Abstract
We apply a zircon redox index to a global compilation of detrital zircons to track the variation of oxida-tion state,expressed as △FMQ,through Earth's history.Those from I-type rocks,which comprise mantle and crustal igneous protoliths,including tonalite-trondhjemite-granodiorites(TTGs),generally have a high oxidation state(△FMQ＞0).In contrast,zircons from igneous rocks derived from supracrustal source rocks(S-type)are commonly reduced(△FMQ＜0).With the probability density function derived from the Gaussian-Kernel-Density-Estimation,we use the maximum likelihood estimation(MLE)to distinguish S-type from I-type zircons through Earth's history using zircon redox.Voluminous S-type magma produc-tion shows a ca.600 Ma cyclicity that is closely related to the supercontinent cycle.We link a cyclic drop in redox values after 2.6 Ga to periodic S-type magma generation associated with burial and melting of metasedimentary rocks during supercontinent assembly and amalgamation.The △FMQ of the detrital zircons rise at～3.5 Ga followed by a consistent average △FMQ＞0 over the last 3 Ga.Given that the redox state of magmas is independent of crustal thickness and silica variation,and elevated values are likely more closely related to tectonic setting,we suggest that the consistent average △FMQ＞0 from ca.3.5 Ga onwards relates to recycling of oceanic lithosphere back into the mantle in what eventually became established as subduction zones.The more reduced magmas associated with sedimentary sources,became established at 2.6 Ga,presumably in response to continental rocks rising above sea-level,and follow peaks of productivity associated with the supercontinent cycle.
基金项目
National Natural Science Foundation of China(42225204)
National Natural Science Foundation of China(42121002)
Australian Research Council(FL160100168)
Fundamental Research Funds for the Central Universities(2652023001)
Programme of Introducing Talents of Discipline to Universities(111 Project)
Programme of Introducing Talents of Discipline to Universities(B18048)
万方数据