Progress in Earth andPlanetary Science(2021) 8:51
Wang et al. Prog Earth Planet Sci
https://doi.org/10.1186/s40645-021-00446-3

Open Access

RESEARCH ARTICLE

NanoSIMS and EPMA dating of lunar
zirconolite
Nian Wang1,2†, Qian Mao3†, Ting Zhang1,2, Jialong Hao1 and Yangting Lin1*

Abstract: Zirconolite is a common Zr-rich accessary mineral in mafic rocks. It is also an ideal U–Pb/Pb–Pb chronometer because it commonly contains high U content (mostly 0.1–10 wt%) and negligible initial Pb. However, zirconolite
is usually very small (e.g., ~ 1 μm in width) in lunar rocks, requiring a high spatial resolution analysis. We analyzed asingle, large (25 μm × 20 μm) grain of zirconolite in lunar meteorite NWA 4485 using Pb–Pb dating by NanoSIMS
and U–Th–Pb dating by EPMA. The resultant U–Th–Pb age is 4540 ± 340 Ma (2σ) with a spatial resolution of 1.3 μm.
The Pb–Pb age by NanoSIMS is 4348.5 ± 4.8 Ma (2σ) with a spatial resolution of ~ 2 μm, consistent with the ageof 4352 ± 10 Ma and 4344 ± 14 Ma reported in the same meteorite and its paired meteorite NWA 4472. Although
U–Th–Pb age is somewhat older, it still includes the NanoSIMS results within the analytical uncertainty. This work
demonstrates the potential application of the combined EPMA dating and REE analysis of lunar zirconolite, with thebenefits of high spatial resolution, non-destructive, and readily accessibility of the instrument. The precision of the
EPMA dating (7.6%, 2σ) can be improved by increasing the counting time for Pb, U and Th. We expect to apply thisEPMA technique for a quick and non-destructive age survey and geochemical study of zirconolite grains from thelunar mare basalts newly returned by Chang’E-5 mission which landed on a very young (1.2–2.0 Ga by crater-counting
chronology) basalt unit in Procellarum KREEP Terrain.
Keywords: Zirconolite, Chemical age, Lunar sample, NWA 4485, Chang’E-5, Lunar basalt

1 Introduction
Zirconolite ­(CaZrTi2O7) has been recognized as a fairly
common accessory mineral first in terrestrial rocks (Williams and Giere 1996) and then in lunar basaltic rocks
from Apollo 11 and 12 (Lovering and Wark 1971; Warket al. 1973). Zirconolite usually contains high U (mostly
0.1–10 wt%) with negligible common Pb (Williams andGiere 1996), making it a potential U–Pb chronometer.
Since the work by Rasmussen and Fletcher (2004), it has
been demonstrated as an ideal mineral for U–Pb geochronology using sensitive high-resolution ion microprobe (SHRIMP) and secondary ion mass spectrometry(SIMS) techniques with reliable age precision (Downes
et al. 2016; Norman and Nemchin 2014; Rasmussen et al.
*Correspondence: linyt@mail.iggcas.ac.cn†
Nian Wang and Qian Mao contributed equally to this work
1
Key Laboratory of Earth and Planetary Physics, Institute of Geology
and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Full list of author information is available at the end of the article

2008 2009; Wu et al. 2010; Zhang et al. 2010). Meanwhile,the in situ U–Pb geochronology of zirconolite has also
demonstrated that it yields Pb–Pb ages that are more
precise than those obtained from coexisting zircon andbaddeleyite (Rasmussen and Fletcher 2004).
Lunar zirconolite was commonly reported as a ubiquitous trace mineral in the late stage mesostasis of lunar
mare basalt (Day et al. 2006; Rasmussen et al. 2008; Warket al. 1973; Zeigler et al. 2005). It usually contains lower
U and Th contents than terrestrial zirconolite and therefore less degree of metamictization and Pb-loss causedby alpha-decay damage. However, most lunar zirconolite grains are always fine-grained or elongated “strings”,
ranging in shapes from laths to tubular rods (Rasmussen et al. 2008; Seddio et al. 2013). They rarely grow up
to 10 μm in size and frequently appear as needle-likestrings with length up to tens of μm but width less than
2 μm (Rasmussen and Fletcher 2004; Seddio et al. 2013).
This typical morphology of zirconolite makes mostoccurrences too small for traditional analyses like SIMS

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Wang et al. Prog Earth Planet Sci(2021) 8:51

or SHRIMP dating. Therefore, higher lateral resolution
secondary ion spectrometer like CAMECA NanoSIMS
50L is more appropriate for small size zirconolite dating,which can recently achieve the submicron spatial resolution for Pb–Pb dating but with significant depth effectafter equipped with the new radio-frequency iron source(Hao et al. 2021).
For traditional ion microprobes, such as SIMS,SHRIMP, and NanoSIMS, their major disadvantage isthat they are destructive for zirconolite grains when analyzing. In addition, only limited elements or isotopes
concentrations can be acquired at once by ion microprobes due to their limited detectors. For precious lunar
sample, such as the recently returned Chang’E-5 lunar
soil, damage-free and more effective dating method like
EPMA U–Th–Pb chemical dating coupled with REE
measurements is very useful for a quick prelude dating
survey before destructive analyses. Regarding EPMA
chemical dating, it was first published in Bowles (1990)
and used on uraninite ­(UO2), and then developed foruse on other U-bearing minerals, such as monazite, zircon, and xenotime in Suzuki and Adachi (1991a, b).
Later, numerous publications have demonstrated its
usage in both terrestrial and lunar rocks, and analyticaltechniques to obtain the best result were also presented
in these studies (Bowles 2015; Chatterjee et al. 2017;
Cocherie and Legendre 2007; Cross et al. 2011; Downes
et al. 2016; Hazarika et al. 2017; Montel et al. 1996; Pyleet al. 2005; Seddio et al. 2014, 2013; Suzuki et al. 1994;
Yonemura et al. 2013). Among these work, several studies have tried to apply EPMA chemical dating to zirconolite, such as: Rajesh et al. (2006) reported EPMA datingof zirconolite from terrestrial samples, assuming that
all Pb analyzed are radiogenic; Seddio et al. (2013) used
EPMA to date the zirconolite from Apollo 12,032 granite.
Although the accuracy of the EPMA dating is consideredpoor compared to the isotopic ages, its potential superior
spatial resolution up to 1 μm, good integrating of minor
elements and age information, non-destructive, and easier access of the facility, make EPMA chemical dating acomplementary technique to SIMS dating (Hazarika
et al. 2017; Montel et al. 1996).
To verify the reliability of EPMA dating of lunar zirconolite, a KREEP-rich lunar meteorite NWA 4485 (Araiet al. 2009) was used for study, which is a polymict regolith breccia and paired with NWA 4472 (Joy et al. 2011).
Consistent with its high KREEP contents, there are many
Zr-rich minerals including zircon, baddeleyite, and zirconolite that are suitable for dating measurements in
NWA 4485. A single, large (25 μm × 20 μm) grain of zirconolite was found and analyzed using Pb–Pb dating by
NanoSIMS and U–Th–Pb dating by EPMA, and then the

Page 2 of 8

result of chemical age is compared with that of Pb–Pb
isotope age.

2 Methods
A polished section (1.2 × 1 ­cm2) of NWA 4485 was prepared from a chip of the meteorite, and it was carbon
coated. The section was observed in backscatter electron (BSE) images using a field emission scanning electron microscope NOVA NANOSEM450 equipped witha Gatan cathodoluminescence (CL) detector at Instituteof Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). The operating conditions were 15 kV
accelerating voltage and 3.2 nA beam current. Quantitative analysis of zirconolite was determined using a
Cameca SXFiveFE electron probe microanalyzer (EPMA)
equipped with wavelength-dispersive X-ray spectrometers (WDS) at IGGCAS. The accelerating voltage of
20 kV and a beam current of 70 nA (~ 1 μm in diameter)
were used. During data acquisition, peak counting timefor each element is the same as their background counting time: Ca (Kα, 10 s), Ti (Kα, 10 s), Fe (Kα, 20 s), Y(Lα,20 s), Zr (Lα, 20 s); Mg (Kα, 30 s), Al (Kα, 30 s), Si (Kα,30 s), La (Lα, 30 s), Ce (Lα, 30 s), Nd (Lα, 30 s), Sm (Lβ,30 s), Gd (Lα, 30 s), Pb (Mα, 30 s), Th (Mα, 100 s), and U(Mβ, 100 s). Additionally, Pb, Th, and U lines are all measured on LPET crystals. Overlapping correction method
was used for interference correction according to themethod reported by Pyle et al. (2005). Corrections forthe interference of YLγ2,3 on PbMα, SmLβ7 on UMβ, andThMζ1 on PbMα were precisely carried out. Due to thesmall correction factor of PbMα/ThMζ1 and low Th concentration in NWA 4485 zirconolite, the interference ofThMζ1 on PbMα was too small to affect the Pb concentration and can be negligible. The full range WDS spectra
acquired with TAP, LPEP, and LiF diffractors are shown
in Additional file 1: Fig. S1. The standard materials used
for U, Th were both synthesized glasses: 7.40 wt% Al,
27.25 wt% Si, 15.76 wt% Ca, 5.18 wt% Th, and 44.63 wt%
O for Th; 7.42 wt% Al, 27.52 wt% Si, 16.07 wt% Ca, 3.85
wt% U, and 44.90 wt% O for U. Natural crocoite (­ PbCrO4)
was used as Pb standard material. Other synthetic andnatural standards were periclase (MgO) for Mg, corundum ­(Al2O3) for Al, wollastonite (­CaSiO3) for Si andCa, rutile ­(TiO2) for Ti, hematite ­(Fe2O3) for Fe, yttrium
aluminum garnet (­ Y3Al5O12) for Y, and 10% REE Si–Al–
Ca–O glasses for La, Ce, Nd, Sm and Gd, respectively.
Detection limits are 30–50 ppm for Mg, Al, Si, Ca andTi, 70–90 ppm for Fe, Th and U, 110–120 ppm for Y and
Gd, 130 ppm for Pb, 220 ppm for Zr, 150–170 ppm for
La, Ce and Nd, 300 ppm for Sm. The Phi-Rho-Z matrix
correction were applied for all data (Merlet 1994). In
addition, Monte Carlo simulation of electron scattering

Wang et al. Prog Earth Planet Sci(2021) 8:51

in zirconolite was generated using Casino (Drouin et al.
2007) at accelerating voltage of 20 kV. The density of zirconolite is defined as 4.8 g/cm3. 1 × ­104 electron trajectories were calculated and used for displaying images.
The resultant spatial resolution for our EPMA analyses
is shown in Additional file 1: Fig. S2. We acquired thesmallest interaction volume of electrons and generation
volume of X-rays of 1.3 μm diameter when the focused
beam size is used. The corresponding YZ energy distribution shows 95% of energy are distributed less than 1.5 μm
in depth.
Following the method of Montel et al. (1996) formonazite, we calculated the chemical age of zirconolite, assuming that all the Pb is radiogenic. This assumption is verified by the negligible ­Pb204/Pb206 ratio in our
NanoSIMS analyses in Sect. 3.3. Given this assumption,
the amount of Pb produced is the sum of the Pb from thedecay of both U and Th:
Pb =



Th  232 t
U  238 tee− 1 208 + 0.9928− 1 206232
238.04
U  235 t+ 0.0072− 1 207e
238.04

where Pb, Th, U are in ppm, and λ232
(4.9475 × ­10–11 ­year−1; Steiger and Jäger 1977), λ235
(9.8485 × ­10–10 ­year−1; Steiger and Jäger 1977), and λ238
(1.55125 × ­10–10 ­year−1; Steiger and Jäger 1977) are theradioactive decay constants for 232Th, 235U and 238U,
respectively.
Because of the lack of zirconolite references, the fractionation between U and Pb during the SIMS analysis
cannot be calibrated. Instead, since the instrumental
mass fractionation (IMF) of Pb isotopes is negligible(Yang et al. 2012), Pb–Pb ages of the zirconolite can bemeasured without U–Pb calibration. Therefore, Pb–Pb
dating was carried out on the same zirconolite grain by
a CAMECA NanoSIMS 50L at IGGCAS, following themethod for Pb–Pb dating (Yang et al. 2012). The O­−
primary beam was accelerated at 16 kV with a currentof ~ 500 pA and a beam size of ~ 1.7 μm in diameter. In
order to achieve the maximum spatial resolution, thescanning off mode was used (Yang et al. 2012). Magnetic
peak-switching mode was applied for the Pb–Pb dating, and four magnetic fields were used in the following
sequence: B1 for Pb background (203.5), B2 for 204Pb, B3
for 96Zr, 206Pb, 238U, 232Th16O, 238U16O2, and B4 for 89Y
and 207Pb, among which lead background (203.5) and
Pb isotopes (204Pb, 206Pb, 207Pb) were measured with thesame EM#4 detector. Before data acquisition, the sample
surface was pre-sputtered by rastering the beam over 3
× 3 μm2 area for 3 min in order to remove the surface
contamination of terrestrial common Pb. M257 zircon(206Pb/238U age = 561.3 Ma) and Phalaborwa baddeleyite

Page 3 of 8

(207Pb/206Pb age = 2059.6 Ma) references (Yang et al.
2012) were measured to assess the potential drift of the
instrument during the analytical session. Measured
204
Pb/206Pb ratios were used for the correction of common Pb based on the two-stage evolution model of Stacey and Kramers (1975). Uncertainties of individual
analysis are reported at 1 sigma level. Weighted average
Pb–Pb age was processed using Isoplot program (Ludwig
2003) and quoted at 2 sigma level.

3 Results
3.1 Occurrence of zirconolite

Zirconolite is an accessory mineral in NWA 4485. It
appears as light gray and is less reflective than ilmenite and troilite, but more reflective than zircon underreflected light microscope. A relatively large grain of
zirconolite (25 μm × 20 μm in size) was identified as amineral fragment in the regolith matrix of NWA 4485
(Fig. 1), surrounded by pyroxene, plagioclase and silicate melts (Fig. 1a). SEM and CL images of the zirconolite grain (Fig. 1b, c) revealed no compositional zoning orother internal features.
3.2 EPMA quantitative analysis of zirconolite

Major and minor composition of zirconolite Five EPMA
analyses were carried out on the zirconolite grain. The
quantitative analyses do not show significant variationfrom the core to the rim, confirming the homogeneous
BSE and CL images. The EPMA results and the formulas of cations calculated based on 7 atoms of oxygen are
given in Table 1. It contains 36.4 wt% Z­ rO2, 35.0 wt%­TiO2, 7.90 wt% CaO, 5.80 wt% FeO, within the rangeof other zirconolite grains reported from lunar samples (Norman and Nemchin 2014; Rasmussen et al.
2008; Seddio et al. 2013) and terrestrial mafic igneous
intrusions (Giere et al. 1998; Williams and Giere 1996).
The U, Th, and Pb average concentrations of this grain
were 0.21 ± 0.01 wt%, 0.56 ± 0.01 wt%, and 0.43 ± 0.02
wt%, respectively. In addition, the concentrations offive REEs (La, Ce, Nd, Sm, Gd) and Y in the zirconolite were measured. Europium was below the detection
limit (0.02 wt%) in all analysis, which resulted in a negative Eu anomaly (Fig. 2). The CI-normalized REEs andY pattern is plotted in Fig. 2, with Y locating between
Ho and Er (Korotev 1996; Seddio et al. 2013). LREE
concentrations are relatively lower than those of middle-REE, increasing from 3800 × CI for La to 33,000 ×
CI for Gd. The CI-normalized Y concentration (22,500
× CI) is slightly lower than that of Gd. The chondritenormalized REE pattern of zirconolite in NWA 4485 ischaracteristically convex and parallel to those of Apollo
lunar zirconolites (Fig. 2) which show strong enrichment of REE (La 3834 × CI, Y 22,500 × CI) in Apollo

Wang et al. Prog Earth Planet Sci(2021) 8:51

10,047 (Rasmussen et al. 2008). The other minor elements are MgO (0.44 wt%), A­ l2O3 (0.52 wt%) and S­ iO2(0.16 wt%). Low analysis totals reflect the presence ofother elements probably including Nb, Ta, and HREEs.
EPMA Chemical dating of zirconolite Following themethod of Montel et al. (1996), we calculated the chemical ages for the zirconolite EPMA analyses using theirTh, U, and Pb concentrations listed in Table 1. Five analyses yield a weighted mean age of 4540 ± 340 Ma (2σ)
with mean square weighted deviation (MSWD) = 0.17
and probability = 0.96 (Fig. 3).
3.3 NanoSIMS Pb–Pb dating

We carried out two NanoSIMS Pb–Pb analyses on thezirconolite grain and the results are listed in Table 2.
It shows that the zirconolite contains minimal common Pb with measured 204Pb/206Pb ratios less than ­10–5­(f206 < ­10–6). The analytical uncertainty is rather small(3.4 Ma, 1σ), and both analyses are the same within theanalytical uncertainty. The weighted mean Pb–Pb age
is 4348.5 ± 4.8 Ma (2σ) with a mean square weighted
deviation (MSWD) = 0.70 and probability = 0.40.

4 Discussion
4.1 Accuracy and uncertainty of EPMA dating

Zirconolite is a common accessary mineral phase, characterized by a large variation of chemical compositioneven for major elements (Zr, Ca, and Ti) due to extensive
substitutions under different formation conditions (Giere
et al. 1998; Hurai et al. 2018; Norman and Nemchin 2014;
Rasmussen et al. 2008; Seddio et al. 2013; Williams et al.
2001; Williams and Giere 1996). For U and Th, theymainly substitute Zr to a concentration level which canbe estimated by EPMA analyses. According to the U, Th,
and Pb composition reported in previous literatures andour study, it is evidenced that zirconolite is a good candidate for EPMA chemical dating.

Page 4 of 8Generally, our EPMA chemical U–Th–Pb age of4540 ± 340 Ma (2σ) is somewhat older than that of
NanoSIMS Pb–Pb age of 4348.5 ± 4.8 Ma, but still
includes the NanoSIMS result within the analyticaluncertainty. The upper limit of chemical age is higher
than the age of the Moon, making it meaningless. Its
lower limit includes the Pb–Pb age result, making it anacceptable result but with poor accuracy. As for analytical uncertainty, the 2σ relative deviation of chemical
age is 7.6%, which is consistent with 7.2% of Apollo zirconolite chemical age reported by Seddio et al. (2013),
but significantly poor than 2.3% in Rajesh et al. (2006).
This is mainly because the terrestrial zirconolites in
Rajesh et al. (2006) contain extremely high contents of­UO2 (6.51–9.64 wt%), ­ThO2 (3.43–4.05 wt%) and PbO(0.50–0.72 wt%), leading to low instrumental counting statistics error. Thus, in order to increase age precision for zirconolite with low ­UO2, ­ThO2, and PbO,
extend of peak counting time to improve the statistics
for these elements is of great significance. Regarding the poor accuracy of chemical age, an increase of
0.03 wt% in the U or a decrease of 0.03 wt% in the Pb
would be enough to make the EPMA date correspondto the NanoSIMS date. However, both 0.03 wt% for U
and 0.03 wt% for Pb are larger than the 2σ standard
deviation for five analyses. This indicates that there is asmall systematic deviation for our EPMA analyses compared with the NanoSIMS Pb–Pb dating, resulting thehigher U–Th–Pb chemical age for zirconolite. In order
to eliminate this systematic deviation, more elements
selected for analyses such as HREEs, Hf, and Nb arenecessary to make the total content closer to 100 wt%.
More careful elements interference correction for these
unselected elements with high concentration on U, Th
and Pb, such as the potential interference of HoL1 on
ThMα, HoLα on ­UMβ, need to be considered and corrected in future lunar samples analyses. In addition, thepossible effects of primary and secondary florescence ofFig. 1 The occurrence of zirconolite grain from NWA 4485. a BSE image of the zirconolite grain, occurring as a mineral fragment in matrix of thelunar regolith breccia. This grain is surrounded by plagioclase (Pl), pyroxene (Px), and silicate melts (Melt). b Contrast-enhanced backscattered imageof the grain, showing a homogeneous composition. c The grain is dark in CL image, showing no trace elements heterogeneity or dislocation

Wang et al. Prog Earth Planet Sci(2021) 8:51

Page 5 of 8

Table 1 EPMA analyses of the zirconolite grain from NWA 4485, in wt%
Point #1

Point #2

Point #3

Point #4

Point #5

Average

MgO

0.45

0.43

0.43

0.43

0.45

0.44

Al2O3

0.52

0.52

0.52

0.52

0.52

0.52

SiO2

0.13

0.17

0.18

0.19

0.12

0.16

CaO

7.84

7.83

7.85

8.09

7.89

7.90

TiO2

35.1

35.0

34.9

35.2

35.0

35.0

FeO

5.86

5.86

5.81

5.71

5.77

5.80

Y2O3

4.46

4.40

4.38

4.42

4.38

4.41

ZrO2

36.6

36.4

36.5

36.5

35.9

36.4

La2O3

0.10

0.10

0.07

0.09

0.10

0.09

Ce2O3

0.78

0.75

0.74

0.81

0.76

0.77

Nd2O3

1.17

1.17

1.17

1.19

1.20

1.18

Sm2O3

0.48

0.49

0.49

0.52

0.47

0.49

Gd2O3

0.74

0.75

0.76

0.77

0.77

0.76

PbO

0.47

0.46

0.43

0.49

0.44

0.46

ThO2

0.64

0.64

0.64

0.64

0.63

0.64

UO2

0.24

0.25

0.25

0.23

0.23

0.24

Total

95.6

95.2

95.1

95.8

94.6

95.3

Pb

0.44

0.43

0.40

0.46

0.41

0.43

Th

0.57

0.56

0.57

0.56

0.55

0.56
0.21

U

0.21

0.22

0.22

0.20

0.21

Age (Ma)

4610

4466

4353

4760

4483

SD

380

381

395

371

393

Atomic ratios based on 7 atoms of oxygen
Al

0.039

0.039

0.039

0.039

0.040

0.039

Si

0.009

0.011

0.012

0.012

0.008

0.010

Ca

0.537

0.538

0.540

0.553

0.545

0.543

Ti

1.689

1.690

1.686

1.688

1.698

1.690

Fe

0.313

0.314

0.312

0.304

0.311

0.311

Y

0.152

0.150

0.150

0.150

0.150

0.150

Zr

1.140

1.138

1.142

1.135

1.129

1.137

La

0.002

0.002

0.002

0.002

0.002

0.002

Ce

0.018

0.018

0.017

0.019

0.018

0.018

Nd

0.027

0.027

0.027

0.027

0.028

0.027

Sm

0.011

0.012

0.012

0.012

0.011

0.012

Gd

0.016

0.016

0.016

0.016

0.016

0.016

Pb

0.008

0.008

0.007

0.008

0.008

0.008

Th

0.009

0.009

0.009

0.009

0.009

0.009

U

0.003

0.004

0.004

0.003

0.003

0.003

Total

4.017

4.016

4.016

4.020

4.020

4.018

SD standard deviationneighboring phases might also be a potential factor forthe poor accuracy. In our work, the neighboring phasesof zirconolite are all silicates or silicate melts with negligible K concentration. The 0.16 wt% ­SiO2 contents of
our analyses are low and within the range of ­SiO2 composition for lunar zirconolite (up to 1.9 wt% but mostless than 0.3 wt%; Williams and Giere 1996). Therefore,

there are little florescence effects and negligible KKαinterference on ­UMβ from neighboring phases in our
analyses.
For zirconolite with younger ages, their Pb concentration depends both on its U, Th concentrations and on
their ages. Due to low initial content of Pb for zirconolite, most contribution of Pb comes from the decay of

Wang et al. Prog Earth Planet Sci(2021) 8:51

Page 6 of 8

zirconolite with younger ages, crystallized from a U, Th-rich source region, such as PKT area, will also make it apotential candidate for EPMA chemical dating.
4.2 Accuracy and uncertainty of NanoSIMS Pb–Pb dating

Fig. 2 Chondrite-normalized REE pattern of zirconolite fromNWA 4485. It is compared with Apollo lunar zirconolites (Norman
and Nemchin 2014; Rasmussen et al. 2008; Seddio et al. 2013)
and terrestrial grains from tholeiites (Rasmussen et al. 2008) andcarbonatites (Wu et al. 2010). The Eu composition in our grain ispredicted to be lower than 100 × CI based on Apollo lunar zirconolite
studies

In contrast, due to the high contents of Pb and U comparedwith zircon and baddeleyite, the NanoSIMS Pb–Pb age ofzirconolite has a remarkable precision of 0.11%, showingthat zirconolite is an ideal mineral phase for isotopic Pb–
Pb dating. The weighted average age of 4348.5 ± 4.8 Ma(2σ) is consistent with the age of 4352 ± 10 Ma of NWA
4485 in Arai et al. (2010) and 4344 ± 14 Ma reported of its
paired meteorite NWA 4472 in Joy et al. (2011). In addition, the negligible common Pb in zirconolite measured by
NanoSIMS confirmed the assumption that all Pb is radiogenic in zirconolite. The NanoSIMS analysis on zirconolite demonstrated that it can be used to date ancient rocks
using a very small ion beam with a high precision of few
million years in 207Pb/206Pb ratios superior to that of thecoexisting zircon and baddeleyite.
4.3 REE pattern of zirconolite

Fig. 3 Weighted mean U–Th–Pb EPMA chemical ages of zirconolite
in NWA 4485

U and Th. Therefore, crystallizing from high U, Th concentration magma melts can also lead to high radiogenic
Pb content even with younger ages. As zirconolite from
Apollo 12 sample 12,032 granite fragment reported in
Seddio et al. (2013), it contains higher U, Th, and Pb concentrations than our zirconolite from NWA 4485 evenwith younger age of 3.9 ± 0.3 Ga. Therefore, for lunar

Lunar zirconolite crystallized at a late stage from interstitial in the lunar basalts (Busche et al. 1972) and is anaccessory mineral able to accommodate many incompatible elements, such as REE, U, Th Zr, Hf, like zircon.
As such, it has the potential for playing a significant rolein the petrological/geochemical evolution of these rocktypes in which it crystallized. For example, several studies have provided evidence that zirconolite can reflectchanges in the composition of the fluid during its evolutionary history, both in metasomatic system (Williams
and Giere 1988, 1996), and in magmatic fractional process (Platt et al. 1987). For our analyses, the REE patternshown in Fig. 3 displays apparent negative Eu anomaly,
which indicates that this zirconolite grain formed after
plagioclase as plagioclase is the main sink of Eu due to­Eu2+ substitution for ­Ca2+ during crystallization.

5 Implication
Our result demonstrates the reliability and potentialof EPMA U–Th–Pb dating of lunar zirconolite, which
is a non-destructive, quick, and high-spatial resolution

Table 2 Pb isotopic data of zirconolite in NWA 4485 obtained by NanoSIMS
Spot #

204

Pb/206Pb

1σ (%)

207

Pb/206Pb

1σ (%)

207

Pb*/206Pb*

1σ (%)

204

Pb/206Pb Age± (1σ) (Ma)10.000003

44

0.538630.23

0.538610.23

4350.53.4

20.000014

24

0.537220.23

0.537140.23

4346.5

3.4

207

Pb*/206Pb* ratios are 204Pb-corrected for terrestrial common Pb

Wang et al. Prog Earth Planet Sci(2021) 8:51

technique. In addition, zirconolite contains high Pb,
U and Th, and it was commonly reported as a ubiquitous trace mineral especially in lunar KREEPy basalts(Day et al. 2006; Lovering and Wark 1971; Rasmussen
et al. 2008; Wark et al. 1973; Zeigler et al. 2005; Zhang
et al. 2010). The recently returned Chang’E-5 samples
are expected to be young mare basalt with the age of
1.2–2.2 Ga and rich in KREEP component (Hiesinger
et al. 2010; Qian et al. 2018; Zhao et al. 2017). Therefore, the development of EPMA U–Th–Pb dating isappropriate for a quick prelude dating survey of the
new lunar sample with no sample damage, and also forzirconolite grains less than 2 μm which are too small
for SIMS. Besides, the simultaneously acquired REE
data can also help to study the geochemical evolutionof the Chang’E-5 rock in which it crystallized.
Abbreviations
NanoSIMS: nanometer secondary ion mass spectrometry; SIMS: secondary
ion mass spectrometry; EPMA: electron probe microanalyzer; REE: rare earth
elements; KREEP: potassium, rare earth element, and phosphorus; BSE: backscatter electron; CL: cathodoluminescence; MSWD: mean square weighted
deviates.

Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40645-​021-​00446-3.
Additional file 1. Fig. S1. Full range WDS Wavescans of the large zirconolite grain acquired with TAP (a), LPET (b, d), and LLiF (c) diffractors. The
enlarged map of blue rectangle in (b) are displayed in (d), showing thedetails of low cps peaks. Fig. S2. Monte Carlo simulations of the interaction volumes of electrons and generation volumes of X-rays in zirconolite
generated using Casino (Drouin et al., 2007) at 20 kV with a focused beam.
The density of zirconolite is defined as 4.8 g/cm3. 1*104 electron trajectories were calculated and displayed. In order to acquire the smallest beamsize, we plotted the correlation between electrons and X-rays volumes
and EPMA beam diameter (a). The smallest XY dimensional diameter ofelectrons and X-rays of 1.3 μm was acquired when the focused EPMA
beam diameter are no more than 200 nm. (b) The interaction volumes ofelectrons and generation volumes of X-rays at 20 kV with 200 nm EPMA
beam diameter. (c) The XY dimensional energy distribution with 20 kV
voltage and 200 nm beam size. (d) The YZ dimensional energy distribution with 20 kV voltage and 200 nm beam size shows 95% of energy are
distributed less than 1.5 μm in depth.
Acknowledgements
We thank Dr. Yuchen Xu, Di Zhang, and Jing Li for their kind assistance in our
experiments and data processing. We are also grateful to the Associate Editor
Dr. Noriko Kita and two reviewers (Dr. John Bowles and one anonymous
reviewer) for their constructive suggestions on the manuscript.
Authors’ contributions
YL proposed the topic, conceived and designed the study. NW carried out theexperimental study and wrote the manuscript. TZ helped to construct andmodify the manuscript. QM conducted the EPMA analysis and helped in thedata interpretation. JH helped to carry out the NanoSIMS analysis. All authors
read and approved the final manuscript.

Page 7 of 8

Funding
This work was supported by Key Research Program of Frontier Sciences, CAS(QYZDJ-SSW-DQC001).
Availability of data and materials
The datasets supporting the conclusions of this article are included within thearticle.

Declarations
Competing interests
The authors declare that they have no competing interest.
Author details
1
Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. 2 Universityof Chinese Academy of Sciences, Beijing 100049, China. 3 State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese
Academy of Sciences, Beijing 100029, China.
Received: 14 April 2021 Accepted: 2 September 2021

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