HOT AND STEAMY ALTERATION of the PRIMORDIAL MARTIAN CRUST by - - PowerPoint PPT Presentation

HOT AND STEAMY

ALTERATION of the PRIMORDIAL MARTIAN CRUST by SUPERCRITICAL FLUIDS during MAGMA OCEAN COOLING

Kevin M. Cannon Stephen W. Parman John F. Mustard

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from Carter et al. 2013

Crustal alteration: x-y extent

(Mustard et al. 2008; Carter et al. 2013)

CRISM detections of alteration minerals Detections/Observations/deg2

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Crustal alteration: z extent

(Sun and Milliken 2015)

modifjed from Sun and Milliken 2015

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From whence came Mars’ clays?

from Ehlmann et al. 2012 (Ehlmann et al. 2012; Tornabene et al. 2013; Carter et al. 2015)

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Magma ocean evolution

(Abe 1993; Elkins-Tanton et al. 2005; Elkins-Tanton 2008)

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“In all the models presented for Earth and Mars the final atmospheric pressure from degassing a magma ocean is close to the critical point of water, indicating the likelihood of supercritical fluids on the surface of planets as they cool, and raising the question of their effect on the composition and weathering of the earliest basaltic crusts.”

• Elkins-Tanton, 2008

Magma ocean evolution

(Abe 1993; Elkins-Tanton et al. 2005; Elkins-Tanton 2008)

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SiO2 50.57 MnO 0.3 TiO2 1.04 MgO 8.31 Al2O3 11.92 CaO 9.5 Cr2O3 0.19 Na2O 3.98 FeO 13.83 K2O 0.36 10% 14% 22% 54%

1 mm

Starting material

Plag CPX Olv Gl

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Experiment design

Liquid Vapor Super- critical

20°C/km

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X-ray diffraction

Supercritical Liquid Geotherm Unaltered

X-ray diffraction

10Å 12.6Å

Supercritical Liquid Geotherm Unaltered

VNIR spectra

Fe2+ H2O M-OH

VNIR spectra

1.91μm 2.34μm

Unaltered: SE imaging (20 kv, 4 mm WD)

100μm

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Liquid (325°C, 300 bar)

100μm

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100μm

Liquid (325°C, 300 bar)

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Supercritical (425°C, 300 bar)

100μm

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100μm

Supercritical (425°C, 300 bar)

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Unaltered: EMPA elemental maps

Si Al Ca Glass Olivine Plag CPX

100μm

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Supercritical (425°C, 300 bar) Liquid (325°C, 300 bar)

100μm

Si Al Ca

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Conclusions

W e observe significant phyllosilicate formation in the vicinity of the H2O critical point after just 2 weeks, but none at 100°C at 5km depth-equivalent.

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Conclusions

There is a change in alteration assemblage going from the liquid to the supercritical field, with a transition from smectite to illite and possible increase in alteration extent.

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Conclusions

The final stages of magma ocean cooling should have driven significant crustal alteration, but the duration and depth remains unclear.

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modifjed from Sun and Milliken 2015

Open questions

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What is the volumetric extent of crustal alteration?

Open questions

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What is the volumetric extent of crustal alteration? Is there really a link between phyllosilicates and climate?

Conclusions

W e observe significant phyllosilicate formation in the vicinity of the H2O critical point after just 2 weeks, but none at 100°C at 5km depth-equivalent. There is a change in alteration assemblage going from the liquid to the supercritical field, with a transition from smectite to illite and possible increase in alteration extent. The final stages of magma ocean cooling should have driven significant crustal alteration, but the duration and depth remains unclear.

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Extras

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Total impact melt ~5x107 km3

(Rivera-Valentin and Craig 2015)

Martian crust, outer 15 km 2.2x109 km3

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