Publications

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2017
Pommier, A, Evans RL.  2017.  Constraints on fluids in subduction zones from electromagnetic data. Geosphere. 13:1026-1041.   10.1130/ges01473.1   AbstractWebsite

Magnetotelluric data have been increasingly used to image subduction zones. Models of electrical resistivity commonly show features related to the release of fluids at several depths through the systems imaged, consistent with thermal and petrologic models of dehydration of the downgoing slab. Imaging the release of fluids from sediments and pore space in the crust requires controlled source electromagnetic techniques, which have to date only been used in one setting, offshore Nicaragua. The release of fluids related to the transition of basalt to eclogite is commonly imaged with magnetotelluric data. Deeper fluid release signals, from the breakdown of minerals like serpentine, are highly variable. We hypothesize that regions where very strong conductive anomalies are observed in the mantle wedge at depths of similar to 80-100 km are related to the subduction of anomalous seafloor, either related to excessive fracturing of the crust (e.g., fracture zones), subduction of seamounts, or other ridges and areas of high relief. These features deform the seafloor prior to entering the trench, permitting more widespread serpentinization of the mantle than would otherwise occur. An alternative explanation is that the large conductors represent melts with higher contents of crustal-derived volatiles (such as C and H), suggesting in particular locally higher fluxes of carbon into the mantle wedge, perhaps also associated with subduction of anomalous seafloor structures with greater degrees of hydrothermal alteration.

2014
Khan, A, Connolly JAD, Pommier A, Noir J.  2014.  Geophysical evidence for melt in the deep lunar interior and implications for lunar evolution. Journal of Geophysical Research-Planets. 119:2197-2221.   10.1002/2014je004661   AbstractWebsite

Analysis of lunar laser ranging and seismic data has yielded evidence that has been interpreted to indicate a molten zone in the lowermost mantle overlying a fluid core. Such a zone provides strong constraints on models of lunar thermal evolution. Here we determine thermochemical and physical structure of the deep Moon by inverting lunar geophysical data (mean mass and moment of inertia, tidal Love number, and electromagnetic sounding data) in combination with phase-equilibrium computations. Specifically, we assess whether a molten layer is required by the geophysical data. The main conclusion drawn from this study is that a region with high dissipation located deep within the Moon is required to explain the geophysical data. This region is located within the mantle where the solidus is crossed at a depth of approximate to 1200 km (1600 degrees C). Inverted compositions for the partially molten layer (150-200 km thick) are enriched in FeO and TiO2 relative to the surrounding mantle. The melt phase is neutrally buoyant at pressures of similar to 4.5-4.6 GPa but contains less TiO2 (<15 wt %) than the Ti-rich (similar to 16 wt %) melts that produced a set of high-density primitive lunar magmas (density of 3.4 g/cm(3)). Melt densities computed here range from 3.25 to 3.45 g/cm(3) bracketing the density of lunar magmas with moderate-to-high TiO2 contents. Our results are consistent with a model of lunar evolution in which the cumulate pile formed from crystallization of the magma ocean as it overturned, trapping heat-producing elements in the lower mantle.