The distribution of water in the upper mantle is believed to have strong influence upon global dynamics by influencing mantle rheology, modal mineralogy, melting systematics and chemical differentiation. The principal input of water is the process of subduction which is estimated to have introduced several ocean volumes to the mantle over Earth history. In principal, a large proportion of this water may be dissolved in the nominally anhydrous silicate minerals (NAMs), but quantifying this has been challenging. Xenoliths only sample the upper 200 km, less mostly, and suffer concern about alteration on the way to emplacement. Recent laboratory data show that seismic velocity is not sensitive to intracrystalline hydration. However, electrical conductivity is strongly sensitive and could provide estimates of mineral water content with suitable constraints. An 1300 km E-W transect of ~400 magnetotelluric (MT) soundings spanning the period range 0.01 to 17,480 s has been acquired from the northern California coast over the Gorda plate, across the Great Basin of Nevada and western Utah, and spanning most of the Colorado Plateau of eastern Utah. Regularized 2D inversion reveals an upper mantle whose resistivity below the broad Great Basin falls progressively with depth from values of ~100 ohm-m near 50 km to <10 ohm-m by 400 km depth. We test the hypothesis that the vertical resistivity profile is consistent with the maximal hydration degree allowed by ambient T-P short of triggering H2O-undersaturated melting (cf. Ardia, 2012, EPSL). An obvious possible source of hydration would be the Gorda, and to some extent the prior Farallon, subducting plates. Assuming standard and enhanced adiabats, deep resistivity profiles predicted using lab data of Novella (2017, Sci Rpts) suggest only resistivities in the near ‘hanging wall’ of the Gorda subduction zone under northwestern Nevada are low enough to represent full NAMs hydration. Under the central (eastern Nevada) and eastern (western Utah) Great Basin, large-scale resistivities are 2-3x too high, nominally. However, channelization of fluid upward from the plate could mean a mixed saturated-unsaturated peridotite upper mantle. Support has been from U.S. Dept of Energy contract DE-0006732 and National Science Foundation grants EAR-0838043 and OPP-1443532, and numerous prior.

We present PetroChron Antarctica, a new relational database including petrological, geochemical and geochronological datasets along with computed rock properties from geological samples across Antarctica. The database contains whole-rock geochemistry with major/trace element and isotope analyses, geochronology from multiple isotopic systems and minerals for given samples, as well as an internally consistent rock classification based on chemical analysis and derived rock properties (i.e., chemical indices, density, p-velocity and heat production). A broad range of meta-information such as geographic location, petrology, mineralogy, age statistics and significance are also included and can be used to filter and assess the quality of the data. Currently, the database contains 11,559 entries representing 10,056 unique samples with varying amounts of geochemical and geochronological data. The distribution of rock types is dominated by mafic (36%) and felsic (33%) compositions, followed by intermediate (22%) and ultramafic (9%) compositions. Maps of age distribution and isotopic composition highlight major episodes of tectonic and thermal activity that define well known crustal heterogeneities across the continent, with the oldest rocks preserved in East Antarctica and more juvenile lithosphere characterising West Antarctica. PetroChron Antarctica allows spatial and temporal variations in geology to be explored at the continental scale and integrated with other Earth-cryosphere-biosphere-ocean datasets. As such, it provides a powerful resource ready for diverse applications including plate tectonic reconstructions, geological/geophysical maps, geothermal heat flow models, lithospheric and glacial isostasy, geomorphology, ice sheet reconstructions, biodiversity evolution, and oceanography.

Geothermal heat flux (GHF) is an important basal boundary condition for models of ice sheet dynamics, but is poorly constrained by conventional borehole-based estimates. The accuracy and uncertainties associated with geophysical proxy-based GHF models are contingent upon reliable models of heat production and thermal conductivity that are difficult to constrain. In this study, we examine (1) the statistical distribution of these thermal properties to gain insight into the Antarctic crust, (2) revaluate GHF estimates using these new constraints, and (3) identify areas where a lack of knowledge still hampers our ability to produce accurate models of GHF. Our approach centers on developing statistical models for the thermal properties based on global and regional distributions from global geochemical datasets. We then calibrate our heat production models of Antarctica using a combination of exposed Antarctic terranes, conjugate terranes and crustal tomography models of Antarctica. Regions where exposures and conjugate terranes are not accessible, we use a terrane model of Antarctica to reduce uncertainty. We then estimate GHF for different proxy-based temperature models using our thermal property calibrations. We find more diversity in GHF models derived from geophysical-based proxies when using a standardized crustal property model than predicted by the original. We suggest that there is still much to learn about the thermal state of Antarctica, which requires further improvements in predictors of thermal properties, especially their variation with depth.