DISTINÇÃO ENTRE TEXTURA SPINIFEX E ARRANJOS DE OLlVINA METAMÓRFICA

LÉO AFRANEO HARTMANN, MARCUS V. REMUS, JAIR C. KOPPE

Resumo


Elongated blades of olivine in a talc-carbonate (or sulphide) matrix are formed by metamorphic processes from serpentinites, and have been misidentified as igneous spinifex texrures. The two types may be distinguished texturally and chemically. Metamorphic olivines show straight borders and the crystals overlap in poiquiloblastic habit, whereas volcanic olivines are often skeletal and crystals do not overlap. Whenever crystals are not entirely serpentinized, those of metamorphic origin will show negative elongation , and igneous crystals will show positive elongation. Fo contem is strongly controlled by the Fe/Mg ratio of the rock. Samples with elongated metamorphic olivines in a talc matrix contain approximately 40-43%MgO, as opposed to spinifex textured igneous samples which show less than 33%MgO. Ti02 is much lower in olivíne-talc metamorphic rocks.

Texto completo:

PDF

Apontamentos

  • Não há apontamentos.