[1] Elemental fractionation effects during analysis are the most significant impediment to obtaining precise and accurate U-Pb ages by laser ablation ICPMS. Several methods have been proposed to minimize the degree of downhole fractionation, typically by rastering or limiting acquisition to relatively short intervals of time, but these compromise minimum target size or the temporal resolution of data. Alternatively, other methods have been developed which attempt to correct for the effects of downhole elemental fractionation. A common feature of all these techniques, however, is that they impose an expected model of elemental fractionation behavior; thus, any variance in actual fractionation response between laboratories, mineral types, or matrix types cannot be easily accommodated. Here we investigate an alternate approach that aims to reverse the problem by first observing the elemental fractionation response and then applying an appropriate (and often unique) model to the data. This approach has the versatility to treat data from any laboratory, regardless of the expression of downhole fractionation under any given set of analytical conditions. We demonstrate that the use of more complex models of elemental fractionation such as exponential curves and smoothed cubic splines can efficiently correct complex fractionation trends, allowing detection of spatial heterogeneities, while simultaneously maintaining data quality. We present a data reduction module for use with the Iolite software package that implements this methodology and which may provide the means for simpler interlaboratory comparisons and, perhaps most importantly, enable the rapid reduction of large quantities of data with maximum feedback to the user at each stage.

Variations in the intensity of high-latitude Northern Hemisphere summer insolation, driven largely by precession of the equinoxes, are widely thought to control the timing of Late Pleistocene glacial terminations. However, recently it has been suggested that changes in Earth's obliquity may be a more important mechanism. We present a new speleothem-based North Atlantic marine chronology that shows that the penultimate glacial termination (Termination II) commenced 141,000 +/- 2500 years before the present, too early to be explained by Northern Hemisphere summer insolation but consistent with changes in Earth's obliquity. Our record reveals that Terminations I and II are separated by three obliquity cycles and that they started at near-identical obliquity phases.

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We report new geochemical data for boninites and backarc basin‐type basalts recovered from the northern termination of the Tonga trench and Lau Basin. Boninitic pillow lavas, ranging from high‐Mg compositions to andesites and dacites, have been erupted within large submarine volcanic edifices (calderas and volcanoes) associated with active rifting of both the northern end of the Tofua volcanic arc and in a backarc position relative to the arc volcanoes on the northern Tonga Ridge. The mantle sources in the area are a complex mixture of (1) the “normal” Tongan mantle wedge source that has “Pacific”‐type isotopic signature with (2) the plume‐related components (EMI, EMII, and HIMU) and (3) an “Indian”‐type source upwelling beneath the backarc spreading. Some of these sources, such as the “normal” mantle wedge and variably depleted residual plume mantle, are fluxed by subduction components from the slab, which produces boninites, tholeiites, and mixtures thereof. Other mantle sources, such as “Indian”‐type backarc mantle and also some of the plume mantle, produce melts due to adiabatic decompression. These melts are variably mixed with each other and with the slab‐fluid fluxed subduction‐related melts to form the observed spectrum of magma compositions.

In situ Sr-isotope analysis by laser ablation multi-collector ICP-MS is a potentially powerful tracer technique with widespread application to many fields of study. The usefulness of the method, however, depends very strongly upon the quality of data that can be obtained (compared with conventional 'solution-based' analyses), and the spatial resolution, particularly in samples with strong compositional zonation or fine-scale growth banding. In this contribution we show that highly accurate (B50 ppm) and precise (external precision B125 ppm) analyses of carbonate materials can be obtained in situ and further demonstrate that, by utilising the aperture-imaging optics of an excimer laser system with appropriate time-resolved software, isotopic variations on the scale of tens of micrometres can be resolved. An example is shown using relatively small (B500 mm diameter) otoliths from a diadromous fish species, Galaxias maculatus.