Possible sub‐arc origin of podiform chromitites

Abstract

The sub-arc mantle condition possibly favors the formation of podiform chromitites.The Cr/(Cr + Al) atomic ratio (= Cr#) of their chromian spinel frequently is higher than 0.7, which js comparable with the range for arc-related primitive magmas. This almost excludes the possibility of their sub-oceanic origin, because both oceanic peridotites and MORB have chromian spinel with the Cr# < 0.6. Precipitation of chromitite and associated dunite enhances a relative depletion of high-field strength elements (HFSE) to large-ion lithophile elements (LILE), one of chemical characteristics of arc magmas, for the involved magma. This cannot alter completely, however, the MORB to the arc-type magma, especially for Ti and Zr. The presence of chromitite xenoliths, similar both in texture and in chemistry to podiform chromitites of some ophiolitic complexes, in some Cenozoic alkali basalts from the southwest Japan arc indicates directly that the upper mantle beneath the Japan arcs has chromitites.

Paleozoic serpentinite-enclosed chromitites from Tehuitzingo (Acatlán Complex, southern Mexico): a petrological and mineralogical study

“…This is consistent with the chemical composition of the primary chromites in the serpentinites and the abundance of chromitites in the area (Robert, 1988;Arai and Abe, 1994;Arai and Yurimoto, 1995;Zhou and Robinson, 1997;Proenza et al, 1999;Matveev and Ballhaus, 2002).…”

“…However, the most recent interpretations of the genesis of ophiolitic chromitites suggest a suprasubduction-zone setting. By contrast, no ophiolitic chromitites are thought to form in mature spreading centers, such as mid-ocean ridges (Robert, 1988;Arai and Abe, 1994;Arai and Yurimoto, 1995;Robinson et al, 1997;Schiano et al, 1997;Zhou and Robinson, 1997;Zhou et al, 1998;Proenza et al, 1999;Edwards et al, 2000). From experiments in water-oversaturated basalts, Matveev and Ballhaus (2002) concluded that ophiolitic chromite deposits would form only where there are primitive melts saturated in olivine-chromite and rich in water.…”

Origin and emplacement of Archean ophiolites of the central orogenic belt, North China craton

“…Chromite is used as it is often the only unaltered mineral and the composition is believed to represent crystallization compositions (Ahmed et al, 2001;Arai, 1992;Dick and Bullen, 1984;Irvine, 1967), particularly for chromite from lava flows, and within massive chromitite, and dunite. The low diffusivity of Cr, Al, Ti and V within olivine, makes these elements ideal for indicating crystallization compositions (Arai and Yurimoto, 1995). The Cr # indicates the degree of depletion of the mantle source from which the melt was derived, and to a lesser extent, the degree of melt fractionation (Dick and Bullen, 1984;Irvine, 1967Irvine, , 1965.…”

Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

“…Alchromite suggest that the Cr-spinel crystallized through high degrees of partial melting at the shallowest levels of an upper mantle source (within the Moho Transition Zone), i.e., close to the layered gabbro sequence (e.g. [60][61][62][63][64][65]). Trace element enrichment of Cs, Rb, Pb, Sb, Sr are caused due serpentinization process, tremolite and/or carbonate precipitation also caused Pb, Sb enrichment and produces in serpentinites (cf.…”