ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Clinochlore, which is, within the limits of error, the thermally most stable member of the Mg-chlorites, breaks down at $$P_{{\text{H}}_{\text{2}} {\text{O}}} $$ = P tot to the assemblage enstatite+forsterite+spinel+H2O along a univariant curve located at 11 kb, 838 ° C; 15kb, 862 ° C; and 18 kb, 880 ° C (±1 kb ±10 ° C). At water pressures above that of an invariant point at 20.3 kb and 894 ° C involving the phases clinochlore, enstatite, forsterite, spinel, pyrope, and hydrous vapor, clinochlore disintegrates to pyrope+forsterite+spinel+H2O. The resulting univariant curve has a steep, negative dP/dT slope of −930 bar/ °C at least up to 35 kb. Thus, given the proper chemical environment, Mg-chlorites have the potential of appearing as stable phases within the earth's upper mantle to maximum depths between about 60 and 100 km depending on the prevailing undisturbed geotherm, and to still greater depths in subduction zones. However, unequivocal criteria for mantle derived Mg-chlorites are difficult to find in ultrabasic rocks.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00374367
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