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Dehydration of diasporite to corundite in nature and experiment

A. Feenstra and B. Wunder
Dehydration of diasporite to corundite in nature and experiment
Geology (Boulder) (February 2002) 30 (2): 119-122


The diasporite-corundite rock transformation, which releases 6-8 wt% H (sub 2) O in an average metabauxite, was studied experimentally. The results are compared with petrological observations on the island of Naxos (Greece), where the transformation occurred in metakarst bauxites during prograde regional metamorphism. Dehydration experiments were started with fine-grained natural diasporite embedded in marble. The samples were first annealed in the diaspore stability field, then slowly brought to the final pressure-temperature (P-T) conditions in the corundum field and kept there five to seven days. Overstepping the diaspore-corundum equilibrium by approximately 30 degrees C at 8 kbar resulted in partial dehydration of diaspore. As with the corundum-in isograd on Naxos, the corundum grew preferentially along the bauxite-marble contact. Experiments at 17-40 kbar with T oversteps of 40-150 degrees C resulted in complete diaspore breakdown. A high-porosity zone containing corundum and silicates developed along the bauxite-marble boundary, resulting from the solid volume decreases associated with the diaspore-corundum and decarbonation reactions. In nature, the marble similarly behaved as a barrier for liberated fluid, as indicated by coarse corundum-chloritoid segregations along metabauxite rims. In the 30-40 kbar experiments, the porous contact zone acted as fluid pathway, allowing partial dissolution of metabauxite. This demonstrates pronounced Al, Fe, and Ti mobility at high P and T of 600-800 degrees C.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 30
Serial Issue: 2
Title: Dehydration of diasporite to corundite in nature and experiment
Affiliation: GeoForschungsZentrum Potsdam, Potsdam, Federal Republic of Germany
Pages: 119-122
Published: 200202
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 16
Accession Number: 2002-014637
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
N37°07'00" - N37°07'00", E25°25'00" - E25°25'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200206
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