An Integrated Paleomagnetic, Multimethod‐Paleointensity, and Radiometric Study on Cretaceous and Paleogene Lavas From the Lesser Caucasus: Geomagnetic and Tectonic Implications

Calvo‐Rathert, Manuel; Bógalo, María Felicidad; Morales, J.; Goguitchaichvili, A.; Lebedev, V. A.; Vashakidze, G. T.; Redondo, Natalia García; Herrero‐Bervera, E.

doi:10.1029/2020jb020019

Cited by 4 publications

(1 citation statement)

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“…Besides, the Time‐Averaged Field (TAF) value for the last 5 Ma, according to different authors, varies between 4.1 and 5.6 × 10 22 Am 2 (Cromwell et al., 2015b; Juárez and Tauxe, 2000; Lawrence et al., 2009; Wang et al., 2015). For larger periods such as the last 160, 200, and 300 Ma, TAF is estimated between 4.2 and 4.8 × 10 22 Am 2 (Calvo‐Rathert et al., 2020; Juárez et al., 1998; Selkin and Tauxe, 2000; Tauxe 2006; Tauxe et al., 2013). All these observations allow to infer that the lower Apnia section records the initial stage of a reversal while the upper part of the sequence displays the recuperation of the EMF intensity following the polarity transition.…”

Section: Discussionmentioning

confidence: 99%

Paleointensity Results From Pliocene Lavas of the Lesser Caucasus Obtained Using the Multispecimen Parallel Differential pTRM Method: A Comparison With Thellier‐Thellier and IZZI Data

et al. 2021

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We report paleointensity results obtained with the multispecimen method (MSP) over the Pliocene sequence of Apnia (Georgia) which records a polarity reversal. Paleointensity determinations with the multispecimen technique were performed on 12 flows with the original (MSP‐DB) and the domain‐state corrected (MSP‐DSC) protocol. Eight MSP‐DSC determinations passed the proposed quality criteria. To obtain highly reliable data through the agreement between intensity values from different methods, MSP results were combined with paleointensities from a previous study with Thellier‐type methods and especially strict selection criteria (RCRIT) on same flows (Sánchez‐Moreno et al., 2020). Application of this multimethod procedure resulted in three new paleointensities including both MSP and Thellier‐type results and an additional one obtained with two different Thellier‐type methods, yielding one paleointensity of 36.9 µT in the normal‐polarity, and three paleointensities between 19.2 and 24.1 µT in the reverse‐polarity section. Additionally, Thellier‐type data have been reinterpreted in this study with more flexible criteria (TTP) and the results combined with the MSP data. As a result, four flows yield paleointensities including MSP and Thellier‐type determinations and seven include paleointensities obtained with two different Thellier‐type methods. Results range from 37.2 and 44.3 μT in the normal‐polarity and from 12.5 to 24.6 μT in the reverse‐polarity section. Comparison of results from the four flows yielding multimethod determinations applying RCRIT criteria with those from the same flows under TTP criteria yields no significant difference in paleointensity values and their experimental uncertainty. Thus, application of a multimethod approach supports the possibility of using TTP criteria.

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Section: Discussionmentioning

confidence: 99%

Paleointensity Results From Pliocene Lavas of the Lesser Caucasus Obtained Using the Multispecimen Parallel Differential pTRM Method: A Comparison With Thellier‐Thellier and IZZI Data

et al. 2021

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MCADAM: A Continuous Paleomagnetic Dipole Moment Model for at Least 3.7 Billion Years

Bono

Paterson

Biggin

2022

Geophysical Research Letters

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The evolution of Earth's deep interior since core formation (Nimmo, 2015) >4 billion years ago (Ga) remains a topic of considerable study. Obtaining information of the deep interior is generally restricted to present-day observations. Alternatively, insights on processes occurring before the modern era require sampling geologic materials that formed at, or were transported to, Earth's surface. However, the geomagnetic field is generated in the liquid fraction of Earth's core through the geodynamo, and changes in the morphology, strength and variability in the geodynamo may reflect the evolution of core processes and the pattern of heat flux across the core-mantle boundary. The geomagnetic field is also a critical component for Earth's habitability (Rodríguez-Mozos & Moya, 2017) due to the protective envelope provided by the magnetosphere against atmospheric erosion by charged solar particles. It is speculated that changes in the paleomagnetosphere may have contributed to substantial changes in the evolution of life (e.g., Meert et al., 2016).Paleomagnetic studies offer the potential to help close this gap: when rocks bearing magnetic carriers form, the geomagnetic field imparts a remanent magnetization that under ideal circumstances can be robustly preserved for billions of years. The strength of the geodynamo can be described by the magnitude of the dipole moment, the first-degree spherical harmonic component of the field, which should reflect ∼90% of the surface field signal. A fundamental question regarding Earth's dynamo is how the dipole moment has changed over long timescales (≫millions of years). Paleointensities measured from the same geologic time (e.g., from the same cooling-unit, referred to as a "site") can be related to paleointensities from other locations by transforming the paleointensity (B) into a virtual (axial) dipole moment (V(A)DM) using the following equation (Smith, 1967):

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Multimethod palaeointensity results from a rapidly emitted upper Miocene lava flow sequence in São Vicente (Cape Verde): new data for the African record

Calvo Rathert,

Carrancho,

Morales

et al. 2022

Geophysical Journal International

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We present new radiometric ages and full-vector paleomagnetic data from São Vicente Island, Cape Verde. Samples were obtained from a sequence of 11 nephelinitic flows. A K-Ar age determination was performed on the lowermost flow of the sequence, yielding an upper Miocene age of 6.07 ± 0.16 (2σ) Ma. Considering the normal polarity observed in all flows, the age of the sequence could be narrowed down to an interval between 6.03 and 6.23 Ma. The mean paleomagnetic direction of the studied sequence was compared with the expected direction, calculated from the African Apparent Polar Wander Path (5 Ma). While inclinations approximately agree, the paleodeclination appears westwardly deviated by 26.5° ± 2.9°. Moreover, nearly no scatter of virtual geomagnetic poles around their mean value is observed and its comparison with the scatter observed in paleomagnetic directions obtained from geomagnetic field model SHA.DIF.14k suggests that the sequence was very rapidly emplaced in only a few centuries. Thus, the obtained anomalous paleomagnetic direction seems to reflect the effect of non-averaged secular variation, although a local vertical-axis counterclockwise rotation of the sequence, cannot be entirely ruled out. Thellier-Coe paleointensity experiments on 66 specimens yielded 22 successful determinations and multispecimen paleointensity experiments on 11 samples yielded 8 successful determinations. In the upper part of the sequence, Thellier-Coe determinations fail due to the presence of multidomain grains, but the multispecimen method yields successful results in several of these flows, demonstrating that this method can provide reliable paleointensity determinations on samples with a higher multidomain grain fraction. A mean paleointensity BSV = (18.5 ± 1.9) µT is obtained from the joint analysis of the results from both methods. This value lies clearly below the present-day value BP = 33.1 μT. The virtual axial dipole moment (VADM = 4.3 × 1022 Am2), however, cannot be considered anomalous if compared to available upper Miocene-Pliocene data and represents a new high-reliability contribution to the very limited African paleointensity database.

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An Integrated Paleomagnetic, Multimethod‐Paleointensity, and Radiometric Study on Cretaceous and Paleogene Lavas From the Lesser Caucasus: Geomagnetic and Tectonic Implications

Cited by 4 publications

References 83 publications

Paleointensity Results From Pliocene Lavas of the Lesser Caucasus Obtained Using the Multispecimen Parallel Differential pTRM Method: A Comparison With Thellier‐Thellier and IZZI Data

Paleointensity Results From Pliocene Lavas of the Lesser Caucasus Obtained Using the Multispecimen Parallel Differential pTRM Method: A Comparison With Thellier‐Thellier and IZZI Data

MCADAM: A Continuous Paleomagnetic Dipole Moment Model for at Least 3.7 Billion Years

Multimethod palaeointensity results from a rapidly emitted upper Miocene lava flow sequence in São Vicente (Cape Verde): new data for the African record

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