U_Pb_Geochronology

406 358954 b 327406 357663 c 341707 358558 d 331308

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Unformatted text preview: a decompressor are needed to see this picture. 340 206Pb/238U 336 0.0535 332 0.0525 Intercepts at 328 0±0 & 357.4±2.2 [±4.9] Ma MSWD = 0.85 324 0.0515 0.375 0.385 0.395 0.405 207 0.415 0.425 Pb/235U From Murphy et al. (2006) Wednesday, 15 August, 12 Detrital Zircon Geochronology • • Done to study provenance of sedimentary rocks. • • • • • Requires lots of analyses (>100-200) from a sample. • Interested in patterns, not absolute ages. Has blossomed in recent years due to SHRIMP and LAICP-MS. We present errors as 1σ ages rather than 2σ. We will accept samples up to 30% discordant. Typically use the 207Pb/206Pb ages. Plot on concordia and cumulative frequency diagrams (bump-o-grams!). Wednesday, 15 August, 12 Example: Snowcap Assemblage, Yukon data-point error ellipses are 68.3% conf. 0.65 3000 0.55 206Pb/238U 2600 0.45 2200 0.35 1800 1400 0.25 0.15 1000 0.05 0 4 8 12 207 Pb/235 Wednesday, 15 August, 12 16 20 From Piercey and Colpron (1999) Relative probability Example: Snowcap Assemblage, Yukon 800 1200 1600 2000 Age Wednesday, 1...
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