At Cima Uzza, the tonalitic Adamello batholith and volumetrically minor
gabbroic stocks and dikes were emplaced into a thick sequence of
silica-poor dolostone. Stable isotopic data from dolomite in dolomitic
marble in the contact aureole [delta(18)O = 29.7 +/- 1.3 parts per
thousand (1 sigma), delta(13)C = 2.2 +/- 1.3 parts per thousand] and
from equivalent dolostone outside the aureole (delta(18)O = 28.8 +/- 1.1
parts per thousand, delta(13)C = 2.5 +/- 0.2 parts per thousand) are
indistinguishable. These high and uniform delta(18)O values in the
dominant lithology suggest metamorphism in a closed system, as does a
closed-system reaction model that is consistent with observed isograd
development. Localized fluid infiltration is reflected by low delta(18)O
(13.2-18.5 parts per thousand) and delta(13)C (-2.6 to -6.7 parts per
thousand) calcite values in siliceous marble xenoliths entrained in
small gabbroic stocks at the tonalite margin. Such siliceous marble
probably formed by Si and Al metasomatism of dolomitic marble during
infiltration of magmatic fluids because no equivalent lithology occurs
outside the aureole. Brucite marble, which occurs in xenoliths and as
reaction rims around mafic dikes, displays a wide range of delta(18)O
and delta(13)C values which are generally intermediate between those for
siliceous marble and dolomitic marble. This range of isotopic values in
brucite marble is consistent with a hydrothermal formation from a
silica-poor dolostone protolith. In contrast, high delta(18)O values
from centimeter-scale calc-silicate nodules and layers, which are
irregularly distributed in the dolomitic contact aureole, indicate a
sedimentary origin for such rocks. Hydrothermal alteration of dolomitic
marble at Cima Uzza is limited to small areas near gabbroic stocks and
dikes, whereas negligible country rock alteration is associated with the
larger tonalite. The limited infiltration of magmatic fluids possibly
reflects a low volatile content in the tonalitic magma. In addition, low
permeability in the thick sequence of dolomitic marble could explain the
small amount of fluid flow relative to other carbonate contact aureoles.