Boron in granitic magmas: stability of tourmaline in equilibrium with biotite and cordierite

Article Abstract:

Phase equilibrium experiments were conducted to investigate the stability of tourmaline and equilibria during the crystallization of silicic melts and the tourmaline stability during anatexis of protoliths, such as metapelites, with a high probability of having tourmaline. The experiment was performed at 200 MPa(H2O) and majority were made at 750 degrees C. The results showed the effect of tourmaline stability on the activity product of tourmaline components, namely boron and aluminum. Moreover, tourmaline was found to be unstable in metaluminous to partly peraluminous melts at 750 degrees C.

Analysis, Competitions, Crystallization, Magma, Boron, Boron (Chemical element), Biotite

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Natural metastable reactions involving garnet, staurolite and cordierite: implications for petrogenetic grids and the extensional collapse of the Betic-Rif Belt

Article Abstract:

Research was conducted to examine the origin of cordierite in mineral assemblages consisting of garnet, staurolite, cordierite, biotite, kyanite, sillimanite, andalusite, muscovite and quartz. Also, its bearing on current P-T grids and the development of extensional collapse of the Beltic-Rif Belt was analyzed. Results are in agreement with independent evidence suggesting that the termination of alpine metamorphism in the western Betic-Rif Belt was associated with the extensional collapse of thickened crust.

Petrogenesis, Garnet

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Tourmaline in a low grade clastic metasedimentary rock: an example of the petrogenetic potential of tourmaline

Article Abstract:

Three aspects of tourmaline development as deduced from a chlorite zone metawacke are analyzed. Results show that tourmaline has three well-defines zones: detrital core, inner rim and outer rim of an overgrowth. The outer rim of tourmaline grains records the chemical evolution of the sample as it underwent sulfide-silicate reactions during diagenesis and metamorphism. Lastly, the compositional discontinuity between the inner and outer rims indicate a sporadic release of boron to form overgrowths.

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