Petrogenesis of the magmatic complex at Mount Ascutney,Vermont, USA     

K. A. Foland  C. M. B. Henderson  Jim Gleason 《Contributions to Mineralogy and Petrology》1985,90(4):331-345

The Ascutney Mountain igneous complex in eastern Vermont, USA, is composed of three principal units with compositions ranging from gabbro to granite. Sr and O isotopic and major element relationships for mafic rocks, granites, and nearby gneissic and schistose country rock have been investigated in order to describe the petrogenesis of the mafic suite which ranges from gabbro to diorite. The entire complex appears to have been formed within a short interval 122.2±1.2 m.y. ago. The granites with ¹⁸O near +7.8 had an initial ⁸⁷Sr/⁸⁶Sr of 0.70395(±6) which is indistinguishable from the initial ratio of the most primitive gabbro. Initial ⁸⁷Sr/⁸⁶Sr ratios and ¹⁸O values for the mafic rocks range from 0.7039 to 0.7057 and +6.1 to +8.6, respectively. The isotopic ratios are highly correlated with major element trends and reflect considerable crustal contamination of a mantle-derived basaltic parent magma. The likely contaminant was Precambrian gneiss similar to exposed bedrock into which the basic rocks were emplaced. A new approach to modelling of assimilation during the formation of a cogenetic igneous rock suite is illustrated. Chemical and isotopic modelling indicate that the mafic rocks were produced by simultaneous assimilation and fractional crystallization. The relative amounts of fractionation and assimilation varied considerably. The mafic suite was not produced by a single batch of magma undergoing progressive contamination; rather, the various rocks probably were derived from separate batches of magma each of which followed a separate course of evolution. The late stage granite was apparently derived from basaltic magma by fractionation with little or no crustal assimilation. The early intrusive phases are much more highly contaminated than the final one. The observed relationships have important implications for the formation of comagmatic complexes and for isotopic modelling of crustal contamination.  相似文献   

An EXAFS study of glassy and crystalline phases of compositions CaAl2Si2O8 (anorthite) and CaMgSi2O6 (diopside)     

N. Binsted  G. N. Greaves  C. M. B. Henderson 《Contributions to Mineralogy and Petrology》1985,89(2-3):103-109

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Base-isolated buildings with soil-structure interaction     

M. Novak  P. Henderson 《地震工程与结构动力学》1989,18(6):751-765

The equations of motion of building systems with soil-structure interaction are formulated for foundations comprising a joint mat or a set of individual spread footings. The influence of soil-structure interaction and the possible effects of building and foundation rocking are examined by investigating the modal properties. Simplifications in the analysis are also suggested.  相似文献   

Reaction relationships in the Bayan Obo Fe-REE-Nb deposit Inner Mongolia, China: implications for the relative stability of rare-earth element phosphates and fluorocarbonates   总被引：2，自引：1，他引：1  

M. P. Smith  P. Henderson  Zhang Peishan 《Contributions to Mineralogy and Petrology》1999,134(2-3):294-310

Textural relationships occurring in a range of settings from the Bayan Obo Fe-REE-Nb deposit, Inner Mongolia, China, indicate reaction between monazite [(REE)PO₄], bastnäsite [(REE)(CO₃)F] and apatite. Within dolomite marble-hosted ores monazite grains occur surrounded by zones of intergrown bastnäsite and apatite. In fluoritised dolomite marble-hosted amphibole-calcite veins, co-existing apatite and bastnäsite are separated by zones of monazite plus calcite, whilst in aegirine-apatite veins hosted by banded aegirine-fluorite-magnetite-bastnäsite rocks, they are separated by zones of monazite and fluorite. Modal proportions for minerals in the reaction zones have been used to derive reaction stoichiometries, and suggest the following reactions: Consideration of these reactions, along with published experimental data and other reported mineral assemblages, suggests that the factors controlling the relative stabilities of monazite and bastnäsite are the pH, and the activities of HF?°, CO₃ ^2?, Ca²⁺ and PO₄ ^3?. Textures indicating reaction between REE phosphates and fluorocarbonates have been reported from a number of other settings and are consistent with the controls on reaction inferred from this study. The range of assemblages seen at Bayan Obo is a result of the variation between relatively unbuffered fluid compositions, and those buffered by the fluoritisation of the carbonate host rock. Mass-balance calculations suggest some mobilisation of the REE into the fluid phase during reaction, although this did not significantly alter the REE distribution in monazite and bastnäsite. The mineral compositions also reveal variation in the REE distribution with different paragenetic settings indicating variation in the composition of the metasomatic fluids. These changes may be related to changes in the fluid source region, or to variations in the fluid chemistry, particularly X _CO2, leading to different REE solubilities at different periods in the development of the deposit.  相似文献   

A County‐Level Risk Assessment of the Deep Water Horizon Oil Spill in the Gulf of Mexico          下载免费PDF全文

Naomi W. Lazarus 《Geographical review》2016,106(3):360-380

This paper undertakes a risk assessment of coastal counties in the Gulf of Mexico impacted by the 2010 Deep Water Horizon oil spill. The study evaluates hazard risk from the perspective of community resilience, social capital, and access to resources. The proposed hazard risk location model re‐specifies risk as a function of hazard, exposure, and coping ability. The model employs an autoregressive function and a threshold analysis to develop a place‐based risk assessment. The results indicate that spatial variation in risk levels coincides with locational differences in social capital across the study area. Geographical proximity to the spill, population density, and unemployment rate are also key factors in determining overall risk. Furthermore, temporal variation in risk levels is determined by exposure to previous hazard events and changes in the business cycle.  相似文献   

Prediction of northern summer low-frequency circulation using a high-order vector auto-regressive model     

Lei Wang  Mingfang Ting  David Chapman  Dong Eun Lee  Naomi Henderson  Xiaojun Yuan 《Climate Dynamics》2016,46(3-4):693-709

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Multilevel vector autoregressive prediction of sea surface temperature in the North Tropical Atlantic Ocean and the Caribbean Sea     

Dong Eun Lee  David Chapman  Naomi Henderson  Chen Chen  Mark A. Cane 《Climate Dynamics》2016,47(1-2):95-106

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Ramp sedimentation across a middle Albian,Arctic embayment: Influence of subsidence,eustasy and sediment supply on stratal architecture and facies distribution,Lower Cretaceous,Western Canada Foreland Basin          下载免费PDF全文

Robin A. Buckley  A. Guy Plint  Olivia A. Henderson  Kathleen M. Vannelli 《Sedimentology》2016,63(3):699-742

Regional mapping of Middle Albian, shallow‐marine clastic strata over ca 100 000 km² of the Western Canada Foreland Basin was undertaken to investigate the relationship between large‐scale stratal architecture and lithology. Results suggest that, over ca 5 Myr, stratal geometry and facies were dynamically linked to tectonic activity in the adjacent Cordillera. Higher frequency modulation of accommodation is most reasonably ascribed to eustasy. The Harmon and Cadotte alloformations were deposited at the southern end of an embayment of the Arctic Ocean. The Harmon alloformation, forming the lower part of the succession, constitutes a wedge of marine mudstone that thickens westward over 400 km from <5 m near the forebulge to >150 m in the foredeep. Constituent allomembers are also wedge‐shaped but lack distinct clinothems, a rollover point or downlapping geometry. Ubiquitous wave ripples indicate that the sea floor lay above storm wave base. Deposition took place on an extremely low‐gradient ramp, where accommodation was limited by effective wave base. Lobate, river‐dominated deltas fringed the southern margin of the basin. The largest deltas are stacked in the same area, suggesting protracted stability of the feeder river. A buried palaeo‐valley on the underlying sub‐Cretaceous unconformity may have influenced compaction and controlled river location for ca 3 Myr. Adjacent to the western Cordillera, a predominantly mudstone succession is interbedded with abundant storm beds of very fine‐grained sandstone and siltstone that reflect supply from the adjacent orogen. Bioturbation indices in the Harmon alloformation range from zero to six which reflects the influence of stressors related to river‐mouth proximity. Harmon alloformation mudstone grades abruptly upward into marine sandstone and conglomerate of the overlying Cadotte alloformation. The Cadotte is composed of three allomembers ‘CA’ to ‘CC’, that represent the deposits of prograding strandplains 200 × 300 km in extent. Allomembers ‘CA’ and ‘CB’ are strongly sandstone‐dominated, whereas allomember ‘CC’ contains abundant conglomerate in the west. The dominantly aggradational wedge of Harmon alloformation mudstone records flexural subsidence driven by active thickening in the adjacent orogen: the high accommodation rate trapped coarser clastic detritus close to the basin margin. In contrast, the tabular, highly progradational sandstone and conglomerate bodies of the Cadotte alloformation record a low subsidence rate, implying tectonic quiescence in the adjacent orogen. Erosional unloading of the orogen through Cadotte time steepened rivers to the extent that they delivered gravel to the shore. These observations support an ‘anti‐tectonic’ model of gravel supply proposed previously for the United States portion of the Cretaceous foreland basin. Because Cadotte allomembers do not thicken appreciably into the foredeep, accommodation changes that controlled these transgressive–regressive successions were probably of eustatic origin.  相似文献   

Some Possible Effects Of Energy Shortages On Residential Preferences     

Floyd M. Henderson  Michael P. Voiland 《The Professional geographer》1975,27(3):323-326

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Origin and decomposition of sinking particulate organic matter in the deep water column inferred from the vertical distributions of its δN, δ and δ     

Takeshi Nakatsuka  Nobuhiko Handa  Naomi Harada  Tatsuhiro Sugimoto  Shigemi Imaizumi 《Deep Sea Research Part I: Oceanographic Research Papers》1997,44(12):1957-1979

Sinking particles were analyzed for their nitrogen isotopic ratio δ¹⁵N) of total particulate nitrogen (PN), stable carbon isotopic ratio (δ¹³C) and radioactive isotopic ratio (δ¹⁴C) of total particulate organic carbon (POC), at three different latitudinal (temperate, subpolar and equatorial) and geomorphological (trench, proximal abyssal plain and distal abyssal plain) sites in the western North Pacific Ocean using year-long time series sediment trap systems, to clarify the common vertical trends of the isotopic signals in deep water columns. Although the δ¹⁵N and δ¹³C values of sinking particulate organic matter (POM) were partly affected by the resuspension of sedimentary POM from the sea floor, especially in the trench, the changes in δ¹⁵N and δ¹³C values owing to the resuspension could be corrected by calculation of the isotopic mass balance from δ¹⁴C of sinking POC. After this correction, common downward decreasing trends in δ¹⁵N and δ¹³C values were obtained in the deep water columns, irrespective of the latitudes and depths. These coincidental isotopic signals between δ¹⁵N and δ¹³C values provide new constraints for the decomposition process of sinking POM, such as the preferential degradation of ¹⁵N- and ¹³C-rich compounds and the successive re-formation of the sinking particles by higher trophic level organisms in the deep water column.  相似文献