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Lunar monazite: A late-stage (mesostasis) phase in mare basalt
Earth and Planetary Science Letters, 21 (1974) 1 6 4 - 1 6 8 © North-Holland Publishing C o m p a n y , A m s t e r d a m
Printed in The Netherlands
31
LUNAR MONAZITE: A LATE-STAGE (MESOSTASIS) PHASE IN M A R E B A S A L T
J.F. LOVERING, D.A. WARK, A.J.W. GLEADOW and R. BRITTEN Department of Geology, School of Earth Sciences, University of Melbourne, Parkville, Vict. (Australia)
Received 15 October 1973
Thorium-poor monazite occurs as an inclusion in a ferrohedenbergite grain within a mesostasis area of the relatively coarse-grained Apollo 11 basalt 10047, 68. Only a single grain of monazite (~ 4 x 15 ,zm) has been observed but it is possible that monazite m a y exist as a more significant phase at smaller grain sizes. Electron probe analyses indicate chondrite-normalized REE fractionation patterns for b o t h lunar and terrestrial monazites in which the light REE's (La to Sin) are highly enriched relative to the heavy REE's (Gd to Lu). Lunar monazite shows a distinct Eu anomaly which is absent from the terrestrial sample. Crystallization of monazite from late-stage liquids forming during crystallization of lunar igneous rocks could lead to these liquids becoming increasingly depleted in the light R E E ' s relative to the heavy REE's.
1. Introduction
2. Occurrence of monazite in lunar basalt 10047,68
The interstitial, mesostasis regions in lunar basaltic rocks contain phases which have crystallized from the very late-stage liquids remaining after the crystallization of the major silicate and oxide phases. These latestage liquids are characteristically enriched in selected elements of which some of the most geochemically important are the rare-earth elements (REE's), yttrium, uranium and thorium. The result is that the mesostasis regions are the sites of crystallization of a suite of minerals enriched in those particular elements and a detailed characterization of the composition of these minerals is of considerable importance to understanding the REE fractionation patterns and the evolution of the radiogenic Pb observed in lunar rocks. To date, the suite of mesostasis minerals in lunar basalts enriched in REE's, U and Th include whitlockite, apatite, baddeleyite, and tranquillityite, [1, 2], zirconolite [3] and, very rarely, zircon [4]. In this work we will describe the occurrence of another REE-, U-, Th-bearing mineral, monazite, in the Apollo 11 coarse-grained basalt 10047,68.
The basalt 10047 was one of the coarsest-grained volcanic rocks collected at the Apollo 11 site and the mesostasis areas in this rock contained some of the largest grains of the late-stage minerals apatite, whitlockite, baddeleyite, tranquillityite and zicrono~;
i/
-
\"
Energy {key]
Fig. 1. X-ray spectrum of terrestrial and lunar monazite (10047,68). (Nuclear Diode 180 eV Si(Li) E D A X detector system, 25 kV electron beam, JEOL JSM-U3 scanning electron microscope.)
J.l.: Lovering et aL, Lunar monazite
165
Fig. 2. (a) Mesostasis area in lunar basalt 10047,68 showing monazite (18) grain in clinopyroxene (2A) associated with K-feldspar (3), plagioclase (1), troilite (6), ulv6spinel (17), SiO2-phase (13), and tranquillityite (14). (Reflected light with Nomarski interference contrast.) (b) Monazite (18) grain in clinopyroxene (ferrohedenbergite) enlarged from occurrence in Fig. 2a. (Secondary electron image in JSM-U3 scanning electron microscope.)
lite ever observed by us. In the course of identifying U-enriched phases in the mesostasis regions of a plished block 10047,68 of this rock, a grain of unusual chemistry was observed as the result of a
partial solid-state X-ray analysis during a survey on a scanning electron microscope. This preliminary analysis (Fig. 1) indicated a composition very sunilar to a terrestrial monazite and subsequent detailed anal-
166
J.b: Lovering et aL, Lunar monazite
ysis by electron probe X-ray microanalyser has confirmed this. The occurrence of the only grain unequivocally identified as monazite is illustrated by the secondary electron image in a scanning electron microscope (Fig. 2b). The optical photograph (Fig. 2a) was taken using reflected light with Nomarski interference contrast and illustrates the difficulty in differentiating the monazite grain which occurs as an inclusion in an Fe-rich clinopyroxene grain associated with K-feldspar and close to tranquillityite in a typical coarse-grained mesostasis environment. The difficulty in recognizing the monazite in reflected light is due to the close similarity in reflectance between the monazite and the host clinopyroxene. The monazite is dark grey and weakly anisotropic in reflected light with a minimum reflectivity of 8.4%. Since this reflectivity includes a contribution from appreciable internal reflections, the minimum refractive index from this reflectivity would be slightly less than the calculated value of 1.81 +- 0.015
151. Even though only one monazite grain has been positively identified in this section, it is highly probable that many micrometer and sub-micrometer grains recognized as U-enriched phases by fission track studies on this sample might be monazite. However, they would be too small for satisfactory electron probe (or scanning electron microscope) X-ray microanalysis.
or multiple measurements, which ever was the greater. Special problems arose as a result of the excessively small size (average width ~ 4 ~m) of the lunar monazite grain. Experiments demonstrated that the least contamination of the lunar monazite analysis by contributions from elements in the host pyroxene occurred when an electron beam energy of 25 keV and a minimum beam diameter (of ~ 0.2/am) was used for analysis. A partial average analysis of this clinopyroxene (SiO 2 : 46%; A120 3 " 0.8%; FeO : 34%; MgO: 0.4%; CaO: ~ 11%; MnO: 0.8%) indicates a ferrohedenbergitic composition which is completely in keeping with its occurrence as a very late-stage crystallization product in the mesostasis. On this basis at least portion of the SiO 2, CaO, FeO, MnO and AI203 abundances reported in the electron probe analysis of the lunar monazite (Table 1) are due to a contribution from the matrix clinopyroxene. In view of the problems associated with the accurate analysis of such a small grain, it is not at all surprising that the analysis total (Table 1) is rather high (~ 104%) The most unusual feature of the lunar monazite is the low Th (and U) content when compared with most terrestrial monazites ([8] and Table 1). However, a Th-depleted monazite has been recorded from
6
3. Chemical composition The lunar monazite was analysed in a computercontrolled JEOL JXA-5A electron probe using a terrestrial monazite as a sub-standard. The terrestrial monazite had been analysed previously in the electron probe using the following primary standards: apatite (P); kaersutite (Si, Ca, Fe, Mg, AI); U, Th and Mn as metals; galena (Pb); pure Y and REE oxide glasses checked against Y- and REE-doped silicate glasses [6]. Standard electron probe analytical procedures were used with special attention given to precise determination of backgrounds and the effects of unavoidable spectral interferences on the analyses of the REE's [7]. The analytical uncertainties in Table 1 were derived from X-ray counting statistics
105
C~ ~
',
l 104
'b"-. a %'-'0.
g
"9.
U')
"'o b F
• Lunar Monazite from 1001,7,68
103 Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig. 3. Chondrite-normalized REE fractionation pattern for terrestrial and lunar monazite (10047,68).
J.Iq Lovering et aL, Lunar monazite
167
TABLE 1 Electron probe analyses of terrestrial monazite (unknown locality) and lunar monazite (mare basalt 10047,68)
P205 SiOz ThO2 UO2 PbO MgO CaO FeO *1 MnO AI20 s Y203 La203 CeaO 3 Pr203 Nd203 Sm203 Eu203 Gd203 Tb203 DY203
Terrestrial monazite (unknown locality)
Lunar monazite (10047,68)
N u m b e r s o f ions on the base o f O = 16
25.37 -+ 0.11 2.01 +0.08
26.36 + 0.23 1.30 + 0.08 *2
P Si
3.5452 ] 3 . 8 7 7 0 0.3318
3.5374 0.2061
0.76 0.03 0.05 ~0.02 0.60 1.17 0.19 0.11 1.11 16.51 30.08 4.30 14.91 4.09 0.36 1.55 0.13 0.33
Th U4÷ Pb 2+ Mg Ca Fe 2+ Mn AI Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
0.32530.0129 0.0227
0.0274 0.0011 0.0021
0.0177
0.1019 0.1551 0.0255 0.0206 0.0936 0.9653 1.7456 0.2483 0.8441 0.2234 0.0204 0.0814 0.0068 0.0169
Er203 Tm203 Yb203 Lu203
8.66 0.33 0.51 <~0.02 0.10 (0.02 0.06 0.04 2.62 8.28 23.56 3.25 15.10 6.03 1.21 1.79 0.16 0.76 0.10 0.23 ~0.02 0.10 0.01
Total
100.28
Ho203
+ 0.26 + 0.05 + 0.09 + 0.01 + 0.04 -+ 0.02 +0.17 +- 0.06 + 0.20 + 0.09 + 0.14 + 0.06 +0.04 +0.06 -+ 0.01 -+ 0.02 --- 0.09 -+ 0.10
-+ 0.10 -+ 0.03 + 0.09
+ 0.02 *2 -+ 0.04 *2 + 0.02 *2 + 0.04 *2 +0.23 + 0.15 --- 0.30 + 0.15 + 0.20 + 0.13 +0.04 *3 -+0.12 -+ 0.03 + 0.07 0.18 -+ 0.09
+ 0.06 -+ 0.008
-
Y
0.0084 0.0078 0.2301 0.5041 1.4237 -4.2191 0.1955 0.8902 0.3429 0.0682 0.0979 0.0087 0.0404 0.0052 0.0119 0.0050 0.0005
3.7435
-4.5884
0.0090
J
104.12 *4
• 1 Total Fe reported as FeO. • 2 Probably some contribution from surrounding ferrohedenbergite matrix due to very small size of grain (~4//rn X 15/.tin). • 3 Calculated in lunar monazite as EuO. • 4 High total due to small grain analysed. Llallagua (Bolivia) [9]. T h e w e i g h t r a t i o T h / U for the l u n a r m o n a z i t e in T a b l e 1 is 25 ( w i t h a relatively high u n c e r t a i n t y ) b u t it is similar to the terrestrial m o n a z i t e r a t i o o f 26.
4. REE fractionation patterns and discussion The chondrite normalized REE fractionation p a t t e r n s for the l u n a r a n d terrestrial m o n a z i t e s (Fig. 3) s h o w similar generalized t r e n d s in t h a t t h e light R E E ' s ( L a to Sin) are relatively very m u c h m o r e a b u n d a n t t h a n the h e a v y R E E ' s ( G d to Lu).
T h e l u n a r and terrestrial m o n a z i t e f r a c t i o n a t i o n p a t t e r n s do s h o w c e r t a i n d i f f e r e n c e s in detail. One i m p o r t a n t difference is the E u - a n o m a l y o b s e r v e d in the l u n a r m o n a z i t e p a t t e r n b u t n o t p r e s e n t in the terrestrial m o n a z i t e . The e x t e n t o f t h e Eu d e p l e t i o n in t h e l u n a r m o n a zite is very similar t o t h a t o b s e r v e d for the t o t a l r o c k sample o f 1 0 0 4 7 [10]. O t h e r d i f f e r e n c e s o b s e r v e d are t h e greater e n r i c h m e n t in light R E E ' s , a n d t h e greater d e p l e t i o n in h e a v y R E E ' s and y t t r i u m , in t h e l u n a r m o n a z i t e relative to t h e terrestrial sample a n a l y s e d (Fig. 3). Clearly these results i n d i c a t e t h a t c r y s t a l l i z a t i o n
168
J. b: Lovering et al., Lunar monazite
of m o n a z i t e from the late-stage liquids forming during the crystallization of lunar basaltic rocks could lead 1o these liquids b e c o m i n g highly depleted in the light R E E ' s relative to the heavy R E E ' s
Acknowledgements We are i n d e b t e d to M. Haukka and V. Biskupsky for assistance with i n d e p e n d e n t analyses o f minerals used as electron probe standards and to J.A. mcA n d r e w for optical m e a s u r e m e n t s on the monazite. The w o r k was supported by a grant to one o f us (J.F. Lovering) from the Australian Research Grants Committee.
References 1 J.F. Lovering and D.A. Warm Uranium-enriched phases in Apollo 11 and Apollo 12 basaltic rocks, Proc. Second Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 2, 1 (1971) 151. 2 J.F. Lovering, D.A. Wark, A.F. Reid, N.G. Ware, K. Keil, M. Prinz, T.E. Bunch, A. E1 Goresy, P. Ramdohr, G.M. Brown, A. Peckett, R. Phillips, E.N. Cameron, J.A.V.
Douglas and A.G. Plant, Tranquillityite : a new silicate mineral from Apollo 11 and Apollo 12 basaltic rocks, Proc. Second Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 2, 1 (1971) 39. 3 D.A. Wark, A.F. Reid, J.F. Lovering and A. E1 Goresy, Zirconolite (versus zirkelite) in lunar rocks, in : Lunar Science IV, ed. J.W. Chamberlain and C. Watkins (Lunar Sci, Inst., Houston, 1973) 764. 4 J.F. Lovering, D.A. Wark, D. Sewell and C. Frick, Uranium geochemistry and late-stage (mesostasis) mineralogy of Apollo 14 lunar rocks, in : Lunar Science III, ed. C. Watkins, Contrib. No. 88 (lunar Sci. Inst., Houston, 1972) 493.' 5 J.A. McAndrew (written communication). 6 M.J. Drake and D.F. Weill, New rare-earth element standards for electron microprobe analysis, Chem. Geol. 10 (1972) 179. 7 D.A. Wark, J.F. Lovering, A.F. Reid and A. E1 Goresy, Lunar zirconolite: a late-stage (mesostasis) phase in lunar igneous rocks, (in preparation). 8 W.A. Deer, R.A. Howie and J. Zussman, Rock-forming Minerals, Vol. 5. Non-silicates (Longmans, London, 1962). 9 S.G. Gordon, Thorium-free monazite from Llallagua, Bolivia, Notulae Naturae Acad. Nat. Sci. Philadelphia, No. 2 (1939) 7 pp. 10 H. Wakita, R.A. Schmitt and P. Rey, Elemental abundance of major, minor and trace elements in Apollo 11 lunar rocks, soil and core samples, Proc. Apollo 11 Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 1, 2 (1970) 1685.
Printed in The Netherlands
31
LUNAR MONAZITE: A LATE-STAGE (MESOSTASIS) PHASE IN M A R E B A S A L T
J.F. LOVERING, D.A. WARK, A.J.W. GLEADOW and R. BRITTEN Department of Geology, School of Earth Sciences, University of Melbourne, Parkville, Vict. (Australia)
Received 15 October 1973
Thorium-poor monazite occurs as an inclusion in a ferrohedenbergite grain within a mesostasis area of the relatively coarse-grained Apollo 11 basalt 10047, 68. Only a single grain of monazite (~ 4 x 15 ,zm) has been observed but it is possible that monazite m a y exist as a more significant phase at smaller grain sizes. Electron probe analyses indicate chondrite-normalized REE fractionation patterns for b o t h lunar and terrestrial monazites in which the light REE's (La to Sin) are highly enriched relative to the heavy REE's (Gd to Lu). Lunar monazite shows a distinct Eu anomaly which is absent from the terrestrial sample. Crystallization of monazite from late-stage liquids forming during crystallization of lunar igneous rocks could lead to these liquids becoming increasingly depleted in the light R E E ' s relative to the heavy REE's.
1. Introduction
2. Occurrence of monazite in lunar basalt 10047,68
The interstitial, mesostasis regions in lunar basaltic rocks contain phases which have crystallized from the very late-stage liquids remaining after the crystallization of the major silicate and oxide phases. These latestage liquids are characteristically enriched in selected elements of which some of the most geochemically important are the rare-earth elements (REE's), yttrium, uranium and thorium. The result is that the mesostasis regions are the sites of crystallization of a suite of minerals enriched in those particular elements and a detailed characterization of the composition of these minerals is of considerable importance to understanding the REE fractionation patterns and the evolution of the radiogenic Pb observed in lunar rocks. To date, the suite of mesostasis minerals in lunar basalts enriched in REE's, U and Th include whitlockite, apatite, baddeleyite, and tranquillityite, [1, 2], zirconolite [3] and, very rarely, zircon [4]. In this work we will describe the occurrence of another REE-, U-, Th-bearing mineral, monazite, in the Apollo 11 coarse-grained basalt 10047,68.
The basalt 10047 was one of the coarsest-grained volcanic rocks collected at the Apollo 11 site and the mesostasis areas in this rock contained some of the largest grains of the late-stage minerals apatite, whitlockite, baddeleyite, tranquillityite and zicrono~;
i/
-
\"
Energy {key]
Fig. 1. X-ray spectrum of terrestrial and lunar monazite (10047,68). (Nuclear Diode 180 eV Si(Li) E D A X detector system, 25 kV electron beam, JEOL JSM-U3 scanning electron microscope.)
J.l.: Lovering et aL, Lunar monazite
165
Fig. 2. (a) Mesostasis area in lunar basalt 10047,68 showing monazite (18) grain in clinopyroxene (2A) associated with K-feldspar (3), plagioclase (1), troilite (6), ulv6spinel (17), SiO2-phase (13), and tranquillityite (14). (Reflected light with Nomarski interference contrast.) (b) Monazite (18) grain in clinopyroxene (ferrohedenbergite) enlarged from occurrence in Fig. 2a. (Secondary electron image in JSM-U3 scanning electron microscope.)
lite ever observed by us. In the course of identifying U-enriched phases in the mesostasis regions of a plished block 10047,68 of this rock, a grain of unusual chemistry was observed as the result of a
partial solid-state X-ray analysis during a survey on a scanning electron microscope. This preliminary analysis (Fig. 1) indicated a composition very sunilar to a terrestrial monazite and subsequent detailed anal-
166
J.b: Lovering et aL, Lunar monazite
ysis by electron probe X-ray microanalyser has confirmed this. The occurrence of the only grain unequivocally identified as monazite is illustrated by the secondary electron image in a scanning electron microscope (Fig. 2b). The optical photograph (Fig. 2a) was taken using reflected light with Nomarski interference contrast and illustrates the difficulty in differentiating the monazite grain which occurs as an inclusion in an Fe-rich clinopyroxene grain associated with K-feldspar and close to tranquillityite in a typical coarse-grained mesostasis environment. The difficulty in recognizing the monazite in reflected light is due to the close similarity in reflectance between the monazite and the host clinopyroxene. The monazite is dark grey and weakly anisotropic in reflected light with a minimum reflectivity of 8.4%. Since this reflectivity includes a contribution from appreciable internal reflections, the minimum refractive index from this reflectivity would be slightly less than the calculated value of 1.81 +- 0.015
151. Even though only one monazite grain has been positively identified in this section, it is highly probable that many micrometer and sub-micrometer grains recognized as U-enriched phases by fission track studies on this sample might be monazite. However, they would be too small for satisfactory electron probe (or scanning electron microscope) X-ray microanalysis.
or multiple measurements, which ever was the greater. Special problems arose as a result of the excessively small size (average width ~ 4 ~m) of the lunar monazite grain. Experiments demonstrated that the least contamination of the lunar monazite analysis by contributions from elements in the host pyroxene occurred when an electron beam energy of 25 keV and a minimum beam diameter (of ~ 0.2/am) was used for analysis. A partial average analysis of this clinopyroxene (SiO 2 : 46%; A120 3 " 0.8%; FeO : 34%; MgO: 0.4%; CaO: ~ 11%; MnO: 0.8%) indicates a ferrohedenbergitic composition which is completely in keeping with its occurrence as a very late-stage crystallization product in the mesostasis. On this basis at least portion of the SiO 2, CaO, FeO, MnO and AI203 abundances reported in the electron probe analysis of the lunar monazite (Table 1) are due to a contribution from the matrix clinopyroxene. In view of the problems associated with the accurate analysis of such a small grain, it is not at all surprising that the analysis total (Table 1) is rather high (~ 104%) The most unusual feature of the lunar monazite is the low Th (and U) content when compared with most terrestrial monazites ([8] and Table 1). However, a Th-depleted monazite has been recorded from
6
3. Chemical composition The lunar monazite was analysed in a computercontrolled JEOL JXA-5A electron probe using a terrestrial monazite as a sub-standard. The terrestrial monazite had been analysed previously in the electron probe using the following primary standards: apatite (P); kaersutite (Si, Ca, Fe, Mg, AI); U, Th and Mn as metals; galena (Pb); pure Y and REE oxide glasses checked against Y- and REE-doped silicate glasses [6]. Standard electron probe analytical procedures were used with special attention given to precise determination of backgrounds and the effects of unavoidable spectral interferences on the analyses of the REE's [7]. The analytical uncertainties in Table 1 were derived from X-ray counting statistics
105
C~ ~
',
l 104
'b"-. a %'-'0.
g
"9.
U')
"'o b F
• Lunar Monazite from 1001,7,68
103 Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig. 3. Chondrite-normalized REE fractionation pattern for terrestrial and lunar monazite (10047,68).
J.Iq Lovering et aL, Lunar monazite
167
TABLE 1 Electron probe analyses of terrestrial monazite (unknown locality) and lunar monazite (mare basalt 10047,68)
P205 SiOz ThO2 UO2 PbO MgO CaO FeO *1 MnO AI20 s Y203 La203 CeaO 3 Pr203 Nd203 Sm203 Eu203 Gd203 Tb203 DY203
Terrestrial monazite (unknown locality)
Lunar monazite (10047,68)
N u m b e r s o f ions on the base o f O = 16
25.37 -+ 0.11 2.01 +0.08
26.36 + 0.23 1.30 + 0.08 *2
P Si
3.5452 ] 3 . 8 7 7 0 0.3318
3.5374 0.2061
0.76 0.03 0.05 ~0.02 0.60 1.17 0.19 0.11 1.11 16.51 30.08 4.30 14.91 4.09 0.36 1.55 0.13 0.33
Th U4÷ Pb 2+ Mg Ca Fe 2+ Mn AI Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
0.32530.0129 0.0227
0.0274 0.0011 0.0021
0.0177
0.1019 0.1551 0.0255 0.0206 0.0936 0.9653 1.7456 0.2483 0.8441 0.2234 0.0204 0.0814 0.0068 0.0169
Er203 Tm203 Yb203 Lu203
8.66 0.33 0.51 <~0.02 0.10 (0.02 0.06 0.04 2.62 8.28 23.56 3.25 15.10 6.03 1.21 1.79 0.16 0.76 0.10 0.23 ~0.02 0.10 0.01
Total
100.28
Ho203
+ 0.26 + 0.05 + 0.09 + 0.01 + 0.04 -+ 0.02 +0.17 +- 0.06 + 0.20 + 0.09 + 0.14 + 0.06 +0.04 +0.06 -+ 0.01 -+ 0.02 --- 0.09 -+ 0.10
-+ 0.10 -+ 0.03 + 0.09
+ 0.02 *2 -+ 0.04 *2 + 0.02 *2 + 0.04 *2 +0.23 + 0.15 --- 0.30 + 0.15 + 0.20 + 0.13 +0.04 *3 -+0.12 -+ 0.03 + 0.07 0.18 -+ 0.09
+ 0.06 -+ 0.008
-
Y
0.0084 0.0078 0.2301 0.5041 1.4237 -4.2191 0.1955 0.8902 0.3429 0.0682 0.0979 0.0087 0.0404 0.0052 0.0119 0.0050 0.0005
3.7435
-4.5884
0.0090
J
104.12 *4
• 1 Total Fe reported as FeO. • 2 Probably some contribution from surrounding ferrohedenbergite matrix due to very small size of grain (~4//rn X 15/.tin). • 3 Calculated in lunar monazite as EuO. • 4 High total due to small grain analysed. Llallagua (Bolivia) [9]. T h e w e i g h t r a t i o T h / U for the l u n a r m o n a z i t e in T a b l e 1 is 25 ( w i t h a relatively high u n c e r t a i n t y ) b u t it is similar to the terrestrial m o n a z i t e r a t i o o f 26.
4. REE fractionation patterns and discussion The chondrite normalized REE fractionation p a t t e r n s for the l u n a r a n d terrestrial m o n a z i t e s (Fig. 3) s h o w similar generalized t r e n d s in t h a t t h e light R E E ' s ( L a to Sin) are relatively very m u c h m o r e a b u n d a n t t h a n the h e a v y R E E ' s ( G d to Lu).
T h e l u n a r and terrestrial m o n a z i t e f r a c t i o n a t i o n p a t t e r n s do s h o w c e r t a i n d i f f e r e n c e s in detail. One i m p o r t a n t difference is the E u - a n o m a l y o b s e r v e d in the l u n a r m o n a z i t e p a t t e r n b u t n o t p r e s e n t in the terrestrial m o n a z i t e . The e x t e n t o f t h e Eu d e p l e t i o n in t h e l u n a r m o n a zite is very similar t o t h a t o b s e r v e d for the t o t a l r o c k sample o f 1 0 0 4 7 [10]. O t h e r d i f f e r e n c e s o b s e r v e d are t h e greater e n r i c h m e n t in light R E E ' s , a n d t h e greater d e p l e t i o n in h e a v y R E E ' s and y t t r i u m , in t h e l u n a r m o n a z i t e relative to t h e terrestrial sample a n a l y s e d (Fig. 3). Clearly these results i n d i c a t e t h a t c r y s t a l l i z a t i o n
168
J. b: Lovering et al., Lunar monazite
of m o n a z i t e from the late-stage liquids forming during the crystallization of lunar basaltic rocks could lead 1o these liquids b e c o m i n g highly depleted in the light R E E ' s relative to the heavy R E E ' s
Acknowledgements We are i n d e b t e d to M. Haukka and V. Biskupsky for assistance with i n d e p e n d e n t analyses o f minerals used as electron probe standards and to J.A. mcA n d r e w for optical m e a s u r e m e n t s on the monazite. The w o r k was supported by a grant to one o f us (J.F. Lovering) from the Australian Research Grants Committee.
References 1 J.F. Lovering and D.A. Warm Uranium-enriched phases in Apollo 11 and Apollo 12 basaltic rocks, Proc. Second Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 2, 1 (1971) 151. 2 J.F. Lovering, D.A. Wark, A.F. Reid, N.G. Ware, K. Keil, M. Prinz, T.E. Bunch, A. E1 Goresy, P. Ramdohr, G.M. Brown, A. Peckett, R. Phillips, E.N. Cameron, J.A.V.
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