News from Academy Bay

New Faces and New Projects in a New CDRS Department. International Workshop: Feral Goat Eradication Program. Geologists to Invade Galápagos. GIS in Galápagos. The Isabela Project: Off and Running. A Pig-Free Santiago: Is it a Dream or on the Horizon? The Special Law for Galápagos

Magma chambers versus mush zones: constraining the architecture of sub-volcanic plumbing systems from microstructural analysis of crystalline enclaves.

There are clear microstructural differences between mafic plutonic rocks that formed in a dynamic liquid-rich environment, in which crystals can be moved and re-arranged by magmatic currents, and those in which crystal nucleation and growth are essentially in situ and static. Crystalline enclaves, derived from deep crustal mushy zones and erupted in many volcanic settings, afford a unique opportunity to use the understanding of microstructural development, established from the study of intrusive plutons, to place constraints on the architecture of sub-volcanic systems. Here, we review the relevant microstructural literature, before applying these techniques to interrogate the crystallization environments of enclaves from the Kameni Islands of Santorini and Rábida Volcano in the Galápagos. Crystals in samples of deep-sourced material from both case studies preserve evidence of at least some time spent in a liquid-rich environment. The Kameni enclaves appear to record an early stage of crystallization during which crystals were free to move, with the bulk of crystallization occurring in a static, mushy environment. By contrast, the Rábida enclaves were sourced from an environment in which hydrodynamic sorting and re-arrangement by magmatic currents were common, consistent with a liquid-rich magma chamber. While presently active volcanoes are thought to be underlain by extensive regions rich in crystal mush, these examples preserve robust evidence for the presence of liquid-rich magma chambers in the geological record. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'

Construction of the Galapagos platform by large submarine volcanic terraces

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q03015, doi:10.1029/2007GC001795.New multibeam bathymetric and side-scan sonar data from the southwestern edge of the Galápagos platform reveal the presence of ∼60 large, stepped submarine terraces between depths of 800 m and 3500 m. These terraces are unique features, as none are known from any other archipelago that share this geomorphic form or size. The terraces slope seaward at 3000 m) lava flow fields west of Fernandina and Isabela Islands. The terraces are formed of thick sequences of lava flows that coalesce to form the foundation of the Galápagos platform, on which the subaerial central volcanoes are built. The compositions of basalts dredged from the submarine terraces indicate that most lavas are chemically similar to subaerial lavas erupted from Sierra Negra volcano on southern Isabela Island. There are no regular major element, trace element, or isotopic variations in the submarine lavas as a function of depth, relative stratigraphic position, or geographic location along the southwest margin of the platform. We hypothesize that magma supply at the western edge of the Galápagos hot spot, which is influenced by both plume and mid-ocean ridge magmatic processes, leads to episodic eruption of large lava flows. These large lava flows coalesce to form the archipelagic apron upon which the island volcanoes are built.This work was supported by the National Science Foundation grants OCE0002818 and EAR0207605 (D.G.), OCE0002461 (D.J.F. and M.K.), OCE05-25864 (M.K.), and EAR0207425 (K.H.)

The Grizzly, March 2, 1998

Ursinus Offers Free Practice GRE Exam to Students • Eating Disorder Screening Offered at Wellness • A Meeting Educates UC • Texas Winners Tell All • Letters to the Editor: Greeks Respond to Rudolfs Article; Response to New Bookstore • A Tribe Called Graffiti • Safety Issues Crossing Main Street • Gross Honored in Who\u27s Who • Sexual Assault Awareness Week • Outdoor Adventure Club Comes to Ursinus • Bears Run Into a Wall at Hopkins • Solid Performance at Championships for UC Swimming • Indoor Track Championships • Tribute to the Unsung Hero • USA D-III Mardi Gras All-Star Classic • UC Gymnasts Headed All the Way to the Tophttps://digitalcommons.ursinus.edu/grizzlynews/1416/thumbnail.jp

An upper mantle seismic discontinuity beneath the Galápagos Archipelago and its implications for studies of the lithosphere‐asthenosphere boundary

An upper mantle seismic discontinuity (the Gutenberg or G discontinuity), at which shear wave velocity decreases with depth, has been mapped from S‐to‐p conversions in radial receiver functions recorded across the Galápagos Archipelago. The mean depth of the discontinuity is 91 ± 8 km beneath the southeastern archipelago and 72 ± 5 km beneath surrounding regions. The discontinuity appears deeper beneath the portion of the Nazca plate that we infer passed over the Galápagos mantle plume than elsewhere in the region. We equate the depth of the G discontinuity to the maximum depth extent of anhydrous melting, which forms an overlying layer of dehydrated and depleted mantle. We attribute areas of shallow discontinuity depth to the formation of the dehydrated layer near the Galápagos Spreading Center and areas of greater discontinuity depth to its modification over a mantle plume with an excess temperature of 115 ± 30°C. The G discontinuity lies within a high‐seismic‐velocity anomaly that we conclude forms by partial dehydration and a gradual but steady increase in seismic velocity with decreasing depth after upwelling mantle first encounters the solidus for volatile‐bearing mantle material. At the depth of the solidus for anhydrous mantle material, removal of remaining water creates a sharp decrease in velocity with depth; this discontinuity may also mark a site of melt accumulation. Results from seismic imaging, the compositions of Galápagos lavas, and rare‐earth‐element concentrations across the archipelago require that mantle upwelling and partial melting occur over a broad region within the dehydrated and depleted layer. We conclude that the G discontinuity beneath the archipelago does not mark the boundary between rigid lithosphere and convecting asthenosphere