CN105572217A - Double dating method for single-particle monazite - Google Patents

Abstract

The invention discloses a double dating method for single-particle monazite. The method includes the steps that the crystallization age, namely the occurrence time of a magmatic intrusion incident , of a granite geologic body where the monazite is located can be obtained; (U-Th)/He age of the monazite can be obtained and represents the uplift-related cooling age, namely the time of fast tectonic uplift of the geologic body. The intrusion history and the tectonic uplift history of the geologic body where the monazite is located can be obtained through U-Pb and (U-Th)/He double dating of the single monazite at the same time, and the double dating method is of important geological significance.

Description

A kind of two dating methods of individual particle monazite

Technical field

The present invention relates to dating methods, particularly relate to a kind of two dating methods of individual particle monazite.

Background technology

Radioactive isotope dating developed dating technology rapidly in recent years, and its maturation facilitates the development of geologic chronology greatly.What current application was more is that zircon, apatite are carried out to U-Pb and surveys year or (U-Th)/He survey year, and study its crystallization age or cooling age, technology is comparative maturity also.But, the dating methods of current domestic nobody to monazite is studied, have extremely indivedual scholar to carry out separately U-Pb to monazite abroad at present to survey year or carry out separately (U-Th)/He survey year, but two survey year methods no one's research so far that two kinds of methods are joined together.Innovative point of the present invention realizes the two dating methods application of U-Pb and (U-Th)/He exactly on same monazite particle.

Summary of the invention

The present invention is to solve above-mentioned deficiency, provides a kind of two dating methods of individual particle monazite.

Above-mentioned purpose of the present invention is realized by following technical scheme: a kind of two dating methods of individual particle monazite, is characterized in that: comprise the following steps:

(1) select crystal formation complete and not containing the individual particle monazite of inclusion, take pictures by digital camera, obtaining the accurate shape and size of monazite particle, for calculating α particle injection correction parameter F _t, computing formula is:

$F_T=1-\frac{3S}{4R}+\frac{S^3}{16R^3}$

Wherein F _t: α particle injection correction parameter; S: the stop distance of α particle when U and Th occurs to decay in monazite; R: the inscribed sphere radius of individual particle monazite crystal, in order to more accurately calculate F _t, the value of R is preferably 60-70 μm;

(2) individual particle monazite is fixed on double sticky tape, carries out U-Pb with laser ablation Inductively coupled plasma mass spectrometry (LA-ICPMS) and survey year; With the outside surface of laser direct irradiation monazite particle, beam size is 20 μm, and the degree of depth of rhegmalypt is about 20 μm; Be less than to the monazite of 1300Ma the age, adopt ²⁰⁶pb/ ²³⁸u represents its U-Pb age; Be greater than to the monazite of 1300Ma the age, adopt ²⁰⁷pb/ ²⁰⁶pb represents its U-Pb age;

(3) above-mentioned individual particle monazite is stripped down, put into 1mm ³in metal foil containers, by LASER HEATING to 1300 DEG C, continue 20 minutes, by more than 99% in monazite ⁴he discharges; With 10ncc (1ncc=1 × 10 ^-9ml) ³he is to discharge ⁴he dilutes, with activated charcoal pair ⁴he and ³he carries out gathering and profound hypothermia (16K) purifying; Then quadrupole mass spectroscope (QMS) is used to measure in a static mode ⁴he/ ³the ratio of He, obtains ⁴the content of He;

(4) will discharge ⁴monazite after He put into through calibration ²³³u and ²²⁹in Th solution, the nitric acid adding 30% dissolves, and then uses plasma mass spectrometry (ICPMS) to measure ²³⁸u/ ²³³u, ²³⁵u/ ²³³u and ²³²th/ ²²⁹the ratio of Th, obtains ²³⁸u, ²³⁵u and ²³²the content of Th;

(5) (U-Th)/He age is calculated according to following formula;

$N_{4_{He}}=8\·N_{{238}_U}\·(e^{{\mathrm{\λ}}_8\·t}-1)+7\·N_{{235}_U}\·(e^{{\mathrm{\λ}}_5\·t}-1)+6\·N_{{232}_{Th}}\·(e^{{\mathrm{\λ}}_2\·t}-1)$

Wherein: record ⁴the atomicity of He; record ²³⁸the atomicity of U; record ²³⁵the atomicity of U; record ²³²the atomicity of Th; λ ₈: ²³⁸the disintegration constant of U; λ ₅: ²³⁵the disintegration constant of U; λ ₂: ²³²the disintegration constant of Th; T: the time that decay continues, i.e. (U-Th)/He age;

(6) according to α particle injection correction parameter, measured value is corrected;

$T=\frac{T_m}{F_T}$

Wherein: T: through (U-Th)/He age of overcorrect; T _m: measure (the U-Th)/He age obtained; F _t: α particle injection correction parameter.

Of the present invention pair of dating methods can obtain the crystallization age of the grouan geologic body at monazite place, i.e. the time of igneous invasion event generation; Secondly can obtain again (U-Th)/He age of this monazite, it represents the age of this grouan geologic body lifting cooling, i.e. the time of this geologic body generation Fast Construction lifting.

Ultimate principle of the present invention be according to radioelement uranium (U) in the monazite in grouan and thorium (Th) content higher, U can generate lead (Pb) through decay, U and Th can generate helium (He) through decay, therefore by measuring the content of parent isotope U and Th and daughter isotope Pb and He in monazite, just just can be calculated the time of decay by decay law, namely monazite U-Pb system and (U-Th)/He start time of closing.

The present invention's advantage is compared with prior art: of the present invention pair of dating methods surveys the intrusion history and structure rising history that can obtain monazite location plastid year by individual particle monazite U-Pb and (U-Th)/He is two simultaneously, has important geological Significance.

Embodiment

Below in conjunction with embodiment, the present invention is described in further detail.

Two dating methods of a kind of individual particle monazite of the present invention, comprise the following steps:

(1) select crystal formation complete and not containing the individual particle monazite of inclusion, take pictures by digital camera, obtaining the accurate shape and size of monazite particle, for calculating α particle injection correction parameter F _t, computing formula is:

$F_T=1-\frac{3S}{4R}+\frac{S^3}{16R^3}$

Wherein F _t: α particle injection correction parameter; S: the stop distance of α particle when U and Th occurs to decay in monazite; R: the inscribed sphere radius of individual particle monazite crystal, in order to more accurately calculate F _t, the value of R is preferably 60-70 μm;

(2) individual particle monazite is fixed on double sticky tape, carries out U-Pb with laser ablation Inductively coupled plasma mass spectrometry (LA-ICPMS) and survey year; With the outside surface of laser direct irradiation monazite particle, beam size is 20 μm, and the degree of depth of rhegmalypt is about 20 μm; Be less than to the monazite of 1300Ma the age, adopt ²⁰⁶pb/ ²³⁸u represents its U-Pb age; Be greater than to the monazite of 1300Ma the age, adopt ²⁰⁷pb/ ²⁰⁶pb represents its U-Pb age;

(3) above-mentioned individual particle monazite is stripped down, put into 1mm ³in metal foil containers, by LASER HEATING to 1300 DEG C, continue 20 minutes, by more than 99% in monazite ⁴he discharges; With 10ncc (1ncc=1 × 10 ^-9ml) ³he is to discharge ⁴he dilutes, with activated charcoal pair ⁴he and ³he carries out gathering and profound hypothermia (16K) purifying; Then quadrupole mass spectroscope (QMS) is used to measure in a static mode ⁴he/ ³the ratio of He, obtains ⁴the content of He;

(4) will discharge ⁴monazite after He put into through calibration ²³³u and ²²⁹in Th solution, the nitric acid adding 30% dissolves, and then uses plasma mass spectrometry (ICPMS) to measure ²³⁸u/ ²³³u, ²³⁵u/ ²³³u and ²³²th/ ²²⁹the ratio of Th, obtains ²³⁸u, ²³⁵u and ²³²the content of Th;

(5) (U-Th)/He age is calculated according to following formula;

$N_{4_{He}}=8\·N_{{238}_U}\·(e^{{\mathrm{\λ}}_8\·t}-1)+7\·N_{{235}_U}\·(e^{{\mathrm{\λ}}_5\·t}-1)+6\·N_{{232}_{Th}}\·(e^{{\mathrm{\λ}}_2\·t}-1)$

Wherein: record ⁴the atomicity of He; record ²³⁸the atomicity of U; record ²³⁵the atomicity of U; record ²³²the atomicity of Th; λ ₈: ²³⁸the disintegration constant of U; λ ₅: ²³⁵the disintegration constant of U; λ ₂: ²³²the disintegration constant of Th; T: the time that decay continues, i.e. (U-Th)/He age;

(6) according to α particle injection correction parameter, measured value is corrected;

$T=\frac{T_m}{F_T}$

Wherein: T: through (U-Th)/He age of overcorrect; T _m: measure (the U-Th)/He age obtained; F _t: α particle injection correction parameter.

The foregoing is only embodiments of the invention; not thereby the scope of the claims of the present invention is limited; every utilize instructions of the present invention and embodiment content to do equivalent structure or equivalent flow process conversion; or be directly or indirectly used in other relevant technical fields, be all in like manner included in scope of patent protection of the present invention.

Claims (1)

1. two dating methods for individual particle monazite, is characterized in that: comprise the following steps:

(1) select crystal formation complete and not containing the individual particle monazite of inclusion, take pictures by digital camera, obtaining the accurate shape and size of monazite particle, for calculating α particle injection correction parameter F _t, computing formula is:

$F_T=1-\frac{3S}{4R}+\frac{S^3}{16R^3}$

Wherein F _t: α particle injection correction parameter; S: the stop distance of α particle when U and Th occurs to decay in monazite; R: the inscribed sphere radius of individual particle monazite crystal, in order to more accurately calculate F _t, the value of R is preferably 60-70 μm;

(2) individual particle monazite is fixed on double sticky tape, carries out U-Pb with laser ablation Inductively coupled plasma mass spectrometry (LA-ICPMS) and survey year; With the outside surface of laser direct irradiation monazite particle, beam size is 20 μm, and the degree of depth of rhegmalypt is about 20 μm; Be less than to the monazite of 1300Ma the age, adopt ²⁰⁶pb/ ²³⁸u represents its U-Pb age; Be greater than to the monazite of 1300Ma the age, adopt ²⁰⁷pb/ ²⁰⁶pb represents its U-Pb age;

(3) above-mentioned individual particle monazite is stripped down, put into 1mm ³in metal foil containers, by LASER HEATING to 1300 DEG C, continue 20 minutes, by more than 99% in monazite ⁴he discharges; With 10ncc (1ncc=1 × 10 ^-9ml) ³he is to discharge ⁴he dilutes, with activated charcoal pair ⁴he and ³he carries out gathering and profound hypothermia (16K) purifying; Then quadrupole mass spectroscope (QMS) is used to measure in a static mode ⁴he/ ³the ratio of He, obtains ⁴the content of He;

(4) will discharge ⁴monazite after He put into through calibration ²³³u and ²²⁹in Th solution, the nitric acid adding 30% dissolves, and then uses plasma mass spectrometry (ICPMS) to measure ²³⁸u/ ²³³u, ²³⁵u/ ²³³u and ²³²th/ ²²⁹the ratio of Th, obtains ²³⁸u, ²³⁵u and ²³²the content of Th;

(5) (U-Th)/He age is calculated according to following formula;

$N_{4_{He}}=8\·N_{{238}_U}\·(e^{{\mathrm{\λ}}_8\·t}-1)+7\·N_{{235}_U}\·(e^{{\mathrm{\λ}}_5\·t}-1)+6\·N_{{232}_{Th}}\·(e^{{\mathrm{\λ}}_2\·t}-1)$

Wherein: record ⁴the atomicity of He; record ²³⁸the atomicity of U; record ²³⁵the atomicity of U; record ²³²the atomicity of Th; λ ₈: ²³⁸the disintegration constant of U; λ ₅: ²³⁵the disintegration constant of U; λ ₂: ²³²the disintegration constant of Th; T: the time that decay continues, i.e. (U-Th)/He age;

(6) according to α particle injection correction parameter, measured value is corrected;

$T=\frac{T_m}{F_T}$

Wherein: T: through (U-Th)/He age of overcorrect; T _m: measure (the U-Th)/He age obtained; F _t: α particle injection correction parameter.