oxida- Quantitative constraints from hydrothermal
2
contrasting example, in Permian–Triassic tion of organic matter were significant in springs: Earth and Planetary Science Letters,
time after Pangea’s assembly, atmospheric magnitude during the Cretaceous, conti- v. 265, no. 3–4, p. 616–629, https://doi.org/
10.1016/j.epsl.2007.10.046.
pCO increases while metamorphic CO nental arc metamorphism likely contributed Berner, R.A., and Caldeira, K., 1997, The need for
2
2
fluxes drop by a factor of 2. Does atmo- the largest fraction of CO of all endogenic mass balance and feedback in the geochemical car-
2
spheric pCO increase because the aridifica- fluxes. With further quantifications of en- bon cycle: Geology, v. 25, no. 10, p. 955–956,
2
tion of continental interiors inhibits silicate dogenic CO fluxes and their variation https://doi.org/10.1130/0091-7613(1997) 025<0955:
2
weathering? If so, can modest CO outputs through time, benchmarked against known TNFMBA>2.3.CO;2.
2
from continental arcs with diminished sili- climatic changes, the role of tectonic out- Bowman, J.R., 1998, Stable-isotope systematics of
skarns, in Lentz, D.R., ed., Mineralized intrusion-re-
cate weathering fluxes be enough to increase gassing in the evolution of Earth’s climate lated skarn systems: Quebec, Mineralogical Associa-
atmospheric pCO by a factor of 2, or are will become increasingly clear. tion of Canada, Short Course Series, v. 26, p. 99–145.
2
www.geosociety.org/gsatoday 9