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Recent extensional tectonics on the Moon revealed by the Lunar Reconnaissance Orbiter Camera

Nature Geoscience volume 5, pages 181185 (2012) | Download Citation

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Abstract

Large-scale expressions of lunar tectonics—contractional wrinkle ridges and extensional rilles or graben—are directly related to stresses induced by mare basalt-filled basins1,2. Basin-related extensional tectonic activity ceased about 3.6 Gyr ago, whereas contractional tectonics continued until about 1.2 Gyr ago2. In the lunar highlands, relatively young contractional lobate scarps, less than 1 Gyr in age, were first identified in Apollo-era photographs3. However, no evidence of extensional landforms was found beyond the influence of mare basalt-filled basins and floor-fractured craters. Here we identify previously undetected small-scale graben in the farside highlands and in the mare basalts in images from the Lunar Reconnaissance Orbiter Camera. Crosscut impact craters with diameters as small as about 10 m, a lack of superposed craters, and graben depths as shallow as 1 m suggest these pristine-appearing graben are less than 50 Myr old. Thus, the young graben indicate recent extensional tectonic activity on the Moon where extensional stresses locally exceeded compressional stresses. We propose that these findings may be inconsistent with a totally molten early Moon, given that thermal history models for this scenario predict a high level of late-stage compressional stress4,5,6 that might be expected to completely suppress the formation of graben.

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Acknowledgements

We thank H.J. Melosh for helpful comments that greatly improved the manuscript. We gratefully acknowledge the LRO and LROC engineers and technical support personnel. This work was supported by National Aeronautics and Space Administration (NASA) Grant NNX08AM73G.

Author information

Affiliations

  1. Center for Earth and Planetary Studies, Smithsonian Institution, Washington, District of Columbia 20560, USA

    • Thomas R. Watters
    •  & Maria E. Banks
  2. School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85251, USA

    • Mark S. Robinson
    •  & Thanh Tran
  3. The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA

    • Brett W. Denevi

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Contributions

T.R.W. drafted the manuscript. M.S.R. is the principal investigator of the LRO Cameras, was responsible for development and operation of the camera system, and contributed to scientific interpretations. M.E.B. assisted with NAC image processing and the identification of tectonic features. T.T. generated the NAC digital terrain models used in the investigation. B.W.D. assisted in the age estimates of the tectonic features. All of the authors contributed to interpretation and analysis of the data.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Thomas R. Watters.

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DOI

https://doi.org/10.1038/ngeo1387

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