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Abstract:
We present Li and B isotope data for muscovite, biotite, and feldspar + quartz separated
from two-mica granite and biotite granite samples from the Huayang-Wulong granite suite
(south Qinling, central China). Our data demonstrate systematic differences in the Li and
B isotopic compositions among these minerals. Our results indicate that early-crystallizing
minerals have lower δ7
Li and δ11B values than the original melt and that residual melts and
late magmatic fluids may acquire anomalously high δ7
Li and δ11B values. Furthermore, our
data imply that (1) late melts and magmatic fluids do not reflect the composition of their
source melt, (2) minerals that crystallized over a large segment of magma evolution may be
isotopically zoned, and (3) mineral-selective alteration by late magmatic fluids camouflages
the source of the fluid, whose δ7
Li and δ11B values reflect the isotopic compositions of the
altered minerals rather than the composition of the remaining rock.
