Melt pathways in the mantle

Article Abstract:

Studies on the Oman ophiolite show that the melt pathways in the asthenosphere are marked by dunites which are formed by the reaction of the melts moving up with the peridotite wall-rocks. Mixing takes place when these melts move up the channels. An equilibrium exists between a mid-ocean-ridge basalt-like liquid and the dunite pods while the peridotite is not in equilibrium with the liquid, implying that the liquid-dunite reaction occurs in the asthenosphere. The dunites are probably formed by perturbations of porosity which increase the flow of melts and the channels formed are a means of energy and mass transfer from the core to the crust.

Earth, Core (Geology), Ophiolites

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Reading garnet's signature

Article Abstract:

Temperature differences between mid-ocean-ridge basalt (MORB) source regions are a primary cause of variations in oceanic crust production. Uranium -series radioisotope data from MORB show that melting begins at greater depths beneath shallow ridges with thick crusts. The new findings conflict with the previous ones on the role of garnet in MORB petrogenesis. The large 230Th excesses, characteristic of thick crust regions, are unexplainable by shallow termination of melting. Further, the Sm/Yb and Nd-Hf observations remain unexplained by lateral variations in temperature.

Analysis, Influence, Garnet

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Evidence from the asymmetry of fast-spreading ridges that the axial topographic high is due to extensional stresses

Article Abstract:

Smaller topographic low flank the axial high along the majority of the East Pacific Rise. Models of the origin of th axial high predict the existence of such lows. One postulates that the high is created by buoyant uplift, and another suggested that the high is created by dynamic extensional lithosphere stresses. Each model can be altered to suit the asymmetry on individual profiles.

Usage, Relief models

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