U–Pb geochronology and zircon composition of late Variscan S- and I-type granitoids from the Spanish Central System batholith     

David Orejana  Carlos Villaseca  Pablo Valverde-Vaquero  Elena A. Belousova  Richard A. Armstrong 《International Journal of Earth Sciences》2012,101(7):1789-1815

The Spanish Central System (SCS) batholith, located in the Central Iberian Zone, is one of the largest masses of granite in the European Variscan Belt. This batholith is a composite unit of late- and post-kinematic granitoids dominated by S- and I-type series granite, with subordinate leucogranite and granodiorite. Zircon trace element contents, from two representative S-type and three I-type granitoids from the eastern portion of the SCS batholith, indicate a heterogeneous composition due to magma differentiation and co-crystallisation of other trace element-rich accessory phases. In situ, U–Pb dating of these zircons by SHRIMP and LA-ICP-MS shows 479–462-Ma inherited zircon ages in the I-type intrusions, indicating the involvement of an Ordovician metaigneous protolith, while the S-type intrusions exclusively contain Cadomian and older zircon ages. The zircon crystallisation ages show that these granites have been emplaced at ca. 300?Ma with a time span between 303?±?3?Ma and 298?±?3?Ma. Precise dating by CA-ID-TIMS reveals a pulse at 305.7?±?0.4?Ma and confirms the major pulse at 300.7?±?0.6?Ma. These ages match the Permo-Carboniferous age for granulite-facies metamorphism of the lower crust under the SCS batholith and coincide with a widespread granitic event throughout the Southern Variscides. Ti-in zircon thermometry indicates temperatures between 844 and 784°C for both the S- and I-type granites, reinforcing the hypothesis that these granites are derived from deep crustal sources.  相似文献   

Pumped rainfall simulators: the impact of rain pulses on sediment concentration and size     

A. Armstrong  J. N. Quinton 《地球表面变化过程与地形》2009,34(9):1310-1314

Many pumped rainfall simulators used in soil erosion studies use pulsed rain to control the rainfall intensity. We examined the effect of the rain pulsing on sediment concentration and size using three different pulse cycles with the same rainfall intensity. There was considerable variation in sediment concentration through the pulse cycle: the highest concentration was up to four times that of the lowest concentration. Furthermore, the particle size distribution also varied: the peak median particle size was double the lowest median particle size. The magnitude of differences in sediment concentration and particle size were greater the longer the pulse cycle and these dynamics will vary between rainfall simulators and studies. We suggest the impact of the pulsing on sediment is significant and should be investigated prior to experimentation so that sampling periods are designed to avoid bias introduced by fine temporal scale sediment dynamics. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Can One-Run-Fixed-Arrhenius Kerogen Analysis Provide Comparable Organofacies Results to Detailed Palynological Analysis? A Case Study from a Prospective Mississippian Source Rock Reservoir (Bowland Shale,UK)     

Newport  Sarah M.  Hennissen  Jan A. I.  Armstrong  James P.  Taylor  Kevin G.  Newport  Leo P.  Hough  Edward 《Natural Resources Research》2020,29(3):2011-2031

Natural Resources Research - Organofacies analysis, a fundamental component within source rock appraisal based on the study of kerogen within a source rock, is typically produced from microscopy...  相似文献   

Seasonal variation in the importance of pelagic fish in the diet of piscivorous fish in the Moray Firth, NE Scotland: a response to variation in prey abundance?   总被引：5，自引：2，他引：3  

Greenstreet  Simon P.R.; McMillan  Julie A.; Armstrong  Eric 《ICES Journal of Marine Science》1998,55(1):121-133

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Jupiter at five microns     

K.R. Armstrong  R.B. Minton  G.H. Rieke  F.J. Low 《Icarus》1976,29(2):287-298

Maps of Jupiter at 5 um provide detailed information about the complex of emission features at this wavelength. Previous indications of a correlation between infrared sources and visual features are confirmed with a few significant exceptions. The behavior of Jupiter at 5 um is compared with that of other bodies in the outer solar system. Recent observations indicate emission features on Jupiter at other infrared wavelengths.  相似文献   

Magnetic resonance imaging of the Lake Agassiz–Lake Winnipeg transition     

F. R. Rack  B. J. Balcom  R. P. MacGregor  R. L. Armstrong 《Journal of Paleolimnology》1998,19(3):255-264

As part of the Geologic Survey of Canada (GSC) Lake Winnipeg Study, we have successfully imaged the Lake Agassiz to Lake Winnipeg transition in Section 4 of Core Namao 94-900-122a (i.e., from 313 cm to 465 cm), using a newly-developed magnetic resonance imaging (MRI) technique called SPRITE (Single-Point, Ramped Imaging with T₁ Enhancement). Whole core, gamma-ray attenuation measurements have been used to calculate the bulk porosity of the sediment at 1 cm intervals for comparison with the SPRITE images. Image contrast and image intensities observed in the SPRITE images of Section 4 are related to local porosity and magnetic susceptibility variations. In general, regions of the core with low signal intensity contain high porosity and low magnetic susceptibility. The best contrast between sediment layers is observed from regions of the core with high magnetic susceptibility. High signal intensity is observed from regions with low porosity and/or high magnetic susceptibility.  相似文献   

A combination of meteorological and satellite-based drought indices in a better drought assessment and forecasting in Northeast Thailand     

Watinee Thavorntam  Netnapid Tantemsapya  Leisa Armstrong 《Natural Hazards》2015,77(3):1453-1474

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Geochronology,Nd isotopes and reconnaissance geochemistry of volcanic and metavolcanic rocks of the São Luís Craton,northern Brazil: Implications for tectonic setting and crustal evolution     

Evandro L. Klein  Renê Luzardo  Candido A.V. Moura  Denise C. Lobato  Reinaldo S.C. Brito  Richard Armstrong 《Journal of South American Earth Sciences》2009,27(2-3):129-145

New field work, in addition to zircon geochronology, Nd isotopes and reconnaissance geochemical data allow the recognition of Paleoproterozoic volcanic and metavolcanic sequences in the São Luís Craton of northern Brazil. These sequences record at least five volcanic pulses occurring probably in three distinct epochs and in different tectonic settings. (1) The Pirocaua Formation of the Aurizona Group comprises early arc-related calc-alkaline metapyroclastic rocks of 2240 ± 5 Ma formed from juvenile protoliths in addition to minor older crustal components. (2) The Matará Formation of the Aurizona Group holds mafic tholeiitic and ultramafic metavolcanic rocks of back arc and/or island arc setting, which are likely coeval to the Pirocaua Formation. (3) The Serra do Jacaré volcanic unit is composed of tholeiitic basalts and predominantly metaluminous, normal- to high-K calc-alkaline andesites of 2164 ± 3 Ma formed in mature arc or active continental margin from juvenile protoliths along with subordinate older (Paleoproterozoic) materials and associated to the main calc-alkaline orogenic stage. (4) The Rio Diamante Formation consists of late-orogenic metaluminous, medium-K, calc-alkaline rhyolite to dacite and tuffs of 2160 ± 8 Ma formed in continental margin setting from reworked Paleoproterozoic crust (island arc) with incipient Archean contribution. (5) The Rosilha volcanic unit is composed of weakly peraluminous, medium-K, calc-alkaline dacite and tuff formed probably at about 2068 Ma from reworked crustal protoliths. As a whole the volcanic and metavolcanic rocks record and characterized better the previously proposed orogenic evolution of the São Luís Craton.  相似文献   

High‐frequency precipitation and stream water quality time series from Plynlimon,Wales: an openly accessible data resource spanning the periodic table     

Colin Neal  Brian Reynolds  James W. Kirchner  Phil Rowland  Dave Norris  Darren Sleep  Alan Lawlor  Clive Woods  Sarah Thacker  Hayley Guyatt  Colin Vincent  Kathryn Lehto  Simon Grant  Jeremy Williams  Margaret Neal  Heather Wickham  Sarah Harman  Linda Armstrong 《水文研究》2013,27(17):2531-2539

This scientific briefing announces the availability of a new multi‐element high‐frequency water quality data set that is openly accessible to the research community. The data set comprises up to 2 years of 7‐hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in Mid‐Wales. The measurements cover 50 analytes ranging from H⁺ to U and spanning six orders of magnitude in concentration, including major, minor and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together, the weekly and 7‐hourly time series provide a unique data set for studying both long‐term trends and short‐term dynamics. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The ecological and economic value of cold-water coral ecosystems     

Naomi S. Foley  Tom M. van Rensburg  Claire W. Armstrong 《Ocean & Coastal Management》2010,53(7):313-326

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