DOI: 10.1016/j.epsl.2021.117025
论文题名: An extended period of extremely weak geomagnetic field suggested by palaeointensities from the Ediacaran Grenville dykes (SE Canada)
作者: Thallner D. ; Biggin A.J. ; Halls H.C.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2021
卷: 568 语种: 英语
中文关键词: Ediacaran
; Grenville dykes
; Laurentia
; paleointensity
英文关键词: Dispersions
; Ediacaran
; Field strengths
; Field switching
; Geomagnetic fields
; Geomagnetics
; Grenville dyke
; Laurentia
; Low-intensity
; Palaeointensity
; Paleo-intensities
; Geomagnetism
; dike
; dike swarm
; Ediacaran
; geomagnetic field
; Laurentia
; paleointensity
; secular variation
; spatiotemporal analysis
; Canada
英文摘要: Long-term variations of the geomagnetic field, observed in the palaeomagnetic record, have the potential to shed much light on the evolution of Earth's deep interior. With a geomagnetic field characterised by anomalous directions and ultra-low intensities, the Ediacaran period (635-538 Ma) is a time of special interest. Steep and shallow directions, leading to virtual geomagnetic poles (VGPs) separated by angles of up to 90° and very close in age could have recorded a geomagnetic field switching between axial and equatorial dipole-dominated states. Alternatively, the field may simply have been highly nondipolar and subject to rapid reversals. Palaeointensity determinations of units that record the anomalous directions could potentially help to discriminate between morphologies but the spatial and temporal distribution of palaeomagnetic data require improvement. Here we present new palaeointensities from 6 dykes from the western end of the Grenville Dyke swarm that recorded directionally anomalous geomagnetic fields around ∼585 Ma. Results from double-heating Thellier experiments failed to satisfy the used selection criteria, but successful microwave Thellier, Shaw and pseudo-Thellier experiments lead to palaeointensities that show field strength values of 2.9 ± 2.2 μT and corresponding virtual dipole moments of 0.3-1.7×1022 A m2. These field strengths are an order of magnitude weaker than the present-day field. VGPs grouping in two distinct clusters with almost identical angular dispersions of VGPs (SB=18.5° and 18.9°) may argue for the presence of an equatorial dipole. In contrast, the palaeointensities associated with the steep and shallow components are indistinguishable. Although based on a low number of results, this observation, together with the overall very large VGP dispersion may rather support that the Grenville Dykes have recorded enhanced secular variation linked to a highly unstable and rapidly reversing field. © 2021 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165688
Appears in Collections: 气候变化与战略
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作者单位: Dept. of Earth, Ocean and Ecological Sciences, University of LiverpoolL69 3BX, United Kingdom; Department of Earth Sciences, University of Toronto, 22 Ursula Franklin Street, Toronto, M5S 3B1, Canada
Recommended Citation:
Thallner D.,Biggin A.J.,Halls H.C.. An extended period of extremely weak geomagnetic field suggested by palaeointensities from the Ediacaran Grenville dykes (SE Canada)[J]. Earth and Planetary Science Letters,2021-01-01,568