Stephanie Quintana

GEOL 2860 Schaber, G. (1973) Lava flows in Mare Inbrium: Geological evaluation for Apollo orbital photography Bugiolacchi, R. and Guest, J. (2008) Compositional and temporal investigation of exposed lunar basalts in the Mare Imbrium region

Background Three primary lava emplacement periods Special focus on Period III Summary Discussion Questions

Magma ocean extensive differentiation bottom-up fractional crystallization

Mafic materials settle ferriferous and titaniferous ultramafic cumulate settle KREEP crystallization

Late production of picritic and ultramafic liquids at 130-480 km

Basin formed around 3.85 Ga in relatively thin crust Did not penetrate down to

the mantle Extensive structural

modification Basin infilling over 800

million years Did not commence soon

after excavation phase 2nd largest basaltic region

on Moon Complex suite of low to

high-Ti basaltic lava units

NASA/JPL Galileo Spacecraft PIA00405

Bugiolacchi & Guest (2008)

Bugiolacchi & Guest (2008)

Bugiolacchi & Guest (2008)

Bugiolacchi & Guest (2008)

Three periods of emplacement

Slightly decreasing levels of Ti and Fe with age

Bugiolacchi & Guest (2008)

Bugiolacchi & Guest (2008)

Period Age Extent (km)

Schaber ’73

TiO2 (wt%)

Bugiolacchi and Guest ‘08

FeO (wt%)

Bugiolacchi and Guest ‘08

Average age (Ga)

Bugiolacchi and Guest ‘08

Average age (Ga) Schaber ‘73

I Late Imbrian Epoch

1200 1.4–6.2 15.2–17.5 3.3 ± 0.1 3.0 ± 0.4

II ‘Early’ Eratosthenian Period

600 2.5–7.1 16.0–17.9 3.0 ± 0.2 2.7 ± 0.3

III ‘Middle’ Eratosthenian Period

400 2.5–9.8 15.2–18.8 2.3 ± 0.5 2.5 ± 0.3

Source between Imbrian and “Copernican” ring structures Control migration to

surface Source could be

associated with locus of one active lunar seismic region

Morphology: Scarps 30-35 m high

Leveed channels ~20 km

Apollo 17 M-2450 Photograph

Euler

Copernicus

Columbia River and Hawaii

Lava viscosity is less on Moon compared to Earth

Flow Velocity (Moon compared to Hawaii/Columbia River)

▪ Laminar: 1.0-1.5 times greater / 1.5-3.0 times greater

▪ Turbulent: 1.75-2.5 times less / 1.6-3.0 times less

Flow Thickness (Moon compared to Columbia River)

▪ Moon has lower gravity and a higher density lava: 1.7 times greater

Rate of extrusion likely more significant than viscosity —extrusion rate must have been large on Moon

Three primary phases of eruption

Possibly from same source

Large flow lengths mean a high extrusion rate Extrusion rate decreased over time Ti and Fe content increased over time

Follow a trend and appear correlated

How does eruption in a vacuum affect the flow features we are used to seeing?

What evidence do we have of magma storage beneath the surface? What kind of structure do we expect? What does the scope and composition of the lavas say about the

storage of magma beneath the surface? What evidence do we see for lava produced by

vents/fissures/volcanoes? How does flow thickness and extrusion rate change for these

features? How does the evidence for lava flows and magma storage

change in other regions of the Moon? Why might basin infilling have commenced after basin

formation?

Bugiolacchi and Guest use craters >500m in their crater counting statistics, and avoid obvious secondary craters. Is this size still too small to obtain an accurate count (or is it still skewed by secondaries)?

Apparent bimodal distribution of TiO2

Bimodal distribution examples Left: Clementine Right: Samples