Abstract

Data suggesting that the Cooma Granodiorite, New South Wales, Australia, originated by essentially in situ anatexis of adjacent metasedimentary rocks are in apparent conflict with the low-pressure metamorphic environment, unless unrealistically high and localized geothermal gradients (about 55 °C/km) are invoked. If it is assumed that the granodiorite is a diapiric intrusion, the geometry of model diapirs suggests that, although the granodiorite probably formed by partial melting of the adjacent high-grade migmatitic rocks, this high-grade envelope may have been dragged up to higher crustal levels by the intruding granitic diapir. If so, the metamorphic zones around the Cooma Granodiorite may be a greatly compressed section of the metamorphic grade changes between the depths of magma generation and magma emplacement.

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