Comparison of U-Th and U-Pb zircon ages from erupted plutonic clasts and 40Ar/39Ar eruption ages from Newberry Volcano, Oregon
Abstract
The magmatic plumbing systems of Quaternary volcanoes are poorly understood due to insufficient uplift and erosion to expose their intrusive roots. These intrusive bodies remained in the plumbing system for longer timescales than the eruptive melt; therefore, plutonic rocks record a more extensive history of the entire magmatic system. Occasionally, large-scale eruptions can expose regions of the plumbing system and/or erupt plutonic clasts (EPC) to the surface. We are investigating EPCs found within Newberry ash flow tuffs and hydrothermal drill cores to understand subsurface processes occurring within the magmatic plumbing system. Newberry Volcano is a large shield-shaped composite volcano located in central Oregon that has experienced recurrent volcanism from ca. 500 ka to 1,300 ybp. This study uses the EPC ages to link the intrusive rocks inferred to be representative of the Newberry magmatic plumbing system, and to discern a systematic relationship with volcanism. SHRIMP U-Th disequilibrium and U-Pb zircon ages were analyzed from six EPCs and two hydrothermal granitoids from separate drill cuttings. We compare these new SHRIMP ages to existing 40Ar/39Ar geochronology of Newberry volcanic strata. Three EPCs have unimodal zircon ages of 140 ka, two EPCs display ages of 300 ka, and one has three distinct zircon age populations of 120 ka, 200 ka, and 300 ka. Zircons from separate drill cuttings have ages of 350 ka and 1.9 Ma. All the EPC zircon ages are less than 500 kyr, implying that these clasts are related to the Newberry magmatic system. The granitoid with 1.9 Myr zircons was penetrated by drilling at 2.6 km depth, and could be related to Newberry magmatism and represent an earlier phase of intrusive activity. The 140 kyr zircons record a single crystallization event that took place during a period of frequent volcanism, while the three remaining age populations represent multiple periods of growth that overlap with timeframes of waning activity. Combining EPC zircon ages with 40Ar/39Ar eruption ages may test the temporal relationship between plutonism and volcanism within a variety of tectonic settings.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.V53C3109S
- Keywords:
-
- 8419 Volcano monitoring;
- VOLCANOLOGYDE: 8434 Magma migration and fragmentation;
- VOLCANOLOGYDE: 8439 Physics and chemistry of magma bodies;
- VOLCANOLOGYDE: 8486 Field relationships;
- VOLCANOLOGY