Plesovice zircon : A new natural reference material for U-Pb and Hf isotopic microanalysis

An Astronomically Tuned Neogene Time Scale (ATNTS2012) is presented, as an update of ATNTS2004 in GTS2004. The new scale is not fundamentally different from its predecessor and the numerical ages are identical or almost so. Astronomical tuning has in principle the potential of generating a stable Neogene time scale as a function of the accuracy of the La2004 astronomical solution used for both scales. Minor problems remain in the tuning of the Lower Miocene. In GTS2012 we will summarize what has been modified or added since the publication of ATNTS2004 for incorporation in its successor, ATNTS2012. Mammal biostratigraphy and its chronology are elaborated, and the regional Neogene stages of the Paratethys and New Zealand are briefy discussed. To keep changes to ATNTS2004 transparent we maintain its subdivision into headings as much as possible.

The Neogene Period

This paper reviews the basic principles of radiometric geochronology as implemented in a new software package called IsoplotR, which was designed to be free, flexible and future-proof. IsoplotR is free because it is written in non-proprietary languages (R, Javascript and HTML) and is released under the GPL license. The program is flexible because its graphical user interface (GUI) is separated from the command line functionality, and because its code is completely open for inspection and modification. To increase future-proofness, the software is built on free and platform-independent foundations that adhere to international standards, have existed for several decades, and continue to grow in popularity. IsoplotR currently includes functions for U-Pb, Pb-Pb, 40 Ar/ 39 Ar, Rb-Sr, Sm-Nd, Lu-Hf, Re-Os, U-Th-He, fission track and U-series disequilibrium dating. It implements isochron regression in two and three dimensions, visualises multi-aliquot datasets as cumulative age distributions, kernel density estimates and radial plots, and calculates weighted mean ages using a modified Chauvenet outlier detection criterion that accounts for the analytical uncertainties in heteroscedastic datasets. Overdispersion of geochronological data with respect to these analytical uncertainties can be attributed to either a proportional underestimation of the analytical uncertainties, or to an additive geological scatter term. IsoplotR keeps track of error correlations of the isotopic ratio measurements within aliquots of the same samples. It uses a statistical framework that will allow it to handle error correlations between aliquots in the future. Other ongoing developments include the implementation of alternative user interfaces and the integration of IsoplotR with other data reduction software.

IsoplotR: A free and open toolbox for geochronology

Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of ∼1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40 Ar/ 39 Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40 Ar/ 39 Ar geochronology. This calibration results in a more precise older age of 28.201 ± 0.046 million years ago (Ma) and reduces the 40 Ar/ 39 Ar method9s absolute uncertainty from ∼2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of ∼65.95 Ma for the Cretaceous/Tertiary boundary.

https://science.sciencemag.org/content/sci/320/5875/500.full.pdf

Synchronizing Rock Clocks of Earth History

Age constraint on Burmese amber based on U–Pb dating of zircons

Timing of injection and of thermal maturation in a mid-crustal Variscan bimodal intrusion

. The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high spatial resolution, high throughput in situ isotopic and elemental analysis techniques such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision ( LREE-I alteration index and providing new insight into the mechanism of chemical abrasion, the interpretation and reconciliation of these results suggests that Pb-loss is largely driven by low-temperature aqueous recrystallization, and that regional thermal events may act to halt – not initiate – Pb-loss from metamict domains in the Hadean Jack Hills zircons.

Stepwise chemical abrasion ID-TIMS-TEA of microfractured Hadean zircon

Thermal evolution of magma reservoirs in the shallow crust and incidence on magma differentiation: the St-Jean-du-Doigt layered intrusion (Brittany, France)

Mercury stratigraphy of deccan trap volcanism in marine sediments linked to climate change, biotic turnover, end-cretaceous mass extinction and delayed recovery

Blair Schoene

Papers

Timing of injection and of thermal maturation in a mid-crustal Variscan bimodal intrusion

Stepwise chemical abrasion ID-TIMS-TEA of microfractured Hadean zircon

Thermal evolution of magma reservoirs in the shallow crust and incidence on magma differentiation: the St-Jean-du-Doigt layered intrusion (Brittany, France)

Mercury stratigraphy of deccan trap volcanism in marine sediments linked to climate change, biotic turnover, end-cretaceous mass extinction and delayed recovery

Timing and Tempo of Deccan Volcanism Revealed by Mercury Anomalies