Episodic growth and homogenization of plutonic roots in arc volcanoes from combined U–Th and (U–Th)/He zircon dating
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- 作者：Axel K. Schmitt ; Daniel F. Stockli ; Jan M. Lindsay ; Richard Robertson ; Oscar M. Lovera ; Roman Kislitsyn
- 关键词：zircon residence time ; Quaternary geochronology ; arc volcanism ; magma chambers ; plutons
- 刊名：Earth and Planetary Science Letters
- 出版年：2010
- 出版时间：15 June 2010
- 年：2010
- 卷：295
- 期：1-2
- 页码：91-103
- 全文大小：702 K
文摘
Tracing the fate of unerupted magma is challenging because plutonic roots of young volcanoes are largely inaccessible. Here we develop the use of zircon age spectra to determine crystal provenance and source rocks for volcanic products, in analogy to detrital crystals in sediments. U–Th zircon crystallization ages for the Soufrière Volcanic Complex, Saint Lucia (Lesser Antilles) frequently predate their eruption as determined from combined U–Th and (U–Th)/He zircon dating. The oldest dated eruptions are 273 ± 15 ka and 264 ± 8 ka (1σ uncertainty) for Morne Bonin dacite and Bellevue pumice deposit, respectively. The most recent eruptions formed morphologically pristine domes in the center of the Qualibou depression (Belfond: 13.6 ± 0.4 ka; Terre Blanche: 15.3 ± 0.4 ka). U–Th (U–Pb) zircon crystallization ages determined for crystal rims and interiors range between near-eruption ages to 600 ka. Older xenocrysts are absent. Zircon crystallization age distributions are complex, yet systematic: crystal rim ages in the most recently erupted volcanic rocks match those of co-erupted plutonic inclusions, whereas crystal interiors are equivalent to the cumulative distribution of zircon ages from older eruptions. This is evidence that silicic lava domes and pyroclastic flows share a common source that is located underneath the Qualibou depression, where the intrusive roots of this long-lived arc volcanic system became homogenized through thermal and mechanical reprocessing of individual batches of unerupted magma from earlier volcanic episodes within timescales of < 100 ka.