magma evolution of poikilitic shergottite nwa 7397 from ... · magma evolution of poikilitic...

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NWA 7397

• Poikilitic shergottite

• Discovered in Morocco in June, 2012 [1]

• 2.13 kg, partially covered in fusion crust

• 3rd REE-enriched permafic (after RBT 04262 and GRV 020090) [2]

• Crystallization age: ??

• Comprised of 2 lithologies [2] :

Poikilitic: olivine, pyroxene, chromite

Non-poikilitic: olivine, pyroxene, maskelynite, minor spinel, phosphate, sulfide, Fe-oxide

• Olivine of both lithologies contain melt inclusions (MIs)

Introduction

• Determine the melt inclusion (MI)-source magmas and their progressivedifferentiation using textural observations

• Understand the evolution of shergottite magmatic systems

Objectives

7 MIs of a thick section of NWA 7397 (Fig. 3) were studied by-

• EDX-elemental maps and BSE-images JEOL-SEM 7600F @ NASA-JSC

• Major oxide analysis of host olivines and MIs Cameca SX-100 electronmicroprobe @ NASA-JSC

• Modal composition (in wt.%) calculation of MIs ImageJ software

• Post-entrapment Fe-Mg re-equilibration correction PETROLOG3 software

Methods

Melt Inclusions (MIs)

References

[1] Meteoritical Bulletin Database. [2] Howarth et al. (2014) MAPS, 49, 1812-1830. [3] Danyushevsky et al. (2002) Chem Geo, 183, 5-24. [4] Potter et al. (2015) LPSC XLVI, Abstr. #2945. [5] Basu Sarbadhikari et al. (2011) GCA, 75, 6803-6820. [6] Basu Sarbadhikari et al. (2016) MAPS, 1-17. [7] Agee et al. (2013) Science, 339, 780-785. [8] Filiberto & Dasgupta (2011) EPSL, 304, 527-537. [9] McSween et al. (2009) Science, 324, 736-739. [10] McSween et al. (2006) JGR, 111, E02S10. [11] Schmidt et al. (2014) JGR, 119, 64-81.

Compared to RBT 04262

1University of Houston, Houston TX 77204, USA, jferdous@uh.edu, 2Jacobs, NASA-Johnson Space Center, Mail Code X13, Houston TX 77058, USA

J. Ferdous1, A. D. Brandon1 and A. H. Peslier2

Magma Evolution of Poikilitic Shergottite NWA 7397

from its Olivine-hosted Melt Inclusions

Figure 1: NWA 7397. block is 1 cm.

Source: www.meteoritemarket.com

Figure 3: Energy Dispersive X-ray (EDX) map of NWA 7397 thick section showing major phaseswith the poikilitic (P) and non-poikilitic (nP) lithologies outlined by the black line. The analyzedmelt inclusion (MI) locations are marked by red boxes.

Figure 5: Compositional diagram of primarypyroxenes [2] and MI-pyroxenes (MI PX) ofNWA 7397.

Melt Compositions

Figure 2: Major phases and modalabundances of NWA 7397 [2].

Host OlivineMI Ca-poor PXMI Ca-rich PX

a)Host OlivineMI Ca-poor PXMI Ca-rich PX

b)

Host OlivineMI-1 Mg-rich PX rimMI-1,2 K-Na-rich GlassMI-2 Ca-rich PX rim

c)

MI-1

MI-2

Host OlivineMI-1,2 PXMI-1,2 K-Na-rich Glass

d)

MI-1

MI-2

Host OlivineMI Mg-rich PX rimMI Ca-rich PX rimMI Plag-rich GlassMI K-feld-rich Glass

e) f)Host OlivineMI Ca-P-rich PXMI Plag-rich Glass

Figure 4: Compositional maps of NWA7397 melt inclusions generated usingImageJ software. Poikilitic MIs (a-b) andNon-poikilitc MIs (c-g). PX= pyroxene,Plag= plagioclase, K-feld= K-feldspar.

Host OlivineMI Plag-rich GlassMI K-feld-rich GlassMI SulfideMI Phosphate

g)

Primary PXMI PX

Figure 6: MgO/FeO ratios of NWA 7397 MIs andcorrected for Fe-Mg exchange with host olivinevs. forsterite content (Fo) of host olivine. Blackarrow= equilibrium conditions between olivineand basaltic melt [3].

Figure 8: SiO2 vs. (a) FeO/MgO ratio and (b) Na2O+K2O- diagrams of MI-trapped magma

compositions (MC) of NWA 7397, RBT 04262 [4], LAR 06319 [5] and Tissint [6] with other

Martian surface rocks [7,8] and Martian mantle average [8]. Blue arrows= fractionation trends in

terrestrial magmas [9]. Blue shaded area= SNC-bulk composition field, Pink shaded area= Gusev

crater rock composition field [10], Green shaded area= Gale crater rock composition field [11].

Figure 7: Molar Mg# vs. (a) SiO2, (b) Al2O3, (c) CaO and (d) CaO/Al2O3 contents of MIs of NWA7397 and another olivine-phyric shergottite RBT 04262 [4] before and after the post-entrapmentcorrections [3]. P= Poikilitic MI, nP= Non-poikilitic MI, PBC= Present Bulk Composition, MC=Trapped Magma Composition.

Compared to Other Meteorites and Rover data

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Al 2

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Conclusions

• MI of NWA 7397 and RBT 04262 have higher SiO2 and distinct alkali-contentscompared to SNC bulk-rock and Bounce rock. Their compositions can be linkedby fractional crystallization processes.

• Some MI of NWA 7397 and RBT 04262 have compositions resembling that ofrocks analyzed by the Pathfinder rover.

• One MI from NWA 7397 has a composition similar to those of Gale craterrocks.

45

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SiO

2(w

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NWA-P-PBC NWA-P-MC NWA-nP-PBC

NWA-nP-MC RBT-P-PBC RBT-P-MC

RBT-nP-PBC RBT-nP-MC(a)