Early Mesoproterozoic evolution of midcontinental Laurentia: Defining the geon 14 Baraboo orogeny     

L. Gordon Medaris  Brad S. Singer  Brian R. Jicha  David H. Malone  Joshua J. Schwartz  Esther K. Stewart  Amanda Van Lankvelt  Michael L. Williams  Peter W. Reiners 《地学前缘(英文版)》2021,12(5):101174

New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,deformation,and sedimentation.Evidence for such metamorphism and deformation is best seen in siliciclastic sedimentary rocks of the Baraboo Interval,which were deposited closely following the1.65-1.63 Ga Mazatzal orogeny.In Baraboo Interval strata,muscovite parallel to slatey cleavage,in hydrothermal veins,in quartzite breccia,and in metamorphosed paleosol yielded ~(40)Ar/~(39)Ar plateau age s of 1493-1465 Ma.In addition,U-Th-total Pb dating of neoblastic overgrowths on detrital monazite gave an age of 1488±20 Ma,and recrystallized hematite in folded metapelite gave a mean U/Th-He age of 1411± 39 Ma.Post-Baraboo,arkosic polymictic conglomerate,which contains detrital zircon with a minimum peak age of 1493 Ma,was intruded by a 1470 Ma granite porphyry at the northeastern margin of the Wolf River batholith.This episode of magmatism,regional deformation and metamorphism,and sedimentation,which is designated herein as the Baraboo orogeny,provides a midcontinental link between the Picuris orogeny to the southwe st and the Pinware orogeny to the northeast,completing the extent of early Mesoproterozoic(Calymmian) orogenesis for 5000 km along the southern margin of Laurentia.This transcontinental orogen is unique among Precambrian orogenies for its great width(～1600 km),the predominance of ferroan granites derived from partial melting of lower continental crust,and the prevalence of re gional high T-P metamorphism related to advective heating by granitic magmas emplaced in the middle to upper crust.  相似文献   

The complexity of sediment recycling as revealed by common Pb isotopes in K-feldspar   总被引：1，自引：0，他引：1  

Simon P.Johnson  Christopher L.Kirkland  Noreen J.Evans  Brad J.Mc Donald  Huntly N.Cutten 《地学前缘(英文版)》2018,9(5):1515-1527

Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.  相似文献   

Effect of rapidly changing river stage on uranium flux through the hyporheic zone   总被引：2，自引：1，他引：1  

Fritz BG  Arntzen EV 《Ground water》2007,45(6):753-760

Measurement of ground water/surface water interaction within the hyporheic zone is increasingly recognized as an important aspect of subsurface contaminant fate and transport. Understanding the interaction between ground water and surface water is critical in developing a complete conceptual model of contaminant transport through the hyporheic zone. At the Hanford Site near Richland, Washington, ground water contaminated with uranium discharges to the Columbia River through the hyporheic zone. Ground water flux varies according to changes in hydraulic gradient caused by fluctuating river stage, which changes in response to operation of dams on the Columbia River. Piezometers and continuous water quality monitoring probes were installed in the hyporheic zone to provide long-term, high-frequency measurement of hydraulic gradient and estimated uranium concentrations. Subsequently, the flux of water and uranium was calculated for each half-hour time period over a 15-month study period. In addition, measurement of water levels in the near-shore unconfined aquifer enhanced the understanding of the relationship between river stage, aquifer elevation, and uranium flux. Changing river stage resulted in fluctuating hydraulic gradient within the hyporheic zone. Further, influx of river water caused lower uranium concentrations as a result of dilution. The methods employed in this study provide a better understanding of the interaction between surface and ground water in a situation with a dynamically varying vertical hydraulic gradient and illustrate how the combination of relatively standard methods can be used to derive an accurate estimation of water and contaminant flux through the hyporheic zone.  相似文献   

Tornado fatalities and mobile homes in the United States   总被引：1，自引：1，他引：0  

Daniel Sutter  Kevin M. Simmons 《Natural Hazards》2010,53(1):125-137

Fatalities from tornadoes have declined dramatically over the last century in the United States. Despite the overall reduction in tornado lethality, fatalities from mobile homes remain high. In fact, research suggests that the likelihood of a fatality in a mobile home is ten times or more than that in a permanent home. This study examines possible explanations of the mobile home tornado problem, including the potential for concentration of these homes in tornado prone states, the relation to Fujita Scale rating, and incidence during the day. We find that mobile home fatalities are concentrated in the Southeastern US, significantly more likely in weaker tornadoes, and occur disproportionately at night.  相似文献   

Response of reindeer and caribou to human activities   总被引：4，自引：0，他引：4  

Scott A. Wolfe  Brad Griffith  Carrie A. Gray Wolfe 《Polar research》2000,19(1):63-73

Petroleum and mineral exploration and extraction, hydroelectric development, atmospheric transport of contaminants, timber harvesting and tourism are increasing worldwide, especially in the Arctic. This development may adversely affect populations of reindeer/caribou ( Rangifer tarandus ) which are the basis of subsistence economies for northern indigenous peoples. Our purpose is to present a survey of the literature that has investigated the response of reindeer/caribou to human activities. Individuals and groups of reindeer/caribou: 1) move away from point sources of disturbance; 2) increase activity and energy expenditure near disturbance; 3) delay crossing or fail to cross linear structures; 4) shift away from areas of extensive and intensive development; and 5) are killed by collisions with vehicles and by hunting along roads. Cows and calves during the calving season are the most easily disturbed group. Bulls in general and all reindeer/caribou during insect harassment are least likely to avoid development areas. Estimation of the proportion of a population that is exposed to disturbance and the implications of this exposure to annual energy budgets, survival and productivity of reindeer/caribou has received little attention. Future advances in understanding the implications of human disturbance to reindeer/caribou will require cumulative effects assessment at annual, population and regional scales. Although some level of cumulative effect is likely, clear separation of cumulative effects of development from natural variation in caribou habitat use and demography will be difficult.  相似文献