@article{FranzSudoKhomenko2022,
  author    = {Franz, Gerhard and Sudo, Masafumi and Khomenko, Vladimir},
  title     = {40Ar/39Ar dating of a hydrothermal pegmatitic buddingtonite-muscovite assemblage from Volyn, Ukraine},
  series = {European journal of mineralogy : EJM : an international journal on mineralogy, petrology, geochemistry, and related sciences},
  volume    = {34},
  journal   = {European journal of mineralogy : EJM : an international journal on mineralogy, petrology, geochemistry, and related sciences},
  number    = {1},
  publisher = {Copernicus},
  address   = {G{\"o}ttingen},
  issn      = {0935-1221},
  doi       = {10.5194/ejm-34-7-2022},
  pages     = {7 -- 18},
  year      = {2022},
  abstract  = {We determined Ar-40/Ar-39 ages of buddingtonite, occurring together with muscovite, with the laser-ablation method. This is the first attempt to date the NH4-feldspar buddingtonite, which is typical for sedimentary-diagenetic environments of sediments, rich in organic matter, or in hydrothermal environments, associated with volcanic geyser systems. The sample is a hydrothermal breccia, coming from the Paleoproterozoic pegmatite field of the Korosten Plutonic Complex, Volyn, Ukraine. A detailed characterization by optical methods, electron microprobe analyses, backscattered electron imaging, and IR analyses showed that the buddingtonite consists of euhedral-appearing platy crystals of tens of micrometers wide, 100 or more micrometers in length, which consist of fine-grained fibers of <= 1 mu m thickness. The crystals are sector and growth zoned in terms of K-NH4-H3O content. The content of K allows for an age determination with the Ar-40/Ar-39 method, as well as in the accompanying muscovite, intimately intergrown with the buddingtonite. The determinations on muscovite yielded an age of 1491 +/- 9 Ma, interpreted as the hydrothermal event forming the breccia. However, buddingtonite apparent ages yielded a range of 563 +/- 14 Ma down to 383 +/- 12 Ma, which are interpreted as reset ages due to Ar loss of the fibrous buddingtonite crystals during later heating. We conclude that buddingtonite is suited for Ar-40/Ar-39 age determinations as a supplementary method, together with other methods and minerals; however, it requires a detailed mineralogical characterization, and the ages will likely represent minimum ages.},
  language  = {en}
}
@article{RiedlMelnickNjueetal.2022,
  author    = {Riedl, Simon and Melnick, Daniel and Njue, Lucy and Sudo, Masafumi and Strecker, Manfred},
  title     = {Mid-Pleistocene to recent crustal extension in the inner graben of the Northern Kenya Rift},
  series = {Geochemistry, geophysics, geosystems},
  volume    = {23},
  journal   = {Geochemistry, geophysics, geosystems},
  number    = {3},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {1525-2027},
  doi       = {10.1029/2021GC010123},
  pages     = {25},
  year      = {2022},
  abstract  = {Magmatic continental rifts often constitute nascent plate boundaries, yet long-term extension rates and transient rate changes associated with these early stages of continental breakup remain difficult to determine. Here, we derive a time-averaged minimum extension rate for the inner graben of the Northern Kenya Rift (NKR) of the East African Rift System for the last 0.5 m.y. We use the TanDEM-X science digital elevation model to evaluate fault-scarp geometries and determine fault throws across the volcano-tectonic axis of the inner graben of the NKR. Along rift-perpendicular profiles, amounts of cumulative extension are determined, and by integrating four new Ar-40/Ar-39 radiometric dates for the Silali volcano into the existing geochronology of the faulted volcanic units, time-averaged extension rates are calculated. This study reveals that in the inner graben of the NKR, the long-term extension rate based on mid-Pleistocene to recent brittle deformation has minimum values of 1.0-1.6 mm yr(-1), locally with values up to 2.0 mm yr(-1). A comparison with the decadal, geodetically determined extension rate reveals that at least 65\% of the extension must be accommodated within a narrow, 20-km-wide zone of the inner rift. In light of virtually inactive border faults of the NKR, we show that extension is focused in the region of the active volcano-tectonic axis in the inner graben, thus highlighting the maturing of continental rifting in the NKR.},
  language  = {en}
}