Dynamic role of the rheological contrast between cratonic and oceanic lithospheres in the longevity of cratonic lithosphere: A three-dimensional numerical study

摘要

In the numerical modeling of mantle convection, it is still difficult to find the conditions which allow both stable cratonic lithosphere and plate tectonics. The three-dimensional numerical model presented herein makes it possible to model the cratonic lithosphere that survives for a sufficiently long geological timescale. An important factor in the longevity of cratonic lithosphere is the localized rheological (viscosity) contrast between the cratonic and oceanic lithospheres, i.e., the presence of a weak (low-viscosity) continental margin (WCM), such as tectonically mobile (orogenic) belts, that surrounds the lateral side of cratonic lithosphere. The WCM protects the cratonic lithosphere from being stretched by the surrounding convection force. In addition to the presence of a WCM, the higher viscosity of the cratonic lithosphere itself effectively contributes to the stability of the cratonic lithosphere, as suggested by the previous numerical modeling. However, the results of the present study suggest that the WCM plays a primary role in the longevity of cratonic lithosphere, even if the viscosity contrast between the cratonic and oceanic lithospheres is quite high, 10 ~3, and the high-viscosity of cratonic lithosphere may play a secondary role in the longevity of cratonic lithosphere. The combination of the presence of a WCM and the high-viscosity of cratonic lithosphere may realize the longevity of cratonic lithosphere that survives for over two billion years.