173 / 352
157
from those of Zr and Hf (Hoskin & Schaltegger,
2003).
H
Hf
(t)
values of all analysed zircon fall into the
MORB-depleted mantle field. This observation
strongly suggests that the protolith mafic rock
was crystallised almost directly from a DM
source.
The low amount of zircon grains with a
protolith origin (domain I,
n
= 4/82; zircon only
analysed with U–Pb systematics) in contrast
to the high amount of zircon formed during
the HP metamorphic event (domain II,
n
=
78/82), suggests that the HP metamorphic event
induced an extreme solid-state recrystallisation
of the protolith zircon in this sample. Some of
the domain II metamorphic zircon conserve
xenocrystic cores, which are most probably
remains of the magmatic domain II zircon (see
Fig. 33).
As stated in the results section when zircon
from this sample was hand-picked many Ap
crystals were picked by mistake. This error
resembles the high amount of Ap in the sample,
which from their low luminescence, appreciated
from CL images, their REE contents are thought
to be very high. The presence of REE enriched Ap
in the sample can be explained by the Zrn REE
purge triggered by solid-state recrystallisation.
Phosphorus and REE are relatively abundant and
they are common impurities in zircon, and when
these elements were purged from the zircon
structure they formed abundant Ap.
7.3. ECLOGITES