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Tolstoj Quadrangle

Mark Robinson and Brett Denevi

Arizona State University

Scott Murchie, APL

MESSENGER GDG Telecon 11/20/2007

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Quick Reminder

System Major Unit Base Age LunarKuiperian crater materials 1.0 Gyr CopernicanMansurian crater materials 3.0-3.5 Gyr Eratosthenian

Calorian

Caloris Group; plains, craters, small basin materials 3.9 Gyr Imbrian

Tolstojan

Goya formation; craters, small basins, plains material 3.9 - 4.0 Gyr Nectarian

pre-Tolstojan

Intercrater plains, multiring basins, crater materials PRE-4.0 Gyr pre-Nectarian

From Spudis and Guest in Mercury (1988)

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http://ser.sese.asu.edu/M10/GAZET/index.html

Tolstoj Quadrangle (H8)

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Main features

• Intercrater plains (light orange color)

• Tolstoj Basin (350 km, 3.97 Gyr)• Southern portion of Caloris

(1300 km, 3.77 Gyr)– Odin formation (medium blue)

similar to Alpes of Imbrium

• Tolstoj, Tir, Budh (peach color) and Caloris smooth plains occupy much of the region

• Mozart - fresh, large (285 km) crater on terminator

• Complex structural features

BudhBudh

Tir Plan

itia

Tir Plan

itia

TolstojTolstoj

MozartMozart

CalorisCaloris

Hummocky plainsHummocky plains

Intercrater plainsIntercrater plainsTolstoj rim materialTolstoj rim material

Smooth plains

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Significant Features

• Smooth Plains (Tolstoj, Tir, Budh)• Low albedo, blue material around Tolstoj• High albedo enigmatic crater floor deposits

(Tyagaraja, Zeami, Balzac)• Structural features (wrinkle ridges, lobate

scarps)

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Smooth plains

• Tir, Tolstoj, and Budh planitia all radar bright compared to surrounding intercrater plains (Harmon et al., 2004) – Opposite of lunar mare, which are

radar dark due to Fe, Ti

– Compositional differences between smooth plains and surroundings?

– Rougher small-scale surface texture than surroundings?

• Lots of small bright craters in Budh planitia (0.2-0.3)

Budh Planitia

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Low albedo region around Tolstoj

• Tolstoj smooth plains overlie dark material (below one std deviation of average Mercury albedo)

• High UV/Orange ratio (among bluest material on planet), enriched in opaques (Robinson and Taylor, 2001)

• Ancient crustal material or secondary process such as pyroclastic?

Arrows and X indicate low reflectancematerial, image 675 km wide.

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Enigmatic crater floor materials

• Good examples of these materials in Tolstoj quad

• Albedos up to ~0.3• Dark halo? Mentioned in

literature…• Dzurisin (1977) - local

physio-chemical alteration along impact-induced fractures

• Schultz (1977) - compositional or endogenic modification possible causes of color differences

Tyagaraja

Zeami

Balzac

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Structural Features

• Chock full of wrinkle ridges in smooth plains

• A few lobate scarps

• Local compression, plains contained in broad depressions

• Global compression result in lobate scarps?

Smooth plains, wrinkle ridges in Tostoj Quadrangle (Tir), 800 km wide

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Tectonics, Geology,

Image

White worms indicateWrinkle ridges

Black with triangle showLobate scarps

Thanks to T. Watters!

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Tolstoj Quad questions for MESSENGER

• Composition of smooth plains?• Why are the smooth plains

radar bright?• Why is the Tolstoj material so

blue?• What are the weird crater floor

deposits?• Origin of structural features?• Relative Ages?

M1 coverage of Tolstoj Quad