Abstract
Cratons are stable parts of the Earth’s continental lithosphere that
have remained largely undeformed for several billion years. These
consist of crustal granite-greenstone terrains coupled to roots of
strong, buoyant cratonic lithospheric mantle that extend up to several
hundreds of kms depth. Due to their stability, cratons preserve a record
of the tectonics and the thermal evolution of the mantle in the early
Earth. These observations suggest that the highly viscous (strong)
character of cratons hampered the viability of early Earth tectonics,
thereby affecting mantle convection patterns and cooling. In this study,
we investigate the controls of stiff cratons on the initiation of
subduction and mantle thermal evolution on the early Earth. Using
numerical models, we simulate the effects of strong and buoyant cratons
on mantle convection. We vary a set of parameters including (i) width
and thickness of cratons, and (ii) viscosity ratio between cratonic
lithosphere and cratonic crust. We test initial conditions varying the
number of cratons, which is unconstrained for early Earth and associated
it to mantle cooling rates. Our preliminary results show that the mantle
cooling rate decreases with increasing number of cratons. Because mantle
cooling rates affect the early Earth transition from a basaltic drip
regime to initiation of subduction, we show that the craton coverage on
the early Earth controls the time of onset of plate tectonics.
Furthermore, we observe that cratons will remain separate or combine
depending on the convective cell size, which is function of mantle
cooling.