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Constraining in situ cosmogenic nuclide paleo-production rates using sequential lava flows during a paleomagnetic field strength low

Balbas, A. M. and Farley, K. A. (2020) Constraining in situ cosmogenic nuclide paleo-production rates using sequential lava flows during a paleomagnetic field strength low. Chemical Geology, 532 . Art. No. 119355. ISSN 0009-2541. https://resolver.caltech.edu/CaltechAUTHORS:20191105-094210699

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Abstract

The geomagnetic field prevents a portion of incoming cosmic rays from reaching Earth’s atmosphere. During magnetic reversals and excursions, the field strength can decrease by up to 90% relative to the modern-day value. During such anomalies, cosmic ray bombardment to Earth’s atmosphere increases as evident from atmospheric ¹⁰Be anomalies recorded in sediment and ice cores. However, how the flux of cosmic rays to Earth’s surface varies during such geomagnetic anomalies is not well constrained. We measured fossil cosmogenic ³He in olivine from the tops of two pairs of ⁴⁰Ar/³⁹Ar age-dated Tahitian lava flows that erupted during the Matuyama-Brunhes reversal precursor event. We corrected these raw values for the diffusive loss of helium caused by heating from the overlying flow with a diffusion model using cooling rates and maximum temperature conditions based on field measurements of active lava flows from Kilauea, Hawaii. We assume the maximum temperature suggested by field measurements and thus present a limiting case for the highest diffusive loss corrections and thus the highest paleo-production rates. Based on paleomagnetic field strength reconstructions and scaling factor models, the upper limits of the corrected in situ 3He paleo-production rates (100 ± 23, 144 ± 35 atoms g⁻¹ a⁻¹) are in agreement with those expected during the period of a geomagnetic field strength low when these flow tops were exposed. However, the more plausible contact temperatures (<700°C maximum temperature in diffusion model) are associated with diffusion corrected paleo-production rates lower than those predicted by scalar models. This potential underestimation is likely a function of changes in local non-dipole field components, atmospheric density and/or an overestimation of the dipole field strength reduction during the M-B precursor event.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.chemgeo.2019.119355DOIArticle
ORCID:
AuthorORCID
Balbas, A. M.0000-0002-4855-3507
Farley, K. A.0000-0002-7846-7546
Additional Information:© 2019 Elsevier B.V. Received 6 August 2019, Revised 26 September 2019, Accepted 31 October 2019, Available online 1 November 2019. We thank Kevin Konrad for providing the in vacuo crushed olivine results and helpful discussions. This work was supported by an NSF AGEP Fellowship for A. Balbas and benefitted greatly from discussions with Peter Clark, Joe Stoner, Brendan Reilly, Ed Brook and Anthony Koppers. We thank two anonymous reviewers for helpful comments that improved the manuscript. Declaration of Competing Interest: None.
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Funding AgencyGrant Number
NSFUNSPECIFIED
Subject Keywords:Cosmogenic Nuclides; Paleomagnetism; Matuyama-Bruhnes; Magnetic Reversal; Helium-3; production rates; cosmic rays
Record Number:CaltechAUTHORS:20191105-094210699
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191105-094210699
Official Citation:A.M. Balbas, K.A. Farley, Constraining in situ cosmogenic nuclide paleo-production rates using sequential lava flows during a paleomagnetic field strength low, Chemical Geology, Volume 532, 2020, 119355, ISSN 0009-2541, https://doi.org/10.1016/j.chemgeo.2019.119355. (http://www.sciencedirect.com/science/article/pii/S000925411930484X)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99665
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:05 Nov 2019 18:10
Last Modified:19 Nov 2019 19:03

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