Oxygen isotope measurements using SIMS and laser-fluorination methods
confirm the presence of concentric and sector zoning in low-temperature
(200 degrees C to < 400 degrees C) hydrothermal quartz from Alpine
veins. While concentric zoning is most readily explained by changes in
the chemical composition of the fluid or temperature of crystallization,
the reasons for sector zoning are more difficult to explain. Relative
enrichment in (18)O for crystallographically different sectors of quartz
corresponds to m > r > z. Sector zoning is, however, largely limited to
the exterior zones of crystals and/or to crystals with large Al (> 1000
ppm) and trace element contents, probably formed at temperatures < 250
degrees C. Differences in delta(18)O between the prismatic (m) relative
to the rhombohedral (r and z) growth sectors of up to 2 parts per
thousand can be explained by a combination of a face-related
crystallographic and/or a growth rate control. In contrast, isotopic
sector zoning of up to about 1.5 parts per thousand amongst the
different rhombohedral faces increases in parallel with the trace
element content and is likely to represent disequilibrium growth. This
is indicated by non-systematic, up to 2 parts per thousand, differences
within single growth zones and the irregular, larger or smaller,
delta(18)O values (of several permil) of the exterior compared to the
inner zones of the same crystals. Disequilibrium growth may be related
to the large trace element content incorporated into the growing quartz
at lower temperatures (< 250 degrees C) and/or be related to
fluid-vapour separation, allowing crystal growth from both a vapour as
well as a liquid phase.