Why are lithium-cesium-tantalum (LCT) pegmatites relatively common in some Phanerozoic orogenic belts but rare or absent in others? For example, the 3500-km-long Appalachian orogen, from Alabama and Newfoundland, has seventeen LCT districts, whereas the 8000-km-long Cordilleran orogen, from Mexico to Alaska, has only three. A related question is: why are LCT pegmatites so unevenly distributed in orogens such as the Appalachians, with alterating LCT-rich and LCT-absent sectors? Possible controlling factors involve plate-tectonic setting, paleoclimate, and exhumation history, alone or in combinations. Most if not all LCT pegmatites are emplaced during the closing stages of Wilson Cycles, so a sensible starting...

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