Variations in melting dynamics and mantle compositions along the Eastern Volcanic Zone of the Gakkel Ridge: insights from olivine-hosted melt inclusions
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We present major element, trace element, and volatile concentrations from 66 naturally glassy, olivine-hosted melt inclusions erupted along the Eastern Volcanic Zone (EVZ) of the ultraslow-spreading Gakkel Ridge. Melt inclusion compositions suggest that there are systematic variations in the mantle source composition and melting dynamics from the eastern to the western end of the EVZ. This includes increasing water contents and highly incompatible trace element concentrations (e.g., Ba and Nb) and decreasing light and middle rare earth element concentrations. Ratios of light to heavy rare earth elements in the easternmost melt inclusions are relatively homogeneous, but become more variable to the west. To determine the source of the geochemical variability observed along the EVZ, we model trace elements associated with mantle melting in one- and two-component systems. We consider four possible mantle sources and a range of melting regime shapes, from a full melting triangle to a vertical melting column centered beneath the ridge axes. The observed geochemical variations can be explained by melting of a heterogeneous mantle source composed of depleted MORB mantle plus a metasomatized mantle, where the proportion of the metasomatized component and the extent of melting increases toward the west. Lower rare earth element concentrations and trace element ratios in the westernmost sites also suggest inefficient melt focusing from the outer edges of the melting region. Our results indicate that despite variations in the size of the melting zone and the composition of the mantle source along the ridge axis, the region over which the melts are pooled back to the ridge axis is relatively constant (~10–20 km), suggesting that there is a limit to the distance melts can be transported from off-axis in ultraslow-spreading environments.
KeywordsMelt inclusions Mantle melting Ultraslow-spreading ridge Gakkel Ridge Water Carbon
We thank B. Monteleone at the WHOI ion microprobe facility, R. Hervick and L. Williams at ASU ion microprobe facility, and N. Chatterjee at the MIT electron microprobe facility for their analytical assistance. G. Toltin is thanked for his help with sample preparation and H. Dick for supplying the EVZ samples. We thank the editor and an anonymous reviewer for their comments. This work was supported by NSF Grant OCE-0926422 (AMS), OCE-PRF-1226130 (VDW), EAR-09-48666 (MDB), and internal Grants from DOEI at WHOI (VDW & MDB).
- Dixon JE, Stolper EM (1995) An experimental study of water and carbon dioxide solubilities in mid-ocean ridge basaltic liquids. Part II: applications to degassing. J Petrol 36:1633–1646Google Scholar
- Gregg PM, Behn MD, Lin J (2009) Melt generation, crystallization, and extraction beneath segmented oceanic transform faults. J Geophys Res 114:1–16Google Scholar
- Jakobsson M, Mayer L, Coakley B (2012) The international bathymetric chart of the Arctic Ocean (IBCAO) version 3.0—jakobsson—2012—geophysical research letters—wiley online library. Geophys Res Lett 39:1–6Google Scholar
- Jochum KP et al (2006) MPI-DING reference glasses for in situ microanalysis: new reference values for element concentrations and isotope ratios. Geochem Geophys Geosystems 7. doi: 10.1029/2005GC001060
- Klein E (2005) Geochemistry of the Igneous Oceanic Crust. Crust: Treatise Geochem 3:433–464Google Scholar
- Langmuir C, Klein E, Plank T (1992) Petrological systematics of mid-ocean ridge basalts: constraints on melt generation beneath ocean ridges. AGU Geophys Monogr 71:183–280Google Scholar
- Reid I, Jackson HR (1981) Oceanic spreading rage and crustal thickness. Mar Geophys Res 5:165–172Google Scholar
- Shaw D (2006) Trace elements in magmas: a theoretical treatment. 1–243Google Scholar
- Warren JM, Shimizu N, Sakaguchi C, Dick H (2009) An assessment of upper mantle heterogeneity based on abyssal peridotite isotopic compositions. J Geophys Res 114:1–36Google Scholar
- Waters CL (2010) Temporal and petrogenetic constraints on volcanic accretionary processes at 9-10 degrees North East Pacific Rise. 1–258Google Scholar