Decompression melting

The sharp melting poiat and the low melt viscosity also mean that nylon can give problems with nozzle drool and/or premature freeze-off For this reason, it is normally necessary to use either a reverse-taper nozzle (fitted with a heater to avoid freeze-off), a mechanical shut-off nozzle, or melt decompression. Melt decompression, or suck-back, iavolves the screw retractiag slightly after the screw retractioa time, pulling the material back and... 

Allegre CJ, Dupre B, Lewin E (1986) Thorium/uranium ratio of the Earth. Chem Geol 56 217-227 Allegre CJ, Turcotte D (1986) Implications of a two-component marble-cake mantle. Nature 323 123-127 Asimow PD, Hirschmann MM, Ghiorso MS, O Hara MJ Stolper EM (1995) The effect of pressure-induced solid-solid phase transitions on decompression melting of the mantle. Geochim Cosmochim Acta 59 4489-4506... 

Equations (5.95), (5.96) and (5.97) are suitable for constant critical melting porosity. In a one dimensional steady state melting column as a result of decompression melting, the porosity may increase from the bottom to the top of the column. If melting porosities change as a function of the spatial position, the related differential equations need to be solved numerically. More details of various melt transport models by porous flow have been given by Spiegelman and Elliott (1993), Iwamori, (1994), and Lundstrom (2000). 

Lithospheric stretching, passive upwelling of asthenosphere and variable degrees of decompression melting at various mantle levels in an intracontinental rifting setting ... 

LIPs are generally believed to be formed by decompression melting of upwelling hotter mantle, known as mantle plumes. Although ideas about hotpots and mantle plumes have been around for almost 40 years (Wilson, 1963), it is only in the past 15 years that LIPs have become the focus of major research. One of the main reasons for the increased research activity into LIPs is the realization that significant proportions of these LIPs erupted over a relatively short time, often less than 2-3 Myr (see review in Coffin, 1994). 

Plume flattens along the base of the lithosphere and undergoes decompression melting Asthenosphere Plume head fed by narrow tail... 

Figure 2 Cartoon to illustrate how mantle plumes are believed to (a) rise through the asthenosphere from either the 670 km discontinuity or and (b) flatten along the base of the lithosphere and undergo decompression melting to produce a LIP (after Saunders et ai, 1992).

Oceanic plateaus represent overthickened areas of oceanic crust (10-35 km), which appear to have formed as a result of decompression melting of a large mantle plume head, often (although not always) within 1 -2 Ma. Geological and geochemical evidence suggests that oceanic plateaus have formed throughout a considerable period of Earth s history. 

Conder J. A., Weins D. A., and Morris J. (2002) On the decompression melting structure at volcanic arcs and back-arc spreading centers. Geophys. Res. Lett. 29(15), 4pp. 

These studies have implications for the stability of cratons and diamond exploration. The steep gradients focus flow and adiabatic decompression melting along cratonic boundaries where exten-sional body forces arising from the density contrast between normal asthenosphere and hot plume material will be the largest, indirectly focusing tectonism. This in turn further shields the cratonic cores, although lateral erosion of... 

Passive rise of the mantle beneath oceanic spreading centers results in the decompression melting of upwelling peridotite which gives rise to a spectrum of MORB compositions varying from extremely... 

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