| Popis: |
In the last 130 million years, perhaps as much as 2000 km of intra-continental shortening has taken place within Asia during 10,000 km of convergence between Siberia and India (with ∼8000 km being accommodated by oceanic subduction). Given that Earth was hotter during the Paleoproterozoic, crustal shortening at this time may have been equally, if not more, significant compared to today, warranting a search of the paleomagnetic data base for any supporting evidence. Paleomagnetic data from units on either side of the Paleoproterozoic Trans Hudson orogen in Canada have been chosen because this orogen bears close similarity both in size and history to the India-Siberia one. The data do not prove, but can accommodate, continental crustal shortening between the Archean Slave and Superior Provinces of about 3000 ± 1000 km. The results allow crustal shortening to have been a significant component of continental collision in the Paleoproterozoic, an important issue in any re-assembly of Precambrian continents. If true, the present dimensions of Precambrian shields, may be significantly different compared to those existing in earlier times. |
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