Fluorine and chlorine in mantle minerals and the halogen budget of the Earth’s mantle
Urann, Benjamin M.
Le Roux, Véronique
Marschall, Horst R.
Lee, Cin-Ty A.
MetadataShow full item record
The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth's upper mantle, and their distribution in peridotite minerals, remains to be constrained. Here we developed a method to measure low concentrations of halogens (≥ 0.4 μg/g F and ≥ 0.3 μg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine ~ orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (< 1 μg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4–31 μg/g F and 0.14–0.38 μg/g Cl. The bulk F content of oceanic-like peridotites (2.1–9.4 μg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that nearly all MORB may be somewhat contaminated by seawater-rich material and that the Cl content of DMM could be overestimated. With this study, we demonstrate that the halogen contents of natural peridotite minerals are a unique tool to understand the cycling of halogens, from ridge settings to subduction zones.
Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Contributions to Mineralogy and Petrology 172 (2017): 51, doi:10.1007/s00410-017-1368-7.
Suggested CitationPreprint: Urann, Benjamin M., Le Roux, Véronique, Hammond, Keiji, Marschall, Horst R., Lee, Cin-Ty A., "Fluorine and chlorine in mantle minerals and the halogen budget of the Earth’s mantle", 2017-05-01, https://doi.org/10.1007/s00410-017-1368-7, https://hdl.handle.net/1912/9189
Showing items related by title, author, creator and subject.
Sharp thermal transition in the forearc mantle wedge as a consequence of nonlinear mantle wedge flow Wada, Ikuko; Rychert, Catherine A.; Wang, Kelin (American Geophysical Union, 2011-07-08)In the forearc mantle wedge, the thermal field depends strongly on slab-driven mantle wedge flow. The flow is in turn affected by the thermal field via the temperature dependence of mantle rheology. Using thermal modeling, ...
Global mantle flow and the development of seismic anisotropy : differences between the oceanic and continental upper mantle Conrad, Clinton P.; Behn, Mark D.; Silver, Paul G. (American Geophysical Union, 2007-07-26)Viscous shear in the asthenosphere accommodates relative motion between Earth's surface plates and underlying mantle, generating lattice-preferred orientation (LPO) in olivine aggregates and a seismically anisotropic fabric. ...
Ito, Garrett T. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1996-09)We analyze bathymetric and gravity anomalies at five plume-ridge systems to constrain crustal and mantle density structure at these prominent oceanic features. Numerical models are then used to explore the physical ...