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Paleomagnetism and Ar-40/Ar-39 geochronology of Yemeni Oligocene volcanics: Implications for timing and duration of Afro-Arabian traps and geometry of the Oligocene paleomagnetic field

Riisager, Peter LU ; Knight, KB; Baker, JA; Peate, IU; Al-Kadasi, M; Al-Subbary, A and Renne, PR (2005) In Earth and Planetary Science Letters 237(3-4). p.647-672
Abstract
A combined paleomagnetic and Ar-40/Ar-39 study was carried out along eight stratigraphically overlapping sections in the Oligocene Afro-Arabian flood volcanic province in Yemen (73 sites). The composite section covers the entire volcanic stratigraphy in the sampling region and represents five polarity zones that are correlated to the geomagnetic polarity time scale based on Ar-40/Ar-39 ages from this and previous studies. The resulting magnetostratigraphy is similar to that of the conjugate margin in Ethiopia. The earliest basaltic volcanism took place in a reverse polarity chron that appears to correspond to C11r, while the massive rhyolitic ignimbrite eruptions correlated to ash layers in Oligocene Indian Ocean sediment 2700 km away from... (More)
A combined paleomagnetic and Ar-40/Ar-39 study was carried out along eight stratigraphically overlapping sections in the Oligocene Afro-Arabian flood volcanic province in Yemen (73 sites). The composite section covers the entire volcanic stratigraphy in the sampling region and represents five polarity zones that are correlated to the geomagnetic polarity time scale based on Ar-40/Ar-39 ages from this and previous studies. The resulting magnetostratigraphy is similar to that of the conjugate margin in Ethiopia. The earliest basaltic volcanism took place in a reverse polarity chron that appears to correspond to C11r, while the massive rhyolitic ignimbrite eruptions correlated to ash layers in Oligocene Indian Ocean sediment 2700 km away from the Afro-Arabian traps, appear to have taken place during magnetochron C11n. The youngest ignimbrite was emplaced during magnetochron C9n. Both 40Ar/39Ar and paleornagnetic data suggest rapid < 1 Ma eruption of the basal basalt units and punctuated eruption of the upper silicic units over a duration potentially as long as 3 Ma with interspersed eruptive hiatuses. Eruption of the basal basalts may have preceded the Oi2 cooling event. The paleornagnetic pole lambda=74.2 degrees N, phi=249.1 degrees E (A95=3.6 degrees; N=48) is supported by a positive reversal test. Paleosecular variation, estimated as the angular standard deviation of the VGP distribution 14.2 degrees+2.3 degrees/-1.7 degrees, is close to expected, suggesting that the paleornagnetic pole represents a time-averaged field. The pole is in excellent accord with the paleornagnetic poles obtained from the Ethiopian part of the Afro-Arabian province, after closure of the Red Sea. By analyzing Afro-Arabian paleomagnetic data in conjunction with contemporaneous paleomagnetic poles available from different latitudes we argue that the Oligocene paleomagnetic field was dominated by the axial dipole with insignificant non-dipole field contributions. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Afro-Arabian traps, Yemen, Oligocene, Ar-40/Ar-39 geochronology, paleomagnetic pole, magnetostratigraphy, large igneous province
in
Earth and Planetary Science Letters
volume
237
issue
3-4
pages
647 - 672
publisher
Elsevier
external identifiers
  • wos:000232155200024
  • scopus:24144499192
ISSN
1385-013X
DOI
10.1016/j.epsl.2005.06.016
language
English
LU publication?
yes
id
795e1d3a-5bc1-41ef-83d8-563ab794eeb2 (old id 223165)
date added to LUP
2007-08-22 15:37:03
date last changed
2017-07-23 03:35:33
@article{795e1d3a-5bc1-41ef-83d8-563ab794eeb2,
  abstract     = {A combined paleomagnetic and Ar-40/Ar-39 study was carried out along eight stratigraphically overlapping sections in the Oligocene Afro-Arabian flood volcanic province in Yemen (73 sites). The composite section covers the entire volcanic stratigraphy in the sampling region and represents five polarity zones that are correlated to the geomagnetic polarity time scale based on Ar-40/Ar-39 ages from this and previous studies. The resulting magnetostratigraphy is similar to that of the conjugate margin in Ethiopia. The earliest basaltic volcanism took place in a reverse polarity chron that appears to correspond to C11r, while the massive rhyolitic ignimbrite eruptions correlated to ash layers in Oligocene Indian Ocean sediment 2700 km away from the Afro-Arabian traps, appear to have taken place during magnetochron C11n. The youngest ignimbrite was emplaced during magnetochron C9n. Both 40Ar/39Ar and paleornagnetic data suggest rapid &lt; 1 Ma eruption of the basal basalt units and punctuated eruption of the upper silicic units over a duration potentially as long as 3 Ma with interspersed eruptive hiatuses. Eruption of the basal basalts may have preceded the Oi2 cooling event. The paleornagnetic pole lambda=74.2 degrees N, phi=249.1 degrees E (A95=3.6 degrees; N=48) is supported by a positive reversal test. Paleosecular variation, estimated as the angular standard deviation of the VGP distribution 14.2 degrees+2.3 degrees/-1.7 degrees, is close to expected, suggesting that the paleornagnetic pole represents a time-averaged field. The pole is in excellent accord with the paleornagnetic poles obtained from the Ethiopian part of the Afro-Arabian province, after closure of the Red Sea. By analyzing Afro-Arabian paleomagnetic data in conjunction with contemporaneous paleomagnetic poles available from different latitudes we argue that the Oligocene paleomagnetic field was dominated by the axial dipole with insignificant non-dipole field contributions.},
  author       = {Riisager, Peter and Knight, KB and Baker, JA and Peate, IU and Al-Kadasi, M and Al-Subbary, A and Renne, PR},
  issn         = {1385-013X},
  keyword      = {Afro-Arabian traps,Yemen,Oligocene,Ar-40/Ar-39 geochronology,paleomagnetic pole,magnetostratigraphy,large igneous province},
  language     = {eng},
  number       = {3-4},
  pages        = {647--672},
  publisher    = {Elsevier},
  series       = {Earth and Planetary Science Letters},
  title        = {Paleomagnetism and Ar-40/Ar-39 geochronology of Yemeni Oligocene volcanics: Implications for timing and duration of Afro-Arabian traps and geometry of the Oligocene paleomagnetic field},
  url          = {http://dx.doi.org/10.1016/j.epsl.2005.06.016},
  volume       = {237},
  year         = {2005},
}