Magmatic Evolution of Zoned and Unzoned Ignimbrites: Evidence for a Complex Crustal Architecture Feeding four Rapid-sequence, Caldera-forming Eruptions in the San Juan Mountains, Colorado
نویسندگان
چکیده
Abstract The last four caldera-forming ignimbrites in the central San Juan caldera cluster, Colorado, erupted 1400 km3 ≤80 kyr and alternated between zoned crystal-poor rhyolite to crystal-rich dacite unzoned, dacite. 150 Rat Creek Tuff (26·91 Ma), unzoned 250 Cebolla Tuff, 500 Nelson Mountain (26·90 Ma) formed nested Luis complex with slightly offset calderas, Snowshoe (26·87 Creede south. have similar mineral assemblages of plagioclase, sanidine, quartz, biotite, hornblende, clinopyroxene, Fe–Ti oxides, accessory zircon, titanite, apatite. differs from other three more abundant hornblende a lack quartz sanidine. Trace element compositions interstitial glass are unique each ignimbrite, correlating inferred crystallization depths. Glass, feldspar, clinopyroxene thermobarometry calculations provide evidence for vertically extensive crustal magma reservoirs common magmatic zone at ∼435–470 MPa (∼16–17 km) showing transition into shallow pre-eruptive ∼110 340 (∼4–13 km), estimated reservoir architecture Altiplano Puna Volcanic Complex. upper portions eruptible parts (215 ± 50 MPa, ∼810–820 °C), (340 20 ∼860–880 ∼745–800 (110 40 825 10 °C) occupied levels crust cluster. modelling correlates deep signature typified by flat trend Ba versus Sr whole-rock chemistry. steep chemistry interpreted as shallower signature. Similarly, flatter slopes FeO An space plagioclase difficulty physically mixing Fe-rich mafic recharge owing higher viscosity. feasible lower eruption was probably triggered injection, but mingling textures pumice, suggesting that mechanisms were important causing such large eruptions. After prolonged period mantle-derived injection heating (∼25 000 Conejos Formation during ∼35–29 body became robust versatile producer diverse magmas short time periods its Oligocene ignimbrite flare-up.
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ژورنال
عنوان ژورنال: Journal of Petrology
سال: 2021
ISSN: ['1460-2415', '0022-3530']
DOI: https://doi.org/10.1093/petrology/egab006