Geology Reference
In-Depth Information
Table 7.1 General characteristics and possible origin of I-S-A-TTG-type granitoids.
Classification
I-type
A-type
TTG
S-type
Overall petrology
Part of a broad spectrum
from diorite or tonalite
through granodiorite to
granite
Spectrum including
peralkaline granites,
alkali syenites and
fayalite granites
Trondhjemite-Tonalite-
Granodiorite (Dacite as
volcanic equivalent)
Restricted to leucocratic
granites
Distinctive
minerals/ chemistry
Hornblende, biotite,
magnetite, sphene
Alkali feldspar dominant,
riebeckite, fayalite,
rapakivi structure,
fluorine-rich
Amphibole, plagioclase,
high Na, high ratios of
Sr/Y, La/Yb, low Y
Muscovite, biotite,
cordierite, monazite,
garnet, ilmenite
Enclaves
Mainly magmatic enclaves
May contain all enclave
types
Mafic enclaves rare in
trondhjemites
Mainly metasedimentary
xenoliths
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