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Large-amplitude gravity and magnetic highs over northeast Iowa are interpreted to reflect a buried intrusive complex composed of mafic-ultramafic rocks, the northeast Iowa intrusive complex (NEIIC), intruding Yavapai province (1.8-1.72 Ga) rocks. The age of the complex is unproven, although it has been considered to be Keweenawan (~1.1 Ga). Because only four boreholes reach the complex, which is covered by 200-700 m of Paleozoic sedimentary rocks, geophysical methods are critical to developing a better understanding of the nature and mineral resource potential of the NEIIC. Lithologic and cross-cutting relations interpreted from high-resolution aeromagnetic and airborne gravity gradient data are presented in the form of a preliminary geologic map of the basement Precambrian rocks. Numerous magnetic anomalies are coincident with airborne gravity gradient (AGG) highs, indicating widespread strongly magnetized and dense rocks of likely mafic-ultramafic composition. A Yavapai-age metagabbro unit is interpreted to be part of a layered intrusion with subvertical dip. Another presumed Yavapai unit has low density and weak magnetization, observations consistent with felsic plutons. Northeast-trending, linear magnetic lows are interpreted to reflect reversely magnetized diabase dikes and have properties consistent with Keweenawan rocks. The interpreted dikes are cut in places by normally magnetized mafic-ultramafic rocks, suggesting that the latter represent younger Keweenawan rocks. Distinctive horseshoe-shaped magnetic and AGG highs correspond with a known gabbro, and surround rocks with weaker magnetization and lower density. Here, informally called the Decorah complex, the source body has notable geophysical similarities to Keweenawan alkaline ring complexes, such as the Coldwell and Killala Lake complexes, and Mesoproterozoic anorogenic complexes, such as the Kiglapait, Hettasch, and Voisey's Bay intrusions in Labrador. Results presented here suggest that much of the NEIIC is composed of such complexes, and broadly speaking, may be a discontinuous group of several intrusive bodies. Most units are cut by suspected northwest-trending faults imaged as magnetic lineaments, and one produces apparent sinistral fault separation of a dike in the eastern part of the survey area. The location, trend, and apparent sinistral sense of motion are consistent with the suspected faults being part of the Belle Plaine fault zone, a complex transform fault zone within the Midcontinent rift system that is here proposed to correspond with a major structural discontinuity. De grandes cretes magnetiques et gravimetriques sur le nord-est de l'Iowa sont interpretees comme etant le reflet d'un complexe intrusif enfoui compose de roches mafiques et ultramafiques, soit le complexe intrusif du nord-est de l'Iowa (NEIIC), lequel penetre les roches de la Province de Yavapai (1,8-1,72 Ga). L'age du complexe n'a pas ete prouve, bien qu'il soit considere comme datant du Keweenawien (~1.1 Ga). Puisque seulement quatre sondages ont atteint le complexe, lequel est recouvert de 200 a 700 m de roches sedimentaires paleozoiques, les methodes geophysiques sont essentielles au developpement d'une meilleure comprehension de la nature et du potentiel mineral du NEIIC, Des relations lithologiques et de recoupement, interpretees a partir de donnees aeromagnetiques et de gradients de gravite aeroportes a haute resolution, sont presentees sous la forme d'une carte geologique preliminaire des roches du socle precambrien. De nombreuses anomalies magnetiques coincident avec les cretes des gradients de gravite aeroportes (AGG), indiquant des roches denses fortement magnetisees, probablement de composition mafique-ultramafique. Une unite de metagabbro d'age Yavapai est interpretee comme faisant partie d'une intrusion stratifiee avec un pendage subvertical. Une autre unite, presumee Yavapai, a une faible densite et une faible magnetisation; ce qui concorde avec des plutons felsiques. Des creux magnetiques, a tendance nord-est, sont interpretes comme etant le reflet de dykes de diabase a magnetisation inverse; leurs proprietes concordent avec celles de roches keweenawiennes. Les dykes interpretes sont par endroits recoupes par des roches mafiques-ultramafiques a magnetisation normale, suggerant que ces dernieres representent des roches keweenawiennes plus jeunes. Des cretes distinctes magnetiques et d'AGG en forme de fer a cheval correspondent a un gabbro connu et elles entourent des roches a magnetisation plus faible et a densite moindre. L'amas source, ici nomme de maniere informelle complexe de Decorah, presente des similarites geophysiques remarquables aux complexes annulaires alcalins keweenawiens, tels que les complexes de Coldwell et de Killala Lake, et a des complexes anorogeniques datant du Mesoproterozoique, tels que les intrusions de Kiglapait, de Hettasch et de Voisey's Bay au Labrador. Selon les resultats presentes ici, une grande partie du NEIIC serait composee de tels complexes et, de maniere generale, elle pourrait constituer un groupe discontinu de plusieurs amas intrusifs. La plupart des unites sont recoupees par des failles presumees a tendance nord-ouest dont l'imagerie donne des lineaments magnetiques; une unite a donne une separation, par une faille apparente senestre, d'un dyke dans la partie est du secteur a l'etude. L'endroit, la tendance et le sens senestre apparent de mouvement concordent avec le fait que les failles en question appartiendraient a la zone de faille de Belle Plaine, une zone de failles transformantes dans le systeme de rifts medio-continental que l'on propose ici correspondre a une discontinuite structurale majeure. [Traduit par la Redaction], Introduction Mineral exploration trends indicate that exploration for deposits in crystalline rocks under sedimentary cover is increasing, as exposed and shallowly buried deposits are discovered less frequently (Witherly 2012; Williams [...]

In the Lake Superior region of North America, deposition of most banded iron formations (BIFs) ended abruptly 1.85 Ga ago, coincident with the oceanic impact of the giant Sudbury extraterrestrial bolide. We propose a new model in which this impact produced global mixing of shallow oxic and deep anoxic waters of the Paleoproterozoic ocean, creating a suboxic redox state for deep seawater. This suboxic state, characterized by only small concentrations of dissolved [O.sub.2] (~1 [micro]M), prevented transport of hydrothermally derived Fe(II) from the deep ocean to continental-margin settings, ending an ~1.1 billion-year-long period of episodic BIF mineralization. The model is supported by the nature of Precambrian deep-water exhalative chemical sediments, which changed from predominantly sulfide facies prior to ca. 1.85 Ga to mainly oxide facies thereafter. doi: 10.1130/G30259A.1

Abstract: A geochronological study of the Chocolay Group at the base of the Paleoproterozoic Marquette Range Supergroup in Michigan, Lake Superior Region, is attempted for the first time. Age data [...]

If you really want to spook yourself some stormy night, try reading Exploring Consciousness by science writer Rita Carter (University of California Press, $35). Carter tells us about the centuries-old [...]

The electrostatic properties of dihydrofolate reductase are characterized using the Poisson-Boltzmann and quantum chemical vibrational frequency calculations. Findings suggest that a pKa of 6.5 is consistent with tautomerization of the pterin ring of 7,8 dihydrofolate to the 4-hydroxypterin. The stimulating force for this chemical step is the change in the substrate's dielectric environment and active site when binding which leads to the burial of the negative charge on Asp 27.

A deep seismic-reflection profile in northern Lake Michigan, midcontinent North America, provides a cross section of the crust across the 1850 Ma Penokean orogen, in which an Early Proterozoic island-arc complex was deformed between two converging Archean continental masses. The island-arc crust is about 40 km thick and has a few kilometres of intensely reflective rocks near its base, above which it is variably reflective to transparent. The Archean terranes have thicker crust, as much as 50 km, the lower 20-25 km of which is strongly reflective. Abrupt offsets of Moho near terrane boundaries may have been preserved since accretion during the Penokean orogeny.

One of the great apocryphal stories in the annals of science is how the Greek mathematician Archimedes ran naked through Syracuse shouting, 'Eureka!' - fresh from the bath where he [...]

The Best American Science and Nature Writing 2000. David Quammen, editor; Burkhard Bilger, series editor. xxii + 265 pp. Houghton Mifflin, 2000. $27.50, cloth; $13, paper. The Best American Science [...]

Science Is Fiction: The Films of Jean Painleve. Edited by Andy Masaki Bellows and Marina McDougall with Brigitte Berg. Translations by Jeanine Herman. xviii + 213 PP. The MIT Press/Brico [...]

In the land of year-round flower gardens, where the Green River Killer and Ted Bundy planted fellow citizens on banks and hillsides, where the movie Hype documented the emergence of [...]

Backgammon. Checkers. Scrabble. And, most famously, chess. One by one, computers are gobbling up the human advantage in games we thought we'd mastered. Now one of the last strongholds of [...]

THE BEST AMERICAN SCIENCE AND NATURE WRITING 2008. Edited by Jerome Groopman. Series editor, Tim Folger. xx + 330 pp. Houghton Mifflin, 2008. $14 paper. THE BEST AMERICAN SCIENCE WRITING [...]

At the U.S. Olympic Training Center in Colorado Springs, promising elite athletes train effectively. Up the road at the University of Colorado at Boulder, compromised petite athletes train defectively. The [...]

JAMES D. KEYSER. University of Washington Press, Seattle, 1992. 139 pp., photographs, maps, figures, glossary, bibliography, index. $35.00 (cloth); $17.50 (paper). Reviewed by William J. Cannon, Bureau of Land Management, [...]

ALEX PATTERSON. Johnson Books, Boulder, Colorado, 1992. xv + 256 pp., illustrations, indexes, bilblography. $15.95 (paper). Reviewed by William J. Cannon, Bureau of Land Management, Oregon. In the past, rock [...]

POLLY SCHAAFSMA. Museum of New Mexico Press, Santa Fe, 1992. vii + 17 5 pp., photographs, maps, works cited, index. $29.95 (paper). Reviewed by William J. Cannon, Bureau of Land [...]

Horticulturist and inventor George Washington Carver's rough beginnings, his eventual higher education in racially tolerant Iowa, his delivery of 'scientific farming' and its mantra of soil conservation to the Deep [...]