Thermal annealing experiments Luigi Solari, UNAM, CGEO Goldschmidt - - PowerPoint PPT Presentation

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Thermal annealing experiments Luigi Solari, UNAM, CGEO Goldschmidt - - PowerPoint PPT Presentation

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Thermal annealing experiments Luigi Solari, UNAM, CGEO Goldschmidt Workshop, Aug 2015 Objectives Try to see whether thermally annealed zircons have less scatter, better age accuracy and precision What happens to complex zircons, in terms

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Goldschmidt Workshop, Aug 2015

Thermal annealing experiments

Luigi Solari, UNAM, CGEO

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Objectives

✤ Try to see whether thermally annealed zircons have less scatter,

better age accuracy and precision

✤ What happens to complex zircons, in terms of age reproducibility of

not annealed vs annealed zircons?

✤ See what happens to trace elements in thermally annealed zircons:

do they retain zoning?

✤ What about Hf isotopes? Are they (and Yb-Lu correction) affected? ✤ Causes? Just some hint

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Methodology

✤ Zircons separated and split ✤ One group thermally annealed in a muffle, 48 hrs @ 850ºC ✤ Both na and thermally annealed (each sample) mounted together in epoxy mount, polished and imaged

(CL and SEM)

✤ Both analysed in the same day, same experiment, same conditions: ✤ 32 um spot, 5 Hz, fluence 6 J/cm2 (measured before and after analysis) ✤ Resolution M050+Xseries II ✤ Si, P, Ti, Y, Nb, REE’s, Hf, Pb’s, Th, U ✤ Data reduced using Iolite (VizualAge+Trace_Elements DRS) ✤ 91500 (annealed) internal std; Plesovice (annealed) control std; several samples from 1000 to 12 Ma

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PLESOVI CE

  • 91500 ann as

standard

  • results of three

sessions averaged

  • TIMS age is

337.13±0.37 Ma

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SLIDE 5
  • Fragments of a

large (ca. 5 cm) crystal

  • TIMS age:

963.7±1.2 (no CA, no abraded, > 1 mg large fragments)

PANCHITA PEGMATI TE

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  • Age poorly

constrained between 129 and 52 Ma.

  • Nearby granite

stocks are 62- 65 Ma

XOLAPA PEGMATI TE

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Result #2: trace elements

  • Examples of

Plesovice and 91500

  • Annealed

zircons are more reproducible and less scatter.

  • Precision

(±2SE) is the same

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Result #3: complex zircons

  • Large and

complex zircons with

  • vergrowths
  • Differences in

age zoning prior to annealing, are preserved

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Result #3: complex zircons

Chemical differences are preserved after annealing

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Result #4: Hf isotopes

Thermal annealing does not affect accuracy/precision for Hf isotopes

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SLIDE 11

Some hints: SEM images

thermally annealed not annealed