Subducted lithosphere and crust are chem1cally d1stinct from amb1ent mantle, and some have hypoth.,sized that the result1ng anomdlous buoyancy may affect m1x1ng and, in particular, may CciUSe chem1cal heterogeneity topers ist. To explore th1s effect, two-dimensional convective mix1ng calculations have been carried out. Boundary cond1tions m1micking features of plate kinematics have been imposed...

[1] ODP Legs 129 and 185 sampled the upper 474 m of 170 Ma ocean crust in the western Pacific in order to investigate alteration processes in fast spread crust and to determine inputs to subduction. Fourteen composite bulk samples of altered upper oceanic crust from Site 801 have dO = 8.7–25.7%, dD = 69.4% to 90.4%, and dC = 2.7% to 1.8%. The intensity of alteration and the amount of sediment w...

Abstmct: Island arc lavas from New Britain and the Marianas have 143 Nd/144 Nd similar to other oceanic basalts and distinctly different from continental flood basalts and thus appear to be derived from a high Sm/Nd, light-REE-depleted reservoir. Consideration of both Nd and Sr isotopes suggests seawater involvement in the generation of some island arc lavas and thus indicates that they may be ...

The mechanism of heat extraction from the lower oceanic crust near the ridge axis is poorly constrained despite its importance for understanding both the process of accretion of the plutonic complex and the mass fluxes associated with ridge hydrothermal systems. We have investigated the role of zones of focussed fluid flow in the plutonic complex of the Oman ophiolite in the near-axis cooling o...

Editor: T.M. Harrison Non-arc basalts of Archean and Proterozoic age have model primary magmas that exhibit mantle potential temperatures TP that increase from 1350 °C at the present to a maximum of ∼1500–1600 °C at 2.5–3.0 Ga. The overall trend of these temperatures converges smoothly to that of the present-day MORB source, supporting the interpretation that the non-arc basalts formed by the m...

[1] Documenting the mass flux through convergent plate margins is important to the understanding of petrogenesis in arc settings and to the origin of the continental crust, since subduction zones are the only major routes by which material extracted from the mantle can be returned to great depths within the Earth. Despite their significance, there has been a tendency to view subduction zones as...

Combined analysis of high-resolution seismic images of the Alaska and Cascadia subduction zones reveals where metamorphic fl uids are released. Both images show the subducted oceanic crust as a dipping low-velocity layer with a clear termination depth. However, in Alaska the crust is thicker (15–20 km compared to 8 km) and terminates at greater depth (120 km compared to 40 km) than in Cascadia....

Natural basaltic glasses recovered from Leg 37 of the Deep Sea Drilling Project have been dated by fission track methods. Close agreement in results indicates that the age of the oceanic crust drilled at Site 332 is 3.67 ±0.40 m.y. The age of the crust at Site 335 is less well defined, the average of the three dates obtained from this site being 14.45 ±2.27 m.y.

Atmospheric carbon dioxide (CO2) data for the last 420 million years (My) show long-term fluctuations related to supercontinent cycles as well as shorter cycles at 26 to 32 My whose origin is unknown. Periodicities of 26 to 30 My occur in diverse geological phenomena including mass extinctions, flood basalt volcanism, ocean anoxic events, deposition of massive evaporites, sequence boundaries, a...