Origin of podiform chromitites
Abstract
Podiform chromitite with a dunite envelope can be interpreted to be a product ofinteraction between mantle harzburgite and an exotic magma, combined with magma mixing. The secondary Si- and Cr-rich melt which is produced by the selective dissolution of orthopyroxene can be mixed with a subsequently supplied primitive melt with the mixed melt oversaturated with spinel to effectively. precipitate chromitite. The dunite envelope is of replacive origin. A moderately refractory harzburgite, which has chromian spinel with an intermediate Cr # (=Cr/[Cr + All atomic ratio), around 0.5, is the most suitable host for large-scale podiform chromitites. Lherzolite wall is too low in Cr # to concentrate chromian spinel; the mixed magma is relatively low in the degree of spinel-oversaturation because of the geometrical constraint from the liquidus phase boundary between olivine and spinel. Highly refractory harzburgite wall is low in the amount of Cr2O3 and Al2O3, which can be the source of chromian spinel during the interaction. The podiform chromitite can be produced at both oceanic and arc-related settings. The arc-related setting is, however, favorable for most of the podiform chromitites, especially for large-scale economically important deposits. The Cr # of spinel in most of the podiform chromitites, 0.7 to 0.8, cannot be covered with the compositional range of spinel in oceanic rocks, especially in MORB. The Cr # of spinel, 0.7 to 0.8, is comparable with the ratio in primitive arc magmas.
- Publication:
-
Journal of Asian Earth Sciences
- Pub Date:
- 1997
- DOI:
- 10.1016/S0743-9547(97)00015-9
- Bibcode:
- 1997JAESc..15..303A