High Pressure Experimental Investigation of the Interaction between Partial Melts of Eclogite and Mantle Peridotite during Upwelling

Abstract:

Many mantle-derived magmas may originate through partial melting of complex, mixed mantle rocks including not only peridotite, but also oceanic crust recycled into the mantle [1,2]. There is, however, little detailed knowledge concerning how such material is produced, how it melts, the types of liquids produced and how they are extracted from the mantle.

We have conducted a series of peridotite/basalt layered experiments using an average altered mid-ocean ridge basalt GA2 [3] and fertile peridotite HZ1 [4] doped with Ir to act as a redox sensor [5,6]. Experiments were performed at 3-10 GPa, 1235-1660°C, using a multi anvil apparatus.

The compositions of minerals and melts were analysed using an electron microprobe. Fourier-transform infrared and Mössbauer spectroscopy were also employed to determine the concentrations of small amounts of volatiles and the Fe³⁺/ΣFe ratio, respectively.

Experiments yielded well-crystallised heterogeneous mantle assemblages. Similar to previous studies [3,7], ‘dry’ eclogite starts to melt at higher depths than ambient ‘dry’ mantle along adiabatic paths. Highly siliceous melts produced through near-adiabatic ascent freeze into ambient peridotite, forming distinct orthopyroxene-rich reaction zones [8].

We demonstrate that impregnating partial melts of eclogite in an upwelling mantle differ in their metasomatic effects depending on the particular adiabatic path, as suggested previously [7]. Thus, melt compositions formed by subsequent re-melting of such metasomatic assemblages strongly depend on potential temperature of the adiabat [7].

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