Diapositive 1

1
Relationships between phyllosilicates and
fluvial landforms
Mangold, Loizeau, Bouley, Ansan, Masson IDES
OrsayLPG Nantes Poulet, Bibring, Langevin,
Gondet IAS Orsay
1. Chronology What is the timing of
phyllosilicates formation relative to fluvial
valleys? 2. Process Are aqueous processes at
the surface involved in phyllosilicates formation?
Or is hydrothermal alteration predominant?
2
Mawrth
1. Nili
2. Thyrrena
Bibring et al, 2006
Fluvial valleys formation peaks in the Late
Noachian-Early Hesperian period Phyllosilicates
found on Noachian Terrains in the vicinity of
valleys gt Coincidence or not?
Valley networks on Noachian terrain
3
Nili Fossae
NF trough
1.93 band
Phyllosilicates in highlands and crater ejecta
No signatures on plains Of Early Hesperian age
Syrtis Plain
4
MOC
Contact 2 Syrtis volcanism
Olivine
Contact 1 Bedrock/olivine
Altered crust with veins
Crust
300 m
Low-T Hydrothermal alteration is favored for
altered crustal rocks
Syrtis-Nili Fossae Lava flows
See Mustard et al, JGR, 2007 Mangold et
al., JGR, 2007
1.93 mm band
5
A sapping-like valleys and associated fans in
trough
1.93 band
Fan
Valleys
10 km
HRSC
6
Fan at the outlet of sapping-like valleys Slight
hydration compared to bedrock gt Transport of
crustal rocks
1.93 band (band increases from purple to white)
MOC
valley
7
Fan at the outlet of sapping-like valleys Slight
hydration compared to bedrock gt Transport of
crustal rocks Valleys cut the olivine-rich layer
gt Post-olivine fluvial deposition
1.93 band
MOC
Olivine-rich layer cut by the valley
8
Jezero crater fans
10 km
CRISM data shows phyllosilicates
9
Olivine unit crossed by valleys
Highland crust
Fans formed after the olivine rich unit
10
Sapping like valleys with fans
Jezero fans
Old valleys
Alteration

• 1. Chronology
• Phyllosilicates formed before most fluvial
  landforms in this region
• 2. Process
• Late fans suggest transport and deposition better
  than in situ formation
• Ancient terrain gt Hydrothermal processes highly
  possible in Nili Fossae
• But chronologically not inconsistent with a
  formation coeval to valleys
• gt See Elhmann CRISM data with kaolinite

11
Tyrrhena Terra Known to present hydrated
craters ejecta Local phyllosilicates exposures on
bedrock
Geological map (HHesperian/NNoachian)
12
Pyroxene
Olivine
Hydration (1.93 band)
100 km

• Plains Type 1OlivinePyroxene
• Volcanic material
• Typical Early Hesperian lava plains

13
Pyroxene
Olivine
Hydration (1.93 band)

• Plains type 2PyroxeneHydration
• Different from lava flows
• (no other bands to discriminate minerals)

14
Viking MDIM
Fluvial valleys in highlands
40 km
3000 m
2000 m
1000 m
Plainsalluvial plains or catchment basin
15
Fluvial valleys in highlands
gt Hydrated minerals in alluvial plains
OMEGA 1.9 band over THEMIS day mosaic
16

• Hydrated minerals in light toned deposits
• Sediments deposited by fluvial activity

300 m
MOC
17

• Chronology Alteration lt Early Hesperian
  volcanic plains
• Process Alteration closely related to
  aqueous processes
• No strong alteration signatures in highlands,
• but valleys coud have collected them into the
  basin

Summary
Highland with poor alteration minerals Signatures
but many fluvial landforms
Late Noachian-Early Hesperian alluvial plains
with alteration
Early Hesperian volcanic plains
18
Crater with hydration gt excavated material from
the plain below
19
Conclusions
Arvidson, 2006

• Chronology
• - In the three regions studied, phyllosilicates
  formed
• before or during the fluvial episodes (expected
  LN/EH)
• before Early Hesperian volcanic plains

- Remember, sulfates such as in Terra
Meridiani seat on top of the dissected highlands
valleys

• Process
• Very difficult to conclude if the formation of
  some
• phyllosilicates is due to the surface processes
  (transport and deposition certainly exist)
• The formation before or during fluvial episodes
  suggest it is possible
• Tyrrhena region in progress to evaluate these
  hypotheses

20
Mawrth Vallis region
21
Valleys present on the clay-rich unit
HRSC
22

• Chronology relative to valley networks
• Valleys formed after clay-rich unit

2. Process No evidence except shallow formation
gtValleys formed inside the clay-rich unit gt
Material inside the valley inverted by erosion to
the West