DOI: 10.25349/d94k79
title: Dataset for: Heat Transfer and Production in Cratonic Continental Crust: Constraints from U-Pb Thermochronology of Xenoliths from the Siberian Craton

description: Coupled U-Pb and trace-element analyses of accessory phases in crustal
 xenoliths from the Late Devonian Udachnaya kimberlite (Siberian
 craton, Russia) are used to constrain Moho temperature and crustal heat
 production at the time of kimberlite eruption. Rutile and apatite
 in lower-crustal garnet granulites record U-Pb dates that extend from 1.8
 Ga to 360 Ma (timing of kimberlite eruption). This contrasts with
 upper-crustal tonalites and amphibolites that contain solely
 Paleoproterozoic apatite. Depth profiling of rutile from the lower-crustal
 xenoliths show that U-Pb dates increase gradually from rim to core over
 µm-scale distances, with slower-diffusing elements (e.g., Al) increasing
 in concentration across similar length-scales. The U-Pb and trace element
 gradients in rutile are incompatible with partial Pb loss during slow
 cooling, but are consistent with neocrystallization and re-heating of the
 lower crust for &lt;1 Myr prior to eruption. Because Paleoproterozoic
 rutile and apatite dates are preserved, we infer that long-term ambient
 lower-crustal temperatures before this thermal perturbation were cooler
 than the Pb closure temperature of rutile and probably apatite
 (&lt;400 °C). The lower-crustal temperature bounds from these data are
 consistent with pressure-temperature arrays of Udachnaya peridotite
 xenoliths that suggest relatively cool geothermal gradients, signifying
 that the mantle xenoliths accurately capture the thermal state of the
 lithosphere prior to eruption. Combined, the xenolith data imply low
 crustal heat production for the Siberian craton (~0.3
 µW/m3). Nevertheless, such values produce surface heat flow
 values of 20–40 mW/m2, higher than measured around Udachnaya (average 19
 mW/m2), suggesting that the surface heat flow measurements are inaccurate.
description: <strong>Electron probe
 microanalyses</strong> Quantitative elemental
 analyses of major mineral phases were done using a Cameca SX-100 electron
 probe micro analyzer (EPMA) housed at the University of California, Santa
 Barbara (UCSB). Measurements were made using the following beam
 conditions: an accelerating voltage of 20 kV, a beam current of 200 nA and
 a defocused beam of 2–5 µm diameter. A series of natural and synthetic
 standards were analyzed for calibration purposes.
 <strong>Laser ablation split-stream
 analyses</strong> The xenoliths were processed
 using standard mineral separation techniques to recover whole grains (hand
 crushing, magnetic separation, and heavy liquid separation). Coupled U-Pb
 and trace element analyses on zircon, rutile, and apatite were done by
 laser ablation split stream inductively coupled plasma mass spectrometry
 (LASS) at UC Santa Barbara (Kylander-Clark et al., 2013; Kylander-Clark,
 2017). Analyses were conducted on polished grain interiors for
 conventional LASS analyses and on the unpolished exterior of whole grains
 for depth profiling. Analytical protocols are detailed in Supplementary
 Information. The quoted uncertainties for all laser ablation data are 2σ
 and incorporate analytical uncertainty as well as additional uncertainties
 associated with reproducibility of secondary matrix-matched reference
 materials (RMs) (Horstwood et al., 2012). Reported uncertainties for
 trace-element data are 2σ and only include analytical uncertainties. All
 U-Pb data are shown in Tera-Wasserburg concordia plots (Vermeesch, 2018)
 and are uncorrected for common-Pb. The quoted U-Pb dates for apatite and
 rutile are common-Pb corrected using a common-Pb intercept defined by a
 linear regression through the U-Pb data or assuming a Stacey and Kramers
 (1975) initial <sup>207</sup>Pb/<sup>206</sup>Pb
 composition. The quoted dates for zircon
 are <sup>207</sup>Pb/<sup>206</sup>Pb dates that
 are within 5% concordance of their
 respective <sup>206</sup>Pb/<sup>238</sup>U
 date. The sampling resolution of laser ablation spot
 analyses described above (50-µm-diameter spots for rutile) is too coarse
 to resolve age gradients. For this reason, depth profiling was done using
 continuous laser pulsing at a low frequency (e.g., Cottle et al., 2009b;
 Smye and Stockli, 2014; Holder et al., 2019; Apen et al., 2020; Garber et
 al., 2020). Details regarding depth profiling are also reported in the
 Supplementary Information. Final pit depths were measured on the SEM and
 are on average ~13 µm. The depth profile data are reported at 1 s
 intervals and the reported U-Pb uncertainties take into account the
 reproducibility of multiple reference rutiles (~6%
 on <sup>238</sup>U/<sup>206</sup>Pb and ~4%
 on <sup>207</sup>Pb/<sup>206</sup>Pb). In addition
 to U-Pb ratios, we also report Pb concentration profiles, which we divided
 into radiogenic Pb (Pb*) and non-radiogenic (common) Pb
 (Pb<sub>c</sub>) (see also Holder et al., 2019; Garber et al.,
 2020). The total concentrations of <sup>207,206</sup>Pb at
 each depth interval were calculated using the
 measured <sup>238</sup>U/<sup>206</sup>Pb
 ratio, <sup>207</sup>Pb/<sup>206</sup>Pb ratio,
 and U concentration and assuming an
 invariant <sup>238</sup>U/<sup>235</sup>U ratio of
 137.818 (Heiss et al., 2012). Concentrations
 of <sup>207,206</sup>Pb* were determined using common-Pb
 corrected dates and measured U concentrations. From this, we calculated
 the proportion of Pb<sub>c</sub> by
 subtracting <sup>207,206</sup>Pb* from the
 total <sup>207,206</sup>Pb concentrations. The
 final <sup>207,206</sup>Pb* profiles were further corrected
 for radiogenic Pb ingrowth following kimberlite eruption at 360
 Ma.
description: Folder contains a README.txt file and data to reproduce figures
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