T128 Unravelling Timescales of Magmatism, Metamorphism, and Crustal Evolution II

Monday, 16 October 2023
1:30 PM - 5:30 PM
327

PRECISE LA-ICP-MS U-PB SCHORLOMITE GARNET AND PEROVSKITE AGES: NEW CONSTRAINTS ON EMPLACEMENT OF THE MAGNET COVE IGNEOUS COMPLEX, AR

Paper number: T128-4
Program: Technical Sessions
Time: 2:10 PM – 2:25 PM

Authors

Abstract

The Magnet Cove Intrusive Complex (MCIC), AR, is one of the enigmatic mid-Cretaceous magmatic complexes in North America for which very different mantle melting models have been proposed. The ring complex includes jacupirangite, ijolite, phonolite, nepheline syenite and carbonatite units. It is a renowned host of unique or rare minerals. Potentially suitable for U-Pb geochronology are perovskite, Ti-rich (schorlomite) and Zr-rich (kimzeyite) garnet, as well as titanite. Earlier geochronological studies using K/Ar, Ar/Ar, Rb-Sr and fission track dating established an age of 94-100 Ma for intrusion and fast cooling, with individual uncertainties of 5 Ma or more on individual dates.

We investigate the potential for U-Pb dating of the mentioned Ca-Ti-Zr minerals and their suitability as reference materials (RM) motivated by the expansion of laser ablation U-Pb dating of such non-traditional minerals.

First results on perovskite from the carbonatite give clustered, but discordant U-Pb results. The data do not form a long linear array, not suitable as a primary RM, but they have potential as a secondary, validation RM. A suitable comPb composition can be established from analysis of cogenetic calcite or from published whole rock data.

Schorlomite garnets from four samples give precise (1-2%) U-Pb dates in two groups, 97-100 Ma and 100.5-103.5 Ma. The perovskite result lies in between these groups. The results do not bear out the bulls-eye outside-in younging pattern proposed earlier. Future work will include more rock types and minerals, and will establish feasibility to obtain larger, clean material quantities for use as RMs.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-394821

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