CN106908510B - A method of the uranium lead age of measurement zircon sample - Google Patents
A method of the uranium lead age of measurement zircon sample Download PDFInfo
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Abstract
A kind of method that the present invention discloses uranium lead age for measuring zircon sample, described method includes following steps: sample target is made in zircon sample and standard substance；Laser ablation is carried out to obtain solid sols；Solid sols are loaded into receive icp ms ion source (plasmas) more and carry out ionization to obtain primary ions；Make primary ions by the mass spectrometric electric and magnetic fields, realizes energy and direction double focusing and reach ion detection system；Detect and calculate the original uranium lead ratio value of zircon sample and zircon standard substance primary ions；The original uranium lead ratio value of zircon sample is corrected using zircon standard uranium lead ratio value to obtain the uranium lead ratio value after zircon sample corrects；Use the uranium lead age of the uranium lead ratio calculation zircon sample after correction.The method of the present invention has high-precision and highly sensitive, requires sample size low, and denudation depth is shallow, can be used in degrading space high-resolution Zircon U lead of the diameter less than 10 microns and determines year.
Description
Technical field
The present invention relates to microcell isotopics analysis methods more particularly to a kind of uranium lead ages for measuring zircon sample
Method.
Background technique
Zircon is the important accessory mineral of one of nature rock, since its U, Pb content with higher becomes U-
The object most often studied in Pb isotopic geochronology, and gradually formed the extremely wide branch of an application prospect and learned
Section-zircon (zirconology).In particular, being in conjunction with the isotopes such as its microelement and Hf, O by zircon U-Pb age
The markers and process for inquiring into geologic process provide important Geochemical Parameters.
According to the property of institute's sample, micro zircon is mainly used in U-Pb Zircon isotopic geochronology at present
Three kinds of method, Single-grain Zircon method and micro-zone analysis methods.But from the point of view of the spatial resolution of analysis and the technology used, above-mentioned side
Method is basically divided into thermal ionization mass spectrometry (tims) (TIMS) and micro-zone in situ (in situ) analyzes two classes.Wherein TIMS analysis precision highest,
But the disadvantage is that cannot get the spatial information of Zircon age variation.Therefore, it is same to constitute U-Pb in recent years for the micro-zone in situ analysis of zircon
The main trend of the plain geochronology in position, and itself with regard to the technology, easy quick, high spatial resolution and high assay precision
It is the main direction of development.
Many in natural zircon sample to have core, curtain and the complicated zonary structure on side, usual curtain and side are very narrow (micro- less than 10
Rice), high-resolution U-Pb is carried out to these complicated annulus and determines year, can reveal that the complicated geological with complicated annulus zircon experience is gone through
History, therefore high-resolution microcell dating technique has very important significance to the Zircon dating with labyrinth, it is available
The multiple groups age in zircon different structure region, these ages may correspond respectively to the protolith epoch of zircon host's rock, go bad
The age etc. of event time (phase and/or more phases) and source region residual zircon.
In micro-zone analysis method, there are two types of zircon microcell dating technique, ion probe (Secondary Ion Mass
Spectrometry, SIMS) and laser ablation plasma mass (laser ablation-inductively coupled
Plasma-mass spectrometry, LA-ICP-MS).Ion probe has SHRIMP and two kinds of CAMECA.Since it can be to zirconium
Stone carries out micro-zone in situ high-precision fixed year, has been the current main means for studying complicated Zircon age, and as since the eighties
The important technical of geological sciences innovation achievement supports.The research of ion probe U-Pb Zircon Geochronology and the achievement obtained are not only comprehensive
Pushed the rapid development of geoscience, at the same also driven a series of isotope geochemistry analytical technologies and method into
Step.
Although can get the age of degree of precision with ion probe, instrument price valuableness (every 3,000 ten thousand yuan of people
It is more than coin), and global limited amount, it is difficult to meet the needs of Zircon U-Pb Age.Therefore after ion probe, zircon swashs
The development that light degrades plasma mass (LA-ICP-MS) dating technique keeps zircon microcell U-Pb chronology more economical and letter
Just.In recent ten years, due to the improvement of technology especially laser technology, U-Pb age precision, the LA-ICP-MS of zircon are improved
Measuring method is quickly popularized.
Surveyed in year in current zircon LA-ICP-MS U-Pb, the instrument used be mainly various types of quadrupole rods (or
Magnetic-type) list reception mass spectrum, which has the characteristics that scanning is quick, but has apparent limitation in terms of isotope analysis, such as
Low and non-flat peak of adundance sensitivity etc., therefore analysis precision is caused to be usually 3-5%, spatial resolution is not high, usually 30-
80 microns (erosion pit diameter), simultaneously because being needed using from low quality end to high quality end or reverse order scanning technique
Total minute is longer, and common denudation depth is 20 microns.Generally speaking, laser ablation quadrupole rod (or magnetic-type) is single
Receive plasma mass Zircon U-Pb Age technology there are the problem of: (1) due to use sequential scanning technique, thus receive
Efficiency is lower, for example U-Pb determines to receive in year202Hg,204(Hg+Pb),206Pb,207Pb,208Pb,232Th and238U ion stream, and it is more
Receiver simultaneously compare by reception technique, theoretically needs to consume 7 times of time, corresponding denudation depth increases by 7 times.Therefore cause
Longitudinal resolution is low, usually 20 microns.(2) since instrumental sensitivity is lower, so, in identical signal strength conditions
Under, it needs more to degrade substance, i.e., needs the bigger area that degrades under the conditions of identical degrade, therefore lead to horizontal space
Resolution ratio is poor, and usually degrading diameter is 30-80 microns, can achieve 20 microns to individual high-content samples.However, natural
The annulus width overwhelming majority of zircon sample is less than the resolution ratio.
In this background, become mesh with more reception plasma mass spectrographs (LA-MC-ICPMS) equipped with laser
Important technology in preceding Zircon U-Pb Age research, it not only increases analysis speed, while also improving analysis precision, display
Good analytic potential and application prospect out.Since lead content is lower in zircon, ion counter detection can only be suitable for,
So the technology is received using ion counter at present204Pb,206Pb,207Pb and208Pb is received with Faraday cup238U is (such as: marquis
Can army etc., LA-MC-ICP-MS zircon micro-zone in situ U-Pb dating technique, geology of mineral deposit, the 4th phase 481-492 of volume 28；
Scott Johnston etc., Small-volume U-Pb zircon geochronology by laser ablation-
Multicollector-ICP-MS, Chemical Geology 259 (2009) 218-229), hereinafter referred to as mixing receives mould
Formula is degraded using single-point in this mode,206Pb/238The measurement accuracy of U isotopic ratio is 2-4% (2S), spatial resolution
For 15 microns of trans D, denudation depth 4-10 microns.However, receiving plasma mass using laser ablation more
Instrument (LA-MC-ICPMS) carries out Zircon U-Pb Age technology, and presently, there are following problems: (1) being received using ion counter202Hg,204(Hg+Pb),206Pb,207Pb and208Pb is received with Faraday cup238The mixing reception pattern of U, due to Faraday cup
Poor sensitivity, to 5mV signal below, measurement accuracy is very poor, leads to not be suitable for degrading U-Pb of the diameter less than 10 microns
Determine year analysis；In fact, the annulus width of many zonary structure zircon samples is both less than 10 microns.Also, the zirconium of some samples
Stone particle is inherently less than 10 microns, such as the zircon particle in ultrabasic rock and meteoritic sample；(2) in natural zircon sample
U-Pb changes of contents is larger, has height to have low, and the low U content sample of 5mV is less than to signal strength, and U-Pb determines the age precision in year
Difference.
Summary of the invention
In order to solve the above problem in the prior art, the present invention provides a kind of uranium lead ages for measuring zircon sample
New method, described method includes following steps:
(1) zircon sample and zircon standard substance are respectively embedded into epoxy resin so that sample target is made；
(2) laser ablation is carried out to zircon in the sample target respectively using laser beam, to obtain solid sols；
(3) solid sols are loaded into the plasma ions for receiving icp ms more using carrier gas
It is ionized in source, to obtain primary ions；
(4) make the primary ions by the electric and magnetic fields in the mass spectrograph to realize energy and direction double focusing
It is burnt；
(5) primary ions Jing Guo double focusing are detected using ion counter and calculates the zircon sample and described
The original uranium lead ratio value of the primary ions of zircon standard substance；
(6) using the known nominal uranium lead ratio value of the zircon standard substance and measured original uranium lead ratio value to institute
The original uranium lead ratio value for stating zircon sample is corrected, thus the uranium lead ratio value after obtaining the correction of the zircon sample；
(7) using the uranium lead age of zircon sample described in the uranium lead ratio calculation after the correction.
For the present inventor it is discovered by experiment that in the identical situation of signal strength, the measurement accuracy of ion counter is opposite
There is apparent advantage in Faraday cup, in other words, under the conditions of keeping identical measurement accuracy, use ion counter can be with
Measure lower concentration.If concentration is similar, under the conditions of laser ablation, it is meant that needs to degrade substance less, it may be assumed that can be with
Area or denudation depth are degraded using smaller, to improve the spatial resolution of micro-zone analysis.And by further real
It issues after examination and approval now, is received simultaneously using ion counter and Faraday cup206Pb and238In the mixing reception pattern of U ion stream, due to
Faraday cup measurement238Ion counter measurement is obviously lagged behind when U signal is to reach to peak value206Pb signal, this lag effect
It should make measurement206Pb with238The isotopic ratio of U, which changes, to be increased, and then seriously affects the result precision that U-Pb determines year.If
It is received simultaneously using multiple ion counters206Pb and238U ion stream, measures206Pb and238U signal variation is fully synchronized！Meaning
Taste measurement206Pb with238The isotopic ratio variation of U is small, and precision is high, that is, under same laser sampling condition, using ion
It is significantly higher than mixing reception pattern that counter reception pattern acquisition U-Pb determines year precision.Then, current inventor provides one kind
Low to sample size requirement with high-precision and high sensitivity, denudation depth is shallow, can be used in degrading diameter less than 10 microns
Space high-resolution Zircon U lead determines year.
Detailed description of the invention
The precision that Fig. 1 shows that ion counter and Faraday cup measure small signal under solution sampling condition compares.
Fig. 2 shows that ion counter and Faraday cup received signal compare under laser ablation sampling condition.
Fig. 3 shows the laser ablation system used in the specific embodiment of the present invention and more reception inductance couplings
Close the connection type of plasma mass spectrograph.
Fig. 4 shows laser ablation depth experiments result.
Fig. 5 shows the dynamic linear response range between ion counter: 0~720,000cps.
Fig. 6 is shown receives inductivity coupled plasma mass spectrometry space high-resolution Zircon U-Pb Age skill with laser in-situ more
The standard Zircon age of art measurement, it is completely the same with bibliographic reference value in error range.
Fig. 7, which shows to pick up from big other pressure metamorphic gneiss sample, has complicated annulus Zircon age distribution map, red
Color region is the laser ablation region of this analysis, and age unit is Ma, error 2s.
Fig. 8 shows the age consonance figure of the core of zircon sample, curtain and edge.
Specific embodiment
In order to make the object, technical scheme and advantages of the embodiment of the invention clearer, below in conjunction with of the invention specific
Technical solution of the present invention is clearly and completely described in embodiment, it is clear that described specific embodiment is this hair
Bright a part of embodiment, rather than whole embodiments.Based on the embodiment in the present invention, ordinary skill
Personnel's every other embodiment obtained without making creative work belongs to the model that the present invention protects
It encloses.
As described above, the method includes such as the present invention provides a kind of method of uranium lead age for measuring zircon sample
Lower step:
(1) zircon sample and zircon standard substance are respectively embedded into epoxy resin so that sample target is made；
(2) laser ablation is carried out to the sample target respectively using laser beam, to obtain solid sols；
(3) solid sols are loaded into using carrier gas and receive icp ms (such as Neptune more
Plus type receives icp ms (Neptune Plus MC-ICP-MS, manufacturer: Thermo more
Fisher Scientific, Germany)) ion source in ionize, to obtain primary ions；
(4) make the primary ions by the electric and magnetic fields in the mass spectrograph to realize energy and direction double focusing
It is burnt；
(5) primary ions Jing Guo double focusing are detected using ion counter and calculates the zircon sample and described
The original uranium lead ratio value of the primary ions of zircon standard substance；
(6) using the known nominal uranium lead ratio value of the zircon standard substance and measured original uranium lead ratio value to institute
The original uranium lead ratio value for stating zircon sample is corrected, thus the uranium lead ratio value after obtaining the correction of the zircon sample；
(7) using the uranium lead age of zircon sample described in the uranium lead ratio calculation after the correction.
The zircon standard substance can selected from by Phalaborwa, 91500, GJ-1, Temora, Pl ě sovice,
The zircon standard substance of Qinghu and SK10-2 composition.In the preparation, zircon standard substance can be embedded in such as 2.54 centimetres
In the epoxy resin samples target of (1 inch) or 1.77 centimetres (half inch), by unknown zircon sample to be measured be placed in it is same or
In another epoxy resin samples target, sample target is thus made.
It is more that such as Neptune Plus type can be used in the laser ablation mostly reception icp ms
Receive icp ms (Neptune Plus MC-ICP-MS, manufacturer: Thermo Fisher
Scientific, Germany), can equipped at least six ion counters, such as 7 ion counters IC4, IC5,
IC3A, IC2, IC1B1, IC6 and IC7, these ion counters are respectively used to receive simultaneously202Hg,204(Pb+Hg),206Pb,207Pb,208Pb,232Th and238U ion stream.The mass spectrograph may be equipped with micro-zone in situ sampling equipment, such as Analyte G2
Type 193nm excimer laser degrades system (manufacturer: Photon Machines, USA).In sample introduction, can using as
Before the sample solid sols of laser ablation are loaded into plasma ion source by the helium of carrier gas, the nitrogen of 2-4 ml/min is added
Gas, then the argon gas by a concentric vortex mixer addition as make-up gas.In a specific embodiment, the method for the present invention
The instrument teaming method of use is as shown in figure 3, include that 193 nm excimer lasers degrade system (model: Analyte G2), more
Receive icp ms (model: Neptune PLUS) and circuit connection section.Wherein, 193 nm excimer
Laser ablation system includes laser attenuator assembly 1, laser homogenizer 2, grating 3, ATL193nm excimer laser generator 4 and stripping
Reflecting mirror M1, M2 and M3 in pond 6 and optical path are lost, zircon sample 5 to be detected, which is placed on, to be degraded in pond 6；It is receive inductance more
Couple plasma mass spectrometer includes electric sector 7, plasma (ion source) 8, sectorial magnetic field 9 and ion counter 10.It carries
Gas helium (He), make-up gas (Ar) and nitrogen (N2) are mixed using the coaxial vortex mixer 11 in connection gas circuit.
In some embodiments, the laser beam is 193 nanometers of (wavelength) laser beams；The beam spot diameter, of the laser beam
It is arranged to 5 microns.
In some embodiments, the carrier gas be helium, make-up gas is argon gas, and the solid sols be loaded into from
Solid sols described in the forward direction of component are mixed into nitrogen.
In some embodiments, the size of the sample target is 2.54 centimetres (1 inches) or 1.77 centimetres (half inch).
In some embodiments, the laser pulse quantity of the laser ablation be 8 to 45, such as 8,14,19,25,
30,35,40 and 45；Denudation depth is 1 to 5.4 micron, and for example, 0.96,1.68,2.28,3,3.6,4.2,4.8 and 5.4 are micro-
Rice.Preferably, the laser pulse quantity of the laser ablation is 8 to 25, and denudation depth is 1 to 3 micron.Most preferably
It is that the laser pulse quantity of the laser ablation is 19, denudation depth is 2.28 microns.
In some embodiments, the mass spectrograph is equipped with micro-zone in situ sampling equipment (such as Analyte G2 type
193nm excimer laser degrades system (manufacturer: Photon Machines, USA)) and at least six ion counters.
8, according to the method described in claim 7, in some embodiments, the mass spectrograph is same equipped with being respectively used to
When receive202Hg、204(Pb+Hg)、206Pb、207Pb、208Pb、232Th and2387 ion counters of U ion stream, for example,
Neptune Plus type more receive icp ms (Neptune Plus MC-ICP-MS, manufacturer:
Thermo Fisher Scientific, Germany) be equipped with 7 ion counters IC4, IC5, IC3A, IC2, IC1B1,
IC6 and IC7.
In some embodiments, the parameter of the laser ablation system can be using following setting: the beam spot of laser beam
Diameter is set as 5 microns, and degrading frequency is 4 hertz, and energy density is 4 joules/square centimeter.
In some embodiments, the mass spectrometric location parameter can be using following setting: the time of integration 0.131
Second, it integrating 150 times, laser ablation is used to measure background intensity before starting for 10 seconds, and it opens laser and sample degrade 6 seconds,
Laser pulse number is 25, and denudation depth is less than 3 microns.
In some embodiments, U, Th and the Pb corrected using NIST610 normal glass sample in zircon sample is contained
Amount, corrects zircon sample using standard zircon207Pb/206Pb,207Pb/235U and206Pb/238U isotopic ratio, isotope
Ratiometric correction is carried out using following formula:
Wherein,WithThe respectively isotopic ratio and the isotopic ratio after correction of zircon sample measurement,
For the isotopic ratio recommendation of standard zircon,WithMeasure standard zircon twice respectively before and after zircon sample
Isotopic ratio, tsam、WithRespectively zircon sample and its front and back time for measuring standard zircon twice；
Formula of error transmission in the calculating of isotopic ratio Fractionation Correction are as follows:
Wherein,WithThe respectively isotopic ratio and the isotopic ratio after correction of zircon sample measurement,
For the isotopic ratio recommendation of standard zircon,WithMeasure standard zircon twice respectively before and after zircon sample
Isotopic ratio；
WithRespectively the uncertainty of sample, the uncertainty of standard zircon recommendation, before and after sample
The uncertainty of standard zircon is measured twice；tsam、WithRespectively zircon sample and its front and back measures standard twice
The time of zircon.
Embodiment
Hereafter the present invention will be further detailed by way of example, but protection scope of the present invention is not limited to
These embodiments.
1 ion counter of embodiment and Faraday cup measure the ability comparative experiments (instrument that this experiment uses of small signal
For Neptune Plus MC-ICP-MS, manufacturer: Thermo Fisher Scientific, Germany)
This experiment carries out the lead solution containing various concentration (referring to Fig. 1) with laser ablation zircon condition shown in table 1
Experiment, is first measured with ion counter IC3 and IC2 simultaneously respectively206Pb and207Pb (ion counter mode reception pattern), no
The precision result of the isotopic ratio measured with the lead solution of concentration indicates referring to Fig. 1 with empty circles, what IC3 was measured206Pb
Ion intensity of flow indicates beside circle, and unit is cps；Then it is surveyed simultaneously with Faraday cup L1 and ion counter IC1 respectively
Amount206Pb and207Pb (mixing reception pattern), measurement result is indicated referring to Fig. 1 with solid circles, what L1 was measured206Pb ion stream
Intensity indicates beside circle, and unit is mV.The results show, when measuring small signal (being less than 10mV), in signal strength
In identical situation, the measurement accuracy of ion counter has apparent advantage relative to Faraday cup.In other words, phase is being kept
Under the conditions of same measurement accuracy, lower concentration can be measured using ion counter.If solubility is similar, in laser ablation item
Under part, it is meant that needs to degrade substance less, it may be assumed that area can be degraded using smaller, to improve the sky of micro-zone analysis
Between resolution ratio.
2 multi-ion-counter configuration reception pattern of embodiment is real compared with ion counter-Faraday cup mixing reception pattern
It tests
This experiment first uses ion counter IC3 and farad under the conditions of laser ablation zircon same as Example 1 respectively
The L4 is received simultaneously206Pb and238U ion stream, obtained signal intensity are shown in fig. 2 a.It will be apparent from this figure that method
The L4 is drawn to measure238Ion counter IC3 measurement is obviously lagged behind when U signal is to reach to peak value206Pb signal, this lag
Effect makes measurement206Pb with238The isotopic ratio of U, which changes, to be increased, and then seriously affects the result precision that U-Pb determines year.So
It is received simultaneously with ion counter IC3 and IC7 respectively afterwards206Pb and238U ion stream, obtained signal intensity are shown in Fig. 2 b, from
It can be seen that measuring in figure206Pb and238U signal variation is fully synchronized, it is meant that measurement206Pb with238The isotopic ratio of U
Change small, precision height.That is, it is fixed to obtain U-Pb using ion counter reception pattern under same laser sampling condition
Year ratio of precision mixing reception pattern is higher.
Embodiment 3
Based on above-mentioned experiment 1 and 2 as a result, devising following technical scheme solves current laser ablation in-situ micro area U-
Main problem present in Pb dating technique.
Preparation of samples: 7 following standard zircons are used in this experiment: Phalaborwa, 91500, GJ-1, Temora,
Pl ě sovice, Qinghu and SK10-2.This 7 zircon particles are embedded in the epoxy resin samples target of 2.54 centimetres (1 inch),
Unknown sample is placed in same or another epoxy resin samples target, shoots cathodoluminescence image with scanning electron microscope after polishing,
To distinguish the core, curtain and side structural relation of zircon mineral particle.
Instrument is set up: measure mass spectrograph used: Neptune Plus type receives icp ms more
(Neptune Plus MC-ICP-MS, manufacturer: Thermo Fisher Scientific, Germany), equipped with 7 from
Sub-count device IC4, IC5, IC3A, IC2, IC1B1, IC6 and IC7 are respectively used to receive simultaneously202Hg,204(Pb+Hg),206Pb
,207Pb,208Pb,232Th and238U ion stream (referring to table 1).Micro-zone in situ sampling equipment: Analyte G2 type 193nm quasi-molecule
Laser ablation system (manufacturer: Photon Machines, USA).The sample solid sols of laser ablation are loaded into plasma by helium
Before body, the nitrogen of 2-4 ml/min is added and then make-up gas (argon gas, additional amount are added by a concentric vortex mixer
Signal strength of being subject to is optimal), the instrument teaming method used in experiment is as shown in Figure 3.
Denudation depth: it in order to obtain optimal denudation depth, devises following experiment: setting straight for laser ablation beam spot
5 microns of diameter, be standard with standard zircon 91500 using standard zircon GJ-1 as sample, respectively with 8,14,19,25,30,35,40
Carry out U-Pb with 45 laser pulses and determine year to test, corresponding denudation depth is respectively 0.96,1.68,2.28,3,3.6,4.2,
4.8 and 5.4 microns, the U-Pb of acquisition determines annual bearing and is listed in Fig. 4.The experimental results showed that using in 8-45 pulsating sphere, it is corresponding
Denudation depth be 1-5.4 micron, can obtain and reference value completely the same age result in error range, wherein using
19 umber of pulses, denudation depth are 2.28 microns, and the U-Pb age precision of acquisition is best, later with the increase of denudation depth,
Age precision is gradually deteriorated.As a result illustrate, using 8-25 umber of pulse, 1-3 microns of denudation depth, can obtain less than 0.42%
High-precision age data.
Instrument testing: dark noise and platform voltage and its dynamic linear model before sample analysis, to ion counter
It encloses and is measured, the dynamic linear response range between ion counter: 0~720,000cps are shown in Fig. 5, and to yield and dead time
It is corrected.Plasma parameter is adjusted, to obtain optimal sensitivity.Later, mass spectrograph is transferred to laser ablation system
System, sets 5 microns for laser beam spot diameter, is carrier gas with helium, and argon gas is make-up gas, before sample is loaded into plasma
Sensitivity (connection type is shown in Fig. 3) can be significantly improved by being mixed into a small amount of nitrogen, optimize laser sampling condition with NIST610 glass,
Meanwhile it monitoring238U and232The mass fractionation generated in the signal strength and optimization denudation of Th, the instrument after optimization, which works, joins
Ordered series of numbers is in table 1.
Table more than 1 receives icp ms (model: Neptune PLUS) and 193 nanometer lasers degrade and are
System (model: Analyte G2) instrument parameter
Measuring method: laser ablation system parameter: laser beam spot diameter is set as 5 microns, and degrading frequency is 4 hertz, energy
Metric density is 4 joules/square centimeter.Primary point degrades mass spectrometric location parameter in analysis are as follows: and the time of integration 0.131 second, product
Divide 150 times, laser ablation is used to measure background intensity before starting for 10 seconds, then, opens laser and is degraded about 6 seconds to sample
Left and right, laser pulse number are 25 or so, and denudation depth is less than 3 microns.
Using helium as laser ablation substance carrier gas, after three mercury filters filter, measure202Hg、204(Hg+
Pb)、206Pb、207Pb and208The background intensity of Pb is respectively 2460,539,35,30 and 60cps, and232Th and238U background intensity
Respectively less than 5cps.The Fractionation Correction generated in correction, mass fractionation correction and denudation between ion counter all passes through
Standard-sample interpolation technique (SSB) is completed.
Each analysis process is degraded analysis with a NIST610 normal glass point and is started, then carries out 2 standard zircon point strippings
Erosion analysis, then, 2 standard sample points of progress degrade analysis after every 5 sample spots degrade analysis, before analysis process terminates
A NIST610 normal glass sample spot is carried out again degrades analysis.Through timing, an analysis process carries out 30 sample spots and degrades
Analysis, required analysis time is only 50 minutes or so.NIST610 normal glass is for U, Th and the Pb content in zircon sample
Correction, standard zircon are used to correct zircon sample207Pb/206Pb,207Pb/235U and206Pb/238U isotopic ratio.Isotope
The formula that ratiometric correction uses is as follows:
WithThe respectively isotopic ratio and the isotopic ratio after correction of sample measurement,For standard zircon
Isotopic ratio recommendation,WithMeasure the isotopic ratio of standard zircon twice respectively before and after sample,
tsam、WithRespectively sample and its front and back measure the time of standard zircon (to analyze order generation in practical calculating twice
Table time change), it corrects the software used and (is write by China University of Geosciences professor Liu Yongsheng) for ICPMSDataCal9.0, U-
The software that the weighted mean at Pb age calculates and consonance figure uses for Isoplot3.0 (Kenneth R.Ludwig volume,
2012)。
Formula of error transmission in the calculating of isotopic ratio Fractionation Correction are as follows:
WithRespectively the uncertainty of sample, standard zircon recommendation be not
Degree of certainty, the uncertainty for measuring standard zircon twice before and after sample.The software used is corrected as ICPMSDataCal9.0
(being write by China University of Geosciences professor Liu Yongsheng), the software that the weighted mean at U-Pb age calculates and consonance figure uses for
Isoplot3.0。
Method is examined: using standard zircon 91500 as calibration standard, using GJ-1 standard zircon as sample, according to above-mentioned
Method has carried out 6 measurements in three months；Use standard zircon GJ-1 as calibration standard, standard zircon Phalaborwa,
Temora, Pl ě sovice, Qinghu and SK10-2 are measured in three months as sample, also according to the above method, are surveyed
Determine result and is listed in Fig. 6.Measurement result show the Zircon age that measures of space high-resolution measuring method researched and developed with the present inventor with
Bibliographic reference value be in error range it is completely the same, the assay result of U-Th-Pb in error range with document knot
Fruit is also completely the same, and for the precision of 30 duplicate measurements weighted means less than 1% (2s), the precision that single-point degrades measurement is 1-
4% (2s).The result shows that the spatial resolution of laser ablation in-situ micro area U-Pb dating technique is increased to by the method for the present invention
5.8 × 7.4 microns (transverse direction), denudation depth does not lose precision not only less than 3 microns, but also compared with prior art using big stripping
The result precision that beam spot (such as: 30 microns of diameter) obtains is lost also slightly to improve.It, should for expensive ion probe technology
Method is efficient and practical, is easy to universal.
Surface sweeping analysis is carried out to erosion pit with atomic force microscope the result shows that, be set as 5 microns in laser beam spot diameter,
Laser energy density is 4 joules/square centimeter, and under conditions of umber of pulse is 25, the shape for obtaining erosion pit is 5.8 × 7.4 micro-
Rice ellipse, denudation depth are 3 microns.
Embodiment 4
It is picked up from the pressure metamorphic gneiss research of Dabie Mountains Region using technique study same as Example 3, mesh
Be whether the determining rock experienced UHP metamorphism and pressure metamorphic epoch.As a result, it has been found that the gneiss sample
Zircon in product has apparent core, curtain and the structure on side, and curtain and side are all very narrow (Fig. 7), and usually less than 10 microns, using current
Existing laser ablation in-situ micro area dating technique can not carry out U-Pb to the zircon sample and determine year analysis, using the method for the present invention
Obtain good chronological data.Data result shows curtain portion and edge is all metamorphic zircon, represents two phases rotten work
With it is 230Ma (1000000 years) Zuo You that the time interval that this two phases metamorphism occurs is close, and core portion is original zircons, is had recorded
Two phase magmatic events, the time of generation are respectively 840Ma and 750Ma or so (Fig. 8).
Finally, it should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations；Although
Present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that: it still may be used
To modify the technical solutions described in the foregoing embodiments or equivalent replacement of some of the technical features；
And these are modified or replaceed, technical solution of various embodiments of the present invention that it does not separate the essence of the corresponding technical solution spirit and
Range.
Claims (11)
1. a kind of method for the uranium lead age for measuring zircon sample, which is characterized in that described method includes following steps:
(1) zircon sample and zircon standard substance are respectively embedded into epoxy resin so that sample target is made；
(2) laser ablation is carried out to zircon in the sample target respectively using laser beam, to obtain solid sols；
(3) solid sols are loaded into the plasma ion sources for receiving icp ms more using carrier gas
It is ionized, to obtain primary ions；
(4) make the primary ions by the electric and magnetic fields in the mass spectrograph to realize energy and direction double focusing；
(5) primary ions Jing Guo double focusing are detected using ion counter and calculates the zircon sample and the zircon
The original uranium lead ratio value of the primary ions of standard substance；
(6) using the known nominal uranium lead ratio value of the zircon standard substance and measured original uranium lead ratio value to the zirconium
The original uranium lead ratio value of stone sample is corrected, thus the uranium lead ratio value after obtaining the correction of the zircon sample；
(7) using the uranium lead age of zircon sample described in the uranium lead ratio calculation after the correction.
2. according to the method described in claim 1, it is characterized by:
The laser beam is 193 nanometer laser beams；
The beam spot diameter, of the laser beam is arranged to 5 microns.
3. make-up gas is argon gas, and in institute the method according to claim 1, wherein the carrier gas is helium
It states solid sols and is loaded into the nitrogen that solid sols described in the forward direction of plasma are mixed into 2-4 ml/min.
4. the method according to claim 1, wherein the size of the sample target is 2.54 centimetres or 1.77 lis
Rice.
5. according to the method described in claim 1, it is characterized by:
The laser pulse quantity of the laser ablation is 8 to 45, and denudation depth is 1 to 5.4 micron.
6. according to the method described in claim 1, it is characterized by:
The laser pulse quantity of the laser ablation is 8 to 25, and denudation depth is 1 to 3 micron.
7. according to the method described in claim 1, it is characterized by:
The laser pulse quantity of the laser ablation is 19, and denudation depth is 2.28 microns.
8. the method according to claim 1, wherein the mass spectrograph is equipped with micro-zone in situ sampling equipment and extremely
Few 6 ion counters.
9. according to the method described in claim 6, it is characterized in that, the mass spectrograph is equipped with being respectively used to receive simultaneously202Hg、204(Pb+Hg)、206Pb、207Pb、208Pb、232Th and2387 ion counters of U ion stream.
10. according to the method described in claim 1, it is characterized by:
The parameter of the laser ablation is using following setting: the beam spot diameter, of laser beam is set as 5 microns, and degrading frequency is 4 hertz
Hereby, energy density is 4 joules/square centimeter；
The mass spectrometric location parameter is using following setting: the time of integration 0.131 second, integrating 150 times, laser ablation starts it
It for measuring background intensity, opens laser and sample degrade 6 seconds, laser pulse number 25, denudation depth is less than 3 within first 10 seconds
Micron.
11. according to the method described in claim 10, it is characterized by:
U, Th and Pb content in zircon sample are corrected using NIST610 normal glass sample, are corrected using standard zircon
Zircon sample207Pb/206Pb,207Pb/235U and206Pb/238U isotopic ratio, isotopic ratio correction using following formula into
Row:
Wherein,WithThe respectively isotopic ratio and the isotopic ratio after correction of zircon sample measurement,For mark
The isotopic ratio recommendation of quasi- zircon,WithMeasure the same position of standard zircon twice respectively before and after zircon sample
Plain ratio, tsam、WithRespectively zircon sample and its front and back time for measuring standard zircon twice；
Formula of error transmission in the calculating of isotopic ratio Fractionation Correction are as follows:
Wherein,WithThe respectively isotopic ratio and the isotopic ratio after correction of zircon sample measurement,For mark
The isotopic ratio recommendation of quasi- zircon,WithMeasure the same position of standard zircon twice respectively before and after zircon sample
Plain ratio； WithRespectively the uncertainty of sample, standard zircon recommendation it is uncertain
Degree, the uncertainty for measuring standard zircon twice before and after sample；tsam、WithRespectively zircon sample and its front and back
The time of standard zircon is measured twice.
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