Molybdenum systematics of subducted crust record reactive fluid flow from underlying slab serpentine dehydration.

Fluids liberated from subducting slabs are critical in global geochemical cycles. We investigate the behaviour of Mo during slab dehydration using two suites of exhumed fragments of subducted, oceanic lithosphere. Our samples display a positive correlation of δMo with Mo/Ce, from compositions close to typical mantle (-0.

Testing the mantle plume hypothesis: an IODP effort to drill into the Kamchatka-Okhotsk Sea basement.

The great mantle plume debate (GPD) has been going on for ∼15years (Foulger and Natland, 2003; Anderson, 2004; Niu, 2005; Davies, 2005; Foulger, 2005; Campbell, 2005; Campbell and Davies, 2006), centered on whether mantle plumes exist as a result of Earth's cooling or whether their existence is purely required for convenience in explaining certain Earth phenomena (Niu, 2005). Despite the mounting evidence that many of the so-called plumes may be localized melting anomalies, the debate is likely to continue. We recognize that the slow progress of the debate results from communication difficulties.

Simple and cost-effective methods for precise analysis of trace element abundances in geological materials with ICP-MS.

Inductively coupled plasma mass spectrometry (ICP-MS) is the most commonly used technique to determine the abundances of trace elements in a wide range of geological materials. However, incomplete sample digestion, isobaric interferences and instrumental drift remain obvious problems that must be overcome in order to obtain precise and accurate results. For this reason, we have done many experiments and developed a set of simple, cost-effective and practical methods widely applicable for precise and rapid determination of trace element abundances in geological materials using ICP-MS.

Magmatic record of India-Asia collision.

New geochronological and geochemical data on magmatic activity from the India-Asia collision zone enables recognition of a distinct magmatic flare-up event that we ascribe to slab breakoff. This tie-point in the collisional record can be used to back-date to the time of initial impingement of the Indian continent with the Asian margin. Continental arc magmatism in southern Tibet during 80-40 Ma migrated from south to north and then back to south with significant mantle input at 70-43 Ma.

The terrestrial uranium isotope cycle.

Changing conditions on the Earth's surface can have a remarkable influence on the composition of its overwhelmingly more massive interior. The global distribution of uranium is a notable example. In early Earth history, the continental crust was enriched in uranium.

Lithium isotope evidence for subduction-enriched mantle in the source of mid-ocean-ridge basalts.

'Recycled' crustal materials, returned from the Earth's surface to the mantle by subduction, have long been invoked to explain compositional heterogeneity in the upper mantle. Yet increasingly, problems have been noted with this model. The debate can be definitively addressed using stable isotope ratios, which should only significantly vary in primitive, mantle-derived materials as a consequence of recycling.

Constraints on melt movement beneath the East Pacific Rise from 230Th-238U disequilibrium.

We report 230Th-238U disequilibrium data on mid-ocean ridge basalts recovered 5 to 40 kilometers off the ridge axis near 9 degrees 30'N of the East Pacific Rise. These data indicate near-symmetrical eruptions of normal mid-ocean ridge basalts (NMORBs) and incompatible element-enriched mid-ocean ridge basalts (EMORBs) as far as 20 kilometers off axis. Our results suggest large-scale subsurface lateral transport of NMORB melt at 19 to 21 centimeters per year and also provide constraints on the petrogenesis of EMORBs of off-axis origin.