It has also long been recognized that major changes occur in the geologic record between 3.0 and 2.5 Ga, all of which must be accommodated in any thermal model for Earth. In addition, Hf isotopic model ages suggest that between 50 and 70% of the continental crust was produced during this time interval. Also coinciding with this time window are a maximum in mantle potential temperature and the degree of melting of the upper mantle, a minimum in lithosphere thickness and density, and a crossover between the minimum subductable thickness of oceanic lithosphere and the equilibrium lithospheric thickness for a stagnant lid thermal regime. We suggest that changes during this time interval may all be related to a change from an active stagnant lid to a plate tectonic cooling regime in the mantle and that zircon age peaks, which are superimposed on Earth's cooling curve, reflect collisional preservation events during the supercontinent cycle beginning about 3 Ga. Earth may have evolved through three stages: 1) first is an early active stagnant lid regime that began after the magma ocean phase (following the moon-forming event) and lasted until about 3.5 Ga; 2) the mantle then transitioned into an episodic regime characterized by alternating stagnant lid and plate tectonic phases between 3.5 and about 2.2 Ga, with plate tectonics becoming very widespread between 2.7 and 2.5 Ga; the final stagnant lid regime occurred from 2.4-2.2 Ga; and lastly, 3) the modern plate tectonic regime which continued from 2.2 Ga to the present.
|Number of pages||1|
|Publication status||Published - 2012|
|Event||International Geological Congress (34th : 2012) - Brisbane, Australia|
Duration: 5 Aug 2012 → 10 Aug 2012
|Conference||International Geological Congress (34th : 2012)|
|Period||5/08/12 → 10/08/12|