Sayh al Uhaymir (SaU) 094 and SaU 005 are olivine-phyric shergottites from the Oman desert and are considered as pairs. [e.g., 1]. They are very similar to the Libyan desert shergottite Dar al Gani (DaG) 476 in petrology, chemistry and ejection age [2-6]. This group of shergottites, also recognized as depleted shergottites [e.g. 7] has been strongly shocked and contains very low abundances of light rare earth elements (REE). In addition, terrestrial contaminants are commonly present in meteorites found in desert environments. Age-dating these samples is very challenging, but lower calcite contents in the SaU meteorites suggest that they have been subjected to less severe desert weathering than their DaG counterparts [3-4]. In this report, we present Rb-Sr and Sm-Nd isotopic results for SaU 094 and SaU 005, discuss the correlation of their ages with those of other similar shergottites, and discuss their petrogenesis

Nyquist, L. E.

Reese, Y.

Shih, C.-Y.

NASA Technical Reports Server

Rb-Sr AND Sm-Nd ISOTOPIC STUDIES OF MARTIAN DEPLETED SHERGOTTITES SaU 094/005.  C.-
Y. Shih1, L. E. Nyquist2, and Y. Reese3, 1Mail Code JE-23, ESCG/Jacobs Sverdrup, P.O. Box 58477, Houston, TX 
77258-8477, chi-yu.shih-1@nasa.gov; 2Mail Code KR, NASA Johnson Space Center, Houston, TX 77058-3696, 
laurence.e.nyquist@nasa.gov; 3Mail Code JE-23, ESCG/Muniz Engineering, Houston, TX 77058, young.reese-
1@nasa.gov. 
 
Introduction: Sayh al Uhaymir (SaU) 094 and SaU 005 
are olivine-phyric shergottites from the Oman desert and are 
considered as pairs. [e.g., 1]. They are very similar to the 
Libyan desert shergottite Dar al Gani (DaG) 476 in petrol-
ogy, chemistry and ejection age [2-6]. This group of shergot-
tites, also recognized as depleted shergottites [e.g. 7] has 
been strongly shocked and contains very low abundances of 
light rare earth elements (REE). In addition, terrestrial con-
taminants are commonly present in meteorites found in de-
sert environments. Age-dating these samples is very chal-
lenging, but lower calcite contents in the SaU meteorites 
suggest that they have been subjected to less severe desert 
weathering than their DaG counterparts [3-4]. In this report, 
we present Rb-Sr and Sm-Nd isotopic results for SaU 094 
and SaU 005, discuss the correlation of their ages with those 
of other similar shergottites, and discuss their petrogenesis.  
Samples and Analytical Procedures: The SaU samples 
were kindly provided by Dr. Beda A. Hofmann. A large chip 
of SaU 005, weighing ~0.6 g was picked out and initially 
processed in 2001. The sample was further crushed gently to 
pass a nylon sieve of opening size <149 μm. About 100 mg 
was taken as the bulk rock sample (WR). The rest of the 
sample was sieved into 149-74 μm and 74-44 μm size frac-
tions. Minerals (Plag and Px) in both size fractions were 
separated by Franz magnetic separator following the proce-
dure used for DaG 476 [8]. We processed the SaU 094 slab 
in 2006, initially chipping off fusion crusts. The sample is 
extremely compact and great efforts were needed to break 
and pulverize it. Interior chips totaling 685 mg were picked 
out for this study. The bulk rock sample (WR) of 139 mg 
was taken from the  <149 μm size fraction prior to finer siev-
ing. Minerals were separated by densities using heavy liq-
uids. At density fraction <2.85 g/cm3, we obtained the pla-
gioclase (Plag). In the density fraction (2.85-3.32 g/cm3), we 
obtained the plagioclase-pyroxene mixture (Im Plag). The 
pyroxenes (Px1 and Px2) were separated in the slightly 
higher density fraction (3.32-3.45 g/cm3). An olivine sample 
(Ol) was separated with a heavier liquid of density 3.45 
g/cm3. In addition, the bulk rock and all mineral samples 
were washed with 1N HCl (for Plag, Im Plag, Ol), 2N HCl 
(for Px, Px1, Px rej) and 3N HF (for Px2) in an ultrasonic 
bath for 10 minutes to eliminate possible post-crystallization, 
pre- or terrestrial, contamination. Both the WR residues (r) 
and WR leaches (l) of these samples were analyzed. The acid 
washes from all minerals (Leach) were combined and also 
analyzed. 
Rb-Sr isotopic results: The 87Rb/86Sr and 87Sr/86Sr data 
for seven SaU 005 (squares) and nine SaU 094 (circles) sam-
ples are shown in Fig 1. As for DaG 476 [8], the Rb-Sr iso-
topic data are so scattered that no Rb-Sr isochron, and thus, 
no age information can be obtained from these sixteen un-
washed and washed samples. The two acid leachates, WR(l) 
and Leach, plot close to the present-day sea water value of 
87Sr/86Sr =~0.709, indicating that all the samples, even those 
washed with acids, still contain significant amounts of desert 
contaminants. The SaU 094 samples plot closer toward the 
sea water 87Sr/86Sr  value, and are probably more severely 
altered than the SaU 005 samples. An estimate of the initial 
87Sr/86Sr =0.701303±15 (λ(87Rb) =0.01402 Ga-1) for 
SaU005/094 can be made using the SaU 005 Plag(r) datum 
and the Sm-Nd age of 445 Ga (shown in Fig. 2). This value 
is slightly higher than the DaG 476 value [8], but close to 
that of Y980459 [7]. A higher initial 87Sr/86Sr estimate of 
0.702272±12 is obtained from the Plag(r) of SaU 094. A 
two-stage model calculation indicates that the time-averaged 
87Rb/86Sr for the SaU source region is ~0.04-0.05. 
Depleted Shergottites - SaU 005/094
87Rb/86Sr
0.00 0.05 0.10 0.15
87
S
r/8
6 S
r
0.700
0.702
0.704
0.706
0.708
0.710
WR(r)
WR(l)
WR
WR(r)
WR
WR(l),
Leach
Px(r)
Px1(r)
Plag(r)
SaU 094
  SaU 005
Plag(r)
Im Plag(r)
Px2(r)
Px rej(r)
Px2(r)
Ol(r) Sea Water
TSm-Nd=445 Ma
I(Sr)=0.701303±15
 
Figure 1. Rb-Sr data of SaU 005/094. 
147Sm/144Nd
0.2 0.4 0.6 0.8 1.0 1.2
14
3 N
d/
14
4 N
d
0.5140
0.5145
0.5150
0.5155
0.5160
0.5165
Depleted Shergottites - SaU 005/094
Px rej(r)
147Sm/144Nd
0.4 0.6 0.8 1.0 1.2
εNd
-1
0
1 +18Ma
-18Ma
WR(r)WR(r)
Px(r)Px1(r)
Px2(r)
WR(l)
Leach
WR
WR
T=445±18 Ma
εNd=+38.0±1.3
SaU 094
SaU 005
Figure 2. Sm-Nd data of SaU 005/094. 
Sm-Nd isotopic results: Fig. 2 shows 147Sm/144Nd and 
143Nd/144Nd data of ten SaU samples. Unlike the Rb-Sr data, 
the Sm-Nd data form a linear array. Using the Isoplot regres-
sion routines [9], four SaU 005 samples (solid squares) con-
sisting of WR, WR leachate and two washed Px, yield an age 
of 446±13 Ma for λ(147Sm)=0.00654 Ga-1 and an initial 
εNd=+37.4±1.2. One small WR(r) sample having only 0.3 ng 
Nd (open square), plots off the isochron and may contain a 
https://ntrs.nasa.gov/search.jsp?R=20070003723 2019-08-30T00:17:34+00:00Z
ISOTOPIC AGE OF DEP. SHERGOTTITES SaU 005/094:  C.-Y. Shih et al. 
 
significant portion of desert alteration products. The similar 
SaU 094 WR-Leach-Px assemblage yields an almost identi-
cal age of 448±21 Ma and initial εNd =+38.1±1.4. All the 
other samples have too small amounts of Sm and Nd (<1 ng) 
and did not run well. Since SaU 005 and SaU 094 are likely 
paired meteorites [1], we regressed all nine SaU samples to 
obtain an age of 445±18 Ma and initial εNd=+38.0±1.3, rep-
resenting the SaU igneous event.  
Recently, we reported the Sm-Nd age of 472±27 Ma and 
the initial εNd =+36.9±2.2 for Y980459 [7]. These age and 
isotopic data are indistinguishable from the 474±11 Ma age 
and the +36.6±0.8 initial εNd obtained for DaG 476 in [8]. In 
addition, both meteorites have essentially the same young 
exposure age of ~1.2 Ma [5,10]. All these data suggest that 
they both could come from the same magma flow during a 
single impact-ejection event. In this case, Y980459 probably 
represents a sample from the rapidly cooling outermost por-
tion of the flow and DaG 476 from the slower cooling inte-
rior portion of the flow. An Isoplot [9] regression of ten Sm-
Nd data, 7 from Y980459 and 4 from DaG 476, yields an age 
of 470±12 Ma and initial εNd =+37.0±0.7. This age probably 
best defines the time of the DaG/Y98 magmatic event.  
Petrogenetic implications: The εNd-values and ages of 
two depleted shergottite pairs, SaU 005/094 and DaG/Y98, 
are summarized in Fig. 3. The two parallelograms, defined 
by their respective age and εNd-value uncertainties, do not 
overlap, showing that the pairs represent two different co-
magmatic flows. These flows probably extruded contempo-
raneously ~460 Ma ago in the same igneous complex, as 
suggested by their similar petrology, chemistry and ejection 
age [3-6,10]. Based on two-stage model calculations, the 
time-averaged source 147Sm/144Nd ratio for these shergottite 
pairs could be 0.268 and 0.266, respectively. These high 
values suggest they were derived from strongly LREE-
depleted mantle sources. To produce even more LREE-
depleted melts of 147Sm/144Nd ~0.51 found in the 
SaU/DaG/Y98 shergottites by a partial melting event at ~460 
Ma is not straightforward. It could have involved multiple 
episodes of remelting of residues at ~460 Ma, as suggested 
for the genesis of depleted shergottite QUE 94201 [11].  
Alternatively, these depleted shergottites (DS) could 
have been produced by processes with three major stages, as 
shown in Fig. 4. This model starts with the formation of a DS 
source precursor at ~4.553 Ga, soon after martian core for-
mation, and while the short-lived nuclides 146Sm (most) and 
182Hf (some) were still alive [12-15]. This source precursor 
could have been a garnet-bearing peridotitic cumulate crys-
tallized during the early martian mantle differentiation. The 
model cumulate had nakhlite-like  147Sm/144Nd = ~0.235, but 
un-nakhlite-like low 87Rb/86Sr =~0.04 . It evolved until ~925 
Ma, when partial melting produced nakhlite-like LREE-
enriched melts and their corresponding highly LREE-
depleted residues. These residues became the direct DS 
sources, from which SaU/DaG/Y98 DS finally were pro-
duced by large degree melting ~460 Ma ago. This three-
stage model can also explain the nakhlite-like positive 142Nd 
anomalies (~+0.6 ε)  of DS [e.g. 13, 15]. The Sm and Nd 
abundances of DS Y980459 were reproduced by this model 
in [7]. The model suggests that we should have more martain 
meteorites of the Hesperian era, corresponding to LREE-
enriched nakhlite-like melts produced between  ~925 Ma and 
~1.38 Ga, and associated with the production of DS sources. 
The ages of these basalt melts, although not so far sampled, 
would support the wide distribution of Hesperian volcanic 
materials on the martian surface implied by the revised cra-
ter-frequency curve of [16].  
 
Dep. Shergottites - SaU 005/094 & DaG/Y98
Time Before Present (Ga)
0.40 0.45 0.50 0.55
ε (1
43
N
d)
i
+34
+36
+38
+40
μ=0.266
μ=0.268
SaU 094/005
T=445±18 Ma
μ=(147Sm/144Nd)
Two-stage
time-averaged
sources :
DaG 476/
Y980459
T=470±12 Ma
μ=0.509To Present T=460±3 Ma
Figure 3.  εNd vs. T(age) of SaU 005/094 and DaG/Y980459. 
 
Depleted Shergottites Genesis
Time before Present (Ga)
0 1 2 3 4 5
ε  (1
43
N
d)
+0
+20
+40
+60 μ=147Sm/144Nd
Mars=~CHUR
Nakhlites
QUE
SaU/
DaG/
Y98/
Dho
Two-stage
SaU/DaG/Y98
source
μ=0.267
Differentiation
@ ~4.553 Ga
Nakhlites
~460 Ma
~925 Ma
Nak-like
melts
Three-stage
SaU/DaG/Y98
(DS source
precursor)
μ=0.235
 
Figure 4. εNd vs. T(age) of dep. shergottites & nakhlites. 
 
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Rb-Sr and Sm-Nd Isotopic Studies of Martian Depleted Shergottes SaU 094/005

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