The Cooma Granodiorite, Australia: An example of in situ crustal anatexis?

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.