200 / 352
184
which can be related to the mingling process.
176
Lu/
177
Hf,
176
Yb/
177
Hf,
176
Hf/
177
Hf
(t)
and Th/U
ratios do not show any variation related with U–
Pb age variations.These observations leads one to
conclude that the convoluted light zonings were
not formed by a dissolution-recrystallisation
process but by a pseudomorphic alteration and
most likely with no presence of fluid phases.
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1R GDWD
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Fig. 75.
CL images (cathodoluminescence) of representative zircons from the studied sample. Laser ablation pits for U–Pb
analyses (red line circles) have 23 and 33
μ
m diameters. Laser ablation pits for Lu–Hf analyses (green line circles) have 26
and 40
μ
m diameters. White numbers are the reference number of the analysis, red numbers are the U–Pb age and its 2
σ
error (Ma) and the green numbers are the
H
Hf values for the U–Pb age.
7.4. ORTHOGNEISSES