European Geosciences Union General Assembly 2015 - Garnet Classification
Ti and Zr in garnet - different metasomatic types
Based on Ti concentrations, garnets were divided into two main groups:
Low-Ti group:
1. Low-Ti (< 0.27 wt.%) and low-
Zr (<20 ppm) garnets are
comparable with depleted
mantle peridotite garnets by
[Griffin et al., 1999]; these are
the most part of garnet
central zones;
2. Low-Ti (<0.15 wt.%) and
high-Zr (30-60 ppm) garnets
are comparable with
secondary kimberlitic (Ca,
Cr)-poor garnets [Ziberna et
al., 2013] and with low-T
"phlogopite" metasomatic
garnets by [Griffin et al.,
1999]; these garnets were
formed after crystallization of
Ti-bearing megacryst
minerals (ilmenite).
High-Ti group:
1. High-Ti (0.62-0.94 wt.%) and high-Zr (20-60 ppm) garnets
are comparable with megacrysts or garnets of
"ilmenite" paragenesis [Sablukov et al., 2008] and with
garnets of high-T "melt" metasomatic origin by [Griffin et
al., 1999]; these garnets were formed before megacrysts
crystallization.
100
Zr (ppm)
low-T garnet
(Griffin et al., 1999)
10
secondary garnet
(Ziberna et al., 2013),
10
Ti/Zr = 10
Ti/Zr = 100
Megacrysts
high-T garnet
(Griffin et al., 1999)
depleted peridotite
garnet (Griffin et al., 1999)
1
10
100
1000
Ti (ppm)
10000
fields after Griffin et al., 1999
8
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