Detrital zircon dating

However, the character of the subducting slab has changed through time and has included subduction of normal oceanic crust, a spreading ridge, and an oceanic plateau.

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One presumption that has led workers astray in detrital mineral geochronology is the belief that if a sufficient number of age observations are made in a sample, then the measured distribution of ages will approach the “true” distribution present in a given sedimentary system with sufficient accuracy to make geologically sound interpretations (e.g., Pullen et al., 2014).

This premise remains ignorant of how detrital minerals fractionate within sedimentary environments, and also presumes that biases introduced through sample selection and processing are negligible (Sircombe and Stern, 2002; Sláma and Košler, 2012).

Does statistical convergence necessarily translate into geological convergence? In a new paper in , six geologists tested a widely-used technique of gathering detrital zircons: crystals of zirconium that often contain uranium (U) and its daughter product lead (Pb), found in debris piles below a slope.

They tested the assumptions in their samples collected in Venezuela.

What we want to ask, now that this paper has shown a significant “unknown” in geological sample collection and testing, is what other unknowns are still out there? Do any of them really know how old their samples are?

Subduction along the southern margin of Alaska, USA, has been ongoing since at least the Jurassic.

Most studies, they say, ignore these “inconvenient and commonly ignored issues” with the source data.

Factors other than age (i.e., sediment transport) can skew the interpretation.

Geologists, in actual practice, do attempt to minimize error.

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