40Ar/39Ar UV laser dating, EBSD and EMP analysis of 1040-940 Ma metamorphic/deformation/cooling events recorded in Sibao Orogen white micas, South China.

Wartho, J.-A. , Li, Z.-X., Occhipinti, S. A. and Reddy, S. (2008) 40Ar/39Ar UV laser dating, EBSD and EMP analysis of 1040-940 Ma metamorphic/deformation/cooling events recorded in Sibao Orogen white micas, South China. [Talk] In: Goldschmidt Conference 2008. , 13.-18.07.2008, Vancouver, Canada .

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Abstract

The Tianli Schist is the largest meta-sedimentary complex
of the eastern portion of the Grenville-aged Sibaon Orogen in
South China, and is linked to the assembly of the
Neoproterozoic supercontinent Rodinia. These well-preserved
mica-bearing samples were subjected to: (1) Electron
Backscattered Detection (EBSD) mapping to characterise the
deformation fabrics, (2) electron microprobe (EMP) analyses
to discern subtle chemical differences between three white
mica populations, and (3) 40Ar/39Ar ultra-violet (UV) laser
spot dating of specific white mica and biotite fabrics. This
combined approach includes EBSD mapping of white micas,
which has previously been hampered by difficulties in
preparing the samples and issues with mis-indexing of these
monoclinic minerals.
The results yield a series of texturally- and chemicallydefined
40Ar/39Ar ages that can be tied to an initial 1042 ±
7 Ma Grenville metamorphic event and three subsequent
deformation/cooling episodes at 1015 ± 4, 968 ± 4 and 942 ±
8 Ma (all 2 σ). The high-resolution 1042 ± 7 Ma 40Ar/39Ar
Grenville metamorphic age is consistent with a Tianli Schist
207Pb/206Pb SHRIMP detrital zircon Pb-loss age of 1029 ±
24 Ma (2σ) [1], and a previous Sm-Nd mineral isochron age
of 1034 ± 24 Ma from the nearby Zhangshudun ultramafic
complex [2].
The multi-faceted EBSD and EMP approach towards
characterising the metamorphic and deformation fabrics in the
Tianli Shist has broadened our understanding of the
interpretation of the metamorphic/deformation/cooling
40Ar/39Ar ages preserved in the white micas.

Document Type: Conference or Workshop Item (Talk)
Additional Information: Abstract: Geochimica et Geophysica Acta, 2008, Supplement, p. A1006
Date Deposited: 05 Sep 2016 07:28
Last Modified: 05 Sep 2016 07:28
URI: http://oceanrep.geomar.de/id/eprint/33706

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