HR: 0800h
AN: T41C-0708    [Abstracts]
TI: Episodic Volcanism and Geochemistry in Western Nicaragua
AU: * Saginor, I
EM: saginor@rci.rutgers.edu
AF: Rutgers University, 610 Taylor Rd, Piscataway, NJ 08854, United States
AU: Carr, M J
EM: carr@rci.rutgers.edu
AF: Rutgers University, 610 Taylor Rd, Piscataway, NJ 08854, United States
AU: Gazel, E
EM: egazel@eden.rutgers.edu
AF: Rutgers University, 610 Taylor Rd, Piscataway, NJ 08854, United States
AU: Swisher, C
EM: cswish@rci.rutgers.edu
AF: Rutgers University, 610 Taylor Rd, Piscataway, NJ 08854, United States
AU: Turrin, B
EM: bturrin@rci.rutgers.edu
AF: Rutgers University, 610 Taylor Rd, Piscataway, NJ 08854, United States
AB: The active volcanic arc in western Nicaragua is separated from the Miocene arc by a temporal gap in the volcanic record, during which little volcanic material was erupted. Previous work suggested that this gap lasted from 7 to 1.6 Ma, during which volcanic production in Nicaragua was limited or nonexistent. Because the precise timing and duration of this gap has been poorly constrained, recent fieldwork has focused on locating samples that may have erupted close to or even during this apparent hiatus in activity. Recent 40Ar/39Ar dates reveal pulses of low- level episodic volcanism at 7 Ma and 1 Ma between the active and Miocene arcs with current volcanism beginning ~350 ka. In addition, sampling from an inactive area between Coseguina and San Cristobal yielded two distinct groupings of ages; one of Tamarindo age (13 Ma) and the other around 3.5 Ma-the only samples of that age collected on-strike with the active arc. This raises the possibility the bases of the other active volcanoes contain lavas that are older than expected, but have been covered by subsequent eruptions. The Miocene arc differs from the active arc in Central America in several ways, with the latter having higher Ba/La and U/Th values due to increased slab input and changes in subducted sediment composition. Analysis of sample C-51 and others taken from the same area may shed light on the timing of this shift from high to low Ba/La and U/Th values. More importantly, it may help explain why the arc experienced such a dramatic downturn in volcanic production during this time. We also report 25 new major and trace element analyses that shed some light on the origins of these minor episodes of Nicaraguan volcanism. These samples are currently awaiting Sr and Nd isotopic analyses.
DE: 1115 Radioisotope geochronology
DE: 8410 Geochemical modeling (1009, 3610)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting