ChemCam is an active remote sensing instrument suite that has operated successfully on MSL since landing Aug. 6th, 2012. It uses laser pulses to remove dust and to analyze rocks up to 7 m away. Laser-induced breakdown spectroscopy (LIBS) obtains emission spectra of materials ablated from the samples in electronically excited states. The intensities of the emission lines scale with the abundances of the related element. ChemCam is sensitive to most major rock-forming elements as well as to a set of minor and trace elements such as F, Cl, Li, P, Sr, Ba, and Rb. The measured chemical composition can then be used to infer the mineralogical composition of the ablated material. Here, we report a summary of inferred apatite detections along the MSL traverse at Gale Crater. We present the geologic settings of these findings and derive some interpretations about the formation conditions of apatite in time and space

Blaney, D. L.

Clegg, S. M.

Cousin, A.

David, G.

Dehouck, E.

Drouet, C.

Forni, O.

Gasnault, O.

Lasue, J.

Mangold, N.

Maurice, S.

Meslin, P.-Y.

Nachon, M.

Newsom, H.

Ollila, A. M.

Rampe, E. B.

Wiens, R.C.

English

NASA Technical Reports Server

APATITES IN GALE CRATER. O. Forni1, P.-Y. Meslin1, C. Drouet2, A. Cousin1, G. David1, N. Mangold3, E. 
Dehouck4, E.B. Rampe5, O. Gasnault1, M. Nachon6, H. Newsom7, D. L. Blaney8, S. M. Clegg9, A. M. Ollila7, J. Lasue1, 
S. Maurice1, R.C. Wiens7, 1Institut de Recherche en Astrophysique et Planétologie, Toulouse, France, 2CIRIMAT, 
Toulouse, France 3LPGN, Nantes, France, 4LPL-TPE, Lyon, France, 5NASA JSC, Houston, USA, 6Texas A&M Uni-
versity, USA, 7UNM, Albuquerque, USA, 8JPL, Pasadena, USA, 9LANL, Los Alamos, USA; [oliv-
ier.forni@irap.omp.eu]     
 
    Introduction:  ChemCam is an active remote sensing 
instrument suite that has operated successfully on MSL 
since landing Aug. 6th, 2012 [1, 2]. It uses laser pulses 
to remove dust and to analyze rocks up to 7 m away. 
Laser-induced breakdown spectroscopy (LIBS) obtains 
emission spectra of materials ablated from the samples 
in electronically excited states. The intensities of the 
emission lines scale with the abundances of the related 
element. ChemCam is sensitive to most major rock-
forming elements [3] as well as to a set of minor and 
trace elements such as F, Cl, Li, P, Sr, Ba, and Rb [4]. 
The measured chemical composition can then be used 
to infer the mineralogical composition of the ablated 
material. Here, we report a summary of inferred apatite 
detections [5] along the MSL traverse at Gale Crater. 
We present the geologic settings of these findings and 
derive some interpretations about the formation condi-
tions of apatite in time and space.  
  Geological context: From Sol 14 to Sol 750, the Curi-
osity rover explored the Bradbury Group, which con-
sists of the Yellowknife Bay formation [6] (composed 
of basalt-derived fine, medium-, and coarse-grained 
sandstones), the Rocknest formation [7] and the Kim-
berley formation where Curiosity spent sols 572-632 an-
alyzing its outcrops of sandstone, siltstone, and con-
glomerate [8]. The Murray formation follows up-sec-
tion and its contacts with the Bradbury group are con-
sidered transitional with interfingering facies [6]. Rocks 
comprising the Murray formation (> 300 m thick) are 
presently divided into eight members representing three 
major facies associations. The eight members in ascend-
ing order are: Pahrump Hills, which consists of finely 
laminated mudstones, with interstratified cross-bedded 
basaltic sandstones [9]; Hartmann’s Valley, Karasburg, 
Sutton Island, Blunts Point, Pettegrove Point and Jura 
that together make the Vera Rubin Ridge [10]. The Jura 
member comprises bedrock showing areas of red and 
gray coloration. VRR is comprised of planar-laminated 
mudstones similar to lithologies observed in the under-
lying members of the Murray formation [11]. 
      Apatite detection: Apatites are identified with 
ChemCam mainly through the combined detection of 
calcium, fluorine, chlorine and,when large enough, with 
phosphorus [5]. The detection of fluorine and chlorine 
is made possible by the identification of molecular 
emissions of CaF and CaCl, respectively, created in the 
laser plasma. For chlorine, the atomic line is also used. 
A combination of Ca, P and F or Cl was detected in ~50 
individual points, which represent the most robust apa-
tite detections. When P was not detected, shot to shot 
correlations between calcium lines and fluorine molec-
ular emissions were performed in order to detect possi-
ble candidates by the association of both elements. With 
these criteria, more than 280 tentative detections of ap-
atites were obtained (Fig 1.).  
 
Figure 1: Number of apatite candidates as a function of elevation. The bin 
height is 10 m. 
   Apatite settings: First, apatites have been detected in 
igneous rocks found on Mars [12]. They are associated 
in intrusive fine-grained rocks like Beacon, in porphyric 
effusive rocks like Harrison but also in aphanitic effu-
sive rocks and in the float rocks of the Bressay lag de-
posit Their presence is ubiquitous to the igneous rocks, 
independently of their basaltic or trachy-andesitic com-
position. They are probably primary and of magmatic 
origin. They also can represent the source of detrital ap-
atites found in the sediments.  
   Apatites have been found in many conglomerates en-
countered during the traverse – like the Goulburn and 
Deloro conglomerates belonging to the Bradbury group 
– but also at the base of the Pahrump Hills member in 
the Bald Mountain conglomerates [13]. They have also 
been identified in the Rocknest sandstone [7] which is 
characterized by low silicon content and high iron and 
titanium, reflecting the probable presence of ferrous 
and/or titano-ferrous oxides like magnetite, hematite, 
and/or ilmenite. Apatites are observed in the lower part 
https://ntrs.nasa.gov/search.jsp?R=20200001801 2020-05-24T04:18:12+00:00Z
of the Pahrump Hills member and found in association 
with dentritic features and veins [14]. Fluorapatites 
were also detected at the 1-2wt% by CheMin at this lo-
cation [9]. Apatites were also found at the contact be-
tween the Stimson and Murray formations which also 
exhibit calcium sulphate veins [15]. The majority of the 
detections was made very close to the unconformity be-
tween the Murray mudstone and the Stimson sandstone 
and is mainly located in the Stimson formation. Apatites 
observed after Marias Pass were observed in the Nauk-
luft Plateau and in the area of Murray Buttes. These de-
tections are mainly found in fracture fills, in dark-toned 
veins or maybe in the interstitial space between these 
veins and the sulphate veins [16]. Higher in the Murray 
formation, some candidate apatites are found in the 
VRR. More than half are located in the Pettegrove Point 
member and the remaining are equally distributed be-
tween red and grey Jura members and associated with 
the bedrock [17]. They are also found in the Stoer and 
Rock Hall drill holes, as confirmed by CheMin for the 
latter [18].    
    Discussion: Mainly three types of apatites have been 
identified: primary igneous apatites, detrital apatites 
mainly found in the conglomerates, in Rocknest and in 
the Bressay rock lag deposit, and secondary apatites 
found throughout the Murray formation. The common 
characteristic of these apatites is that they are mainly 
fluorapatites (i.e., with F as the dominant monovalent 
anion). Chlorine was also detected in a subset of apa-
tites, but to a few exceptions, Cl appears to be less abun-
dant than F in the structural formula and seem to be pre-
dominantly associated with the igneous rocks like the 
Harrsion target (Fig. 2). This observation, which is sup-
ported by CheMin through modelling of the XRD pat-
tern of the apatite peak (Rampe, pers. comm.), contrasts 
with what is currently observed in SNC meteorites. [19], 
[20] [21] and [22] have observed that there are two pop-
ulations of terrestrial apatite: fluorine-rich, water-poor 
types found in the melt-inclusions, and chlorine-rich 
types found in the interstitial space. They concluded that 
the fluorapatites formed in a closed system process 
within the melt inclusions while the chlorapatites 
formed via open system fluid migration. Various expla-
nations may elucidate the discrepancy between ob-
servations in Gale crater and those of Mars meteor-
ites. With LIBS spectroscopy, the detection limit of 
chlorine in apatites is poorer/larger than that of flu-
orine. Moreover, the formation of the CaCl molecular 
line is less favoured when competing with the CaF 
molecular emission [23]. Nevertheless, the preva-
lence of F-rich apatites is also observed in a majority 
of samples where chlorine has also been detected. It 
is worth noting that many apatites are associated 
with high-iron content, like in the Rocknest sand-
stone. This can indicate that those apatites are detri-
tal, deriving from a source that underwent strong 
hydrothermal activity, similar to what is observed for 
the Durango apatites in the Tertiary iron-magnetite de-
posits of Cerro de Mercado, Mexico [22]. However, in 
the VRR mudstones with their strong diagenetic im-
print [23], the context of these apatites suggests a 
formation through precipitation by fluids, perhaps 
from initially acidic fluids that dissolve P-bearing 
minerals and reprecipitate apatite after these fluids 
were neutralized.  
    Conclusion: Apatite is a ubiquitous minor phase 
whose stability field and conditions of formation can 
constrain the temperature and pH conditions that 
prevailed at the time of their occurrence. The apa-
tites found at Gale so far are mainly fluorapatites, in 
contrast to what is found in SNC meteorites. No clear 
signature of REE has been identified so far in these ap-
atites [24] 
       
Figure 2: Spectral extract of two igneous rocks in the fluorine-chlorine mo-
lecular region showing the presence of CaCl for the target Harrison and 
not for the target Beacon (dashed line, left).  
 Acknowledgements: This work has benefited from support 
from INSU-CNES, NASA and from ANR “Mars Prime”.          
   References: : [1] Maurice et al. (2012) SSR, 170,95-166 [2] Wiens 
et al. (2012)  SSR, 170, 167. [3] Clegg et al. (2017), SCAB, 129, 64. 
[4] Payré  et al. (2017) JGR, 122, 650.  [5] Forni et al. (2015) GRL, 
42, 1020 [6] Grotzinger et al. (2015) Science, 350, 6257 [7] Blaney et 
al. (2014) JGR, 119, 2109  [7] Blaney et al. (2015), EPSC, 391 [8] Le 
Deit at al. (2016), JGR 121, 784 [9] Rampe et al., (2017) EPSL, 471, 
172 [10] Fedo et al. (2019), 9th Int. Mars Conf., 6308. [11] Fraeman 
A.A. et al. (2019) LPSC 50, 2118 [12] Cousin et al, (2017), Icarus, 
288, 265 [13] Mangold et al. (2016), JGR, 121, 353. [14] Nachon et 
al. (2017) Icarus, 281, 121 [15] Newsom et al. (2016), LPSC, 47, 1397 
[16] Meslin et al. (2016) LIBS-2016 Conf. [17] David et al. (2020) 
JGR (submitted) [18] Rampe at al. (2020) JGR (submitted) [19] Patiño 
Douce and Roden (2006) Geochimica & Cosmochimica Acta, 70, 
3173  [20] McCubbin et al. (2013) MAPS. 48, 819 [21] Patiño Douce 
et al. (2011) Chem. Geol., 288, 14. [22] Humayun el al. (2019) 9th. 
Int. Mars Conf. [21] Vogt et al. (2020) Icarus (accepted) [22] Piccoli 
and Candela, (2002), in Phosphates: 255. [23] Fraeman et al. (2020) 
JGR (submitted). [24] Ollila et al. (2020) this meeting. 


Apatites in Gale Crater

Apatites in Gale Crater

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