Evolution of metallogeny of granitic pegmatites associated with orogens throughout geological time

2016-06-21T12:26:22Z (GMT) by A. V. Tkachev
<p>Since <em>c.</em> 3.1 Ga, pegmatite mineral deposits in orogenic areas have been formed throughout geological time in pulses, alternating with total absence of generating activity. The higher activity peaks of 2.65–2.60, 1.90–1.85, 1.00–0.95, and 0.30–0.25 Ga suggest a quasi-regular periodicity of 0.8±0.1 Ga. This series is dominated by pegmatites of Laurasian blocks. The lower peaks at 2.85–2.80, 2.10–2.05, 1.20–1.15, and the higher one at 0.55–0.50 make up another series represented by pegmatites in Gondwanan blocks only. Each pegmatite class is characterized by a life cycle of its own, from inception to peak through to decline and eventual extinction. The longest cycle is recorded for the rare-metal class deposits, which first appeared in the Mesoarchaean and persisted through all the later eras, deteriorating gradually after the Early Precambrian. Muscovite pegmatites first appeared in the Palaeoproterozoic and reached the end of their life cycle at the Palaeozoic–Mesozoic boundary. The miarolitic class of pegmatite deposits in orogenic setting first came into being in the terminal Mesoproterozoic and dominated the pegmatite metallogeny of many Phanerozoic belts. The evolution of the pegmatite classes was controlled by the general cooling of the Earth and by associated changes in the tectonics of the lithosphere. </p>