T239 Planetary Mantles—Using Samples to Explore Earth, the Moon, and Mars: Memorial Session in Memory of Lawrence A. Taylor

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 235

LUNAR MANTLE HETEROGENEITY IN THE VICINITY OF OR BENEATH THE APOLLO 17 SITE EMPHASIZED BY NEW BASALT CLAST IN 79135

Paper number: T239-9
Program: Technical Sessions
Time: 10:05 AM – 10:20 AM

Authors

Abstract

Returned samples have illustrated mantle heterogeneity beneath the Apollo 17 site with distinct mare basalt types. A “new” coarse-grained high-Ti mare basalt clast (~2.9 mm diameter) in lunar regolith breccia 79135, distinct from previously studied Apollo samples, may further reveal the nature of this heterogeneity. An SEM elemental scan of 79135,14, augmented with electron microprobe chemical analyses of specific mineral phases, indicates the clast is composed of ~1.8% olivine (Fo59-70), 6.3% plagioclase (An85-87), 14.6% ilmenite (Mg# 9-16), 13.3% pigeonite (Wo7-19, En38-67), 64% augite (Wo28-37, En41-53), and trace amounts of K-feldspar and silica.

The texture and major/minor element mineral compositions of the clast are distinct from Apollo 17 Type B2, C, and D basalts. While mineral chemistry is similar to Type A and B1 basalts, the 79135 clast could potentially represent a new type of Apollo 17 basalt. At least one Type A basalt fragment (79265) has been identified from trench soils near the drive tube of Station 9 where 79135 was also collected; in contrast, if the clast is a B1 basalt, it would represent the first of its type identified from Station 9 and one of the few found east of Station 1, indicating a more pervasive presence of that basalt type.

Despite some broad similarities to other Apollo 17 basalt types, the 79135,14 clast may represent a unique basalt type, thus further emphasizing the mantle heterogeneity. The clast’s petrology (e.g., texture, modal mineralogy, and estimated bulk Mg#) and trace element chemistry (e.g., olivine Ti/V ratio) indicate that it may have been produced from a different mantle source region and/or via a different set of magmatic processes than previously described in Apollo 17 mare basalts.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-322163

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