Master's Thesis Defense by Adomas Valantinas – Niels Bohr Institute - University of Copenhagen

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Master's Thesis Defense by Adomas Valantinas

A Study of Young Geologic Features on the Moon

Abstract:

The conventional understanding of the Moon states that it is a differentiated but currently a geologically ‘dead’ body. It is known from Apollo and Luna returned samples that most of the lunar mare volcanism took place ~4-3 Ga (billion years) ago and basin related extensional tectonics ended 3.6 Ga ago [1]. There is evidence for younger (0.9Ga -1.2 Ga) volcanic units [2,3] and some degree of contractional tectonics up to 1.2 Ga [4]. Other study [5], however, using Apollo orbital images identified evidence for ongoing tectonics based on narrow fractures and several young wrinkle ridges crossing the highlands and small craters. Interestingly, this was one of the very first ideas for recent tectonic activity on the Moon and was overlooked by the planetary science community for decades.

Recently, using high resolution images provided by NASA’s Lunar Reconnaissance Orbiter (LRO) evidence for young (<100 Ma) Irregular Mare Patches (IMPs) have been discovered but their origin is still debated [6-8]. Other teams identified tectonic surface expressions such as small graben and lobate scarps which were found to be <~100 Ma [9,10].

In this thesis, using LRO data I analyze several contractional lunar wrinkle ridge systems which are thought to be manifestations of global stress fields along nearside maria edges [11]. My results suggest that there are several young (<50 Ma) wrinkle ridges in the nearside of Moon and they might be even forming today.

The precise formation mechanism of these intricate wrinkle ridge systems is still debated but these findings support the model of totally molten early Moon which states that there should have been high level of late-stage compressional stresses [14,15].

[1] Basaltic Volcanism Study Project, Basaltic volcanism on the terrestrial planets, 948–974, 1981. [2] Schultz, P. H. & Spudis, P. D., Nature, 302, 184-186, 1983. [3] Hiesinger, H. et al., Geological Society of America Special Papers, 477, 2011.[4] Watters, T. R.  & Johnson, C. L., Planetary Tectonics, 121-182, 2010. [5] Schultz, P. H., Moon Morphology, 1976. [6] Schultz, P. H. et al., Nature, 444, 184-186, 2006. [7] Braden et al., Nature Geosci., 7, 787-791, 2014. [8] Qiao, et al., Geology, 45, 455, 2017. [9] Watters, T. R. et al., Nature Geosci, 5, 181-185, 2012. [10] Clark, J. D. et al., LPSC XLVI, #1730, 2015. [11] Yue, Z. et al., J. Geophys. Res. Planets, 120, 978–994, 2015. [12] Basilevsky, A. T.  et al., Planet. Space Sci., 89, 118-126, 2013. [13] Ghent, R. R. et al., Geology, 42, 1059-1062, 2014. [14] Binder, A. B., The Moon and the Planets, 26:117–133, 1982. [15] Pritchard, M. E. and Stevenson, D. J., Thermal Aspects of a Lunar Origin by Giant Impact, 2000. 

Supervisor: Kjartan M. Kinch