Crystallization of Podiform Chromitites from Silicate Magmas and the Formation of Nodular Textures |
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| Authors: | Mei-Fu ZHOU John MALPAS Paul T ROBINSON Min SUN Jian-Wei LI |
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| Institution: | Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR, China [e-mail: ] |
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| Abstract: | Abstract: Podiform chromite deposits consist of numerous individual accumulations of chromite in the mantle sequences of ophiolites, suggesting formation in separate, mini-magma conduits in the upper mantle. They may show unique nodular and orbicular textures. Simple mixing of two distinct magmas, invoked for chromite deposits in layered intrusions, is inadequate to explain the formation of podiform chromite deposits. More likely, melt/rock interaction triggers the precipitation of chromite by addition of newly-formed droplets of melt to the main body of magma passing through a conduit, a process similar to that of magma mingling but involving a turbulent, moving magma so that newly-formed melt droplets behave like snowballs. These droplets concentrate chromite to form an outer shell and, while the magma is moving upwards, less dense silicate melts are squeezed out of the droplets as the shell collapses to form a nodule. Upon cooling, both orbicular and nodular textures are preserved in the chromitite. |
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| Keywords: | podiform chromitite nodular texture melt/rock interaction magma mingling |
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