Phosphorus Zoning in Olivines: A critical tool for tracking magma ascent and storage in the martian crust

Petrogenetic linkages among fO2, isotopic enrichments-depletions and crystallization history in Martian basalts. Evidence from the distribution of phosphorus in olivine megacrysts

Petrogenesis of olivine-phyric shergottite Larkman Nunatak 06319: Implications for enriched components in martian basalts

The preservation of zoning patterns for major and trace elements in olivine and pyroxene reflect their differing diffusion rates. These have been applied to develop insights into the plumbing systems of olivine-phyric and poikilitic shergottite volcanoes, their eruption triggers and timescales. Here, we exploit crystal zoning to reconstruct magmatic histories recorded in martian meteorites, applying a combination of microanalytical techniques. We investigate eleven olivine-phyric and poikilitic shergottites, which have long been distinguished via the unique textural relationships between their large olivine and pyroxene phenocrysts. Major element compositions of large olivine crystals in the olivine-phyric shergottites indicate that the cores of the phenocrysts formed from earlier, less fractionated magma (Fo = 62-75) than the rims (Fo = 50-62), which in turn formed at the same time as a secondary generation of smaller olivine crystals (Fo = 48-56). Olivine crystals in the poikilitic shergottites are unzoned but have more fractionated compositions in light rare earth element-enriched samples (Fo = 59-61) than in intermediate samples (Fo = 68-71). We interpret that the olivine in olivine-phyric shergottites crystallised from an evolving magma, whereas olivine in poikilitic shergottites crystallised from two distinct magmas, either evolved with high Mn concentrations or primitive with lower Mn. Although olivine major elements show gradual zoning patterns or no zoning, slower diffusing trace elements show that multiple magma recharge events occurred within the shergottite magma reservoirs. LA-ICP-MS trace element mapping reveals oscillatory P and Sc zoning, which when coupled with Ti zoning, indicates that up to three recharge events occurred before final emplacement of the olivine-phyric shergottites within the shallow crust. Diffusion timescales for Fo and Ni zoning are comparable to those obtained in basaltic hotspot systems on Earth (such as Hawaii). The magmas that formed the poikilitic shergottites also experienced multiple recharge events, which are recorded by P and Ti zoning within olivine. Pyroxene crystals support three recharge events for the olivine-phyric shergottites, involving increasingly Cr- and Ca-rich magmas. In contrast, pyroxene oikocrysts in the poikilitic shergottites record one recharge event, which formed augite rims. While the host magma was still hot, Ca and trace elements from the augite rim diffused into the pigeonite cores of the pyroxenes. Prolonged storage at relatively high temperatures allowed significant diffusion that caused most of the olivine and pyroxene crystals to fully equilibrate, removing any previous major element zoning patterns. Through detailed examination of these phenocrysts, we build on the existing models of the two volcanic plumbing systems of the poikilitic and olivine-phyric shergottites, and construct quantitative models, revealing that the olivine-phyric shergottites experienced crystallisation and short storage at depth followed by shallow emplacement, whereas the poikilitic shergottites experienced prolonged deep storage before final shallow emplacement.

Crystallization history of enriched shergottites from Fe and Mg isotope fractionation in olivine megacrysts

Oxygen isotopes were measured in mineral separates from martian meteorites using laser fluorination and were found to be remarkably uniform in both δ18O and Δ17O, suggesting that martian magmas did not assimilate aqueously altered crust regardless of any other geochemical variations. Measurements of Cl, F, H, and S in apatite from martian meteorites were made using the SIMS and NanoSIMS. Martian apatites are typically higher in Cl than terrestrial apatites from mafic and ultramafic rocks, signifying that Mars is inherently higher in Cl than Earth. Apatites from basaltic and olivine-phyric shergottites are as high in water as any terrestrial apatite from mafic and utramafic rocks, implying the possibility that martian magmas may be more similar in water abundance to terrestrial magmas than previously thought. Apatites from lherzolitic shergottites, nakhlites, chassignites, and ALH 84001 (all of which are cumulate rocks) are all lower in water than the basaltic and olivine-phyric shergottites, indicating that the slow-cooling accumulation process allows escape of water from trapped melts where apatite later formed. Sulfur is only high in some apatites from basaltic and olivine-phyric shergottites and low in all other SNCs from this study, which could mean that cumulate SNCs are low in all volatiles and that there are other controlling factors in basaltic and olivine-phyric magmas dictating the inclusion of sulfur into apatite. Sulfur Kα X-rays were measured in SNC apatites using the electron probe. None of the peaks in the SNC spectra reside in the same position as anhydrite (where sulfur is 100% sulfate) or pyrite (where sulfur is 100% sulfide), but instead all SNC spectra peaks lie in between these two end member peaks, which implies that SNC apatites may be substituting some sulfide, as well as sulfate, into their structure. However, further work is needed to verify this hypothesis.

Constraints on martian depleted shergottite volcanism from the petrogenesis of olivine-phyric shergottites NWA 2046 and NWA 4925

The martian water cycle, a key for the habitability of Mars, largely relies on the abundance of water in martian magmas and their mantle sources, yet martian (SNC: shergottite, nakhlite, and chassigny classes) meteorites contain minimal water. However, some experimental studies have suggested that martian parental magmas contained as much as 2% H2O. Here we integrate mineral-chemical, experimental, and cosmochemical constraints to show that martian magmas contained little water but abundant chlorine. Apatite and amphibole in martian meteorites are chlorine rich and water poor; this constrains the chlorine contents in their parental magmas to >0.3 wt% and water contents to <0.3 wt%. Our experimental work has shown that large amounts of water are not needed to explain the mineralogy of the martian meteorites because chlorine has effects similar to those of water on crystallization. Such chlorine-rich, water-poor martian magmas are consistent with Mars being chlorine rich (~2.5 ×) compared with the Earth. Furthermore, the bulk Cl composition of martian meteorites shows that they have not preferentially lost Cl by degassing of an H2O-rich vapor. Together, these results show that chlorine, not water, was the dominant volatile species in martian basalts, and that these basalts contributed little H2O to Mars' surface environment.

The generation, segregation, ascent and emplacement of granite magma: the migmatite-to-crustally-derived granite connection in thickened orogens

New bulk sulfur measurements of Martian meteorites and modeling the fate of sulfur during melting and crystallization – Implications for sulfur transfer from Martian mantle to crust–atmosphere system

Light lithophile elements in pyroxenes of Northwest Africa (NWA) 817 and other Martian meteorites: Implications for water in Martian magmas

. IntroductionMartian meteorites are, by the moment, the only Martian samples than can be studied in Earth laboratories. The minerals in Martian meteorites contain information about (a) &amp;#160;alteration processes suffered in the Martian surface, (b) due to the shock event that sent Martian materials to the space, (c) originated from pressure and thermal transformation during entry and (d) due to the terrestrial weathering processes after its landing. Thus, any Martian meteorite could have signals of these four alteration processes.The studies of meteorites make use of microscopic techniques. Among such techniques, Raman micro-spectroscopy is becoming more and more used due to its versatility to detect both crystalline and amorphous minerals at the micrometric level. The RLS (Raman Laser Spectrometer) instrument on board Rosalind Franklin rover of the Exomars 2022 mission has such micrometric capability to study the drilled samples, at 50 microns of spot size.This work compares the capability of a RLS-like Raman instrument (532 nm continuous excitation laser, focusing at 50 microns), and a High Resolution Raman micro-spectrometer, to detect mineral assemblages in the Dar al Gani 735 Martian meteorite (DaG 735), an olivine-phyric Shergottite with olivine/pyroxene &amp;#8220;megacrysts&amp;#8221; [1]. The aim is to identify terrestrial and non-terrestrial alterations suffered by the meteorite. Dar al Gani 735 was selected due to the size of individual crystals [1], the presence of large pockets of brownish-colored recrystallized impact glass associated with pyroxene and olivine [3], and the absence of fusion crust but presence of weathering compounds [2].The Dar al Gani paired Martian Meteorites were ejected from the parent body 1.18 &amp;#177; 0.17 My ago while the terrestrial age is estimated around 60 &amp;#177; 20 ky. The isotopic compositions of Sm and Gd suggest a mixing between basaltic lava and regolith to form the bulk of the ejected material [3]. The large amount of literature information about the DaG 735 and paired meteorites [4-10] gave us the basic knowledge to first confirm the positive identification of the referred mineral phases with a HR Raman micro-spectrometer. Then, the RLS-like instrument [11] will tell us which, of the minerals detected with the HR system, could be detected at the 50 microns of spot size2. ExperimentalAn InVia micro-Raman instrument, provided with 532 nm excitation lasers and Peltier cooled CCD detector (-70&amp;#186;C) was used as the HR Raman instrument; details of the working conditions are given elsewhere [12]. The RLS-like instrument used was a BWTek 532 Raman spectrometer, equipped with an objective to focus at 50 microns. Both spectrometers were daily calibrated with the 520.5 cm&amp;#8722;1 silicon line. The results were interpreted by comparing the collected Raman spectra with Raman spectra of pure standard compounds.3. Results and DiscussionThe analysis showed the main matrix of pyroxene (clinopyroxenes like diopside-hedenbergite, CaMgSi2O6, or augite, CaMgFe)2Si2O6, and ortopyroxene like enstatite, MgSiO3) with olivine megacrysts (different ratios between forsterite, Mg2SiO4, and fayalite, Fe2SiO4) together with a remarkable presence of chromite (FeCr2O4) were detected as reported in literature [4-6].&amp;#160;The analysis on cracks/veins shown the largest fractures filled with calcite as a terrestrial weathering compound. Others were filled with hematite (Fe2O3) coming from terrestrial weathering of the original Fe-bearing mineralsApart from the high Ca presence in fractures, the Raman spectrum of the calcite crystals in the bulk shown displaced bands at 1088, 714, 283 and 157 cm-1, belonging to shocked calcite. Suggesting these calcite crystals as original from Mars altered by the shock effect that formed the meteorite.Relatively high size crystals of &amp;#946;-anhydrite were detected. This &amp;#946;-anhydrite cannot be assigned to terrestrial weathering because high temperature (&gt;300oC) is required for its formation. As gypsum changes to &amp;#946;-anhydrite under high pressure (&gt; 2.56 GPa) and temperatures (&gt; 583 K), the source of this &amp;#946;-anhydrite could be shocked original gypsum.Ilmenite (Fe2+Ti4+O3) was also detected but at higher wavenumbers, 686, 230 and 375 cm-1, than terrestrial ilmenite, suggesting again the effect of high pressures to which this ilmenite was subjected (estimation of 18 GPa with the 686 cm-1 band or 14 GPa with the 230 cm-1 one) during the shock event.The identification of anatase is also important to be highlighted. In terrestrial environments, the occurrence of anatase is indicative of low-temperature aqueous alteration, probably from the oxidation of the Fe(II) in ilmenite to form irreversibly hematite and anatase.All these mineral phases were also detected with the RLS-like Raman spectrometer, suggesting that RLS on board the Rosalind Franklin rover could not only detect mineral but most interestingly all the mineral phases related to aqueous driven alteration processes occurred in Mars.&amp;#160;4. ConclusionsThe characterization of the DaG 735 meteorite with a HR Raman micro-spectrometer was successful because not only the expected mineral phases were detected but also new minerals identified. In particular, Raman spectroscopy was able to detect shocked calcite, anhydrite and ilmenite. Also alterations due to weathering were detected in enough amount as to be also identified by the RLS-like Raman instrument. This provides information about the future data that will be sent by the Raman technique implemented on the Rosalind Franklin rover (Exomars2022 mission from ESA), for the new explorations of Mars materials.5. Acknowledgements:This work was financed by the Ministry of Economy and Competitiveness (MINECO, grants ESP2014-56138-C3-2-R and ESP2017-87690-C3-1-R). The authors gratefully acknowledge the support of the SIGUE-Mars consortium (MINECO, grant RDE2018-102600-T).6.

Larkman Nunatak (LAR) 12095 and LAR 12240 are recent olivine-phyric shergottite lnds. We report the results of petrographic and chemical analyses of these two samples to understand their petrogenesis on Mars. Based on our analyses, we suggest that these samples are likely paired and are most similar to other depleted olivine-phyric shergottites, particularly Dar al Gani (DaG) 476 and Sayh al Uhaymir (SaU) 005 (and samples paired with those). The olivine megacryst cores in LAR 12095 and LAR 12240 are not in equilibrium with the groundmass olivines. We infer that these megacrysts are phenocrysts and their major element compositions have been homogenized by diffusion (the cores of the olivine megacrysts have Mg# ~70, whereas megacryst rims and groundmass olivines typically have Mg# ~58–60). The rare earth element (REE) microdistributions in the various phases (olivine, low- and high-Ca pyroxene, maskelynite, and merrillite) in both samples are similar and support the likelihood that these two shergottites are indeed paired. The calculated parent melt (i.e., in equilibrium with the low-Ca pyroxene, which is one of the earliest formed REE-bearing minerals) has an REE pattern parallel to that of melt in equilibrium with merrillite (i.e., one of the last-formed minerals). This suggests that the LAR 12095/12240 paired shergottites represent the product of closed-system fractional crystallization following magma emplacement and crystal accumulation. Utilizing the europium oxybarometer, we estimate that the magmatic oxygen fugacity early in the crystallization sequence was ~IW. Finally, petrographic evidence indicates that LAR 12095/12240 experienced extensive shock prior to being ejected from Mars.

Abstract— The SNC meteorites are thought to be igneous martian rocks, based on their young crystallization ages and a close match between the composition of gases implanted in them during shock and the atmosphere of Mars. A related meteorite, ALH84001, may be older and thus may represent ancient martian crust. These petrologically diverse basalts and ultramafic rocks are mostly cumulates, but their parent magmas share geochemical and radiogenic isotopic characteristics that suggest they may have formed by remelting the same mantle source region at different times. Information and inferences about martian geology drawn from these samples include the following: Planetary differentiation occurred early at ∼4.5 Ga, probably concurrently with accretion. The martian mantle contains different abundances of moderately volatile and siderophile elements and is more Fe‐rich than that of the Earth, which has implications for its mineralogy, density, and origin. The estimated core composition has a S abundance near the threshold value for inner core solidification. The former presence of a core dynamo may be suggested by remanent magnetization in SNC meteorites, although these rocks may have been magnetized during shock. The mineralogy of martian surface units, inferred from reflectance spectra, matches that of basaltic shergottites, but SNC lithologies thought to have crystallized in the subsurface are not presently recognized. The rheological properties of martian magmas are more accurately derived from these meteorites than from observations of martian flow morphology, although the sampled range of magma compositions is limited. Estimates of planetary water abundance and the amount of outgassed water based on these meteorites are contradictory but overlap estimates based on geological observations and atmospheric measurements. Stable isotope measurements indicate that the martian hydrosphere experienced only limited exchange with the lithosphere, but it is in isotopic equilibrium with the atmosphere and has been since 1.3 Ga. The isotopically heavy atmosphere/hydrosphere composition deduced from these rocks reflects a loss process more severe than current atmospheric evolution models, and the occurrence of carbonates in SNC meteorites suggests that they, rather than scapolite or hydrous carbonates, are the major crustal sink for CO2. Weathering products in SNC meteorites support the idea of limited alteration of the lithosphere by small volumes of saline, CO2‐bearing water. Atmospheric composition and evolution are further constrained by noble gases in these meteorites, although Xe and Kr isotopes suggest different origins for the atmosphere. Planetary ejection of these rocks has promoted an advance in the understanding of impact physics, which has been accomplished by a model involving spallation during large cratering events. Ejection of all the SNC meteorites (except ALH84001) in one or two events may provide a plausible solution to most constraints imposed by chronology, geochemistry, and cosmic ray exposure, although problems remain with this scenario; ALH84001 may represent older martian crust sampled during a separate impact.

Merrillite is a ubiquitous accessory phase in a variety of Martian meteorite lithologies. The Martian merrillites exhibit a positive correlation between Mg# and Na and a negative correlation between Mg# and both Mn and vacancies in the octahedral Na‐site. Their REE patterns are varied and range from LREE‐depleted to LREE‐enriched. The dominant cation substitutions in the Martian merrillites are Fe2+VI Mg‐site⇔Mg2+VI Mg‐site and Ca2+VI Na‐site + □VI Na‐site⇔2Na+VI Na‐site. The REE substitution into the 8‐fold coordinated Ca‐site is accommodated by the coupled substitution CaVIII Ca‐site + (Na)VI Na‐site ⇔(Y3+ + REE3+)VIII Ca‐site + □VI Na‐site. The REE substitution is significantly more prevalent in lunar merrillite and can be used as a “fingerprint” to distinguish lunar from Martian meteorites. The substitution of OH− (whitlockite) and/or F− (bobdownsite) for O2− on one of the phosphate tetrahedrons appears to be rather insignificant. The correlations among Na, Mg#, Mn, and Na‐site vacancies are linked to the premerrillite crystallization history of the melt and the crystal chemical behavior of the Mg‐ and Na‐sites. The former reflects the sequence and extent of plagioclase and pyroxene crystallization. The differences in REE pattern shapes among the merrillites reflect source regions for the Martian basalts and the shapes are not greatly perturbed by the crystallization history. The occurrence of merrillite does not imply low‐volatile component in the Martian magmas. However, the low whitlockite and bobdownsite contents suggest that these samples were not altered by hydrothermal fluids and therefore not reset owing to aqueous fluid interactions. Consequently, the young ages of the shergottites are probably true igneous crystallization ages.

Petrogenesis of the NWA 7320 enriched martian gabbroic shergottite: Insight into the martian crust