T256 Radiogenic Isotopes as Tracers of Geologic Processes: Dates, Rates, and Proxies II

Wednesday, 12 October 2022
1:30 PM - 5:30 PM
502

PRECISE TEMPORAL CORRELATION OF GEOSPHERE-BIOSPHERE INTERACTION IN THE GEOLOGICAL PAST THROUGH HIGH-PRECISION U-PB GEOCHRONOLOGY

Paper number: T256-2
Program: Technical Sessions
Time: 1:35 PM – 1:50 PM

Authors

Abstract

Volatiles injected into the atmosphere during periods of massive volcanism in Large Igneous Provinces (LIPs) are considered drivers of climate change, by altering the marine and terrestrial environment. To connect these geosphere and biosphere processes during ancient periods, it is crucial to test the synchronicity, particularly at high precision. Therefore, we focus on the highest precision and accuracy geochronological technique, chemical abrasion – isotope dilution – thermal ionization mass spectrometry U-Pb dating of zircon.

However, dating mafic rocks of LIPs through this technique is challenging, as mantle-derived melts are often not enriched in Zr and Si, suppressing crystallization of zircon or baddeleyite. New data from the Karoo LIP in South Africa show that emplacement-level contamination by sedimentary material provides the geochemical conditions that stabilize zircon and baddeleyite and render mafic LIP lithologies datable by U-Pb. This contamination can be identified from xenocrystic U-Pb components in some zircon crystals, as well as non-radiogenic Hf-isotope compositions, both likely sourced from nucleation of new zircon growth on detrital precursors. Despite the complexity added by this sedimentary contamination, we may establish precise emplacement ages for LIP sills and dykes. These data provide the duration of LIP activity, permitting calculation of intrusive magma flux, and subsequent modeling of volumes and rates of volatile extraction.

These data can then be compared to high-precision U-Pb geochronology from well-characterized sedimentary sections. Combined with additional stratigraphic data, we can attempt to reconstruct the timing and duration of carbon isotope excursions, biochronological zones and biodiversity fluctuations, and compare them with the duration of magmatic activity of a LIP. By applying Bayesian age-depth modeling to precise U-Pb geochronology data sets it is possible to calibrate the biochronology and geochemical proxies across different sedimentary settings, or between sedimentary sections in paleo-geographically disparate positions,

By combining these two distinct geochronologic records, it is possible to evaluate the potential causal relationships between magmatism, environmental disturbance and biological crisis.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-378653

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