Application of Laser Ablation ICP-MS to U-Th-Pb Dating of Monazite   总被引：2，自引：1，他引：2  

Jan Kosler  Mike N. Tubrett  Paul J. Sylvester 《Geostandards and Geoanalytical Research》2001,25(2-3):375-386

Recent advances in laser ablation ICP-MS techniques allow accurate U-Th-Pb age dating of monazites that are as young as several tens of million years to a precision better than 2%. Accuracy of the age determinations has been improved by true real-time mass bias correction via nebulisation of a solution containing enriched ²³³U and natural Tl isotopes. The Tl-U tracer solution eliminates possible effects of variable sample matrices on the precision and accuracy of measured isotopic ratios. Mass bias corrections based on measured ²⁰⁵Tl/²³³U ratios in the tracer solution allow direct measurement of ²³⁵U in monazite. Combined with high-sensitivity laser ablation ICP-MS measurements, direct measurement of ²³⁵U particularly improves the precision of U-Pb dating of young monazites. Correction for laser-induced Pb/U and Pb/Th elemental fractionation is based on a mathematical treatment of time resolved count-rate data that is independent of laser ablation characteristics, does not require external standardisation and allows variable laser pit size or raster patterns for each measurement. The new procedures make the LA ICP-MS technique more flexible for in situ U-Th-Pb analysis.  相似文献   

Editorial     

Mike Bradshaw  & Heather H. Viles 《Area》2001,33(1):3-4

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Editor's Report, 2000     

Mike Bradshaw 《Area》2001,33(1):5-6

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Editorial report     

Mike Kirkby 《地球表面变化过程与地形》1995,20(8):709-710

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Changes in phytoplankton following nitrate and phosphate additions to large enclosures in Marion Lake,British Columbia     

Mike Dickman 《Aquatic Sciences - Research Across Boundaries》1973,35(1):114-120

The addition of nitrate, phosphate and a nitrate phosphate combination to replicated wooden enclosures in Marion Lake resulted in significant increases in primary productivity and algal standing crop in each of the three types of treated enclosures. This indicated that no single nutrient is likely to simultaneously limit the growth of all phytoplankton species present at any one time in the lake epilimnion. The relevance of this to the detergent controversy is discussed. Canadian Contribution to the International Biological Programme No. CCIBP 208.  相似文献   

Origin of the 3500-3300 Ma calc-alkaline rocks in the Pilbara Archaean: isotopic and geochemical constraints from the Shaw Batholith   总被引：1，自引：0，他引：1  

M.J. Bickle  L.F. Bettenay  H.J. Chapman  D.I. Groves  N.J. McNaughton  I.H. Campbell  J.R. de Laeter 《Precambrian Research》1993,60(1-4)

Calc-alkaline plutonic rocks, intruded at 3450Ma, comprise a major component of the Shaw Batholith in the Archaean east Pilbara Block, Western Australia. New whole-rock Pb isotopic geochronology confirms the extent of these rocks, but a minor plutonic phase is dated at 3338±52 Ma and represents a second plutonic event of the same age as much of the nearby Mt Edgar Batholith. The Sm----Nd isotopic systematics of the 3450Ma rocks imply their derivation from a heterogeneous source, which probably included a slightly older crustal component as well as a depleted mantle component. The 3338±52 Ma pluton includes components derived from crustal sources older than 3600 Ma. The geochemistry and Sm---Nd isotopic systematics of these rocks are consistent with crustal growth in the early Archaean from upper mantle sources as depleted as the modern upper mantle. The Shaw Batholith calc-alkaline suites exhibit very similar chemical trends on variation diagrams to modern calc-alkaline plutonic rocks which can be modelled by a combination of mixing and fractionation. A suite collected from outcrops displaying prominent igneous layering shows distinct geochemical trends which can be modelled by differentiation into a component enriched in ferromagnesian minerals, principally hornblende, and possibly sphene, magnetite and epidote, and into a leucocratic component containing quartz, plagioclase and K-feld-par. These Archaean calc-alkaline plutonic rocks, in common with rocks from many other Archaean calc-alkaline provinces, exhibit very fractionated REE patterns with depleted HREE contents, a feature considered to result from equilibrium with garnet at depth in lower crustal regions. The geochemistry of the Pilbara Archaean calc-alkaline rocks is identical to the subset of modern continental-margin calc-alkaline plutonic rocks with fractionated REE patterns, such as those from the central and eastern Peninsular Ranges Batholith, western USA. The tectonic setting in which the Archaean calc-alkaline rocks formed is still not known. This reflects both uncertainty associated with the petrogenesis and environments of modern calc-alkaline rocks, as well as the limited knowledge of the precise timing and relationships of plutonic, depositional and tectonic events in the Pilbara Archaean.  相似文献   

The petrogenesis of peridotitic komatiites: Evidence from high-pressure melting experiments     

M.J. Bickle  C.E. Ford  E.G. Nisbet 《Earth and Planetary Science Letters》1977,37(1):97-106

The compositions of liquidus olivines and orthopyroxenes of natural specimens of spinifex- and quench-textured peridotitic komatiites from the Belingwe Greenstone Belt, Rhodesia have been determined for pressures between 10 and 40 kbars. In conjunction with the chemical variation exhibited by these peridotitic komatiites it is concluded that the more magnesian lavas cannot be derived by concentration of olivine phenocrysts, fractional crystallisation or equilibrium partial melting. The peridotitic komatiites could evolve by polybaric assimilation and complete melting of garnet lherzolite into an initial liquid containing about 24% MgO.  相似文献   

Heat loss from the earth: A constraint on Archaean tectonics from the relation between geothermal gradients and the rate of plate production     

M.J. Bickle   《Earth and Planetary Science Letters》1978,40(3):301-315

The models suggested for the oceanic lithosphere which best predict oceanic heat flow and depth profiles are the constant thickness model and a model in which the lithosphere thickens away from the ridge with a heat source at its base. The latter is considered to be more physically realistic. Such a model, constrained by the observed oceanic heat flow and depth profiles and a temperature at the ridge crest of between 1100°C and 1300°C, requires a heat source at the base of the lithosphere of between 0.5 and 0.9 h.f.u., thermal conductivities for the mantle between 0.005 and 0.0095 cal cm⁻¹ °C⁻¹ s⁻¹ and a coefficient of thermal expansion at 840°C between 4.1 × 10⁻⁵ and 5.1 × 10⁻⁵ °C⁻¹. Plate creation and subduction are calculated to dissipate about 45% of the total earth heat loss for this model. The efficiency of this mechanism of heat loss is shown to be strongly dependent on the magnitude of the basal heat source. A relation is derived for total earth heat loss as a function of the rate of plate creation and the amount of heat transported to the base of plates. The estimated heat transport to the base of the oceanic lithosphere is similar to estimates of mantle heat flow into the base of the continental lithosphere. If this relation existed in the past and if metamorphic conditions in late Archaean high-grade terrains can be used to provide a maximum constraint on equilibrium Archaean continental thermal gradients, heat flow into the base of the lithosphere in the late Archaean must have been less than about 1.2–1.5 h.f.u. The relation between earth heat loss, the rate of plate creation and the rate of heat transport to the base of the lithosphere suggests that a significant proportion of the heat loss in the Archaean must have taken place by the processes of plate creation and subduction. The Archaean plate processes may have involved much more rapid production of plates only slightly thinner than at present.  相似文献   

Plate tectonics in the Eastern Alps     

C.J. Hawkesworth  D.J. Waters  M.J. Bickle 《Earth and Planetary Science Letters》1975,24(3):405-413

The weight of the geological evidence, which includes the recognition of a late Cretaceous paired metamorphic belt, suggests that a southward dipping subduction zone existed in the Eastern Alps. On this basis a new plate tectonic model is presented for the post-Palaeozoic evolution of that orogen.  相似文献   

Eradication success down under: heat treatment of a sunken trawler to kill the invasive seaweed Undaria pinnatifida     

Wotton DM  O'Brien C  Stuart MD  Fergus DJ 《Marine pollution bulletin》2004,49(9-10):844-849

Eradication of invasive species is difficult in the marine environment, and there have only been a few successes. We report the successful eradication of the invasive seaweed Undaria pinnatifida from a sunken trawler in the Chatham Islands, New Zealand. New heat-treatment methods were developed as the most cost effective and environmentally acceptable option to kill Undaria. Monitoring of the trawler for three years after it sank found no Undaria after the vessel was treated. Key factors in the success of the eradication programme included: early detection, a rapid response, pre-existing knowledge of Undaria, an adaptive management approach, targeting of multiple life history stages, and the cooperation of the vessel's insurer.  相似文献