Geochronologic evidence of upper-crustal in situ differentiation: Silicic magmatism at the Organ caldera complex, New Mexico
Matthew J. Zimmerer and William C. McIntosh, Dept. of Earth and Environmental Science and New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA. First posted online 11 Jan. 2013; now part of the Feb. 2013 issue; http://geosphere.gsapubs.org/content/9/1/155.abstract.
Determining the processes that generate caldera-related silicic magmas and the origin of compositional zonation patterns of ignimbrites is central to our understanding of caldera-forming eruptions. Though the hazards associated with calderas are well known, caldera eruptions are infrequent and have not been directly observed. Because of this, most caldera magmatism models are developed using extinct caldera systems. In this study, Matthew Zimmerer and William McIntosh, conducted 40Ar/39Ar and laser ablation-inductively coupled plasma-mass spectrometry U/Pb zircon dating of the volcanic and plutonic rocks from the Organ caldera complex in order to accomplish two primary goals: (1) to investigate the time scales of caldera magmatism, from inception to cessation; and (2) to determine whether the caldera-forming silicic ignimbrites were generated by upper-crustal in situ differentiation or were generated at deeper crustal levels. This was accomplished by comparing the timing of caldera ignimbrite eruptions to the emplacement history of the Organ Needle pluton, the proposed residual crystal mush of the caldera magma chamber.
Atlas of Alteration Textures in Volcanic Glass from the Ocean Basins
Martin Fisk, College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97330, USA; and Nicola McLoughlin. First posted online 5 Feb. 2013; '/>"/>
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