Stratigraphic Relationships in Northeast Syrtis Major, Mars: Approximately 250 Million Years of Geological History Spanning the Noachian–Hesperian Boundary

Mike Bramble and Jack Mustard Brown University

LPSC 2016 – Abstract No. 2582 Outstanding questions of the Nili Fossae region How was the regional olivine-rich unit emplaced? e.g. Basaltic lava flows? Impact melt?

How were the carbonate minerals formed? e.g. Hydrothermal alteration? Contact alteration?

Stratigraphy offers important clues Units are well-exposed in Northeast Syrtis Major

local stratigraphic relationships highest spatial resolution constrain outstanding questions Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Stratigraphy of Northeast Syrtis Major ~3.7 Ga Syrtis Major Volcanics (3.7–3.8 Ga, Hiesinger & Head, 2004)

(3.5–3.7 Ga, Ivanov et al., 2012) → [Ehlmann et al., 2008; 2009; 2010; 2011; Ehlmann and Mustard, 2012; Mangold et al., 2007; Mustard et al.,

2007; 2008; 2009] YOUNGER YOUNGER Olivine-rich unit Isidis-forming impact (3.96 Ga, Werner, 2005)

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Context

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars 3 Ring Structures 1100, 1900 km (Schultz and Frey, 1990) 1500 km (Frey et al., 2000)

Mapping area in black

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Results

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Paired Morphology and Mineralogy

Complexity and diversity unifiable under 5 distinct geomorphic units. Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Olivine-Rich Unit “Fractured Unit”

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars OMEGA Olivine-Rich Unit Map Blue (Ody et al., 2012) Largest olivine-rich Hesperian & Younger Terrains Masked in White geologic unit on Mars

Emplacement Mechanism?

[Reyes and Christensen, 1994; Hoefen et al., 2003; Hamilton et al., 2003; Hamilton & Christensen, 2005; Mustard et al., 1997; 2007; 2009; Tornabene et al., 2008; Poulet et al., 2009; Ody et al., 2013] NE Syrtis Major Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars a'

Vertically a Exaggerated

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Observations: Sharp angles Conforms to troughs Evidence for pooling

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Observations: Various orientations

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Observations olivine-rich unit emplacement mechanism must explain: • Draping texture on both local and regional scales • Large linear features both conforming to troughs and forming sharp angles at 60, 90, and 120 degrees. • Sharp contacts below with low-Ca pyroxene/smectite basement and above with Capping Unit. • Coarse grain size. Modelled at > 1 mm (Mark Salvatore) • Corroborates deep and broad ~1 µm olivine bands.

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Olivine-Rich Unit Emplacement Hypotheses Hypotheses to be reconciled with observations: • Intrusive complex or basaltic volcanic flows pre-dating the Isidis impact • Picritic lava flows emplaced subsequent to the Isidis basin • Impact melt produced from the formation of the Isidis basin • Other Hypotheses? Komatiites? Mobile Erosion Product?

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Olivine-Rich Unit Emplacement Hypotheses Hypotheses reconciled with observations: in NE Syrtis Major • Extrusive complex? or basaltic volcanic flows pre-dating the Isidis impact varying stress field? • Picritic lava flows emplaced subsequent to the Isidis basin • Impact melt produced from the formation of the Isidis basin • Other Hypotheses? Komatiites? Mobile Erosion Product?

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Carbonate Formation

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Carbonate-bearing Units Bramble & Mustard, 2016 Formation Mechanism?

Testable Hypotheses

[Ehlmann et al., 2008; Ehlmann et al., 2009; Brown et al., 2010; Ehlmann and Mustard, 2012; Viviano et al., 2013; Mustard et al., 2014]

Viviano et al., 2013

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Targeting contact between olivine-rich unit and basement

Olivine-rich Unit CRISM Spectra Basement

No 2.5 µm No carbonate

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Observations formation mechanism must explain: •Olivine-rich unit overlying a Fe/Mg smectite basement •Carbonate only observed within the olivine-rich unit Capping • Not as a distinct stratum Unit Olivine-rich unit AND carbonate

Phyllosilicate- bearing basement: Fe/Mg smectite Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Carbonate Formation in Northeast Syrtis Major Hypotheses to be reconciled with observations: • In situ hydrothermal alteration or percolation of groundwater through the olivine-rich host rock. • Contact hydrothermal alteration on the contact between a hot olivine-rich unit and phyllosilicate-rich basement. • Surface weathering in a manner akin to carbonates on Antarctic meteorites • Tuesday Night – Poster #324 Abstract #2553 – Come Chat! • Precipitation from shallow lakes

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Carbonate Formation in Northeast Syrtis Major Hypotheses reconciled with observations: • In situ hydrothermal alteration or percolation of groundwater through the olivine-rich host rock. • Contact hydrothermal alteration on the contact between a hot olivine-rich unit and phyllosilicate-rich basement. • Surface weathering in a manner akin to carbonates on Antarctic meteorites • Tuesday Night – Poster #324 Abstract #2553 – Come Chat! • Precipitation from shallow lakes

Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars Conclusions – Northeast Syrtis Major —Stratigraphy spans the Noachian-Hesperian boundary (~250 Myr). Great small-scale morphological heterogeneity, but unifiable under five distinct geomorphic units. In Northeast Syrtis Major: —Olivine-rich unit was emplaced as an impact melt sheet or via extrusive volcanism shortly after the impact. —Observations support the in situ formation of carbonate via hydrothermal alteration, or as a surface-weathering product.

NE Syrtis from the rim of Jezero, CTX mosaic DEM, 3x VE Bramble and Mustard – Abstract 2582 – @mbramble Stratigraphic Relationships in Northeast Syrtis Major, Mars