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U/Pb dating is accomplished by laser-ablation ICP-MS in a small pit on the exterior of the crystal, and He dates are then determined on the bulk grain by conventional laser-heating and dissolution techniques.
We present examples from Mesozoic aeolian sandstones, both modern and Paleogene fluvial sediments, and active margin turbidite assemblages from the Cascadia and Kamchatka margins.
Highlights• The central uplift of the Manicouagan impact structure has been dated by (U–Th)/He• A (U–Th)/He central age (207.1 ± 6.4 Ma, 2 standard error, n = 40) has been determined• This age reflects the rapid uplift, cooling and closure of He in ~ 1 Gyr-old titanites• This correlates with the previously determined U–Pb impact-melt age of 214 ± 1 Ma• Our new approach enables dating complex impact structures that lack impact melt rocks Abstract Forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the Manicouagan impact structure were dated by the (U–Th)/He technique.
A (U–Th)/He central age of 207.1 ± 6.4 Ma (2 standard error (SE), n = 40) has been determined.
Nevertheless, the pooled, isochron and central age methods can be easily generalized to the case of (U–Th–Sm)/He dating.
Geochronology and thermochronology on detrital material provides unique constraints on sedimentary provenance, depositional ages, and orogenic evolution of source terrains.
Including Sm as a fourth parent element precludes a straightforward visualization of the age equation on a two-dimensional plot.
The central age is the most accurate and statistically robust way to calculate a sample average of several single-grain analyses because U, Th and He form a ternary system and only the central age adequately captures the statistics of this compositional data space.