Pseudotachylyte

Purple and green pseudotachylyte veins in outcrop (Sierra Nevada Mountains, California)

Pseudotachylyte (sometimes written as pseudotachylite) is an extremely fine-grained to glassy, dark, cohesive rock occurring as veins[1] that form through frictional melting and subsequent quenching during earthquakes,[2] large-scale landslides, and impacts events.[3] Chemical composition of pseudotachylyte generally reflects the local bulk chemistry, though may skew to slightly more mafic compositions due to the preferential incorporation of hydrous and ferro-magnesian minerals (mica and amphibole, respectively) into the melt phase.[4]

Pseudotachylyte was first documented by Shand in the Vredefort Impact Structure and was named due to its close resemblance to tachylyte, a basaltic glass.[5] Though pseudotachylyte is reported to have a glassy appearance, they are extremely susceptible to alteration and are thus rarely found to be entirely composed of glass.[6][7] Typically, they are completely devitrified into a very fine-grained material with quench textures such as chilled margins,[8][9] radial and concentric clusters of microcrystalites (spherulites)[10][11] or as radial overgrowths of microcrystalites on clasts,[12] as well as skeletal and spinifex microcrystalites.[6][10]

Radial overgrowth of plagioclase microcrystallite laths on plagioclase survivor grain in pseudotachylyte (Asbestos Mountain Fault, California)
  1. ^ Trouw, R.A.J., C.W. Passchier, and D.J. Wiersma (2010) Atlas of Mylonites- and related microstructures. Springer-Verlag, Berlin, Germany. 322 pp. ISBN 978-3-642-03607-1
  2. ^ Sibson, R.H. (1975). "Generation of pseudotachylyte by ancient seismic faulting". Geophysical Journal International. 43 (3): 775–794. Bibcode:1975GeoJ...43..775S. doi:10.1111/j.1365-246x.1975.tb06195.x.
  3. ^ Lin, A. (2007). Fossil earthquakes: the formation and preservation of Pseudotachylytes. Lecture Notes in Earth Sciences. Vol. 111. Springer. p. 348. ISBN 978-3-540-74235-7. Retrieved 2009-11-02.
  4. ^ Magloughlin, J.F.; Spray, J.G. (1992). "Frictional melting processes and products in geological materials: introduction and discussion". Tectonophysics. 204 (3–4): 197–206. Bibcode:1992Tectp.204..197M. doi:10.1016/0040-1951(92)90307-R – via Elsevier Science Direct.
  5. ^ Shand, S. James (1916-02-01). "The Pseudotachylyte of Parijs (Orange Free State), and its Relation to 'Trap-Shotten Gneiss' and 'Flinty Crush-Rock'". Quarterly Journal of the Geological Society. 72 (1–4): 198–221. doi:10.1144/GSL.JGS.1916.072.01-04.12. ISSN 0370-291X. S2CID 129174160.
  6. ^ a b Kirkpatrick, James D.; Rowe, Christen D. (2013). "Disappearing ink: How pseudotahcylytes are lost from the rock record". Journal of Structural Geology. 52: 183–198. Bibcode:2013JSG....52..183K. doi:10.1016/j.jsg.2013.03.003.
  7. ^ Fondriest, Michele; Mecklenburgh, Julian; Francois Xavier, Passelegue; Gilberto, Artioli; Nestola, Fabrizio; Spagnuolo, Elena; Rempe, Marieke; Di Toro, Guilio (2020). "Pseudotachylyte alteration and the rapid fade of earthquake scars from the geological record". Geophysical Research Letters. 47 (22). Bibcode:2020GeoRL..4790020F. doi:10.1029/2020GL090020. hdl:11577/3377649. S2CID 228918611.
  8. ^ Bjornerud, Marcia (2010). "Rethinking conditions necessary for pseudotachylyte formation: Observations from the Otago schists, South Island, New Zealand". Tectonophysics. 490 (1–2): 68–80. Bibcode:2010Tectp.490...69B. doi:10.1016/j.tecto.2010.04.028.
  9. ^ Kirkpatrick, J.D.; Shipton, Z.K.; Persano, C. (2009). "Pseudotachylytes: Rarely generated, rarely preserved, or rarely reported?". Bulletin of the Seismological Society of America. 99 (1): 382–388. Bibcode:2009BuSSA..99..382K. doi:10.1785/0120080114.
  10. ^ a b Lin, Aiming (1994). "Glassy pseudotachylyte veins from the Fuyun fault zone, northwest China". Journal of Structural Geology. 16 (1): 71–83. Bibcode:1994JSG....16...71L. doi:10.1016/0191-8141(94)90019-1.
  11. ^ Dunkel, K.G.; Morales, L.F.G.; Jamveit, B. (2021). "Pristine microstructures in pseudotachylytes formed in dry lower crust, Lofoten, Norway". Philosophical Transactions A. 379 (2193). Bibcode:2021RSPTA.37990423D. doi:10.1098/rsta.2019.0423. PMC 7898121. PMID 33517873.
  12. ^ Prante, Mitchell R.; Evans, James P. (2015). "Pseudotachylyte and fluid alteration at seismogenic depths (Glacier Lakes and Granite Pass Faults), Central Sierra Nevada, USA". Pure and Applied Geophysics. 172 (5): 1203–1227. Bibcode:2015PApGe.172.1203P. doi:10.1007/s00024-014-0989-2. S2CID 129906270 – via Springer.