Cretaceous age, composition, and microstructure of pseudotachylyte in the Otago Schist, New Zealand

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 for...

Full description

Saved in:
Bibliographic Details
Published in:New Zealand journal of geology and geophysics 2010-03, Vol.53 (1), p.15-29
Main Authors: Barker, Shaun LL, Sibson, Richard H, Palin, J Michael, FitzGerald, John D, Reddy, Steve, Warr, Laurence N, van der Pluijm, Ben A
Format: Article
Language:English
Subjects:
Ar-Ar
friction melting
geochronology
Otago
pseudotachylyte
schist
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary: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× enrichment of K 2 O, Ba, and Rb, and similar depletion of Na 2 O, CaO, Sr, and Eu, as compared to host schist. Formation age of pseudotachylyte is 95.9±1.8 Ma as measured by total fusion 40 Ar/ 39 Ar analyses. Stepwise heating of pseudotachylyte matrix yields an excellently defined 40 Ar/ 39 Ar 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.
ISSN:0028-8306
1175-8791
DOI:10.1080/00288301003631764