Apollo Next Generation Sample Analysis: What to expect among Rock Fragments in Apollo 17 Core Samples 73001 and 73002

Abstract:

With the opening of Apollo 17 double drive tube 73001/73002 as part of the Apollo Next Generation Sample Analysis (ANGSA) program, we present information about the lithologic makeup of rock components of Station 3 regolith. We report compositions and petrologic classification of 2-4 mm rock fragments (73243) of Station 3 trench soil 73240. The trench was 40 m from the rim of 620 m diameter Lara crater and within its ejecta blanket. The drive tube was collected 10 m SE of the trench and 50 m from Lara’s rim. Station 3 was selected for its location on the “light mantle” and contains landslide material from South Massif. Soil samples, including 73001/2, an ~70 cm core, offer the possibility to identify lithologic components associated with the landslide, and perhaps ejecta from Tycho crater, the event thought to have triggered the landslide.

Known nonmare rock types at Apollo 17 include impact-melt breccias (IMB) of the poikilitic, aphanitic, and incompatible-element-rich types; (2) granulitic breccias; (3) Mg-suite rocks (dunite, troctolite, anorthosite, norite, gabbro); and (4) regolith and fragmental breccias. Rocks from Station 3 include 73215 and 73235 aphanitic IMBs; 73216 and 73218 crystalline IMBs, 73275 poikilitic IMB, and clast-rich IMBs 73217 and 73255. These groups of IMBs have distinctive petrographic and compositional characteristics. The poikilitic IMBs, more abundant in North Massif samples, are those most commonly interpreted to represent Serenitatis impact melt. The aphanitic and unusual IMBs among the station 3 rocks may come from Serenitatis or from another impact basin such as Imbrium.

If ejecta from Tycho struck the top of South Massif and caused the South Massif landslide 110 Myr ago, a glass component in the soil might be the best candidate for a remnant of this material. Such a component would have to record the ~110 Myr age associated with cosmic ray exposure evidence at the Apollo 17 site. Given current knowledge of Apollo 17 compositional and lithologic components, Sta. 3 drive tube 73001/2, collected in the light mantle, may provide the best opportunity for a fresh search for Tycho components and a new test of the hypothesis that Tycho ejecta caused the landslide. Of particular interest will be lithic fragments in 73001/2, which may represent regolith samples from different parts of the South Massif slope.