Discussion
Which of the following Eon characterizes the more tonalitic batholiths, more biomodal volcanic suites and the komatites ?
Answer: C
These features characterise the Archean eon.
Archean crust (4.0 to 2.5 billion years ago) is dominated by granite-greenstone terrains. The granitoids are mostly tonalite-trondhjemite-granodiorite (TTG) batholiths, the greenstone belts contain bimodal volcanic suites of basalt and felsic volcanics, and komatiites, ultramafic lavas erupted at very high temperatures, are almost confined to the Archean because the mantle was then hotter.
Phanerozoic and Proterozoic crust has more potassic granites and almost no komatiites, and the Mesozoic is an era within the Phanerozoic, not an eon.
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