The structural and geochemical evolution of the continental crust: Support for the oceanic plateau model of continental growth

The problem of the origin of the continental crust can be resolved into two fundamental questions: (1) the location and mechanisms of initial mantle extraction of the primitive crust and (2) the processes by which this primitive crust is converted into the continental crust that presently exists. We know that Archean continental crust is compositionally distinct from younger continental crust. Archean magmatism was dominantly bimodal, mafic thoeleiitic plus dacitic, heavy rare earth element depleted, in contrast to the dominantly unimodal, roughly andesitic calc-alkaline magmatism on younger crust [Taylor and McLennan, 1985; Condie, 1989]. The problem is whether these compositional differences are primarily due to different mechanisms of crustal extraction from the mantle or to different mechanisms of differentiation and alteration of newly formed continental crust

Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health

This paper is not subject to U.S. copyright. The definitive version was published in Harmful Algae 14 (2012): 271-300, doi:10.1016/j.hal.2011.10.025.Over the last decade, our understanding of the environmental controls on Pseudo-nitzschia blooms and domoic acid (DA) production has matured. Pseudo-nitzschia have been found along most of the world's coastlines, while the impacts of its toxin, DA, are most persistent and detrimental in upwelling systems. However, Pseudo-nitzschia and DA have recently been detected in the open ocean's high-nitrate, low-chlorophyll regions, in addition to fjords, gulfs and bays, showing their presence in diverse environments. The toxin has been measured in zooplankton, shellfish, crustaceans, echinoderms, worms, marine mammals and birds, as well as in sediments, demonstrating its stable transfer through the marine food web and abiotically to the benthos. The linkage of DA production to nitrogenous nutrient physiology, trace metal acquisition, and even salinity, suggests that the control of toxin production is complex and likely influenced by a suite of environmental factors that may be unique to a particular region. Advances in our knowledge of Pseudo-nitzschia sexual reproduction, also in field populations, illustrate its importance in bloom dynamics and toxicity. The combination of careful taxonomy and powerful new molecular methods now allow for the complete characterization of Pseudo-nitzschia populations and how they respond to environmental changes. Here we summarize research that represents our increased knowledge over the last decade of Pseudo-nitzschia and its production of DA, including changes in worldwide range, phylogeny, physiology, ecology, monitoring and public health impacts

Coming out of nowhere: Alaska homestead poems

An Alaska memoir told in poems.--Provided by publisher.Country of Strangers -- Driving by the Old Homestead -- Mountains Like Ribs -- The Homesteader's Wife -- Today Is All They Have -- Baking Lessons -- Momma Said -- The Winter Meat -- My Father Hilling Potatoes -- Girl Made of Fog -- Summer Untethered -- Hum -- Leda -- Horse Called Charlie -- Along the Print -- Sleepwalking toward Myself -- Stealing the Strawberries -- No One Asks about the Bridge -- In the Playhouse -- Sleeping the Chickens -- Childhood, Swallow -- Ice's Apprentice -- December's Tree -- Survival Tactics -- Painting the Stones -- The Button Box -- Above the Garage -- The Card Shark -- Because Music Is Green -- Neighbors -- The Earth Is Breakable -- I Watch the Hired Men Pick Potatoes -- Our Father Leaving Us -- Night Sounds -- He's Talking -- Someone Should Have Kicked the Pedophiles off Our Place -- Tower Bells -- Leaving for the University -- Whole -- Her Garden -- May, at My Father's Burial -- To Dust -- On Being Disinherited -- Coming Out of Nowhere

The stress regime in a Rotliegend reservoir of the Northeast German Basin

In-situ stresses have significant impact, either positive or negative, on the short and long term behaviour of fractured reservoirs. The knowledge of the stress conditions are therefore important for planning and utilization of man-made geothermal reservoirs. The geothermal field Groß Schönebeck (40 km north of Berlin/Germany) belongs to the key sites in the northeastern German Basin. We present a stress state determination for this Lower Permian (Rotliegend) reservoir by an integrated approach of 3D structural modelling, 3D fault mapping, stress ratio definition based on frictional constraints, and slip-tendency analysis. The results indicate stress ratios of the minimum horizontal stress S being equal or increasing 0.55 times the amount of the vertical stress S (S ≥ 0.55S) and of the maximum horizontal stress S ≤ 0.78-1.00S in stress regimes from normal to strike slip faulting. Thus, acting stresses in the 4,100-m deep reservoir are S = 100 MPa, S = 55 MPa and S = 78-100 MPa. Values from hydraulic fracturing support these results. Various fault sets of the reservoir are characterized in terms of their potential to conduct geothermal fluids based on their slip and dilatation tendency. This combined approach can be adopted to any other geothermal site investigation

Deformational History of the Neoproterozoic Keraf Zone in NE Sudan, Revealed by Shuttle Imaging Radar

The location of the boundary between juvenile Neoproterozoic crust of the Arabian-Nubian Shield in the Red Sea Hills and older crust of the Nile craton to the west is defined by the Keraf zone in northern Sudan, but little is known about its deformation history. Shuttle Imaging Radar (SIR-A), Landsat Thematic Mapper (TM), and Large Format Camera (LFC) images, combined with ground investigation, were used to carry out the first detailed study of the Keraf zone. This N-trending zone is ~45 km wide and is defined by multiply deformed carbonate-rich turbidites and volcanogenic sediments. Six deformational phases (D1 to D6) were identified, associated with two tectonic events: (1) D1 and D2 are related to emplacement of SSE-verging ophiolitic nappes due to collision between the Haifa and Bayuda terranes along the ENE-trending Atmur suture at ~800-700 Ma. The Atmur suture marks the site of a former Neoproterozoic oceanic re-entrant that extended WSW from the Mozambique ocean into the interior of the Nile craton. D1 produced SSE-verging tight folds and thrusts, whereas D2 deformed the D1-structures into ENE-trending upright folds. (2) D3 to D6 reflect shortening across the Keraf zone. D3 produced N-trending, upright, isoclinal to open folds. D4 was superimposed on D3 as coaxial W-verging tight folds. D5 refolded older structures about steeply, east- to ENE-plunging fold axes. D6 manifests development of local NE-trending dextral and NW-trending sinistral shear zones. We suggest that this deformation reflects oblique collision between composite arc terranes of the Arabian-Nubian Shield and the Nile craton along the Keraf zone at ~750-650 Ma