摘要
Eight lines of evidence indicate that the Orosirian Period in mid-Paleoproterozoic time was characterized by plate tectonics:ophiolites,low T/P metamorphism including eclogites,passive margin formation,tall mountains,paleomagnetic constraints,ore deposits,abundant S-type granites,and seismic images of paleo-subduction zones.This plate tectonic episode occurred about 1 billion years earlier than the present plate tectonic episode began in Neoproterozoic time.The two plate tectonic episodes bracket the‘Boring Billion’,which may have been a protracted single lid tectonic episode that began when the supercontinent Nuna or Columbia formed.Recognition of multiple lines of evidence for Orosirian plate tectonics demonstrates that Earth’s tectonic style can be reconstructed with some confidence back to at least Early Paleoproterozoic time,and thus the absence of compelling evidence for Mesoproterozoic plate tectonics is not obvious due to poor preservation.A tectono-magmatic lull2.3 Ga suggests an earlier episode of single lid tectonics.Evidence for two episodes of plate tectonics and two episodes of single lid tectonics indicates that Earth switched between single lid and plate tectonics multiple times during the last 2.4 Ga.
