Robert Duncan Shuster

Recent volcanism in the Siqueiros transform fault: picritic basalts and implications for MORB magma genesis

Small constructional volcanic landforms and very fresh-looking lava flows are present along one of the inferred active strike-slip faults that connect two small spreading centers (A and B) in the western portion of the Siqueiros transform domain. The most primitive lavas (picritic and olivine-phyric basalts), exclusively recovered from the young-looking flows within the A-B strike-slip fault, contain millimeter-sized olivine phenocrysts (up to 20 modal%) that have a limited compositional range (Fo91.5-Fo89.5) and complexly zoned CrAl spinels. High-MgO (9.5–10.6 wt%) glasses sampled from the young lava flows contain 1–7% olivine phenocrysts (Fo90.5-Fo89) that could have formed by equilibrium crystallization from basaltic melts with Mg# values between 71 and 74. These high MgO (and high Al2O3) glasses may be near-primary melts from incompatible-element depleted oceanic mantle and little modified by crustal mixing and/or fractionation processes. Phase chemistry and major element systematics indicate that the picritic basalts are not primary liquids and formed by the accumulation of olivine and minor spinel from high-MgO melts (10% < MgO < 14%). Compared to typical N-MORB from the East Pacific Rise, the Siqueiros lavas are more primitive and depleted in incompatible elements. Phase equilibria calculations and comparisons with experimental data and trace element modeling support this hypothesis. They indicate such primary mid-ocean ridge basalt magmas formed by 10–18% accumulative decompression melting in the spinel peridotite field (but small amounts of melting in the garnet peridotite field are not precluded). The compositional variations of the primitive magmas may result from the accumulation of different small batch melt fractions from a polybaric melting column.

Precambrian zircons from the Florida basement: A Gondwanan connection

A Gondwanan origin for the pre-Cretaceous basement of Florida is suggested by U- Pb ages of 515 to 2860 Ma for single zircons separated from subsurface samples of lower Paleozoic sandstone of the Suwannee basin (Alachua County, Florida) and Neoproterozoic Osceola granite (Osceola County, Florida). Forty individual grains analyzed by SHRIMP ion microprobe yielded ages from 515 to 2860 Ma; ages >1000 Ma were predominantly concordant. Two principal populations are evident: (1) 515 to 637 Ma (avg. = 574 Ma; 206 Pb/ 238 U ages) and (2) 1967 to 2282 Ma (avg. = 2130 Ma; 207 Pb/ 206 Pb ages). Only six zircons were recovered from the granite; four are Pan-African and two are Archean. For the sandstone, the similarity between the Sm-Nd model age (1245 Ma) and the average of the single zircon ages (1326 Ma) suggests that these zircons are chronologically representative of the aggregate provenance of the sandstone. The two dominant zircon age groupings correspond chronologically to the Pan-African and Birimian or Eburnian (Africa) and to the Brasiliano and Trans-Amazonian (South America) orogenic cycles. The presence of detritus from rocks of these two orogenic cycles clearly places the basement of Florida in Gondwanaland proximal to the West African and/or Trans-Amazonian-San Luis cratons in the early Paleozoic, a location it probably shared with other circum-Atlantic exotic terranes (Avalonian, Cadomian, and/or Carolina).

Chalcedony vein horizons and clastic dikes in the White River Group as products of diagenetically driven deformation

Chalcedony veins occur as local stratabound arrays at multiple levels within the finer-grained sediments of the White River Group, making up to 2%–3% of the outcrop volume. The veins are commonly deformed by small folds, faults with well-developed striae, and various fold-fault combinations, and they also exhibit striae and slickenslides on vein walls. These indicate significant vertical shortening of the veins. The combination of a stratabound distribution and vertical shortening is consistent with an origin by diagenetically driven deformation, where changes in clay and/or silica phases drive syneresis and associated dewatering and compaction. In this way, the chalcedony veins bear similarities in origin to stratabound polygonal normal fault systems seen in fine-grained marine strata. Smectite clays, silica phases, and clinoptolite in the White River Group are associated with diagenetic reactions that could produce syneresis. At different localities, vein strike distributions vary from being statistically random to highly organized. These distributions are also consistent with a syneresis origin, with local stress fields organizing the distribution into multiple coeval directions in some cases. Chalcedony veins locally occur inside and parallel to clastic dikes, clearly indicating that the veins were emplaced at the same time as or after the dikes. Thin-section textures from dike-vein composites indicate that vein formation occurred while the clastic fill was unlithified and still mobile. These relationships, along with common orientations when in proximity, link clastic dike and chalcedony vein formation. Dikes also show complex strike orientation distributions that differ by locality. Internal dike features indicate multiple fill events with intervening lithification. Evidence for vertical dike shortening suggests synchronous or later compaction. The clastic dikes are also postulated to result from syneresis. We suggest that chalcedony vein formation, silica mobilization, local uranium mineralization, and clastic dike formation are part of diagenetically driven fracture development that produced a fluid flow network, initiating feedback relationships among diagenesis, dewatering, fluid migration, and associated compaction. Given that the clastic dikes occur within the Sharps Formation, the event was Miocene or later.

Iron ooid beds of the Carolinefjellet Formation, Spitsbergen, Norway

Iron ooid beds are unusual deposits that have been linked to greenhouse conditions and the transgressive flooding of shallow shelves, and which were globally prevalent during certain periods. Within the marine, Aptian–Albian, Carolinefjellet Formation of Spitsbergen, chamosite ooids have been found within distinctive sandstone beds at six localities, and at a consistent stratigraphic position within the basal Dalkjegla Member. Distinctive characteristics include the iron ooids themselves, a coarser grain size, intercalation with silty siderites, grading, cross-beds indicating offshore or longshore transport, and a lack of burrowing. The enclosing sands display planar and hummocky crossstratification and abundant oscillation ripple marks, and are interpreted as lagoon-attached bar complexes. The stratigraphic position and traits of the iron ooid sands are consistent with seaward storm transport and preservation within interbar swales. Ooids vary in shape considerably, and display evidence for multiple growth events. Nuclei of quartz, opaques, carbonate clasts and laminated crusts are typically encircled by finer grained tangential chamosite and opaque laminae, sometimes with outer overgrowths of calcite and/or radial chamosite. The Dalkjegla Member is the marine portion of a large-scale transgressive tract, attached to underlying fluvio-estuarine Helvetiafjellet Formation strata. A lagoonal environment associated with the basal shales of the Dalkjegla Member represents a logical setting, where riverine iron concentration and iron silicate growth could occur. The Spitsbergen iron ooid beds extend the known occurrence of Cretaceous examples, representing a less common High-Latitude example, and one not directly associated with a transgressive flooding surface.

Genuine Faculty-Mentored Research Experiences for In-Service Science Teachers: Increases in Science Knowledge, Perception, and Confidence Levels

ABSTRACT The overall purpose of this multifocused study was to explore how participation in genuine mentored scientific research experiences impacts in-service science teachers and the knowledge and skills needed for their own science teaching. The research experiences resulted from a partnership between the University of Nebraska at Omaha and the Omaha Public School District. This Teacher-Researcher Partnership Program facilitated opportunities in inquiry, science content, interaction with laboratory instrumentation and technologies, critical discussion of literature, and dissemination of findings for participating in-service science teacher professional development utilizing an inquiry-based theoretical framework wherein we examined science teacher preparation via inquiry-based methods in the research laboratory. A mixed-methods approach with a convergent typology (i.e., qualitative and quantitative analyses conducted separately and integrated) was used to investigate the impact of the program on teachers. Our research question was as follows: How do teachers define and approach scientific research before and after a genuine research experience? We observed 3 emergent nodes or themes by which teachers indicated significant gains: science content knowledge, confidence, and perception. Moreover, we determined that participation by science teachers in a mentored research experience using current scientific technologies and tools improved teacher confidence in science and inquiry as well as an ongoing commitment to provide similar types of experiences to their students. These data support the need for the participation of in-service science teachers in genuine research experiences to boost technological and pedagogical content knowledge, con fidence in process and content, and the perception of translatability to the classroom.