Basement and Sedimentary Recycling-2: Time Dimension to Global Tectonics

Abstract

If plotted on mass (volume, area, tonnage) vs. time diagrams, geologic entities-for example, continental and oceanic crust, sediments, and mineral resources-display an exponential (power law) relationship, with entity per unit time increasing toward the present. This relationship is consistent with the concept of recycling and can be simulated mathematically. The authors' approach is based on the plate tectonic theory and considers area-age or mass-age distributions of crystalline basement and sediments for major global tectonic realms. Each tectonic realm is characterized by a specific lifespan, which is an inverse function of its recycling rate (b). The estimated average half-area or half-mass ages ($$\tau_{50}$$) are the following: basins of active margins ~30 Ma, oceanic sediments ~40 Ma, oceanic crust ~55 Ma, basins of passive margins ~80 Ma, immature orogenic belts ~100 Ma, mature orogenic belts ~380 Ma, and platforms ~380 Ma. The corresponding parameters for continental crust are ~690 Ma for K/Ar, and ~1200 Ma for Rb/Sr and U-Th/ Pb dating pairs. For Sm/Nd $$\tau_{50}$$ is $$\leq 1800 Ma$$, suggesting either that continental crust was growing during geologic history and/or its recycling via mantle (or lower crust) was more vigorous prior to 2500 Ma ago. The estimated maximal survival (or oblivion) ages for these tectonic realms are ~3-3.5 times longer than their $$\tau_{50}$$. Tectonic diversity preserved in the geologic record is therefore a function of time, with oce…