Search

The geochemical characteristics of melt inclusions and their host olivines provide important information on the processes that create magmas and the nature of their mantle and crustal source regions. We report chemical compositions of melt inclusions, their host olivines and bulk rocks of Xindian basalts in Chifeng area, North China Craton. Compositions of both bulk rocks and melt inclusions are tholeiitic. Based on petrographic observations and compositional variation of melt inclusions, the crystallizing sequence of Xindian basalts is as follows: olivine (at MgO > ~5.5 wt%), plagioclase (beginning at MgO = ~5.5 wt%), clinopyroxene and ilmenite (at MgO < 5.0 wt%). High Ni contents and Fe/Mn ratios, and low Ca and Mn contents in olivine phenocrysts, combining with low CaO contents of relatively high MgO melt inclusions (MgO > 6 wt%), indicate that Xindian basalts are possibly derived from a pyroxenite source rather than a peridotite source. In the CS-MS-A diagram, all the high MgO melt inclusions (MgO > 6.0 wt%) project in the field between garnet + clinopyroxene + liquid and garnet + clinopyroxene + orthopyroxene + liquid near 3.0 GPa, further suggesting that residual minerals are mainly garnet and clinopyroxene, with possible presence of orthopyroxene, but without olivine. Modeling calculations using MELTS show that the water content of Xindian basalts is 0.3-0.7 wt% at MgO = 8.13 wt%. Using 20-25% of partial melting estimated by moderately incompatible element ratios, the water content in the source of Xindian basalts is inferred to be ≥450 ppm, much higher than 6-85 ppm in dry lithospheric mantle. The melting depth is inferred to be ~3.0 GPa, much deeper than that of tholeiitic lavas (< 2.0 GPa), assuming a peridotite source with a normal mantle potential temperature. Such melting depth is virtually equal to the thickness of lithosphere beneath Chifeng area (~100 km), suggesting that Xindian basalts are derived from the asthenospheric mantle, if the lithospheric lid effect model is assumed. Keywords Melt inclusion * Olivine chemistry * Pyroxenite source * Water * Basalts * North China Craton, Introduction For years, it was thought that peridotite (olivine mode >40%), the predominant lithology in the upper mantle, is the source of mafic magmas (peridotite melts; e.g., Green and Ringwood [...]

Presents a study that investigated two-phase coexistence of iron-nickel alloys synthesized by ball milling. Expression for the corrected peak intensity for Lorentz polarization, multiplicity and structure factors in a standard way; Types of x-ray peak broadening analysis used to obtain the average grain size and root-mean-squared strain; Features of two-phase coexistence of the alloys.

Deals with a study which examined steady-state phases in alloys of the Fe[sub3]X composition prepared through mechanical alloying. Experimental details; Results; Discussion; Conclusion.