LASER ABLATION ICP MS ANALYSIS OF MINERALS, FLUID AND MELT INCLUSIONS

ANALYTICAL SEQUENCE - SOLIDS

ANALYTICAL SEQUENCE - MELT INCLUSIONS

A) NIST610 glass standard is analyzed, twice, as follows: 1) With Laser OFF He gas background is collected for ~ 60 s; 2) Laser is turned on and NIST is ablated for ~ 40 to 60 s;B) Sample(s) is analyzed as follows: 1) With Laser OFF He gas background is collected for ~ 60 s; 2) Laser is turned on and sample is ablated for ~ 40 to 60 s;C) NIST610 glass standard is analyzed twice as in “A” to compensate

for instrumental drift.

Inlet - He Flow ~ 1 L/mOutlet to the Mass

Spectrometer

Fast purge ablation chamber (< 100 ms), diamond-shaped to reduce turbulence

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Co

un

ts

Na

M g

Al

S i

K

Ca

Ti

Cr

M n

Fe

Ni

Co

RbB1

B2

DATA REDUCTION - AMS SOFTWARE

ANALYTICAL SEQUENCE - FLUID INCLUSIONS

Olivine analysis. Major, minor and trace elements can be analyzed simultaneously. Typical analytical setup includes 20+ elements, but larger numbers (40+) can be easily collected during a single analysis.

A) NIST610 glass standard is analyzed, twice, as follows: 1) With Laser OFF He gas background is collected for ~ 60 s; 2) Laser is turned on and NIST is ablated for ~ 40 to 60 s;B) Sample(s) is analyzed as follows: 1) With Laser OFF He gas background is collected for ~ 60 s;

2) Laser is turned on and sample is ablated gradually, first drilling into the sample with a small beam(i.e. smaller than the inclusion);

3) Drilling is continued with larger beam size, up to the inclusion dimension. Signal is monitored to achieve complete analysis of the inclusion;

C) NIST610 glass standard is analyzed again as in “A”to compensate for instrumental drift.

A) NIST610 glass standard is analyzed, twice, as follows: 1) With Laser OFF He gas background is collected for ~ 60 s; 2) Laser is turned on and NIST is ablated for ~ 40 to 60 s;B) Sample(s) is analyzed as follows: 1) With Laser OFF He gas background is collected for ~ 60 s;

2) Laser is turned on and sample is ablated gradually as follows:2a) if inclusion is glassy and exposed a beam size smaller than the

inclusion is used. Signal is monitored during ablation;2b) if inclusion is not exposed (can also be partially or totally

crystallized), a beam size slightly larger than the inclusion is used. Signal is monitored during ablation;

C) NIST610 glass standard is analyzed again, twice as in A, to compensate for instrumental drift.

Ene

rgy

Distance

Ene

rgy

Distance

LASER BEAM

LASER BEAM

NON HOMOGENIZED ENERGY PROFILE

HOMOGENIZED ENERGY PROFILE

HOMOGENIZING

OPTICS

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L iNaM gKCaM nFeNiCuQzAsSrCd

HOST SIGNAL- QZ

FLINC SIGNAL

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NaM gAlS iKCaTiM nFeRbYZrCePbTh

2a

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NaA lS iKCaTiM nFeRb

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MIs NON EXPOSED in Quartz

QUARTZEXPOSED

QUARTZNON EXPOSED

280 µm

MI exposed in Olivine

Large melt inclusion in olivine, with laser ablation pits. 100 µm

Laser ablation pits in quartz100 µm 50 µm 100 µmFluid Inclusions in Quartz

Mineral SurfaceAblation Pit

Melt InclusionHost volumeanalyzed withthe melt inclusion

Ablation of a non exposed melt inclusion. Notice that during ablation a mixed signal [HOST + MI] is collected.

The AMS graphic interface displaying a signal from an olivine

With LA-ICP-MS it is possible to analyze the inclusion as found in the sample (A), but better results can be achieved if the inclusion is re-heated and quenched into an homogeneous glass (B), and then exposed either by hand polishing or by the use of the laser prior to analysis.

Naturally re-crystallized melt inclusion in olivine;

A B

The same inclusion after re-heating and quenching to produce an homogeneous glass.

Vapour Bubble

3) Using microthermometry data (salinity as NaCl wt.% equiv.) in combination with equation (1), it is possible to calculate absolute elements concentrations using the relationship

(4)

and solutions by iteration;4) Is a particular case of (1) and (2), the same approach is used

for data reduction;

The AMS software allows LA-ICP-MS data reduction (with drift correction) in the following cases:

1) Analysis of solids with use of explicit internal standard;2) Analysis of solids without use of explicit internal standard;3) Analysis of fluid inclusion based on microthermometry data;4) Analysis of glassy melt inclusions exposed, with and without

use of explicit internal standard;5) Analysis of non-exposed melt inclusions, glassy or partially

crystallized (i.e. deconvolution HOST signal – MIs signal).

Depending upon each case AMS applies different algorithms, all generally adopted and available in the published literature:

1) In this case AMS uses the general formula

(1)

(Na is the internal standard and Ca is the sought element. I is the net intensity after background subtraction)

2) In absence of internal standards, in some cases it is possible to reduce the data analyzing all the major and minor elements in the unknown (in addition to the sought trace elements). For minerals this typically requires to measure Si, Ti, Al, Fe, Mg, Mn, Ca, Na, K, P etc. (depending upon the mineral).

We know that: (2) where is the cation weight fraction in the sample. Dividing (2) by a reference cation (which can be any of

the major elements analyzed), we can write the following:

(3)

This allows us to determine the reference cation , and subsequently all the remaining cation fractions by multiply

with (which can be determined using equation

(1) and iterative calculations). Once the major elements are known, one of them can be used as internal standard to determine the sought trace elements.

dS

CaSampleNa

dSNa

SampleCa

dSNa

dSCa

SampleNa

SampleCa

IIII

CC

CC

tan

tan

tan

tan

××

×=

∑=

=N

i

SaiX

11

SaiX

SarX

SarX

( )∑ ≠

+= N

riiSar

Sai

Sar

XXX

,/1

1

Sar

Sai XX /

5) Deconvolution of a mixed HOST-MI signal requires knowledge of the following:

a. Composition of the HOST, obtainable by LA-ICP-MS using either (1) or (2) as data reduction approach. The HOST signal can be acquired either away from the MI, or as first part of the ablation signal before the non-exposed MI is reached (cfr. Fig. 2b);

b. Concentration of one major element i in the MI, which is also a minor in the HOST (this can be determined in various ways);

c. The LA-ICP-MS signal collected from the MI;The mixed signal can be separated in its two components calculating the mass ratio:

(5)

Where all the Ci members are known. Once x is known (5) can be rearranged and applied to all the other elements.

.......%)(22+++= FeClCaClNaCl CCCwtNaCl

INCLi

HOSTi

MIXi

HOSTi

MIX

INCL

CCCC

mmx

−−

==