Chapter 2 Precambrian Tectonic Style: A Liberal Uniformitarian Interpretation

摘要: Abstract Major uncertainties impeding clarification of the Precambrian geologic record are: (1) its thermal history; (2) history growth continental crust; and (3) tectonic style. The only certainty is that average surface heat flow has declined. From an appraisal current ideas on mechanics contemporary plate tectonics, it seems pull associated with subduction cold, negatively buoyant oceanic lithosphere dominant force (buoyancy-powered subduction). If this valid, then less likely earlier in earth when was higher. However, higher flow, rate convective circulation mantle faster, viscous drag forces at base may have been stronger. Simple assumptions calculations suggest a model which: Initially, vigorously convecting earth, were sufficient to crust back into (viscous No survived recycling, but enhanced upward concentration sialic components earth. With cooling, slowing convection passage time, buoyant, possibly continuous global scum-crust intermediate composition would developed. This effectively decoupled from recycled as result volcanic addition remelting removal base. further cooling became coupled mantle; density increased ultimately buoyancy-powered could begin. Subduction segments entire lithosphere, where thin, initiated plate-tectonic style continent-ocean dichotomy. Simultaneously, decoupling sinking separated caused intracontinental mobile-belt orogeny. (4) continued decrease strength boundary between become more difficult; orogeny now rare or impossible. leaves predominant orogenic force. These four stages are considered be consistent available can roughly equated Pre-Archaean, Archaean, Proterozoic Phanerozoic.