TY - JOUR
T1 - Cretaceous age, composition, and microstructure of pseudotachylyte in the Otago Schist, New Zealand
AU - Barker, Shaun L.L.
AU - Sibson, Richard H.
AU - Palin, J. Michael
AU - FitzGerald, John D.
AU - Reddy, Steve
AU - Warr, Laurence N.
AU - Van Der Pluijm, Ben A.
PY - 2010/3
Y1 - 2010/3
N2 - At Tucker Hill, in Central Otago, New Zealand, a series of pseudotachylyte veins are hosted in quartzofeldspathic schist. Chilled margins, microlites, flow banding, and the crystallisation of mineral phases absent from the host rock provide unequivocal evidence for melting during pseudotachylyte formation. Whole rock analyses of pseudotachylyte reveal c. 3 x enrichment of K2O, Ba, and Rb, and similar depletion of Na2O, CaO, Sr, and Eu, as compared to host schist. Formation age of pseudotachylyte is 95.9 ± 1.8 Ma as measured by total fusion 40Ar/39Ar analyses. Stepwise heating of pseudotachylyte matrix yields an excellently defined 40Ar/39Ar plateau age of 96.0 ±0.3 Ma. These well-defined ages are attributed to the presence of potassium feldspar, low abundance of inherited lithic material from the host rock, and few fluid inclusions containing extraneous Ar. We propose that formation of these pseudotachylyte veins was related to Cretaceous extensional uplift and exhumation of the Otago Schist.
AB - At Tucker Hill, in Central Otago, New Zealand, a series of pseudotachylyte veins are hosted in quartzofeldspathic schist. Chilled margins, microlites, flow banding, and the crystallisation of mineral phases absent from the host rock provide unequivocal evidence for melting during pseudotachylyte formation. Whole rock analyses of pseudotachylyte reveal c. 3 x enrichment of K2O, Ba, and Rb, and similar depletion of Na2O, CaO, Sr, and Eu, as compared to host schist. Formation age of pseudotachylyte is 95.9 ± 1.8 Ma as measured by total fusion 40Ar/39Ar analyses. Stepwise heating of pseudotachylyte matrix yields an excellently defined 40Ar/39Ar plateau age of 96.0 ±0.3 Ma. These well-defined ages are attributed to the presence of potassium feldspar, low abundance of inherited lithic material from the host rock, and few fluid inclusions containing extraneous Ar. We propose that formation of these pseudotachylyte veins was related to Cretaceous extensional uplift and exhumation of the Otago Schist.
KW - Ar-Ar
KW - Friction melting
KW - Geochronology
KW - Otago
KW - Pseudotachylyte
KW - Schist
UR - http://www.scopus.com/inward/record.url?scp=77954029758&partnerID=8YFLogxK
U2 - 10.1080/00288301003631764
DO - 10.1080/00288301003631764
M3 - Article
SN - 0028-8306
VL - 53
SP - 15
EP - 29
JO - New Zealand Journal of Geology, and Geophysics
JF - New Zealand Journal of Geology, and Geophysics
IS - 1
ER -