Can crystallization of olivine tholeiite give rise to potassic rhyolites?—an experimental investigation   总被引：6，自引：0，他引：6  

Matthew L. Whitaker  Hanna Nekvasil  Donald H. Lindsley  Michael McCurry 《Bulletin of Volcanology》2008,70(3):417-434

Experiments were conducted to determine whether the rhyolites and basalts of the intraplate silica-saturated potassic suites could be genetically related through crystallization. Extreme crystallization (96–97%) of a high-MgO (10.62 wt%) olivine tholeiite from the Snake River Plain with an initial bulk water content of 0.4 wt% at a mid-crustal pressure of 4.3 kbar generated potassic rhyolitic liquids similar in major element chemistry to those found in the Quaternary rhyolite domes of the Snake River Plain and their plutonic equivalents in the Proterozoic Laramie Anorthosite Complex. Residual liquids comparable in composition to the bulk rock compositions of intermediate rocks found at the Craters of the Moon and Cedar Butte eruptive centers in the Snake River Plain are also generated along this crystallization path. This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic rhyolites.  相似文献   

Geochemical and Physical Controls on Vadose Zone Hydrology of Holocene Carbonate Sands,Grand Bahama Island     

S. M. Brooks  F. F. Whitaker 《地球表面变化过程与地形》1997,22(1):45-58

This paper explores the relationship between vadose zone hydrology and geochemical changes in mixed mineralogy carbonate sands from a Bahamian coastal dune of Holocene age. Cores were taken from two sites: at site A, a shallow humic Entisol is developed beneath open scrub vegetation, while at site B a deeper, more organic-rich Inceptisol has formed beneath a mature hardwood coppice. X-ray diffraction analysis reveals significant contrasts in mineralogy both within and between the two sites, with partial stabilization of high-Mg calcite and aragonite, to low-Mg calcite. Stabilization is greater at site B, and is accompanied by a significant increase in total porosity. Diagenetic changes in pore-size distribution have implications for residence times of percolating water, as determined using measurements of moisture retention characteristics using pressure plate apparatus, and hydrological models of unsaturated zone moisture flux. The diagenetically more mature sands from site B have a 50–100 per cent higher moisture retention, although unsaturated hydraulic conductivity is also higher, particularly at greater suctions. The increase in water retention is likely to enhance further rates of mineral-controlled reactions, while development of an organic-rich soil also enhances the geochemical drive for dissolution. Carbonate diagenesis thus appears to be strongly linked to vadose zone hydrology, and the interactions identified here have important consequences for the nature and long-term rates of mineral stabilization. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Resonance-fluorescence in barium ion clouds     

Henry G. Horak  Rodney W. Whitaker 《Planetary and Space Science》1982,30(9):897-907

The problem of resonant-fluorescent scattering of sunlight by a high altitude, plane-parallel, barium ion cloud is solved numerically. Line strengths and profiles are computed using our modified version of the computer program LINEAR (Auer, Heasley and Milkey, 1972). Hyperfine structure of the spectral lines becomes important for very thick layers and is taken into account. Comparisons are made between coherent and completely noncoherent scattering results and finally the influence of collisions on the radiation field is estimated.  相似文献   

Crustal structure above the Iceland mantle plume imaged by the ICEMELT refraction profile   总被引：2，自引：0，他引：2  

Fiona A. Darbyshire  Ingi Th. Bjarnason  Robert S. White  & Ólafur G. Flóvenz 《Geophysical Journal International》1998,135(3):1131-1149

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Nannofossils: the smoking gun for the Canarian hotspot          下载免费PDF全文

Valentin R. Troll  Frances M. Deegan  Steffi Burchardt  Kirsten Zaczek  Juan‐Carlos Carracedo  Fiona C. Meade  Vicente Soler  Mario Cachao  Jorge Ferreira  Abigail K. Barker 《Geology Today》2015,31(4):137-145

The origin of volcanism in the Canary Islands has been a matter of controversy for several decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of superheated mantle material. However, the debate has recently come to a conclusion following the discovery of nannofossils preserved in the products of the 2011–2012 submarine eruption at El Hierro, which tell us about the age and growth history of the western‐most island of the archipelago. Light coloured, pumice‐like ‘floating rocks’ were found on the sea surface during the first days of the eruption and have been shown to contain fragments of pre‐island sedimentary strata. These sedimentary rock fragments were picked up by ascending magma and transported to the surface during the eruption, and remarkably retained specimens of pre‐island Upper Cretaceous to Pliocene calcareous nannofossils (e.g. coccolithophores). These marine microorganisms are well known biostratigraphical markers and now provide crucial evidence that the westernmost and youngest island in the Canaries is underlain by the youngest sediment relative to the other islands in the archipelago. This finding supports an age progression for the onset of volcanism at the individual islands of the archipeligo. Importantly, as fracture‐related volcanism is known to produce non‐systematic age‐distributions within volcanic alignments, the now‐confirmed age progression corroberates to the relative motion of the African plate over an underlying mantle plume or hotspot as the cause for the present‐day Canary volcanism.  相似文献   

Ordinary meeting: Friday,July 6th, 1900     

W. Whitaker 《Proceedings of the Geologists' Association. Geologists' Association》1900,16(10):535

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Chronology,stratigraphy and palaeoenvironmental interpretation of a Late Pleistocene to mid‐Holocene cave accumulation on Kangaroo Island,South Australia     

Matthew C. McDowell  Erick A. Bestland  Fiona Bertuch  Linda K. Ayliffe  John C. Hellstrom  Geraldine E. Jacobsen  Gavin J. Prideaux 《Boreas: An International Journal of Quaternary Research》2013,42(4):974-994

Chronological, sedimentological and geochemical analyses of a clastic infill from Kelly Hill Cave (5K1), Kangaroo Island, document a palaeoenvironmental record that spans from the Late Pleistocene to the middle Holocene. We AMS radiocarbon‐dated bone collagen and U–Th‐dated speleothem to determine that fossiliferous sediments were deposited between >20 ka and 7 ka ago. Most of the 15 sedimentary layers are dominated by sand‐ and silt‐sized quartz that is physically and geochemically comparable with surface soils in the Kelly Hill area. Late Pleistocene and Last Glacial Maximum strata are represented primarily by homogeneous, poorly sorted quartz‐rich sediments that contain little organic matter, but include a thin layer composed largely of silt‐sized clay pellets that resemble sediments deflated from playa lakes. Microstructures observed in petrographic slides indicate that, with the exception of one layer, all sediments experienced little reworking once deposited in the cave. Some layers display pedogenic microstructures such as redeposited clays and opaline silica infilling that indicate postdepositional modification; that is, cave‐floor soil development. Overlying Holocene‐aged sediments also consist mainly of quartz but have much greater organic matter content. Some of these sediments have been strongly influenced by re‐precipitated organic matter that appears to have been transported into the cave via vadose drip water. The presence of dissolved organic matter in soil/vadose waters suggests a high vegetation density and acidic soils, which are congruent with the more equitable climatic conditions characteristic of the Holocene. The sediments described here provide a valuable palaeoenvironmental record that will facilitate future interpretation of associated vertebrate fossils.  相似文献   

Excursion to the Croydon Bourne: Saturday,March 12th, 1910     

W. Whitaker  A.C. Young 《Proceedings of the Geologists' Association. Geologists' Association》1910,21(8):456

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Report of an excursion to the north downs,Marden Park     

W. Whitaker 《Proceedings of the Geologists' Association. Geologists' Association》1915,26(2):138-140

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New quantitative approaches for classifying and predicting local-scale habitats in estuaries     

Fiona J. Valesini  Mathew Hourston  Michelle D. Wildsmith  Natasha J. Coen  Ian C. Potter 《Estuarine, Coastal and Shelf Science》2010

This study has developed quantitative approaches for firstly classifying local-scale nearshore habitats in an estuary and then predicting the habitat of any nearshore site in that system. Both approaches employ measurements for a suite of enduring environmental criteria that are biologically relevant and can be easily derived from readily available maps. While the approaches were developed for south-western Australian estuaries, with a focus here on the Swan and Peel-Harvey, they can easily be tailored to any system.  相似文献