There is a growing need for new zircon reference materials for in situ Hf‐isotope analysis by laser ablation‐multicollector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS). In this contribution we document the results of a preliminary investigation of seven natural zircons, conducted in order to test their suitability in this regard. Solution MC‐ICP‐MS data on separated Lu and Hf fractions provided reference compositional data while the results of ca. 750 in situ LA‐MC‐ICP‐MS analyses allowed assessment of potential micrometre‐scale heterogeneity. On the basis of these analyses and additional relevant considerations such as availability, size and (Lu)Yb/Hf ratio, we suggest that, of the currently available zircons, Temora‐2 and Mud Tank are most likely to provide robust reference materials for Hf isotope determinations both at the present time and into the future. The former has the advantage of also being well‐characterised for U‐Th‐Pb systematics and suitable for in situ age determination, while the latter is the most readily available and is of very large grain size. Additional materials such as BR266, and 91500, although limited in supply, show more consistent Lu/Hf ratios and are thus of use in monitoring elemental fractionation during ICP‐MS analysis.

Quaternary volcanic rocks from the New Britain island arc display INTRODUCTION a wide range in chemical compositions. The source of the lavas The New Britain region of Papua New Guinea represents shares isotopic characteristics with Indian Ocean type mid-ocean an outstanding opportunity to reach an understanding ridge basalt (MORB). In contrast, the high field strength elements of the processes of magma genesis in an oceanic island (HFSE) are extremely depleted in the volcanic front rocks compared arc. The Quaternary volcanoes found there define the with MORB. We propose that this results from a previous melteastern part of the Bismarck volcanic arc, and have extraction event-hypotheses invoking residual phases in either the formed in response to northward subduction of the small mantle wedge or subducting slab cannot account for the depletion Solomon plate beneath the Bismarck plate (Fig. 1). The relative to MORB. In addition, elements other than the HFSE are New Britain arc is outstanding for two main reasons: also affected. Chemical signatures in parts of the New Britain arc(1) Arc volcanism in the central sector of the island and Manus Basin may relate to a previous subduction episode has taken place over an exceptionally wide range of along the now inactive Vitiaz-West Melanesian trench. Ultradepths to the Wadati-Benioff zone-from~100 km deep depleted volcanic front basalts invariably have strong 'fluid'-related at the 'volcanic front' (closest to the submarine trench) trace element signatures, including high Sr/Nd and U/Th (and down to~600 km in the northwest beneath the Witu 238 U disequilibrium), together with positive Eu anomalies that can Islands. The reasons for the correspondingly large width be related to the mobility of Eu 2+ in the slab-derived flux. Negative of the volcanic arc are still unknown, but isotopic and Ce anomalies are attributed to a minor sedimentary component. elemental differences between the rocks are systematic Across-arc geochemical profiles record a decrease in the degree of as depths to the Wadati-Benioff zone increase. We believe partial melting and diminishing influence of a slab-derived fluid that these differences provide unparalleled insights into with depth, superimposed upon the depleted mantle composition the geochemical architecture of subduction-zone systems. beneath the volcanic front. Element partitioning into (and not(2) Rocks of the New Britain volcanic front are low in necessarily the source of) the fluid is considered to exert strong control potassium, range from basalt to rhyolite, and have (as on the chemistry of volcanic front magmas, a feature that may go illustrated below) exceptional depletions in high field some way to explaining the contradictory estimates of the slab flux strength elements (HFSE). Indeed, they may represent derived from isotope vs trace element data in many subduction suites. the most HFSE-depleted arc rocks known. These rocks therefore should provide valuable constraints on the controls of HFSE abundances in island-arc magmas. The depl...

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The NIST glass certified reference materials, SRM 610‐617, have been widely adopted by the geological community as calibration samples for a variety of in situ trace element analytical techniques. There is now an urgent requirement for similar reference materials for in situ isotopic analytical techniques. We have analysed SRM 610, 612 and 614 for their Pb, Sr and Nd isotopic compositions using thermal ionisation mass spectrometry. Large differences in isotopic composition were observed between each CRM, suggesting a significant trace element content in the initial starting material (base glass). As a result, isotopic compositions for one CRM cannot be extrapolated to another, and each must be calibrated for use independently. We present the first compilation of working values for these glasses.

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