Dating deformation using sheared leucogranite: temporal constraints by 40Ar/39Ar thermochronology for the Mae Ping shear zone, NW Thailand

Yu Ling Lin*, Tung Yi Lee, Ching Hua Lo, Sarah C. Sherlock, Yoshiyuki Iizuka, Tadashi Usuki, Long Xiang Quek, Punya Charusiri

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

The Mae Ping shear zone (MPSZ) is one of the major ductile strike-slip systems associated with the Cenozoic extrusion tectonics in Southeast Asia. However, its sinistral shear lacks a robust temporal constraint. This study attempts to acquire the deformation timing by applying 40Ar/39Ar thermochronology on a sheared pegmatitic leucogranite showing sinistral S–C fabrics with a thrust component. The contact of the leucogranite sub-paralleling to the major foliation in host gneiss indicates it could be a pre- to syn-shearing intrusion. Most minerals, including garnet, muscovite, K-feldspar, albite, and quartz, exhibit ductile to brittle deformation. Mineral microstructural analysis suggests a retrograde sinistral shear from > 600 to 250 °C. In situ 40Ar/39Ar dating on muscovite yield ages mainly within 42–38 Ma with calculated closure temperatures of 435–330 °C. Fine-grained muscovite aggregates are slightly older than fish, implying that grain size reduction may not always reset 40Ar/39Ar ages. The K-feldspar 40Ar/39Ar step heating age spectrum with two segments of contiguous steps at 24.5 and 35.4 Ma may reflect the coexistence of high-T porphyroclast and low-T K-rich fine-grain recrystallizing at pressure shadows. The reconstructed cooling path and inferred deformation temperatures constrain a shear duration of 42–30 Ma for the MPSZ. The activation of the MPSZ before 42 Ma could be linked to the Eocene metamorphism within a transpressional regime triggering crustal thickening that may further induce the leucogranitic melt. This study also shows leucogranite can be a nice thermal history recorder for a shear zone regarding its petrogenesis and suitable mineral assemblage for thermochronology.

Original languageEnglish
Article number65
JournalContributions to Mineralogy and Petrology
Volume176
Issue number9
DOIs
Publication statusPublished - 2021 Sep

Keywords

  • In situ muscovite Ar/Ar dating
  • K-feldspar Ar/Ar step heating
  • Lan Sang gneisses
  • Leucogranite
  • Mae Ping shear zone
  • Thermochronology

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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