reSeArCH Letter
Methods
KDEs (Figs. 1 , 2a) and bimodal mixed-Gaussian distributions (Fig. 2b, Extended
Data Table 1) were calculated using the ksdensity and fitgmdist functions, respectively,
of Matlab release R2018b. The linear regressions and corresponding 95% confidence
envelopes, shown in Fig. 2c, were calculated by Monte Carlo analysis (number of
regressions: 10,000). For each regression, values of T/P and age were selected at
random from each modelled Gaussian distribution (Fig. 2b, Extended Data Table 1)
and the age ranges used to bin the data for the mixed-Gaussian fitting (0–0.2 Gyr,
0.2–0.85 Gyr, 0.85–1.4 Gyr and 1.4–2.2 Gyr). To plot mantle potential temperatures
(temperature corrected adiabatically for pressure) from ref.^22 in Fig. 3 , the reported
‘magma-generation’ (P, T) conditions for ‘depleted mantle’ compositions were used
and corrected for pressure assuming a liquid adiabat of 30 °C GPa−^1. Quadratic
regressions and 95% prediction envelopes of the mantle potential temperature
(Fig. 3 ) were calculated using the curve-fitting toolbox of Matlab release R2018b.
Data availability
The metamorphic pressure and temperature data used in this study are avail-
able online with their original publication (ref.^4 ) and in the EarthChem
community data repository (http://www.earthchem.org/library; doi:10.1594/
IEDA/111316).
Acknowledgements This work was funded by the Morton K. Blaustein
Department of Earth and Planetary Sciences at Johns Hopkins University. T.E.J.
acknowledges support from the State Key Laboratory for Geological Processes
and Mineral Resources, China University of Geosciences, Wuhan (Open
Fund GPMR210704). R. Rudnick and B. Hacker provided helpful discussion
in the project’s infancy. The authors thank P. Cawood and R. Stern for their
constructive reviews of this work.Author contributions R.M.H.: conceptualization, formal analysis, methodology,
visualization and writing (original draft, review and editing). D.R.V.: funding
acquisition, visualization and writing (original draft, review and editing). M.B.:
data curation, investigation, visualization and writing (original draft, review and
editing). T.E.J.: data curation, investigation, visualization and writing (original
draft, review and editing).Competing interests The authors declare no competing interests.Additional information
Correspondence and requests for materials should be addressed to R.M.H.
Peer review information Nature thanks Peter Cawood and Robert Stern for their
contribution to the peer review of this work.
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