Trace element mapping of high-pressure, high-temperature experimental samples with laser ablation ICP time-of-flight mass spectrometry - Illuminating melt-rock reactions in the lithospheric mantle

Bussweiler Y, Gervasoni F, Rittner M, Berndt J, Klemme S

Abstract

Laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) is a fast,relatively high-spatial resolution method which allows to measure and visualize major, minor and traceelements in fine-grained samples. Thus, it is a promising tool for the investigation of high-pressure, hightemperature(HP-HT) reaction experiments that typically produce small grain sizes. Here, we apply LAICP-TOFMS mapping to HP-HT reaction experiments by Gervasoni et al. 2017 between a) hydrous eclogiteand fertile peridotite, which simulates metasomatism in subduction zones, and b) ultramafic silicatecarbonatemelt and peridotite, which simulates metasomatism at the base of cratonic lithosphericmantle. A spatial resolution (i.e., laser spot size) of 5 mm and an acquisition rate of 20 multi-elementpixels per second (i.e., laser repetition rate of 20 Hz) were used for mapping of the experimental samples.We demonstrate the applicability of LA-ICP-TOFMS by comparison of our results to maps createdwith electron probe micro-analysis (EPMA) and elemental concentrations measured by conventional (i.e.,crater-drilling) LA-ICP-MS. Our new data suggest that metasomatism in subduction zones is expected toresult in the formation of AleTi-rich amphiboles that strongly fractionate the rare earth elements (REE)and high-field strength elements (HFSE) from other trace elements. In contrast, metasomatism of thecratonic lithosphere involves fractionation in the light and middle REE, large ion lithophile elements(LILE) and HFSE, leaving Ni and heavy REE behind in olivine and garnet, respectively. The trace elementenrichment patterns of the resulting melt bear a general resemblance to those of natural Group Ikimberlites.

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