CHEMICAL CHARACTERISATION OF CRACK-SEAL IN METAMORPHOSED MANTLE CHROMITITES

摘要

Chromitites from Tehuitzingo serpentinite (Puebla State, SW Mexico) occur as pods and layers ofa few meters long and less than 2 m thick embedded in metaharzburgites. The chromite grainsfrom these chromitites are systematically altered: the primary magmatic chromites, which areAl-rich (Cr# [Cr/(Cr+Al)] = 0.53 - 0.57; ), are being overprinted by porous and/or homogeneousrims which are less rich in Al (Cr# = 0.72 - 0.94; ). The primary compositions are only preservedin the cores of some grains and enveloped by rims of porous chromite. Locally, these cores presenthealed fractures of micrometric width containing aligned inclusions between 1 and 15 μm in size(Fig. 1a). The alignment of the inclusions suggests that they formed coeval to the formation of thefracture.